Abstract
To evaluate the fatigue life of Q420C steel welded joints, fatigue tests were performed on butt-welded joints, cross-butt-welded joints and cross-fillet-welded joints. The fatigue strength S-N curves of the joints were fitted. Then the formation and development of fatigue cracks were analyzed by fracture morphology. The fatigue properties of joints were compared with literature data and standard curves. The results showed that the fatigue test data of the three types of welded joints were roughly above the standard curves. Moreover, the fatigue strength of butt-welded joint was significantly higher than the calculated values of standards, indicating a large safety margin. The test value of cross-butt-welded joint was close to the calculated values of standards, so it is suggested to moderately reduce the standard values. In addition, all the three standards could well predict the fatigue life of cross-fillet-welded joint. The fracture morphology of the specimens showed the development process of fatigue damage, and the fatigue displacement curve and damage curve proved the formation of the fatigue fracture in specimens.
Highlights
With the wide application of Q420 steel in transmission towers, offshore drilling platforms and large public structures, the strength, toughness, fatigue resistance, machinability, welding performance and corrosion resistance of Q420 steel welded joints have become the focuses of structural engineers
Lei et al (2010) summarized the research progress in the fatigue of steel structures in China in the past 30 years from six aspects, and pointed out the fatigue problems to be solved for steel structure
The results showed that Q420C steel had an advantage over Q420B steel in fatigue performance under the same conditions, and the test results were much higher than the value prescribed in the GB 50017-2003 standard
Summary
With the wide application of Q420 steel in transmission towers, offshore drilling platforms and large public structures, the strength, toughness, fatigue resistance, machinability, welding performance and corrosion resistance of Q420 steel welded joints have become the focuses of structural engineers. Jia et al (2017) carried out static tensile test and axial tensile fatigue test respectively on standard round rod specimens and hourglass-shaped smooth specimens They found that Q345qD butted weld had better fatigue, and the fatigue life was significantly improved with the decreasing stress, and gave the fitting formula of fatigue life with varying stress. Zong et al (2017a, 2017b) performed fatigue tests on 26 non-bearing Q345qD steel cross-fillet welds, and plotted the SN curve of weld leg failure and root failure. Through S-N curve and microstructure analysis, Zhang et al (2020) studied the fatigue properties of Q420 steel butt welds treated with three different welding processes (SMAW, SMAW+FCAW and SMAW+SAW). The development of fatigue cracks is analyzed based on the fracture morphology, and the fatigue life of welded joints is compared with literature data and specification curves, which provides reference for the fatigue performance of Q420C structural steel welded joints
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