Modeling and simulation of elasto-plastic lattice structures for energy absorption

The introduction of additive manufacturing technologies allowed the production of lattice structure with different types of repeated unit cells. Lattice structures offer a significant structural mass reduction and can highly improve mechanical specific properties which are traits that are sought in sectors like aerospace and automotive. In this thesis six types of unit cells (BCC, BCCZ, FCC, FCCZ, FBCC and FBCCZ) are analyzed through static simulations under compression and shear using ANSYS Workbench. The material is AlSi10Mg, one of the most used metal in additive manufacturing. The aim of this work is to create a model that can predict the mechanical properties of structures with different geometrical parameters through the simulation’s results of unit cells with four aspect ratios. The engineering stress strain plots from the simulations are first summarized with bilinear curves through three parameters: linear stiffness, yielding point and plastic stiffness. Each of these mechanical properties is linked to the relative density by applying Gibson-Ashby model and the relationship between relative density and aspect ratio is also investigated. This allows to predict an approximation of the stress strain curve by selecting the type of cell and its aspect ratio. Several verification tests are performed to study the effectiveness of the model. A homogenization model is then proposed to reduce the simulation’s time: in order to do so some assumptions are taken with the intent of better approximating the homogenized structure results in the plastic stage. Afterwards, some graded structures are modelled and compressive simulations are performed. Homogenization is then applied to investigate its efficacy. Next some explicit dynamic simulations of high speed compression are executed to observe the influence of the geometrical parameters and to assess which unit cell has better properties regarding energy absorption. Lastly a comparison is made between the linear stiffness derived through simulations and the one from literature obtained through experiment.