Variability in the Mechanical Properties of Laser Sintered PA-12 Components

The quasi-static mechanical properties of Laser Sintered (LS) PA-12 material are highly influenced by the thermal history of the thermoplastic material during the production, as this impacts critical material properties such as the degree of crystallinity and porosity in the resulting component. Many process-related parameters, including preheating temperature, laser energy density, layer interaction time and post-build cooling cycle, were already shown to influence the thermal history significantly. Due to the large, mainly epistemic, variability in these parameters, the mechanical response of produced components is often difficult to predict and is moreover governed by non-isotropic constitutive equations. This work therefore focusses on the identification of this variability in the mechanical behavior and the validation of experimentally obtained non-deterministic material models. A non-deterministic (variable) constitutive model is built experimentally, based on 90 uniaxial tensile tests, performed on LS samples that were built under different orientations. This model is subsequently validated by building a well-defined benchmark sample, containing complex stress states upon loading. This sample is tested using Digital Image Correlation. Finally, a novel way of identifying non-isotropic material properties, the Virtual Fields Method, is applied to this benchmark sample to identify the constitutive parameters.