Effects of pre-strain on tensile mechanical properties of commercially pure titanium TA2 welded joint
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摘要: 以工业纯钛TA2焊接接头为研究对象，开展了预应变后的室温拉伸力学性能测试。结果表明，预应变后应力应变曲线上升，屈服强度及抗拉强度随着预应变量的增加而增加。综合考虑预应变量及应变速率影响，建立了预应变后材料强度的经验表达式。根据Hollomon本构方程，研究了预应变后应变速率敏感性指数及应变强化指数的变化，确定了预应变试样的拉伸本构方程。断口观察表明，预应变后材料延伸率下降，断口收缩率及韧窝尺寸均下降。Abstract: In this paper, room temperature tensile mechanical properties of commercially pure titanium TA2 welded joint after pre-straining were studied. The results show that stress-strain curves rises and yield strength and tensile strength increase with the degree of pre-strain. With considering effects of pre-strain and strain rate, the empirical expression for the strength of the material after pre-strain was developed. According to Hollomon constitutive equation, the variations of strain rate sensitivity index and strain hardening exponent were analyzed. Meanwhile, the tensile constitutive equation for the pre-strained samples was determined. The observation of fracture surface indicates that the reduction of fracture surface and the size of dimples decreases after pre-straining due to the decrease of elongation of the material.
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Key words:
- TA2 /
- welded joint /
- tensile properties /
- pre-strain /
- constitutive equation
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图 3 应力应变曲线
Figure 3. Stress-strain curves (effect of pre-strain(a) and strain rate(b))
图 4 强度随应变速率的变化
Figure 4. Variation of strength parameter with strain rate (yield strength(a) and tensile strength(b))
图 5 强度随预应变的变化
Figure 5. Variation of strength parameter with pre-strain (yield strength(a) and tensile strength(b))
图 6 强度预测值与试验结果对比
Figure 6. Comparison between the predicted strength parameter and experimental results
图 7 不同试样预测值与试验值对比
Figure 7. Comparison between prediction results and experiment results of different samples
图 8 2%预应变试样在应变速率为0.0005/s下拉伸断裂后的断口
Figure 8. Micrographs of fractured surfaces of 2% pre-strained sample at the strain rate of 0.0005/s
图 9 预应变试样的断口形貌及其中间区域放大
（a）(a1)2%预应变，应变速率0.0005/s；（b）(b1)4%预应变，应变速率0.0005/s；（c）(c1)8%预应变，应变速率0.0005/s；（d）(d1)2%预应变，应变速率0.005/s；（e）(e1)4%预应变，应变速率0.005/s；（f）(f1)8%预应变，应变速率0.005/s
Figure 9. Fractured surfaces of pre-strained samples and enlarged view of central region
表 1 不同预应变下不同应变的应变速率敏感性指数m
Table 1. Strain rate sensitivity index m at different strain points under different pre-strains
应变/% 应变速率敏感指数m 预应变ε=2% 预应变ε=4% 1 0.0149 0.0336 2 0.0126 0.0308 3 0.0122 0.0293 4 0.0169 0.028 均值 0.0141 0.0304 
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表 2 不同预应变下不同应变速率的应变硬化指数n
Table 2. Strain hardening index n under different pre-strains and different strain rates
应变速率/s−1 应变硬化指数n 预应变ε=2% 预应变ε=4% 0.005 0.0644 0.036 0.0005 0.0578 0.0274 0.00005 0.067 0.0175 均值 0.063 0.027
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表 3 不同预应变下不同应变速率的强度系数K值
Table 3. Strengthening coefficient K values under different strain rates and pre-strains
应变速率/s−1 K值 预应变ε=2% 预应变ε=4% 0.005 675.78 697.8 0.0005 693.79 704.7 0.00005 677.79 707.92 均值 682.5 703.46
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