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

对焊接T型接头试件进行了弯曲和拉伸联合载荷试验。通过改变材料性能、主板厚度、主板预应变方法和温度对试件进行测试。几个试件在沿焊趾处引入疲劳裂纹后进行了测试。第一道裂纹出现在焊趾处的主板中心区域。该裂纹不仅沿焊趾方向稳定扩展，而且在贯穿厚度方向也稳定扩展。有些试件在某个阶段突然失效，显示出不稳定的裂纹扩展，而另一些试件则表现为延性撕裂。板厚越大，预应变越大，温度越低，试件的脆性越大。宏观裂纹的萌生深度约为0.1 mm，可以用应力三轴度、Mise等效塑性应变和材料的最大均匀应变的简单函数来预测。此函数基于CONTI…更多的努姆损害理论。延性裂纹对荷载-挠度曲线没有明显影响，直到深度达到0.5~2.5 mm，才能稳定生长，非线性有限元分析可以准确地再现该曲线。在此之后，裂纹扩展得相当快，导致延性或脆性破坏。在裂纹快速扩展后导致最终断裂的载荷-变形曲线不能用任何数值技术再现。裂纹尖端钝化，在尖端根部形成新的裂纹。通过有限元分析发现，这种行为是可重现的。目前正在研究采用合适的断裂参数(如J积分或COA)来控制裂纹扩展的可行数值方法。失效评估图被发现是预测有缺陷的焊接接头失效的一种可行方法。神户地震揭示了现代钢结构框架在强近场地震影响下可能发生脆性断裂。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。首先，对高层Ahiyahama公寓楼箱形截面柱的脆性断裂进行了研究。尽管几个原因应该综合起来导致这样的失效，但高应变率的影响被发现是一个重要的原因。此外，还进行了足尺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节点性能的影响。较少

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