模拟金属与合金多轴疲劳破坏的统一直接途径

发布时间：2018-10-26 08:31

【摘要】：本文提出一个适用于多轴有限变形非线性联合硬化的新弹塑性模型,用来模拟金属和合金的多轴热耦合疲劳失效.新模型与先前模型相比,有如下几个创新点:(i)对比于经典弹塑性模型,所提出新模型结构简单并且在下述意义上完全自由且是光滑的:该模型无需引入为表征塑性行为须强加的屈服条件以及加载卸载条件,而是自动包含这些塑性特征作为模型的固有本构特征,此外,该模型给出连续弹塑性切模量,避免了通常模型所涉及的模量强间断问题;(ii)新模型可自动表征金属和合金的多轴热耦合疲劳失效,无需涉及任何假定的损伤状变量以及任何特设的失效判据;(iii)可以自动模拟金属和合金的高周、低周疲劳直至最终失效破坏行为;(iv)新模型符合热力学一致性条件,进一步意义上,比熵函数和Helmholtz自由能函数可以显式表达,如此,Clausius-Duhem不等式所规定的热力学限制可以自动满足.以下三个方面的新结果可从模型预测直接得到.即,(i)热耦合疲劳破坏的复杂特征可以通过所引进硬化函数的简单渐近性质自动表征;(ii)可以导出临界破坏状态的统一判据;(iii)特别是,可以经由建立统一直接步骤确定在循环以及非循环热力耦合多轴变形情形下的疲劳寿命.针对各种典型的疲劳破坏问题给出的一系列数值算例表明,模型预言一致地符合相关实验数据.
[Abstract]:In this paper, a new elastoplastic model for nonlinear combined hardening of multiaxial finite deformation is proposed, which is used to simulate the multiaxial thermal coupled fatigue failure of metals and alloys. Compared with the previous model, the new model has the following innovations: (i) is compared to the classical elastoplastic model. The proposed new model is simple in structure and completely free and smooth in the sense that it does not require the introduction of yield conditions imposed to characterize plastic behavior and loading and unloading conditions. These plastic characteristics are automatically included as the inherent constitutive characteristics of the model. In addition, the model gives the continuous elastic-plastic shear modulus, which avoids the problem of strong discontinuity of the modulus involved in the usual model. The new (ii) model can automatically characterize the multiaxial thermally coupled fatigue failure of metals and alloys without any assumed damage variables and any special failure criteria. (iii) can automatically simulate the high cycle, low cycle fatigue and ultimate failure behavior of metals and alloys. The new (iv) model conforms to the thermodynamic consistency condition. Furthermore, the specific entropy function and the Helmholtz free energy function can be expressed explicitly. Thus, the thermodynamic limits stipulated by the Clausius-Duhem inequality can be satisfied automatically. The following three new results can be obtained directly from the model prediction. That is, the complex characteristics of, (i) thermal coupled fatigue failure can be automatically characterized by introducing a simple asymptotic property of hardening function, and the unified criterion of critical failure state can be derived by; (ii). (iii) in particular can determine fatigue life under cyclic and non-cyclic coupled multiaxial deformation by establishing a unified direct step. A series of numerical examples for various typical fatigue failure problems show that the prediction of the model is consistent with the experimental data.
【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG111

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