Strength and Fatigue Life Modeling of Bonded Joints in Composite Structure

Abstract

The aerospace industry lacks a validated, practical analysis method for the strength, durability, and damage tolerance evaluation of composite bonded joints. This paper presents the results of a combined strength and fracture analysis approach applied to typical bonded joint configurations found in rotorcraft composite structures. The analysis uses detailed 2-D non-linear finite element models of the local bondline. Strength-of-materials failure criteria are used to predict critical damage initiation loads and locations. A fracture mechanics approach is used to predict damage growth and failure under static and cyclic loads based on test data for static fracture toughness (GIc, GIIc) and crack growth rate (da/dN). Results are presented from the application of the analysis approach to two joint configurations: 1) a skin-stiffener T-joint and; 2) a bonded repair lap joint. The results show that the proposed approach can be used to predict critical failure modes, damage initiation loads and locations, crack and/or delamination stability, static strength, residual strength, and fatigue life. Discussion is also included on how this approach can be applied in damage tolerance evaluations of composite bonded joints.