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本文首先分析了线弹性下的J=(2U)/(Bb)的精确度问题,针对它的误差,给出了相应的修正系数M_J。其次,对弹塑性下的J的计算提出了经钝化区修正后的单点法计算J_(1C)的公式;用四种高强钢材在同一试样(属小范围屈服)上同时测定J(1C)和K(IC)的结果验证了本文提出的单点法计算公式;还对中强钢40Mn B小试样(属大范围屈服),用比较四种方法计算J_(1C)以及相应的K_(IC)的结果,以说明本文提出的单点法公式是偏于安全的实用计算公式。最后简要介绍测定J_(1C)的有关测试设备和实验方法(包括试样尺寸要求、P—δ曲线自动记录、电位法和二次疲劳法确定开裂点、激光全息摄影实测塑性区等)。
In this paper, we firstly analyze the accuracy of J = (2U) / (Bb) under linear elasticity and give the corresponding correction coefficient M_J for its error. Secondly, the formula of J_ (1C) calculated by the single-point method after the passivation zone correction is put forward for the calculation of J under elastic-plasticity. Simultaneous determination of J ( 1C) and K (IC) results verify the single-point calculation formula proposed in this paper; also for the medium-strength steel 40Mn B small samples (a wide range of yield), compared with the four methods to calculate J_ (1C) and the corresponding K_ (IC) results to show that the proposed single-point formula is biased to a safer practical formula. Finally, the related test equipment and experimental methods (including sample size requirements, P-δ curve automatic recording, potentiometric method and secondary fatigue method to determine the cracking point, laser holographic plastic zone, etc.) for the determination of J_ (1C) are briefly introduced.