Damage evolution in carbon fiber-reinforced polymer (CFRP) composites under shear fatigue loading

Abstract

Composite structures present high strength, low weight and design flexibility in terms of fiber orientation and number of plies and used vastly in advanced and modern applications. Among them, carbon fiber-reinforced polymer composites (CFRP) are used widely in aeronautic and automotive industries in which components are subjected to different loading types and this will double the necessity of investigation on fatigue and fracture analysis using damage mechanics concepts. The reliability of structures made of composites, depends on continual process of damage initiation and propagation. In the current research, a specific CFRP composite is being tested and finite element simulated under monotonic loading and subsequent cyclic loading with dominant shear stress along its length. The specimen is designed so that the damage development can be tracked easily on the localized interface. The 3ENF experiments and FE simulation have been used simultaneously to investigate the damage under mode II fracture loading condition. Damage model used is cohesive zone model (CZM) which is developed and validated before. The key contribution of the current research is to present and describe a concept to extend current damage model to account for material behavior in cyclic loading in terms of development of damage. Damage is interpreted as degradation of penalty stiffness in normal and shear directions. Monotonic results showed that the CZM-based FE model is correlated well with experimental results and based on the experimental-computational approach, CZM parameters can be obtained and damage model will be characterized so that finite element method can be validated and stress and deformation analyses using FE results are feasible. The cyclic tests are also conducted for different load amplitude and number of cycles and necessary results are extracted to monitor and investigation on degradation in material stiffness and fracture energy as an effect of fatigue phenomenon and also being utilized to obtain presented fatigue damage model and as guidance and useful resource for future finite element simulation applying proper user-written subroutine into FE package.