11 - Mixed-mode fatigue of bonded joints in composites: Experiments and modelling

Abstract

This chapter presents first an extensive experimental investigation on composite bonded joints under mixed mode (I+II) static and cyclic loading conditions oriented to understand the influence of the mode mixity on the propagation of a bondline crack. double cantilever beam (DCB), end notch flexure (ENF) and mixed mode bending (MMB) tests were carried out on precracked samples, and fracture toughness and crack propagation resistance were seen to increase, for both static and fatigue loading, respectively, as the mode II contribution increases. Careful observations of crack propagation and damage evolution revealed a strong dependence of the propagation mode on the mode mixity. Then, a damage-based model was developed on the basis of the actual damage mechanisms occurring in a properly defined process zone. The proposed model has been validated on the experimental results obtained from DCB, ENF and MMB tests as well as from single lap bonded joints.