论复合型表面裂纹准则

Further Research on Mixed-Mode Surface Crack Criteria

本文用理论和试验分析相结合的方法研讨了作者和前人先后提出的表面裂纹复合型断裂准则[G]max、[S]min、[σ_θ]max、[U_v]max、[σ_α]max和[r_p]max六个准则;再次证明了后三个准则优于前三准则;实测出了表面裂纹最深点的起裂角和临界起裂载荷随表面裂纹倾斜角的变化规律;最后指出了断裂准则中断裂参数应建立在相同的力学基准上,从而为工程应用和理论研究提供了可靠的依据。

In order to make clear the contributions of this paper, it is necessary toreview briefly past research. The initiation of mixed-mode surface crack is usually determined bymixed-mode fracture initiation criteria. During the past two decades, the[G]max、[S]min and [σ_θ]max criteria have been presented one after another. In1986, Chen found that there are some defects in these criteria[1]. To eliminate the defects found by Chen, three fracture criteria were proposedby the authors in Ref.[2]. Based on the research results of Ref.[2], further research on the [U_v]max、[σ_α]max. and [r_p]min criteria proposed in Ref.[2] is presented in this paper.The main contributions of this paper are as follows: 1. Theoretical calculations and experiments confirm that it is allowable touse the assumptions made in Ref. [2] that the initiation of three-dimensioncrack takes place in the normal planes of crack-tip points. 2. The special physical meanings of the fracture parameters sclected forthe [U_v]max、[U_α]max and [r_p]min criteria are precisely stated. 3. By using 'local section' method, the initiative angles and critical initiativeloads are successfully measured. The measured results confirm the correctness ofthe results computed by using [U_v]max、[σ_α]max and [r_p]min criteria. 4. The last but most important contribution of this paper is believed to bethat the authors are the first to determine experimentally the curves that givethe relations of the initiative angle and critical initiative load at the deepestpoint of surface crack with the inclined angle of surface crack. This experimentaldetermination was obtained after overcoming quite serious difficulties. Such anexperimental curve also agrees very well with that computed by using the[U_v]max、[σ_α]max and [r_p]min criteria.