Characteristics of brittle fracture under general combined modes including those under bi-axial tensile loads
Characteristics of brittle fracture under general combined modes including those under bi-axial tensile loads
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DOI：
10.1016/0013-7944(83)90007-3
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发表时间：
1983
影响因子：
5.4
通讯作者：
Ueda Yukio;I. Kazuo;Yao Tetsuya;Aoki Mitsuru
中科院分区：
文献类型：
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作者：
Ueda Yukio;I. Kazuo;Yao Tetsuya;Aoki Mitsuru
本文从理论和实验两方面研究了打开模式（ⅰ型）、滑动模式（ⅱ型）和撕裂模式（ⅲ型）一般组合下的脆性断裂起裂特性。首先，对PMMA（聚甲基丙烯酸甲酯）试样进行了完全脆性断裂试验，测试了所有可能的断裂模式组合，包括各自的纯模式。将实验断裂强度与断裂准则预测的断裂强度进行了比较，断裂准则为：(1)最大切向应力[σgq]max，扩展到一般组合模式；(2)小弯曲裂纹扩展时的最大能量释放率[Gk(γ)]max;(3)新导出的小弯曲裂纹启动时的最大能量释放率[G(γ)]max。结果表明，[Gk(γ)]maxor [G(γ)] maxor准则对于预测初始裂纹扩展方向和断裂强度都是非常有效的。这些能量释放率以封闭形式表示，并推导出ⅰ、ⅱ、ⅲ三种模式任意组合下脆性断裂强度的相互作用曲线。接下来，对于伴随塑性变形的断裂，在不同低温下施加双轴拉伸载荷的低碳钢（sm41）试样上进行了试验。然后，在模式I和II的组合下发生塑性变形的脆性断裂。在小尺度屈服脆性断裂情况下，[G(γ)]最大准则较好地预测了初始裂纹扩展方向，但估计的断裂强度仅低于实验值。在大屈服和一般屈服的脆性断裂中，从断裂试验中发现，在缺口尖端的张开模式和滑动模式下，裂纹的初始扩展方向与裂纹张开位移的合矢量几乎是垂直的。对于这类断裂，修正COD准则较好地预测了初始裂纹扩展方向，但断裂强度较低。在塑性变形影响下发生脆性断裂时，如上述三种情况，实际断裂强度高于最可靠准则的预测值，并且随着II型变形的增大而增大。
In this paper, the brittle fracture initiation characteristics under general combination of the opening mode (Mode I), sliding mode (Mode II) and tearing mode (Mode III) were investigated both theoretically and experimentally.First, the perfectly brittle fracture tests were conducted on specimens of PMMA (Polymethylmethacrylate) for all possible combinations of the fracture modes including respective pure modes. The experimental fracture strengths were compared with those predicted by the fracture criteria which are represented in terms of: (1) maximum tangential stress, [σgq]max, extended to general combined modes, (2) maximum energy release rate at the propagation of a small kinked crack, [Gk(γ)]max, and (3) newly derived maximum energy release rate at the initiation of a small kinked crack, [G(γ)]max. It was found that the [Gk(γ)]maxor [G(γ)]maxcriterion was very effective to predict both the direction of initial crack propagation and the fracture strength. These energy release rates are expressed in closed forms, and the interaction curves of the brittle fracture strength under arbitrary combinations of Modes I, II and III were derived.Next, for fracture accompanied by plastic deformation, tests were carried out on specimens of mild steel (SM 41) imposing bi-axial tensile loads at various low temperatures. Then, brittle fracture with plastic deformation occurs under a combination of Modes I and II. In the case of brittle fracture with small scale yielding, the [G(γ)]maxcriterion predicts well the direction of initial crack propagation but estimates only lower fracture strength than the experimental one. In the cases of brittle fracture with large scale yielding and under general yielding, it was found from the fracture tests that the direction of initial crack propagation was nearly normal to the resultant vector of the crack opening displacements in the opening and sliding modes at the notch tip. To this type of fracture, the modified COD criterion predicts well the direction of initial crack propagation, but lower fracture strength.When brittle fracture occurs under the influence of plastic deformation, in such cases as the last three mentioned above, the actual fracture strength is higher than what the most reliable criterion predicts and it increases as deformation in Mode II becomes larger.