Materials Science Forum Vols. 580-582

Abstract: In order to reduce the number of fabricating processes, it is preferable to control welding distortion during welding; instead of using restraints before the process, or correcting the distortion after the process. The benefits of eliminating extra processes include the reduction of the time and manufacturing cost. This paper presents a method of back heating and welding in tandem, with the back heating occurring at a constant distance from the welding torch during welding. Traditionally, the back heating method has reduced angular distortion in two different ways; One is to bend the welded material in the opposite direction, and the other is homogenization of temperature distribution along the thickness. But, it has recently become known that the angular distortion produced by multiple heat sources, in tandem placement, is not always predicted by the total heat input to the welded joint; and it is possible for the distortion to differ greatly due to factors such as the distance between two heat sources, heat input parameters, and the heat input ratio. Based on these findings, angular distortion is expected to be reduced more effectively by choosing the proper condition for the heat source arrangement in back heating. In this paper, reduction of angular distortion by in-process control welding, using a back heating source, is numerically analyzed by the three-dimensional thermal elastic-plastic analysis, considering moving heat source with weld metal deposition. It was confirmed that the back heating method is effective in reducing angular distortion without restraint or correction. Proper condition concerning the heat source arrangement can be chosen and angular distortion can be perfectly controlled by back heating with ten percent of the welding heat input.

Abstract: In recent time there are vigorous requirements for the use of thick steel plate in various industrial fields, including shipbuilding industry. Especially, application of TMCP steel plates on steel structure is progressively increasing now. Welding process with high heat input is necessary to be used in thick steel assembly for the purpose of the high productivity. However, HAZ softening of TMCP steel plates has a possibility to reduce the strength of welded joint. In this study, therefore, the tensile strength of TMCP weldments, having softened HAZ, was examined using the numerical calculation and experiments.

Abstract: The fatigue crack growth (FCG) in dissimilar weld metal joints between SA 508 Cl.3 low-alloy steel and AISI 316L stainless steel (SS) was investigated. The dissimilar weld metal joint was made after buttering alloy 82 on the SA 508 Cl.3 side by gas tungsten arc welding (GTAW). Alloy 82 welding consumable was selected to join these two metals. The fatigue crack growth rate (FCGR) in each material in the dissimilar weld metal joint increased in the order: weldment, AISI 316L SS and SA 508 Cl.3, at the same stress intensity factor range, /K. As the crack propagated across the AISI 316L SS and heat affected zone (HAZ) into the weldment or across the SA 508 Cl.3 and HAZ, into the weldment, the FCGR in the HAZ region did not change or decrease, in spite of the increase in /K. The retardation in the FCGR in the HAZ region was discussed in terms of the welding residual stress.

Abstract: The evolution of the strain-induced α′ martensite during the cyclic deformation of austenitic AISI 316L stainless steel (SS) was investigated. The low-cycle fatigue (LCF) test was conducted at various strain amplitudes in air. The amount of α′ martensite was determined for the fatigue-failed specimens as well as for the specimens interrupted after a specific number of cycles. The volume fraction of α′ martensite increased with increasing strain amplitude and number of fatigue cycles. The cyclic hardening behavior was discussed in terms of the dislocation density and strain-induced α′ martensite transformation.

Abstract: In this study, a methodology for the assessment of fatigue failure modes of weldments due to partial penetration weld has been carried out by using structural stress method. Structural stress calculation procedure, using shell element based on equilibrium consideration using nodal forces and moments, is employed. It is important to note that the structural stress calculation procedures for partial penetration welds can be used to determine a minimum weld leg length, beyond which, weld root failure modes can be effectively suppressed. An example study, with respect to a fillet weld leg length design, is compared with a design criterion, and they are found to be in agreement.

Abstract: Residual stresses play an important role in the mechanical behavior of steels and welded structures. To examine the effect of residual stresses on tensile behavior and fatigue, residual stresses in the specimens were generated by welding. Experimental stress-strain curves of the specimens with/without residual stresses were obtained and compared to simulated curves obtained by the finite element analysis. The two results are in a good agreement. Finally, to study the relaxation of the residual stresses during fatigue crack propagation, we carried out fatigue crack propagation analysis by a 3-D cohesive zone model. Initial welding residual stresses decrease as the number of cycles increases.

Abstract: This paper is focused on the three strategies to improve efficiency and accuracy of approximate optimization models using Kriging. The strategies are performed by the stochastic process which is called stochastic-localization method as the criterion to move the local domains and the design of experiments, the classical design and space-filling design. We also propose the methodology conducted by the max-min reused sampling and a sequential adaptation algorithm of correlation functions. The proposed strategies are applied to the known analytical function such as Sandgren’s pressure vessel and three-bar truss for practical examples.

Abstract: During welding process to make joints, residual stress is inevitably produced and weld metal should be used. These influence the static and dynamic behavior of steel structures with welded joints, such as steel piles. In steel structures, dynamic mechanical behavior is different to static mechanical behavior. Therefore, to accurately predict the behavior of steel piles with a welded joint under static-dynamic loading, the research on influence of a welded joint on the static and dynamic behavior of steel piles is necessary. For that purpose, a rate-dependent plasticity model was used, considering strain rate hardening and temperature rise. In this paper, the distribution of welding residual stress in a welded joint was computed by using three-dimensional heat conduction analysis and three-dimensional thermal elastic-plastic analysis. The behavior of steel piles with a welded joint under axial static and dynamic loading was investigated by using three-dimensional elastic-plastic finite element analysis, which employed a rate-dependent plasticity model and included residual stress and mechanical properties of weld metal in a welded joint. The rate-dependent plasticity model used in this paper is proposed by the authors based on the static-dynamic loading tests. Numerical analysis results of steel piles with a welded joint were compared to those without a welded joint. In comparison, the characteristics of static and dynamic behavior of steel piles with a welded joint were investigated.

Abstract: Self-Piercing Riveting(SPR) is becoming an important joining technique for various material sheets and shapes, of automotive application. Fatigue behavior of SPR connections needs to be investigated experimentally and numerically to predict SPR fatigue lives. The simulations of various SPR specimens (Coach-Peel specimen, Cross-Tension specimen, Tensile-Shear specimen, Pure-Shear specimen) are performed to predict the fatigue life of SPR connections under different shape combinations. Finite element models of various SPR specimens are developed using a FEMFAT SPOT SPR pre-processor. The fatigue lives of SPR specimens are predicted using a FEMFAT 4.4e based on the linear finite element analysis.

Abstract: The light weight components, crucial in automobiles and machinery, is require hight strength. Mach peening process is one of many of techniques utilized for improving fatigue properties. From the results of rotary bending fatigue tests, the fatigue strength increases up to 129% in mach peening specimen compared with un-peening. A layer of highly compressed residual stress is obtained by mach peening. The compressive residual stress, induced by mach peening, seems to be an important factor for increasing the fatigue strength.