基于分子动力学研究孔隙率对FeO/Fe界面裂纹扩展的影响

Molecular Dynamics-based Study of Effect of Porosity on Crack Propagation at FeO/Fe Interface

孔隙率是影响氧化皮与钢基体界面裂纹扩展的重要因素,采用分子动力学模拟软件LAMMPS建立模型Ⅰ(定孔缺陷数量模型)和模型Ⅱ(定孔缺陷尺寸模型)两种模型,从抗拉强度、中心对称分析(CSP)以及界面局部应力分布3个方面研究了孔隙率对于界面裂纹扩展的影响。结果表明,相同孔隙率下,模型Ⅱ比模型Ⅰ的抗拉强度低,表明孔缺陷分布范围比孔缺陷的尺寸对于材料的抗拉强度影响更大。同时裂纹扩展时动态不稳定性导致裂纹非对称性扩展,孔隙率的增加会阻碍应力增长和裂纹扩展速度,增强裂纹扩展的不对称性。当孔隙率达到9%时,在界面裂纹扩展后,模型Ⅰ+x方向裂尖偏转界面上方孔缺陷,模型Ⅱ则为界面裂纹扩展后,上方孔缺陷融合发展。

Porosity is an important factor affecting the crack extension at the interface between oxide and steel matrix.In this paper,two models including Model I(fixed pore defect number model)and ModelⅡ(fixed pore defect size model),were established by the molecular dynamics simulation software LAMMPS,and the effect of porosity on the crack extension at the interface was investigated in terms of tensile strength,centrosymmetry parameter(CSP)analysis and local stress distribution at the interface.The results show that the tensile strength of modelⅡis lower than that of modelⅠat the same porosity,indicating that the range of pore defect distribution has more influence on the tensile strength of the material than the size of pore defects.Meanwhile,the dynamic instability during crack expansion leads to asymmetric crack expansion,and the increase of porosity will hinder the stress growth and crack expansion rate and enhance the asymmetry of crack expansion.When the porosity reaches to 9%,after the interface crack extension,the+x direction crack tip in modelⅠdeflects the pore defects above the interface,and the upper square pore defects in modelⅡshows the fusion development after the interface crack extension.