FIELD

The present disclosure relates to snow gliding devices, such as but not limited to skis and snowboards, including both cross country and alpine skis. In particular, this disclosure relates to skis and snowboards having as a component at least one morphing structure (such as a bistable structure) to enable a non-linear flex-force relationship that affords a performance advantage over linear force-flex response equipment. This disclosure also relates to hybrid snow-gliding structures that are able to store energy and then release it at advantageous moments during various elements of snow sliding sports, such as turning, carving, gripping, striding, gliding or when performing tricks, resulting in increased performance for given workloads. BACKGROUND

Cross-country skis are typically designed to include a slight upward curve or profile near its middle section when not subjected to applied load, known as a camber (positive in this case). When a load is applied, the described camber responds by flexing, and causes the force transferred from the skier through the ski to the ground to be more evenly distributed. Alpine skis and snowboards also exhibit cambers and rockers (also described as reverse, or negative cambers), and some include a medley of cambers and rockers. Skis and boards in a plethora of techniques and styles have cambers and rockers. For example, Boards may be Freestyle, Freeride, powder, all-teraine,

Racing/Alpine, splitboard or dual snowboards. Skis may be all kinds of skis such as alpine, slalom , cross country skate or classic/free technique, freestyle, snowblades, Telemark, ski flying, ski jumping, ski mountaineering, skijoring, speed skiing, superpipe skiing, backcountry skiing, extreme, free, glade, grass, half-pipe, mogul, para-skiing, ski cross slope-style, kite-skiing, snow kiting, touring, skis/runners/gliding surfaces on manual or automated sleds.

The camber shape of the ski or board will generally be designed to reduce frictional contact with the snow when in a free-gliding state, while also maintaining flexibility in the ski or board such that when downward force is applied to the ski and the camber is accordingly depressed (or "engaged" or "closed"), sufficient gripping or edging is achieved.

The stiffness and flex of a ski, snowblade or snowboard is generally dictated by the materials, dimension and orientation of the camber/rocker. However, the materials and design required to meet the flex/stiffness requirements for good grip, glide and edging properties collectively are not necessarily those best suited for optimal performance for each specific element individually. The force required to flex a ski or board and change the shape has traditionally exhibited a linear relationship because prior to this disclosure skis have been constructed as simple spring structures. When a skier or boarder applies force or pressure to a cambered or rockered area, the rocker or camber changes shape and when the force or pressure is eased up, the camber or rocker immediately begins to change back to its original shape, the change of shape being proportional to the amount of force applied at any moment in time.

A threshold force response mechanism for braking of skis is disclosed in DE 44 38 636. Releasing inhibitors (i.e., pins 10 and a front flap 12) are deployed to their braking positions when the skier applies a force exceeding a predetermined threshold. The flap 12 on the underside of the ski (in contact with the snow) remains flush with the underside of the ski until it opens to an acute angle facing downhill behind the skier so that in the braking position the back edge of flap 1 2 grips into the snow to prevent the skier sliding backwards. The mechanism seen in DE 44 38 636 is of a characteristic shape and bulk that makes seamless integration, a requirement for performance skis, impossible.

Accordingly, there is a need for new ski, and snowboard design that provide improved performance optimization and move away from the traditional linear force-flex relationship.

SUMMARY

The present disclosure relates to the application of morphing structures, such as bistable spring structures, incorporated into snow gliding devices, such as skis and snowboards, to invoke a non-linear flex pattern in the operation of skis and snowboards. Another embodiment of the present disclosure relates to the design of a waxless cross-country ski which incorporates morphing structures, in particular, as a functional element to engage and hold gripping mechanisms of a waxless ski.

An embodiment disclosed herein provides a ski or snowboard, comprising: at least one morphing structure incorporated with a portion of said ski or snowboard that undergoes flexing, wherein the morphing structure exhibits a first shape in a first stable state and a second shape in a second stable state and is configured to change the force required to flex said portion of said ski or snowboard at one or more points throughout a displacement of said portion of said ski or snowboard undergoing flexing, upon transitioning or partially transitioning from said first stable state to said second stable state or from said second stable state to said first stable state, the morphing structure being configured such that it transitions or partially transitions from said first stable state to said second stable state or from said second stable state to said first stable state once a force threshold specific to each transition is reached. Incorporation of one or more bistable structures such as bistable springs into the construction of skis or boards allows for a tailored non-linear force- flex relationships, whereby the shape of camber may be changed by applying a force that exceeds a minimum threshold force required for the spring(s) to engage, causing the ski to flex to a 'closed' position (flat shape in which the mid-section of the ski is also in contact with the snow) and this closed configuration is held (as the skier or boarder) pressure/force on the ski or board is eased up, thereby storing energy in the spring until opposing forces exceed the threshold required for the spring to return to its primary stable state ("reopen").

Incorporation of bistable springs into skis and boards results in enhanced responsiveness - skis and boards that are peppier and maintain their edges or grip better, resulting in easier turns and tricks, less energy required to sustain grip and edge contact and more defined and distinct Open' and 'closed' camber/rocker states. Also, the application of springs in this way to skis or boards can more completely change the shape of the ski or board over the target zone, as in contrast to traditional skis and boards, application of sufficient force to change the state of the bistable spring can affect the entire length of the bistable spring (for example, flattening the entire camber that the bistable spring spans), instead of only flattening a portion of the camber. According to an aspect of the present disclosure, a ski or snowboard is provided which comprises at least one morphing structure within a rockered or cambered portion of the ski, or board. The morphing structure(s) exhibit a first stable state and a second stable state, and are configured to change the force required to flex the camber or rocker at various points throughout its displacement by transitioning, either in part or in full, from a first stable state to a second stable state, or, conversely, from a second stable state to a first stable state, once a force threshold specific to each transition is reached. The morphing structure is fabricated such that it transitions, in full or in part, from the first stable state to the second stable state, or from the second stable state to the first stable state, in response to some originating force, either greater or lesser in magnitude than some threshold force value, exerted on the ski. This originating force could be a downward or upward force provided by the product user, or a force originating from the inherent flex or tension of the bistable spring, ski or board, or, even, a torsional force, such as when a ski or board is edging.

According to another aspect of the present disclosure, the ski may be a cross-country ski which comprises:

a main ski body which defines front and rear gliding zones separated by a middle grip zone, the grip zone including the cambered portion, the main ski body terminating at a tip and a tail; a top plate affixed to a top surface of the grip zone of the ski, and providing a point of contact for mounting a ski binding; two bistable springs affixed at opposing ends of the top plate, the top plate spanning a length within the cambered portion of the ski effective to facilitate transitioning of the bistable springs from the first stable state to the second stable state upon receiving the downward force beyond the threshold level; and a gripping mechanism formed within the grip zone at a base of the ski, wherein the bistable springs activate the ski camber to a closed or flat position and hold it there upon transitioning or partially transitioning from said first stable state to said second stable state, allowing said gripping mechanism to make contact with and grip snow during use.

According to another aspect of the disclosure, the ski may be a crosscountry or downhill ski or board which comprises: a main gliding body which defines front and rear gliding zones separated by a middle raised cambered or grip zone, the grip zone including the cambered portion, the gliding body terminating at the ends; a single length-wise bistable spring embedded within the gliding body in a permanent or removable manner to facilitate transitioning of the camber via the bistable spring, from the first stable state to the second stable state upon receiving the downward force beyond the threshold level of the spring; and wherein the bistable spring activate the gliding body camber to a closed or flat position and hold it there upon transitioning or partially transitioning from said first stable state to said second stable state, allowing said gripping or edging surfaces to make contact with and grip or edge the snow during use.

According to another aspect of the disclosure, the ski may be any ski or board which comprises:

a main ski body which defines front and rear gliding zones separated by a middle grip zone, the grip zone including the cambered portion, the main ski body terminating at a tip and a tail;

a top plate affixed to a top surface of the grip zone of the ski, and providing a point of contact for mounting a ski binding;

two bistable springs affixed at opposing ends of the top plate, the top plate spanning a length within the cambered portion of the ski effective to facilitate transitioning of the bistable springs from the first stable state to the second stable state upon receiving the downward force beyond the threshold level; and

wherein the bistable springs activate the ski camber to a closed or flat position and hold it there upon transitioning or partially transitioning from said first stable state to said second stable state, allowing edges to make contact with snow during use.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present disclosure will become more apparent from the description in which reference is made to the following appended drawings.

