Analytical and numerical modelling of plasticity-induced fatigue crack closure near cold-expanded holes in aircraft structures

• Main Author: Matos,Paulo F. P. de
• Publication Date: 2008
• Other Authors: Nowell,David
• Format: Article
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://scielo.pt/scielo.php?script=sci_arttext&pid=S0870-83122008000100016
• topic: Cold-expanded holes; Residual stresses; Fatigue crack propagation; crack closure

Over the last few years considerable effort has been put into the improvement of the fatigue life of aircraft structures. Aircraft experience complex loading conditions during flight and safe operation requires understanding of the underlying mechanics of fatigue crack growth. One of the outcomes of the research carried out over the last thirty years is that fatigue cracks in metals are partially closed over part of a load cycle. This phenomenon is thought by many researchers to be the key to understanding the effect of non-uniform loading. Understanding crack closure is particularly challenging when initial residual stress fields (e.g. due to manufacturing or mechanical treatment) need to be taken into account. For example, rivet holes are a critical area for fatigue and they are usually cold expanded to create a beneficial residual stress field and to improve the fatigue performance. This paper describes the development of a simple analytical model for plasticity-induced fatigue crack closure taking into account the residual stresses due to cold expansion of rivet holes. The model is compared to a more sophisticated finite element analysis of plasticity-induced crack closure. The results show that the residual stress field has a strong influence on the closure behaviour and therefore on fatigue crack propagation. The potential for the application of this model to real components is assessed by modelling some experiments taken from the literature. The model results agree with the experimental findings for the location of fatigue crack initiation. Residual stresses from FE analyses of cold expansion were used as an input to the analytical closure model, which successfully predicted crack propagation from cold-expanded holes. The results obtained show that this approach has potential for use as a life prediction technique in design.