Abstract:Inspired by a previously published peel stopper design for foam cored composite sandwich structures, three novel markedly lighter peel stoppers were evaluated with respect to their ability to deflect and arrest propagating face debond cracks. Of the three novel peel stopper configurations, C1, C2 and C3, C1 was similar to the previous design, whereas C2 and C3 were modified with layers of glass fibre fabric extending from the peel stopper tip into the face sheet (C2) or into the face sheet/core interface (C3). The previous peel stopper was validated under mode II dominated conditions, but the novel designs were investigated under mode I dominated crack propagation conditions, which are of higher practical relevance. Both quasi-static and fatigue loading scenarios were investigated. The mechanisms controlling crack propagation at the internal peel stopper tip were studied using Thermoelastic Stress analysis (TSA) and Finite Element (FE) analysis. The TSA has revealed significant new information about the local stress fields in the vicinity of the tri-material junction (peel stopper tip) as well as the fracture process zone. Configuration C1 was unable to deflect debond cracks consistently, albeit it did so in most cases, whereas it was incapable of achieving crack arrest. C2 and C3 both performed better in that they consistently demonstrated the ability to deflect propagating cracks, whereas only C2 could arrest the cracks consistently as well. Detailed fracture mechanics analyses confirmed and explained the experimental observations.

This paper is concerned with the mechanical behaviour of a curved orthotropic beam on an elastic foundation under flexural loading. The differential equation in this case is derived from forcemoment equilibrium consideratios and classical laminated orthotropic plate theory. General solutions for various loading conditions are derived using a stress function approach. Finally, the effects of various parameters such as the anisotropy ratio, foundation modulus and radius of the beam on stresses are presented from a design perspective.

A theoretical approach is developed for the case of delamination of a curved composite beam under an opening bending moment. This is based on linear curved beam theory coupled with fracture mechanics concepts. The general solution is applied to analyse a speci®c case of delamination occurring at the mid-plane. The effects of the arc angle of delamination crack and the radius of curvature of the beam on the critical load are also studied.

The work described in the paper investigates the stresses in the vicinity of a debond between the face sheet and core in a foam core / composite sandwich beam. Experiments were conducted in which the damaged side of the beam was loaded in compression in a four point bend test. Thermoelastic stress analysis (TSA) was used to obtain a measure of the stress field in the central part of the beam to evaluate its potential for damage detection and assessment. It is shown that TSA is capable of both identifying the damage and assessing its severity in terms of the remnant load carrying capacity of the beam. Fatigue tests were also performed, which showed that the cyclic load applied as a necessity for TSA did not cause the damage to grow, thereby demonstrating the potential of TSA as a non-destructive method for inspecting sandwich structures.