Abstract: Dissimilar metal welds are commonly found in the primary piping of pressurized water
nuclear reactor power plants. The safety assessment practice for such welds requires residual stresses to be taken into consideration. In the present paper the finite element method is utilized for the simulation of the welding process and prediction of the residual stress field in a dissimilar metal weld pipe joint. Although it is common practice to develop in-house finite element codes for weld simulation, the ANSYS commercial finite element code is selected. This is mainly due to the fact
that industry focuses on commercial software, since residual stress analysis procedures based on them can be readily transferred to industrial applications. A simplified 2-D axi-symmetric model, in which residual stresses are produced due to the thermo-mechanical properties mismatch during cooling of the weld, is compared with a detailed model in which the complete multi-pass welding procedure is simulated. The latter incorporates the “birth & death of elements” technique,
temperature dependant material properties and kinematic hardening material behavior. The aim of this comparison is to establish the degree of model detail and complexity, necessary to obtain satisfactory results and consequently to define a golden rule between computational cost and practically accurate predictions. Identifying the specific simulation parameters and variables, that have the highest impact on the accuracy of the computed results, is also important. It is concluded
that, a bead-by-bead or lump-by-lump detailed simulation is necessary in order to obtain reasonably accurate residual stresses that cannot be predicted by a simplified model. A general conclusion is that the proposed method, being simple in implementation and cost effective concerning model complexity and analysis time, is a potential weld residual stress prediction tool.
Abstract: For measuring in-depth residual stress in 3D cylinder structure easily in this paper,
the semi-destructive incremental hole drilling technique combined with finite element method is used, the calibration coefficients of 3D cylinder components are calculated, and the relationship between strain and stress is determined, the changes of calibration coefficients are analysed, the residual stress of one steering joint of automobile is measured, and the errors of residual stress are discussed.
Abstract: The aim of this work is to reach a better understanding of the ultrasonic shot-peening
process and, in particular, the evolution of the shot speed distribution. A simple 1D modelling of the interaction between the shots and the sonotrode is carried out. The impact is considered as inelastic with an energy absorption that depends on the speed of the shot. It is found that after about 10 interactions (» 1s) the speed distribution in the chamber follows a Maxwell-Boltzmann distribution, which is the
distribution found in a perfect gas at equilibrium. The influence of various process parameters such as the sonotrode amplitude, the vibration frequency on the average speed and on the Almen intensity is studied.
Abstract: Recently, austempered ductile iron (ADI) has emerged as a new class of ferrous materials and represents a major achievement in cast iron technology . The mechanical strength and impact toughness of nodular iron are provided by the precipitation of the graphite phase as spheroids surrounded by ferrite (bull’s-eye structure) in a continuous pearlite matrix. The quality of ductile iron increases with the number of the graphite spheroids. A high spheroids volume fraction, which is mainly controlled by the inoculation process, limits the chemical segregation during solidification and ensures the structural homogeneity of the component. In this work, a lower value of Young modulus was obtained when the graphite phase was taken
into account in the self-consistent modelling. For 12% of graphite the theoretical Young modulus agrees with the measured one (mechanical tensile test). The volume fraction of graphite was confirmed independently by micrographic observation (14%). It can be concluded that the macroscopic behaviour of ADI steel can be modelled by the self-consistent approach in which the austeno-ferritic aggregate is represented by an effective matrix, while instead of the graphite spherical empty spaces are introduced. Using such an approach it was shown that in the elasto-plastic range of deformation, presence of graphite phase caused stress relaxation.
Abstract: This paper presents results of detailed three-dimensional finite element simulation of
residual stress distribution in welded Pipe-Flange Joints with emphasis on the effect of welding parameters and geometrical size of the model. Single-pass Metal Inert Gas welding with single “V” Butt-weld geometry is used in the study. The effect of two basic welding parameters including welding current and speed and two geometrical parameters i.e. pipe diameter and wall-thickness are examined. For both welding current and welding speed, three sets of parameters comprising of low, medium and high values are used. To analyze the effect of each parameter explicitly only one parameter is changed at one time. In most of the cases 100 mm nominal pipe diameter is used. A FE Model for 200 mm nominal pipe diameter is also analyzed to determine the effect of pipe diameter.
Abstract: A numerical simulation system, which integrated FDM (Finite Difference Method) and FEM (Finite Element Method) and coupled temperature field and stress field, was established. This system was then validated by simulation of a stress frame casting. The calculated results are satisfactory and in good agreement with the theoretical analysis. As a practical application, a wave-guide casting was simulated. The stress evolution during casting solidification, residual stress and deformation are predicted.
Abstract: An autofrettage model considering the material strain-hardening behavior and the
Bauschinger effect, based on the actual tensile–compressive curve of material and modified yield criterion, has been proposed. The analytic expressions of residual stress distribution and the autofrettage pressure have been obtained. This model has stronger curve fitting ability, nearly all of the strain-stress curves of materials used in making autoefrettage tubes can be fitted well by this model, and each of those models based on the simplified strain hardening relationship of material is a
special case of the model. It was used to predict the residual stress distributions of an autofrettaged tube. The results show that the residual stress distributions predicted by the present model are in good agreement with the experimental data.
Abstract: A novel deep cryogenic treatment is presented to relieve residual stresses in 7050
aluminum alloy parts, in which the parts are submerged in liquid nitrogen and uphill quenched in proprietary QCW-01 quenchant. The optimum parameters of uphill quenching process were concluded in an attempt to combine maximum stress relief with the required levels of mechanical properties. The experimental results show that this novel deep cryogenic treatment can relieve as much as roughly 71% of residual stresses, higher than the traditional treatment uphill quenched in boiling water. An application example is highlighted, in which this uphill quench treatment has resulted in lower levels of residual stresses and machining distortions for an aircraft bulkhead
Abstract: The existence of residual stresses caused by the welding process is an important reason of cracking and distortion in welded metal structures that may affect the fatigue life and dimensional stability significantly. Heat treatment is one of the traditional methods to relieve the residual stresses. But it is often limited by the manufacturing condition and the size of the structures. In this paper a procedure called vibratory stress relief (VSR) is discussed. VSR is a process to reduce and re-distribute the internal residual stresses of welded structures by means of post-weld mechanical vibration. The effectiveness of VSR on the residual stresses of welded structures, including the drums of hoist machine and thick stainless steel plate are investigated. Parameters of VSR procedure are described in the paper. Residual stresses on weld bead are measured before and after VSR treatment by hole-drilling method and about 30%~50% reduction of residual stresses are observed. The results show that VSR process can reduce the residual stress both middle carbon steel (Q345) and stainless steel (304L) welded structures effectively.
Abstract: It’s a key problem in the mechanical field that the machining stress and original stress redistribute in the workpiece when cutting. In the study of this problem, we found a phenomenon of stress wave in the cutting, as in dynamics; Because of the effect of stress wave, the machined workpieces with complicated structure may have more stress focuses, particularly, the aeronautic and astronautic products have many frame structures, the dynamic stress in the machining can undergo many changes because of the structure’s restrain, and leads to the stress focus in the corner of frame. This is the main factor to cause the workpiece distortion. So, the study of this paper is of great value to explain the law of pockety stress in the machined workpiece, and can help to determine reasonable technique to control and adjust the workpiece’s stress, and finally improve the quality of workpieces.