Low-cycle Fatigue Of Welded Joints Research Articles

Effects of weld geometry and HAZ property on low-cycle fatigue behavior of welded joint

A previous experimental study by the authors clearly indicated that, due to the delay of the crack initiation, the butt-welded joint with smoother weld toe profile and harder weld metal had a longer low-cycle fatigue life. In the present study, supplementary numerical studies considering weld geometries and inhomogeneous mechanical properties are executed. Monotonic tensile and strain-controlled low-cycle fatigue tests on the reheated round bars are firstly conducted to characterize the mechanical properties for different zones of the butt-welded joints. The test results are used to calibrate the material constitutive model, which is then embedded into three-dimensional finite element models to investigate the low-cycle fatigue behavior of the butt-welded joints. The numerical results suggest the necessity of considering the effects of inhomogeneous material properties when evaluating the low-cycle fatigue of welded joints. It is also confirmed that decreasing weld toe stress concentration and simultaneously increasing weld metal strength can maximally increase the low-cycle fatigue life of welded joints compared to the individual changes for either one. These findings are expected to provide some insights into the low-cycle fatigue life improvement of welded joints.

Constructive and technological method of increasing durability of “choke connections”

Welded circular seams of “choke joints”, as a rule, have deviations from the specified diameter. This leads to uneven deformation, and sometimes to the absence of deformations in some areas of the seam. With repeated static loads, destruction arises in these places. To connect to the maintenance system of connections with the base metal, used as a guide, surface plastic deformation of the zone zone is carried out. A technology and equipment have been developed that allow plastically deforming the area of transition from the weld to the base metal along the entire length of the circular weld. As a result of plastic deformation along the technological groove, the characteristics of low-cycle fatigue of welded joints are obtained, which are not inferior to the base metal. To reduce stresses in the zone of transition from the weld to the base metal, it is proposed, first, to perform a circular groove on the base metal by machining, as close as possible to the specified zone. To assess the influence of the shape and size of the groove on the stress-strain state of the zone of conjugation of the weld metal with the base metal, FEM calculations were carried out

Low-cycle fatigue of welded structures made from domestic and imported materials

In various branches of modern engineering, corrosion-resistant steels and titanium alloys are widely used as structural materials. At the same time, it is possible to connect parts made from domestic and imported alloys using automatic argon-arc electric welding, which leads to the formation of a material with unexplored properties in the weld. Welded joints are stress concentrators and currently there is no information about low-cycle fatigue of welded joints obtained by fusing domestic and imported materials. In the course of the research, the modes of welding and heat treatment of butt welded joints obtained from sheet titanium alloys and corrosion-resistant steel of domestic and foreign production have been developed. Resource tests for low-cycle fatigue of samples of welded joints were carried out. Tests on low-cycle fatigue were carried out on the upgraded testing machine UMM-10 with repeated static stretching with an asymmetry factor of +0.1 and at a frequency of 0.6–0.8 Hz. The maximum tensile stress was 80% of the temporary tensile strength of the weakest alloy in the pair. The main stress axis from external loading in all cases was perpendicular to the weld. The tests were carried out until the destruction of the sample. As a result of research, it was established that all welded joints were destroyed along the fusion line, which is explained by the simultaneous action of geometric and structural stress concentrators. In this case, the destruction of the samples, as a rule, began near the seam from the side of the weakest alloy in the pair. It was also established that the use of temperatures of incomplete annealing in comparison with the full one allows to increase the cyclic durability for welded joints of titanium alloys by 1.3–2 times. From the results of comparative tests of samples of corrosion-resistant steels, it follows that domestic and imported steels, as well as their welded joints, have similar properties, both in strength and in re-static durability.

Low-cycle fatigue of welded joints of 08Kh18N10T steel

We present systematized experimental data on low-cycle fatigue strength at 20 and 350°C for 08Kh18N10T steel and its welds, made by manual electric arc welding with EA-400/10U electrodes and argon-arc welding with a nonconsumable electrode and using Sv-04Kh19N11M3 filler wire. The data obtained are compared with the “Standards for Strength Analysis” PNAE G-7-002-86.

Low-cycle fatigue of welded joints: coupled initiation propagation model

This paper deals with the low-cycle fatigue (LCF) design of welded structures, the aim being the critical analysis of the rule used in the RCC-MR [Design and construction rules for mechanical components of FBR nuclear islands, AFCEN, 1993], for the design and construction of fast breeder reactors. The study takes into account the evolution of the material behavior laws and damage accumulation during the fatigue loading. The adopted model consists of analyzing separately the behavior and the damage evolutions. It allows us to determine the damage ratio corresponding to initiation and propagation of a significant crack in order to determine the life duration. This model suggests the existence of a threshold level of loading, above which micro-cracks initiate. The initiation fatigue life can then be neglected below the threshold level. This work shows also that the RCC-MR rules are valid below this threshold load level.

Low-cycle fatigue of welded joints in 10GN2MFA steel

Low-cycle fatigue of welded joints in 10GN2MFA steel

Investigation of low-cycle fatigue of welded joints in copper and brass

Investigation of low-cycle fatigue of welded joints in copper and brass

Low-cycle fatigue of welded joints of alloy AMg5

The authors study the low-cycle fatigue of welded joints of aluminum alloy AMg5 in order to determine the cyclic strength coefficient of welded seams. Tests were carried out on cylindrical specimens of the parent metal, welded specimens, and models of welded vessels. The average values of mechanical properties of the specimens and the parent metal are shown. It is shown that when designing welded vessels of aluminum alloy AMg5, the permissible amplitudes of conventional compressive stresses are recommended to be determined as the lower of the two values calculated using the equations presented.

Low-cycle fatigue of welded joints of structural steels during the formation and propagation of cracks during biaxial bending

Low-cycle fatigue of welded joints of structural steels during the formation and propagation of cracks during biaxial bending

Investigation of low-cycle fatigue of welded joints in light alloys

Investigation of low-cycle fatigue of welded joints in light alloys