Papers by Author: Ryo Kubota

Abstract: Magnesium alloy is the lightest metal that is used as a structural material. It has a higher specific tensile strength and specific stiffness than Iron and Aluminum alloy, and the dent is not caused easily from Iron and Aluminum alloy at the impact. Therefore, Magnesium alloy is widely used in many areas, especially as an external shell of a mobile device and automotive parts which replaces iron and plastic, etc., and its demand is expected to grow in the future. In this paper we studied the hypervelocity impact with a ballistic range to clarify the characteristic of Magnesium alloys which had such a characteristic. The effect of impact velocity, temperature and the size of perforation hole were investigated experimentally. The perforation resistance of Magnesium alloys and their impact behavior were characterized.

Abstract: The dynamic fracture experiments were conducted on the heat treated magnesium alloys; AZ31B-O, AZ31B-200 °C, and AZ31B-430 °C. Cross shaped specimens with the crack on their center were used for the experiments. Dynamic fracture behavior near a crack tip under equal and unequal biaxial stress was observed by the caustics method. From the observation, the stress intensity factor and the fracture toughness value were calculated. As a result, the effect of heat treatment was found. However, no clear relation such as correlation between dynamic stress intensity factor and heat treatment temperature was deduced.

Abstract: Static and dynamic loading fracture experiments were conducted on magnesium alloy under equal and unequal biaxial stress. Cross shape specimens with a crack on their center were used for tests. Fracture behavior was observed by two methods; the caustic and the one point gauge method. From the observation, the stress intensity factors and the fracture toughness values were calculated. It was found that the one point gauge method was not suitable for calculating the stress intensity factor with a strain gauge widely available. The fracture toughness values obtained under equal biaxial stress were 1.2~2.3 times greater than those of magnesium alloy naturally inherited. Moreover, plate thickness was negatively related to the fracture toughness value.

Abstract: In this study, the dynamic behaviors of cracks under dynamic biaxial stress are investigated. We conduct dynamic loading fracture experiments on the aluminum (2024-T3) and the magnesium alloy (AZ31B-O) under equitable biaxial stress with a hydraulic high-speed biaxial experimental machine. The processed specimens are cruciform with a crack. Different kinds of cracks are defined by their crack angles. We analyze the results by the caustic method. We obtained the stress intensity factor and the fracture toughness value in the neighborhood of the crack tip under dynamic biaxial stress. We analyzed the obtained data, and then, we compared results.

Abstract: In this study, dynamic behavior of the crack under dynamic biaxial stress was investigated concerning of these situations. Specimen shape was assumed to be a biaxial fracture, and the load device was with a hydraulic high-speed biaxial experiment device, which this laboratory had developed. Dynamic stress intensity factors and strain behaviors in the crack tip, angle of the pre-crack and crack propagation direction, and relate about the dynamic fracture toughness value under a dynamic biaxial stress was studied.