Contrast Study On Fatigue Performance Of Engineering Structure Material Welded Joint

The fatigue performance of the four engineering structure materialsQ235B, the high-strength steel WELDOX960,5A06 aluminum alloy and AZ31B magnesium alloy is studied.The experimental results were assessed by the method of the nominal stress;some parameters concerned to the fatigue strength were received.Compared the fatigue performance of this four metals,some useful conclusions were found.The fatigue performance of four welded joints of Q235B - butt joint, transverse cross joint,longitudinal cross joint and side-weld joint was studied. The experimental results showed that the fatigue strength of the butt joint, transverse cross joint,longitudinal cross joint and side-weld joint was respectively 157.8MPa,164.8MPa,118.3MPa and 113.0MPa under the cycle number of the 2×10~6.The fatigue strength of the four joints reached the criteria of the International Welding Institute.The fatigue performance of three welded joints of WELDOX960-butt joint,transverse cross joint and longitudinal cross joint was studied.The experimental results showed that the fatigue strength of the butt joint, transverse cross joint,longitudinal cross joint and side-weld joint was respectively 192.0 MPa,147.9MPa and 132.4MPa under the cycle number of the 2×10~6.The fatigue strength of the three joints reached the criteria of the International Welding Institute.The fatigue performance of five specimens of 5A06-base metal,butt joint,transverse cross joint,longitudinal cross joint and side-weld joint was studied.The experimental results showed that the fatigue strength of the base metal,butt joint,transverse cross joint,longitudinal cross joint and side-weld joint was respectively 99.97MPa,70.96MPa,57.48MPa,41.80MPa and 48.20MPa under the cycle number of the 2×10~6.The fatigue strength of the four joints reached the criteria of the International Welding Institute.The fatigue performance of five specimens of AZ31B -base metal,butt joint,transverse cross joint,longitudinal cross joint and side-weld joint was studied.The experimental results showed that the fatigue strength of the base metal,butt joint,transverse cross joint,longitudinal cross joint and side-weld joint was respectively 66.72MPa,39.00MPa,24.38MPa,32.18MPa and 24.40 MPa under the cycle number of the 2×10~6.The fatigue strength of the four joints did not reach the criteria of the International Welding Institute of Aluminum alloy.The fatigue performance of the Q235B,the high-strength steel WELDOX960,5A06 aluminum alloy and AZ31B magnesium alloy was contrasted.The fatigue performance of the WELDOX960 welded joints was better than the Q235B;and the 5A06 was better than the AZ31B.The fatigue fracture appearance of the welded joints of the aluminum alloy and the magnesium alloy was observed by the scanning electron microscope.The fatigue bright ripple was clearly found in the fracture face of the aluminum alloy.There were lots of dimples and secondary cracks in the partial area,and the fine cleavage steps were found.So the fatigue rupture of the aluminum alloy welded joints was a quasi-cleavage pattern of the brittle rupture.But there were no continual and clear fatigue stripes in the fracture face of the magnesium alloy welded joints.Mostly areas were formed of the fine and dense cleavage steps,fan-shaped designs and fluvial designs.And there were different size of the secondary cracks in the fracture face. Therefore,the fatigue rupture of the magnesium alloy welded joints was a cleavage pattern of the brittle rupture.