TITLE: Deformable Elements made from Composite Structures The invention relates to deformable elements, like crash elements for vehicles, constructed from composite layer (or sandwich or laminate) structures comprising at least one first and at least one second cover sheet (layer) between which a core (or intermediate) sheet (layer) with a filling material is provided. (The terms "composite", "sandwich"and laminate"structure shall be considered equivalent in this disclosure. The same applies for the terms"sheet"and"layer".) The cover sheets and the filling material each can be made of steel, aluminium or any other metallic materials, even alloys, or can be made of non-metallic materials like synthetic materials (for example nylon), ceramics, textiles or paperboard, or substances or compounds composed of those, wherein the cover sheets itself can be made of different materials as well.

The filling material comprises for example a composition of flock material or fibers like short cutted fibers (flock fibers) and an adhesive. For the filling material, the same materials as those mentioned in the previous paragraph can be used. Further, the filling material and at least one of the cover sheets can be made of the same or different materials, wherein according to the type. of application nearly any combination of materials for the cover sheets and the filling material of the core sheet can be chosen.

Exemplary materials for the cover sheets and the core sheet as well as methods for the production of those sandwich structures are disclosed in EP 1 059 160 and EP 0 333 685 which by reference shall be made to a part of this disclosure.

These flat (plain or planar) or at least substantially flat (plain or planar) composite layer materials (plates) have numerous advantages over solid materials with the same dimensions. In dependency of the type, the form, the density, the thickness, the length and the orientation of the fibers and the properties of the adhesive, for example a particular low weight, a high flexural strength or a superior mouldability and flexibility, respectively, as well as a very high mechanical and acoustic energy absorption and isolation can be obtained, wherein the structures furthermore can be provided with an insensitive and corrosion resistant surface.

All these properties can be optimized according to the proposed machining (like bending, deep-drawing, welding, cutting and so on) as well as according to the application of the composite material.

WO 98/01295 discloses formable sandwich construction materials which comprise at least two plates with intermediate metallic fibers. By this, substantially a higher temperature resistance shall be obtained in comparison to those structures which comprise fibers of organic materials. The manufacture is conducted by covering the plates with an adhesive and then by electrostatic deposition of the fibers onto the adhesive ("electrostatic flocking") so that they are substantially perpendicularly fixed on at least one of the plates. Then the plates are pressed onto each other and the adhesive is hardened.

In the MIT (Massachusetts Institute of Technology) Report No.: 71"Experimental and Theoretical Study of the Crushing of HSSA Double-Cell Profiles"by D. Mohr and T. Wierzbicki, several investigations regarding the properties of sandwich structures crushed under axial loading are disclosed. Furthermore, models for predicting shear-folding and the mean crushing force as well as the deformation characteristic of several hollow profiles are disclosed.

It is a generell object of the invention to realize the above mentioned advantages of composite layer structures for deformable elements with an at least

substantially non-reversible deformation as well and to provide such deformable elements which are especially usefull for energy absorption.

Furthermore, it is an object of the invention to provide deformable elements whose deformation characteristic or deformability can be controlled or predetermined in a desired manner by way of at least one of the design parameters of the elements.

It is as well an object of the invention to provide deformable elements which can be designed, constructed and optimized in a relatively simple manner for the absorption of energy acting upon the element in either an axial direction, in a direction perpendicular to the axis or as a torque.

It is another object of the invention to provide deformable elements which upon affected by a force show an increased and progressive energy absorption, i. e. a displacement which is dependent upon the exerted force over a region which is considerably larger than with usual deformable elements.

These objects are solved according to claim 1.

A specific advantage of this solution is the fact that in dependence of the design of the composite structure used for the manufacture of the deformable element, a plurality of different properties regarding the relationship between the force acting upon the deformable element and the length and form of deformation can be obtained.

Preferred applications for such deformable elements are crash members or crash elements for controlled degradation and absorption of crash energy, for example for use in vehicles.

The subclaims disclose advantageous embodiments of the invention.

