Abstract

Besides the design freedom offered by additive manufacturing, another asset lies within its potential to accelerate product development processes by rapid fabrication of functional prototypes. The premise to fully exploit this benefit for lightweight design is the accurate structural response prediction prior to part production. However, the peculiar material behavior, characterized by anisotropy, thickness dependency and scatter, still constitutes a major challenge. Hence, a modeling approach for finite element analysis that accounts for this inhomogeneous behavior is developed by example of laser-sintered short-fiber-reinforced polyamide 12. Orthotropic and thickness-dependent Young’s moduli and Poisson’s ratios were determined via quasi-static tensile tests. Thereof, material models were generated and implemented in a property mapping routine for finite element models. Additionally, a framework for stochastic finite element analysis was set up for the consideration of scatter in material properties. For validation, thin-walled parts on sub-component level were fabricated and tested in quasi-static three-point bending experiments. Elastic parameters showed considerable anisotropy, thickness dependency and scatter. A comparison of the predicted forces with experimentally evaluated reaction forces disclosed substantially improved accuracy when utilizing the novel inhomogeneous approach instead of conventional homogeneous approaches. Furthermore, the variability observed in the structural response of loaded parts could be reproduced by the stochastic simulations.

Highlights

  • Wherever intricate lightweight structures are sought after, production via additive manufacturing (AM) appears as promising solution, owing its capability to directly fabricate components from three-dimensional computer models in unprecedented geometrical complexity [1]

  • The magnitude of the material parameters for the different orientations as determined by the 4 mm thick tensile coupons lies within the range reported in related research investigating laser sintering (LS) PA12 CF [19,20]

  • A novel material modeling approach for the structural response prediction of components fabricated from orthotropic materials displaying thickness dependency and scatter in mechanical properties was developed based on a shell property mapping strategy proposed by Sindinger et al [37]

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Summary

Introduction

Wherever intricate lightweight structures are sought after, production via additive manufacturing (AM) appears as promising solution, owing its capability to directly fabricate components from three-dimensional computer models in unprecedented geometrical complexity [1]. Large-scale structural components can be fabricated via powder bed fusion (PBF) technologies like selective laser melting (SLM) or electron beam melting (EBM) for metals as well as laser sintering (LS) for polymers and polymer matrix composites This is on the one hand related to their good mechanical properties and on the other to the fact that these processes simultaneously offer the capability to produce relatively large parts (102 mm scale) at high geometrical resolution (10−1 mm scale), the latter being pivotal for the realization lightweight designs featuring thin-walled shell structures [6]. If load bearing plastic components are required, the utilization of laser-sintered short-carbon-fiber-reinforced polyamide 12 (LS PA12 CF) stands to reason, as it offers significantly improved stiffness and strength compared to the plain counterpart

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