Session: 02-01-04: 7th Annual Conference-Wide Symposium on Additive Manufacturing: Polymers II

Paper Number: 99393

99393 - Multiscale Modeling of Elasticity and Fracture in Additively Manufactured Polymers 

Polymer additive manufacturing (AM), or 3D printing, has been transiting from demonstrative prototypes to functional products that are impacting a wide variety of sectors, from biomedical, electronic, and automotive to aerospace industries. However, the reduced fracture performance often observed in 3D printed parts limits their applications to multi-functional structures and devices. The layered additive deposition process in 3D printing leads to anisotropic fracture behaviors and complicated crack propagation patterns, which brings challenges in modeling and analysis. This study aims to develop a computational modeling framework to predict anisotropic elastic and fracture properties of additively manufactured polymers for enhanced performance. The approaches involve 1) Homogenization of microscopic models to predict anisotropic properties at the macro scale, and 2) Anisotropic extended finite element method (XFEM) to predict AM process-dependent crack initiation and propagation patterns.

First, Micro-CT images are used to quantify microstructures and porosities of 3D printed polymers to set up representative volume element (RVE) models. The models are subjected to macroscopically uniform boundary conditions (BCs) admitted by the Hill-Mandel condition to determine anisotropic elastic properties. Scale-dependent bounds from those BCs were used to establish the convergence of RVE responses. Parametric studies are performed by varying layer height, filament width, and bond width to investigate their effects on the anisotropic properties. It is found that porosity plays a significant role, and more porosity leads to larger elastic anisotropies in additively manufactured polymers.

Next, single edge notch tension fracture specimens made of ABS materials through fused filament fabrication with various build/raster orientations are studied, namely, horizontal builds with 45°/−45° or 0°/90° raster orientations, and vertical builds with layers perpendicular to the notch. The measured fracture properties were found to highly depend on the build/raster orientations and crack kinking was observed in 45°/−45° samples to follow the weak inter-filament weld-lines. The XFEM with a cohesive segment approach of anisotropic damage initiation and evolution criteria was developed in software Abaqus to capture the dependency of fracture behaviors on build orientations and raster angles. Numerical parametric studies further show that the inter-filament bonding strength could be tuned to create alternate crack paths for maximum fracture energy. Finally, toughening mechanisms using topological patterns on the sample surface to deflect crack propagations are studied. An anisotropic phase-field fracture model is developed to predict complicated crack deflections in 3D printed patterned structures coupled with material anisotropies. Modeling of residual stresses was also discussed. This study sheds light on predicting fracture in 3D printed materials and structures with optimal build and topology designs for enhanced performance.

Presenting Author: Jun Li University of Massachusetts Dartmouth

Presenting Author Biography: Dr. Jun Li is an assistant professor in Mechanical Engineering at the University of Massachusetts Dartmouth. He obtained his Ph.D. in Mechanical Engineering from the University of Illinois at Urbana-Champaign in 2012, where he also earned M.S. degrees in Mathematics and in Theoretical and Applied Mechanics. After that, he worked as a postdoctoral scholar in Aerospace at California Institute of Technology and then as a quality assurance manager at Dassault Systemes SIMULIA before joining UMass Dartmouth in 2016. His research interest is in computational mechanics and materials in support of advanced manufacturing, energy, and biotechnology. He was the recipient of NASA RHG Exceptional Achievement for Engineering award in 2016 and “Emerging Researchers in Biomedical Engineering” first place award in ASME International Mechanical Engineering Congress and Exposition in 2011.

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