Calculation Of The Stress Intensity Factor Variation Due To Residual StressFollowing An Overload

Abstract

In this paper, we propose a new approach to model the loading interaction effect due to the overload during fatigue constant amplitude loading. This approach concerns the retardation period immediately following the overload, until the minimum fatigue crack growth rate is reached. The calculation of this minimum crack growth rate, after an overload, depends on the calculation of the restriction amount of the stress intensity factor KR, which may have several definitions: The first corresponds to the opening stress intensity factor due to Elber [l] KOP = KRThe second, KpR = KR, was introduced by Lang and Marci [2], in order to distinguish the principal mechanism of the crack growth propagation. This parameter was established following the development of a test methodology, named CLPM [2]. Our model proposes a new numerical decoupling between the reversals of the overload. This analysis is based on the residual compressive stresses ahead of the crack tip taking into account the Bauschinger effect. This modelling is performed by means of finite element analysis, and determines the restriction stress intensity factor which we name KRCs (RCS for Residual Compressive Stress). The decoupling method is divided into three steps: 1) Creation of the plastic zones and application of the overload; 2) Unloading after overload by the application of a reversal compressive loading; Transactions on Engineering Sciences vol 40, © 2003 WIT Press, www.witpress.com, ISSN 1743-3533