Experimental Comparative Analysis of the Through-Thickness and In-Plane Compression Moduli of Unidirectional CFRP Laminates

Abstract

This study explores the experimental characterization of the through-thickness compression properties in unidirectional laminates using cube compression tests. Cubical specimens, each with an edge length of 10 mm, were symmetrically outfitted with biaxial strain gauges and subjected to a compression test. While similar methodologies exist in the literature, this work primarily addresses the potential biases inherent in the testing procedure and their mitigation. The influence of friction-induced non-uniform deformation behavior is compensated through a scaling of the stiffness measurements using finite element (FE) analysis results. This scaling significantly enhances the accuracy of the resulting parameters of the experiments. The ultimate failure of the specimens, originating from stress concentrations at the edges, resulted in fracture angles ranging between 60° and 67°. Such fracture patterns, consistent with findings from other researchers, are attributed to shear stress induced by friction at the load introduction faces. The key findings of this research are the comparisons between the through-thickness modulus (E33c) and strength (X33c) and their in-plane counterparts (E22c and X22c). The results indicate deteriorations of E33c and X33c from E22c and X22c by margins of 5% and 7%, respectively. Furthermore, the results for E22c and X22c were compared with the results obtained through a standard test, revealing a 12% enhancement in strength X22c and 4% underestimated stiffness E22c in the cube compression test.