Numerical modelling and nanoindentation experiment to study the brazed residual stresses in an X-type lattice truss sandwich structure

The lattice truss sandwich structures are considered as the most promising advanced lightweight materials used in modern industries and aircrafts. Most sandwich panel structures are fractured at brazed joints named node failure during static and dynamic testing, which is mainly influenced by brazing residual stresses. Finite element method (FEM) was used to study the brazing residual stresses in a stainless steel X-type lattice truss sandwich structure. And the nanoindentation experiment is used to verify the validity of FEM. The effects of braze processing parameters including applied load, face sheet thickness, truss thickness and truss length on residual stresses have been investigated. It is shown than the residual stresses are concentrated on the brazed joint, which has a significant effect on node failure. As the applied load increases, the residual stresses decrease first and then remain unchanged, and the optimal applied load is around 1 MPa. As the face sheet thickness increasing, the residual stresses are increased. Too thin face sheet can cause large residual stresses on the top surface of face sheet. With truss thickness and truss length increase, the residual stresses are decreased first and then increased. The optimized face sheet, truss thickness and truss length are found to be 2 mm, 1 mm and 26 mm.