Modeling of microstructure effects on the mechanical behavior of ultrafine-grained nickels processed by hot isostatic pressing

Bulk ultrafine-grained nickel specimens having grain sizes in the range of 0.25-5 μm were consolidated by hot isostatic pressing technique. The resulting microstructures were characterized by transmission electron microscopy and X-ray diffraction analysis. Compression tests were carried out at room temperature and at strain rate of 1.6×10⁻⁴ s⁻¹. It was found that the measured yield strength does not follow the Hall-Petch law as a consequence of the presence of oxide phase. Therefore, the use of micromechanics based model, which takes into account only the Hall-Petch relationship at grain level for predicting the grain sized effects on mechanical behavior of this kind of materials, is not accurate yet. In this study, a modification made to the generalized self-consistent model was proposed for studying both grain size and oxide phase dependence of ultrafine-grained materials behavior. Because of the novel modification, an optimization procedure with two steps was required to identify the parameters of micromechanical model. An acceptable agreement between experimental and numerical results was achieved. Moreover, the influence of texture on the yield strength and the application of the proposed model to the spark plasma sintering processed materials were also discussed.     

A revisited generalized self-consistent polycrystal model following an incremental small strain formulation and including grain-size distribution effect

A generalized self-consistent approach, recently proposed by Jiang and Weng (2004) [B. Jiang, G.J. Weng, A generalized self-consistent polycrystal model for the yield strength of Nanocrystalline materials, Journal of the Mechanics and Physics of Solids 52 (2004a) 1125-1149; B. Jiang, G.J. Weng, A theory of compressive yield strength of nano-grained ceramics, International Journal of Plasticity 20 (2004b) 2007-2056.] for investigating the so-called “breakdown” of the Hall-Petch law in the case of nanocrystalline (NC) materials, is revisited and reformulated following an incremental small strain scheme. The NC material is modelled as a composite material that takes each oriented grain and its immediate grain boundary to form a pair, which in turn is embedded in the infinite effective medium with a property representing the average orientation of all these pairs. The plastic deformation of the inclusion phase takes into account the dislocation glide mechanism whereas boundary phase is modelled as an amorphous material. As an application, the model’s parameters are identified under an optimization code with respect to data stated from pure copper submitted to tensile load. The aggregate is composed of spherical randomly distributed grains with a grain-size distribution following a log-normal statistical function.     

Investigations of Local Corrosion Behavior of Plasma-Sprayed FeCr Nanocomposite Coating by SECM

FeCr alloy coating can be sprayed on low-carbon steel to improve the corrosion resistance because of FeCr alloy’s high anti-corrosion capacity. In this paper, Fe microparticles/Cr nanoparticles coating (NFC) and FeCr microparticles coating (MFC) were prepared by atmospheric plasma spraying and NFC was heat-treated under hydrogen atmosphere at 800 °C (HNFC). EDS mapping showed no penetration of Ni in MFC and NFC while penetration of Ni occurred in HNFC. X-ray diffraction results indicated the form of the NiCrFe (bcc) solid solution in HNFC. SECM testing in 3.5 (wt.%) NaCl revealed that the anti-corrosion capacity of NFC improved compared with MFC, while HNFC improved further.     

Heat-Transfer analysis for quenched impact test specimens of polymers

An approximate but simple method for the low temperature mechanical testing of polymers is frequently used. It consists of quenching the polymer sample into liquid nitrogen and then installing it on the testing apparatus. The required test temperature is determined by the time where the experiment is started. In this work, the time-temperature patterns of two quenched impact test samples, in high density polyethylene and polyurethane, were first measured and then compared with the values obtained from a graphical method of unsteady-state heat conduction. The agreement between experimental data and calculated values is better than 8% in terms of relative error.     

