In this paper, a strain rate-dependent distortional hardening model is firstly proposed to describe strain rate-dependent material behaviors under linear and nonlinear strain paths changes in 0≤θpathchange≤180∘. The proposed model is formulated based on the simplified strain rate-independent distortional hardening model (Choi and Yoon, 2023). Any yield function could be used for the strain rate-dependent isotropic and anisotropic yielding. For the linear strain path, the strain rate-dependent isotropic hardening behavior could be explained by two state variables representing rate-dependent yielding and convergence rate of flow stress under monotonically increasing loading condition, respectively. For the nonlinear strain paths, the strain rate-dependent material behaviors such as Bauschinger effect, yield surface contraction, permanent softening, and nonlinear transient behavior could be described by modifying the evolution equations of the simplified strain rate-independent distortional hardening model with a logarithmic term of strain rate. For the verification purpose, it was used the strain-rate dependent tension-compression experiments of TRIP980 and TWIP980 (Joo et al., 2019). In addition, a high speed U-draw bending test was conducted with original and pre-strained specimens. The springback prediction in high speed U-draw bending test was performed by using strain rate-independent isotropic, strain rate-dependent isotropic-kinematic and distortional hardening models. It is identified that the proposed model showed the most accurate prediction for the pre-strained specimen where the possible bilinear and trilinear path change in 0≤θpathchange≤180∘ is observed while it showed the same accuracy for the original specimen where main strain path change occur in forward-reverse manner (θpathchange=180∘).

中文翻译：

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非线性应变路径的应变率相关畸变硬化模型


本文首先提出了一种应变速率相关型变形硬化模型，用于描述在 0≤θpathchange≤180∘ 的线性和非线性应变路径变化下应变率相关材料的行为。所提出的模型是基于简化的与应变率无关的畸变硬化模型 （Choi and Yoon， 2023） 制定的。任何屈服函数都可用于应变速率依赖性的各向同性和各向异性屈服。对于线性应变路径，应变速率依赖性各向同性硬化行为可以用两个状态变量来解释，这两个状态变量分别表示单调增加载荷条件动应力的速率依赖屈服和收敛速率。对于非线性应变路径，可以通过用应变率的对数项修改简化的与应变率无关的畸变硬化模型的演化方程来描述应变率相关的材料行为，例如 Bauschinger 效应、屈服表面收缩、永久软化和非线性瞬态行为。为了验证目的，使用了 TRIP980 和 TWIP980 的应变速率依赖性拉伸压缩实验（Joo et al.， 2019）。此外，还对原始试样和预应变试样进行了高速 U 型拉伸弯曲试验。高速 U 型拉伸弯曲试验中的回弹预测采用与应变速率无关的各向同性、应变率依赖的各向同性运动学和畸变硬化模型进行。 结果表明，所提出的模型对预应变试样的预测最准确，其中观察到可能的双线性和三线性路径变化为 0≤θpathchange≤180∘，而对于原始试样，主应变路径变化以正向-反向方式发生 （θpathchange=180∘）。