Redistribution Of Residual Stresses Research Articles

Influence of Residual Stresses on Fretting Fatigue Life Prediction in Ti-6Al-4V

Abstract The objective of this work was to evaluate life prediction methodologies involving fretting fatigue of turbine engine materials with advanced surface treatments. Fretting fatigue tests were performed on Ti-6Al-4V dovetail specimens with and without advanced surface treatments. These tests were representative of the conditions found in a turbine engine blade to disk attachment. Laser shock processing and low plasticity burnishing have been shown to produce deep compressive residual stresses with relatively little cold work. Testing showed these advanced surface treatments improved fretting fatigue strength by approximately 50 %. In addition to advanced surface treatments, several specimens were also coated with diamond-like carbon applied through a nonline-of-sight process capable of coating small dovetail slots in an engine disk. Testing with this coating alone and combined with advanced surface treatments also significantly improved fretting fatigue strength due to a decreased coefficient of friction along with the compressive residual stresses. This work presents a mechanics based lifing analysis of these tests that takes into account the local plasticity and the redistribution of residual stresses due to the contact loading. The use of superposition of the residual stresses into the contact stress analysis results in unconservative crack growth life predictions. Finite element analyses were conducted to predict the redistribution of residual stresses due to the contact loading. The redistributed residual stresses were used to make improved crack growth life predictions when possible. The results showed very little redistribution of residual stresses for the advanced surface treatments, however, a significant change in shot peened residual stress gradients was predicted.

Residual Stress Relief and Redistribution of Welded Metals by Vibratory Stress Relaxation

In this study, research work on the effects of vibrational energy on the microstructure of welds and Charpy toughness is performed. The results show that vibration during welding exhibits positive effects on the microstructure constituent formation by reducing the amount and thickness of grain boundary ferrite and suppressing the formation of the Widmanstatten structure. And also due to the finer microstructure developed by the vibration, toughness value of the weld metal increases.

Three-dimensional numerical simulation of brazed residual stress and its high-temperature redistribution for stainless steel plate-fin structure

A numerical simulated procedure is presented for analyzing the brazed residual stress and its high-temperature redistribution for stainless steel plate-fin structure applied to recuperative heat exchanger in gas-turbine power generation. Based on the finite element ABAQUS code, firstly, the as-brazed residual stress generated during cooling from brazing temperature to room temperature was obtained. Secondly, the residual stress redistribution due to creep relaxation behavior was simulated, which is implemented by Norton creep constitutive equation. Calculated results show that large residual stress with a complex distribution exists in the brazed joint. The peak stress is presented in the fillets where the crack would initiate and propagate. This is mainly caused by the mechanical properties mismatching between filler metal and base metal. But the as-brazed residual stress is greatly relieved and redistributed due to the creep relaxation at elevated temperature. The stress evolution regularity with time at 600 °C is achieved.

The Thermal Residual Stress Redistribution in a Bamboo Interconnect

An analytical expression is developed to predict the thermal residual stress redistribution in a passivated bamboo interconnect based on the coupling of the grain boundary diffusion with the interconnect-passivation interface diffusion. Quantitative results show that the thermal stress redistribution in the interconnect depends strongly on the microstructure of the interconnect, the initial state of the thermal residual stress and the diffusivity ratio of the grain boundary to the interface.

4005 2024-T3摩擦攪拌接合継手のき裂進展特性に関する研究(S62-2 宇宙構造・材料(2),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

In this study, crack propagation tests were conducted to clarify property for the fatigue crack propagation of friction stir welded 2024-T3 aluminum alloy. The welding line of the specimens inclined 0 and 30 degree to direction of applied stress. Results showed that crack propagation rate was accelerated by the tensile residual stress around the welding line. After the crack tip run thought the welding line, the crack propagation rate was accelerated by tensile stress that was caused by the residual stress redistribution during crack propagation. The crack grew perpendicular to the loading direction regardless of the angle of the welding line. And crack propagation rate was not affected by the angel of FSW joint.

