Use of Dynamic Mechanical Analysers to Characterize Shape Memory Alloys: Cautions and Considerations from an Experimental Analysis

Dynamic mechanical analyzers (DMA) are applied in the thermomechanical characterization of shape memory alloys (SMA). The great sensitivity and capacity to detect small changes in mechanical properties, especially under temperature sweeping mode, make these equipment excellent options to characterize these smart metals. However, previous studies have reported differences between transformation temperatures of SMA measured by DMA in comparison with other characterization techniques, such as differential scanning calorimetry (DSC) and electrical resistance variation with temperature (ERT). In this sense, this work proposes an analysis of the use of DMA equipment to measure SMA phase transformation phenomena. For this, a micro-thermocouple was installed directly on a NiTi SMA ribbon sample during tests in the DMA equipment using increasing heating rates. A comparison of the transformation temperatures obtained from DMA with those obtained by DSC and ERT showed a significant difference in these temperatures, which was associated with the significant heat transfer between the sample and clamps. It was observed that the heat exchanges during DMA tests cause an intense temperature heterogeneity on the sample, even at heating rates as low as 1 °C·min−1.