Reinforcement of polymers with multiple inclusions of varying length scales and morphologies enable enhancement and tailorability of thermo-mechanical properties in resulting polymers. Computational material models can eliminate the trial-and-error approach of developing these hybrid reinforced polymers, enable prediction of interphase properties, and allow virtual exploration of design space. In this work, computational models, specifically representative volume elements were developed for acrylonitrile butadiene styrene polymer reinforced with nanoscale iron oxide particles and micro-scale short carbon fibers. These representative volume elements were used to predict the tensile modulus of resulting polymer nanocomposite with varying particle concentrations, orientations, interphases, and clustering to realistically replicate the actual material as observed in optical and electron microscopy. The interphase elastic modulus was obtained through established analytical formulations and incorporated into the representative volume elements by defining an interphase region around the reinforcements. The tensile modulus estimated using representative volume elements agreed well with the experiments, evidently showing that the effective tensile modulus of the polymer nanocomposite increased with increase in interphase thickness, aspect ratio, and particle content. Clustering was only observed in Fe3O4 nanoparticles but its size did not have any effect on the effective tensile modulus. The developed computational modeling framework and the resultant prediction of tensile modulus offers a design path which can be extended to other polymer nanocomposites containing multiple inclusions.
Purpose
Material extrusion additive manufacturing processes inevitably produce bead-shaped surface patterns on the walls of parts, which create stress concentrations under load. This study aims to investigate the influence of such stress concentrations on the strength along the build direction (“Z-strength”).
Design/methodology/approach
This work consists of two main parts – an experimental demonstration to show the significance of stress concentrations on the Z-strength, followed by numerical modeling to evaluate the theoretical stress concentration factors (kt) for such shapes. Meso-scale finite element analysis (FEA) was performed to evaluate kt at the roots of the intersecting bead shapes. The critical bead shape parameters influencing kt were identified, and parametric FEA studies were performed on different bead shapes by varying the normalized parameters.
Findings
The experimental results showed that up to a 40% reduction in the effective Z-strength could be attributed only to the presence of surface bead shapes. Bead overhang and root radius were identified as critical shape parameters influencing kt. The results of the parametric FEA studies were used to generate a single empirical equation to determine kt for any bead shape.
Originality/value
Predictive models for Z-strength often focus on crystallization kinetics and polymer chain interdiffusion to predict interlayer adhesion strength. The authors propose that the results of such studies must be combined with surface bead-shape induced stress concentration factors to obtain the combined, “effective” Z-strength.
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