Figure 1 is a graph illustrating a total force profile of a cross-country skier throughout the ski stride. Figure 2 illustrates, by way of an example, the force vectors and projections of diagonal stride kick.

Figure 3 illustrates an example of the angle created by a skier during a carving turn, shown as a view from back of the skier during a left-hand turn.

Figure 4 illustrates an example of a side-cut of a pair of alpine skis.

Figure 5 illustrates an example of the camber (A) (positive, unloaded, open); and reverse camber (B) (negative camber) of a ski. A 'closed camber' describes the case where sufficient force is applied to a positive camber shape to cause deflection to full flattening or beyond of the initial unloaded shape, with the presence of the ground under the ski preventing deflection to a negative camber shape.

Figure 6 shows the reverse camber of a pair of skis during the course of a skier's carving turn, the arrow representing the direction of travel.

Figure 7 illustrates a typical bistable spring and its morphologies, including: (A) (i) the spring's primary stable state, and (ii) a portion of the spring in its secondary stable state; and (B) the stress contours of a saddle-shaped bistable structure, both (i) after relaxation, i.e. in the first stable state where it has a longitudinal curvature; and (ii) after snap through, i.e. in the second stable state.

Figure 8 provides a graph showing the bistable spring deployment dynamics for a given force load.

Figures 9A and 9B illustrate the cross-section of a classical cross country ski in accordance with one example of an embodiment of the disclosure, shown from the front looking towards the back of the ski, with 9(A) a bistable spring in its primary stable state; and 9(B) in its secondary stable state.

Figure 10 shows the full length classical cross-country ski (2) illustrated in Figure 9.

Figure 11 illustrates an exploded view of one example of a waxless cross-country ski, according to an embodiment of the disclosure incorporating bistable springs and a series of gripping flaps.

Figure 12 illustrates a partial cross-sectional view of the waxless crosscountry ski shown in Figure 11 (at 1/2 width).

Figure 13 provides an enlarged view of the gripping flaps and the actuation pins or posts of the waxless cross-country ski shown in Figure 11. Figures 14 and 15 provide enlarged perspective views of the gripping flaps and the actuation pins or posts, taken from two different angles, of the waxless cross-country ski shown in Figure 11 .

Figure 16 provides a cross-sectional view of the waxless cross-country ski shown in Figure 11 , taken to illustrate the gripping flaps and the actuation pins or posts.

Figures 17A and 17B illustrate just one example of bistable springs applied to an alpine ski having two (2) bistable springs embedded therein in which Figure 17A illustrates the alpine ski in its state most favorable for gliding, and the two (2) bistable springs in their primary stable states;

Figure 17B illustrates the alpine ski during a carving turn, where the two (2) bistable springs are in their secondary stable states.

Figure 18 provides a view of the MSC/NASTRAN model used in the finite element analysis.

Figure 19 A is a cross-sectional view of the bistable spring contained in the housing.

Figure 19 B provides a complete exterior view of the morphing structure as it is contained in the housing.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.

As used herein, the terms "comprises" and "comprising" are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms "comprises" and

"comprising" and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components. As used herein, the term "exemplary" means "serving as an example, instance, or illustration," and should not be construed as preferred or advantageous over other configurations disclosed herein.

As used herein, the terms "about" and "approximately" are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. As used herein, the terms "ski" and "snowboard" are specific examples of devices designed to glide over snow. As such the phrase "a wearable snow gliding device" can refer to any type of ski, alpine, cross country or nordic, as well as any other device worn by a user for gliding over snow.

As used herein, the phrase "morphing structure" means any shaped, shell structure that, due to its shape, composition and pre-stress, when flexed any resultant materials strain remains within the elastic range and the structure can reversibly and repeatedly transition from one morphology to one or more other morphologies, by transitioning through a maximum in the strain energy contained in the structure, and/or exhibiting an accompanying change in the force/energy required for subsequent flex/shape change. This includes, for example, bistable tape springs, cross-curve springs, saddles, and multi-stable shapes and shell, dome structures or part of any of the above, that is able to transition in the manner described above.

Described herein are snow gliding structures, such as, but not limited to, cross-country and alpine skis and snowboards which incorporate morphing structures, such as those described in the previous paragraph, to enhance camber and flex performance, and to also enable the use of gripping flaps in waxless cross-country skis. One or more morphing structures may be incorporated with a portion of each ski or board which undergoes flexing, either entirely in the interior of the depending, or on the exterior top surface of the ski, or partially embedded in the interior as well as partially on the exterior, top surface, depending on where they are positioned in the ski and the direction of orientation of the bi-stability. Additionally, the cambered section of the ski may be comprised entirely of the morphing structure.

As used herein, the meaning of the word "configured" such as where it is stated "....wherein said morphing structure is configured to change the force required ", means tailoring the force required to transition a morphing structure from one state to one or more other states by adjusting a combination of factors, including:

a) the designed bending moment in the primary axis of bending of the structure which is dependent on the thickness of the structure, the mechanical properties of the material from which the structure consists of, specifically the elastic modulus of one or more component materials and the orientation of anisotropic properties of any fiber, filament or internal subcomponent materials relative to intended/specific loads experienced by the structure;

b) the shape and curvature of the morphing structure, in either one or two planes, that imparts the stability to each morphology due to the introduction of a higher energy, strained, state through which the shape of the structure must pass to change from one morphological state to another. The radius of curvature influences the magnitude of strain required in the regions that undergo highest strain during transition from one morphing state to another, and so the configuration of a morphing structure primarily refers to adjusting the stress/strain response of the material in the regions that experience high strain during morphological transition, by prescribing material amount (thickness, cross sectional area, density of reinforcing materials) and materials properties.

Alpine skis and snowboards also exhibit rockers, or reverse cambers. Some ski and board designs have a medley of cambers including sections with convex and concave cambers. For all skis and boards, the aim is to make a ski or board camber shape that minimizes frictional contact with the snow while in its free-gliding state, yet is soft enough to flex so that when the camber is depressed or engaged for a turn the edge can make continuous contact with the snow and the sidecut (or skier technique) can do its job to change the ski's direction. Additionally, the ski must also be torsionally stiff to resist twisting as the ski is pressured during the turn. A traditional camber/rocker design is based on the shape of the ski, the stiffness and flex (which is dictated by the material and amount and orientation of it), and works (to be flattened) when sufficient pressure is maintained on the camber.

Typically, skis and boards exhibit linear flex patterns. Cambers, a specific type of flex, are also a type of spring, and, therefore, follow essentially Hooke's law, which relates the force, F, required to move the spring some distance, x, by F = kx, where k is the spring constant of the camber. In the traditional ski, the closure of the camber follows this principle. In skis and boards as described herein, the camber relationship can be influenced significantly by the morphing structure properties.

Camber shape has also been designed to provide enhanced crosscountry ski performance, but in the traditional camber designs, the force on the camber must be fully maintained to keep the camber engaged with the snow (flat), which is required for gripping and the relationship between camber engagement and force is linear. This is in contrast to the present disclosure which incorporates the use of morphing structures such as bistable spring structures, where the camber is flattened once a threshold force is applied and the flatness is maintained until a lower and opposing threshold force is reached.

The use of morphing structure technology can therefore enhance the stability of the camber in its engaged or flattened form, and make it easier (less force required) to attain and/or maintain this flattened state, meaning that more stable, stiffer skis may be used by a skier. This technology is applicable to all alpine skis, boards as well as skate and classic cross-country skis. The bistable springs may be oriented parallel to or perpendicular to the running direction of the gliding body. Regardless of orientation of the bistable springs (or spring), these structures function to change the camber and flex of the ski or board. In a classical cross-country ski, the structures assist in holding the ski in a gripping state so that the gripping mechanism - whether it be wax, activated mechanical grips or other gripping mechanisms (eg. Zero-fibers, hairies etc. ) - maintain contact with the snow with less required force. In other skis or boards, the structures assist in maintaining the shape of the ski or board, which is required for a specific technical aspect of the skiing or snowboarding style, such as stability, edging or gripping.

