Integration of gradient based and response surface methods to develop a cascade optimisation strategy for Y-shaped tube hydroforming process design

In the last years a strong research effort was produced in order to develop and design new forming technologies able to overcome the typical drawbacks of traditional forming operations. Among such new technologies, hydroforming proved to be one of the most promising. The design of tube hydroforming operations is mainly aimed to prevent bursting or buckling occurrence and such issues can be pursued only if a proper control of both material feeding history and internal pressure path during the process is performed.In this paper, a proper optimisation strategy was developed on Y-shaped tube hydroforming process which is characterized by a quite complex process mechanics with respect to axi-symmetric tube hydroforming operations. The design procedure was aimed to properly calibrate the internal pressure histories. The basic idea, in this paper, is to integrate a steepest descent method with a moving least squares approach in order to reach the optimal internal pressure curve in the hydroforming of an Y-shaped steel tube. Thus, a cascade optimisation procedure was implemented which consisted of two optimisation steps: the former is focused on the application of a steepest descent method, the latter is based on a response surface approach utilising a moving least squares approximation. The cascade procedure was driven by the will to reduce the total number of numerical simulations necessary to reach the optimum with respect to other optimisation methods.     

Modelling the nucleation process in alumina lamellae deposited on a steel substrate

A one-dimensional model has been developed to address the non-equilibrium heat transfer between an alumina lamella deposited by plasma spraying, and a steel or alumina substrate. The model includes under-cooling phenomenon, heterogeneous nucleation and crystal growth kinetics, allowing for the prediction of the temperature evolution in the lamella and substrate and of the nucleation temperature, grain density and size distribution. The effect on the nucleation process of the contact angle between the nucleus and substrate surface and of the quality of the contact at the splat–substrate interface is emphasized. The influence of the splat thickness, substrate material and substrate oxidation on the grain size distribution is also discussed.     

地铁用高强度不锈钢弧形板冷弯成形过程的模拟及实验

针对不锈钢弧形板尺寸精度要求高导致成形工艺难度大的问题,以符拉索夫开口薄壁梁理论为基础,推导出符合高强度不锈钢弧形板成形过程中横向变形、纵向变形的能量计算式及弯曲角度的表达式,并编制出成形工艺。以理论计算为基础建立数学模型,模拟弧形板成形过程,根据在成形过程中出现的褶皱、翻边等问题对模型进行修正,增加侧辊,最终获得理想的板形。以成形过程中的轧制力大小及不锈钢弧形板成形后的回弹量;判定理论道次变形量分配的合理性。对合作企业的冷弯成形机组进行改造,依据最优仿真结果进行实验,反复修正后的工艺模型能顺利辊弯出高强度不锈钢弧形板产品,而且机组的轧制力能稳定,成形后的回弹量较小,产品质量满足用户精度要求。该研究对形成最优成形工艺,提高辊弯质量和精度具有重要指导作用。     

Ti6Al4V表面TiN/Ti复合膜的制备及摩擦学性能研究

采用直流磁控溅射法在Ti6Al4V表面制备TiN/Ti复合膜。分别用FESEM、GDEOS和XRD分析薄膜表面的成分及相结构;利用划痕仪分析膜基结合强度;通过球盘磨损机和轮廓仪测试磨痕形貌和磨损体积,评价膜层的摩擦学性能。结果表明,TiN/Ti复合膜表面致密光滑,呈金黄色金属光泽;膜基结合强度大于100 N;表面镀有TiN/Ti复合膜的Ti6Al4V合金虽没有减磨作用,但提高了耐磨性。     

The influence of dark feature on optical and thermal property of DC Arc Plasma Jet CVD diamond films

Different grades of CVD diamond films were prepared by 100 kW DC Arc Plasma Jet system. The films were characterized using optical microscope (OM), high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), and Raman spectroscopy. The results show that dark feature mainly is inclusions in CVD diamond films, the concentration are amorphous carbon and nitrogen. As for transparent optical grade diamond film, it has very high IR transparency and high thermal conductivity. The appearance of dark feature degraded the quality of CVD diamond film, apparently influencing IR transparency and thermal conductivity. But even in optical grade diamond film, there are very strong absorption features in the 7–9 μm region, this will limit the practical applications of diamond films grown by Plasma Jet as IR windows for CO₂ lasers.     

