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本文采用单边缺口板状试样研究了四种含碳量的CrNiMo钢缺口根部的疲劳裂纹萌生寿命及其萌生机制。裂纹萌生可能有四种方式—沿驻留滑移带压入挤出、微孔聚集型切变、准解理和沿晶机制。文中论述了钢的含碳量、热处理规范及外加应力水平对裂纹形核机制的影响。研究表明:在双对数坐标中,表观循环应力范围和萌生寿命的关系可用两段不同斜率的直线来描述,两段萌生线的分界点随钢的强度水平提高而迅速向低周次范围推移,但两段的裂纹萌生均仍属于应力疲劳范畴。文中分析了微观塑性变形对缺口根部实际循环应力范围和应力循环比的影响,给出了对它们进行修正估算的方法。修正后的实际循环应力范围和萌生寿命的关系可用一条直线反映出来。在此基础上,提出了一种用光滑试样应力疲劳曲线估算缺口根部裂纹萌生寿命的新方法。
In this paper, unilateral notch plate-like specimens were used to study the fatigue crack initiation life and the germination mechanism of four kinds of CrNiMo steel with notched root. Crack initiation may occur in four ways - extrusion along the resident slip band, microporous aggregate shear, quasi-cleavage, and intergranular mechanisms. The paper discusses the carbon content of steel, heat treatment specifications and the level of stress on the crack nucleation mechanism. The research shows that in the double logarithmic coordinates, the relationship between the apparent cyclic stress range and the germination life can be described by two straight lines with different slopes. The demarcation point of the two sprouting lines increases rapidly with the increase of the steel strength, However, the crack initiation in both sections still belongs to the category of stress and fatigue. The influence of microcosmic plastic deformation on the actual cyclic stress range and stress cycle ratio of notched root is analyzed in this paper, and a method to correct them is given. Corrected the actual cycle stress and initiation of life span can be a straight line reflected. On this basis, a new method to estimate the crack initiation life of notched root by using the stress fatigue curve of smooth specimen is proposed.