Mechanical flaps have been previously incorporated into cross-country skis. However, they typically do not function well in these prior examples because the conventional spring mechanism that is used does not engage enough of the mechanical flaps, nor is the force threshold control mechanism sufficiently streamlined into the ski construction.

Incorporating morphing structure(s) into the cambers of a ski and snowboard construction may provide more 'pop' when desired, for example, when jumping off of rails and/or ramps. The equipment is more responsive and 'peppier'. The distinct states of the camber (distinct open versus closed states) are more distinctly felt by the skier or boarder and exert more control with less effort. Once the threshold to 'close' the camber of a ski or board is exceeded, the bistable spring and camber shape are held in the secondary stable state, even while the skier or boarder physical force begins to be reduced, storing the energy in the spring until a reverse force (such as the natural linear tension in camber, exerts sufficient force to cause the bistable spring and camber to revert to its original position.

In addition, the engagement of the bistable spring mechanism in downhill skis or boards (or free-technique cross country skis) can permit longer-lasting contact of the camber shape required for turning, thereby enhancing the prominence of the rocker(s) to deal with potential powder conditions, and keeping the edge in contact with the snow to provide stronger edging and better control, especially when turning.

In comparison to traditional Nordic ski design, the application of the bistable spring mechanism to classic Nordic skis will mean that the grip surfaces 5 are completely flattened, flattened easier (using less force), maintained flat even during the latter stages of the kick and will provide for more propulsion for all skiers ranging from Olympic level to recreational users.

In general, there are many possible applications of morphing structures, such as bistable structures, to both cross-country and alpine skis and snowboards that can be envisioned to improve performance. The traditional flex patterns of alpine and cross-country skis and snowboards are linear in nature, and the addition of bistable structures enables the realization of non-linear flex patterns which have many desirable outcomes.

Incorporation of a morphing structure or structures may be accomplished in several ways while constructing skis and boards. The simplest construction would be to incorporate a single bistable spring, or lay down fibers for a bistable structure as a layer in laminate or 'sandwich' construction. The construction method is ideally suited to insertion of a spring or spring-like structure as some traditional constructions already allow for movement between layers, which enables the ski or board to follow terrain better at very high speeds. The incorporation of the morphing structure may, otherwise, include internal spaces to allow for the geometrical shape changes of the spring.

The morphing structure may be constructed from fibers laid down during a layered ski or snow board construction. The morphing structure may be constructed of composites, carbon fiber or carbon fiber composites or metal or any engineered material. The bistable spring or spring-like structures may also be inserted into Torsion-box, Monocoque/Cap, and other methods of construction.

If two cambers are desired, as in a medley/camber/rocker structure, two or more bistable springs may be embedded in longitudinal sequence to achieve, for example, a double camber. Alternatively, two smaller bistable springs may be inserted into the construction of the ski at either end of a stiff plate to activate the camber to the engaged or flat position, when sufficient force to overcome the threshold is applied. The inherent flex of the ski, causing the ski to return to its most relaxed state, needs to be sufficiently large to overcome the aiding forces provided by the springs. These springs and this plate may be on top of the ski or embedded into the construction of the ski. Embedding the linear bistable-spring structures into the ski or putting a plate- spring structure on top of the ski may also confer additional torsional stability to the ski, allowing the ski to run faster in a variety of conditions, depending on how the springs are integrated.

Accordingly, in embodiments of the disclosure as will be described in further detail herein, bistable springs may be used: i) to alter the flex dynamics of skis or snowboards from ones that are traditionally linear in nature to ones that are non-linear; and/or ii) to provide a mechanism for improving the function of traditional waxable cross country skis, and for enabling the functioning of a waxless cross-country ski for the classical technique.

Morphing Structures (Bistable Springs)

Bistable springs have two predominate morphologies in which they are energetically stable, and morphologies of higher energy states that must be transitioned through to change from one to the other morphology. Figure 7A illustrates the bending and deployment morphologies of a typical bistable spring (K. A. Steffen, S. Pellegrino (1983), Deployment Dynamics of Tape Springs, Proceedings: Mathematical, Physical and Engineering Sciences, Vol. 455, No. 1983, pp 1003-1 048).

Image (i) in Figure 7A illustrates the spring's primary stable state, characterized most predominately by a transverse curvature throughout the entire length of the spring. Image (ii) illustrates a portion of the spring in its secondary stable state. The middle portion of the spring, where there exists the conspicuous bend, is illustrative of the spring's secondary stable state. This state is predominately characterized by its longitudinal curvature. The secondary stable state is characterized by a relative minima thermal energy, but is still less stable than the primary stable state. The absolute and relative magnitudes of the primary and secondary stable states are entirely dependent on the composite and fiber orientation, the composite matrix, and the selected geometries of each state and the engineered properties of the spring. The energy state's dependency on these elements results in the morphing structure's incredibly high versatility with respect to the applications available, and no real theoretical constraint.

In Figure 7A, the spring depicted has a small radius of curvature, seen in both the primary and secondary stable states. The springs utilized in skis and boards as described herein, on the other hand, may contain bistable spring structures that have a more subtle, larger radius for their secondary stable state. Alternatively, if two bistable springs are used to activate a plate in the middle of a ski, such as will be discussed below, springs with a smaller radius of curvature may be employed. The radius and mechanical thresholds of the morphing structures may be selected to enable tailoring of the length of the contact or grip zone, in the case of a classical cross-country ski, as well as the force required to 'close' the camber of the skis.

Figure 7B illustrates an example of a saddle-shape morphing structure and its morphologies, exaggerated for purposes of illustration. (Jong-Gu Lee, Junghyun Ryu, Hyeok Lee, Maenghyo Cho (2014), 'Saddle-Shaped, bistable morphing panel with shape memory alloy spring actuator', Smart Materials and Structures 23 (2014) 074013 (9pp)) (with stress contours from finite element analysis). Figure 8 illustrates the force dynamics associated with deployment, or otherwise referred to as buckling, of a bistable spring in the opposite-sense direction (Steffen and Pellegrino, supra). Of particular note, M _max represents the maximum moment force a bistable spring will sustain and the force that results in its buckling. Beginning at the origin, point O, as a moment force is applied to one end of a spring, the ratio of the moment force to the flexural angle of the spring follows the dark line, past point E, and up to point A. At point A, the spring buckles, and the force required to further increase the deployed angle drops significantly, represented by M ^* , and remains essentially constant between points B and C. The spring in this state is in its secondary stable state, with the primary stable state represented at the origin. As the spring returns to its primary stable state, instead of following the path back to A from B, it follows the path from D to E, and then eventually back to O, the origin.

Saddle-shaped bistable structures have also been investigated in the literature (Jong-Gu Lee, supra). It is expected that more complex geometries, such as saddle-shaped bistable structures, can also be incorporated into the flex dynamics of skis and snowboards in order to achieve better performance results.

1. Classic Cross-Country Ski

Diagonal stride during classic technique consists of two phases: i) the impulse/propulsion phase, and; ii) the gliding phase. With the classic ski technique, an impulse is delivered to the ski by applying the skier's weight to a single ski, and then additionally applying a muscular force to enable contact between the center of the base of the ski with the snow.

