Strength and stressed state of asymmetric mechanically inhomogeneous welded joints with incomplete fusion at the center of the weld under biaxial loading

Abstract

An approximate solution of the plane problem of the theory of plasticity for main pipelines, cylindrical vessels, and shell structures subjected to biaxial loading is proposed which allows one to perform theoretical analysis aimed at evaluation of strength and stressed state of asymmetric mechanically inhomogeneous welded joints with incomplete fusion at the center of the weld in the case of ductile fracture. Regulating the degree of mechanical inhomogeneity and thickness of the soft interlayer, it is possible to get the uniform strength of welded joints with incomplete fusion and shift fracture processes to the base metal under biaxial tension. We also determine the range of sizes of the domain of incomplete fusion for which the uniformity of strength is attained for the joint with asymmetric mechanical inhomogeneity of the butt weld with incomplete fusion.Keywords: butt joint, soft interlayer, incomplete fusion, ultimate tensile force, contact hardening, asymmetric mechanical inhomogeneity, tangential stresses on the fusion line of the weld, coefficients of mechanical inhomogeneity.The durability and reliability of welded structures in the process of their operation are determined, together with numerous other factors, by the presence of stress and strain concentrators. The role of concentrators is played, e.g., by the events of incomplete fusion in the middle of the weld in the case of two-sided butt welding and in the root of the weld for one-sided welding, the events of faulty fusion between the layers in the case of multilayer welding and along the edges, as well as by the notches, pores, slag and oxide inclusions, and the defective form of strengthening of the weld [1]. These technological defects are often encountered in the process of welding of structures and, hence, the possibility of objective evaluation of their influence on the strength of the joint is an urgent problem that should be solved in designing and monitoring new welded structures.The strength of homogeneous welded joints of low-carbon steels and Kh18N9T steel under conditions of static tension is determined by the net section [1][2][3]. In the case where mechanically inhomogeneous welded joints contain sections with lowered resistance to plastic deformation (soft butt welds), the technological defects of welding are responsible for the complex nonlinear character of changes in static strength [4,5]. This can be explained by the development of three-dimensional stressed state near the defect and in the soft interlayer (weld) as a whole due to the effect of contact hardening of the latter [6,7]. The well-known experimental [1,8,9] and theoretical [5,10] investigations are devoted to the evaluation of the effect of incomplete fusion on the strength of the welds in uniaxial tension.In [1,8], one can find a survey of experimental investigations of the effect of incomplete fusion on the strength of the welds.A zone of incomplete fusion located in the central part of the soft interlayer (in the zone of maximum stiffness of the stressed state) is...