Fracture Toughness Assessment of Weld Toes by Means of Simple Model Testing

对焊接T形接头试件进行了弯曲和拉伸复合载荷试验。通过改变材料性能、主板厚度、主板预紧方法和温度对试件进行了测试。在沿焊缝脚趾引入疲劳裂纹后，对少数试件进行了试验。第一个裂纹是在焊接脚趾处主板的中心区域发现的。裂纹不仅沿焊趾方向稳定扩展，而且沿厚度方向稳定扩展。有的试件在某一阶段突然破坏，表现为不稳定裂纹扩展，有的试件则表现为延性撕裂破坏。板厚越大，预应变越大，温度越低，试件脆性破坏越明显。深约0.1 mm的宏观裂纹的产生可以通过应力三轴性、米塞斯等效塑性应变和材料的最大均匀应变的简单函数来预测。这个函数是基于conti…More numum损伤理论。塑性裂纹对载荷-挠度曲线没有明显的影响，非线性有限元分析可以精确地再现，直到它们达到约0.5至2.5 mm的深度，只要它们稳定增长。在此之后，裂缝增长得相当快，导致延性或脆性破坏。由于裂纹的快速扩展，导致最终断裂的荷载-变形曲线无法用任何数值方法再现。裂纹尖端被钝化，在尖端的根部形成新的裂纹。通过有限元分析发现这种行为是可重复的。目前，研究人员正在寻找可行的数值方法，通过使用适当的断裂参数（如J积分或COA）来控制裂纹扩展。发现失效评估图是一种预测缺陷焊接接头失效的可行方法。神户地震揭示了现代钢结构建筑框架在强近场地震的作用下能够承受脆性断裂。从最近地震中吸取的经验教训被列入本研究项目的研究主题。本文首先对高层公寓楼的箱形截面柱脆性断裂进行了研究。虽然应该有几个原因共同导致这种破坏，但高应变率的影响被发现是一个重要原因。此外，还进行了全尺寸梁柱组件的循环加载试验，以评估焊接缺陷的影响。试验结果指出了缺陷的几何形状和位置对连接性能的影响。少

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 … More 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