Minimization Of Residual Stresses Research Articles

Numerical study on the residual stress distributions in GTA welded dissimilar metal components

Residual stresses are inherently self-balanced stresses that arise due to non-uniform development of Eigen strains during processes like welding. Tensile residual stress in weld joints have a detrimental effect on the structural integrity and life of an engineering component, Accurate estimation and minimization of residual stress is a pre-requisite to qualify a component for durable service in severe environments e.g. in nuclear power plants. Dissimilar weld joints are fabricated to provide the structural and functional continuity whenever equipment in a process line is fabricated. A typical and relevant example is the weld joint between Modified 9Cr-1Mo steel (P91) and AISI type stainless steel 304 which finds application in nuclear power plants and process industries. Computer aided numerical simulation provide detailed information of the magnitude and distribution of residual stress in the component. This paper describes a numerical study carried out for evaluation of residual stress occurring in dissimilar butt weld joints between P91 and SS304 plates and circumferentially welded pipes. This covers sequential coupled thermo-metallurgical and mechanical FEM time-step analysis using three-dimensional models. The model predicted residual stresses are compared with residual stresses in weld joints of P91 and SS304.

Minimization of Residual Stress in an Al-Cu Alloy Forged Plate by Different Heat Treatments

In order to improve the balance of mechanical properties and residual stress, various quenching and aging treatments were applied to Al-Cu alloy forged plate. Residual stresses determined by the x-ray diffraction method and slitting method were compared. The surface residual stress measured by x-ray diffraction method was consistent with that measured by slitting method. The residual stress distribution of samples quenched in water with different temperatures (20, 60, 80, and 100 °C) was measured, and the results showed that the boiling water quenching results in a 91.4% reduction in residual stress magnitudes compared with cold water quenching (20 °C), but the tensile properties of samples quenched in boiling water were unacceptably low. Quenching in 80 °C water results in 75% reduction of residual stress, and the reduction of yield strength is 12.7%. The residual stress and yield strength level are considerable for the dimensional stability of aluminum alloy. Quenching samples into 30% polyalkylene glycol quenchants produced 52.2% reduction in the maximum compressive residual stress, and the reduction in yield strength is 19.7%. Moreover, the effects of uphill quenching and thermal-cold cycling on the residual stress were also investigated. Uphill quenching and thermal-cold cycling produced approximately 25-40% reduction in residual stress, while the effect on tensile properties is quite slight.

Minimization of Residual Stresses in Submerged Arc Welding Process of Oil and Gas Steel Pipes by Committee Machine

Submerged arc welding (SAW) is a well-known method to weld seam in manufacturing of large diameters steel pipes in oil and gas industry. The main subject of SAW design is selection of the optimum combination of input variables for achieving the desired output variables of weld. Input variables include voltage, amperage and speed of welding and output variables include residual stresses due to welding. On the other hand, main target in multi response optimization (MRO) problem is to find input variables values to achieve to desired output variables. Current study is a combination and modification of some works of authors in MRO and SAW subjects. This study utilizes an experiment design according to Taguchi arrays. Also a committee machine (CM) modeling the problem by CM using two approaches. The first CM consists eight experts with traditional approach in computation and second CM includes elite experts. Genetic algorithm was applied to find CM weights and desired responses. Results show that proposed approach in CM has a smaller root mean squire error (RMSE) than traditional approach. The validation of CM model is done by comparison of results with simulation of SAW process and residual stresses in a finite element environment. Finally, the results show few differences between the real case responses and the proposed algorithm responses.

Effect of substrate temperature on residual stress of ZnO thin films prepared by ion beam deposition

We have investigated the effect of substrate temperature on micro-structural properties of ZnO thin films prepared by ion beam deposition technique. ZnO thin films were deposited on AlN-buffered Si (111) and sapphire (001) substrates at various substrate temperatures. The structural properties and surface morphologies were examined by high resolution X-ray diffraction (XRD) and field emission scanning electron microscopy, respectively. The RMS roughness was measured by atomic force microscopy. XRD measurements confirmed that the ZnO thin films were grown well on the AlN-buffered Si (111) and sapphire (001) substrates along the c-axis. Minimization of residual stress was carried out by tuning the substrate temperature. The structural properties were notably improved with increasing substrate temperature.

