Applied Mechanics and Materials Vols. 184-185

Abstract: According to the results of cement-soil uniaxial compressive test, consider cement-soil stress-strain relations as a continuous random process, the function of random variable obeys Weibull distribution, and introduce generalized hooke′s law in order to establish Weibull distribution of cement-soil constitutive model, solve the softening problem that a variety of incremental nonlinear elastic models cannot reflect the cement-soil. This paper discussed the parameter character of Weibull distribution model of cement-soil, presented the solving method of parameters of cement-soil Weibull distribution constitutive model, verified by results of test, revealed the rationality of the model and shows that the proposed model is more convenient than other model, have widely application value.

Abstract: Porous Al₂O₃ ceramics with a lamellar pore microstructure have been fabricated by a directional freezing process using the micro-sized and nano-sized Al₂O₃ powders. At the same solid loading and freezing temperature, compared with the suspensions of micro-sized Al₂O₃, the porous ceramics prepared from the suspensions of nano-sized Al₂O₃ had the narrower lamellar pore channels and thicker channel walls, which were caused by the higher viscosity, stronger inter-particle attraction and more ice nucleation sites in the nano-sized Al₂O₃ suspensions. For both types of Al₂O₃ at a specific solid loading, with the increasing of freezing temperature, the wider pore channels and thinner channel walls were observed. These tendencies were weaker by using the nano-sized Al₂O₃ . The above results show the lower porosity in the ceramics using the nano-sized Al₂O₃. However, due to the higher sintering activity for the smaller particles, the pore channel walls by using the nano-sized Al₂O₃ was denser than using the micro-sized Al₂O₃, leading to the higher mechanical strength of ceramics.

Abstract: A sonochemical method has been applied to prepared PbWO4 crystals by using different precursors. The as-prepared samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the precursor played an important role in the synthesis of PbWO4 crystals. PbWO4 nanostructures with different morphologies, such as flower-like, rod-like, and dendrite-like, have been successfully obtained via a mild sonochemical method corresponding to the precursor PbCO3, Pb(NO3)2, and Pb(Ac)2, respectively.

Abstract: K0.5Bi0.5TiO3 nanoparticles and quadrate nanoflakes were successfully prepared by a hydrothermal process. The as-synthesized powders were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results suggest that the precursor plays an important role on the formation of K0.5Bi0.5TiO3 crystals and the formation mechanism was also discussed.

Abstract: High speed roll casting of AA5182 aluminum alloy was tried using a vertical type high speed twin roll caster equipped with mild-steel rolls. Parting material was not used and speed was 80m/min. AA5182 strip, which thickness was 2.1mm, could be cast continuously. However, porosity occurred at center area at the thickness direction of the strip of the as-cast strip. Si was added to original AA5182 to improve the porosity at 0.2, 0.4, 0.6, 0.8 and 1.0 mass%. The porosity was improved as the content of the Si increased. The elongation resulting from the tension test was the best when 0.2mass%Si was added. The clack on the surface was improved by the increase of the Si content. Roll casting ability was improved by the Si, too.

Abstract: The present study was undertaken to investigate the effect of thermo-mechanical treatment (TMT) on the microstructure and mechanical behaviour of low alloy steel. Hot forging is carried out at 1200°C using mechanical press of 500 and 800 ton. The effect of hot forging reduction ratios (1.11 and 1.29) on the hardness and mechanical properties are studied. TMT samples are given different heat treatment i.e. annealing (A), normalizing (N), hardening (H), hardening and tempering (H/T) and their corresponding impact toughness are obtained. Selected heat treatment (normalizing and annealing) are given to tensile test samples and their corresponding strength and ductility are obtained. Ultimate tensile, 0.2% offset yield strength and percent elongation are measured. Hardness and impact toughness measurements were carried out for all alloy conditions. Hardness (HV), ultimate tensile stress (UTS-MPa) and 0.2% offset yield stress (MPa) increases with increasing reduction ratio. TMT leads to a sharp rise in alloy hardness and strength. Normalizing and annealing following TMT revealed a low hardness values compared to those observed in the TMT condition. Annealing reduces hardness and strength but increases ductility and impact toughness. This could be attributed to the recovery and coarsening effect. Pro-eutectoid ferrite phase are observed along the grain boundaries of low alloy steel in the TMT conditions regardless of the reduction ratios. Normalized samples show a refined pearlitic microstructure while coarse pearlite is observed in the annealed one. Good mechanical properties can be obtained by a combination of plastic deformation and thermal treatment. Heat treatment is one of the major factors used to enhance the mechanical properties of low alloy steel. An understanding of the combined effect of TMT and subsequent heat treatment on the structure and mechanical properties of low alloy steel would help in selecting conditions required to achieve the optimum mechanical properties and alloy high strength to weight ratio. This may be achieved by measuring hardness, impact toughness, strength and ductility resulting from different heat treatment following TMT.

Abstract: WC steel-bonded cemented carbides were prepared by microwave sintering through ball milling, press forming and sintering with iron powders as the matrix, WC particles as the reinforcements. The effect of WC contents on microstructure and properties of steel-bonded cemented carbide was studied. The results show that the steel-bonded cemented carbide sintered at 1280 °C is considered as a liquid phase sintering and Fe7W6, Fe2W2C and Fe6W6C new phases are generated during the sintering process. The relative density, microhardness and bending strength of the steel-bonded cemented carbide increase with increasing the WC contents. Moreover, the mechanical properties of steel-bonded cemented carbide are obviously improved after heat treatment.

Abstract: Internal cracks in 30Cr2Ni4MoV steel were produced by compressing cylindrical sample with drilled hole. In order to consider the effects of deformation degree, temperature, strain rate and holding time on the crack healing, the hot compression tests were performed on Gleeble-1500 thermo-simulation machine under different process conditions. By in situ observation under optical microscope and scanning electron microscope, effects of process condition on crack healing and the behaviours of crack healing were revealed successfully: (1) the result of crack healing improves as the melt temperature, reduction and holding time increase, (2) the effect of crack healing decreases as the strain rate increases. By the energy dispersive spectroscopy, it is also found that the chemical composition of the healed crack area is different from that of the matrix.

Abstract: Backside cracks were found universally in the ultra-low carbon austenitic stainless steel (316LMod) inner linings of urea reactors in recent years, and led to urea reactors leakage. Analyses on the sample revealed that, the backside cracks were caused by the interaction of wet hydrogen sulfide (H₂S) and chloride ions (Cl^-) stress corrosion cracking (SCC), and H₂S played a dominant role. The source of H₂S and chloride ions was the leak detection steam. Furthermore, measures to avoid backside cracks in 316LMod inner linings of urea reactors were put forward and verified.

Abstract: In this paper, poly (vinylalcohol glycidyl ether) (PVAGE) was synthesized as a novel reactive stiffening agent to improve the stiffness of cotton fabric. Cotton fabric could be grafted with PVAGE under high temperature and the grafting rate would increase with the increase of PVAGE concentration. The cotton fabric grafted with PVAGE has excellent washing durability. The wearability of cotton fabric grafted with PVAGE was also studied. As the increase of grafting rate, the flexural stiffness increased dramaticly; tensile strength increased a little; cockle elastic decreased slightly; and air permeability and whiteness also decreased but were still in acceptable range.