Advanced Materials Research Vols. 311-313

Abstract: The paper researched the isothermal time and temperature affects the solid particles evolution of semisolid AZ91D alloy, and the alloy be produced by the method of strain induced melt activation (SIMA) ,and the method of compression ratio is 40%. The research demonstrated that the solid fraction decreased and solid particle size increased when increasing temperature and time. The isothermal coarsening of solid particles obeys Ostwald ripening which depending on the curvature of the interface, thus creating concentration gradients and the diffusion transport of material. As a result, the large particles coarsening and little particles minish even dissolved and creating change of distribution frequency of solid particle size. The fitting curves reveal that the experimental data are well fitted to the coarsening equation. The quantitative analysis of solid fraction and solid particle size demonstrated that the appropriate isothermal holding temperature is 550°C -590°C and corresponding isothermal holding time is (45-60min)-(6-20min) in 40% compression ratio.

Abstract: Tabular alumina, α-Al₂O₃ powder, TiO₂ powder and metal aluminum powder in purity of 99%(by mass) were uesd to prepare the Al₂O₃-TiN composite ceramics by mechanical mixing and thermal reduction of aluminum in situ reaction sintering in the flow of nitrogen gas under atmospheric pressure;the influences of phase composition and microstructure changes at 1200°C-1500°C nitridation reaction in situ,different amount of TiN formations and sintering temperature on the properties of the samples were analyzed by thermal analysis, XRDand SEM. The results show that: TiO₂ was reduced by Al and then nitrided as TiN in the test temperature, the porosity has been increasesd while the bulk density has been decreased with the increased content of TiN formation because of the process of nucleation growth and the strong exothermic of the reaction.The mechanical properties of the composites are relatively better of TiN generated 10%content,because the structure of the skeleton formed by corundum was filled of part matrix evenly and was integrated closely by the matrix.

Abstract: Based on the test results of 448 sets of concrete mixtures (which have been divided into three groups), a concrete strength prediction model has been established using a stepwise regression method. The kinds and qualities of raw materials, which has a total comes to 17 factors, has been considered as the independent variables. It has been found that the forecast precision is not always improving along with the increase of independent variable number, so one or more factors may be "redundant" and should be reducted. A rough sets (RS) method has been adopted for the variable reduction, with different parameter combinations are tested. The results has shown that in each cases the forecast precision of the model are higher than the Bowromi formula’s. Some regularities for the parameters’ selections are existed, but not all the parameters can be given positively, so a trial process is still necessary.

Abstract: Titanium alloy castings are made by means of induction melting technology. The relationships thickness of lamellar α+β phase and tensile strength, yield strength, elongation percentage, and Vickers-hardness, as well as the effect of tensile property on the Vickers-hardness are investigated for Ti-6Al-4V alloy castings. The results show that the relationships between thickness of lamellar α+β phase, and tensile strength, yield strength, specific elongation, and Vickers-hardness meet the Hall-Petch equation. And the tensile property increases linearly with Vickers-hardness.

Abstract: Microstructures, static weight loss and potentiodynamic polarization curves were carried out on the Friction-stir welds of Al clad 2524 alloy with the thickness of 1.35 mm. The results indicated that the microstructures of the Nugget had been remarkably reshaped. A dynamical recrystallization took place on the zone of the weld nugget and an equiaxed grain structure formed. The static weight loss and potentiodynamic polarization curves results indicated that the resistance of corrosion of the base material (with aluminum clad) was superior to that of its weld, but the anti-corrosive ability of the weld was superior to that of the base material without aluminum clad.

Abstract: Diesel Particulate Filters (DPFs) provide probably the most effective means of trapping the exhaust emitted particulates from diesel engines. Three-dimension network ceramic filters become a promising alternative to the conventional wall flow filters, since they are effective in filtering small sized particles and provide a large specific surface area for catalytic coating. A mathematical model of pressure drop for a three-dimension network ceramic DPFs is developed. The model calculates the pressure drop of a filter as a function of the geometric filtering properties, operating conditions and structure of trapping. The calculated pressure drops of a filter agree well with the experimental results. The pressure drop of DPFs increases linearly with increasing trap length, and there is a nonlinear relationship between the exhaust gas mass flow rate and pressure drop. For optimized traps, the pressure drops are much lower than those of the filters with a unitary trap structure.

Abstract: Generation of structural stress in aluminum alloy thick plate is divided into three stages including the early, stable and late period using thermodynamics and elasticity theory. With FEM and mechanical state of materials, nonuniform plastic deformation is discussed, and distributions and characters of structural stress are analysized in each stage. Finally, experimental results agreed with date of the FEM. This truth demonstrated that mechanism of stress that changes in the process of thermal field works on formation of the final residual stress in the thick plate.

Abstract: This paper predicted the tension softening curves of dam concrete by employing the BP neural networks based on the experimental data of direct tension tests of dam concrete. This approach can predict the tension softening curves for the same component material but different mixtures dam concrete without performing the direct tension tests which are complex and expensive.

Abstract: intermediate crack-induced debondingis one of the most dominant failure modes in FRP-strengthened RC beams. Different code models and provisions have been proposed to mitigateintermediate crack-induced debondingfailure.However, these models and provisions can not mitigate this failure mode effectively. Recnetly, new models have been proposed to solve this problem. Out of all the existing models, four typical ones are investigated in the current study. A comprehensivecomparison among these models is carried out in order to evaluate their performance and accuracy. Test results offlexural specimens with intermediate crack-induced debonding failurecollected from the existing literature are used in the current comparison. The effectivenessand accuracy of each model have been evaluated based on these experimental results. It is shown that the current modals are all conservative and inadequite to effectively mitigate intermediate crack-induced debonding in flexurally strengthened members.

Abstract: intermediate crack-induced debondingis one of the most dominant failure modes in FRP-strengthened RC beams. Different code models or provisions have been proposed to mitigateintermediate crack-induced debondingfailure.However, these code models or provisions cannot mitigate this failure mode properly. Recently, mew models have been proposed.Out of all the existing proposed models, five typical ones are investigated in the current study. These main available proposed models for mitigating debonding failure of externally bonded fiber reinforced polymer composites appliedto concrete is evaluated based on data obtained from experimental programs. It is shown that all the evaluated proposed models exhibit a high level of dispersion, they are not suitable for limiting the allowable tensile strain at the initiation of debondingof FRP laminates.