Effective Elastic Properties Of Microlattices And Their Sizedependent Mechanics

As new types of materials, lattice materials have gotten a lot of attention and been applied in engineering in recent two decades. These materials show high mechanical performances owing to their geometries and designability, thus play important roles as structure materials at low density following random foams and honeycombs. And the materials have potential to be function materials owing to their open apertures which can be filled with other materials. Microlattices who usually be used to designate those lattice materials whose feature sizes are at micro scale, submicron scale or even nano scale, came even later. Compared with general lattice materials, those materials have a wider function potential application owing to their high surface-volume ratio. Because of their special geometries and multilevel design ideas, those materials would have a fairly good performances with ultralow density. However, there would be a problem to design these materials when their complex geometries are take into account, especially some micro or nano effects are considered, which make the state is hard to explain by classical theories.To solve the above problems, a “from struts to structures” method is proposed. We use the axial, bending and shear stiffness of the struts to obtain the macro effective properties of the whole structures. The method promising to utilize the theoretical, simulating, or experimental results of simple beams to analyze the properties of complex structures. And the concept of lateral restrain ratio is introduced as representation of structure types. Thereout, a formula system for the effective elastic properties of various lattice materials obtained, which can be characterized as high parameterization, widespread applicability and great precision.In this paper, the method is used to study the micro or nano laittice materials. Frist, bending and compression properties of simple beams are analyzed. Second, it’s focus on how to apply the results to study lattice materials. In this way, surface effects and couples stress effects of the elastic properties of microlattice is investigated. We also pay attention to how to get the size-dependent parameters form the experiments and simulations of nano or micro beams. Then the effects of those parameters are discussed, design criteria of microlattice materials is modified and the possible “ultrastiffness” lattice materials at ultra-low density is predicted.