Abstract: To improve the load-carrying capacity of undermatching joints of high strength steel, the shape parameters of butt joints are designed on the principle of “equal load-carrying capacity”(ELCC), i.e. weld and base metal have equal load-carrying capacity. Finite element analysis results indicate that this design makes the stress and strain of weld zone including weld toe and weld root of undermatching butt joints decrease significantly, so the load-carrying capacity of low strength weld is improved. Experimental results show that the strength of ELCC butt joints basically reaches the tensile strength of base metal. In the high stress region, the fatigue strength of ELCC butt joints is very close to that of equalmatching flush joints. In the low stress region, the fatigue strength slightly decreases with the decreasing of mis-match ratio. Compared with as-welded equalmatching butt joint, the fatigue strength of ELCC butt joint (yield strength match ratio is 0.57) corresponding to 1×107 cycles increases about 115%, and reaches 80% of the 0.96 undermatching flush joints. The shortcoming of lower carrying capacity of undermatching joints can be avoided by ELCC design, and the match ratio can be selected in larger range without reducing the applied stress.

Key words: Design of shape parameters, Equal load-carrying capacity, Tensile and fatigue behaviors, Undermatching butt joints