The base of a ski designed for the classical technique can be divided into 10 three sections: the front and rear gliding zones, and the middle grip zone. The camber in this case functions so as to keep the middle grip zone away from contacting the snow as much as possible when the skier has equal weight on their skis, but also to flex in response to a skier's weight transfer and kick so that the grip wax, which is applied to the middle grip zone, can come into contact with the underlying snow to permit sufficient friction between the ski and the snow necessary for forward propulsion. The force with which the skier kicks their skis can be characterized as follows:

where F _y is the vertical component of F and F _x is the horizontal component. The frictional force that is realized between the grip zone of the ski and the snow is expressed as:

where μ ₅ is the coefficient of static friction for the given grip wax and snow, and F _N is the normal force, or, the vertical component of the force with which the middle portion of the grip zone presses the underlying snow. This normal force can also be characterized as:

F N — Fy — F _c

where F _c is the force required to close the camber, and follows Hooke's law. As such, F _c can be rewritten as follows:

Therefore, the expression for f _s can be rewritten as

A common problem in the classical technique in cross-country skiing is back slipping, wherein the frictional force between the grip wax and the snow is insufficient for the force with which the skier kicks their ski, and, as a result, the skier cannot gain the necessary grip of the snow to propel themselves forward. It has been demonstrated that performance is significantly reduced when the magnitude of μ ₅ is reduced in studies performed on roller skis (M. Ainegren, P. Carlsson, M. S. Laaksonen, M. Tinnsten (2012) ' The Influence of Grip on Oxygen Consumption and Leg Forces when using Classical Style Roller Skis', Scandinavian Journal of Medicine & Science in Sports). The only inherent problem with a reduced magnitude of μ is the proportional reduction in f _s . Back slipping occurs the instant or, rewritten as the instance wh

As seen from the expression above, with traditional camber design, back slipping is more likely to occur when F _y is lessened for any reason. Two reasons for a reduction in F _y can be referred to as the biomechanical constraints and the trigonometric constraints.

Figure 1 illustrates the total force, or F, profile of a skier throughout the ski stride. The dark line in the figure represents diagonal stride, and is relevant in this particular context. More specifically, the "Push-off Phase DIA" indicates the force profile associated with the kick. The front side of this peak includes a period of weight shift and force loading of the ski in preparation to get grip, whereas the back side of the peak illustrates a period in which the skier desires grip entirely throughout. As can be seen, the total force decreases towards the end of the kicking phase. This is primarily due to the biomechanical constraints of the kicking technique, which begins with contraction of the larger muscles and progresses towards the smaller muscles. As the kick progresses, then, the magnitude of F _y becomes increasingly susceptible to the biomechanical constraints, and therefore undergoes a natural lessening.

The trigonometric effects can be seen in Figure 2. While the force magnitudes in this illustration are for representation only, it can be seen that as the skier's kick progresses, the angle of F decreases with respect to the ground. As such, F _y becomes increasingly smaller as the kick progresses. This results in reduced camber flex (camber raising), and hence increases the likelihood of backslipping. The combined effects of the biomechanical constraints and the trigonometric effects are such that F _y is substantially reduced as the kick progresses, and, therefore, there is an increasing likelihood that F _x > F _s . (This is in contrast to the present disclosure where the contact is maintained despite 5 lessening of the force keeping the contact / grip, until a threshold in the opposing direction is exceeded.)

In further embodiments, whereby morphing structures are incorporated into classical cross-country skis, when the camber of a classical cross-country ski is not completely flattened, the bi-stable spring is held in its secondary stable state by the inherent spring forces of the ski camber. When the ski is flattened, in preparation for grip, this change in shape of the ski camber enables the bi- stable spring to transition to its primary stable state. In its primary state, the spring will exert a conforming force over the ski, F _conf , helping to maintain the ski in its flattened state even when F _N is reduced. F _conf will be exerted only once the ski has been completely flattened, which, most importantly, includes even the later stages of the skier's kick phase, when the skier is most susceptible to both the biomechanical constraints and the trigonometric effects, thereby reducing energy required to maintain excellent grip. The magnitude of F _conf is in opposition to F _c (but with F _y ) and, as such, enables a greater F _N for a given F _y . A larger F _N results in a greater f _s , and, as such, instances of back slipping can be reduced, and the skier can realize better grip. The primary and secondary stable states of the spring may be reversed for opening and closing the camber, as a means of fine-tuning the performance of the ski : the primary stable state may be either the open or closed position.

It is envisioned that the alternative may also be true: the ski may maintain the spring in its primary stable state below a minimum force threshold, and transition to its secondary stable state beyond some threshold force.

Moreover, the spring may not fully transition from one state to the other. Rather, it may be advantageous to only permit the spring to partially transition from one state to the other, and maintain the spring in the partially transitioned state for improved functionality at that point. This can be advantageous if you don't want the morphing structure to reach its secondary stable state because to return to the primary stable state would require an input of energy to overcome the secondary stable state's energy threshold, whereas with a partial transition, no energy threshold needs to be reached in order to return to the primary stable state, or vice versa.

When F _N is reduced below some lower threshold, such as when the kick is completely finished, then

F _c + F _N ) >

which will cause the spring to return to its secondary stable state, and the ski to its morphology most favorable for gliding. In other words, when F _N is sufficiently reduced, the inherent flex of the ski will overcome the conforming force of the bi- stable spring, and enable the spring to transition back to its secondary stable state. Figures 9A and 9B illustrates the cross-section of one possible embodiment of a classical cross-country ski (2), shown from the front looking towards the back of the ski with a bistable (15) spring incorporated therein. Figure 9A illustrates the ski (2) in its gripping morphology, with the spring (15) in its primary stable state, and Figure 9B in its gliding morphology, with the spring (15) in its secondary stable state. The spring (15) in this embodiment is positioned within a cavity (17) formed within the interior of ski (2). Note that in this figure, the elements of the concept are exaggerated for clarity. In addition, it is envisioned that the spring (15) can be inverted so that the orientation is opposite to what is shown in the figure, with comparable results.

Figure 10 shows the full length classical cross country ski (2) illustrated in Figure 9, and indicates the middle portion of the ski (2) where the bistable spring (15) is located, with the starting (20) and ending (25) points of the spring (15) being shown. In one non-limiting example of the classical cross-country ski (2) shown, which is provided for the sole purpose of exemplifying a possible embodiment of the ski yet without wishing to be limiting in any way, the spring (15) may be approximately 1205 mm long, start approximately 470 mm from the front tip of the ski (2), and span the middle portion of the ski (2) up to the ending point (25) which may be approximately 338.2 mm from the back of the ski or other location, depending on the ski length and construction. Other dimensions of the spring (15) and ski (2) are also envisioned, and may be proportional to the overall length of the ski (2), or otherwise to the height, weight and strength of the skier.

As a guide, yet without intending to limit the present disclosure, the spring (15) may have a thickness of 1 mm or more, which is dependent on the material chosen and its stiffness in general. The transverse radius of curvature when the spring (15) is in its primary stable state is an important characteristic influencing deployment dynamics, and the ideal radius of curvature will preferably be determined experimentally or calculated for the given application. An important consideration, though, is the displacement volume required for the spring (15) to morph between stable states, as this volume will impact the general construction requirements of the ski. It is expected that this volume may be 25mm wide across the cross-country ski, and anywhere from about 1 to about 8mm in height. Alternatively, if the ski (2) is pliable enough, to get better responsiveness, the ski (2) should have adequate flex and the spring (15) strong enough so there is no gap or displacement volume required. However, the length of this displacement volume will be restricted to the length of the spring (15) chosen if needed. Similarly, if the bistable structure is constructed by fibers laid down into the ski (2), then there will be no cavity.

An additional implementation may be to use two or more springs (15) only at the locations on the ski (2) that undergo the greatest flex. In this way, the springs (15) chosen may have a greater transverse radius of curvature since the arc the ski (2) flexes at the particular location is proportional to the transverse radius for an optimally functioning spring (15). In such an

embodiment, it is envisioned that two springs (15), each more or less 50 mm long could be utilized at the locations in front of the skier's binding and just behind the skier's binding. It is in these approximate locations that the flex of a ski (2) may be the greatest.

In traditional ski technologies that employ a linear camber flex, back slipping occurs when

F _x > ^ _s (F _y - kX) .

However, with the implementation of a bi-stable spring, and the manifestation of a non-linear flex pattern of a camber, back slipping occurs when

F > Ps (F _y — kX + F _con f) .

The addition of F _conf to the right side of this inequality has the effect of reducing instances of back slipping, and permitting F _x to be greater by a magnitude equal to _s F _con , and thus permitting a greater force contributing to forward propulsion.

