Design of experiment and analysis of deformation for compression test of lattices using digital image correlation

Compression testing is the common approach to determining the properties of lattices. This study discusses various factors required to design a robust test protocol. A significant number of tests were conducted to evaluate sample geometry and test procedure, as well as data collection and analysis. Several well-known criteria including characteristic diagrams, collapse mechanism, and properties such as modulus of elasticity, yield and plateau stresses, and volumetric energy were considered for investigation. In addition to the macro-level study of size effect (number of cells) with these parameters, digital image correlation (DIC) is used to study convergence at the micro-level by analysis of cell deformation and strain. This is used to determine the size of the lattice sample which optimally represents it as a cellular material. It was demonstrated that the influence of face-plates (boundary effect) on the measured properties is significant. However, their presence helps the repeatability and consistency of the results. At the limited range of strain rates achievable by ordinary hydraulic test machines, the test condition remains quasi-static, and the rate dependency of measured property for this range is generally lower than 10%. In addition, limitations of using DIC were discussed as a suitable tool to analyze the deformation of lattices as cellular material. Some modifications for test set-up and data analysis were presented. This led to a reduction in time and cost by using 2D DIC instead of 3D DIC.