Title: A Predictive Forming Model for Stretch-Broken Carbon Fiber Composites As a Function of State of Stress, Forming Rate, and Resin Viscosity
Authors: Matthew C. Egloff, Bridget Powers, Dalton Nold, Dilpreet Bajwa, Cecily Ryan, Doug Cairns,Roberta Amendola
Abstract: Carbon fiber filaments are brittle, with an elongation at failure of a few percent. This reduces their ability to supplant ductile sheet metal in formed parts with more complex geometries. Stretch broken carbon fiber composite materials consist of a regular distribution of shorter segments of carbon fiber filaments, which are aligned within a resin matrix. The short segments slide apart in the uncured resin matrix, resulting in elongation of tens of percent. This also causes thinning of the effective cross-sectional area. There is also a significant strain rate dependence ascribed to the viscoelasticity of the uncured resin. While the pseudo-ductile forming response of stretch-broken material is similar to sheet metal behavior, the deformation and load transfer mechanisms differ substantially. Testing on a new and novel forming fixture developed by Montana State University Bozeman indicates that the forming force and degree of local thinning depends upon the local state of stress (controlled by geometry), the forming rate (controlled by the test apparatus), and the viscosity of the uncured resin (controlled by temperature). Forming force and local thinning can be predicted and controlled by adjusting these first order parameters. These new tests and models for stretch-broken carbon fiber composites are analogous to those used in sheet metal forming. They can be used to develop stretch-forming processes for these composite materials in the same manner that the analogous tests are used to develop processes for sheet metal.
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Conference: CAMX 2022
Publication Date: 2022/10/17
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