Micromechanical analysis of crack closure mechanism for intelligent material containing TiNi fibers - (2nd report, numerical calculation of stress intensity factor in the process of shape memory shrinkage of TiNi fibers)

In our previous study, the micromechanical modeling of an intelligent material containing TiNi fibers was performed and the stress intensity factor K, at the tip of the crack in the material was expressed in terms of the magnitude of the shape memory shrinkage of the fibers and the thermal expansion strain in the material. In this study, the value of K-i at the tip of the crack in the TiNi/epoxy material is calculated numerically by using analytical expressions obtained in our first report. As a result, we find that the K-i value decreases with increasing shrink strain of the fibers, and this tendency agrees with that of the experimental result obtained by Shimamoto et al. (Trans. Jpn. Soc. Mech. Eng., Vol. 65, No. 634 (1999), pp. 1282 - 1286). Moreover, there exists an optimal value of the shrink strain of the fibers to make the K-i value zero, The change in K-i with temperature during the heating process from the reference temperature to the inverse austenitic finishing temperature of TiNi fiber is also consistent with the experimental result. These results can be explained by the changes in the shrink strain, the thermal expansion strain, and the elastic moduli of TiNi fiber with temperature. These results may be useful in designing intelligent materials containing TiNi fibers from the viewpoint of crack closure.