PSI - Issue 34

Sigfrid-Laurin Sindinger et al. / Procedia Structural Integrity 34 (2021) 78–86 S.-L. Sindinger et al. / Structural Integrity Procedia 00 (2019) 000–000

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various AM processes involving both metals (Barba et al., 2020; Wang et al., 2020a) and polymers (Sindinger et al., 2020; Bell and Siegmund, 2018). Recently, material modeling and property mapping approaches that account for local variations in sti ff ness were proposed for finite element (FE) simulations based on shell meshes. By example of pure and short-carbon-fiber-reinforced laser-sintered polyamide 12 (LS PA12 CF), experimental validation on sub component level disclosed substantially improved accuracy of the predicted load-deformation behavior, when using models with mapped instead of homogeneous elastic material parameters (Sindinger et al., 2021a,b). The inhomogeneity does likewise a ff ect the assessment of strength, as was recently concluded by another group of researchers (Wang et al., 2020b) for powder bed fused components. Hence, it was the aim of this research to investigate the extension of the previously developed property mapping approach (Sindinger et al., 2021b) for failure prediction. All samples, comprising tensile coupons and ribbed bending beams, originated from a single build job that was previously described in (Sindinger et al., 2021b). The samples were fabricated via laser sintering (sPro 140, 3D Systems, Inc., Rock Hill, SC, USA) using commercial LS PA12 CF powder (PDX, Protodynamix GmbH, Wet zikon, CHE). It is noteworthy that the short fibers align themselves with the powder spreading direction, which is constant over the entire process (Chen et al., 2021). Consequently, a global xyz -build-system can be defined that dic tates the material axes of orthotropy, whereby x , y and z correspond to the fiber, transverse in- and out-of-sinter-layer directions (i.e. build direction), respectively. For determination of the nine elastic parameters necessary to model an orthotropic material law as well as the corresponding strength values, tensile coupons complying with ISO 527 (2012) were produced in six orientations as depicted in Fig. 1a. The axis-aligned specimens (XY, YZ, ZX) yield the Young’s moduli, Poisson’s ratios and strengths along the principal material axes, while the 45 ◦ -o ff -axis orientations (XY 45 , YZ 45 , ZX 45 ) were utilized to derive the shear moduli and strengths. To be able to model the thickness dependency of the elastic parameters, per orientation three thicknesses including 1, 2 and 4 mm were manufactured. All other coupon dimensions remained the same. 2. Methods 2.1. Sample Fabrication

(a)

(b)

Fig. 1: ( a ) Rendering of on- and o ff -axis coupon orientations as well as ( b ) ribbed beam structure.

Moreover, thin-walled beams were fabricated in order to investigate the applicability of the proposed modeling ap proach. As shown in Fig. 1b, these parts consist of an outer skin confining a variable thickness sub-structure of curved ribs. The rib layout was derived in Karamba 3D (Preisinger, 2013) and corresponds to principal stress trajectories apparent for a three-point bending configuration. 2.2. Experimental Testing Uni-axial tensile tests were performed according to ISO 527 (2012) at 5 mm / min on an universal testing machine (Z100, ZwickRoell GmbH&Co. KG, Ulm, GER). Young’s moduli E i were determined in the stress-strain curves be-