Advanced Materials Research Vols. 476-478

Abstract: The effects of hydrogen on friction and wear properties of Ti–6Al–4V alloy sliding against GCr15 steel were investigated through dry sliding friction and wear tests in atmosphere at room temperature. Wear mechanism was determined by studying the morphology and chemical element of worn surface using SEM and EDS. Results show that friction coefficient decreases slightly and wear rate increases after hydrogenation. Wear mechanism is discussed.

Abstract: A new composite ceramics of Si₃N₄/ SiC were prepared by a two step sintering method with SiC powders and Si powders as main material. Its properties and structures were characterized by the porosity, bulk density, flexural Strength, XRD, SEM and EDS. The effects of particle grade and sintering temperature on its properties were studied. The results show that bulk density of powders is the largest when coarse powder of SiC (average diameter 120 um) is about 40% (by weight), with average diameter 80um of SiC is about 20% (by weight) and fine powder (average diameter 35 um) of of SiC is 10% (by weight). A minimum porosity, a maximum bulk density and flexural Strength were achieved by nitriding at 1450 °C for 2h and then two states sintering at 1700 °C. XRD analysis indicated that the the main crystalline phase of the ceramic made from α-SiC, α-Si₃N₄ and β-Si₃N₄. SEM and EDS analysis indicated that a larger of wisker like α-Si₃N₄ and some little β-Si₃N₄ are found coating with SiC, giving its excellent mechanical properties.

Abstract: The 22wt%WAl₁₂ intermetallic particulate reinforced Al-based matrix composite was successfully fabricated by press-forming technology using high-energy ball-milled powders. X-ray diffraction analysis shows that WAl₁₂ reinforcement phase has been obtained after in situ reaction of Al matrix with W₁₄Al₈₆ alloy at 620°C. The mechanical properties of the composite material were studied at room temperature. The Young’s modulus, microhardness and the maximum ultimate tensile strength of this composite material can reach 75GPa, 1.51GPa and 471MPa, respectively. The results show that there is a good interfacial bonding between the Al matrix and WAl₁₂ particles. However, the composite cannot be applied in high temperature environment because of its fairly low strength residual ratio.

Abstract: Recycled general-purpose plastic, polypropylene gained general acceptance because of its excellent properties. At the moment, most of experimental tests of short-natural fibers reinforced polymer composites have been concentrated on macro level, lead to un-matured of fine, micro mechanics research work. In this paper, flexural property of short flax fiber-reinforced polypropylene composites was numerical estimated using a FEM model. It has been observed that initial modulus of the composites increases with the rise in fiber volume fraction, while short fiber orientation distribution has little effect on composites; the stress-strain curves almost have no change.

Abstract: Failure prediction of laminated composites is performed by progressive failure analysis method. A modified form of Hashin’s failure criterion by Shokrieh is used to detect the failure, where a sudden degradation model is proposed to reduce engineering material constants. The numerical analysis of composite laminates is implemented in ANSYS Parametric Design Language (APDL) with commercial finite element codes ANSYS. The method can predict the initiation and propagation of local damage and response of laminated composite structures from initial loading and ultimate failure. The model has been validated by comparing numerical results with existing experimental results. And then failure analysis specimen fabricated from M40J/Ag80 and investigation on influence of stacking sequences and fiber orientations under in-plane compressive loading have been performed by the proposed model.

Abstract: A new surface reconstruction algorithm is presented for unorganized 3D points in this work. By properly building a graph, the surface is shown to correspond to the minimum s-t cut of the graph. In addition, since our proposed algorithm is based on the three dimensional Delaunay triangulation, it is guaranteed the reconstructed surface is composed by the patches with fine shapes in the Delaunay tetrahedra. Besides, the reconstructed surface can interpolate the input data and can also decimate the outliers automatically through proper adjusting the parameters. The experiments indicate our algorithm is practical and easy to implement.

Abstract: In this paper, according to the characteristics of the sheets of poor plastic at room temperature and good plastic which is significantly increased after heating, the mechanical properties, microstructure evolution, the flow stress, plane anisotropy and fracture mechanism of AZ31 magnesium alloy sheets at high temperature are studied and analyzed, which provide a reliable basis for the stamping processes of the sheets at high temperature. The most suitable heating temperature for deep drawing sheets of AZ31 magnesium alloy are achieved by the hot-stamping test, and the most suitable heating temperature are near to 350°C. The results for the improvement of the hot-formability of AZ31 magnesium alloy sheets at high temperature provide a theoretical basis and new method.

Abstract: In order to determine the mechanical properties of the carbon/polyurethane composite laminate with splicing ply, the tensile testing were performed on laminate specimens which has been designed specially. The tensile elastic modulus and tensile strength were obtained from the experimental datum. The breakage happened in place of joint gap. The stiffness of the composite laminate was affected by the oblique splicing ply significantly, but the strength is mainly determined by the continuous layers. The laminate is failure in low load. The numerical analyses using linear elastic and progressive damage model were conducted with the commercial the finite element model (FEM) software ABAQUS. The linear elastic FEM is established to calculate the inter-laminar stress. The progressive model is used to predict the strength on the basis of numerical computation. There are three different criteria used here in the strength prediction. By combining the damage model with classical lamination theory, the behavior of laminates under plane stress loading is predicted. The results show that the experimental tests are in good agreement with the finite element simulation.

Abstract: The effects of the interface in alumina fiber reinforced Al-Si alloy composites prepared by squeeze casting on the wear resistance of the composites were studied. The results indicated that the fiber combined with the matrix well in the composites and had reinforcing effect on the alloy. The interface in the composites could hold back crack propagation, and the composites had the excellent wear resistance. The alloy elements in the matrix were favourable to forming the good interface to improve wear resistance of the composites.

Abstract: The machining coordinate system of spiral bevel gear machine tool is established through analyzing the machining mechanism of spiral bevel gear, and the three dimensional structure model of large scale spiral bevel gear machine tool is also established using the new cutting feed method. The numerical control machining model of large scale spiral bevel gear machine tool is proposed. Finally, the machining simulation of one pair of given large scale spiral bevel gears has been done, the result indicates that the machining simulation model meets the prospective design requirement.