Further details, features and advantages of the invention result from the following description of exemplary embodiments of the invention in connection with the drawings, in which schematically shows: Fig. 1 a deformable beam partly deformed by a force exerted on the same ; Fig. 2 a test set-up for testing deformation of a deformable beam; Fig. 3 a deformable element in the form of a beam made of a composite structure ; Fig. 4 a first curve showing the dependency between the exerted force and the displacement of the beam according to Figure 3; Fig. 5 a second curve showing the dependency between the exerted force and the displacement of another beam ; Fig. 6 a deformable element according to a first embodiment of the invention; Fig. 7 a longitudinal section through the first embodiment as shown in Figure 6 ; Fig. 8 a view of the first embodiment as shown in Figure 6 after deformation ; Fig. 9 a longitudinal section through a deformable element according to a second embodiment of the invention; Fig. 10 a flat composite structure for the manufacture of a deformable element according to a third embodiment of the invention ; Fig. 11 cross sections through the composite structure according to Figure 10 ; Fig. 12 a deformable element according to a third embodiment of invention ; Fig. 13 a view of a car comprising several deformable elements according to the invention ; Fig. 14 a deformable element according to a fourth embodiment of the invention in the form of a wheel house; Fig. 15 a side view of a car comprising wheel houses according to Figure 14 before deformation ; Fig. 16 the car according to Figure 15 after deformation ; Fig. 17 the wheel house according to Figure 14 after deformation ;

Fig. 18 the deformable element according to the Figure 12 after deformation ; Fig. 19 an application of the deformable element according to Figure 12; Fig. 20 a view of a car comprising deformable elements according to a fifth embodiment of the invention in the form of a first side crash protection element; Fig. 21 the deformable element according to the fifth embodiment of the invention in the form of a first side crash protection element before deformation; Fig. 22 the deformable element according to Figure 21 after deformation; Fig. 23 a deformable element according to a sixth embodiment of the invention in the form of a second side crash protection element before deformation; Fig. 24 the deformable element according to Figure 23 after deformation; and Fig. 25 a deformable element according to a seventh embodiment of the invention in the form of a torque protection element.

According to the above mentioned MIT-Report, Figure 1 shows a very general behavior of a beam-like deformable element 1, made of a composite structure, under the influence of a force F which acts axially onto the deformable element, if this element is fixed on its opposite side. The deformation starts in the region of the side onto which the force F acts upon.

For testing deformable elements under an axial load, a test set-up as shown in Figure 2 can be used. The deformable element 1 to be tested is pressed by means of a press 2 or a similar device against a fixed plane 3. For evaluating the deformation characteristic, the force F exerted onto the element 1 and the displacement z (i. e. the length of deformation) of the tested element 1 are detected.

With such a test set-up and a deformable element 1 in the form of a beam with a single wall which is made of a composite structure and having a substantially

rectangular cross section as shown in Figure 3, a deformation characteristic (crash resistance force curve) according to Figure 4 is obtained.

Figure 4 shows that in a first region (plastic deformation) the deformable element 1 can resist and absorb the exerted force F with a relatively small displacement z which is at least substantially proportional to the exerted force F, until a maximum value of the force F is exceeded and a second region (folding deformation) begins, in which the structure cannot absorb energy anymore but is only deformed and finally destroyed completely (horizontal region of the curve).

However, such a deformation characteristic is in most cases detrimental.

For improving the protective properties, it is often desired to achieve a deformation characteristic which in dependence of the applied force F has a proportionality over a considerably greater length of deformation z. Furthermore, the maximum force F which the deformable element can resist shall often be greater as well. Such an ideal deformation characteristic is schematically shown in Figure 5, curve (a).

An extended proportionality between the length of deformation z and the force F exerted on the deformation element can be obtained for example by increasing the strength of the deformable element progressively in the direction of the impacting force F, i. e. in the direction of its length (z-direction).

This can be achieved for example by providing a deformable element with an increasing diameter and/or an increasing thickness of its walls and/or by variation of the filling material and/or its density within at least one of the core sheets and/or by variation of the material of at least one of the cover sheets.

Exemplarily, Figure 6 shows in a three-dimensional view and Figure 7 in a longitudinal section such a deformable element according to a first embodiment of the invention.

This element is made of a composite structure with a progressively increasing number of layers 10,11, 12,13 which are arranged like in a telescope, which are each provided by at least two cover sheets with one core sheet therebetween.

By this element, a step-by-step course of the dependence between the force F exerted upon the deformation element and the length of deformation z can be achieved according to curve (b) in Figure 5. This curve is composed of first regions in which each one layer 10,11, 12,13 is substantially deformed proportionally to the applied force (plastic deformation) and second regions in which the same layer cannot absorb energy anymore until the deformation reaches the next layer in z-direction. In this way, the curve (b) is composed for each layer of a curve as depicted in Figure 4.

The approximation of curve (a) by curve (b) can be improved for example by increasing the number of layers 10,11, 12,13 over a given length of deformation z.

Figure 8 shows the deformable elements according to Figur 7 in a three dimensional view after deformation.

