A MICRO LATTICE STRUCTURE

CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY

The present application claims priority from Indian patent application(s) number 201921014889.

FIELD OF INVENTION

The present invention in general relates to lattice structures. More particularly, the present invention relates to micro lattice structures with enhanced strength to weight ration and high plastic collapse strength.

BACKGROUND OF INVENTION

Lattice structures are truss-like structures generated by periodic arrangement of cells structures. The cell structures are of pyramidal, tetrahedral and wire oven Kagome structures. Textile lay-up, brazing or welding and forming are some of the manufacturing techniques available for the manufacturing lattice structures. Lattice structures are designed to attain maximum load bearing geometry with reduced total mass of the overall structure. Nowadays, the Lattice structures are reduced from the macro scale to micro scale. If the structure is reduced to micro scale, the material properties like energy absorption capacity and strength to weight ratio increases drastically.

A standard body centered cubic (BCC) structure having a lattice point located at the centre of a cube is represented in Fig. 1A. Each lattice point is connected to the 8 other points. The conventional unit cell contains 8 lattice points at the vertices, each being shared by 8 cells and another lattice point that is completely inside the conventional unit cell. A unit cell of the said BCC structure, which is obtained by connecting the centre points of two nearest cubes is represented in Fig 1A.

The connection between atoms within the said BCC atomic structure is realized by replacing the connections with a micro size link. At each junction/node, eight links are combined together. The overall connection is represented in Fig 1A.

For every mechanical system life decreases due to the excess of vibrations, which are produced by the external forces and weight. Weight reduction, improving the strength to weight ratio is the ever-demanding need of structural applications, especially in aircraft and automobile industries. Lattice structures decreases the weight of the structure and predominantly decreases the vibrations produced in the mechanical systems. This property is essential, especially in the aircraft industry. Most of the aircraft industries are using the sandwich structures because of its strength and stiffness properties. The vibrations in the wings of the aircraft are very high. Most of the aircraft wings failed due to excess vibrations and birds colliding during flight.

Micro lattice structures are being used in the recent past for aerospace applications. However, the lattice structure being used for these applications have a uniform cross-section as represented in Fig 1B, which results in failure of the micro lattice structures during intense vibrations and high load conditions.

The present inventor motivated to pursue their research to obviate the problems associated with the prior arts and focused in the instant invention, which eliminates all the long-standing limitations not limited to the above described and provide a new micro lattice structure with enhanced strength to weight ration and higher plastic collapse strength.

OBJECTIVES OF THE INVENTION

The main object of the present invention is to provide new micro lattice structures of Figure (1A) with improved yield strength, modulus of elasticity and plastic collapse strength as compared to conventional micro lattice structure in a simple and user-friendly manner.

Another objective of the present invention is to provide new micro lattice structures of Figure (1 A) with enhanced strength to weight ratio including the higher plastic collapse strength.

Yet another objective of the present invention is to provide a process for the preparation of the new micro lattice structures of Figure (1A) and their various application thereof.

Still another objective of the present invention is to provide a new micro lattice structures of Figure (1A) in an economical and commercial manner.

SUMMARY OF THE INVENTION

Before the present assembly and its components and its method of use is described, it is to be understood that this disclosure is not limited to the particular apparatus and its arrangement as described, as there can be multiple possible embodiments, which are not expressly illustrated in the present disclosure but may still be practicable within the scope of the invention as determined by claims. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only and is not intended to limit the scope of the present application. This summary is not intended to identify the essential features of the claimed subject matter nor it is intended for use in detecting or limiting the scope of the claimed subject matter.

In an embodiment, a micro lattice structure is disclosed. The micro lattice structure comprise a set of body centred cubic structures. Each body centred cubic structure comprises a set of nodes, wherein each pair of neighbouring nodes, from the set of nodes, is connected by a strut. Further, each strut is a concave cylinder with two extreme ends connecting a pair of neighbouring nodes from the set of nodes and a tapered middle portion. The thickness of the tapered middle portion is less than the two extreme ends. Further, the thickness of the two extreme ends and the tapered middle portion is proportional to length of the strut.

BRIEF DESCRIPTION OF DRAWINGS

The detailed description is described with reference to the accompanying Figures. In the Figures, components are identified by two right-most digits of reference number, however the left most digit in three-digit numbers is used to provide further detailing of a component. The same numbers are used throughout the drawings to refer like features and components.

Figure 1A illustrates eight cells forming standard BCC structures, in accordance with an embodiment of the present disclosure.

Figure 1B illustrates a conventional micro lattice structure, with uniform strut thickness, in accordance with an embodiment of the present disclosure.

Figure 2 illustrates a micro lattice structure with variable strut thickness, in accordance with an embodiment of the present disclosure.

