CiteULike: dchen Shi

Strain Localization and Percolation of Stable Structure in Amorphous Solids

Yunfeng Shi — 2008-08-17T16:23:56-00:00

Physical Review Letters, Vol. 95, No. 9. (2005)

Spontaneous strain localization occurs during mechanical tests of a model amorphous solid simulated using molecular dynamics. The degree of localization depends upon the extent of structural relaxation prior to mechanical testing. In the most rapidly quenched samples higher strain rates lead to increased localization, while the more gradually quenched samples exhibit the opposite strain rate dependence. This transition coincides with the k-core percolation of atoms with quasi-crystal-like short range order. The authors infer the existence of a related microstructural length scale.

Size Dependence of Young's Modulus in ZnO Nanowires

CQ Chen — 2008-03-18T16:20:22-00:00

Physical Review Letters, Vol. 96, No. 7. (2006)

We report a size dependence of Young's modulus in [0001] oriented ZnO nanowires (NWs) with diameters ranging from 17 to 550 nm for the first time. The measured modulus for NWs with diameters smaller than about 120 nm is increasing dramatically with the decreasing diameters, and is significantly higher than that of the larger ones whose modulus tends to that of bulk ZnO. A core-shell composite NW model in terms of the surface stiffening effect correlated with significant bond length contractions occurred near the 100 free surfaces (which extend several layers deep into the bulk and fade off slowly) is proposed to explore the origin of the size dependence, and present experimental result is well explained. Furthermore, it is possible to estimate the size-related elastic properties of GaN nanotubes and relative nanostructures by using this model.

Atomic-scale simulations of strain localization in three-dimensional model amorphous solids

Yunfeng Shi — 2008-04-15T01:29:17-00:00

Physical Review B (Condensed Matter and Materials Physics), Vol. 73, No. 21. (2006)

Molecular-dynamics simulations of the mechanical properties of three different three-dimensional metallic glass analogs reveal that each exhibits a transition from homogeneous flow to localized flow as the quench rate used to produce the glass is decreased. The solid samples are tested in uniaxial compression over more than an order of magnitude range of strain rates. Three different systems are studied including one single-component glass former and two binary alloys. The strain rate sensitivity of the localization changes sign at a critical cooling rate, implying a discontinuous transition in mechanical properties in the low loading rate limit. Analysis of the short-range order using a generalization of the Frank-Kasper criterion reveals that the short-range order is depleted in the shear band in two of the three systems. Moreover, the homogeneous to inhomogeneous deformation transition in the mechanical properties is found to coincide with the percolation of an identifiable aspect of the short-range order in those two systems. The third system studied, the Kob-Anderson glass, is hypothesized not to be amenable to the methods typically used to characterize short-range order due to its non-hard-sphere nature.

Eliminating Segregation in Free-Surface Flows of Particles

Deliang Shi — 2008-03-18T19:31:43-00:00

Physical Review Letters, Vol. 99, No. 14. (2007)

By introducing periodic flow inversions, we show both experimentally and computationally that forcing with a value above a critical frequency can effectively eliminate both density and size segregation. The critical frequency is related to the inverse of the characteristic time of segregation and is shown to scale with the shear rate of the particle flow. This observation could lead to new designs for a vast array of particle processing applications and suggests a new way for researchers to think about segregation problems.