Hydrogen production from CO2 reforming of methane over high pressure H2O2 modified different semi-cokes

H₂O₂ was used under different temperatures and pressures to activate three kinds of different semi-cokes. FTIR, BET, SEM and Boehm titration were used to analyze properties of the semi-cokes surfaces, finding that catalytic activities of these semi-cokes after modification by high temperature and high pressure H₂O₂ were improved. FTIR shows that the characteristic infrared absorption peak of functional groups on the semi-cokes surface does not change, but the absorption peak intensity of some functional groups is increased. The strength of OH absorption peak of Hongce lignite (HCL) semi-coke at 3444 cm⁻¹, carboxyl CO at 1598 cm⁻¹, aliphatic ether, cyclic ether and other organic functional groups at 1023 cm⁻¹ in the modified Shenmu bituminous(SMB) semi-coke and Jincheng anthracite (JCA) semi-coke are increased significantly. BET finds that the specific surface area and pore volume of three semi-cokes are increased after modification. Boehm titration shows that the basic functional group content in semi-coke is increased after modification, and the net alkali content is increased significantly. Compared with the raw semi-coke, SEM shows that the surface of semi-coke modified with H₂O₂ becomes rough. Modified JCA semi-coke surface pitted with holes, modified HCL and SMB semi-coke surface present porous.     

Ti13Nb13Zr 合金离子氮化层的摩擦磨损性能研究

目的提高医用钛合金的耐磨损性能。方法应用等离子渗氮技术在Ti13Nb13Zr基材上制备改性层,并对改性层组织、成分及硬度进行测试。利用往复磨损试验机研究改性层在干摩擦条件下的摩擦磨损性能,并与未处理的基材进行对比。结果 Ti13Nb13Zr合金表面经渗氮后形成致密均匀的改性层,硬度高达1110HV0.025,改性层的磨损体积约为基材的1/23。结论等离子渗氮技术有效地改善了Ti13Nb13Zr合金的摩擦磨损性能。     

Design and preparation of high permeability porous mullite support for membranes by in-situ reaction

The natural mineral kaolin combined with alumina additives Al(OH)₃,α-Al₂O₃ and AlF₃ was used to prepare porous mullite ceramic membrane supports using an in-situ reaction. The effects of composition and sintering temperature on the sintering behavior, pore structure, permeability and microstructure of the resulting porous mullite supports were extensively investigated. The experimental results showed that excess SiO₂ in kaolin can be consumed by adding alumina precursors, which resulted in a stiff skeleton of interlinked needle-like mullite crystals in-situ during the sintering. The needle-like mullite crystals touched each other and formed a short network, which acted as a porous skeletal network structure. This network resulted in a highly permeable porous structure. The resulting support is suitable for the preparation of asymmetric ceramic membranes. The densification and pore structure of the support can be effectively adjusted by control of the quantity of alumina precursors in the composition and the sintering temperature. Sintering the subject mullite compositions at 1500 °C for two hours resulted in support structures with an average porosity of 45.9%, an average pore size of 1.3 µm and a penetrating porosity of 35.9%.     

Plasticity improvement for dendrite/metallic glass matrix composites by pre-deformation

The mechanical properties of in-situ metallic glass matrix composites (MGMCs) are investigated by tensile pre-deformation, followed by compression. The pre-deformation is utilized to exploit notable increases in plasticity, accompanied by slight increases in the compressive strength, and the deformation mechanisms are explored. The increased free volumes in the glass matrix after tensile pre-deformation contribute to the decrease of the Young's modulus of the glass matrix and lead to the increase in the stress concentration, promoting multiplication of shear bands. When the Young's modulus of the glass matrix matches that of the dendrites, the plasticity of in-situ dendrite-reinforced MGMCs is the optimized. Matching Young's modulus opens a door to design the MGMCs with excellent plasticity and remarkable work-hardening capability.