Material modelling and property mapping for structural FEA of thin-walled additively manufactured components

Abstract

Additive manufacturing is progressively paving the way for optimised lightweight components that, due to their typically complex shape, would hardly be feasible with traditional production methods. However, the peculiar mechanical properties of additively manufactured materials limit the accuracy of structural analyses. In this research, a strategy for the implementation of thickness dependent anisotropy into finite element shell models is developed by example of laser sintered polyamide. The material behaviour was modelled by fitting parametric functions to experimental data. Subsequently, a routine was developed to map the adaptive material properties into a finite element model of a complex component. Numeric simulations with standard and mapped properties were compared and validated via experiments. Results show that the proposed approach is superior to the conventional method in predicting the structural response. The method is not only applicable to laser sintered polymers but relevant for all structures, where anisotropy and thickness must be considered.

Structural Response Prediction of Thin-Walled Additively Manufactured Parts Considering Orthotropy, Thickness Dependency and Scatter

“…In this research, 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 ]. Comparison of numerical simulations obtained from the novel method with standard procedures and experimental tests yielded the following conclusions: The thickness dependency of elastic material parameters that was previously reported for various materials fabricated via PBF processes is also inherent in LS PA12 CF polymer matrix composites and needs to be considered for structural simulations of thin-walled components.…”

“…For the evaluation of the latter, a contact-less stereo digital image correlation (DIC) system was used. Based on the deformation of an air brushed speckle pattern applied on the coupon surface, it allows the computation of the strains in loading ( ) and transversal directions ( ) [ 9 , 37 , 44 ]. Consequently, [ 9 ] yields the Poisson’s ratio for the respective coupon orientation.…”

“…Shear moduli, on the other hand, were approximated by Equation ( 2 ) which was proposed by Huber [ 46 ]. Recent publications yielded satisfactory results using Equation ( 2 ) for LS materials [ 9 , 37 , 47 ]. The remaining Poisson’s ratios that were not directly determined in the experiments were computed using Equation (1a–c).…”

“…In contrast to the solid region, for the thin-walled ribbed sub-structure ( 1–3 mm) thickness dependency was considered. In a preceding work, the thickness effect of Young’s modulus and Poisson’s ratio for transversely isotropic LS PA12 without reinforcement fibers was effectively modeled by fitting of Weibull growth and a two terms exponential functions to experimental data, respectively [ 37 ]. A similar empirical approach was pursued in the present research, where instead of the previous two models, a single three parameter model was selected.…”

“…To overcome these issues, in a preceding study of the author’s research group, a novel strategy was proposed to automatically map transversely isotropic and thickness-dependent material properties into finite shell element models [ 37 ]. Comparisons between numerical simulations and physical experiments on a laser-sintered thin-walled sub-component disclosed significantly improved accuracy when inhomogeneous instead of homogeneous anisotropic material properties were implemented.…”