Deformation and fracture resistance of butt-welded joints with mild interlayer under elastoplastic tension

Abstract

Relations are proposed for evaluating the stress-strain state and strength of a butt weld with a mild interlayer under elastoplastic tension in plane-and axisymmetric-strain conditions. The relations allow for the distribution of transverse normal stresses across the interlayer thickness and the interaction and hardening of the metals in the elastoplastic domain. The predicted strain distribution in certain areas of the weld and its strength are verified experimentally Keywords: butt-welded joint, mild interlayer, stress-strain and strength analysis, plane and axisymmetric strains, metal hardening, elastoplastic domainMost welds are mechanically heterogeneous, i.e., they include areas of higher or lower strength compared with that of the base metal. These areas are called hard and mild interlayers, respectively. In some cases, mechanical heterogeneity is produced by welding; in other cases, it appears during operation, especially at high temperatures.Mechanically heterogeneous welds subject to elastoplastic tension are studied intensively, both theoretically and experimentally (see, for example, [2][3][4][5]9]). It was shown in these studies that the mild interlayer strongly affects the strength of the welded joint. In [2,3,5], the stress state of a weld with a mild interlayer was determined disregarding the hardening of the material in the elastoplastic domain (E M As the thickness ratio of the interlayer increases, the stress σ x M decreases, becoming zero after ae > 2. This assumption is

Stress-strain state and durability of mechanically inhomogeneous welds under low-cycle loading

“…A design model and formulas for the determination of the stress components of the materials M and H under tension (compression) are given in [11,14] for a weld with a flat mild interlayer and in [13] for a weld with a hard interlayer. In [13], it is shown that the stresses in a weld with a hard interlayer can be determined from the formulas for a weld with a mild interlayer by replacing its relative thickness k by k = 1.2 and k H = 1.2 by the relative thickness of the hard interlayer k H (1.2 is the relative distance from the contact plane of the cross-section of the base material in which, according to Saint Venant's principle, the metals H and M no longer interact).…”

“…When the cyclic properties change significantly, we have a = -B e s = / e and s s T T e = / s . In a weld with a mild interlayer under tension, the strain distribution depends on its relative thickness k, the mechanical inhomogeneity coefficient g N , and the modulus of hardening in the elastoplastic domain [14]. In the case of cyclic elastoplastic loading, the mechanical inhomogeneity coefficient at given cyclic strain intensity e e e ik ik ik…”

“…Therefore, the parameters of the low-cycle fatigue curve Since the strain distribution in a weld is practically uniform when k = 0.1 [14], the life of the weld decreases only with increase in the hardness of the stress state (decrease in D e ), and a fatigue crack is initiated in the region where the hardness of the stress state is maximum (at the center of the contact plane of the metals M and H) [1].…”

“…Because of the increased hardness of the stress state in a mechanically inhomogeneous weld, the accumulation of plastic strains in the metal M is constrained by the hard metal H. Therefore, A 2 0 depends on the deformation conditions. For the mild material on the contact plane of a mechanically inhomogeneous weld, we have A A A How to calculate strains in mechanically inhomogeneous welds under static tension is explained in [11,13,14]. As g Nk changes and the number of half-cycles increases, cyclic strains are redistributed in separate regions of the weld.…”

“…Samples with a test portion of rectangular cross-section with side lengths 2l = 10 mm and 2B = 30 mm were made from the II type weld [11]. The mechanical characteristics of the I type weld are given in [14], (Table 1). With such thermal treatment, the metals H and M in the I type weld are cyclically softening.…”