Dynamic microbuckling model for compressive strength of polymeric composites

Dynamic compressive strength of off-axis fiber composites in the form of fiber microbuckling was studied. Both fiber misalignments and material nonlinearity were taken into account in this study. A fiber microbuckling model derived using micromechanics based on the nonlinear behavior of the matrix was extended to include the strain rate effect. The critical microbuckling stress was found to be the same as that in Rosen\u27s bifurcation analysis except that elastic shear modulus was replaced by the tangent shear modulus of composites. The tangent shear modulus was rate dependent and described using an elastic/viscoplastic constitutive model. The viscoplasticity model was verified to provide stress-strain relations at high strain rates. S2/8552 glass/epoxy unidirectional composites with small off-axis angles were tested to failure at various strain rates. For strain rates below 1/sec, the compression tests were conducted on an MTS machine, while higher strain rate tests were carried out using a Split Hopkinson Pressure Bar. Comparison with experimental data indicated that the dynamic microbuckling model was suitable for prediction of compressive strengths at different strain rates. The compressive strength of multi-directional laminates was characterized. Laminate plate theory and finite element analysis with material nonlinearity were employed for laminar stress analysis. The critical failure stress in the 0° ply was estimated using the microbuckling model. Based on that, the compressive strength of composite laminates was predicted. The model predictions were compared with experimental data and good agreements were revealed