Nondestructive Estimation of Remaining Fatigue Life: Thermography Technique
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TECHNICAL ARTICLE—PEER-REVIEWED
Nondestructive Estimation of Remaining Fatigue Life: Thermography Technique M. Amiri • M. M. Khonsari
Submitted: 12 May 2012 / in revised form: 21 July 2012 / Published online: 25 August 2012 Ó ASM International 2012
Abstract A technique for the estimation of remaining fatigue life (RFL) of metallic specimens when subjected to cyclic load is presented. The procedure includes evaluation of thermal response of the metal and its correlation with the fatigue life. Results are presented for a series of fully reversed fatigue tests with Stainless Steel 304L at room temperature. It is demonstrated that the slope of temperature rise as a function of time is a good candidate for estimation of RFL. Once the temperature slope is measured, the remaining useful life of the specimen can be effectively estimated. Keywords Remaining fatigue life Nondestructive testing Infra-red thermography
Introduction Reliable prediction of the overall life of a component at the design stage is a difficult task. Indeed, more challenging is the estimation of the useful remaining fatigue life (RFL) of a component that has already been in service. Clearly, an enabling technology that could provide an accurate assessment of RFL via a nondestructive testing procedure has an enormous potential for avoiding the risk of failure. Both time and resources could be saved if reliable methodologies for determining the extent of fatigue damage and an estimation of RFL could be established. In this article, the use of infrared (IR) thermography for fatigue life assessment is explored. Characterization of
fatigue life based on monitoring thermal behavior has a rich history of supporting publications for both metals and composites. The early applications of thermography in fatigue damage detection dates back to the studies of Attermo and Ostberg [1], Reifsnider and Williams [2], Charles et al. [3], and Henneke et al. [4]. More recently, various techniques for prediction of fatigue life based on thermography have been proposed, which are based on the established stages of temperature evolution during fatigue such as initial temperature rise [5, 6], steady-state temperature [7], and sudden rise in temperature before final fracture [8]. These methodologies assume that the specimen is initially pristine. Thus, application of these procedures to a ‘‘degraded’’ specimen may yield grossly inaccurate prediction of RFL. In this article, the question of whether the RFL can be related to the rise of temperature in a specimen that has experienced an unknown number of stress cycles is addressed. For this purpose, a methodology is proposed, which accomplishes this goal by examining the rate of temperature rise during a short-time mechanical loading known as excitation loading [9]. It is shown that an initial rate of temperature increase (slope) induced by the excitation loading can be used to quantify the level of prior fatigue damage. Depending on the material, appropriate excitation load and frequency should be selected by the operator
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