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Moreover, it has been theoretically predicted Vibratory Polishing Machine(Clasius Claypeiron Equation 2) and experimentally determined (Šittner et al., 2014) that the level of mechanical loading necessary to create Stress Induced Martensite (SIM) growths linearly with temperature. These reversible solid-state phase transformations are known as a martensitic transformation that requires to occur, depending on temperature, mechanical loading stresses between 70 to 140 MPa (Duerig et al., 1990).
According to Equation 2 the stress drops to zero at the temperature Ms.
The difficulty to stress induce Martensite continues to increase with temperature until Md, above which the critical stress required to induce Martensite is greater than the stress required to move the dislocations (not reversible plastic deformation).
Therefore the temperature range for SIM is from Ms to Md. For a number of SMA systems, the agreement in the temperature dependence of the stress to form SIM according to the Clausius-Clayperon equation is quite striking.
The equation works equally well for the non-isothermal case, i.e., the case where temperature was held constant while the stress needed to form Martensite was measured.
Super-elasticity occurs when a material is deformed above As, but still below Md. In this range, Martensite could be stabilized with the application of stress, but becomes unstable upon removal of stress.
By mechanical stretching (treatment B in Fig. 1 and 2), in fact, the SMA is deformed to a larger extent (states 3 to 4 in Fig. 1 and structures B19 and B19’ in Fig. 2). This pseudo-plastic deformation is enabled by reorientation of crystallographic variants in the cold temperature phase following twinned (B19) to de-twinned (B19’) martensite transformations. Consequently, the deformation persists after load removal (from state 2 to 3 in Fig. 1). On re-heating, process C in Fig. 1 and 2, the material progressively transforms to Austenite B2 crystal lattice (from state 6 to intermediate state 7 and final state 1 in Fig. 1) recovering its initial shape.
During this shape recovery, large strain changes and large forces are generated that are of particular benefit for the development of temperature-activated actuators.
According to Equation 2 the stress drops to zero at the temperature Ms.
The difficulty to stress induce Martensite continues to increase with temperature until Md, above which the critical stress required to induce Martensite is greater than the stress required to move the dislocations (not reversible plastic deformation).
Therefore the temperature range for SIM is from Ms to Md. For a number of SMA systems, the agreement in the temperature dependence of the stress to form SIM according to the Clausius-Clayperon equation is quite striking.
The equation works equally well for the non-isothermal case, i.e., the case where temperature was held constant while the stress needed to form Martensite was measured.
Super-elasticity occurs when a material is deformed above As, but still below Md. In this range, Martensite could be stabilized with the application of stress, but becomes unstable upon removal of stress.
By mechanical stretching (treatment B in Fig. 1 and 2), in fact, the SMA is deformed to a larger extent (states 3 to 4 in Fig. 1 and structures B19 and B19’ in Fig. 2). This pseudo-plastic deformation is enabled by reorientation of crystallographic variants in the cold temperature phase following twinned (B19) to de-twinned (B19’) martensite transformations. Consequently, the deformation persists after load removal (from state 2 to 3 in Fig. 1). On re-heating, process C in Fig. 1 and 2, the material progressively transforms to Austenite B2 crystal lattice (from state 6 to intermediate state 7 and final state 1 in Fig. 1) recovering its initial shape.
During this shape recovery, large strain changes and large forces are generated that are of particular benefit for the development of temperature-activated actuators.
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