This paper presents a generalized, elastoviscoplastic constitutive model, MIT‐SR, that is capable of describing a wide range of time‐dependent characteristics observed in clays from creep to strain‐rate‐dependent shear behavior. The key component of the proposed model is a novel evolution equation that attributes viscoplastic deformations to a state variable, R_a, referred to as internal strain rate, which represents the perturbation of the clay particle assembly due to historical straining. This state variable is driven by external straining actions (under compression or shear), which can be intrinsically linked to the loading step in classical plasticity theory, and decays with time representing a fading memory process. The proposed framework can be used to extend existing time‐independent elastoplastic models. In this case, MIT‐SR is built upon a prior elastoplastic model (MIT‐S1), which uses 3‐D stress‐space surfaces and hardening laws to represent anisotropic effective stress‐strain‐strength properties, and a paraelastic approach to describe nonlinear hysteretic behavior at small strains. The paper highlights the versatility of the proposed MIT‐SR model in representing a wide range of time‐dependent characteristics for normally consolidation behavior and undrained shear behavior. By varying a strain‐rate sensitivity parameter, β, the model can capture a full spectrum from temporary material response to changing strain rate, to isotache‐type behavior where the normal consolidation and critical state lines are functions of the applied steady strain rate. The paper also showcases the model prediction for undrained creep and undrained relaxation behavior, and its promising capability in describing rate‐effects under cyclic direct simple shear.

中文翻译：

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建立新的弹性黏塑性模型，用于黏土随时间变化的行为

本文提出了一种广义的弹黏塑性本构模型MIT‐SR，该模型能够描述在黏土中观察到的从蠕变到应变速率相关的剪切行为的各种随时间变化的特性。该模型的关键部分是一个新的演化方程，该方程将粘塑性变形归因于状态变量R _a。，称为内部应变率，它表示由于历史应变而引起的粘土颗粒组件的扰动。这个状态变量是由外部应变作用（在压缩或剪切作用下）驱动的，外部应变作用可以与经典可塑性理论中的加载步骤固有地联系在一起，并且随着时间的推移而衰减，这代表了褪色的记忆过程。所提出的框架可用于扩展现有的与时间无关的弹塑性模型。在这种情况下，MIT‐SR建立在先前的弹塑性模型（MIT‐S1）之上，该模型使用3D应力空间表面和硬化定律来表示各向异性的有效应力应变强度特性，并采用超弹性方法来描述非线性小应变时的磁滞行为。本文着重介绍了拟议的MIT-SR模型的通用性，该模型代表了正常固结行为和不排水剪切行为的各种时间相关特性。通过改变应变率灵敏度参数，β，该模型可以捕获从临时材料对变化的应变率的响应到等腰型行为的全谱图，其中正常固结和临界状态线是所施加的稳态应变率的函数。本文还展示了不排水蠕变和不排水松弛行为的模型预测，以及在描述循环直接简单剪切作用下的速率效应方面的有前途的能力。