基于断裂模拟的高温下角焊缝接头承载性能研究

为准确预测火灾高温下正面角焊缝焊接接头的承载性能，结合已有高温下钢结构正面角焊缝焊接接头的拉伸试验数据，采用有限元数值分析方法,对20~700 ℃下20个焊脚尺寸均为12.7 mm的角焊缝焊接接头的断裂模式与实际承载性能进行研究。拟合高温作用下适用于断裂模拟的焊材熔敷金属真实应力-应变关系，标定高温下适用于焊材熔敷金属的剪切断裂模型材料参数，采用试验获得的荷载-位移曲线、断裂破坏模式以及AISC 360-10中的承载力计算方法对数值模拟结果进行验证。研究结果表明：高温作用下角焊缝焊接接头的断裂位置多发生在焊缝区，断裂从焊根部分开始并随荷载的增大向焊脚位置扩展；接头的极限承载力随着温度升高而减小，高温下接头的极限承载力可由断裂面面积及焊材抗拉强度确定；接头在高温作用下（大于500 ℃）的变形量超过5 mm，约为常温作用下的5倍；焊材的剪切断裂模型参数是其抗裂性能的重要参数，也是相应的焊接接头构件变形能力的重要指标，在高温作用下（大于500 ℃），焊材断裂参数是其常温作用下的4.5倍。

Study on load-bearing capacity of steel fillet welded joint based on fracture simulation at elevated temperatures

In order to accurately predict the load-bearing capacity of transverse fillet welded joint, the failure modes and load-bearing capacity of 20 fillet welded joints with a leg size of 12.7 mm at elevated temperatures from 20 to 700 ℃ were investigated using finite element method together with the existing tensile tests results. The true stress-strain curves and shear fracture model parameters of deposited welding metal in steel fillet welded joint at elevated temperatures were calibrated for fracture simulations. The simulated results using finite element method were validated against test results including load-displacement curves and fracture failure modes and compared with the calculated ultimate load-bearing capacity based on current code of practice. This study demonstrates that the fracture of fillet welded joint at elevated temperatures mainly occurs in the welding seam zone, initiating from weld toe and propagating to weld root. The load-bearing capacity of fillet welded joint decreases with the increase of temperature. which can be estimated from the actual area of fracture surface and the tensile strength of welding material. The deformation of the joint at high temperature (T>500 ℃) is more than 5 mm, which is approximately 5 times of that at room temperature. The shear fracture model parameter of welding material is a critical index of its fracture resistance performance, and it is also an important index of the deformation capacity of welded joint. At higher temperature (T>500 ℃), the fracture parameter of welding material is 4.5 times of that at room temperature.