This study demonstrates the control of crystal phase of zirconium oxide (ZrO₂) nanoparticles synthesized from zirconium basic carbonate via supercritical hydrothermal method. The pH of the slurries of starting materials was adjusted using acetic acid. The lower pH reduces the amount of tetragonal phase of ZrO₂ nanoparticles, which are stabilized by CO₂ adsorbed on their surfaces. Single-phase monoclinic ZrO₂ nanoparticles are achieved at a pH of 3.0. This is because the pH of the slurries of the starting materials affects the states of CO₂-H₂O system. These results will lead to large-scale industrial production of phase-controlled ZrO₂ nanoparticles.

In this study, we systematically investigated the effects of number of laser scans per layer (once and twice) combined with two different laser powers (140 W and 400 W) on the porosity, microstructure, hardness, and residual stress values of martensitic stainless steel SUS420J2 fabricated by the laser powder bed fusion (LPBF) method. As a result, there was a significant difference in porosity depending on the laser power when laser-scanned once per layer. However, laser-scanned twice per layer, the porosity was decreased by the progress of melting. There were no significant differences in the constituent phases of each material, because the cooling rate during solidification was high regardless of the laser power or the number of laser scans per layer. On the other hand, in all materials, the volume fraction of the retained γ phase in the middle and lower area were higher due to the thermal effect from the upper layers during build up layers, and the hardness values became lower comparing with the upper area. When the laser power for the first scan was low, the porosity remained high even though laser-scanned twice per layer, so the residual stress value also remained low. On the other hand, when the laser power for the first scan was high, the very low porosity caused the generation of high residual stress. Furthermore, when laser-scanned twice per layer, although the stress was redistributed by remelting, the residual stress value increased because the strain caused by resolidification was added.

The properties of slurries were examined for controlling the thickness of the coat-layers which were vertically drawn from the pool of catalytic nanoparticle alumina suspension. The present slurries showed non-Newton flow behavior and the thickness increased with the increase of the solid concentration. The pseudoplastic flow at low shear rates changed to the Bingham flow in which the plasticity viscosity was obtained in high shear rate region. The relation among various parameters was checked and examined toward the use of the theoretical relation in the Newton fluid to obtain a layer thickness. We found the possibility of the method that could estimate the thickness of coat layers if the plasticity viscosity of the Bingham flow region was applied. The results showed the partial consistence between experimental and calculated thickness of thin layers. The factors of inconsistence were discussed in details using the schematic model which contained the transition phenomenon between the pseudoplastic flow and the Bingham flow. The film-drawing procedure under the high shear rate condition was suggested for better controlled thickness.

Carbon nanotube grafted carbon fibers (CNT-CFs) have high fiber-matrix interfacial shear strength and excellent resin impregnation properties, suggesting their potential to enhance the mechanical properties of Carbon Fiber Reinforced Thermoplastic (CFRTP) laminates. However, when CNT-CFs are used as a reinforcement for CFRTP laminates, it has been reported that aggregated CNTs can hinder resin impregnation and act as crack initiation sites. Therefore, it is necessary to control the density and diameter of CNTs grafted on the carbon fiber surface. In this study, carbon fibers with grafted in low density, large-diameter CNTs were grafted by using Ni, which was electroplated with pulse current as a catalyst. Micro-droplet tests, three-point bending tests, and DCB (double cantilever beam) tests were performed to clarify the effect of CNT grafting on carbon fibers. The CNT-CFs showed high fiber-matrix interfacial shear strength, and CFRTP laminates with these CNT-CFs exhibited high bending modulus. However, their bending strength and mode I fracture toughness showed low value. During the bending test, CFRTP laminates with these CNT-CFs buckled easily, and the fracture surface had areas where the fiber surface was exposed. This was also observed on the fracture surface of the Mode I fracture toughness test. These results indicate that while CNT-CFs have a high fiber matrix interfacial shear strength, the interfacial adhesion strength perpendicular to the fiber axis remains low. Therefore, it is necessary to develop a method to firmly bond CNTs to the carbon fiber surface.

In adhesive joints, debonding usually starts from the interface edge due to the singular stress field at the edge. This is the reason why adhesive strength can be expressed as a constant ISSF (Intensity of Singular Stress Field). However, since the singular stress field and the singularity index vary depending on the local edge geometry at the interface end, the ISSF method cannot be applied to such different local geometries directly. In this study, therefore, a fictitious edge interface crack is assumed at the interface end to evaluate the adhesive strength for different local geometries. In this paper, first, the general expression of the SIF (Stress Intensity Factor) of an edge interface crack useful for butt joint are shown. Next, this edge interface crack method is applied to evaluate the adhesive strength of the lap joints when the local geometries at the interface end are different. The results show that the critical SIFs K_1c are almost constant for all local lap edge geometries. Finally, based on the lots of previous experimental results, the critical values of K_1c are compared for butt and lap joints. Then, it is found that the average strength of lap joints obtained by the edge interface crack method is about five times larger than that of butt joints. In this way, the edge interface crack method is shown to be useful for effectively evaluating the adhesive strength with various geometries and loading.

The ball-bat coefficient of restitution (BBCOR) and surface hardness of amateur wooden baseball bats available in the market were measured to clarify the effect of the surface hardness on restitution performance. As the impact velocity of the ball increased, the BBCOR decreased, and the rate of decrease differed depending on the bat. Therefore, when evaluating the BBCOR ratio at an impact velocity of 180 km/h compared to 120 km/h, the bats were divided into two groups: one in which the BBCOR decreased monotonically and one in which the BBCOR did not decrease up to 180 km/h. The relationship between the BBCOR ratio and the surface hardness or coating hardness is discussed. The Leeb hardness was measured as the surface hardness and the nanoindentation hardness was measured as the coating hardness. Except for two bats with significantly different coating hardnesses, it was found that the BBCOR ratios were related to the surface hardness. The bats with high and low coating hardness had the highest and lowest BBCOR ratios, respectively. Furthermore, when the cross sections were observed using a microscope, one of the bats with high surface hardness and BBCOR ratios underwent deformation by physical external pressure. These findings suggest that the BBCOR of wooden bats is related to surface hardness and coating hardness, and compression of the wood surface could affect BBCOR. In the industrial production of wooden bats, it would be useful to evaluate not only the density and defects such as knots, but also the surface hardness of the wood and coating hardness.

This study investigates the feasibility of integrated injection molding using wet-treated metal surfaces. AMALPHA treatment, a wet process, achieves high bonding strength and airtightness, potentially reducing processes for molding urea water identification sensors in diesel vehicles. We explore the impact of wet processing on bonding interface shape, evaluating its effect on automotive sensor component hermeticity and durability. Joint strength tests were conducted on the AMALPHA treatment to infer the effect of surface conditions on fracture strength and the fracture process. We fabricated a prototype sensor component under conditions of sufficient bond strength and assessed its performance through testing. From the high-temperature urea water immersion test as a durability test, it was considered that urea water causes the formation of interface defects. An anchor shape by wet processing with sufficient durability as a joining method for actual sensors could be obtained.