Abstract
Composite materials have become widely used in engineering applications, in order to reduce the overall weight of structures while retaining their required strength. In this work, a composite material consisting of discontinuous glass fibers in a polypropylene matrix is studied at the microstructural level through coupled experiments and simulations, in order to uncover the mechanisms that cause damage to initiate in the microstructure under macroscopic tension. Specifically, we show how hydrostatic stresses in the matrix can be used as a metric to explain and predict the exact location of microvoid nucleation that occurs during damage initiation within the composite’s microstructure. Furthermore, this work provides evidence that hydrostatic stresses in the matrix can lead to coupled microvoid nucleation and early fiber breakage, and that small fragments of fibers can play an important role in the process of microvoid nucleation. These results significantly improve our understanding of the mechanics that drive the initiation of damage in the complex microstructures of discontinuous fiber reinforced thermoplastics, while also allowing scientists and engineers to predict the microstructural damage behavior of these composites at sub-fiber resolution and with high accuracy.
Highlights
Composite materials have gained attention in many engineering applications, especially in the aerospace and automotive industries due to their low weight and high strength
Efforts in experimentally examining the damage mechanisms of short fiber reinforced thermoplastics through in-situ scanning electron microscopy have shown that under tensile loads, damage initiation appears in the form of microvoid nucleation at fiber tips[11,12]
The specimen was loaded in tension until fracture, and the in-situ X-ray μ-CT images allowed for the observation of the fibers, porosity manufacturing defects, as well as the tracking of microstructural damage events that led to final fracture
Summary
Composite materials have gained attention in many engineering applications, especially in the aerospace and automotive industries due to their low weight and high strength. Polymer matrix composites have allowed for major weight savings and higher performance aircraft and vehicles Despite their high rate of implementation, scientists and engineers have faced challenges in predicting their mechanical behavior and performance, especially past the small strain regime and into the damage initiation and damage propagation regimes, because there exist a number of damage mechanisms which are often coupled and are active throughout the life of a component. Through the coupled experiments and simulation of the exact microstructure, this work provides evidence that microvoid nucleation during damage initiation in a fiber reinforced thermoplastic is hydrostatic stress based, validating and propelling forward engineers’ and scientists’ predictive capabilities past the elastic regime and towards the strength prediction of complex heterogeneous composites
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