Mining the Wheat Grain Proteome

Bread wheat is the most widely cultivated crop worldwide, used in the production of food products and a feed source for animals. Selection tools that can be applied early in the breeding cycle are needed to accelerate genetic gain for increased wheat production while maintaining or improving grain quality if demand from human population growth is to be fulfilled. Proteomics screening assays of wheat flour can assist breeders to select the best performing breeding lines and discard the worst lines. In this study, we optimised a robust LC–MS shotgun quantitative proteomics method to screen thousands of wheat genotypes. Using 6 cultivars and 4 replicates, we tested 3 resuspension ratios (50, 25, and 17 µL/mg), 2 extraction buffers (with urea or guanidine-hydrochloride), 3 sets of proteases (chymotrypsin, Glu-C, and trypsin/Lys-C), and multiple LC settings. Protein identifications by LC–MS/MS were used to select the best parameters. A total 8738 wheat proteins were identified. The best method was validated on an independent set of 96 cultivars and peptides quantities were normalised using sample weights, an internal standard, and quality controls. Data mining tools found particularly useful to explore the flour proteome are presented (UniProt Retrieve/ID mapping tool, KEGG, AgriGO, REVIGO, and Pathway Tools).     

Use of mica in poly(vinyl chloride)

A study was conducted to evaluate mica-poly(vinyl chloride) (PVC) composites. A highly filled PVC pipe formulation was selected as reference and a gradual replacement by mica of the calcium carbonate was conducted. The mica improved the fluxing time of the formulation by a factor of three without markedly affecting the equilibrium or maximum, torque. The results are optimized when there is a partial replacement of the calcium carbonate by mica, Orientation of the mica flakes enhances the young's modulus as well as the yield stress. A theoretical analysis shows a discrepancy from experimental results for high levels of mica. The rheological properties were studied with a Brabender plastograph and mechanical properties with a model TM-SM Instron.     

Open dumping site in Asian developing countries: a potential source of polychlorinated dibenz-p-dioxins and polychlorinated dibenzofurans

Open landfill dumping areas for municipal wastes in Asian developing countries have recently received particular attention with regard to environmental pollution problems. Because of the uncontrolled burning of solid wastes, elevated contamination by various toxic chemicals including dioxins and related compounds in these dumping sites has been anticipated. In this study, concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (PCBs) were determined in soils from dumping sites in the Philippines, Cambodia, India, and Vietnam. Residue concentrations of PCDD/Fs and coplanar PCBs in dumping site soils were apparently greater than those in soils collected in agricultural or urban areas far from dumping sites, suggesting that dumping sites are potential sources of PCDD/Fs and related compounds. Observed PCDD/F concentrations in soils from dumping sites in the Philippines and Cambodia were comparable or higher than those reported for dioxin-contaminated locations in the world (e.g., near the municipal waste incinerators and open landfill dumping sites). Homologue profiles of PCDD/Fs in dumping site soils from the Philippines and, to a lesser extent, from Cambodia and India reflected patterns of samples representing typical emissions, while profiles of agricultural or urban soils were similar to those of typical environmental sinks. This result suggests recent formation of PCDD/Fs in dumping site areas and that open dumping sites are a potential source of dioxins in Asian developing countries. Uncontrolled combustions of solid wastes by waste pickers, generation of methane gas, and low-temperature burning can be major factors for the formation of dioxins in dumping sites. Elevated fluxes of PCDD/Fs to soils in dumping sites were encountered in the Philippines, Cambodia, India, and Vietnam-Hanoi, and these levels were higher than those reported for other countries. Considerable loading rates of PCDD/Fs in the dumping sites of these countries were observed, ranging from 20 to 3900 mg/yr (0.12-35 mg TEQ/yr). PCDD/F concentrations in some soil samples from the Philippines, Cambodia, India, and Vietnam-Hanoi exceeded environmental guideline values, suggesting potential health effects on humans and wildlife living near these dumping sites. The estimated intakes of dioxins via soil ingestion and dermal exposure for children were higher than those for adults, suggesting greater risk of dioxin exposure for children in dumping sites. To our knowledge, this is the first comprehensive study on PCDD/Fs contamination in open dumping sites of Asian developing countries. On the basis of the result of this study, we have addressed a new environmental issue that open dumping sites are potential sources of PCDD/Fs and related compounds, and dioxin contamination in dumping sites may become a key environmental problem in developing countries.     

