平面应变断裂韧度测试的有效性研究

Plane Strain Fracture Toughness Testing

针对平面应变断裂韧度测试厚度存在的问题,研究了几种材料测断裂韧度所需的实际厚度,拟合了平面应力到平面应变过渡状态下σz应力的分布,分析了过渡状态下的裂端应力场。通过分析不同材料特性和应力状态对断裂韧度KΙC的影响,结合金属材料断裂的细观机理,认为平面应变断裂韧度KΙC反映的是材料正断的性能,仅代表材料发生正断的指标。结果表明:对于某些高韧性材料,即使满足平面应变条件厚度要求,断裂以剪断为主,很难测出KΙC;而对于偏脆性材料,即使不满足厚度要求,只要发生正断,也可测出KΙC。结合已有试验结果,为平面应变断裂韧度KΙC测定的厚度选择,提出一种合理的预测方法。借助三片模型的研究,给出平面应变断裂韧度的正断指标。

The evaluated criterion of specimen thickness and the practical thickness for testing KIC of different materials, are experimentally investigated. Combined the microcosmic mechanism of metallic fracture, the conclusion is drawn that the fracture toughness KIC for plane strain as a traction fracture index, only reflects the capability of material traction fracture. Therefore, testing the high-ductile material KIC is difficult even the thickness meet the criterion; and the brittle material KIC can be determined even the thickness does not meet the criterion. A reasonable forecast method for choosing the testing thickness of KIC is put forward based on the existing testing result. And the traction fracture criterion of KIC under plane strain is gained by researching tri-piece model.