This paper presents a calorimetric approach to the measurement of mechanical dissipation in specimens subjected to cyclic tensile tests. Mechanical dissipation, that is, the heat power produced by the material due to mechanical irreversibility, can potentially be deduced from the temperature changes captured on the specimen surface by infrared thermography. However, a difficulty arises for long-term cyclic tests: Results are easily skewed by any change in the specimen's environment. The problem is amplified by the fact that mechanical dissipation is in general small compared to the heat sources associated with thermomechanical couplings, making its estimation difficult. The paper proposes a simple procedure to extract a well-resolved estimation of mechanical dissipation by solving two key points specific to long-term cyclic tests: (a) the reduction of the parasitic effects associated with changes in the specimen's environment by using a specific device based on two references samples and (b) the choice of relevant thermal data acquisition parameters. A test is performed on a copper-based shape-memory alloy whose calorific response comprises three origins of heat sources: thermoelastic coupling, phase transformation, and mechanical irreversibility. The results obtained demonstrate the relevancy of the approach in extracting mechanical dissipation from the thermal response of the specimen subjected to long-term tensile tests in fatigue.
Full-field measurement techniques are now mature. As such, they have profoundly impacted the experimental mechanics community in recent years. The way that shape memory alloys (SMAs) are now tested is not spare from this deep-rooted trend, as reflected by the increasing number of papers published in the SMA literature. In this context, the aim of this contribution is to give an overview of the use of full-field measuring techniques for SMA characterization purposes. We recall first the basic principle of one volume and four surface techniques employed in this community. Several typical papers where such techniques are employed are then presented, by highlighting in each case the extent to which the thermomechanical response of SMAs could be better understood and modeled thanks to these techniques. A classification by several criteria of about 300 references is finally offered and discussed. The main criteria are the type of SMA, the type of technique employed to perform the measurements, and the type of test.
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