Thickness dependent anisotropy of mechanical properties and inhomogeneous porosity characteristics in laser-sintered polyamide 12 specimens
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The unrivalled design freedom of additive manufacturing makes it a valuable technology for the automotive and biomedical industry, where the advanced design- and optimization-driven aspiration of ideal lightweight components often leads to complex thin-walled structures that are, if at all, hardly feasible with conventional production methods. In selective laser sintering, however, the variability of mechanical properties that depends on a multitude of factors still complicates the technology's extensive implementation for the production of structural parts. Recently, build orientation and wall thickness were shown to affect the mechanical properties of laser sintered PA12 considerably. The material behavior arising from the interaction of these two factors remains unclear. To gain a more complete understanding in this matter, mechanical properties were evaluated via tensile testing for coupons in four thicknesses and build orientations. Additionally, porosity characteristics including spatial distributions and pore morphology were analyzed by means of X-ray micro-computed tomography in order to investigate their influence on the mechanical material behavior. Investigations disclosed distinct losses in Young's modulus, tensile strength and elongation at break with decreasing wall thicknesses for all build orientations. Moreover, results revealed that the degree of anisotropy in the mechanical properties changes with decreasing wall thickness. Microstructural porosity analysis delivered valuable insights into the origins of the peculiar macroscopic structural response and yielded a better understanding of the material as well as potential for improvement of the laser sintering process.