PSI - Issue 38

Di Song et al. / Procedia Structural Integrity 38 (2022) 546–553 Di Song and Chao Yu / Structural Integrity Procedia 00 (2021) 000–000

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By fitting the experimental data of the square path 566MPa, the material parameters can be determined as shown in Table 1, this model only use the martensite transformation start and finish stresses of the NiTi SMAs, and four additional material parameters in the predictions. The evolution curves of the experimental and predicted residual strains with different peak stresses for square and butterfly-typed paths are given in Fig. 4. It can be observed that the predicted residual strains accord well with the experimental data, and can represent the accumulation process of the residual strains in all the cyclic loading cases. Table 1 Material parameters in the proposed residual strain prediction model � � � = 472 , � � � = 610 = 6.42 , � = 2 , � = 20 , � = −5.6 ;

Fig.4. The evolution curves of the experimental and predicted residual strains with different peak stress: (a) 566MPa, (b) 637MPa, (c) 683MPa.

3.2. The prediction model for fatigue life

Here we try to propose a life-prediction model for multiaxial loadings based on the accumulation of the residual strains in the uniaxial direction. It has been clarified that the residual strains usually stabilize within 20 cycles for most of the non-proportional multiaxial loadings, thus, we set the accumulated residual strains of the first 20 cycles