Advanced Materials Research Vols. 148-149

Abstract: Deep-drawing is one of the most important methods to form sheet metal ,but wrinkling and fracture are the main failure modes in sheet-metal forming. Blank shape is important for deep-drawing because of an effective way to promote deep formability sheet metal .This paper presents an attempt to determine the effect of circle blank with circular diving equally small hole on edge of circle blank on the fracture and wrinkling and was investigated using 08Al sheet metal .The circular blank with small hole of diameter = was analyzed to eliminate wrinkling and fracture in deep-drawing .The aim of this study is to investigate the circular diving equally small hole on edge of circle blank on formability in the deep-drawing process and to obtain useful date from the industrial field .The experiment show that limit formability promote with punching small holes on circle blank in deep-drawing process.

Abstract: Silicon nitride ceramic ball surface is examined after failure with scanning electron microscopy. The profile of the fatigue spalling takes the shape of an ellipse. The failure cause, fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material, and propagate, to form fatigue spalls under the action of principal tensile stresses. The contours of equal tensile stress of Oxy plane underneath surface are elliptical. Subsurface cracks are shape of ellipses and spall is also of the elliptic shape. The principal tensile stress increases with increasing contact load, causing spall formation and reduction of rolling contact life.

Abstract: Nanocrystalline surface layer was fabricated on a quenched and tempered Cr-Si alloy steel by using Surface mechanical treatment. The microstructure features of various sections in the surface layer were characterized by using transmission electron microscopy (TEM). By analyzing the microstructural characteristic at different depths in the treated surface, the effect of the initial microstructures on grain refinement process of quenched and tempered steel was investigated. Experimental evidence showed the initial subgrains with small angle boundary and lower dislocation density were firstly developed into Lamellar-type dislocation cells (DCs) with dense dislocation walls (DDWs). Some initial subboundaries were moved to DDWs by dislocation activities. The width of lamellar-type DCs was 2-3 times of that of initial lathy subgrains. The size of the DCs and subgrains formed in the interim of refinement process was not uniformity. On the top surface the cementite granules were decomposed or fragmented to hyperfine particles, and the size of the grains tended to uniformity. Experimental analysis indicated the configuration of microstructure was affect by the initial microstructure in the initial stage and the interim of the grain refinement process. Surface nanocrystallization of Cr-Si steel can be attributed to dislocation activities.

Abstract: Gas turbine components are subjected to high temperature and high stress during engine operation, so they often become physically damaged due to the formation of cracks, voids and worn surfaces. In order to develop a new process for repairing gas turbine components with high strength filler materials, an attempt has been made to prepare IN738/NiCrSi/IN738 sandwich-like coating on thermal sensitive superalloy IN738 substrate and heat-treat it in a vacuum furnace. The microstructure morphologies, hardness and element distribution of as-deposited and as- heat-treated coatings have been investigated. The results showed that there were lot of cracks and voids in the deposited ‘sandwich-like’ coating but they could be eliminated by heat treatment. The diffusion of activated element Si in the sublayer NiCrSi of ‘sandwich-like’ coating was beneficial to healing cracks.

Abstract: ZnO product with tetrapod-shaped morphology was simply synthesized by controlling the evaporation and oxidation process of zinc metal. Pure bulk industrial zinc (99.995%) was first cast into small zinc pieces with a weight about 10～50g and then was heated in an alumina crucible in a furnace from room temperature to 1000～1250°C holding temperature, where the zinc pieces were vaporized and oxidized into zinc oxide products. The effects of zinc amount and holding temperature on the morphology of zinc oxide were investigated in this study. The products were confirmed to be zinc oxide with hexagonal wurtzite structure by X-ray diffraction analysis (XRD). Scanning electronic microscopy (SEM) analysis indicated that the morphologies of the products were T-ZnO whisker when the adding amounts of the zinc pieces were 20g and 30g, respectively. Based on the experimental results, it was speculated that crystal growth of T-ZnO comprised the formation of nuclei and the growth of need-like whisker.

Abstract: In this paper, calcined river-snail shell was used as a novel solid base catalyst in the transesterification of soybean oil with methanol for biodiesel production. The calcined river-snail shell was characterized using field emission scanning electron microscope and X-ray diffraction. Effects of transesterification process variables were investigated. The results indicated that river-snail shell calcined at 800 °C catalyzed the transesterification of soybean oil for biodiesel with a yield over 98 % under the conditions including catalyst of 3.0% (w/w), a molar ratio of methanol/oil of 9:1, reaction time of 3 h, and reaction temperature of 65 °C. As a low-cost green catalyst, calcined river-snail shell could not only minimize the environmental wastes resulted from the solid shell, but also reduce the production costs of biodiesel.

Abstract: Graft copolymerization of acrylic acid(AA) and acrylamide(AM) on cellulose to prepare super absorbent resin (SAR) under microwave irradiation were investigated using N,N-methylene bis-acrylamide as crosslinking agent, and potassium persulfate/sodium thiosulfate as initiator. The results indicated that it only needed 5min under the microwave level of 320W to obtain the resin with the maximum absorption amount of 1388g•g-1 , under the conditions that the ratio of acrylic acid to cellulose of 14:1, 0.25wt% initiator to AA, 0.25wt% crosslinking agent, 70% neutralization degree of AA. Under microwave irradiation, the preparation of SAR could be completed without the protection of nitrogen. Compared to conventional heating method, the methods had the striking advantages of short reaction time, simple process and low cost.

Abstract: This article designed 12 kinds of conductive yarns were fabricated by different number of shares and twists, observed the relationship of resistance and elongation through tensile test. It is shown that the resistance variation curve of conductive yarn generally approaches a parabola. That is, the resistance increased during the loading process; and the linearity of conductive yarns improved with the number of shares increased, but the sensitivity will decrease. Among the samples which contain the same number of shares but different twist per meter (TPM), samples were fabricated by 300TPM represented a better stability. Therefore, the textile sensors using conductive yarns could increase the number of shares or twists to improve the linearity in the situation that the sensitivity could achieve the minimum requirements.

Abstract: Adopting chemical coprecipitation and mechanical dispersion to prepare oil based magnetic fluid is a good way to increase the stability of magnetic fluid. This paper uses orthogonal design to analyze the influences from different factors, and The size of nano-particles and saturation magnetization were characterized by TEM and WSM vibration magnetometer. The results show that the NaOH solution adding speed of 0.4 ml/s and reaction temperature of 50 ~55 , sodium oleate solution adding speed of 0.3ml/s and heating temperature of 65 , heat-maintaining time of 20min are proper reaction conditions.

Abstract: With epoxy reinforced by short carbon fiber mats, a skin-like strain sensor, polymer-matrix smart layer was developed, which can continuously cover the structural surface to sense strain for the whole filed. The smart layer was proved to be an effective strain sensor for tensile strain up to 0.8% by a monotonic tension experiment, exceeding this limit cause nonlinearity in the resistance response. The damage sensitivity of the smart layer was revealed by the monitoring for a FRP beam with prefabricated defect. Based on its sensitivities, the smart layers was applied in the health monitoring for a concrete beam under three-point bending, the result showed a good correlation between the resistance change of the smart layer and the load applied on the structure. The emergency of structure damage can be monitored by the turning point on the resistance-deflection curve of the smart layer.