PSI - Issue 43

Raghu V. Prakash / Procedia Structural Integrity 43 (2023) 190–196 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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information plotted as a function of total cycles of loading, and one can infer that by joining the temperature response of the interrupted test, one can obtain a response curve similar to a continuous fatigue test with three distinct regimes (primary, secondary and tertiary response in temperature). Such an approach was found to be consistent across several materials including polymer composite materials that were studied in our laboratory. The observation of increasing slope in temperature response with prior fatigue cycles, when plotted as a function of cumulative cycles of fatigue loading, helps to identify the extent of prior fatigue damage in working components whose temperature profile can be acquired in-situ using a thermal imaging system. One of the points to be noted with regard to use of infrared thermography for polymer composite materials is that the failure mode is quite different from that of metals and most often, failure is in the form of delamination, across the thickness of the specimen. In such cases, it is important to understand the location of delamination if there is a need for repair of such a composite laminate. To address the above issue, we have adopted active thermographic technique (which implies external excitation of thermal field on to the specimen – either using light source or through laser) and studying the cooling response of laminate either in the transmission mode or in the reflection mode [Prakash and Sudevan, 2016]. The results suggested that it is possible to use infrared thermography from being qualitative measurement technique to a quantitative measurement technique for characterizing damage progression.

Fig. 5 – Graph of temperature versus cycles during stress cycling of SS304 specimen.

Fig. 6 – Temperature response for the entire fatigue test till specimen failure.

Fig. 7 – Graph of temperature rise as a function of fatigue cycles for an interrupted test carried out on SS304 test specimen. The increase in initial slope after every test interruption suggests that the material memory effect for prior fatigue cycling.

Fig. 8 – Composite plot for the entire test duration which suggests a possibility to build the total temperature response curve from start to specimen failure, even from interrupted fatigue test data.