Papers by Author: Tetsuya Nemoto

Abstract: This paper describes the results of an experimental investigation on the drop off impact test on a range of sandwich panels. The magnesium alloy sandwich panels were fabricated with rolled sheets at different thickness by pressing and bonding method. Out-plane compression test was employed to obtain its basic deformation-force behavior. The impact experiments were carried out in which a steel cylinder was dropped off at various height levels, ranging from 0.5m to 1.5 cm to impact the panel. A high speed camera was employed to take pictures at 20 thousand frames per second and the low-velocity impact response on the sandwich panels is recorded with a dynamic force senor under the panel simultaneously. The shock response with time and the impact absorption energy were analyzed and compared. The results of this study proved that the magnesium alloy honeycomb sandwich panels have good impact energy absorption performance.

Abstract: Magnetic nanoparticles are widely used in magnetic fluid, magnetic grinding materials, magnetic controllers, magnetic sensors, biomedicine fields and so on. Recently, more and more attentions were focused upon DDS (Drug Delivery System). In this study, Magnetite nanoparticles about 8nm size were synthesized by liquid phase precipitation method. Then the nanoparticles coated with surfactant were dispersed throughout kerosene and inject the solutions into biomaterials. Using strong photon beams in SPring-8 facility, we observed the distribution state and the effect of magnetic field on the behaviour of nanoparticles in biomaterials.

Abstract: Water cavitation peening (WCP) with aeration is a recent promising method in the surface enhancement technique, which can induce compressive residual stress in the near surface of mechanical components by the bubble collapse on the surface of components in the similar way as conventional shot peening. In this paper, the effect of WCP on fatigue crack growth behavior was investigated in single-edge-notched flat tensile specimens of S45C steel. The notched specimens were treated by WCP, and the compressive residual stress distributions in the near surface layer were measured by X-ray diffraction method. The tension-tension (R = Smin/Smax = 0.1, f = 10 Hz) fatigue tests were conducted. A Shimadzu servo-hydraulic fatigue test machine with in-situ observation by JSM-5410LV scanning microscope was used for all testing. Compared with those without WCP treatment, WCP can induce the residual compressive stress in the near surface layer, and delay the fatigue crack initiation, and decrease the rate of fatigue crack growth.

Abstract: Assisted living instruments and medical implants, such as wheelchairs and joint prostheses are usually subjected to biaxial or three-axial stresses instead of uniaxial stress. So, authors already developed a servo biaxial fatigue-testing machine, and clarified about the performance evaluation. Moreover, closed-packed hexagonal lattice metal, such as magnesium and titanium, is frequently used for assisted living instruments or medical implants. In this research, fatigue crack propagation tests of magnesium alloy AZ31B and pure titanium TP340C were conducted under conditions of biaxial and uniaxial loading by using a cruciform specimen in a bi-axial fatigue machine, in order to investigate the effect of non-singular stress cycling on the fatigue crack growth properties ⊿K-da/dN. From these comprehensive experiments, in the magnesium alloy, the re-markable effect was found in the specific biaxial load stress ratio on ⊿K-da/dN relation. When biaxial load stress ratio was 0.5, it turned out that the fatigue crack propagation rate of a magnesium alloy becomes very slow. On the other hand, in the titanium, it was confirmed that there is a little influence of a biaxial load stress ratio on ⊿KⅠ -da/dN relation.

Abstract: The effect of hydrolysis of polycarbonate on tensile behavior were investigated.
The specimens were exposed in a chamber at constant room temperature and water for 300 hours, and measurements were made on the variation of weight and tensile properties. In addition, the increase and decrease of the carbonate part was measured with an ultraviolet spectroscopy. The results are as follows: It was confirmed that it was effective to the examination of the influence of the diffusion of water with an overlay castfilm. It has been understood to the diffusion of water from the surface layer has diffused at the same time by about 6μm, and it has diffused gradually when it is deeper than 6μm. The change in the tensile behavior by the hydrolysis was able to be confirmed by observing the carbonate part of the polycarbonate. It became clear, the break strain has decreased because the carbonate part is taken apart by the hydrolysis. Afterwards, the break strain steadies by constructing a bridge, and the yield stress increases.

Abstract:
Destructive accident sometimes takes place though the equivalent stress is rather low in the viewpoint of strength of materials. The propagation of fatigue cracks under multi-axial stress state and cycling load gives the reason. Fatigue fracture has been considered as one of the most commonly encountered industrial problems that lead to the damage of components in engineering products. In general, the machine structure is always under stress concentration or stress cycles. Moreover, the structure material is usually under two axes or multi-axial stresses instead of uniaxial stress state. It is important, therefore, to clarify the propagation behavior and the fatigue failure problem of the crack under the multi-axial stresses and cycling load from the safety reliability and accident prevention measure. In this study, a biaxial fatigue experimental device was developed which can carry out a wide range of fatigue tests under biaxial stresses. The developed experimental device was identified with a biaxial fatigue experiments including static uniaxial and biaxial tensile test by using the aluminum alloy flat plate as specimens. The propagation behavior of fatigue crack for center notched cruciform specimen in the equal biaxial fatigue test was verified.