Investigation of microstructural characteristics of nanocrystalline 12YWT steel during milling and subsequent annealing by X-ray diffraction line profile analysis

The variations of dislocation density, character of dislocations, and crystallite size as a function of milling time and post-heat-treating temperature were investigated for 12YWT nanocomposite ODS ferritic steel using X-ray diffraction line profile analysis. The modified Williamson–Hall and the modified Warren–Averbach methods, which are based on the dislocation model of the strain anisotropy, were utilized to characterize the microstructural parameters of the nanocomposite material and the matrix alloy. The presence of nano-oxide particles in the ODS steel caused an initially sharp decrease in the average crystallite size; however, with increasing milling time, the crystallite size of the unreinforced alloy reached the comparable value of that of the reinforced material. The subsequent heat treating on the powders milled for 80 h showed that the presence of Y₂O₃ dispersoids increased the recrystallization temperature and suppressed the grain growth up to 800 °C in the 12YWT alloy as compared to the matrix alloy which occurred about 700 °C. The results of X-ray diffraction line profile analysis also showed that the contribution of edge components of the dislocations increased at the initial milling stages, while the screw components tended to increase after 40-h milling time.     

Development of a High-Strength Ultrafine-Grained Ferritic Steel Nanocomposite

This article describes the microstructural and mechanical properties of 12YWT oxide-dispersion-strengthened (ODS)-ferritic steel nanocomposite. According to the annealing results obtained from X-ray diffraction line profile analysis on mechanically alloyed powders milled for 80 hours, the hot extrusion at 1123 K (850 °C) resulted in a nearly equiaxed ultrafine structure with an ultimate tensile strength of 1470 MPa, yield strength of 1390 MPa, and total elongation of 13 pct at room temperature comparable with high-strength 14YWT ODS steel. Maximum total elongation was found at 973 K (600 °C) where fractography of the tensile specimen showed a fully ductile dimple feature compared with the splitting cracks and very fine dimpled structure observed at room temperature. The presence of very small particles on the wall of dimples at 1073 K (800 °C) with nearly chemical composition of the matrix alloy was attributed to the activation of the boundaries decohesion mechanism as a result of diffusion of solute atoms. The results of Charpy impact test also indicated significant improvement of transition temperature with respect to predecessor 12YWT because of the decreased grain size and more homogeneity of grain size distribution. Hence, this alloy represented a good compromise between the strength and Charpy impact properties.     

A comparative study between gravel and rubber drainage columns for mitigation of liquefaction hazards

Liquefaction is one of the most destructive natural hazards that cause damage to engineering structures during an earthquake. This study aims to examine the effect of rubber and gravel drainage columns on the reduction of liquefaction potential of saturated sandy soils using a shaking table. Experiments were carried out in various conditions such as construction materials, different arrangements and diameters of drainage columns. Effects of the relative density and the input motion on the base test were investigated as well. The results demonstrate that rubber drainage columns have slightly better performance compared to gravel drainage columns at high relative density and high input acceleration. Soil improvement using gravel drainage columns, which leads to reduction in liquefaction effects at moderate input acceleration and low relative density, is a more effective method than that using rubber drainage columns. By increasing the number and diameter of gravel and rubber drainage columns, deformations due to liquefaction are reduced. The drainage rate of gravel drains is higher than that of rubber drains after shaking. Totally, the outcomes indicate that densification is the most important factor controlling liquefaction.     

Simulation of carbon dioxide absorption process by aqueous monoethanolamine in a microchannel in annular flow pattern

The process of carbon dioxide absorption by aqueous monoethanolamine solvent was simulated in a microchannel in an annular flow pattern. This simulation has been carried out as a multiphase and three-dimensional process. The effects of different operating parameters such as temperature, superficial gas and liquid velocities, aspect ratio, and concentrations of solvent and solute have been investigated on the mass transfer flux and carbon dioxide conversion. The results of simulating mass transfer flux based on the calculated mass transfer coefficient were well consistent with the experimental data. The result of this study indicated that the mass transfer flux shall increase with the superficial gas and liquid velocities, temperature, concentration of solvent, and increment in the aspect ratio. It also revealed that increasing the concentration of solute would lead to an increase in the mass transfer flux and a decrease in the conversion.     

