Advanced Materials Research Vol. 325

Abstract: Glass transition is the most important factor in the thermo-forming of glass elements of precise geometries such as optical glass lenses. Among many attempts to model the physics of glass transition, the Master equations based on the potential energy landscape (PEL) appear to be apropos. In this study, we used Monte-Carlo approach to approximately solve the master equations and further implement the Monte-Carlo method in the finite element simulation. We used Selenium as an example since its PEL has been quantified. Through the FEM simulations, it is found that the geometrical replication quality is the best when the forming is performed at the viscosity around 10⁵~10⁶ Pa×s, that the residual stress developed in the cooling process can be minimized in the slow cooling process or through post-annealing process after moulding.

Abstract: Glass molding press (GMP) was applied to the fabrication of glass aspherical Fresnel lens for high-efficiency mass production. A pair of molds for the Fresnel lens was precisely fabricated on the Nickel Phosphorous (Ni-P) plating layer by the single diamond cutting with multi-axis machining center. A kind of low transition temperature (T_g) glass was heated to several tens degree centigrade above its T_g and compressed between the two molds. In this way, the shape of the mold was replicated to the glass lens surface. The molding process was simulated by finite element method (FEM), and the molding condition was optimized to minimize the residual stress.

Abstract: In this paper the effect of addition of zirconia and talc as sintering aid has been investigated on mechanical properties and sintering behavior of boron carbide. Different amounts of these materials mainly 0-30 wt% were added to the starting powder and sintered at two different temperatures, 2050°C and 2150°C. Examination of the samples revealed that the both materials improve sintering behavior and mechanical properties of boron carbide. However, talc which is more abundant compare to zirconia could be a proper substituent for zirconia in this system.

Abstract: In this research, deformation behavior of titanium sheet in laser forming was simulated. In preliminary experiments, we had carried out single-straight-line bending and investigated the relationship between the bended angle and the laser processing conditions. It was clarified that the bended angle formed by laser forming to the free edge became larger than the angle formed by laser forming to the center, even if laser scanned in same processing conditions. To investigate the influence of the free edge, heat-transfer analysis and structural analysis were carried out by using a finite element analysis software ANSYS 11.0. It was confirmed that the bended at the free edge became large because the plastic strain of the lower surface has decreased greatly more than the strain of the upper surface decreases.

Abstract: In the paper, a crystal plasticity finite element method (CPFEM) model was developed based on ABAQUS to analyse the surface roughness transfer during metal manufacturing. The simulation result shows a good agreement with the experimental result in the flattening of surface asperity, and the surface roughness decreases significantly with an increase of reduction with considering friction effect. Lubrication can delay surface asperity flattening. The effect of surface roughness on produced metal defect (crack) was also studied, and the surface roughness affects the crack initiation significantly in cold strip rolling. In addition, the surface roughness variation along the metal plate width contributes to stress distribution and then inhibition of crack nucleation.

Abstract: The shot peening process is one of the surface treatments. In this process the peening effects are characterized by the fact that the surface layer undergoes large plastic deformation due to the collision of shots. The effects are greatly influenced by the processing history or the thermal history of material. Little is known about the relation between hardness of the shot peened surface and the processing history of materials. In the present study, the effect of heating and subsequent re-shot peening on the surface characteristics of the shot-peened carbon steel was investigated. Shot peening was performed with an air-type machine using cast steel balls. Hardness and compressive residual stress in the re-shot peened workpieces were measured. When the heat treated workpiece was re-processed by shot peening, surface hardness and fatigue life of carbon steel were improved. It was found that the surface characteristics of the peened carbon steel were improved by heating and subsequent re-shot peening.

Abstract: In general, shot peening is a surface treatment that improves the performance of engineering components, since application of surface compressive stresses reduces the tensile component of stress. In the shot peening process, the medium consists of small spheres, which are usually made of high-carbon cast steel; the diameter of the spheres is in the range from 0.3 to 1.2 mm. More recently, a new type of microshot has been developed to enhance the peening effect. The diameter of the new spheres is in the range from 0.02 to 0.15 mm. The effect of microshot peening on the residual stress of spring steel was investigated. The projective method of the microshot was of the compressed air type. The microshot of 0.1 mm diameter was high-carbon cast steel and cemented carbide, and the workpiece used was the commercially spring steel JIS-SUP10. The effect that process variables such as shot speed and peening time have primarily on residual stress was studied. The surface layer of the workpieces was sufficiently deformed by microshot peening. The residual stress was observed near the surface. At a large number of cycles to fracture, microshot peening can more effectively enhance the fatigue strength. The use of hard microshots such as cemented carbide was found to cause a significantly enhanced peening effect for spring steel.

Abstract: Fine Particle Peening (FPP) treatment, where the surfaces of materials are bombarded with fine shot particles, can transfer shot particle elements on the treated surface. In order to create nanocarbon-transferred surface with FPP treatment, hybridized particles combining steel cores and nanocarbon surface layer are proposed. Mixing with mechanical mortar creates attached layer of carbon-black powders on surface of steel cores, resulting in formation of hybridized particles. FPP using the hybridized particles significantly increases carbon elements on AISI304 steel substrate. This is because of transfer of carbon-black from hybridized particle. Transfer of carbon-black is enhanced when the hybridized particles with high hardness cores are employed. It is revealed that the hybridized particle proposed in the present study is effective to create the modified layer accompanied with transferred nanocarbon.