摘要
采用分子动力学(MD)方法对纳米单晶氩杆进行了机械拉伸变形和断裂的模拟研究。在拉伸过程中可以观察到原子位错,间隙的形成,裂纹的出现,以及后来的断裂分离等现象,与宏观的拉伸试样相似。MD模拟的拉伸试样的真实应力应变图显示,纳米单晶氩杆随着应变的增加应力略有增加,超过某一应变值后,应力急剧增加到最大值。随后,在加载速率较大时试样突然脆性断裂,在加载速率较小时应力却有一个突然的下降变负过程。这说明加载速率对材料的强度影响很大,当加载速度分别为2.16m/s和6.49m/s时,纳米单晶氩材料相应的断裂强度为2.6GPa和6.6GPa。纳米单晶氩材料在断裂前经历了一个较大的塑性变形过程,但其断裂方式却是完全脆性的。另外,纳米单晶氩材料在自由边界条件下充分弛豫后在垂直于拉伸的方向有轻微的收缩,不同于Al,Cu,Ni等具有FCC晶格结构的纳米单晶材料由于内力的作用引起轻微膨胀。
Nano-single crystal FCC cubic argon at two different constant rates of uniaxial tensile loading (2.16 m/s, 6.49 m/s) is studied by molecular dynamics (MD) using L-J(12-6) inter atomic potential. The deformation and fracture of the work materials due to voids formation, their coalescence into nanocracks, and subsequent fracture or separation were observed similar to their behavior at macroscale. The true stress-train diagrams obtained by the MD simulation of the tensile specimens show a long slow increase in stress with a gradual increase in strain, and a rapid increase in stress up to a maximum when the value of strain reaches a certain value followed by a sudden drop to negative or a sudden disappear when the specimen fails by brittle fracture. The rate of loading plays an important role in the ultimate strength of the nanomaterials. The ultimate strengths are 2.6 GPa and 6.6 GPa separately corresponding to the rates of loading as 2.16 m/s and 6.49 m/s. The nanomaterials underwent much more deformation before its sudden rupture than ordinary brittle materials. The brittle rupture form is absolutely different from the ductile rupture form reported previously about ordinary nanomaterials. The specimens after relaxation were found to be slightly tensile due to internal forces, which is different from the compressed form for the specimens of FCC materials, such as Al, Cu and Ni after relaxation.
出处
《航空材料学报》
EI
CAS
CSCD
2004年第4期49-53,62,共6页
Journal of Aeronautical Materials
基金
国家自然科学基金资助项目(10202010)
关键词
纳米单晶氩
机械拉伸
分子动力学
模拟分析
Argon
Deformation
Fracture
Mechanical properties
Molecular dynamics
Single crystals
Tensile strength
