OS10-1-6 Development of a self-reference lock-in thermography for fatigue crack monitoring

Abstract

Thermoelastic stress measurement has been getting an increasing attention as a non-destructive evaluation technique for fatigue crack in steel structures. In the thermoelastic stress measurement, stress distribution is measured by lock-in infrared thermography, which correlates temperature change due to the thermoelastic effect with reference-load signal. Load signal from external source, such as load-cell, strain gage or displacement gage, is usually employed as a reference signal in the conventional lock-in technique. In this study, a self-reference lock-in infrared thermography was newly developed, in which a reference signal was constructed by using the same sequential data on thermoelastic temperature change. It enabled us to measure the distribution of relative intensity of applied stress under random loading without using any external load signal. Proposed self-reference lock-in thermography was applied for crack identification based on the detection of the singular stress field in the vicinity of crack tips. Experimental investigations were conducted using welded steel samples. It was found that significant temperature change was observed at the crack tips, demonstrating the feasibility of the proposed technique.