The micromechanical investigation of fiber cross-section shape effect on the rate sensitive nonlinear behavior of a glass/epoxy was performed at 10-5/s and 1/s, which considering four shapes, square, cross, circle and ellipse. With the strain of different rate loadings measured by Fibre Bragg gratings (FBGs) sensors, the rate-dependent inelastic constitutive relationship of epoxy is built by using an internal state variables viscoplasticity model. Then, through homogenizing the properties of unit cells, the responses of resin and its composites at 30° and 60° off-axis loadings are predicted by a micromechanical model compared with the experiments data. The effect of fiber cross-section fiber on the 30° and 90° off-axis responses are discussed with respect to the viscoplastic parameters of the resin determined. The results indicate that the micromechanical model accurately calculates the behavior of the PMCs employed. The square fiber causes the largest flow stress and plastic strain in the four cases. And the influences on overall responses for the four fiber shapes are enhanced with raising off-axis angles but weaken with the rate increase. However, the elliptical fiber yields the highest modulus in linear elastic stage. The square fiber is the most effective and the elliptical fiber is the least effective in the nonlinear deformation stage. Besides, the elastic properties are unaffected by loading rates when it is less than 1/s.
Ti-Ni based shape memory alloys (SMAs) are of excellent shape memory effect, superelasticity and damping property. These properties of the alloys can be fully displayed only after proper heat treatment. In this paper, the research progresses of the effect of the heat treatment on the microstructure, phase composition, phase transformation behaviors and shape memory properties in Ti-Ni based SMAs are reviewed, the correlation influence mechanism is summarized, and the future research directions in this field are pointed out. It is expected to provide reference for the development of Ti-Ni based SMAs and their heat treatment technologies.
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