DESIGN AND ANALYSIS OF FLEXIBLE INSULATED PAVEMENT FOR COLD REGION APPLICATIONS

Pavements in cold regions suffer from additional deterioration due to the influences of extreme climate on frost-susceptible subgrade layers. To address this problem, one efficient strategy is to add a thermal insulating layer above the frost-susceptible layer. This study aims to evaluate the insulating effects of four materials: XPS boards, tire chips, foamed glass aggregates, and foamed concrete. Large-scale insulated pavement boxes (1.2m×1.2m×0.8m) were constructed to compare the thermal performance of different materials. The thermal performance of each box was evaluated and graded based on indicators related to the short-term temperature decrease and long-term temperature variation. Experimental results show that with the same insulation layer thickness, XPS boards have the best overall performance (65.8/100), followed by foamed glass aggregates (60.1/100), foamed concrete (52.7/100), tire chips (48.8/100), and the control box (38.8/100). Furthermore, finite element method (FEM) models were developed and calibrated to predict the thermo-mechanical coupled performance of insulated pavement structures. Parametric analyses using FEM enable the formulation of a thermally-mechanically balanced insulation pavement design procedure, which can be used to predict the maximum allowable load repetitions under specific local climate conditions. The cost analysis indicates that to achieve equivalent thermal performance in the subgrade layer, using an insulation layer could save approximately $1M/mile in construction cost

Effect of Samarium doping on the nucleation of fcc-Aluminum in undercooled liquids

The effect of Sm doping on the fcc-Al nucleation was investigated in Al-Sm liquids with low Sm concentrations (xSm) with molecular dynamics simulations. The nucleation in the moderately undercooled liquid is achieved by the recently developed persistent-embryo method. Systematically computing the nucleation rate with different xSm (xSm=0%, 1%, 2%, 3%, 5%) at 700 K, we found Sm dopant reduces the nucleation rate by up to 25 orders of magnitudes with only 5% doping concentration. This effect is mostly associated with the increase in the free energy barrier with a minor contribution from suppression of the attachment to the nucleus caused by Sm doping.Comment: 4 figure

Randomly Generating the 3D Mesostructure of Soil Rock Mixtures Based on the Full In Situ Digital Image Processed Information

Understanding the occurrence and evolution of geological disasters, such as landslides and debris flows, is facilitated by research on the performance of soil rock mixes (SRM). Recently, more and more researchers have been interested in studying the mesostructure reconstruction process of SRM. The present mesostructure generation approaches, however, have several weaknesses. One of the weaknesses is that they do not consider the impact of particle shape and therefore cannot ensure similarity to the in situ SRMs. In this study, a new mesostructure generation method that randomly generates SRMs based on the full in situ digital image processing (DIP) information is proposed. The generation procedure of the proposed algorithm considers the geometry characteristics of in situ SRMs, including the size distribution, particle shape, and 2D fractal dimension of the cross-section. A parametric study was performed to examine how the rock content and particle shape affected the fractal dimension of the generated SRMs. The results indicate that as the rock content increases in intensity, the fractal dimension also increases. Only when the angular particle content is less than 75% does it affect the fractal dimension. The fractal dimension of the generated mesostructures increases with the increase in the angular particle proportion under the same rock content

Strain rate effects on the plastic flow in submicron copper pillars:Considering the influence of sample size and dislocation nucleation

Three-dimensional discrete dislocation dynamics (DDD) simulations are performed to investigate the plastic flow behaviors of submicron copper pillars under different loading rates, in which both inertial effect of dislocation motion and surface nucleation are taken into account. It is found that: (1) for pillars with a diameter below similar to 400 nm, there is a transition from internal dislocation multiplication to surface dislocation nucleation as the strain rate increases (>= 10(4) s(-1)); (2) for similar to 1 um diameter pillars, stable internal dislocation sources dominate for both low and high strain rates; (3) in general, a larger strain rate, smaller sample size and less internal dislocation sources make it more probable for a surface nucleation process to take the place of dislocation multiplication. Furthermore, a theoretical model is proposed to predict the submicron plastic behavior at different strain rates when internal dislocation sources prevail. (c) 2017 Elsevier Ltd. All rights reserved

In situ TEM study of deformation-induced crystalline-to-amorphous transition in silicon

The mechanism responsible for deformation-induced crystalline-to-amorphous transition (CAT) in silicon is still under considerable debate, owing to the absence of direct experimental evidence. Here we have devised a novel core/shell configuration to impose confinement on the sample to circumvent early cracking during uniaxial compression of submicron-sized Si pillars. This has enabled large plastic deformation and in situ monitoring of the CAT process inside a transmission electron microscope. We demonstrate that diamond cubic Si transforms into amorphous silicon through slip-mediated generation and storage of stacking faults (SFs), without involving any intermediate crystalline phases. By employing density functional theory simulations, we find that energetically unfavorable single-layer SFs create very strong antibonding interactions, which trigger the subsequent structural rearrangements. Our findings thus resolve the interrelationship between plastic deformation and amorphization in silicon, and shed light on the mechanism underlying deformation-induced CAT in general.National Natural Science Foundation of China (grant 51231005)National Natural Science Foundation of China (grant 51321003)National Natural Science Foundation of China (grant 11132006