Figure 3 illustrates comparison of yield stress ⁱ a _y BCC values for conventional micro lattice structure and micro lattice structure with variable strut thickness using finite elemental analysis (FEA) and experimental results with relative density as plotted, in accordance with an embodiment of the present disclosure. Figure 4 illustrates comparison of Elastic Modulus‘ EBCC values for conventional micro lattice structure and micro lattice structure with variable strut thickness using FEA and experimental results with relative density as plotted, in accordance with an embodiment of the present disclosure.

Figure 5 illustrates comparison of plastic collapse strength s _r i values for conventional micro lattice structure and micro lattice structure with variable strut thickness using FEA and experimental results with relative density as plotted, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a micro lattice structure with improved yield strength, modulus of elasticity and plastic collapse strength as compared to conventional micro lattice structure. The shape of the beams/ struts of the micro lattice structure have varying cross-section with a thinner cross section at the middle and thicker at the node ends.

Referring to figure 1A, eight cells (Al, A2, B l, B2, Cl, C2, Dl and D2) forming four standard BCC structures is illustrated in accordance with an embodiment of the present invention. Each cell contains 8 lattice points at the vertices (104), each being shared by 8 neighbouring cells and a lattice point that is completely inside each cell. The figure 1A represents 8 nearest neighbours (108) and 6 next-nearest neighbours (106) with respect to the reference point (102). Further, the cells A1-A2, B 1-B2, C1-C2, and D1-D2 are placed one above the other and form four standard BCC structures. A standard BCC structure (100) between cells Dl and D2 is realized by replacing the connection between the nodes with a micro size link as represented in figure 1A. Similarly, at each junction, eight links are combined to form the BCC micro lattice structure represented in figure 1B.

Referring to figure 1B, which represents a conventional BBC structures (200) in a conventional micro lattice structure, having uniform strut thickness, in accordance with an embodiment of the present disclosure. The conventional BBC structures (200) comprises six vertices (106) and 8 struts (202). Each strut (202) has uniform cross-sectional area. Due to the uniform cross-sectional area, the bond between the struts (202) formed at the vertices (106) is a week bond and is susceptible to failure during high load or vibrations. As the length of the strut increases, the load bearing capacity of the conventional BBC structures (200) also reduces. Also due to uniform thickness of the strut (202) at the vertices/ nodes (106), the bond between the struts (202) at the nodes (106) are susceptible to failure during high vibration conditions.

To overcome the above problem, a micro lattice structure with variable strut thickness is disclosed in the present invention. The micro lattice structure may comprise a set of Body Centred Cubic (BCC) structures. A BCC structure (300) of the micro lattice structure with variable strut thickness, is represented in figure 2. The body centred cubic structure (300) comprises a set of nodes (308), wherein each pair of neighbouring nodes (308) is connected by a strut (302).

In another embodiment, all the eight struts (302) may be concave cylinders. Each strut may have two extreme ends (304) connecting a pair of neighbouring nodes from the set of nodes (308). Further, the strut (302) may have a tapered middle portion (306).

The thickness of the tapered middle portion (306) is at least less than the two extreme ends (304). The ratio of thickness of the tapered middle portion (306) to the two extreme ends (304) of the strut (302) may be in the range of 1: 1.2 to 1.3. Further, the length of the strut (302) may be in the range of 0.9mm to 2mm. Furthermore, diameter of tapered middle portion (306) may be in the range of 0.18mm to 0.19mm, and wherein the diameter of the two extreme ends (304) may be in the range of 0.2 lmm to 0.24mm.

In another embodiment, the thickness of the two extreme ends (304) and the tapered middle portion (306) is proportional to length of the strut. The variation in the ration of thickness between the tapered middle portion (306) and two extreme ends (304) is dependent on the length of the strut (302). For example, if the length of the strut (302) increases, then the thickness ratio between the tapered middle portion (306) and two extreme ends (304) may also increases. If the length of the strut (302) decreases, then the thickness ratio may also decrease.

In yet another embodiment, the raw material used for manufacturing of the strut may be Stainless Steel 316F. Further, the set of body centred cubic structures may be manufactured using Faser Sintering (Metal 3- dimensional Printing), textile lay-up, brazing, investment casting, or welding and forming technique. In still another embodiment, the set of body centred cubic structures (300) may form a truss structure for supporting high resonating structures. The high resonating structures may be one of oil vessels, an airplane wing(s), and airplane body. The use of the micro-lattice structure with set of body centred cubic structures (300) as cores in the construction of the aircraft wings and fuselage of the aircraft predominantly may enhance the strength, energy absorption capacity and result in less volume damage in case of bird collide conditions. The micro-lattice structure with set of body centred cubic structures (300) may also be used in the construction of big vessels for transferring the oil through shipping. During transporting the oil through shipping, there are many vibrations produced in the vessel. The micro lattice cores with set of body centred cubic structures (300) may be arranged around the vessel to enhance the shock load absorption capacity and safety.