It should be understood that the dimensions, number and placement of the springs in the figures are merely for the purpose of illustration. Rather, the spring (15) dimensions, number and placement can be varied to enable the camber size of the ski (2) or board to be minimized or lengthened. This can be done, for example, by tailoring the strength of the spring (15). A shorter camber may be enabled by a shorter, stiffer spring (15) and vice versa, enabling disconnection of any traditional length requirements to camber stiffness. This is advantageous as it would permit the glide zone on skis (2), especially cross- country skis, to be increased, decreasing the grip pocket size and hence reducing drag. Shorter higher pocket would also keep the grip wax farther off the snow.

Similarly, in glide-only skis and boards, when force is employed to engage the bistable spring (15) to its flat position, the ski (2) will remain flat for longer and enhanced contact with the snow, providing enhanced control of edges/turns. Accordingly, the threshold forces required to close the cambers are less than would be required for a traditional ski (2) and the cambers would remain closed or flat for a longer period than in a traditional linear camber design (while the weight or force closing the camber is beginning to be lifted), enabling conservation of energy of the skier. Similarly, merely needing to exceed the threshold force (as opposed to constant application of a linear force) will mean that the gripping or edging will require less power to effect

engagement of the ski (2). This concept is applicable to both racing and recreational skis and boards for enhanced functioning, enhanced ease of use and less expenditure of energy.

Of additional interest, the dimensions of the ski or board may be reduced, particularly the height of the ski or board (thickness) off of the ground. This is because part of the traditional construction of skis requires a certain height of material to build in a natural camber. If the camber arises primarily or solely from the workings of a bistable spring (15), the cambered (or rockered) section of a ski or board may be entirely or mostly composed of only the bistable spring (15). Depending on the materials chosen for construction, this could eliminate considerable weight from the ski or board which could be an advantage for conserving energy of the skier.

Details of Morphing Structure Integration

Without limiting the disclosed invention, a stainless steel morphing structure as depicted in Figure 18, with the characteristics and dimensions described below, will transition from its primary stable state to its secondary stable state under roughly 580 N of force. In its primary stable state, the bistable spring is 33.52mm in width, 8.48mm in height, 700mm in length, 0.46mm thick, and has a transverse radius of curvature of 30.5mm. The width of the morphing structure in its secondary stable state is 35mm.

This particular structure was modeled using Finite Element Analysis, with MSC/NASTRAN as the solver. A non-linear eigenvalue solution was used to determine the width, height, and transverse radius of curvature in the primary stable state, and the overall thickness and material composition of the bi-stable spring. The transverse curvature was maximized in order to minimize the required thickness to achieve the desired force loads. However, a slightly thicker structure would require a larger transverse radius of curvature, resulting in less overall movement of the structure during transition between states. In a stainless steel structure, it is these parameters, namely the transverse radius of curvature and the material thickness, that can be varied to optimize the particular use case. In a composite structure, on the other hand, the pattern and composition of the layup itself will also influence the force dynamics of the structure. In addition, we assumed initial dimensions that permit integration into a ski, such as the length and longitudinal curvature. In addition, we solved for a transition from primary stable state to secondary stable state to occur under 580N of force.

In order to permit the relative motion of the morphing structure with respect to the main ski body, the structure can be contained in a housing, as seen in Figure 19. This housing demonstrates a linear flex profile similar to the main ski body, but provides the requisite internal space to permit the structure to transition between primary and secondary stable states.

2. Alpine Ski and Snowboard Design

In alpine skiing and snowboarding, a turn made by carving requires a particular set of characteristics. When the skier or boarder initiates a turn by carving (i.e. not skidding), they weight shift to contact and angle the base of the skis or board with respect to the snow surface, thereby maintaining the edge contact on the snow throughout the turn. Figure 3 provides an example of the angle created by the boots (1) and skis (2) of a skier during a carving turn (view from the back of the skier during a left-hand turn). Most skis and boards today are designed with the implementation of a side-cut (10), as illustrated in Figure 4, whereby the tips and tails of the skis or boards are wider than the centre portion where the skier's or boarder's centre of gravity is located.

Traditional skis may also exhibit a camber and/or a reverse camber as illustrated in Figures 5A and 5B. The reverse camber is the longitudinal shape the ski maintains throughout the turn, as long as a sufficiently large f _y is maintained by the skier or snowboarder.

Due to the sidecut of the skis or board, and the f _y generated by the skier, the single edge in contact with the snow maintains a curved shape with a radius equal to that of the turning radius. Therefore, the lateral angle between the ski or board and the snow, together with the side-cut of the ski or board and the f _y maintaining a reverse camber, enables the efficient carving turn as seen in

Figure 6, whereby the arrow (3) represents the direction of travel.

However, by implementing skis and boards that only exhibit linear flex patterns, permitting an effective reverse camber during a turn requires some sacrifice and the loss of a typical camber that may be advantageous during other aspects of skier and boarder technique, such as when turning is not initiated. In other words, in order to enable a reverse camber, F _c must be sufficiently small in order for f _y > F _c , and thus permit enough flex in the ski, only when carving is desired.

Bistable composite structures, however, have the potential to overcome this sacrifice. One possible method of utilizing morphing structures in skis and snowboards is to have a bistable structure positioned along the interior, middle, portion of the ski or board, directly above the base and base supporting materials, or embedded in the ski during ski construction. (The camber size may be made smaller or larger than current structures by use of stiffer or softer bistable springs.) Alternatively, two or more bistable structures positioned throughout the ski or board where the flex of the camber is greatest or most desired. When it is desired for the ski to maintain a traditional camber, or at least a stiffness that resists the ski from entering a reverse camber shape, the bistable structure(s) will be maintained in their primary stable state and exert a conforming force over the ski. Once the ski or board is forced into its flat or reverse camber state, such as when it is placed on its edge, by the

achievement of a threshold force f _y is reached, then the spring transitions to its secondary stable state, and the conforming force the bistable spring exerts on the structure of the ski in its primary stable state is nearly eliminated, and the ski or board can be more easily maintained in a flat or reverse camber shape for the remainder of the turn. Once the turn has been completed, and f _y is reduced below a secondary, lower threshold, the bistable structure can return back to its primary stable state, and once again exert a conforming force over the ski or board when the skier or boarder does not desire a reverse camber shape of their ski or board.

As discussed above, the present disclosure relates to a variety of possible embodiments incorporating bi-stable springs into cross-country skis, alpine skis and snowboards. These will be described in further detail in the following.

One example of an application of the present disclosure therefore involves invoking a bi-stable camber in skis and boards wherein a bistable structure or structures are incorporated integrally with the camber at the location bistability is desired. Alternatively, a plate with two bistable springs can be incorporated - one at each end (oriented perpendicular to the ski length), running the length of the middle portion of a cross-country or alpine ski or board, or covering one or two or more cambers in a board. The spring(s) can be contained inside the ski/board construction or immediately or nearly

immediately above the base supporting materials. A plate or spring structure may also be on top or near the top of the gliding structure body.

The ski camber can be characterized by two fundamental morphologies: i) the camber is not completely flattened, and the skier is gliding or turning (in the case of a reverse camber), and; ii) the camber is completely flat, and the skier/boarder is gripping or edging the snow. For cross-country and alpine skis and boards, the camber (or cambers) is (are) required to be flattened so that the base and edges of the skis or board can make good contact with the snow or rails or other equipment so that control is achieved.

The embodiments disclosed herein can be distinguished from EP 2206538 B1 on several grounds. In particular, the morphing mechanism giving rise to non-linearity in EP 2206538 B1 does not employ a bi-stable spring, however the bi-stable spring is superior for evoking non-linear flex due to its smaller angular range through which it operates. The morphing mechanism employed in EP 2206538 B1 operates over a range of large angular deflections, which makes it unsuitable for alpine skis, and skis and boards generally, whose functional range of angular deflection during flex is restricted to small ranges.

Additionally, the morphing mechanism seen in EP 2206538 B1 employs a multitude of materials and components in order to realize non-linear flex. This added complexity makes it unsuitable for manufacturing, production and maintenance. Whereas a single morphing structure, integrated as a material layer in the ski or board, offers a simple integration process of a suitable structure for the desired effects.

