Diagnostic Technique for Deterioration Inspection of Metallic Products through the In situ Measurement Using a Thermophysical Handy Tester

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This paper proposes a non-destructive technique using a thermophysical handy tester to inspect the deterioration of metallic products. In the early stage of fatigue in a metallic body, many micro-cracks appear on the surface of the stressed body. As fatigue progresses, these micro-cracks multiply and grow, while the apparent thermal conductivity of the surface layer spontaneously decreases. This phenomenon introduces the possibility of determining the progress of deterioration through in situ measurement of thermophysical properties. To estimate the degree of deterioration of materials, a dimensionless deterioration factor α is introduced. In order to corroborate this technique, several fatigue tests using carbon steels were conducted herein. Throughout the tests, apparent thermal conductivities and deterioration factors up to the limit of fatigue were periodically measured using a thermophysical handy tester. Furthermore, microscopic observations to investigate the evolution of micro-cracks were performed for stage-assessment during the period of fatigue tests. The results clearly demonstrate that this technique is useful for the non-destructive diagnosis of such deterioration.