Advanced Materials Research Vols. 154-155

Abstract: Viscous pressure forming (VPF) uses a highly viscous but flowable material as pressure-carrying medium (PCM). Due to the relative low flowability of viscous medium compared with fluid, nonuniform pressure distribution in viscous medium can be used to control and regulate the deformation sequence of the workpiece through controlling the loading mode of viscous medium. In the present study, viscous pressure bulge (VPB) tests with three kinds of loading location of viscous medium (central zone, corner zone and the whole deformation zone) are conducted and the influences of loading location of viscous medium on sheet deformation behavior are investigated via numerical simulations and experiments. It is found that changing the loading location of viscous medium can greatly affect the deformation behavior of sheet metal. When the viscous medium is injected from the die corner zone, a local high pressure formed at the corner zone of sheet metal and a higher limiting dome height and strains are obtained.

Abstract: Under condition that exact values of model parameters can not be calculated accurately in hot tandem mill system and change with the time passing, model parameters are identified by adopting identification method based on the parameter model and sampling the datum on site; Basic automation system is used for the sampling of actual data, MATLAB software is adopted for curve fit. By comparing the experimental data and simulation data, the consequence of simulation testifies the accuracy of identified mathematical model.

Abstract: A201 aluminum alloy plate castings with systematic change in the riser size, together with variation of thickness and length, were cast in different kinds of molds to find out the influence of cooling rate on the mechanical properties and porosity content. The sand molds with end chill for the plate castings were made of 100% silica sand (type A mold), 50%silica sand/50% chromite sand (type B mold) and 100% chromite sand (type Cmold). Both the porosity content and mechanical properties of A201 aluminum alloy plate casting are governed by the cooling rate. Both of tensile strength and elongation are reduced when the porosity content becomes more.

Abstract: This study investigates the feasibility of EDM for processing ZrO2 and Al2O3 of non-conductive ceramics, which were covered by an assisted conductive material, an adherent copper foil, on the workpiece surface. The conductive material adhered on the surface of the non-conductive ceramics would induce a series of electrical discharges between the tool electrode and the workpiece in the initial stage of the EDM process. Thus, the pyrolytic carbon that cracked from kerosene was formed and deposited on the machined surface to maintain the progress of EDM. In this work, the essential EDM machining parameters were varied to determine the effects on material removal rate (MRR), electrode wear rate (EWR), and surface roughness. The stability of EDM progress and the surface integrities of ZrO2 and Al2O3 machined by EDM were also investigated. The aim of this study is to explore the feasibility and development of an applicable process for processing non-conductive ceramics through EDM. Moreover, the exploitation of this work can be applied to industrial applications and used to develop machining techniques for non-conductive ceramics.

Abstract: Compared with unipolar and periodic reverse pulse current electroforming, bipolar pulse current in electroforming is known to result in better precision and surface finish. In this paper, bipolar pulse current electroforming is introduced. The influencing parameters, such as electrolyte parameter, additives, current density, PH value, temperature and pulse current parameters have been studied on experiments. Experiments on nickel and nickel alloys electroforming on micro optical aspheric moulds have been done. The results indicated that bipolar pulse current could improve the quality and precision, reduce internal stress in micro electroforming.

Abstract: The magnetic moments of Co3 clusters on Cu(111), Pd(111), Ne(111) and two polar ZnO surfaces non-magnetic substrates are investigated using first-principles methods based on density-functional theory. Calculated results reveal that the Co magnetic moments are strongly affected by the geometrical structure of the clusters, the interactions between magnetic adatoms and the substrates. Moreover, it is found that the magnetic moments of Co3 clusters on diverse substrates are quite different. Meanwhile, the orbit annihilating induced from the crystalline field of the substrates and the electron transfer from Co3 adatoms to the substrate atoms are used to explain the different change of the average magnetic moments of Co3 on Cu(111), Pd(111), Ne(111).

Abstract: The 40Cr steel surface waiting for being welded was ultra-fined through laser quenching, and isothermal superplastic solid state welding was conducted between the 40Cr steel and Cr12MoV steel. The mechanical properties of the joint were evaluated by tensile testing and microhardness of the joint and thereby. The microstructure of 40Cr steel’s quenching layer and the joint interface zone was observed and analyzed using scan electron microscope. The experimental results show that ultra-fine microstructure is achieved in the 40Cr steel’s surface waiting for being welded. The superplastic solid state welding can be carried out under welding parameters including welding temperature of 800 , pressure welding time of 4 min and initial strain rate of 1.5×10-4 S-1. The tensile strength of joint achieves 81.94% that of 40Cr steel. The microhardness of transition region in the Cr12MoV side is higher than other region. On the contrary, the microhardness in the 40Cr side is lower than other region. The new M7C3 type carbide is checked in the Cr12MoV side. In welding process, the carbon atom has diffused from 40Cr steel side to Cr12MoV steel side. Therefore, isothermal superplastic solid state welding with higher quality can be realized between Cr12MoV steel and the 40Cr steel after microstructure ultra-fining through laser quenching.

Abstract: The effects of rolling parameters on the broadwise deformation of the workpiece are analyzed by rigid-plastic finite element method. At the basis of better grasping the effective law on freedom broadwise deformation ,the effects of the Oval height and Oval width on the Forced /Restricted broadwise deformation in rolling process are analyzed. Considering the equivalent strain,the effects of the Oval height and Oval width are gotten again using the related strain data in the DEFORM-3D post-processing.

Abstract: The formation, flight and penetration process of explosively formed projectile (EFP) was computed by using nonlinear dynamic finite elements code AUTODYN-2D. 10# steel and Copper are chosen for EFP material calculation and Quasi-spherical EFP was technically designed for small-bore warhead, the configuration of EFP with these two kinds of material was optimized respectively. The decay equation of projectile velocity was used to analyze the velocity variation of Quasi-spherical EFP, the impact velocity was obtained. Characterization of EFP penetrate into A3 steel plate was analyzed by compare the results of 10# steel and Copper, EFP made of these two kinds of material are capable to perforate A3 steel plate with a thickness of 0.45 times diameter of charge.

Abstract: Effects of oxygen atom adsorption on work functions of Mo(110) surface and substrate are investigated using first-principles methods based on density functional theory. The calculated results reveal that there exist a most probable site (named f1 site) in the surface oxygen adsorption on Mo(110) surface. Moreover, it is found that work functions of oxygen-adsorbed Mo(110) increase with increasing oxygen coverage, while the adsorption energies of oxygen decrease with increasing oxygen coverage. For a given oxygen coverage such as 0.333ML with surface f1 site, the work functions are insensitive to the distribution of oxygen atoms. In the meantime, the relationship among charge density, surface dipole density and the work function are discussed.