Papers by Author: Akira Shimamoto

Abstract: In this paper, the TiNi fiber reinforced / Polycarbonate(PC) composite material is developed, and its properties is studied. Conducting fatigue experiments, shape memory effect of the material for preventing fatigue crack growth are investigated. The fatigue behavior and crack propagation are observed under increasing temperature with a SEM servo-pulser, which is a fatigue testing instrument with scanning electron microscope. As the results, the effectiveness of fatigue resistance is confirmed. The shape memory effect and expansion behavior of the matrix caused by increasing temperature create the effect of the fatigue crack propagation control. It is verified that the controlling of fatigue crack growth is attributed to the compressive stress field in the matrix which is caused by shrinkage of the TiNi fibers above austenitic finishing temperature (Af).

Abstract: The method of generating the most practicable shape recovery force in smart composite materials which embedded shape-memory alloy (SMA) fiber under the resin matrix is electric heating. However, because the calorie for the heating of the resin matrix increases in the low temperature environment, it is necessary to control the electric heating corresponding to an ambient temperature to obtaining a steady shape recovery force. Then, the method of self-detecting the temperature without using a special temperature sensor by measuring the electrical resistance of the SMA fiber in the composite material was examined.

Abstract: This study examined the dynamic penetration phenomena of high-velocity impact of magnesium alloy
 CFRP (Carbon Fiber Reinforced Plastic) composite. Test materials for investigation are magnesium alloy(AZ31B), the heat-treated magnesium alloy (AZ31B-200°C, AZ31B-300°C, AZ31B-430°C), and carbon/epoxy laminated composite materials with fiber direction [0°]8, [0°/45°]4s, [ 0°/90°]4s, [ 0°/45°/90°]3s and [ 0°/45°/-45°/90°]2s. We used a ballistic range (one-stage light gas gun), and the test specimens were set at 0°obliquity at room temperature. A high-speed camera allowed us to capture and analyzed the dynamic penetration phenomena of the test specimen.

Abstract: An experimental study of high pressure water jet peening treatment on SPA-H and SPCC steel was conducted to study the effects of cavitation impacts of high-speed water on fatigue crack initiation and propagation of notched specimens. Pull-pull fatigue tests’ condition was 350 MPa maximum stress amplitude, 0.1 stress ratio and 10Hz frequency, while in-situ observation by SEM was employed. It was found that fatigue life of water jet peening treated SPA-H specimens has been obviously elongated by comparison with specimens without this treatment. However, for SPCC steel specimens, by comparison with those without water jet peening treatment, fatigue life was a little elongated, almost the same and obviously shortened corresponding to water jet peening treatment time of 5, 10 and 15 minute, respectively. High pressure water jet caused surface corrosion for SPCC low carbon steel, while with almost the same carbon content, copper, chromium and nickel elements increased anti-corrosion properties of SPA-H steel. These resulted in the different fatigue life of SPA-H and SPCC steel. In-situ observation on the crack tips approved above analysis.

Abstract: Stress intensity factor K is analyzed by measuring distribution of sum of the principal stresses around slit tip by an infrared stress measuring device. Under the biaxial tensile stress, both K-values of the isotropic materials with slit angle 0° and 45° show there is no influence of the slit angle at Mode I. The tolerance of the measured K-values of the test specimens which are compared with measured K-values by photoelastic method are around 10-20
and these increase as applied cyclic load increases. These tolerance can be reduced up to about 8% by modifying measurements. The effectiveness of the thermoelastic stress measurement method to KI value analyzing under biaxial tensile stress was confirmed.

Abstract: Recently, high-performance hybrid composites have been used for various applications which require the high strength, high stiffness and low weight. There are growing needs in an automotive, an aircraft, and military applications for composite materials since they have good structural characteristics. They also have good penetration resistance and structural integrity after impact. In order to clarify the mechanism of high-speed destruction for composite materials, this study examined the penetration resistance and the fracture behavior of CFRP (Carbon Fiber Reinforced Plastic) Laminates by using ballistic range (one-stage light gas gun). Test materials for investigation are carbon/epoxy laminated composite materials with fiber direction; [0°]8, [0°/45°]4s, [ 0°/90°]4s, [ 0°/45°/90°]3s and [ 0°/45°/-45°90°]2s. The high speed camera allows us to capture and analyze the dynamic penetration phenomena of the test materials.

Abstract: Polymer materials are used in the structural members such as aircraft, ship, automobiles in order to enlarge and lighten the machinery and structures. In such the machinery and structures, the complex destruction phenomena are generating by the deterioration of use conditions of the polymer materials. And the materials are placed under biaxial or multi-axial stress conditions rather than uni-axial stress conditions due to their complicated structures. To understand the basic deformation behaviours and the features in destruction process under multi-axial stress conditions is more important in the reliability and the accident prevention plan. To help overcome this problem, the authors have developed a hydraulic high-speed biaxial loading test device. In this study, we had comparative study for the values of the dimensionless stress intensity factors, F values by the photoelastic and caustics methods to clarify deformation behaviours and characteristics of polymer materials under biaxial stress conditions.

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: In this study, dynamic penetration phenomena of high-velocity impact of magnesium alloy were investigated. The surface hardness of magnesium alloy (AZ31B-O) and the heat-treated magnesium alloy (AZ31B-200°C, AZ31B-300°C, and AZ31B-430°C) were examined using Micro Vickers, and the influence of the heat treatment temperature was observed. We analyzed the metal organization using a microscope. We also used a ballistic range (two-stage light gas gun), and the test specimens were set at 0°obliquity at room temperature. A high-speed camera allowed us to capture and analyzed the dynamic penetration phenomena of the test specimen.

Abstract: In this research, fatigue crack propagation tests of magnesium alloy AZ31B and aluminum alloy 2024T3 were conducted under conditions of biaxial and uniaxial loading by using a cruciform specimen in a biaxial fatigue machine, in order to investigate the effect of non-singular stress cycling. From these comprehensive experiments, in the magnesium alloy, the remarkable effect was found in the specific biaxial load stress ratio RB (= σx 0/σy 0) on
KI-da/dN relation. On the other hand, in the aluminum alloy, it was confirmed that there is no influence of a RB on
KI-da/dN relation.