Thickness dependent anisotropy of mechanical properties and inhomogeneous porosity characteristics in laser-sintered polyamide 12 specimens

Sindinger, Sigfrid-Laurin; Kralovec, Christoph; Tasch, David; Schagerl, Martin

doi:10.1016/j.addma.2020.101141

Cited by 30 publications

(47 citation statements)

References 36 publications

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“…Young's modulus as well as Poisson's ratio can be directly determined in uniaxial tensile tests and thereof, a reasonable approximation of the shear modulus G ⊥ can be calculated (Faes et al 2017;Lindberg et al 2018) (see Section 2.4.2). Another characteristic of additively manufactured structures is the drastic dependency on local part thickness, which was reported not only for LS (Tasch et al 2018;Wörz and Drummer 2018;Sindinger et al 2020) but also for other polymer-based processes (Bell and Siegmund 2018) and common metal-based AM technologies including selective laser melting (Brown, Everhart, and Dinardo 2016;Barba et al 2020), electron beam melting (Algardh et al 2016;Wang et al 2020b) and laser powder bed fusion (Roach et al 2020). Tasch et al (2018) disclosed a distinct drop of almost 40 % in Young's modulus (E ⊥ ) from a thickness of 2 to 0.6 mm in LS Pa12 tensile coupons built in z-direction.…”

Section: Introductionmentioning

confidence: 93%

“…Between 2 and 4 mm Young's modulus registered a further increase but at a flatter slope, indicating a transition from thin-walled to bulk properties that is supported by findings of Majewski and Hopkinson (2011), who reported a plateau between 4 and 6 mm. Sindinger et al (2020), who on coupon level investigated the effects of build orientation and part thicknesses on the mechanical material behaviour as well as their origin, did not only confirm this non-linear relation of Young's modulus and part thickness but furthermore revealed that the degree of anisotropy is not constant. In fact, the loading direction-dependent differences become more pronounced for thin specimens.…”

Section: Introductionmentioning

confidence: 96%

“…Structural anisotropy is characteristic for additively manufactured parts and is believed to derive from the layer-wise build process that leads to an alignment of pores and un-molten particles in the layer interfaces (Dupin et al 2012;Dewulf et al 2016;Stichel et al 2017;Wang et al 2019aWang et al , 2019bBain et al 2019;Sindinger et al 2020). In Figure 2, a volume element exhibiting such a layered composition is illustrated.…”

Section: Introductionmentioning

confidence: 99%

“…Explanations have been contributed to effects that are more negligible for thick parts but become critical as the cross-section decreases. These, to a minor degree, were attributed to a reduction of effective load bearing area, due to surface roughness and internal voids, as well as process condition-induced inhomogeneous microstructure over the cross-section, which is stipulated to play the principal role (Algardh et al 2016;Brown, Everhart, and Dinardo 2016;Wörz and Drummer 2018;Tasch et al 2018;Bell and Siegmund 2018;Sindinger et al 2020;Barba et al 2020;Roach et al 2020;Wang et al 2020b).…”

Section: Introductionmentioning

confidence: 99%

“…Hence, it is the aim of the present study to develop and validate a novel material property mapping strategy that for the first time allows the implementation of thickness dependent anisotropy in FE analysis of thin-walled additively manufactured components. Therefore, elastic constants derived from uni-axial tensile tests of a preceding study by Sindinger et al (2020) serve as foundation for a new approach to model the characteristic material response. Subsequently, a routine is established that automatically maps adjusted material properties to an FE model that is used to analyse the load-displacement behaviour in the elastic regime.…”

Section: Introductionmentioning

confidence: 99%

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

Sindinger

Marschall

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et al. 2020

Virtual and Physical Prototyping

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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.

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Sindinger

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et al. 2020

Virtual and Physical Prototyping

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Second-order homogenization of 3-D lattice materials towards strain gradient media: numerical modelling and experimental verification

Molavitabrizi

Khakalo

Bengtsson

et al. 2023

Continuum Mech. Thermodyn.

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The literature in the field of higher-order homogenization is mainly focused on 2-D models aimed at composite materials, while it lacks a comprehensive model targeting 3-D lattice materials (with void being the inclusion) with complex cell topologies. For that, a computational homogenization scheme based on Mindlin (type II) strain gradient elasticity theory is developed here. The model is based on variational formulation with periodic boundary conditions, implemented in the open-source software FreeFEM to fully characterize the effective classical elastic, coupling, and gradient elastic matrices in lattice materials. Rigorous mathematical derivations based on equilibrium equations and Hill–Mandel lemma are provided, resulting in the introduction of macroscopic body forces and modifications in gradient elasticity tensors which eliminate the spurious gradient effects in the homogeneous material. The obtained homogenized classical and strain gradient elasticity matrices are positive definite, leading to a positive macroscopic strain energy density value—an important criterion that sometimes is overlooked. The model is employed to study the size effects in 2-D square and 3-D cubic lattice materials. For the case of 3-D cubic material, the model is verified using full-field simulations, isogeometric analysis, and experimental three-point bending tests. The results of computational homogenization scheme implemented through isogeometric simulations show a good agreement with full-field simulations and mechanical tests. The developed model is generic and can be used to derive the effective second-grade continuum for any 3-D architectured material with arbitrary geometry. However, the identification of the proper type of generalized continua for the mechanical analysis of different cell architectures is yet an open question.

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β-Modification in heterogeneous polypropylene for laser-based powder bed fusion of polymers

Cholewa,

Forstner,

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et al. 2024

Prog Addit Manuf

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Currently, polyamides serve as the primary material used in laser-based powder bed fusion of polymers (PBF-LB/P), which prevents the components from exhibiting the mechanical characteristics of traditional manufacturing techniques. As a result, highly ductile and chemical-resistant materials are needed to cover more potential application areas. The preferred material is polypropylene (PP) with various structures and settings. A common practice in conventional manufacturing processes is adjusting the morphology of the component, but studies examining this type of influence in PBF-LB/P are scarce. In addition to examining important PBF-LB/P process characteristics like thermal properties and powder flow behavior, this work first presents potential nucleation agents and then manufactures components to assess the impact of the structure. It was concluded that processing the material is possible despite significantly higher crystallization kinetics. A parameter study was conducted to evaluate the initial PBF-LB/P processability by building single and triple layers. These results led to the creation of mechanical specimens that showed the material system’s processability. For the first time, it was possible to process β-nucleated PP, which displays increased elongation at break for higher β-content.

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Thickness dependent anisotropy of mechanical properties and inhomogeneous porosity characteristics in laser-sintered polyamide 12 specimens

Cited by 30 publications

References 36 publications

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

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

Second-order homogenization of 3-D lattice materials towards strain gradient media: numerical modelling and experimental verification

β-Modification in heterogeneous polypropylene for laser-based powder bed fusion of polymers

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