Phase-field description of fracture in NiTi single crystals
Phase-field description of fracture in NiTi single crystals
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DOI：
10.1016/j.cma.2023.116677
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发表时间：
2024-02
影响因子：
7.2
通讯作者：
D. Kavvadias;Th. Baxevanis
中科院分区：
文献类型：
--
作者：
D. Kavvadias;Th. Baxevanis
本文提出了NiTi单晶级热力诱导断裂的相场模型，即加载路径下的断裂，该断裂可以利用NiTi的功能特性--超弹性或形状记忆效应--，并在运动线性区建立。该模型考虑了奥氏体相向马氏体相的可逆相变、习性平面变种和奥氏体相的塑性变形。相变诱发塑性变形是奥氏体-马氏体界面处局部变形不相容的一种调节机制，并通过在基于Mori-Tanaka和Kröner细观力学假设和马氏体在奥氏体内瞬时长大的假设导出的自由能中引入相互作用项来解释。根据实验观察表明，NiTi断裂是一种应力控制的方式，损伤是由弹性能驱动的，即相变和塑性变形通过应力重分布间接促进裂纹的形成和扩展。该模型仅限于准静态机械载荷(无潜热效应)，热载荷相对于传导换热的时间速率足够慢(无温度梯度)，以及低于Md的温度范围，在此温度范围内奥氏体相稳定，即应力诱发马氏体相变被抑制。模型的数值实现基于相变和塑性变形的有效粘性正则化方案、切线模量法的显式数值积分和未知场耦合的交错格式。该模型能够捕捉到相变诱发的韧化，即在名义等温载荷下裂纹扩展后留下的非弹性变形的屏蔽作用下的稳定裂纹扩展，在恒定偏压载荷下的致裂诱导断裂，以及晶相对裂纹形态的依赖。
A phase-field model for thermomechanically-induced fracture in NiTi at the single crystal level, ie, fracture under loading paths that may take advantage of either of the functional properties of NiTi–superelasticity or shape memory effect–, is presented, formulated within the kinematically linear regime. The model accounts for reversible phase transformation from austenite to martensite habit plane variants and plastic deformation in the austenite phase. Transformation-induced plastic deformation is viewed as a mechanism for accommodation of the local deformation incompatibility at the austenite–martensite interfaces and is accounted for by introducing an interaction term in the free energy derived based on the Mori–Tanaka and Kröner micromechanical assumptions and the hypothesis of martensite instantaneous growth within austenite. Based on experimental observations suggesting that NiTi fractures in a stress-controlled manner, damage is assumed to be driven by the elastic energy, ie, phase transformation and plastic deformation are assumed to contribute in crack formation and growth indirectly through stress redistribution. The model is restricted to quasistatic mechanical loading (no latent heat effects), thermal loading sufficiently slow with respect to the time rate of heat transfer by conduction (no thermal gradients), and a temperature range below M d, which is the temperature above which the austenite phase is stable, ie, stress-induced martensitic transformation is suppressed. The numerical implementation of the model is based on an efficient scheme of viscous regularization in both phase transformation and plastic deformation, an explicit numerical integration via a tangent modulus method, and a staggered scheme for the coupling of the unknown fields. The model is shown able to capture transformation-induced toughening, ie, stable crack advance attributed to the shielding effect of inelastic deformation left in the wake of the growing crack under nominal isothermal loading, actuation-induced fracture under a constant bias load, and crystallographic dependence on crack pattern.