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Failure behavior of woven fiberglass composites under combined environmental and mechanical compressive loading
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Failure behavior of woven fiberglass composites under combined environmental and mechanical compressive loading

Ariana Eliza Paradiso
Master of Science (M.S.), Drexel University
May 2018
DOI:
https://doi.org/10.17918/9rzh-nx29
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Abstract

Composite materials--Mechanical properties Engineering Mechanical Engineering
Woven fiber reinforced polymers are often utilized in naval aircraft structures, where they are valued for their weight reduction with comparable strength to traditional metals. Frequent aircraft launch and landing cycles, as well as defensive maneuvers can load polymer matrix composites (PMCs) under complex, multi-temporal conditions. In addition, extended exposure to seawater in a naval setting can result in water uptake, causing swelling and potentially corrosion to the matrix and fiber-matrix interfaces. The purpose of this study is to quantitatively and systematically characterize the compressive behavior of fiberglass PMCs under combined mechanical and environmental loading, in order to develop more predictive damage evolution models under realistic conditions. Cuboidal samples of G10 garolite, a commercially available epoxy resin woven fiberglass, are used as a model material to examine uniaxial compressive loading perpendicular to the plies under both quasi-static (10^-3 s^-1) and dynamic (10^3 s^-1) strain rates. In order to simulate environmental conditions, certain samples were soaked in either distilled or ASTM standard seawater prior to loading. Two periods of time of environmental conditioning were considered, short term at two weeks, and long term at four months. Results demonstrate that, on average, the dynamic compressive strength of the composite increased 35% from the quasi-static. Moreover, environmentally treated samples generally experienced a decrease in strength, but higher strain to failure, and composites exposed to water for only short periods exhibited signs of the absorbed water sustaining additional load within the material. Ultra high-speed photography along with the full-field imaging technique of digital image correlation (DIC) was used to obtain in-situ full-field strain maps. In all cases, a clear shear band failure mechanism from local instabilities at the tow can be seen, and a Mohr-Coulomb failure criterion is used to extract a mesoscale cohesive shear stress and coefficient of internal friction. The shear failure behavior was also quantified in terms of the rate and speed of formation per loading condition examined.

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