Effect of in-plane fiber waviness in unidirectional CFRP composites

Abstract

This work investigates the effects of fiber waviness in key structural properties of carbon fiber reinforced plastic (CFRP) composites. Fiber waviness is a type of manufacturing defect commonly found in composite material parts. Finite element modeling using the commercial platform Abaqus® was performed to simulate unidirectional laminae containing in-plane graded undulations in the shape of sinusoidal waves. The peak misalignment angle was taken as sole influence parameter. Automated model generation was performed through the use of parametric Python scripting. Composites were subjected to in-plane loading and boundary conditions, with analyses being divided into uniaxial normal longitudinal/transverse and biaxial normal loads. The goal was to provide a computationally efficient analysis framework to support decisions in quality control. Results proved that fiber curvature affects local stresses distribution, leading to stress concentration/relaxation and inducing the occurrence of local stresses other than the original ones found in laminae with no defect. The influence on effective elastic modulus was less significant than on strength values. Initial failure was predicted by Hashin failure criterion, which distinguishes between fiber and matrix failure. A strength knockdown effect was observed as misalignment angle increased, favouring a matrix dominated failure mode. Longitudinal load cases presented a higher strength reduction than observed on transverse loading. Regarding biaxial loads, the case of longitudinal tension + transverse compression was the most severely affected in terms of failure; the case of longitudinal compression + transverse tension was the least susceptible one.