Abstract
Thermoelastic Stress Analysis (TSA) is one of the very few methods allowing the determination of a continuous stress distribution on the object’s surface under variable loading conditions. Such results provide a lot of valuable information in the field of technical condition assessment and residual life prediction. In order to improve the accuracy of the TSA, the Lock-In signal processing method is implemented. This research is aimed at verifying the effectiveness of this improvement and determining the TSA stress detection threshold, as it is important information in terms of the applicability of this method in the low-stress conditions encountered in considerations of fatigue of load-carrying structures. A steel sample with a centrally located hole was subjected to cyclic loads to determine the threshold of stress detection and accuracy of TSA. As a result of the research, the relationship between the magnitude of stress excitations and the underestimation of the measured stresses was developed. Based on the conducted investigations, it was concluded that reasonable TSA results can be acquired for excitations that induce a temperature response above 10 mK (0.5 NEDT). The presented field test example proves that in industrial applications reasonable results can be acquired for thermal responses below the NEDT of the IR camera. It was concluded that it is possible to successfully implement TSA in low-stress applications (temperature response below NEDT).
Highlights
The determination of continuous stress distribution on the surface of an object under variable loading conditions is very important when it comes to condition assessment, predicting residual life, fatigue calculations, etc
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Summary
The determination of continuous stress distribution on the surface of an object under variable loading conditions is very important when it comes to condition assessment, predicting residual life, fatigue calculations, etc. To obtain high-quality results from the TSA, a measured IR signal must be of appropriate strength In the laboratory, this is achieved by maximizing the excitation magnitude that induces stress near the elastic limit of the tested material. The quality of that signal affects the final quality of the analysis results This becomes another important issue because in the vast majority of industrial applications, obtaining a reference signal from external sources such is not possible. The self-reference functionality is based on retrieving the reference signal needed for lock-in processing from the selected area of the recording image The quality of this signal is not as good as obtained from the laboratory testing machines. In such a case, a lower accuracy and detection limit should be expected
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