Figure 9 shows a second embodiment of the deformable element in longitudinal section. In contrary to the first embodiment, the cross section and the thickness of the wall of the deformable element remains constant. This is obtained by extending the cover sheets of each layer 10,11, 12,13 over the whole length of the deformable element (z-direction). However, for obtaining the desired and

above mentioned deformation characteristic, the core sheets remain free of filling material in the regions where the cover sheets have been extended. In this way, the deformable element is as well provided with a progressively increasing strength in the direction of the impacting force F, i. e. in the axial direction of the deformable element.

Alternatively and/or additionally a deformation characteristic with an extended proportionality and an improved approximation of curve (a) in Figure 5 can be achieved for example by choosing different materials with different strength-and flexibility-properties for the cover sheets and/or the filling material of the core sheets (especially fiber material and adhesive) of at least one of the layers 10,11, 12,13 and along at least one of the extensions of the layers in such a way, that the deformation element is provided with an increasing strength in its axial direction.

Furthermore, for influencing the deformation properties, the hollow space within the deformation element and/or within at least one of the core sheets of the layers can for example be filled with a fluid like an oil or a gas like nitrogen.

Finally, even cover sheets and/or core sheets with varying thickness can be used for improving said approximation.

Figure 10 shows a flat composite layer structure 20 which is composed of a plurality of cover sheets with core sheets therebetween in the above mentioned manner. This structure 20 is provided with substantially parallel running lines 22 of a local weakening of the structure.

This weakening is for example obtained by a local annealing of at least one of the cover sheets as schematically indicated in Figure 11 (A) with a bracket and/or by at least one area of at least one core sheet having no filling material or filling material with a decreased density. Figure 11 (B) shows the last alternative for three

core sheets with such areas 23 which are slightly offset from each other in the plane of the structure 20. However these areas 23 could also be aligned above each other in the direction perpendicular to the plane of the structure 20.

Furthermore, the structure 20 is provided on one side with three notches 21 which have a distance from each other and which are so dimensioned with respect to their opening angel that a hollow beam 25 with a substantially rectangular cross- section can be folded according Figure 12, to obtain a third embodiment of a deformable element according to the invention.

This hollow beam 25 comprises at and along its walls a spiral line which runs circumferentially around the beam 25 and which is weakened in comparison to the adjacent areas of the wall. By appropriately choosing the course and dimensioning of this spiral line 22, a certain deformation characteristic is obtained upon a force exerted in axial direction onto the beam 25 which shall be explained later.

Furthermore, the bending stiffness of the beam 25 can be decreased by this line 22.

A certain bending property of the beam in a predefined manner can additionally be achieved if one wall or two opposing walls of the beam 25 have a different stiffness and/or mechanical resistance in comparison to the other walls.

The design of this beam 25 can be combined advantageously with the first or second embodiment of the deformable elements according to Figures 6 and 9 wherein one or more of the layers 10,11, 12,13 are provided in the form of the third embodiment according to Figure 12.

Figure 13 schematically shows a car in which several deformable elements according to the invention and functioning as crash elements are installed. These

are substantially the front inner wheel houses 30, the back inner wheel houses 31 and two so called S-beams 32 running between the front of the car and a part of the engine 35.

Figure 14 shows an enlarged view of the front inner wheel house 30 as a fourth embodiment of the invention. In a similar manner as shown in Figures 10,11 and 12 this deformable element is as well provided with a plurality of weekend lines 301. The weakening can again be obtained by a local annealing of at least one of the cover sheets and/or by providing at least one of the core sheets 302 without filling material or with filling material with a decreased density along the lines.

Reference is made to Figures 11 (A) and (B).

By dimensioning and arranging these lines 301 in an appropriate way, a desired und predefined deformation characteristic can be obtained.

Figures 15 and 16 show in a side view a comparison between these deformable elements in a normal condition (Figur 15) and after a crash of the car (Figure 16).

Figure 16 shows how the deformable elements are affected by such a crash if they are designed with respect to their deformation characteristic appropriately.

Figure 17 shows an enlarged view of the front inner wheel house 30 according to Figure 14 and Figure 16 after deformation. From Figure 17 it is obvious how the deformation characteristic can be controlled in a predefined manner by choosing the number and the course of the weakened lines 301 of the deformable element in an appropriate way.

This as well applies to the beam 25 shown in Figure 12 with respect to its deformation upon the influence of an axially loading force as indicated in Figure 18. This Figure shows that the spiral run of the weakened lines 22 leads to a

deformation characteristic which comprises an axial displacement and a simultaneous turning or twisting of the beam 25 according to the arrow F in Figure 18.