Minimization of residual stress in heat-treated Al–Si–Mg cast alloys using uphill quenching: Mechanisms and effects on static and dynamic properties

A method to minimize residual stresses in heat-treated Al–Si–Mg cast components is presented. Compact tension specimens, commonly used for fatigue crack growth testing, were machined from sand castings and tested after T61 heat treatment. The specimens prepared using a conventional T61 treatment had significant residual stresses, which severely affected their fatigue crack growth behavior. To reduce these residual stresses, a modified quenching methodology was used. The method consists of a conventional quench followed by an uphill quench, designed to counteract the residual stress effects introduced during the original quench. This article explains the mechanisms of residual stress formation, residual stress effects on fatigue crack growth, and methods to evaluate and control residual stresses. It also elaborates on the benefits of uphill quenching method, its underlying rationale, working principles, and processing parameters. The effects of the uphill quench on static and dynamic properties are also presented and discussed.

Strength Design and Minimization of Residual Stresses in Reversible GaAs Wafer Bonding Process

The GaAs wafer bonding process is investigated to reduce the mechanical failures of GaAs wafer based on strength design concept. Three-point bending experiment is performed to measure the fracture strength of GaAs wafer, of which cleavage takes place on (110) plane. We propose a simple method for minimizing the thermal residual stress in a three-layer structure, of which the basic idea is to use an appropriate steady-state temperature gradient to the wafer bonding process. The optimum bonding condition of GaAs/wax/sapphire structure is determined based on the proposed method. The effect of material anisotropy on the thermal residual stress is also analyzed by finite element method.

Multi-criteria thermal optimization in liquid composite molding to reduce processing stresses and cycle time

Liquid Composite Molding (LCM) regroups a number of increasingly used composite manufacturing processes. A proper selection of process parameters is crucial to yield successful molding results and obtain an appropriately cured part with minimum defects. In the case of thermosetting resins, the polymerization shrinkage increases the complexity of the thermo-mechanical problem. Numerical analysis of the internal stresses developed during resin cure and subsequent part cooling does not only help to understand the process, but it is also necessary to make thermal optimization reliable. The scope of this work concerns the optimization of resin cure, cycle time and residual stresses during LCM composite processing. A multi-criteria optimization algorithm called Logical Evolutionary Curing Optimization and Quenching (LeCoq) based on evolutionary algorithms was developed to optimize a multi-dimensional objective function that incorporates the following conflicting goals: minimization of residual stresses, maximization of the final degree of cure and reduction of cycle time. An optimized temperature profile obtained with this approach minimizes cycle time and processing stresses, while avoiding at the same time thermal degradation of the matrix and composite delamination. Process optimization with two different objective functions is conducted for a thick composite part. Two optimized temperature cycles are obtained and numerical results are compared and discussed.

The minimization of residual stresses in magnetic systems with quasi-force-free current distribution

The feasibility of a magnet experiencing very low mechanical stresses is studied. Megagauss fields can be generated without failure of the solenoid winding and excessively increasing the winding dimensions if the current distribution is force-free in its inner part and the axial current closes in its outer part. The approximation of the quasi-force-free current distribution by discrete conductive layers is considered. Analysis and computations are performed for two force-free winding approximations. In the former case, the conductors are divided into N paired balanced layers where the azimuth and poloidal currents, respectively, pass. The equal and oppositely directed forces arising in the layers of a pair are transferred to insulating spacers between the layers. Stresses in the spacers can be reduced down to values N times as low as the magnetic field pressure B 0 2 /(2μ0) at the solenoid axis. If the current direction in each of the layers meets the balance condition, the residual stresses can be N2 times lower than B 0 2 /(2μ0), because the tensile and compressive forces in the layers partially cancel.

Mechanical and fatigue properties of stress relieved type 302 stainless steel wire

Type 302 stainless steel wire is manufactured using a cold extrusion process. The cold working increases the ultimate strength of the wire from approximately 690 MPa to 2070 MPa. However, the cold working process creates residual stresses and surface microcracks in the wire. The residual stresses and microcracks reduce the fatigue life of the wire considerably. Elimination or minimization of residual stresses and microcracks is necessary if longer fatigue life is required. Residual stresses or microcracks in a wire can be minimized by a heat treatment process, which could improve both its mechanical properties and fatigue properties.

Influence of machining temperature on the surface damage, residual stress, and texture of hot-pressed beryllium

The effect of lathe machining temperature ranging from room to 400°C on the depth of twinning, extent of microcracking, residual stress, and texture of hot-pressed, S200-type beryllium was investigated. It was shown that twinning, microcracking, and residual stress were essentially eliminated when machining was performed above the ductile-to-brittle fracture transition range at 400°C. This behavior has been related to the operation of multiple slip systems, which, in terms of the von Mises criterion, satisfies the condition for uninhibited deformation. Minimization of residual stress was attributed to recovery resulting primarily from dislocation annihilation and climb, the latter giving rise to the formation of welldefined low-angle boundaries and stable hexagonal networks adjacent to the machined surface.