Non-linear dynamic finite element analysis of micro-strut lattice structures made by laser powder bed fusion

Abstract

The development of additive manufacturing technologies enables the production of a new type of porous materials for the absorption of mechanical energy. These are, for example, metallic lattice structures produced by laser powder bed fusion. The structures can be made from a wide range of alloys, achieve high specific energy absorption, and can be manufactured as hybrid parts with conventional bulk components. To effectively develop lattice structures, it is necessary to complement experimental tests with simulations using the finite element method (FEM) performed under conditions of increased loading velocities. Therefore, this study focuses on the development of the FEM modelling strategy that reflects the effect of strain rate sensitivity of the base material (SS316L) and the most significant geometrical imperfections of the manufacturing process. The strain rate is reflected by the Cowper-Symonds constitutive law, which parameters are determined by the dynamic tensile test on Hopkinson split bars. The imperfections are captured by optical digitalization. The significance of the Cowper-Symonds parameters and geometric imperfections are studied independently, whereas agreement with the experiment is observed. Tests are performed for several lattice structures with different strut orientations and velocities to evaluate the versatility of the proposed approaches. A good correlation between computational and experimental results in terms of energy absorption is found for structures with an experimentally determined strut diameter and the proposed Cowper-Symonds input parameters.The development of additive manufacturing technologies enables the production of a new type of porous materials for the absorption of mechanical energy. These are, for example, metallic lattice structures produced by laser powder bed fusion. The structures can be made from a wide range of alloys, achieve high specific energy absorption, and can be manufactured as hybrid parts with conventional bulk components. To effectively develop lattice structures, it is necessary to complement experimental tests with simulations using the finite element method (FEM) performed under conditions of increased loading velocities. Therefore, this study focuses on the development of the FEM modelling strategy that reflects the effect of strain rate sensitivity of the base material (SS316L) and the most significant geometrical imperfections of the manufacturing process. The strain rate is reflected by the Cowper-Symonds constitutive law, which parameters are determined by the dynamic tensile test on Hopkinson split bars. The imperfections are captured by optical digitalization. The significance of the Cowper-Symonds parameters and geometric imperfections are studied independently, whereas agreement with the experiment is observed. Tests are performed for several lattice structures with different strut orientations and velocities to evaluate the versatility of the proposed approaches. A good correlation between computational and experimental results in terms of energy absorption is found for structures with an experimentally determined strut diameter and the proposed Cowper-Symonds input parameters.