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采用嵌入原子势的分子动力学模拟方法, 研究了5 × 10 9s –1应变率下, 温度效应对单晶铁中孔洞成核与生长的影响, 并对NAG (nucleation and growth)模型在单晶铁中的适用性进行了探讨. 结果表明: 随着温度的升高, 单晶铁的抗拉强度峰值降低, 1100 K温度下单晶铁抗拉强度峰值比100 K温度下降低了35.9%. 在100—700 K温度下, 拉应力时程曲线表现出双峰值特点, 分析表明, 第一峰值是由于拉应力升高引起内部结构发生相变而产生, 第二峰值则是因发生孔洞成核与生长而产生; 900—1100 K温度下, 拉应力时程曲线表现为单峰值, 孔洞成核与生长是拉应力下降的主要原因. 分析发现, 孔洞在高温下更容易成核, 高应变率下单晶铁中孔洞成核与生长和NAG模型有较好的符合度, 单晶铁中孔洞成核阈值与生长阈值都远高于低碳钢, 并且孔洞成核阈值与生长阈值随着温度的升高而逐渐降低. 研究结果可为建立高应变率下金属材料动态损伤演化模型提供借鉴.In this work, we investigate the triaxial deformation of single crystal iron at a strain rate of 5 × 10 –9s –1by using molecular dynamics simulation through the embedded atomic method, and thus study the temperature effect on the void nucleation and growth, and we also discuss the applicability of nucleation and growth (NAG) model in single crystal iron. The molecular dynamics model size is 28.55 nm × 28.55 nm × 28.55 nm and contains 2 × 10 6atoms. The results show that the maximum tensile stress of single crystal iron decreases with temperature increasing. The maximum tensile stress reduces 35.9% when temperature rises from 100 K to 1100 K. We find that at 100−700 K temperatures, there are two peaks in the tensile stress-time profile. To ascertain the origin of the double-peak in the stress-time profile, we compute the void volume fraction evolution. In addition, we conduct the dislocation analysis, radial distribution function analysis and common neighbor analysis. The analysis results show that the relaxation of tensile stress in the first peak of stress-time profile takes place through the structural change and the body-centered cubic crystal structure transforming into face-centered cubic crystal structure, hexagonal close packed crystal structure and other structures. We find that there are no voids’ nucleation in the first peak of stress-time profile. The second-peak of stress-time profile proceeds through the nucleation and growth of voids. And the rapid increase of the void volume fraction corresponds to the rapid decline of the tensile stress. The void volume evolution can be divided into three stages. With the increase of temperature, the double peak characteristic of the tensile stress-time profile disappears at 900−1100 K. While at 900−1100 K the nucleation and growth of voids are the only way to release the built-up stress. It is shown that the nucleation and growth of voids are more preferred at high temperature than at low temperature. The nucleation and growth of voids in single iron under high strain rate follow the NAG model. We calculate the best-fit NAG parameters at 100−1100 K, and analyze the sensitivity of NAG parameters to temperature. It is shown that the nucleation and growth threshold of the single crystal iron are much higher than those of mild steel. The results can be useful for developing the fracture models of iron at high strain rate to describe the dynamic damage on a continuum length scale.
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温度/K 时间/ps A B C D 100 15.7 16.5 17.5 19.1 300 13.4 14.5 15.4 17.9 500 12.6 13.8 14.9 17.7 700 13.1 13.9 14.6 17.6 
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Pn0/Pa P1/Pa ${\dot N_0}$/m–3·s–1 Pg0/Pa η/Pa·s Rn/m Σ 100 K 1.61 × 1010 1.42 × 107 7.10 × 1015 2.75 × 109 1.72 × 10–1 3.1 × 10–10 0.15 300 K 1.55 × 1010 2.35 × 107 1.22 × 1015 2.48 × 109 2.20 × 10–1 3.1 × 10–10 0.18 500 K 1.51 × 1010 1.18 × 107 5.91 × 1014 2.15 × 109 1.83 × 10–1 3.1 × 10–10 0.14 700 K 1.50 × 1010 3.31 × 107 1.37 × 1016 2.02 × 109 2.17 × 10–1 3.1 × 10–10 0.17 900 K 1.46 × 1010 2.76 × 107 3.29 × 1015 1.98 × 109 2.53 × 10–1 3.1 × 10–10 0.12 1100 K 1.33 × 1010 1.87 × 107 1.88 × 1014 1.95 × 109 2.11 × 10–1 3.1 × 10–10 0.17 低碳钢[54] 1.12 × 109 1.0 × 108 2.5 × 1014 2.0 × 108 2.778 × 102 3.0 × 10–5 下载:
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