Issue 21

C. Maletta et alii, Frattura ed Integrità Strutturale, 21 (2012) 5-12; DOI: 10.3221/IGF-ESIS.21.01 11 Effects of test temperature The effects of test temperature on the indentation response of the SMA have been analyzed by FE simulations by using the Clausius-Clapeyron relationship to calculate the relevant transformation stresses. To that end the FE model was first validated by comparison with experimental measurements carried out at room temperature, as it was not possible to perform indentation tests under temperature-controlled conditions. Fig. 6 compares the load-displacement curves obtained from FE simulation and experiment for indentation at room temperature to a maximum load of 300 mN. The figure clearly illustrates good agreement between the numerical results and experiments in terms of both maximum depth and residual depth, as well as in terms of the recovery and dissipated energy. Figure 6 : Comparison of the Load-Displacement curves obtained from FE simulations and experimentally measured (T=293 K, P=300 mN). Fig. 7 shows the load-displacement curves obtained for different test temperatures (T=293 K, T=303 K, T=313 K) for an indentation load of 300 mN. As expected, a marked effect of temperature on the indentation response of the SMA is observed, in terms of both maximum depth and residual depth, which is a direct consequence of the changes in transformation stresses of the alloy. The evolution of these parameters as a function of temperature and the direct transformation stress   s AM  for an indentation load of 300 mN is illustrated in Fig. 7.b. a) b) Figure 7 . Effects of test temperature on the indentation response of the SMA: a) Load-Displacement curves of the SMA at different temperatures; b) Maximum depth and residual depth vs temperature and direct transformation stress. The figure shows a reduction of both maximum depth and residual depth with increasing test temperature; however the residual depth decreases more rapidly, which indicates an overall improvement of the pseudoelastic response of the SMA