Failure Criterion for PA 12 Multi-Jet Fusion Additive Manufactured Parts

Abstract Offering the possibility of producing complex geometries in a compressed product development cycle, it comes as no surprise that Additive Manufacturing (AM) techniques have become attractive to multiple industries, including the automotive and aerospace segments. Unfortunately, the ubiquitous stratified build approach used by these technologies is responsible for the pain point that hinders their adoption in production of parts that will be subjected to complex loads: the junction of adjacent layers tends to have subpar mechanical properties when compared to those of the bulk material, and thus, assessing the structural integrity of an AM part becomes difficult. In the advent of the industrialization of series production of AM parts for the automotive industry, the necessity to understand and predict how and why AM parts fail under complex stress states becomes of paramount importance. This paper applies a failure criterion for materials with anisotropic properties with stress interactions, to predict failure of multi-jet fusion (MJF) parts manufactured using polyamide 12 powder. The results are compared to the failure surfaces of Selective Laser Sintering (SLS) components. Special test specimens were designed, produced, and tested to measure failure under tensile, compressive, shear, and combined loading scenarios. The results show that much like SLS, MJF parts have a notable difference in tensile and compressive strengths. Unlike SLS however, MJF parts do not exhibit a strong interaction between stresses when under combined loading. The experimental data shows an excellent fit with the failure criterion, precisely capturing the strength behavior of MJF printed parts under complex loading conditions. Of great interest in this study is that the stress interactions with MJF parts were determined to be negligible when compared to SLS specimens, which emphasizes the fact that when performing stress analyses, each one of these powder-based additive manufacturing techniques must be treated differently.