If this deformable element is used as the S-beam 32 according to Figure 13, a crash behavior can be achieved which is schematically shown in Figure 16 and in detail in Figure 19. These Figures show that in case of a crash and upon the turning or twisting deformation of the S-beam 32, the engine 35 of the car is swung down to the ground and consequently away from the passenger of the car.

Figure 20 schematically shows a car with deformable elements 40 according to a fifth embodiment of the invention. These elements 40 are provided as side crash protection elements.

Figure 21 shows such an element in an enlarged view. In contrary to the first, second and third embodiment of the invention this deformable element 40 is designed to receive and degrade crash energy which is exerted perpendicular to the axis of the element 40.

In the regions of its axial ends, this element 40 is provided with each one pair of two weakened lines 41,42 ; 43,44 running parallel to each other and perpendicular to the axis of the deformable element 40, wherein each two lines 41,42, 43,44 enclose a notch-like form for achieving the folding characteristic at the edge as shown in Figure 22.

The weakened lines 41,42 ; 43,44 are obtained again preferably in the same manner as depicted in Figure 11 (A) or (B) so that reference is made to the related description in connection with this Figure.

With these weakened lines 41,42 ; 43,44 a deformation characteristic can be achieved as shown in Figure 22. The advantage of this deformable element 40 is the fact that upon a perpendicularly exerted force, which acts on the intermediate part 45 of the element 40 between the two pairs of lines 41,42 and 43,44, this intermediate part 45 is displaced substantially parallel and along its whole length, without substantially being bended itself by the force, so that a passenger of the car is more efficiently protected against a side crash than with a known bending beam.

Figure 23 shows a deformable element according to a sixth embodiment of the invention in the form of another side crash protection element 50. Additionally to the two first pairs of weakened lines 53,54 ; 55,56, corresponding with those of the fifth embodiment according to Figure 21, two second pairs of weakened lines 51,52 ; 57,58 are provided between the first pairs 53,54 ; 55,56 and the axial ends of the element, wherein these lines 51,52 ; 57,58 extend only along the smaller side of the rectangular cross section of the element 50 and wherein each two lines 51,52, 57, 58 again enclose a notch-like form for achieving the folding characteristic at the related edge as shown in Figure 24.

By this, another deformation characteristic can be achieved according to Figure 24 with respect to the axial end regions of the element. However, the intermediate part 59 of the element 50 between the first pairs of lines 53,54 and 55,56 is again displaced substantially parallel and along its whole length to protect the driver of the car efficiently against a side crash.

Additionally, the deformation characteristics of the elements shown in Figures 21 and 23 can be improved if for example the intermediate parts 45; 59 are provided with an increased stiffness. Furthermore, the elements can be provided especially in the regions of their axial ends with elastic or reversible properties, so that if subjected to a minor crushing force, they are not disturbed but can be used again.

Both this can be achieved for example by a variation of the density, type, orientation etc. of the filling material within one or more of the core sheets or by selecting an appropriate material for at least one of the cover sheets. Alternatively, the intermediate parts 45; 59 can be made of a solid material as well to achieve the desired deformation characteristics, so that the deformable element has a hybrid structure.

Finally, Figure 25 shows a deformable element according to a seventh embodiment of the invention which is provided in the form of a torque protection element 60. This element comprises a shaft 61 with an intermediate section 62 which is weakened with respect to its torque transmission capability in comparison to the other axially adjacent sections of the shaft 61, so that upon exceeding a predetermined torque, the intermediate section 62 will be deformed.

The shaft 61 is made of a cylindrical composite layer structure with a circular cross section which is enclosed by an outer cover sheet. The intermediate section 62 is obtained for example by weakening the cover sheet by annealing it and/or by providing one or more core sheets which are free of filling material or contain a decreased density of the filling material. In other words, a low density MMC ("Metal Matrix Composite") material is used for the intermediate section 62.

Again, reference is made to Figure 11 (A) and (B) and the related description.

Deformable elements according to the invention can be designed in a great number of different shapes, forms and embodiments. Further, if they have an at least substantially longitudinal dimension, they can be designed to absorb axial forces as well as forces acting upon the element in a direction perpendicular to the axis and/or to absorb torque-forces.

Consequently and also because of their low weight, the deformable elements according to the invention can be applied as crash elements for cars, busses, trucks and other vehicles or boats or even airplanes, as well as for example as static or supporting elements having a defined folding characteristic upon loaded with a force which exceeds a predetermined threshold value.

The scope of protection of the invention shall not be restricted to the embodimentsas described above but is defined by the claims as appended.