Geometry Effects on Joint Strength and Failure Modes of Hybrid Aluminum-Composite Countersunk bolted Joints

Abstract

This paper presents the effects of geometry parameters (width/hole diameter, and edge distance/hole diameter ratios) on the damage initiation and growth in the CFRP (Carbon Fiber Reinforced Polymer) composite-aluminum countersunk bolted joints. Strain gauge measurements conducted with an Instron testing machine along with a detailed 3D finite element model incorporating geometric, material, and friction-based contact nonlinearities were used to investigate the geometry parameters on the Progressive Damage Analysis (PDA) of the orthotropic material model. The PDA material model integrates the lamina nonlinear shear deformation, Hashin-type failure criteria, and strain-based continuum degradation rules, using the UMAT user subroutine in the MSC Software Corporation Patran-Nastran commercial software. The results showed that the geometry effects on damage initiation and failure modes are quite accurately predicted by the PDA material model, which proved to be computationally efficient, and therefore can predict failure propagation and damage mechanisms. Plate geometry is an important parameter in the design process of an adequate bolted joint while its effects on damage initiation and failure modes were quite accurately predicted by the analysis. The latter proved to be computationally efficient, and could successfully predict failure propagation and damage mechanism in hybrid metal-composite countersunk bolted joints.