Influence of Geometry on Failure Modes of Hybrid Metal-Composite Protruding Bolted Joints

This article presents the influence of joint geometry on the damage mode in the CFRP (Carbon Fiber Reinforced Polymer) composite plate of the single-lap, protruding, hybrid metal-composite joints. A detailed 3D finite element model incorporating geometric, material and friction-based contact full nonlinearities is developed to numerically investigate the geometry effects on the progressive damage analysis (PDA) of the orthotropic material model. The PDA material model integrates the nonlinear shear response, Hashin-tape failure criteria and strain-based continuum degradation rules being developed using the UMAT user subroutine in Nastran commercial software. In order to validate the geometry effects on the failure modes of the joints with hexagonal head bolts, experiments were conducted using the SHM (Structural Health Monitoring) technique. The results showed that the plate geometry is an important parameter in the design process of an adequate bolted joint and its effects on damage initiation and failure modes were quite accurately predicted by the PDA material model, which proved to be computational efficient and can predict failure propagation and damage mechanism in hybrid metal-composite bolted joints.