Key Engineering Materials Vols. 656-657

Abstract: Gloss of a metal surface is an important aspect for product quality evaluation. Evaluating the specular reflection is almost the same as evaluating the gloss. We propose a method that uses patterned area illumination to evaluate specular reflection. In specular reflection, the angle of incidence equals the angle of reflection. Consequently, when light (ray) of the area illumination, which has a striped pattern, are projected on a glossy metal surface, a striped pattern forms on the reflected image as a mirror-like reflection, and the sharpness of the striped pattern of the image provides information about the specular reflection on the surface. This characteristic is applied to a metal with a hairline surface finish. A hairline surface presents different glossiness at different viewpoints. When the direction of the striped pattern of illumination is changed, the sharpness of striped pattern on the reflected image varies owing to the surface roughness of the hairline finish. Therefore, we can evaluate the glossiness in various directions by rotating the pattern. The relationships between gloss evaluation value and surface roughness were indicated in our study. We tried the reproduction of the gloss evaluation by ray tracing to obtain the more detailed relationships between them. Ray tracing is a technique to generate an image in computer graphics. The approximate reproduction of gloss evaluation was obtained by the simulation.

Abstract: We have proposed a new cold processing method to enlarge the diameter of a short section of a metal shaft using a combination of a cyclic bending load and an axial compressive load that is lower than the yield stress of the sample material. We call this cold processing method the diameter-enlargement working method, and refer to the enlarged section of the processed shaft as the diameter-enlargement section. The processing method produces large plastic deformation, and its key features are as follows: the diameter-enlargement deformation progresses easily under a low axial compressive load at room temperature and the processed part exhibits little temperature increase. However, a crack is generated in the notch near the diameter-enlargement section during processing, and the cause is not yet clearly understood. Therefore, we conducted processing experiments to clarify the crack generation conditions, and simulated the working process using the finite element method to investigate the behaviors of stress and strain during processing. Furthermore, we calculated the low-cycle fatigue damage in the processed shaft using the Manson–Coffin expression. This study clarifies the mechanism of crack generation during processing and evaluates the fatigue strength of the processed part.

Abstract: Single Point Incremental Forming (SPIF) has become a popular technology of forming sheet materials in the recent decades. However, the springback phenomenon, an inborn property of almost all elasto-plastic materials, reduces the precision of dimensions of the products by the finished forming session. This paper attempts to find out a measure to minimize this unwanted obstacle by using both empirical and simulating methods in order to define the relations of springback values among the forming parameters such as diameter of the forming tool, its revolution per minute, its velocity and its feed rate. Analyzing these equations to extract the appropriate parameters of forming for enhancing the precision of SPIF products is the final aim of this paper.

Abstract: Cracking behavior of positive electrode-electrolyte-negative electrode (PEN) assembly in a planar solid oxide fuel cells (pSOFC) during thermal cycling are investigated by using a commercial finite element analysis (FEA). The stress intensity factor for various combinations of surface crack size of 1 μm, 10 μm, and 100 μm and shape of semi-circular and semi-elliptical at highly stressed regions in the PEN are repeatedly calculated at room temperature and steady stage for twenty cycles. Simulation results indicate the stress intensity factor is significantly decreased at room temperature and is slightly increased at steady stage with increasing number of cycle. However, all the calculated stress intensity factors during thermal cycling in the present investigation are less than the corresponding fracture toughness given in the literature.

Abstract: Tensile strength, metallographic and structural analyses of anodized aluminum sheet–copper sheet dissimilar welds produced under various friction stir welding (FSW) conditions were conducted. The 6061 specimens were heated to 530~570 ^oC, held for 1 hour, followed by water quenching and furnace cooling. AA 6061-T6 Al sheets were anodized to thicknesses of 5μm and 12μm, respectively. FSW joints were characterized using microstructural analysis, microhardness measurements and tensile testing. The tensile strength of the 6061-T6/6061-T6 joint using FSW is 145 MPa. However, the tensile strength of the 6061-T6/Cu joint using FSW is decreased to 100 MPa. When the anodized layer was increased the tensile strength of the 6061-T6/Cu joint using FSW was decreased to a value below 50 MPa. Increasing the anodized layer thickness disturbed material mixing and the formation of increasing amounts of oxide rich structures. The oxide phase content and the mixed area homogeneity were increased with increasing layer thickness, decreasing the tensile strength of the FSW joints.

