Papers by Author: Fumio Nogata

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: We have proposed a new technique for visualising trabecular architecture of spongy bone using ultrasound A-mode signals from a transducer of medical ultrasound system. The technique can be established by finding a method to distinguish between bone and bone marrow. Firstly, the A-mode signal intensity was fitted by the form, A=A0exp(-ax), where A, A0, a, and x represent echo intensity, initial value of echo, attenuation factor, and distance, respectively. Then the curve was moved slightly downward or upward by multiplying with the coefficient k (0.9~1.2), and it was used as an index line to distinguish between bone and bone marrow. To clarify the validity of the proposed technique, we examined bovine bone specimen and a spongy-shaped specimen made by ceramics. The pixel size for creating architecture was 0.2 (width) × 0.15 (depth) mm for bone marrow and 0.2 × 0.3 mm for bone substance, and the pixel size differs due to the difference in wave speeds. The visualisation technique was capable to create an image size of ~10 mm depths from the surface of cortical bone. We also tried to visualise the heel bone.