Biaxial fatigue damage in quasi isotropic laminates

An investigation into the biaxial fatigue damage mechanisms in quasi isotropic carbon fiber reinforced polymer (CFRP) composite laminates has been conducted. The goal is to capture early stage damage and obtain an improved understanding of the physics of damage and failure under complex multiaxial loading in anisotropic laminates. Specimen geometry is designed using an optimization technique and digital image correlation (DIC) is performed during static biaxial load tests to validate specimen design. To understand the propagation of damage from the micro-to the macroscale, the fractured surfaces are analyzed during various stages of fatigue using scanning electron microscope (SEM) assisted fractography, and a high-resolution camera is used to capture real time macroscale damage. Specimen stiffness degradation is measured and correlated to the micro-and macroscale damage mechanisms and the biaxial fatigue loading parameters. The results provide critical understanding of the initiation and propagation of damage mechanisms in quasi isotropic laminates under biaxial fatigue.