金属纳米杆弹性模量的直接原子计算

DIRECT ATOMISTIC COMPUTING ON THE ELASTIC MODULUS OF METAL NANOROD

用直接原子计算（分子动力学）的方法来模拟金属纳米杆的拉伸实验,得到纳米杆单向拉伸屈服前的真应力-应变曲线.金属单晶纳米杆屈服前的最大弹性应变约为0.01,应力应变关系表现为非线性弹性,拉伸模量随应变增大而提高,表现为明显的“应变刚化”行为.分析了产生这一现象的原因,主要是尺寸微小,内部无缺陷,弹性变形机理为晶格常数变化,而原子间相互作用势函数导数为增函数.小尺寸和表面效应也是导致纳米杆应变刚化的原因.

The mechanical properties of structure at nanoscale is different from that at macroscale, resulting from small size effect and surface effect. The axial extension test of metal nanorod was simulated by molecular dynamics and embedded atom method. The true stress-strain curve in elastic stage was illustrated. The direct atomistic computing results show that the yield strain is 0.11, the constitutive relation of metal single crystal nanorod is nonlinear elastic. The extension modulus increases with strain, defined as strain-stiffening. The intrinsical mechanism is analyzed. The size of nanorod is very small, and there is no defects. The elastic deformation results from the variation of crystal lattice constants, while the derivative of the potential energy function is an increasing function. Small size and surface effects also lead to the strain-stiffening effect.