3. Waxless Ski Design

The traditional method with which cross-country skiers in the classical technique have enabled grip is with waxing and other gripping/climbing systems, such as "fish-scales" and "Crowns". However, in all cases, finding the best ski or grip wax has been a process of optimization and compromise. In other words, all choices maintain an inherent sacrifice of some characteristics that are vital for performance, most commonly either ski speed or grip. Grip wax that provides sufficient grip will inevitably exert a drag force, thus making it impossible to realize true maximum ski speeds. Additionally, the large varieties of grip waxes represent a similar variety of consistencies and, therefore, are often applied in varying thickness to the ski base. As a result, the appropriate layering of grip waxes in order to limit drag and ensure the highest ski speed becomes exceedingly difficult. Furthermore, the traditional method for selecting classic skis and determining the grip zone length is performed on a perfectly flat surface. However, even in the most firm snow conditions, the ski would appear to rarely interact with a completely flat surface, and in many of the more common snow conditions, contact between the snow and the grip wax would seem significant. In addition, the diagonal stride consists of instances where the skier requires maximum glide performance from their ski, and yet will also be fully balanced on one foot. However, it is rare that skis are fitted with this consideration in mind, and, as a result, during instances of glide in the diagonal stride, traditional classic skis have cambers that are flexed beyond their optimal gliding range. Consequently, there are several factors indicating that grip wax provides an inherent drag force that inevitably makes the realization of true maximum ski speed impossible. Similarly, "fish-scales", "Crowns" or "hairies" provide an inherent drag force that slows down the skis.

Moreover, selection of such wax is dependent on the snow crystallinity, temperature, humidity, skier technique, race length, etc., making the process quite complicated, even for the experienced wax technicians. This process is often burdensome and even prohibitive for some skiers in some situations. Bi- stable springs (15) may also be incorporated into a waxless ski design, as will be discussed in further detail below.

As discussed above, traditional classic ski technology has resulted in ski and wax selection being a process of optimization and compromise - often involving the sacrifice of important characteristics for ski performance. In order to overcome some of the problems associated with this optimization process, bi-stable springs (15) can also be incorporated into a classic cross-country ski (2) to induce a conformational change in the base throughout the grip zone area so as to permit sufficient grip only in response to skier demands for grip, and to also permit maximal glide during instances of skier demands for glide.

Traditional grip waxing technology, which is the current gold standard in the majority of snow conditions, exploits the combined characteristics of grip wax and snow crystalinity, temperature, humidity, etc. The optimal wax choice, however, is highly dependent on these snow characteristics, and changes drastically as they do. The compressive strength of snow, on the other hand, is a characteristic that is far less vulnerable to changing conditions, and can also be exploited for grip across virtually all snow types, as demonstrated by the success of most waxless skis in use today.

As such, it is herein provided that a conformational change to the grip zone of the base of the ski can be enabled by the use of a bistable structure, so as to exploit the compressive strength of snow to enable grip, while also exploiting the most sophisticated glide technologies throughout the entire length of the base of the ski.

Numerous studies on classical ski technique have examined the force profiles of elite skiers. Skier demands for grip can be characterized by a high force impulse delivered through the middle of the foot to the middle portion of the ski. The academic literature indicates that, for performance skiers, kicking forces in diagonal stride range anywhere from 150% of body weight to 200% for each kicking leg (J. C. Pierce, M. H. Pope, P. Renstrom, R. J. Johnson, J.

Dufek, C. Dillman, (1987), 'Force Measurement in Cross-Country Skiing', International Journal of Sport Biomechanics, 1987, 3, pp. 382-391 ). This can be seen in Figure 2. It can be assumed that this force is of sufficient magnitude that it is unique to the portion of a skier's stride wherein they are actively recruiting/setting grip, and all other instances characteristic of a skier's desire for glide consist of forces much less than this. In traditionally constructed skis, the kicking force is required to 'close' the camber of the ski to make good contact of the grip zone with the snow and since this 'closure' of the camber is linearly related to the force applied to it, as soon as a sub-maximal force is felt, as in the latter stages of the kick, the camber becomes less flat and the contact of the grip zone with the snow is diminished, and lack of propulsion or backslipping may result. This is in contrast to the timing and degree of closure of the camber in skis (2) containing morphing structures such as bistable springs.

An example of this waxless ski design is illustrated in further detail in Figures 11 to 16, in which Figure 11 illustrates the gripping portion of the ski (2) in exploded view, Figure 12 illustrates a cross section of the ski at 1/2 width, and Figure 13 provides an enlarged cross-sectional view of the gripping flaps (50) and the actuation pins or posts shown in Figures 11-12. Figures 14 and 15 provide enlarged perspective views of the gripping flaps and the actuation pins or posts (45), taken from two different angles; and Figure 16 provides a cross- sectional view of the ski (2), taken to illustrate the gripping flaps (50)and the actuation pins or posts (45).

As illustrated in the non-limiting embodiment shown in Figure 11 , the 5 waxless ski (2) may include two bi-stable springs (30), a top-plate (35) and an extended plate (36), a main ski body (40), actuator posts, or pins (45), gripping flaps (50) with a contiguous arc at the propulsion providing end in snow contact. The arrows are provided for directionality, and point towards the ski tip (60) and ski tail (61). The top-plate (35) provides the point of contact between the boot of the skier and ski (2). The skier's binding is mounted on top of the top-plate (35). The integration of the top plate (35) with the main ski body can be achieved in several ways, however, depicted in Figure 11 is the "cupping" integration. This cup-like integration, if sufficiently fitted, aims to permit movement of the top- plate (35) in the vertical, y-axis direction only. Without intending to be limited to a particular value, it may be desirable to target movement in this direction to approximately 3mm, or an amount of movement expected to be imperceptible or very near imperceptible to the skier. The extended plate (36) is not visible once the ski is assembled. Rather, it is contained inside a narrow channel of the ski (2) immediately below the top sheet, and functions to engage the gripping flaps (50) located at the forward most portion of the traditional grip pocket of the ski (2).

The actuator posts (45) terminate at their upper end to the underside of the top plate (35), run through a stabilizing channel (not shown) of the main ski body (40), and then likewise terminate with the interior-side of the gripping flaps (50). There are various possible joints envisioned, such as a direct attachment of the posts (45) with the interior-side of the gripping flaps (50), a simple indent in which the post end sits, or a T-shaped terminus, as illustrated in Figures 14 and 15. The actuator posts (45) transfer the energy contained in the high impulse kick exerted by the skier to the gripping flaps (50) in order to deploy their functionality. And, likewise, the posts (45) also transfer the energy exerted by the bi-stable springs (30) as they un-deploy to the gripping flaps (50), thereby providing the force for retraction and reformation of a flush base for optimal gliding. In an alternative embodiment, a channel (lined with low friction (PTFE, FEP etc), may be attached to the flap with a T-shaped terminus to deploy the flaps (50). Other alternative versions of attachment may involve selecting flap (50) material with sufficient elasticity and resilience to enable the flaps (50) to have enough spring on their own so that the posts (45) can be push only. In such embodiments, the posts (45) may not be attached to the flaps (50).

The gripping flaps (50) provide functional grip for the skier. They have been illustrated in Figures 11 to 16 as discrete components, separate from the adjacent base material. However, the forward most edge of the four-sided flap (50) may be continuous with the remaining base material, and additionally is the point of contact where the inherent flex of the base and the supporting materials act as a hinge to allow deployment and retraction. When the bistable spring or springs (30) activate the ski camber to the 'closed' position, the vertical translation of the top-plate (35) and internal extended plate (36) distribute and transfer the force applied by the skier and the activated bistable spring(s) (30) through the actuator posts (45) to the gripping flaps (50), thereby deflecting them such that they protrude out from the ski base to grip the snow. An important element of the gripping flap feature is the consideration of possible snow or ice obstruction. As such, each gripping flap (50) will advantageously incorporate a contiguous arc structure, which is described in further detail below.

