| Co-Investigator(Kenkyū-buntansha) |
OCHI Kenshi Kumamoto Univ.Faculty of Engineering Assoc.Prof., 工学部, 助教授 (20145288)
OGAWA Koji Kumamoto Univ.Faculty of Engineering Assoc.Prof., 工学部, 教授 (80112390)
YAMANARI Minoru Kumamoto Univ.Graduate School of Assistant Science and Technology, 大学院・自然科学研究科, 助手 (90166760)
MAKINO Yuji Kumamoto Univ.Faculty of Engineering Prof., 工学部, 教授 (70040433)
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| Budget Amount *help |
¥9,900,000 (Direct Cost: ¥9,900,000)
Fiscal Year 1996: ¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 1995: ¥5,900,000 (Direct Cost: ¥5,900,000)
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| Research Abstract |
Welded T joint speciments were tested in combined bending and tensile loads. The specimens were tested by varying the material properties, thickness of the main plate, methods of prestraining the main plate, and temperature. A few specimens were tested after introducing fatigue cracks along the weld toes. The first crack was found in the central region of the main plate at te weld toes. This crack extended stably not only along the weld toes but also in the through thickness direction. Some specimens failed suddenly, at a certain stage, showing an unstable crack extension, while other specimens failed y ductile tear. The greater the plate thickness, the larger the prestrain, and the lower the temeprature, the specimens failed in a more brittle manner. The intitation of macrocracks, of about 0.1 mm in depth, was found to be predictable by a simple function of stress triaxiality, Mises's equivalent plastic strain and maximum uniform strain of material. This function is based on the conti
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nuum damage theory. The ductile cracks gave no appreciable effect on load-deflection curves, which can be reproduced accurately by a nonlinear finite element analysis, until they reach about 0.5 to 2.5 mm in depth, as far as they grow stably. After that, the cracks grow rather quickly, leading to ductile or brittle failures. The load-deformation curves leading to a final fracture following quick extensions of cracks have been unable to reproduce by any numerical technique.
A crack tip is blunted and a new crack forms at the root of the tip. This behavior was found to be reproducible by an FE analysis. Study is now under way to find feasible numerical methodologies to control crack growth by using appropriate fracture parameters like the J integral or COA.
The failure assessment diagram was found to be one feasible method to predict failures of welded joints with defects.
The Kobe Earthquake revealed that modern steel building frames could sustain brittle fracture under the influence of a strong near field earthquake. Lessons learned from recent earthquakes were included as the subject of study of this research project. Above all brittle fractures that occurred in box section columns of high-rise Ahiyahama apartment buildings were investigated. Although several causes should have been combined to induce such failures, the effect of high strain rate was found to be one important cause. Additionally, a cyclic loading test of full-scale beam-to-column assemblies were performed to assess effects of weld defects. The test results pointed out the significance of geometry and location of defects in influencing the performance of the connections. Less
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