Abstract To further understand the mixed-mode I/II fracture behavior of Un-plasticized Polyvinyl Chloride (UPVC), a series of mixed-mode I/II experiments on analogy compact tension specimens have been conducted using an MTS 810 hydraulic test machine. The evolution of the displacement field during stable crack extension was monitored by two-dimensional digital image correlation technique. Results obtained from the mechanical testing demonstrate that the maximum load of mode II is about 100% higher than that of mode I, and the load-carrying capacity is dependent on orientation and load condition. Fractography observations indicate that the fracture surface can be divided into fatigue region with relatively smooth characters and stable crack extension region with randomly distribution of honeycomb-like voids. Furthermore, mode I failure (opening) should be the main failure mechanism of UPVC rather than mode II (shear failure). The results also suggest that the value of crack opening displacement (COD) tends to be nearly constant when the length of crack exceeds the thickness of the sample, which is independent on orientation and load condition. Therefore, COD criterion can be used to describe the overall severity of plastic deformation in the near-tip region of UPVC, and components of COD, which is perpendicular to the crack surface, should be the predominant controlling parameter of crack propagation.

中文翻译：

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未增塑聚氯乙烯的塑性变形和混合模式 I/II 断裂行为

摘要 为了进一步了解未增塑聚氯乙烯 (UPVC) 的混合模式 I/II 断裂行为，使用 MTS 810 液压试验机对模拟致密拉伸试样进行了一系列混合模式 I/II 实验。通过二维数字图像相关技术监测裂纹稳定扩展过程中位移场的演变。力学测试结果表明，模式II的最大载荷比模式I高约100%，承载能力取决于方向和载荷条件。断口形貌观察表明，断口可分为特征相对光滑的疲劳区和随机分布的蜂窝状空隙的稳定裂纹扩展区。此外，模式 I 失效（开路）应该是 UPVC 的主要失效机制，而不是模式 II（剪切失效）。结果还表明，当裂纹长度超过样品厚度时，裂纹张开位移 (COD) 的值趋于接近恒定，这与取向和载荷条件无关。因此，COD 准则可用于描述 UPVC 近尖端区域塑性变形的整体严重程度，并且垂直于裂纹表面的 COD 分量应该是裂纹扩展的主要控制参数。这与方向和负载条件无关。因此，COD 准则可用于描述 UPVC 近尖端区域塑性变形的整体严重程度，并且垂直于裂纹表面的 COD 分量应该是裂纹扩展的主要控制参数。这与方向和负载条件无关。因此，COD 准则可用于描述 UPVC 近尖端区域塑性变形的整体严重程度，并且垂直于裂纹表面的 COD 分量应该是裂纹扩展的主要控制参数。