Analysis Methods for Discontinuous Fiber Composites

Thesis (Master's)--University of Washington, 2013The mechanical performance of a Discontinuous Fiber Composite (DFC) material system called HexMC® is considered in this study. Specifically, the goals of the study were to 1) Predict the buckling and failure loads of three sizes of HexMC® angle beams loaded in pure bending. 2) Develop a stochastic modeling method that captures both the stiffness variation and membrane bending coupling effects exhibited by HexMC, and 3) Predict displacements and failure loads of a HexMC® brace with complex geometry subjected to two different loading conditions. The B-range of in-plane isotropic elastic properties was defined during the study. Measured buckling and failure loads of small and large size angles were subsequently predicted to within 16-22% and 18-32%, respectively, based on the B-range in elastic properties. Failure loads of medium size angles that did not buckle prior to fracture were predicted to within 2-14%. A stochastic modeling approach called the Random Laminate Volume Element (RLVE) method was also developed. The RLVE approach greatly improved buckling predictions for the small angles, but had little impact on predictions for the large angles size. Finally, the brace was modeled using the B-range isotropic properties. For the first load case, an FE analysis based on geometrically linear displacements, predicted failure to within 15% if failure occurred away from bolted regions. However when failure occurred near bolted regions the complex stress state in these regions made failure predictions inaccurate, since the actual out-of-plane elastic properties of HexMC® were not used during the FEA analyses. For the second load case, a geometrically nonlinear FE analysis predicted displacements well. However, severe stress concentrations at the failure location rendered the gross section strength values unusable, as measured and predicted strain levels far exceeded the nominal failure strain suggested by failure strength and in-plane modulus