Effect of Micro-Structure and External Geometry on Fatigue Strength of Welded High Tensile Steel
Effect of Micro-Structure and External Geometry on Fatigue Strength of Welded High Tensile Steel
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显微组织和外部几何形状对焊接高强度钢疲劳强度的影响
DOI：
10.2207/qjjws1943.37.1353
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发表时间：
1968
期刊：
影响因子：
--
通讯作者：
K. Yagi
中科院分区：
文献类型：
--
作者：
T. Kawasaki;Y. Sawaki;K. Yagi
本文对80 kg/mm ~ 2（φ 110 ksi）级高强钢焊接接头的疲劳强度进行了测定。该钢的疲劳极限为46 kg/mm ~ 2，焊接使疲劳极限显著降低，仅为13 kg/mm ~ 2左右，焊接引起的金相组织变化似乎不是疲劳强度降低的主要因素。因为当焊接后钢筋被完全切削时，疲劳极限增加到40 kg/mm 2。当钢筋几乎完全修整时，在板的表面上留下微缺陷，疲劳极限再次为40 kg/mm 2。因此，尽管钢筋趾部的微观缺陷是疲劳裂纹的萌生部位，但对疲劳极限的影响不大，钢筋引起的宏观应力集中可能是接头疲劳强度降低的主要原因。然而，对从母材加工的模拟焊接试样的疲劳试验结果，结果表明，焊接接头疲劳强度的衰减系数均未超过3.0，不能完全由其中任何一个因素来解释，而必须由其它因素（如显微组织、应力应变、应力应变等）来加剧焊接接头疲劳强度的衰减。为了确定接头的疲劳极限，提出了一个表观疲劳强度折减系数Kfw，公式为：Kfw=Kf <$Cu <$Cn <$Cs <$Cx其中Kf分别是由于增强、Cu、Cn和Cs的微观缺陷、材料缺口敏感性和结构变化引起的疲劳折减系数。Cx也是其他未知效应的校正因子。根据试验结果确定了除Cx外的各因素的值，并计算了疲劳极限。计算的焊接接头疲劳极限与观察到的疲劳极限之间具有良好的一致性。
The present study was undertaken to determine the fatigue strength of weld joint of high tensile steel of 80 kg/mm2 (≈ 110 ksi) level. The endurance limit of this steel was 46 kg/mm2 obtained from repeated bending fatigue test.The endurance limit was remarkably decreased to only about 13 kg/mm2 due to welding.The metallurgical structural change caused by welding seems not to be a dominant factor for the decrease in the fatigue strength. Because the endurance limit increased to 40 kg/mm2 when the reinforcement was completely machind off after welding.When the reinforcement was almost completely dressed, leaving the micro-defects on the surface of the plate, the endurance limit was again 40 kg/mm2. Therefore, the micro-defects appearing at the toe of the reinforcement have little effect upon the endurance limit, although such defects were always the sites from which fatigue crack was initiated.Macroscopic stress concentration due to reinforcement may be a major factor for the reduction of fatigue strength of the joint. However, fatigue test results on the simulated weld specimens, machined from the base metal, showed that the fatigue strength reduction factor was never higher than 3.0 in the present investigation.It is concluded that the drastic reduction in fatigue strength of weld joint can not be completely explained by any one of factors alone but the strength reduction by the reinforcement must be intensified by the other factors such as micro-defects and metallurgical structural changes.To determine the endurance limit of joint, an apparent fatigue strength reduction factor, Kfw, is proposed as follows, Kfw=Kf⋅Cu⋅Cn⋅Cs⋅Cxwhere Kf is the fatigue reduction factor due to reinforcement, Cu, Cn and Cs correction factors for micro-defects, notch sensitivity of material and structural changes, respectively. And Cx is also a correction factor for other unknown effects. The value of each factor except Cx was determined from the result of present investigation and the calculation of endurance limit was made. A good agreement was obtained between the calculated and observed endurance limits of weld joint.