Stiffness Reduction Resulting from Matrix Cracking in FRP Laminates

Fiber Reinforced Polymer laminates (FRP) have properties, which are highly dependent on the ply fiber orientations and which can be designed for optimum laminate performance. The purpose of this study is to investigate effect of matrix cracking on the mechanical properties of FRP laminates with various off-axis angles. Carbon and glass fiber reinforced polymer laminates (CFRP and GFRP) are tested. FRP prepregs are cured by using autoclave method to form laminates with layups [m/ n]s. The laminates are then loaded monotonically and cyclically to obtain their mechanical properties and the effect of matrix cracks on the properties. One of the main effects is reduction of laminates’ stiffness. In order to obtain higher crack densities in specimens, artificial cracks method was introduced in this study. The measured stiffness reduction as a function of the crack density is compared to an analytical prediction for cracked angle-ply laminates based on a variational stress analysis. The experimental results for stiffness reduction agree well with the analytical results. Understanding the behavior of damaged laminates with simple configurations used in this study is of high importance for prediction of damage effects on laminates with more complex configuration, e.g. with quasi-isotropic layups.