Variation of Stress Distribution in Metal Fracture Process under Compressive, Torsional, and Tensile Loading
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摘要: 为更好地拟合断裂准则（JC、BW、MMC）参数，借助数值模拟手段，对Q345B和921A钢的压缩、扭转、拉伸试件的断裂过程进行了模拟，以应力三轴度、Lode参数作为衡量应力状态变化的重要指标，分析了两种金属材料断裂过程中试件典型位置的变化过程及断裂时刻试件的径向分布趋势，对比分析了Q345B和921A钢的不同类型试件在不同应力三轴度、不同Lode参数表征下的结果。计算结果表明：（1）除扭转试件外，压缩、拉伸试件在断裂过程中的应力状态不断发生变化，试件断裂时刻端口剖面的应力状态分布也不一致；（2）试件断裂过程是一个应力状态不断变化的过程，采用平均应力三轴度、平均Lode参数进行描述更加妥当；（3）对于同一尺寸的拉伸试件，不同金属材料断裂过程中的平均应力三轴度不尽相同。研究成果可为后续断裂准则（JC、BW、MMC）参数的拟合及材料断裂力学性能试验的开展提供指导。Abstract: In order to accurately fit the failure criteria in JC failure model, BW failure model, and MMC failure model, numerical simulations for metal materials Q345B and 921A under various loading conditions of compression, torsion, tension were performed in this work. The variation of stresses, indicated by stress triaxiality and Lode parameter, was investigated during the fracture progress. The results indicated: (1) exclusive of torsional loading, the stress distribution varied in the cracking plane as the crack growth; (2) the average stress triaxiality and Lode parameter are more suitable for describing the stress status; (3) for specimens having the same size, the value of average stress triaxiality was dependent on metal properties. This work would provide useful knowledge for obtaining the failure criterion from material failure experiments.
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Key words:
- failure experiments /
- stress triaxiality /
- Lode parameter /
- stress status
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图 1 光滑圆棒拉伸试件尺寸（单位：mm）
Figure 1. Dimensions of round smooth tension specimen (Unit: mm)
图 2 缺口圆棒拉伸试件尺寸（单位：mm）
Figure 2. Dimensions of notched round tension specimen (Unit: mm)
图 6 试验和有限元计算得到的载荷-位移曲线对比（Q345B钢）
Figure 6. Comparisons of the displacement-load curves between experimental results and simulation results（Q345B steel）
图 7 试验和有限元计算得到的载荷-位移曲线对比（921A钢）
Figure 7. Comparisons of the displacement-load curves between experimental results and simulation results（921A steel）
图 8 压缩试件受力过程中应力三轴度和Lode参数变化（921A钢）
Figure 8. Changes of stress triaxiality and Lode value in the loading process of compression specimen (921A steel)
图 9 扭转试件受力过程中应力三轴度和Lode参数变化（921A钢）
Figure 9. Changes of stress triaxiality and Lode value in the loading process of torsion specimen (921A steel)
图 10 光滑拉伸试件受力过程中应力三轴度和Lode参数变化（921A钢）
Figure 10. Changes of stress triaxiality and Lode value in the loading process of smooth tension specimen (921A steel)
图 11 8 mm缺口拉伸试件受力过程中应力三轴度和Lode参数变化（921A钢）
Figure 11. Changes of stress triaxiality and Lode value in the loading process of tension specimen with a 8 mm notch (921A steel)
图 12 断裂时刻压缩试件应力三轴度和Lode参数的径向分布（Q345B钢）
Figure 12. Radial distribution of stress triaxiality and Lode value of the compressive specimen at final failure（Q345B steel）
图 13 断裂时刻扭转试件应力三轴度和Lode参数的径向分布（Q345B钢）
Figure 13. Radial distribution of stress triaxiality and Lode value of the torsion specimenat final failure（Q345B steel）
图 14 断裂时刻光滑拉伸试件应力三轴度和Lode参数的径向分布（Q345B钢）
Figure 14. Radial distribution of stress triaxiality and Lode value of the smooth tension specimen at final failure（Q345B steel）
图 15 断裂时刻带有2 mm缺口的拉伸试件的应力三轴度和Lode参数径向分布（Q345B钢）
Figure 15. Radial distribution of stress triaxiality and Lode value of the tensile specimen with a 2 mm notch at final failure（Q345B steel）
图 16 不同试件断裂时刻应力三轴度、平均应力三轴度增加百分比的对比
Figure 16. Increases of the stress triaxiality and Lode parameter for specimens at final failure
表 1 JC强度模型参数
Table 1. Parameters of JC strength model
Material A/MPa B/MPa n C $\dot \varepsilon $/s−1 Q345B steel 360 700 0.547 0.046 0.002 921A steel 700 706 0.580 0.013 0.002 
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表 2 各类试件应力三轴度不同表征方法对比
Table 2. Comparison of the stress triaxiality among different specimens
Specimen type Stress triaxiality (Q345B steel) Stress triaxiality (921A steel) Initial Fracture Average Initial Fracture Average Compression −0.333 0.179 −0.120 −0.333 0.156 −0.116 Torsion 0 0 0 0 0 0 Smooth tension 0.333 0.841 0.562 0.333 0.987 0.668 With a 18 mm notch 0.413 0.867 0.663 0.413 1.075 0.825 With a 8 mm notch 0.505 0.915 0.752 0.505 1.133 0.919 With a 6 mm notch 0.556 0.947 0.805 0.556 1.160 0.973 With a 2 mm notch 0.893 1.123 1.085 0.893 1.451 1.400
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表 3 各类试件Lode参数不同表征方法对比
Table 3. Comparison of the Lode parameter among different specimens
Specimen type Lode (Q345B steel) Lode (921A steel) Initial Fracture Average Initial Fracture Average Compression 1.00 −0.73 0.24 1.00 −0.22 0.45 Torsion 0 0 0 0 0 0 Smooth tension −1.00 −1.00 −1.00 −1.00 −1.00 −1.00 With a 18 mm notch −1.00 −1.00 −1.00 −1.00 −1.00 −1.00 With a 8 mm notch −1.00 −1.00 −1.00 −1.00 −1.00 −1.00 With a 6 mm notch −1.00 −1.00 −1.00 −1.00 −1.00 −1.00 With a 2 mm notch −1.00 −1.00 −1.00 −1.00 −1.00 −1.00
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表 4 拟合JC参数取值
Table 4. JC failure model constant
Material D1 D2 D3 Q345B steel 1.816 −0.353 1.056 921A steel 2.475 −0.661 0.650
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