对J积分测试方法中几个问题的讨论

DISCUSSION ON SEVERAL PROBLEMS IN J-INTEGRAL TESTING METHOD

针对延性断裂韧度JⅠC测试中遇到的困难 ,讨论现行J积分测试标准中关于最小裂纹扩展线和对裂纹扩展阻力JR 值的上限限制及JⅠC的定义。研究认为 ,不同金属具有不同的裂纹钝化特征 ,钝化线方程取决于材料的强度、塑性和应变强化能力。测试标准中规定的钝化线方程只与材料强度水平有关 ,而且斜率太低 ,不能准确描述裂纹的钝化行为 ,进而以此钝化线为基础设置最小裂纹扩展线 ,并用它排除裂纹未真实扩展的试验数据势必造成某些不准确判断。因此 ,在提出合理的钝化线方程之前 ,建议采用下列原则处理J积分测试结果 :J =1.5 (σs+σb)Δa作为钝化线方程 ;由钝化线向右偏置 0 0 3mm的平行线作为最小裂纹扩展线 ;JR ≤b0 σY 15作为测试数据的有效性条件。另外对饱和伸张区(criticallengthofthestretchedzonewidth ,SZWC)的测试结果表明 ,钝化线与JR 曲线交点所对应的J值即Ji 可定义为延性断裂韧度JⅠC。文中还比较了不同研究者报告的 16Mn钢测试结果的差别 ,并分析造成差别的原因。

Minimum offset line, maximum allowable value of J R and definition of J ⅠC in current J ⅠC testing method were discussed. It is considered that the crack blunting process of each several material is different and that the blunting equation depends on the dissimilarity in strength, ductility and strain hardening behavior of the materials. However, the blunting equation provided in current testing method is only related to the strength level of materials, while the slope of this blunting line is too low to describe exactly the blunting behavior of the cracks. Therefore it is difficult to exclude accurately the data of uncracking specimens from tested results with the minimum offset line on the basis of this blunting line. It is proposed that J=1.5(σ s+σ b)Δa should be considered as a blunting line, that parallel line of the blunting line deviating 0.03?mm rightly is regarded as a minimum offset line, that J R≤b 0σ Y/15 should be considered as a maximum allowable value of J R, before a reasonable blunting equation is provided. In addition, the results measured critical length of the stretched zone width (SZW C) indicates that the intersection point J i of the blunting line and the J R curve is the critical value of J at the onset of crack extension, ie J i=J ⅠC. The results of steel 16Mn from different authors were compared here.