Nonlinear mechanical properties of lattice truss materials

An increment equivalent continuum method was developed to study the nonlinear mechanical properties of lattice truss composite materials. As the strut material is brittle or elastic-perfectly plastic, the stiffness method is applicable. The stiffness matrix and strengths of the Kagome lattice core material, the pyramid lattice core material and the corresponding octet-truss lattice were deduced. Initial yield surfaces were depicted by polyhedrons in tri-axial stress spaces, pure shearing stress spaces and compared in two-dimensional stress spaces, respectively. As the strut property was nonlinear, the increment method based on the flexibility method was applied to study the plasticity of strain hardening solids. The complete stress-strain equations were deduced by integration. The suggested increment method was valid to model the complete stress-strain curves of the octet-truss composite and the Kagome lattice core of the sandwich panel. The simulations were well consistent with the reference experimental results.