Micromechanical analysis for microscopic damage initiation in fiber/epoxy composite during interference-fit pin installation

The interference-fit joint of composite structures is widely used in thin-walled sheets assembly of aviation field. Understanding the microscopic damage mechanism during interference-fit pin installation process has a great importance for optimal design of interference-fit joints. Therefore, a novel multi-scale modeling approach is proposed to simulate and analyze the squeezed damage of microscopic representative volume elements (RVEs) during interference-fit pin installation process by 2D finite element models on ABAQUS platform with user-defined material subroutine (UMAT). The plane stress and strain formulations are employed for in-plane and through-thickness models respectively. Once the maximum principal stress reaches the corresponding strength, linear elastic carbon fibers fail. The epoxy resin matrix is considered to be elastoplastic. When the ultimate strength is reached, the stiffness properties begin to degrade. A cohesive zone model is used to simulate interface debonding between the fiber and matrix. It's observed that the vicinity of 30° angle between normal pressure and fiber direction at the entrance of hole is the weakest portion. In addition, the plastic deformation of epoxy matrix occurs first, followed by interfacial debonding. Then compressive damage of epoxy matrix is observed with the increase of interference value, which is similar to the micrograph by experiment.