Using ARB process as a solution for dilemma of Si and SiCp distribution in cast Al-Si/SiCp composites

A major challenge in achieving the best potential of SiC_p-reinforced aluminum composites is to homogeneously disperse SiC particles within the aluminum alloys. The presence of coarse Si fibers with non-uniform distribution in cast Al-Si alloys, which may lead to poor mechanical properties, is another important problem that limits the application of these alloys. In order to eliminate these problems, accumulative roll bonding (ARB) process was used in this study as a very effective method for improving the microstructure and mechanical properties of the Al356/SiC_p composite. It was found that when the number of ARB cycles was increased, the uniformity of the Si and SiC_p in the aluminum matrix improved, the Si particles became finer and more spheroidal, the free zones of Si and SiC particles disappeared, the porosity of composite decreased, the bonding quality between SiC_p and matrix improved, and therefore mechanical properties of the composites were improved. The microstructure of the manufactured Al356/SiC_p composite after six ARB cycles indicated a completely modified structure so that its tensile strength and elongation values reached 318 MPa and 5.9%, which were 3.1 and 3.7 times greater than those of the as-cast composite, respectively.     

A hybrid S-N formulation for fatigue life modeling of composite materials and structures

A semi-empirical S-N formulation for the modeling of the constant amplitude fatigue behavior of composite materials and structures is introduced in this paper. The new S-N formulation is based on the commonly used exponential and power law fatigue models. It is a hybrid formulation combining the two existing models in order to improve their modeling accuracy in the low and high cycle fatigue regions. This formulation was applied to a number of fatigue databases for different composite materials and structural elements in order to simulate their fatigue behavior. The modeling accuracy of the hybrid model was compared to the accuracy of commonly used S-N models for composite materials. As proved, the hybrid model performs better in the majority of the examined cases and is able to overcome the disadvantages of previously developed models without introducing any complexity in the fitting procedure.     

Enhanced removal of benzene in nonthermal plasma with ozonation,flow recycling,and flow recirculation

A double stage AC/DC sequential high voltage reactor has been developed to study the decomposition of benzene in the air stream at atmospheric pressure. The removal efficiency was measured as a function of ozonation, flow recycling, and flow recirculation. Ozonation in the inlet, and recycling of the exhaust stream increased the removal of benzene, also with increasing of specific input energy (J l⁻¹) the effect of inlet flow ozonation on benzene decomposition was enhanced. The highest removal efficiency was obtained up to >99% in recirculation six times, while CO₂ selectivity reached 99.9% and energy efficiency was 0.59 g kWh⁻¹. O₃ production/ decomposition > production of OH radicals > electronic and ionic collisions were indicated as the main mechanisms influencing benzene abatement in this research.     

Nanostructured AA5005/Al2O3 composite manufactured by anodising and accumulative roll bonding

In this study, nanostructured AA5005/6 vol.-% Al₂O₃ composite manufactured by anodising and accumulative roll bonding (ARB) processes was investigated. The microstructure of the AA5005/Al₂O₃ composite after ninth ARB cycle exhibited a good distribution of alumina reinforcement particles in the AA5005 matrix. It was found that with increasing the number of cycles, the tensile strength of the monolithic and composite samples increased, but their ductility decreased at the first ARB cycle and then increased. The mean grain size of the composite sample after the ninth cycle was 88?nm. The tensile strength of the composite was 3.3 times higher than the initial AA5005 sheet. Observations revealed that the failure mode in the AA5005/Al₂O₃ composite was the shear ductile fracture.     

An exploration of green supply chain practices and performances in an automotive industry

During recent years, the natural environment has become a challenging topic that business organizations must consider due to the economic and ecological impacts and increasing awareness of environment protection. Globalization and the increased number of countries entering the World Trade Organization (WTO) have promoted green supply chain management (GSCM) practices in manufacturing organizations. GSCM has emerged as an important organizational philosophy and a proactive approach to reduce environmental risks. Increasing pressures such as stricter regulations, increased community, and consumer pressures, and the developing country’s aim to enter the WTO have caused automotive supply chain managers to consider and to implement GSCM practices to improve both their economic and environmental performances. This paper explores the practices and performances of the GSCM based on the GSCM literature, and it considers the relationship between green supply chain practices (initiatives) and performance outcomes. In this paper, two questionnaires were developed and a survey conducted to assess the importance of GSCM practices and performances in an automotive company in a developing country using a fuzzy multiple criteria decision-making method. The result of this paper presents practical guidance for managers in performing GSCM practices by ranking GSCM practices according to their importance which leads to improving GSCM performances.     

Investigation of Park–Ang damage index model for flexural behavior of reinforced concrete columns

One of the most popular damage indexes for reinforced concrete (RC) members is Park–Ang damage index model. This model has been established on the basis of experimental results of RC beams and columns with different modes of damage. It has considerable uncertainty on the basis of its authors' remarks. In this study, precision of Park–Ang model for RC columns is improved by using some experimental results from Pacific Earthquake Engineering Research information bank. In proposed model, it focused on RC columns with specific sections and collapse modes. Finally, in order to define damage index more exactly in concrete columns under seismic loadings, capability of IDARC‐2D computer program has been improved by this proposed model. Copyright © 2012 John Wiley & Sons, Ltd.