Abstract: Since the fiber drawing speed continues to increase in the modern mass manufacturing of optical fibers, the effects of viscous heating on the coating liquid flow could be significant in the capillary coating die of optical fiber coating applicator. Present study investigates the viscous coating resin flows in the micron-sized channel of coating die with temperature dependent viscosity. The computational results find the substantial temperature increase near the die wall and plug-like velocity distribution due to localized viscous heating. Also, final coating thickness is affected by the change of coating die diameter when the fiber drawing speed is high. Thus, the design of glass fiber coating process at high drawing speed requires careful consideration of several key operational parameters.

Abstract: In the 1960s, Opitz discovered the formation of complex oxide protective layers (Belag) on worn surfaces of tools when cutting Ca deoxidized steel. Belag formation is used in a free-cutting technique for steel and cast iron because it significantly reduces diffusional wear by preventing direct contact between the tool and work material; hence, tool life can be dramatically prolonged. For Belag to form, one condition is that the tool material should contain TiC. It has been reported that Belag adheres to tool surfaces because TiC in the tool oxidizes and reacts with Belag. Our study aims to clarify the formation and adhesion mechanisms of Belag. In this study, Ca deoxidized steel was machined with noncoated carbide P10 tools, and the state of the interface between the tool and Belag layer was investigated by transmission electron microscopy (TEM) and elemental analyses. As a result, we found that Belag directly adhered to Ti carbide (Ti–W–C) particles on tool surfaces. In contrast, Belag did not directly adhere to WC or Co on tool surfaces. Unlike previous studies, we could not confirm the formation of the TiC oxide or its oxide layer near the interface to which Belag adhered. In addition, when we machined a Ca deoxidized steel containing MnS, a CaS layer formed in Belag at the interface between the tool and Belag layer.

Abstract: A computer generation holography (CGH) is proposed herein to synthesize square-matrix light spots. Such a design of CGH is possible by reducing the 2-D problem to two 1-D problems. The both 1-D CGHs are designed with the conjugate-gradient method and verified with the Fresnel-Kirchhoff diffraction theory. This quantized 8-levels CGH is fabricated by using optical contact lithography and reactive-ion etching techniques. Measurement demonstrates that the fabricated CGH has the desired optical function, i.e., it forms square-matrix light spots in the image plane at a distance of 40 mm from the CGH. The developed CGH can be applied to the laser patterning system by optical projection and direct etching.

Abstract: A modified large-size MOCVD reactor is developed to produce uniform and large-volume epitaxy thin film layer of gallium nitride (GaN). The full governing equations for continuity, momentum, energy and chemical species are solved numerically. It is investigated how thermal flow field, and the operating parameters affect molar concentration of each reactant, and the thin film uniformity. These parameters are involved such as the chamber pressure (100-700 torr), susceptor rotation rate (100-800). In this paper, the simulation results from these listed parameters shows that an optimum epitaxy layer can be achieved in the large-size reactor.

Abstract: Interaction between granular solids and boundary structures is a fundamental problem encountered in bulk solids handling and subsurface structural design. Current understanding of its mechanism has not been adequate for robust and economical engineering designs, especially for flexible boundary structures. A classic and essential example is uniaxial compression of dry granules in a deformable cylindrical container, where the response of the confined granules under axial loading and the load transmission to the contacting structure still remain not fully understood. This paper comparatively studies such a confined compression scenario using a newly developed numerical procedure (Linked DEM-FEM) and a conventional FEM approach. The examined system involved around 7700 polystyrene beads contained in an acrylic thin-walled tube supported at one rim and gagged by two end platens. The compression was applied by displacing one end platen at a constant rate while fixing the other. Characteristics of the compression system, including load-displacement response, force transmission to boundary structure, mobilised bulk wall friction coefficient, and stress distribution on the wall, were evaluated. The majority of the compared physical quantities show reasonable to good agreement, thus giving a convincing quantitative verification for both approaches.