The present invention defined the micro lattice structures alongwith the set of body centred cubic structures (300), the strength of the structure may be increased by 20 to 30%, which has a greater impact on the energy saving. The energy required to propel the structure is also saved in the similar proportion as the weight reduction is accomplished, which enhances the speed of the aircraft and oil vessels. The micro lattice structures disclosed in the present invention is useful in the jewellery, smartphones and related industries.

EXPERIMENTAL RESULTS

Structures with different sizes of beam/strut length were considered for carrying out FEA analysis. A significant improvement in yield strength, modulus of elasticity and plastic collapse strength was observed in this analysis and represented hereafter.

Four models of conventional BCC micro lattice structures as shown in Figure 1B with four different sizes of edge lengths ‘L’ (2.5mm, 2.0mm, l .5mm, l .25mm) were prepared. The conventional BCC model was prepared with a circularcross-section of diameter 0.2 mm. Similarly, 4 models of enhanced BCC micro lattice structures were prepared as shown in Figure 2 with the same 4 different sizes of edge lengths‘L’. The cross-section diameter of the enhanced structure was varied in the range of 0.23 to 0.17 mm. Finite element analysis was carried out. The material used for the analysis was Stainless Steel 316L (SSL316L). To improve the stiffness of the structure without increasing the mass, the enhanced BBC micro-lattice structure was modified, thereby enhanced with a cross-sectional area in nodal regions and +reduced as the centre of each strut. While increasing the cross-section of each small beam at the node and decreasing it at its mid length care was taken to keep the same overall weight of each beam. Thus, without increasing the weight of the structure significant improvement is obtained in the properties of the structure.

Yield stress, elastic modulus and plastic collapse strength comparison with relative density is represent hereafter.

The yield stress o _y of the BCC lattice stucture with FEA (solid element) and experimental graph for four edge lengths is shown in Table 1. The yield stress a _y of the enhanced BCC lattice stucture of figure 2 with FEA solid element graph for four edge lengths as shown in Table 1.

The elastic modulus of lattice structure is found from stress-strain results. The elastic modulus of the BCC Lattice structure with FEA (solid element) and experimental approach as presented in Table 2. The elastic modulus of the Enhanced BCC Lattice structure with FEA (solid element) approach is presented in Table 2. The theoretical analysis was done by using the emperical equation given by the research paper K. Ushijima et. al.“K. Ushijima, W. J. Cantwell, R. A. W. Mines, S. Tsopanos andM. Smith,“An investigation into the compressive properties of stainless-steel micro-lattice structures”, Journal of Sandwich Structures and Materials, 2011, Vol. 13, pp. 303-329.

The plastic collapse strength of the lattice structure is found to be at 5% of strain value from the designer standards given by the said research paper. The plastic collapse strength of the BCC lattice structure with FEA (solid element) and experimental graphs is shown in Table 3. The plastic collapse strength of the enhanced BCC lattice structure with FEA (solid element) graphs is shown in Table 3. The theoretical analysis is done by using the emperical equation given by the said research paper, whereas the experimental results were achieved based on another research paper for cmparative study. M. Smith et. al.“ Smith, Z. Guan and W. J. Cantwell, “Finite element modelling of the compressive response of lattice structures manufactured using the selective laser melting technique”, International Journal of Mechanical Sciences, 2013, Vol. 67, pp. 28-41.

TABLE 1: Results of yield stress, a _y (M Pa)

* Experimental results taken from M. Smith et. al.

TABLE 2: Results of elastic modulus, EBCC (M Pa).

* Experimental results taken from M. Smith et. al.

TABLE 3: Results of plastic collapse strength, s _r i (M Pa)

* Experimental results taken from M. Smith et. al.

The comparison of yield stress a _y see values for BCC and enhanced BCC lattice structures with FEA and experimental results with relative density as plotted in Fig. 3.

The comparison of Elastic Modulus‘ EBCC values for BCC and Enhanced BCC lattice structures with FEA, empearical and experimental results with relative density are plotted in Fig. 4. The comparison of plastic collapse strength s _r i values for BCC and enhanced BCC lattice structures with FEA, empearical and experimental results with relative density are plotted in Fig. 5.

The percentage error results of FEA are increasing alongwith proportionally decreasing the Unit cell edge length when compared with experimental values. The enhanced BCC lattice structures gives enhanced strength and stiffness results compared with BCC lattice structures. The Enhanced BCC lattice structures are improved to an average of 47% of Yield stress, 40% of elastic modulus and 13% of plastic collapse strength when they are compared with BCC lattice structures. At unit cell edge lengths 2.5mm and 2.0mm models giving better mechanical properties of stress and strain values than 1.5mm and l.25mm. By decreasing the unit cell edge length of the structure, the structure becomes dense structure and it is acting like a porous material.