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The Effect of Single Fiber Elastic Modulus Distribution and Modulus Strain Dependency on Carbon Fiber Tow Behavior



The relation of individual fiber properties to their assemblies, i.e. fiber bundles or tows, is critical to the predictive performance of fiber reinforced polymer composites. Statistical modelling of fiber bundles based on the mechanical behavior of single fibers has demonstrated that a large distribution in single fiber failure strength within a tow will lower the tow failure stress, despite equivalency in mean fiber failure stress. Using very precise mechanical testing, it has been shown by the authors that the elastic properties of single PAN carbon fibers within a small fiber tow (12k) have significant variation as well, which has only recently been quantified using a novel nano-tensile testing system. In this paper, the tensile behavior of a fiber tow is simulated using the property distributions obtained from single carbon fiber tensile testing, in particular the statistical distribution of axial modulus and the dependency of axial modulus on strain amplitude. Considering identical fiber failure statistics, a 15% reduction in tow failure stress was found for a standard deviation in modulus equal to ±8%, a typical value experimentally observed by the authors for high performance carbon fibers. Furthermore, carbon fiber modulus dependency on strain amplitude reduces tow strength if non-uniform fiber loading is considered, indicating that manufacturing process control of fiber alignment and residual stress is critical to improving the overall strength of a polymer reinforced carbon fiber composite.

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