Effect of transformation volume contraction on the toughness of superelastic shape memory alloys
Effect of transformation volume contraction on the toughness of superelastic shape memory alloys
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DOI：
10.1088/0964-1726/11/6/316
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发表时间：
2002-12
影响因子：
4.1
通讯作者：
Wenyi Yan;Chun H. Wang;Xin Ping Zhang;Y. Mai
中科院分区：
文献类型：
--
作者：
Wenyi Yan;Chun H. Wang;Xin Ping Zhang;Y. Mai
形状记忆合金具有两个重要的性质：形状记忆现象和由热弹性马氏体相变引起的超弹性变形。为了充分发挥SMA在机械和生物力学工程中开发功能结构或智能结构的潜力，重要的是要了解和量化SMA的失效机制。本文从理论上研究了相变引起的体积收缩对超弹性形状记忆合金断裂性能的影响。采用一个简单的模型来考虑纯体积变化的正向和反向相变，然后将其应用于数值研究拉伸裂纹尖端附近的相变场。结果表明，在稳态裂纹扩展过程中，由于正向相变，相变区延伸到裂尖之前，而在尾流中发生部分反向相变。此外，作为与马氏体到马氏体的转变相关联的体积收缩的结果，诱导应力强度因子是正的。这与氧化锆陶瓷中实现的负应力强度因子形成鲜明对比，氧化锆陶瓷在相变期间经历体积膨胀。已经发现，逆相变的诱导应力强度因子的影响可以忽略不计。本研究结果的一个重要意义是，在SMA的相变与体积收缩往往会降低其断裂阻力，增加脆性。
Shape memory alloys (SMAs) exhibit two very important properties: shape memory phenomenon and superelastic deformation due to intrinsic thermoelastic martensitic transformation. To fully exploit the potential of SMAs in developing functional structures or smart structures in mechanical and biomechanical engineering, it is important to understand and quantify the failure mechanisms of SMAs. This paper presents a theoretical study of the effect of phase-transformation-induced volume contraction on the fracture properties of superelastic SMAs. A simple model is employed to account for the forward and reverse phase transformation with pure volume change, which is then applied to numerically study the transformation field near the tip of a tensile crack. The results reveal that during steady-state crack propagation, the transformation zone extends ahead of the crack tip due to forward transformation while partial reverse transformation occurs in the wake. Furthermore, as a result of the volume contraction associated with the austenite-to-martensite transformation, the induced stress-intensity factor is positive. This is in stark contrast with the negative stress-intensity factor achieved in zirconia ceramics, which undergoes volume expansion during phase transformation. The reverse transformation has been found to have a negligible effect on the induced stress-intensity factor. An important implication of the present results is that the phase transformation with volume contraction in SMAs tends to reduce their fracture resistance and increase the brittleness.