In the present research, a simple quasi-continuum model, the Cauchy-Born rule model, is used to investigate the size effects of elastic modulus for fcc metals. By considering a nanoplate model and calculating the strain energy for the nano-sized plate under tension and bending, the relationship between the elastic modulus and the plate thickness is found. Size effects of the elastic modulus are displayed by the relative differences of the elastic modulus between the nano-sized plate sample and the bulk sample. By comparing the present results with those of others, the effectiveness of the Cauchy-Born rule model in studying the size effects of material properties are shown.
The prediction of catastrophic rupture of heterogeneous brittle material has been investigated by researchers in the past.In this work,the acoustic emission generated by marble samples under compression was analyzed to verify a power law singularity of index 1/2 as a catastrophe precursor.It is found that prior to catastrophe,the variation of the system response to the controlling parameter follows a power law of negative index,which proves the power law singularity as a common precursor of catastrophe.However,the power indexes vary with variables and samples.The uncertainty reflects sample specificity of an evolution induced catastrophe (EIC) process.
Since rate effect of materials plays a key role in impact engineering, the microscopic mechanism of rate effect is investigated at molecular level in this paper. The results show that rate effect on the strength of atomic system is closely related to the coupled evolution of atomic motions and potential landscapes. Accordingly, it becomes possible to develop a new algorithm of molecular simulation, which could properly and efficiently demonstrate strain rate effect under a wide range of loading rates and unveil the mecha- nisms underlying the strain rate effects.
Pan XiaoJun WangRong YangFu-Jiu KeMeng-Fen XiaYi-Long Bai
In the present research,the measurement fluctuations of mechanical properties in nanowires (NWs) are investigated by using the molecular dynamics simulation.The large numbers of simulations are performed to study the yield behaviors of the NWs.The results have shown that the yield behavior of the smaller diameter NW is more sensitive to the presence of vacancies,and the dispersion of the measured mechanical properties for the small scale NW is larger than that for the large scale NW.Present results have also shown that vacancies escape from the bulk to the free surfaces as a result of high stress applied at the small scale systems similar to the dislocation starvation phenomenon observed in the compression test of nano-pillars,and dislocation nucleation induced by surface defect occurs after the vacancy reaches free surface leading to lower yield strength.Moreover,the strong surface vacancy interactions at the nanoscale level are also investigated.
