SIZE EFFECTS IN SMALL SCALE STRUCTURES
(0) In this work,the strength of small scale structures is investigated using three-dimensional discrete dislocations dynamics (DD) analysis.We focus on two particular problems,one is strengthening in nanolaminate metallic composites,and two is the size-dependence of strength in microscale specimens loaded in uniaxial tension/compression. In the case on nanolaminate composites,strength predictions made by the classical confined layer plasticity model,which is based on the Orowan bowing of glide dislocations (threading dislocations),significantly underestimates the experimentally measured strength.The hardening effect due to the presence of interfacial dislocations generated by previous glide events has been suggested as one of the main reasons tot this discrepancy.Using DD analysis,possible interactions between threading dislocations and intersecting interfacial dislocations are considered and evaluated for their contribution to the higher strength over the strength due to unobstructed threading.It was found that the strongest interaction occurs when both interacting dislocations have collinear Burgers vector and involves two annihilations at the crossing point before the threading dislocation bypasses the obstacle and continue to thread.For layer thickness range of 30 nm and above,the strengthen increase is 50％ over the unobstructed baseline strength prediction.It was also found that if the interfacial dislocations are modeled as pinned and non reacting,as in the case of existing analytical models,the predicted strengthening is weaker than that predicted by the more realistic scenario where dislocations are flexible and can react in the short range.In the case on microscale tensile specimens,it is found that the strength is strongly dependent on the specimen size and the dislocation sources that might be present in the material.The strengthening mechanism in this case is determined by the size of the length of the available dislocations and their interaction with the surface of the specimen.For small scales (0.5 to 2 micrometers) there are a limited number of dislocations sources which dominate the behavior.
H.M.Zbib F.Akasheh D.Bahr
School of Mechanical and Materials Engineering,Washington State University,Pullman.WA 99164-2920,USA
国际会议
第二届国际非均质材料力学会议(The Second International Conference on Heterogeneous Material Mechanics)
安徽黄山
英文
274
2008-06-03（万方平台首次上网日期，不代表论文的发表时间）