Variability, Heterogeneity and Anisotropy in the quasi-static response of laser sintered PA-12 components

First published: 12 December 2016Additive manufacturing (AM) receives an increasing industrial interest thanks to its advantages in the economic production of highly complex and small-series components. Especially laser sintering (LS) is in this context of particular interest for the production of plastic components, as it is generally deemed the most robust AM technology for polymer parts and therefore is expected to enable AM for functional components in the near future. However, to date, designers are often confronted with a severe lack of knowledge on the possible mechanical behavior of AM components. More specifically, the unit-to-unit variability, heterogeneity (within-part variation), and anisotropy of the mechanical properties very often prove to be substantial and therefore require more elaborated studies in order to take these effects into account in the engineering of reliable components. Moreover, typical experimental results that are used for the determination of the elastic stiffness tensor are subject to variability, caused by the influence of the difference in thermal history between produced parts. This work therefore focuses first on the identification and quantification of the variability and heterogeneity in the quasi-static response of laser sintering-polyamide 12 (LS-PA12) components. Second, also the anisotropy in this quasi-static response is studied. For the first part, uniaxial tensile tests are performed and the variability on the quasi-static properties is quantified by means of statistical analysis. Also, the elastic stiffness tensor is identified based on these tests. Next, the heterogeneity in the tested specimens is investigated by means of digital image correlation. Finally, in order to study the anisotropy in the quasi-static properties, the Virtual Fields Method is applied to determine the variability in the elastic stiffness tensor of the LS-PA12 material. A variability with a coefficient of variance of up to 6.5% on Young's modulus was measured. It was also found that the production planning has an important influence on the homogeneity of the mechanical properties of the produced parts. Finally, the Virtual Fields Method showed that, contrary to most literature on the topic, the elastic properties of LS-PA12 material is best described using an isotropic material model.status: publishe