Abstract The spatiotemporal evolution of macro-domain patterns in a NiTi thin strip during stress-induced non-isothermal phase transformation (PT) are investigated through 2D FEM simulations using nonconvex nonlocal continuum model and 1D theoretical analysis. The FEM simulations shows that, with the increase of applied stretching rate (nominal strain rate), the way of PT in a thin strip (30 mm × 2.5 mm × 0.5 mm) changes from the sequential nucleation and growth mode in the low rates range ( ≤ 0.03 / s ) to the emergence of periodic patterns in the medium rates range (0.03/s~3.0/s) and eventually to stable homogeneous deformation mode in the high rates range ( ≥ 3.0 / s ). The domain spacing is governed by a power-law scaling to the strain rate, where the exponent changes from −1/2 (low rates range) to −1/6 (medium rates range). The 1D theoretical analysis further demonstrates that the rate-dependent patterns are essentially governed by a nondimensional internal material parameter A - 0 and a nondimensional external driving parameter k - . A - 0 represents the ratio of adiabatic hardening to isothermal softening in PT of the material, while k - controls the time scale competition of heat release and heat conduction, through which the thermodynamic condition of PT changes from near isothermal ( k - → ∞ ) to near adiabatic ( k - → 0 ) with the increase of the strain rate. It is shown that, as long as the material has the properties of isothermal softening and adiabatic hardening (i.e., A - 0 > 1 ), the conventional nucleation-growth paradigm of PT will eventually break down for small k - (or large stain rate). This is due to the fact that the increase of the energy barrier caused by the thermal and the interfacial effects can convexify the energy landscape of the system near the adiabatic condition and suppress the nucleation events at the macroscopic level.

中文翻译：

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NiTi带材非等温相变时空模式的非局部建模和分析

摘要 通过使用非凸非局部连续介质模型和一维理论分析的二维有限元模拟，研究了在应力诱导的非等温相变 (PT) 过程中 NiTi 薄带中宏观域图案的时空演变。有限元模拟表明，随着施加拉伸速率（标称应变率）的增加，薄带（30 mm × 2.5 mm × 0.5 mm）中的 PT 方式从低速率范围内的顺序成核和生长模式发生变化( ≤ 0.03 / s ) 在中等速率范围 (0.03/s~3.0/s) 中出现周期性模式，并最终在高速率范围 ( ≥ 3.0 / s ) 中稳定均匀变形模式。域间距由应变率的幂律缩放控制，其中指数从 -1/2（低速率范围）到 -1/6（中等速率范围）。一维理论分析进一步表明，速率相关模式基本上受无量纲内部材料参数 A - 0 和无量纲外部驱动参数 k - 控制。A - 0 表示材料在 PT 中绝热硬化与等温软化的比值，而 k - 控制放热和热传导的时间尺度竞争，通过它使 PT 的热力学条件从接近等温 ( k - → ∞ ) 变化随着应变率的增加，接近绝热（ k - → 0 ）。结果表明，只要材料具有等温软化和绝热硬化的特性（即 A - 0 > 1 ），传统的 PT 形核生长范式最终会因小 k -（或大染色率）而失效。 ）。