基于大比例静力模型试验的高强度桩复合地基加筋垫层分析

为研究高强度桩复合地基加筋垫层的作用机理与筋带拉力的计算方法,采用一套自制的桩土差异沉降控制装置,进行了4组不同桩帽尺寸的大比例静力模型试验。测试了各级荷载作用下的加筋垫层筋带拉力,分析了筋带拉力的大小及分布随荷载增加的变化规律。结果表明：随桩顶和桩间土沉降差增加,筋带拉力逐渐增大,筋带拉力最大值出现在桩顶位置;随着桩帽覆盖率增加,桩间土范围内筋带拉力缓慢减小,桩顶范围筋带拉力变化较大,先增大后减小。加筋垫层的破坏模式表现为桩帽边缘的筋带断裂。     

A meshfree model without shear-locking for free vibration analysis of first-order shear deformable plates

Difficulty in imposing essential boundary conditions in the standard element-free Galerkin method (EFG) is due to the lack of Kronecker’s delta function property of shape functions generated by moving least square approximation (MLS). In this paper, we further apply a meshfree model based on the moving Kriging interpolation method (MK) to free vibration analysis of first-order shear deformable plates. The deflection and two rotation field variables of plate are approximated by the MK method, which is employed to construct the shape functions having the delta function property. With this approach, the drawback in enforcement of the boundary conditions caused by the MLS is now avoided. The present formulation is based on the first-order shear deformation plate theory (FSDT) associated with an effective elimination of the shear-locking phenomenon completely, and hence the approach is applicable to both moderately thick and thin plates. Numerical examples considering various aspect ratios and different boundaries are examined and solutions on natural frequencies obtained by the present method are then compared with existing reference solutions, and very good agreements are observed.     

Spatial prediction of landslide susceptibility using data mining-based kernel logistic regression,naive Bayes and RBFNetwork models for the Long County area (China)

The main goal of this study is to assess and compare three advanced machine learning techniques, namely, kernel logistic regression (KLR), naïve Bayes (NB), and radial basis function network (RBFNetwork) models for landslide susceptibility modeling in Long County, China. First, a total of 171 landslide locations were identified within the study area using historical reports, aerial photographs, and extensive field surveys. All the landslides were randomly separated into two parts with a ratio of 70/30 for training and validation purposes. Second, 12 landslide conditioning factors were prepared for landslide susceptibility modeling, including slope aspect, slope angle, plan curvature, profile curvature, elevation, distance to faults, distance to rivers, distance to roads, lithology, NDVI (normalized difference vegetation index), land use, and rainfall. Third, the correlations between the conditioning factors and the occurrence of landslides were analyzed using normalized frequency ratios. A multicollinearity analysis of the landslide conditioning factors was carried out using tolerances and variance inflation factor (VIF) methods. Feature selection was performed using the chi-squared statistic with a 10-fold cross-validation technique to assess the predictive capabilities of the landslide conditioning factors. Then, the landslide conditioning factors with null predictive ability were excluded in order to optimize the landslide models. Finally, the trained KLR, NB, and RBFNetwork models were used to construct landslide susceptibility maps. The receiver operating characteristics (ROC) curve, the area under the curve (AUC), and several statistical measures, such as accuracy (ACC), F-measure, mean absolute error (MAE), and root mean squared error (RMSE), were used for the assessment, validation, and comparison of the resulting models in order to choose the best model in this study. The validation results show that all three models exhibit reasonably good performance, and the KLR model exhibits the most stable and best performance. The KLR model, which has a success rate of 0.847 and a prediction rate of 0.749, is a promising technique for landslide susceptibility mapping. Given the outcomes of the study, all three models could be used efficiently for landslide susceptibility analysis.