Avoidance of Low Strength Failure of Connections Induced by Fibrous Cracks Initiating at Weld Toes

有几个例子表明，焊接连接件在单调或几个循环的反向载荷下，由于从焊趾延伸的纤维裂纹而导致延性不足的过早失效。应避免这种连接破坏，使建筑结构具有塑性变形能力。然而，目前还没有确定的标准来防止这种过早的失败。首先要确定的是材料的特征常数，控制纤维裂纹的萌生在焊趾和裂纹的不稳定扩展的throughthickedirect.In这项研究中，焊接T形连接在拉伸和弯曲载荷的组合模型试验进行：拉伸载荷施加到一个主要成员（板）;此外，通过拉动角焊到主构件上的附接板，将弯矩施加到主构件上。焊趾处狭窄区域的材料承受了较大的张力， ...更多信息 应变小，裂纹沿着焊趾萌生并向主构件扩展。试验中主要构件的板厚和弯拉荷载比，板厚越大，裂缝萌生和扩展时主要构件的最大坡度越小。这意味着当焊趾处的材料承受一定的临界应变时，裂纹开始。临界应变被认为是一个有用的标准来评估焊趾的延性。然而，该试验在准确测量焊趾处的临界值方面遇到了困难。目前正在研究通过非线性有限元分析来估算焊趾处的应变。一个焊接连接的试验实例是K型管节点，在该试验中，由于裂纹而导致的过早失效被可靠的数据记录下来。基于对K型节点大量现有数据的分析，发现了一个简单的规则，用于识别可能发生过早失效的节点的加载条件和几何形状。少

There are a few examples in which welded connections show a premature failure with insufficient ductility owing to fibrous cracks extending from the weld toes under monotonic or a few cycles of reversed loading. This type of connection failure should be avoided so that building structures possess plastic deformation capacity. However, no definite criteria have been established yet to prevent such a premature failure like this. The first step to be made is to identify material's characteristic constants that govern initiation of fibrous cracks at the weld toes and unstable extension of the cracks in the through-thickness direction.In this study a model test of welded T-shaped connections under combined tensile and bending loads was performed : A tensile load was applied to a main member (a plate) ; in addition bending moments were applied to the main member by pulling an attached plate fillet-welded to the main member. The material in a narrow area at the weld toes sustained large tensi … More le strain so that cracks were initiated along the weld toes and extended the the main member. The plate thickness of the main member and the bending to tensile load ratio were in this test.The greater the plate thickness, the smaller the maximum slope of the main member at which cracks initiate and extend. This means that cracks initiate when the material at the weld toes sustains a certain critical strain. The critical strain was found to be a useful criteria to evaluate the ductility of the weld toes. The test, however, came up with difficulties in measuring accurately values of the critical at the weld toes. Now study is in progress to estimate strains at the weld toes by means of nonlinear finite element analysis.An test example of welded connections in which premature failures due to cracks were recorded with reliable data is the tubular K-joint. Based on an analysis of extensive existing data for the K-joints, a simple rule was found to identify the loading conditions and geometry of the joint under which premature failures may occur. Less