Dynamic behavior of fiber-reinforced polymer composites for structural application under in-plane compression
Creators: Kumar, Yogesh
Publisher: name: University of Alberta Library
Year: 2024

<p>Composite materials have become an integral part of aerospace and defense industries owing to the ability to tailor their mechanical properties, thermal, and corrosion resistance. The anisotropic nature of fiber-reinforced composites necessitate the in-depth understanding of the driving failure mechanisms and complex damage morphology based on the architecture of the material system and loading conditions. This thesis is focused on studying the evolution of mechanical response and failure propagation under quasi-static and dynamic loading through experiments and further developing the numerical models for crashworthiness and impact applications. In the first part of this thesis (Chapter 2 and 3), the quasi-static and dynamic behavior of a cross-ply and quasi-isotropic carbon-fiber-reinforced polymer composite under in-plane compression loading has been studied. A part of this section focuses on determining the correlation between the 90◦ ply thickness in a [0/90n]s with global in-plane compressive strength and failure strains. Later, this thesis explores the material behavior at strain rates ranging from 10−5 to 103 s−1 to quantify the strain-rate-dependent response, failure propagation, and damage morphology using advanced imaging systems. Fiber bridging, kink band formation, dominance of interlaminar failure, and inter-fiber failure fracture planes are evidenced through post-mortem analysis. For an in-depth understanding of the failure propagation, crack speeds were determined at different interfaces participating in the crack propagation. Overall these experimental studies provide insights into dynamic fracture and failure mechanisms for advance laminated composites and also serve as design and optimization validation cases for impact resistance in structural applications.</p>

<p>In the second thrust of this thesis (Chapter 4 and 5) involving structural application of fiber-reinforced composites, macro-scale finite element models have been developed for accurately predicting the energy absorption capabilities of a circular thin-walled composite tube, and low-velocity impact response of a woven composite laminate with a rate-dependent progressive damage model. The first section focuses on calibrating the MAT 54/55 material model in LS-Dyna for simulating axial crushing of circular thin-walled quasi-isotropic carbon-fiber reinforced polymer composite specimens. The results of this study showed the applicability of the use of the physical material inputs from material characterization tests (e.g., tensile, in-plane shear, and compression) while demonstrating the necessity of more in-depth calibration processes for the non-physical material inputs. In continuation of that, another study focuses on comparing the two progressive damage models available in the explicit nonlinear finite element software LS-Dyna. To explore the prediction capabilities in terms of mechanical response and dominating failure modes in woven composites, low-velocity impact response at four different energies ranging from 27.9 J to 109.7 J were considered. A macro-homogeneous solid element formulated finite element model was simulated to understand the response and failure mechanics in the laminate under low-velocity impact. The material modeling was carried out with the MAT 55 and MAT 162 material models. The results show that MAT 162 yields a better resemblance with the damage morphology patterns and the delamination for the accounted impact zone, due to the inclusion of the strain-rate effect. Overall, these developed numerical models provide insight into the limitations and advantages of both material models, which establishes the route for the selection of the appropriate material model for simulating crashworthiness and impact behavior in fiber-reinforced polymer composites.</p>