Advanced Materials Research Vols. 146-147

Abstract: α-MnO2, β-MnO2 and Mn2O3 were synthesized from birnessite followed by acid treatment and subsequently calcined under different conditions. These catalysts were used for catalytic combustion of dimethyl ether (DME) and characterized by XRD, BET and H2-TPR techniques. The results showed that the catalytic activity of α-MnO2, β-MnO2 and Mn2O3 are higher than that of birnessite. Larger specific surface area as well as the better reducibility of Mn species in the manganese oxides might be the main contribution for the DME combustion activity.

Abstract: In order to understand the effects of deoxidizer such as titanium, zirconium and magnesium on the impact toughness of heat affected zone (HAZ) of steel, four low carbon steels deoxidized by titanium, zirconium and magnesium were obtained. After smelting, forging, rolling and welding simulation, the effects of Ti, Zr and Mg additives on the impact toughness of HAZ in low carbon steel were studied. The inclusion characteristics (size, morphology and chemistry) analysis, Charpy-type test and the fracture observation of the specimens after the Charpy-type test were carried out respectively. The following results were found. The density of inclusion in Ti-Zr-Mg deoxidized steel is maximal. With the increasing of Ti content in steel, the proportion of inclusions in diameter less than 0.5 μm decreases. The proportion reaches maximum 64.0% in Ti-Zr-Mg deoxidized steel. The addition of Ti-Zr-Mg can enhance the impact toughness of HAZ after welding simulation. The maximal impacting energy is 249J at 253K. The complex particles of MgO-ZrO2-TiOx-MnS are most benefit to enhance impact toughness. The improvement of HAZ is attributable to the role of particle pinning and the formation of intergranular ferrite.

Abstract: The thermal, mechanical, and corrosive properties for Cu50Zr40Ti10 (at. %) metallic glass were also investigated. The glass transition temperature Tg, onset crystallization temperature TX, and under-cooled liquid region △TX are 624.4, 691.1, and 66.7 K, respectively. The elastic strain, fracture strength, and elastic modulus are 2.13 %, 2099.78 MPa, and 86.85 GPa, respectively. The corrosion rates in 1 M HCl, 1 M NaCl, and 0.5 M H2SO4 solutions open to air at 298 K are estimated to be about 0.4759, 0.1076, and 1.758×10-3 mm/year, respectively. The passive films can be observed in HCl and NaCl but not in H2SO4, the corrosion products in the former are looser than those in the latter, resulting in the better corrosion resistance in the latter than in the former.

Abstract: The microstructure and fatigue crack growth behavior of friction stir welding of 6063-T5 aluminum alloys were investigated. For this propose, fatigue crack growth curves were determined in four different locations of notch, which are base metal, middle of welded zone (parallel to weld line), near interface and interface (shoulder limits). The crack initiation and crack propagation of the base metal specimens presented slower than those of stir welded specimens. The microstructure observations show that the grain sizes in stir welded zone are finer than that in the unaffected base material and in the heat affected zone.

Abstract: TA18 alloy was used as the base material to investigate the effect of thermal oxidation (TO) on titanium alloys. The samples were subjected to TO treatment in a conventional muffle furnace at the same duration (210min) for different temperatures under air atmosphere. The results showed that an oxide layer comprised of rutile TiO2 and a small amount of Al2O3 were formed for samples thermally oxidized at 700°C and above, and both rutile and Al2O3 peaks increase with the treating temperature. The surface hardness increased significantly with the treating temperature due to the formation of a thin oxide layer and an oxygen diffusion zone in TO process. The wear test results showed that TO process can significantly improve the wear resistance, and the wear resistance is a function of the treating temperature, with 700°C being the optimum temperature to improve wear resistance of TA18 alloy for the duration of 210min.

Abstract: This paper gives a brief introduction of the developmental history of high performance steel (HPS) all over the world. Emphasis of current paper is on the characteristic studies of HPS 485W, which is new structural weathered steel produced by Wuyang Steel Iron Company using quenching and tempering (Q&T) in China. To obtain the strength and ductility of HPS 485W, the tensile coupons were machined from each 8mm, 10mm, 12mm and 14mm thick plate. Based on the static tensile tests in room temperature, major of material mechanical characters were obtained, such as yield strength, ultimate strength, elastic modulus and so forth. Besides, to examine plate toughness, 30 Charpy V-Notch (CVN) specimens from 12mm thick HPS 485W plate were tested from 20 oC to -196 oC . Compared with conventional bridge steels, the CVN test results show that the fracture toughness of HPS 485W is much higher, and the brittle-ductile transition of HPS occurs at a much lower temperature. A set of 9 single-edge bend specimens were took from 20mm and 30mm thick HPS 485W separately for ductility fracture toughness test. The calculated JIC value is 415.8 kJ/m2 for 18mm thick specimen and 507.79 kJ/m2 for 28mm thick specimen, which shows ideal ductility of HPS 485W.

Abstract: When a magnetic field is applied to magnetic fluids (MF), various structures of MF are formed: chain-like structures in low fields, columnar, lamellar and striped structures in high fields, ellipsoidal structures in pulsed fields, and layered structures in rotating fields. The inner structures and particle distributions of MF in gradient magnetic fields are quite interesting, but very few works have been done on this. In the present study, the effects of magnetic field gradient on the structures of MF are investigated using a two-dimensional Monte Carlo simulation. The results show that a gradient distribution of magnetic particles is formed under gradient magnetic fields. Moreover, with increasing the field gradient, more magnetic particles are pushed to the right region and particle distribution changes from grass-like clusters to needle-like ones.

Abstract: The dynamic responses of the impact phenomena were studied experimentally using ultrasound transducer mounted at the specimen support to capture non-audible structure-borne acoustic signal generated during the impact event. A series of low velocity as well as full capacity impact tests were analysed. Analysis from the time histories record and the signal energy from the power spectral density show that the transient signal generated during the impact event have relation to the impact velocity and impact energy. This paper can be further studied in order to characterise the material properties.

Abstract: Composite T-beam in general use is composed of concrete and steel. Compared with mechanical analysis, little research has been carried on deriving the theoretical model for back analysis of composite T-beam. Firstly for composite T-beam, degraded solid element theory is deduced and the displacement function is obtained. Then Markov error function of mechanical parameters of composite T-beam is founded. The back analysis computing formulas are also obtained by adopting optimization method including revised Powell method. Then the steps of back analysis of mechanical parameters of the composite T-beam are given. Through analysis of a classic example, some important conclusions about revised Powell back analysis of mechanical parameters of composite T-beam are obtained.

Abstract: The wedge splitting test specimens with three series of different relative crack length were used to study the influences of relative crack length on the fracture toughness of common concrete. The suitable formulation for fracture toughness of concrete with different relative crack length was gotten on comparing between fracture toughness test results and computation results of the model developed from Hu formula.