A micromechanics based model for rate dependent compression loaded unidirectional composites

Journal article, 2023

Strain-rate effects in a unidirectional non-crimp fabric carbon/epoxy composite are addressed. To allow for kink-band formation including strain-rate  effects and damage in such composites, the paper advances a recent model focused on compression loading at small off-axis angles. The model is based on computational \textit{homogenization} with a subscale represented by matrix and fibre constituents at finite deformation. The fibre constituent is assumed to be elastic transversely isotropic and the matrix is viscoelastic--viscoplastic with damage degradation. Novel model improvements of special importance to small off-axis loading relate to the \textit{isostress} formulation of the homogenized response in transverse shear. In this context, an enhanced homogenized elastic response is proposed based on Halpin--Tsai corrections to account for the nonuniform stress distribution on the microscale. The model captures the strongly rate sensitive kink-band formation due to localized matrix shearing and fibre rotation, confirming the experimentally observed increase in compressive strength for high strain rates.