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裂纹长度是影响裂纹尖端力学特性及裂纹扩展速率的重要因素,但现有环境致裂研究中的裂纹类型主要为长裂纹而忽略了小裂纹。本工作采用有限元数值计算的方法,研究高温水环境下具有单边裂纹的镍基合金试样环境致裂过程中小裂纹裂尖力学特征。结果表明小裂纹裂尖具有比长裂纹更高的应力和应变,并使小裂纹具有更高的裂纹扩展趋势。研究中给出了计算小裂纹裂尖塑性区尺寸的修正方法,J积分计算的Irwin修正方法适用于长裂纹,但计算小裂纹条件下的J积分时会产生误差。提出在缺乏成熟理论指导下应采用弹塑性有限元数值计算的方法获取准确的小裂纹裂尖J积分。基于小裂纹与长裂纹裂尖力学特征的明显不同,建议在分析核电结构材料环境致裂时,将裂纹扩展分为小裂纹扩展及长裂纹扩展阶段分别研究。
Crack length is an important factor affecting the mechanical properties of crack tip and crack propagation rate. However, the existing crack types in the research of environmental fissures are mainly long cracks and neglect small cracks. In this work, finite element method was used to study the crack tip mechanical characteristics of nickel-based alloy specimens with unilateral cracks in high temperature water environment during the process of environmental cracking. The results show that the small crack tip has higher stress and strain than the long crack, and the crack has a higher trend of crack propagation. The correction method for calculating the plastic zone size of small crack tip is given in this study. The Irwin correction method of J-integral calculation is suitable for long-crack, but the error will be generated when J-integral under small crack is calculated. It is proposed that accurate crack tip J-integral should be obtained by the elastoplastic finite element numerical method under the guidance of the lack of mature theory. Based on the obvious difference between the mechanical characteristics of small crack tip and long crack tip, it is suggested that the crack propagation should be divided into small crack growth and long crack propagation respectively when analyzing the environmental cracking of nuclear material.