Papers by Keyword: Multiple Overloads

Abstract: Constant
K fatigue crack growth tests were performed by applying an intermediate multiple overloads for S45C steel. The purpose of this study is to investigate effects of specimen thickness at various baseline stress intensity factor range levels (
Kb), the application position of the overload (a/W) and the application frequency of the overload (OLHz) on fatigue crack growth retardation behavior. The principal results are summarized as follows. The number of retardation cycles for the constant baseline stress intensity factor level (
Kb ) decreases with increasing specimen thickness. The normalized number of retardation cycles ( Nd / Nc ) decreases with increasing specimen thickness. But, at
Kb = 45 MPa(m)1/2, the cycle increases with increasing specimen thickness.

Abstract: For many fatigue-critical parts of machines and structures, the load history under operating conditions generally involves variable amplitude loading rather than constant amplitude loading. An accurate prediction of fatigue crack propagation life under variable amplitude loading requires a thorough evaluation of the load interaction effects. In this study, fatigue tests under both constant and variable amplitude loading were carried out to investigate the overload effects on fatigue crack propagation of the notched specimens. Strain distributions around the crack tip before and after a tensile overloading were measured using the ESPI (Electronic Speckle Pattern Interferometry) system. The size of the plastic zone was determined from the measured strain distributions. The study proposes a crack propagation prediction model that incorporates the overload ratio effect. A comparative work for the overload ratio effect demonstrated that the prediction by the proposed model was in good agreement with the experimental results. The prediction of fatigue crack propagation including multiple overloads with the proposed model show also a good agreement with test results.