Establishing a finite element model to determine the tensile strength of additively manufactured PA2200 parts

Abstract

Selective laser sintering (SLS) is an additive manufacturing process that produces three-dimensional parts from computer aided design (CAD) models. This process aids in the production of parts that are singular complex and designed for a specific application, which decreases the time and cost of manufacturing components. Structures such as these are mostly optimised using finite element method (FEM) analysis where there is increased difficulty in designing a mathematical prediction model for each individual structure. Most software programs use FEM analysis for designing and optimising structures with isotropic material properties, but the layer-by-layer manufacturing of SLS causes the strength of its structures to be nonuniform in the x-, y- and z-axes; that is, the parts have a certain level of anisotropy. This brings to question the accuracy of simulating parts with anisotropic material properties through FEM analysis. In achieving the aim of this study, a tensile material database was defined for PA2200 structures manufactured with the EOSINT P380 machine. This database was then used to simulate the global structural behaviour of specimens under tensile forces. The test specimens were specimens manufactured at 30° to the 𝑥-𝑦 plane of the print bed and specimens with varying cross-sectional areas in its gauge length. The second set of specimens were defined in two groups as symmetrical and asymmetrical about its longitudinal and lateral axes. The tensile material database displayed Young’s moduli which were very similar to one another, resulting in the conclusion that an isotropic material database can be assumed in the simulation models. The simulation model also defined a solid model with a specified density, which resulted in accurate simulation to experimental data. This indicates that the porosity of PA2200 SLS structures can be disregarded in similar simulations. All specimens were manufactured and tested according to the simulation parameters, and the actual elongation values were compared to the predicted simulation values. The specimens manufactured at 30° to the print bed and the symmetrical structures were within a 10% error margin, which indicates accurate simulation predictions. That of the asymmetrical structures were, however, approximately 40% smaller than the experimental values. The variation in the simulation and experimental data of the asymmetrical structures were ascribed to the variance in 2D cross-sectional areas as determined by the slicing program; the smaller 2D cross-sectional areas tended to laminate from each other, causing high stress regions. The parameters that affect the simulation model accuracy as the complexity of the structures increase must be identified in future studies to better understand the polymer SLS process and the behaviour of the manufactured specimens.