The bi-stable springs (30) facilitate the mechanical operation of the gripping flaps (50), enabling precise deployment and retraction. As will be discussed in further detail below, the dynamics of bi-stable spring deployment can be designed to match skier needs with high precision. Use of the bi-stable spring (30) allows superior contact of the grip flaps (50) with the snow over the entire length of the required grip zone, for a longer duration during the stride than in traditional linear flex systems, and in comparison to other known designs which utilize a bearing-spring mechanism which only enables contact of mechanical grips over a small portion of the grip zone.

Referring to both Figures 10 and 11 , it is envisioned that the bistable springs (15, 30) may be either permanently incorporated in the skis (2) and boards, or replaceable. In embodiments whereby the springs (15, 30) are replaceable, the bistable springs (15, 30) may slide into a sleeve that is otherwise continuous with the top (or middle or bottom) sheet of the ski, or utilize any other method enabling the bistable springs (15, 30) to be easily removable and yet solidly constrained when assembled. When multiple springs (15) or (30) are incorporated into skis or boards, different spring stiffnesses may be inserted into the same ski. Alteratively, a self-adjusting spring that becomes stiffer at lower temperatures may be used and need not be changed. The length and stiffness of the bistable springs (15, 30) may be tailored to adjust the length and appropriate weight range/ force required to activate or close each camber or rocker. The length and volume of the cambered or rockered section may be made up partly or entirely of the bistable spring (15, 30). The bistable springs (15, 30) may be built into the constructed layer(s) of the ski or board, inserted into or positioned on top of a traditional ski or board or on top of a activating plate that changes the shape of the camber or rocker. In the alternative, the entire cambered or rockered section of a ski may be entirely comprised of the spring (15, 30), flanged by sections manufactured using traditional ski construction.

The main ski body (40) may be structured such that it resembles the general structure of traditional skis. Incorporating a bistable structure(s) in accordance with the present disclosure to this design enhances the

performance of the traditional camber and ski flex technologies, and thereby provides for improved glide, edging and grip. It also allows one ski to be tunable to different skiers or different conditions of snow. A shorter stiffer bistable spring (15, 30) may be utilized where a short high camber is desired. Alternatively, longer (bigger radius) bistable springs (15, 30) may be desired when insertion or inclusion of the bistable spring structure is intended to add torsional stability to the ski or board, since the springs (15, 30) when locked into their primary or secondary stable states have more resistance to torsional deformation than material that does not have similar locked or primary or secondary stable states.

Mechanism of Bistable Structures

The mechanism of the bistable structures, which can be applied to all cross-country and alpine skis and snowboards as discussed above, are further described in the example of a waxless classical cross-country ski. It is intended to describe this feature using the most complicated example incorporating a mechanical grip into a classical cross-country ski. However, the same principles apply to all skis and boards, including a plethora of ski types including downhill skis and boards and skate and classic (grip) skis. The application of skier force to engage the spring is the same, although the bistable springs may be tailored specifically to flatten the running surfaces to permit edging/turns or grip contact with the snow and tuned for the weight of the skier and the conditions. In response to a high threshold force, such as one that is delivered only by the impulse that is uniquely associated with skier desire for grip, a single longitudinally positioned bi-stable spring, or two of the bi-stable springs that are perpendicular to the running direction, will deploy from their primary stable state to their secondary stable state. In one example of a two-spring model, this deployment will result in a lowering of the top plate and the extended plate in the vertical direction an amount of approximately 3mm with respect to the main ski body. It is the aim that this movement be practically imperceptible to the skier.

Utilizing a bistable spring in a manner as described herein can reduce the energy output requirement for the classical cross-country skier to maintain grip throughout the kick phase and to maintain grip for a longer portion of the stride. Other skiers and boarders will also experience a reduction in energy required to maintain the gliding surface in the contact state. The skis and boards employing one or more bistable or morphing structures are in a sense hybrid structures that store energy and then release it. The non-linear nature of the flex response to lock flat and then release, enables conservation of energy. In this way, for example for the classic cross country ski, the skier is merely required to reach a high impulse in the vertical direction at the beginning of the kick to engage capacity for sufficient grip, while nearly all force production subsequent to deployment can be targeted to forward momentum.

The ease and longevity of grip is enhanced, not only when deploying mechanical grip mechanisms, but similarly, energy and power requirements are reduced when the bistable spring structures are applied to downhill skis and boards, and waxable or even waxless cross country skis (including zeros, hairies, crown skis, fish scales and the like). The spring mechanism can more easily flatten the glide structures for enhanced edging, glide and stability, and maintain the ski or board flatter for better edge contact and control. The springs not only can enhance the glide, but can also enhance the grip performance on any kind of classic cross-country ski.

Bi-stable springs made out of composites enable the force response characteristics to be fully tailored, tunable via the laminate order, fiber type, fiber alignment and placement, and matrix resin selection. The relative direction alignment to loads of specific fiber types with higher or lower modulii as required will enable the constraint of deformation to desired portions of the spring to achieve the desired deformation at the desired positions along the ski, at the intended threshold forces. Composite construction techniques lend themselves well to placement of material where required for strength, stiffness and anisotropic force response. The processes also enable ease of fabrication of complex designs/shapes that may improve constraints of motion to the desired axis in comparison to metal parts which would require precise machining to accomplish the same spatial control of stiffness.

For example, a structure that is intended to behave as a load bearing component but also have a discrete region that exhibits bistable behavior could be manufactured to ensure that applied forces cause deformation to

concentrate in the desired region. This could be achieved by placing lower modulus fiber reinforcement material such as E-glass at the high strain regions of the bistable spring geometry in a structure that is otherwise carbon fiber reinforced and has a higher bending moment '. This would allow, at forces magnitudes useful to the application described herein, deformation of the portions of the structure that need to deform to enable the bistable behavior. Further, in the created region of lower modulus, to truly reinforce the matrix material the alignment of the mentioned glass fiber reinforcement must be approaching parallel to the loads transferred through the material. Multiple fiber layers in multiple orientations can ensure that the complex load cases encountered within a volume of material undergoing stress/strain as is encountered in a morphing or bistable structure are all reinforced.

The allocation of materials to specific locations on the ski or board where their properties are needed enables minimization of weight through placement of materials and strength where required, and maximizing stiffness in the axes that require maintenance of stiffness. The construction strategies/means of achieving the force response profile required for the particular application may include a solid laminate of a single fiber type, a hybrid laminate of one or more fiber type of differing moduli, a cored laminate structure over which either of the preceding laminate types is adhered, wherein the core is comprised of an isotropic or anisotropic material that could be polymer, polymer foam, randomly oriented fiber filled polymer, or any fatigue resistant metal including steel or titanium or any other material that lends itself to making bistable spring structures.

Since there is also potential for thermal effects on the behavior and 20 performance of the spring, such that the thermal expansion could modify the physical geometry of the spring and therefore the force threshold at which it responds, one possible embodiment may include an integration of a separate bi- stable spring which can be inserted according to the force response load required and the temperature conditions in which they are to be used. This can be achieved by altered geometry, reinforcing fiber modulus, fiber direction, matrix modulus, as well as spring design including, but not limited to, width, thickness, primary and/or secondary curvature. The spring material may be selected to capitalize on these properties such that the spring and hence the ski will become either softer or harder with changes in temperature, as desired. The springs may be inserted/removable or permanent and a option for the permanent spring is that the spring is made of temperature-sensitive self- adjusting materials where the spring and hence the ski become stiffer with colder temperatures, eliminating the need for different skis for 'cold' versus 'warm' conditions.

The camber or rocker portion of a ski or board may alternatively be entirely or partly comprised of spring material. The proportion of spring material versus other material required for ski construction may be variable, depending on desired ski or board characteristics. For example, if the spring is constructed by laying down carbon fibers or composite fibers, these are good for general ski construction, and the entire camber may be comprised of only the spring. The spring camber may be flanked by sections of the ski that are made by traditional ski construction. Alternatively, the bistable spring may be built into, inserted into or placed on top of traditional ski construction.

