弹塑性断裂及含缺陷脆性构件统一破坏准则研究

发布时间：2018-11-08 20:54

【摘要】：断裂现象在工程及生活中随处可见。一些意想不到的断裂会导致灾难性事故的发生,这需要力学工作者们运用断裂力学的知识去尽量避免。经过一百多年的发展,断裂力学中关于线弹性断裂及弹塑性断裂方面的理论已经建立了许多,但是目前在断裂领域中仍然存在一些尚未解决的关键性问题。本文就针对其中的两个——弹塑性断裂准则及含缺陷脆性构件的统一破坏准则进行了深入的研究和探索。主要结论归纳如下:当弹塑性材料中的裂纹发生扩展后,塑性卸载出现导致J积分不再适用,原因在于其中的应变能密度不能得到清晰的定义。目前缺乏一个广泛接受和使用的弹塑性裂纹扩展准则,本工作针对这一问题通过严格的公式推导给出类似于J积分形式的物理量,并提出相应适用范围较广的断裂准则。研究出发点避免了容易引起争议的能量定义,分别研究一个固定围道和一个移动围道所包围面域内的功率平衡,定义两种不同的能量释放率:裂纹面能量释放率sG和局部能量释放率LG。从两者之间的差异推断裂尖应力奇异导致裂尖处的物质点经历应力值的急剧下降从而伴随有动能的耗散。利用内聚力模型和基于裂纹面能量释放率的断裂准则,给出了理想弹塑性材料中存在长达四十多年的Rice悖论的合理解释。对几种不同断裂准则对比讨论后,推荐使用基于裂纹面能量释放率sG的断裂准则解决弹塑性裂纹扩展问题。强度准则和断裂准则存在其各自的适用范围,针对工程中常见的V型缺口、倒角、椭圆孔洞等所导致的构件破坏问题缺少一种合适的准则。本文就这一问题发展一种适用于多种形状缺陷的统一破坏准则。首先明确并提出含缺陷构件的一种基本破坏规律,称之为破坏第零定律,随后对现有的强度准则和断裂准则各自在使用时存在的尺寸局限性进行阐述。提出一种适用于多种形状缺陷的统一破坏准则,并进行实验验证。这种统一破坏准则是一种双参数函数破坏准则,与其它单常数破坏准则讨论对比时,发现后者在某些情况下会存在问题,而前者更合理并具有更广泛的适用性。
[Abstract]:Fracture can be seen everywhere in engineering and life. Some unexpected fractures can lead to catastrophic accidents, which requires mechanics workers to use fracture mechanics knowledge to avoid as far as possible. After more than one hundred years' development, many theories on linear elastic fracture and elastic-plastic fracture have been established in fracture mechanics, but there are still some key problems in the field of fracture. In this paper, two of them, the elastic-plastic fracture criterion and the unified failure criterion for brittle members with defects, are studied and explored. The main conclusions are summarized as follows: after crack propagation occurs in elastic-plastic materials, the plastic unloading occurs and the J-integral is no longer applicable, because the strain energy density is not clearly defined. At present, there is no widely accepted and used elastic-plastic crack growth criterion. In view of this problem, a physical quantity similar to J-integral form is derived through strict formulas, and a corresponding fracture criterion with a wide range of applications is proposed. The starting point of the study avoids the controversial definition of energy and studies the power balance in the area surrounded by a fixed and a moving lane, respectively. Define two different energy release rates: crack surface energy release rate (sG) and local energy release rate (LG.) The stress singularity of the fracture tip from the difference between the two causes the material point at the crack tip to undergo a sharp decrease in stress value which is accompanied by the dissipation of kinetic energy. By using the cohesive force model and the fracture criterion based on the energy release rate of the crack surface, a reasonable explanation for the existence of the Rice paradox in ideal elastic-plastic materials for more than 40 years is given. After comparing and discussing several different fracture criteria, it is recommended to use the fracture criterion based on the energy release rate of crack surface (sG) to solve the problem of elastic-plastic crack propagation. The strength criterion and the fracture criterion have their respective application scope. There is a lack of a suitable criterion for the structural failure problems caused by the common V-shaped notch, chamfer and elliptical hole in engineering. In this paper, a unified failure criterion for various shape defects is developed. At first, a basic failure law of members with defects is defined and put forward, which is called the zero law of failure. Then the size limitations of the existing strength criterion and fracture criterion are expounded respectively. A uniform failure criterion for various shape defects is proposed and verified by experiments. This unified failure criterion is a two-parameter function failure criterion. When compared with other single constant failure criteria, it is found that the latter has some problems in some cases, and the former is more reasonable and has wider applicability.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O346.1

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