Role of external applied stress on the two-way shape memory effect

The two-way shape memory effect (TWME) is not an inherent property of shape memory alloys, TWME should be induced by training procedures. Till now, hundreds of papers have been published and more than 20 different training methods have been developed, in which the common feature is that external applied stress should be used to produce oriented internal stresses in austenite and induce preferential martensite variants during cooling. The present work attempts to classify the different training methods and analyze the characters of different internal stresses induced by different training methods.