Contiguous Arc

Referring to Figure 13, for good ski performance it is important that the gripping flaps (50) have the freedom to deploy and retract under the forces of the kicking cycle only. Snow or ice crystal entrainment into the retraction cavity (55) that might cause an obstruction can exert an extraneous force and prevent the retraction of the gripping flaps (50) into the base of the ski. Snow and ice crystals of sufficient size capable of obstructing the gripping flaps (50), however, can be prevented from actually obstructing the retraction by incorporating a contiguous arc (57) design into the gripping flaps (50), as shown in Figure 13.

The contiguous arc (57) includes a curvature to the face of the gripping flaps (50). This curvature matches the profile of the interior of the ski so as to create a tight fit and prevent any openings or gaps in the base that might otherwise result as the gripping flaps (50) deploy. The contiguous arc (57), therefore, eliminates the possibility for snow chunks and ice crystals of sufficient size for obstruction to actually obstruct the retraction by ensuring a tight fit between gripping flap and adjacent ski base.

Conclusion

The traditional ski or board consists of a camber that flexes

proportionally, with a linear response relationship, with increased force delivered by the skier. The cambers are 'closed' or flattened with application of force or pressure and as soon as this pressure is removed or lessened, the camber begins to Open'. The transitions are gradual and linear (proportional to force), being punctuated only by the higher forces applied by skier/boarder bodies and weight shifting. The disclosure herein embodies cambers and rockers that have properties of morphing bistable structures which permit nonlinear flex responses, conservation of energy and superior responsiveness and performance. To a skier or boarder on equipment enhanced with bistable (spring) structures, it is clear when a camber or rocker is Open' or 'closed' or in the process of transitioning. Once sufficient force is applied to exceed a threshold for the bistable structure to effect 'closure' of the camber, the camber closes and remains closed until sufficient opposing forces (such as the natural shape of the ski) combine with removal of exerted force to transition or snap the ski camber back into its primary stable state. The skis and boards incorporating bistable structures feel more responsive, peppier, make better edge contact and provide more control than those without. The objective for glide-only skis and boards is to obtain the right balance of ski stiffness and camber shape (flex) to permit good glide properties, sufficient torsional strength to confer stability at fast speeds, while having enough softness to permit engagement of the camber to give edge contact and control while cornering/carving or doing tricks or in the case of classic XC skis-getting grip. The camber flex and shape in a traditional ski or board is a linear force-response relationship. By incorporating bistable structures into the ski or board structure as described herein, there is a threshold force that needs to be applied to change the camber shape, and once this minimum force is attained, the camber or rocker remains engaged even while the force applied is eased up, until sufficient force is applied to return the bistable spring based structure to its arched position. Such a non-linear camber flex is suitable to mechanical requirements for hold time and completeness of grip throughout the entire camber zone. Such a non-linear camber flex will also permit enhanced flattening of the ski to allow more contact and edge control on cornering for all skis and boards. The addition of a linear bistable spring structure also reduces torsional distortions while the ski or board is running, enabling faster skis that are less 'skittish'. Hence the use of bistable structures as provided herein is applicable to both racing and recreational skis to enhance performance and ease of use and to confer energy savings while providing increased performance.

This technology is applicable to not only glide-only downhill skis and boards, but is also applicable to cross-country skis where grip is required.

Classic Nordic skis are required to perform two highly disparate tasks: grip the snow sufficiently, and glide maximally. Regardless of what physical method is used for grip (e.g. wax, hairies, crowns, fish-scales or the like), the bistable spring technology allows the camber to be flattened more easily and remain in the flat or contact state for a longer period, while the force on the ski is starting to be reduced during the end of the 'kick'. This allows superior grip and kick for both racing and recreational users and makes the classic ski experience more enjoyable for recreational users that do not have strong kick forces or good weight shift. Moreover, bistable structures can also be incorporated into a new type of classical waxless ski which employs a conformational change in the grip zone of the base during instances of skier demands for grip, so as to enable maximal glide in the ski in the alternative position. This method exploits the compressive properties of snow and structural grip mechanisms, as opposed to the required relationship between the highly variable snow characteristics and the many grip waxes, making it applicable to all snow types, temperatures and humidity conditions.

Thus, disclosed herein are morphing structures included into sliding objects, typically, but not limited to skis and snowboards. One or more morphing structures may be incorporated into the ski or snowboard depending on the type of activity contemplated for the ski or snowboard. When incorporate into skis, the skis may be any kind of ski such as alpine, cross country skate or classic, freestyle, snowblades, telemark, ski flying, ski jumping, ski

mountaineering, skijoring, speed skiing, superpipe skiing, backcountry skiing, extreme, free, glade, grass, half-pipe, mogul, para-skiing, ski cross slope-style, kite-skiing, snow kiting, slalom, touring, skis/runners/gliding surfaces on manual or automated sleds or related variants of ski and gliding technique equipment.

When incorporated into snowboards, the snowboard may be any type of snowboard such as freestyle, park/jib, freeride, carver, powder, all-mountain, racing/alpine, splitboard and dual snowboards or variants thereof. A non- limiting embodiment of a morphing structure is a bistable spring in which the spring axis may be oriented parallel to the running direction of the gliding object or oriented perpendicular to the running direction of the gliding object, or more than one bistable spring may be incorporated, with at least one spring oriented parallel to the running direction of the gliding object and at least one other spring oriented perpendicular to the running direction of the gliding object. The bistable spring functions to change the force-flex relationship of a particular aspect of the ski (or snowboard) whether that be the force-flex relationship of a rocker, a camber, torsional flex, or any other flex of a ski that may be desirable to control more precisely. The bistable spring(s) function to exert a force over the general shape of the ski while in its primary stable state, thus maintaining a desirable ski shape with reduced force input.

The change of shape of the gliding object is maintained for a time, while force exerted by the athlete is decreasing, until an opposing force threshold is exceeded. The bistable spring functions to permit increased flex for a given force input while the spring is in its secondary stable state. The maintenance of the ski shape by the bistable spring when in its primary stable state conserves athlete energy and effort required to maintain the changed, desired shape of the ski. The bistable spring thereby stores energy in the secondary stable state until an opposing force threshold is exceeded. The morphing structure (bistable spring) is configured to change the force required to close a camber, and maintain a closed camber, of the ski or snowboard at at least one point throughout the displacement of the camber.

The morphing structures may be tunable such that the stiffness of the camber and the forces required to close the camber may be tuned so that the camber length may be of short, medium or long length. The bistable structures may be constructed within the body of the ski or snowboard. For example the bistable structures may be inserted into pockets produced within the ski, or they may be positioned on top of a ski, or they may be positioned on top of a plate on top of a ski or snowboard.

The cambered or rockered section(s) of a ski or board may be comprised partly or entirely of one or more bistable springs (where in the extreme, the entire camber section of a ski may be made of spring material) and the springs are flanked by sections of ski or board that are made using traditional construction. The bistable structures may be constructed of fiber reinforced composites that incorporate one or more of: short, long, chopped, or continuous reinforcing fibers of carbon, glass, boron, or ceramic, in a polymer or metallic matrix material that is either cast, extruded, or molded; or alternatively may be constructed of metal alloy (e.g., steel, titanium.). The bistable structures may be constructed of carbon fiber, carbon fiber compositions, metallic material or composites. The inclusion of a bistable structure within a ski or snowboard may be designed to increase the torsional stability of that portion of the ski or board.

The morphing structures may be tuned so that the springs fully transition or partially transition from the first stable state to the second stable state. The forces applied to transition from one of the two stable states to the other may originate from the athlete exerting a force, the tension in the ski or board exerting a force, a camber force, the removal of the force that was originally applied to 'close' the camber, a torsional force, a centripetal force, and vibration.

While the Applicant's teachings described herein are in conjunction with various embodiments for illustrative purposes, it is not intended that the applicant's teachings be limited to such embodiments. On the contrary, the applicant's teachings described and illustrated herein encompass various alternatives, modifications, and equivalents, without departing from the embodiments, the general scope of which is defined in the appended claims.

Except to the extent necessary or inherent in the processes themselves, no particular order to steps or stages of methods or processes described in this disclosure is intended or implied. In many cases the order of process steps may be varied without changing the purpose, effect, or import of the methods described.