Fail-safe design of integral metallic aircraft structures reinforced by bonded crack retarders

Abstract

This paper presents an investigation on the effectiveness of crack growth retarders bonded to integral metallic structures. The study was performed by both numerical modelling and experimental tests. It focuses on aluminium alloy panels reinforced by bonded straps made of carbon-epoxy, glass-epoxy composite materials or a titanium alloy. The goal was to develop a fail-safe design for integrally stiffened skin-stringer panels applicable to aircraft wing structures. The modelling strategy and finite element models are presented and discussed. The requirements that the models should meet are also discussed. The study has focused on establishing the extent of crack retarder benefits, in terms of fatigue crack growth life improvement, by numerical simulation and experimental tests of various crack retarders. The results of predicted fatigue crack growth retardation have been validated by tests of laboratory samples. This study concludes that by bonding discrete straps to an integral structure, the fatigue crack growth life can be significantly improved.

Methods for the prediction of fatigue delamination growth in composites and adhesive bonds – A critical review

“…Despite this, Boscolo, Zhang and co-workers [161,163,165] present test results which are in reasonably good agreement with the growth predicted using the fracture criterion method. The reason for this is that Boscolo et al model a strap bonded to a metal plate containing a fatigue crack.…”

“…Although they do not state it explicitly, Xie and Biggers only employed their model in the investigation of delamination growth under quasi-static load. However Boscolo, Zhang, and co-workers [161][162][163][164][165] have used a similar approach to model delamination growth in a strap bonded to a plate in which a fatigue crack is growing. There is a serious problem with applying this apporach to fatigue delamination growth however, which can be seen by conducting a simple thought experiment.…”

Fracture and damage mechanics modelling of thin-walled structures – An overview

“…The article by Zhang and Irving in this special issue [162] provides additional information on analysis approaches for damage tolerance assessments for structures with bonds or stiffeners. The work in the above cited references also indicates the importance of incorporating residual stress effects and the delamination growth behavior in the analysis models.…”

Effect of impact damage on fatigue performance of structures reinforced with GLARE bonded crack retarders

“…Aircraft structures in service experience a spectrum of loading which, in combination with the relatively high stress values attained can result in the development of fatigue cracks. For this reason, novel crack retarding features are being developed for aircraft structures that rely on integral construction [1,2].…”