Application of secondary and residual stresses to the assessment of the structural integrity of nuclear power-generating plant

Magnox nuclear power stations were built in the 1960s to design codes that, in general, required weldments to be subject to a post-weld heat treatment to remove residual stresses. Implicit in this was the assumption that the heat treatment reduced the stresses significantly such that as stated in the codes “stresses caused by fabrication and welding are practically annulled”. However, it has since been realised that the stresses remaining, although small, could still be significant when incorporated into the subsequently developed failure avoidance methodologies such as R6. Moreover, either at the time of construction or during the operating life, repairs are undertaken to remove manufacturing or service-induced defects. These repairs can be put into service with or without a post-weld heat treatment. As a consequence of a paucity of data for the two- and three-dimensional distribution of the magnitude of these stresses, extremely conservative values of stresses have been adopted to ensure that the plant is secure against the design intent throughout the service life. In this paper, the requirements of the failure-avoidance methodology R6 Revision 4 are briefly reviewed with respect to the categorisation of secondary and residual stresses and the application of the three approaches for determining the as-welded residual stress distribution at room temperature. These three levels comprise, Level 1, simple estimates, Level 2, bounding profiles, and Level 3, detailed evaluation. Examples are presented where knowledge of the residual stresses has been an important component of the overall integrity assessment. The first relates to multi-pass weldments in superheater headers fabricated from a ferritic steel and the second to the weldments in the standpipes, both at Magnox power stations with concrete pressure vessels. Although in these cases the weldments had been subject to a post-weld heat treatment, the remaining residual stresses presented a significant challenge to the perceived structural integrity. Finally, the future requirements for the residual stresses to be incorporated into structural integrity assessments of ferritic steel nuclear power plant components and structures will be discussed. This will be by reference to various weldment geometries and heat treatment cycles including repair welds and fillet attachment welds. In particular, there is a need for improved measurement techniques and analytical/computer models to provide more realistic three-dimensional stress distributions for a range of weldment geometries. In addition, there is a need to revisit the criteria adopted to establish the initiation fracture toughness of ductile ferritic steels with respect to the attendant redistribution of residual stresses.

On the Stress Intensity Factor of Cracks in Residual Stress Field

The use of weight function technique in fatigue crack growth subjected to external cyclic loading and residual stress field has been questioned by several researchers in that the technique is unable to account for the residual stress redistribution during the crack growth. In this paper a center cracked tension specimen containing residual stresses was analyzed by finite element method. The crack growth was simulated by releasing the nodes ahead of crack tip in stepwise and the stress intensity factors induced by residual stresses at different crack lengths were estimated. The results from the numerical analysis are identical to the weight function solution, which demonstrates that the weight function technique can be used for the fatigue crack growth analysis in residual stress field, unless the residual stress distribution is disturbed by the plastic yield.

Residual stresses in coating-based systems, part II: Optimal designing methodologies

In this part of the work, different cases are studied to illustrate the implementation of the analytical models that have been developed in Part I [Front. Mech. Eng. China, 2007, 2(1): 1–12]. Different topics are involved in the optimal design of coating-based systems. Some essential relations among material properties and dimensions of the coating and substrate and the residual stress variations are reflected. For the multilayered coating-based systems, some optimal design methodologies are proposed, such as the decrease in stress discontinuity at the interface between the adjacent layers, the curvature as a function of the coating thickness, the effect of the interlayer on the residual stress redistribution, and so on. For the single-layered coating-based systems, some typical approximations that are often used to predict the residual stresses in the coating-based system or bilayer structure are corrected. A simplified model for predicting the quenching stress in a coating is also developed.

Residual stress measurement in a repair welded header in the as-welded condition and after advanced post weld treatment

Measurements of the residual stresses in a type 316H stainless steel steam header were made using the deep hole drilling (DHD) technique to characterise the through thickness residual stress distribution in a circumferentially repaired weld in the as-welded condition and after an advanced post weld treatment (APWT) had been applied. The measured residual stress field was compared with finite element (FE) predictions. Overall there was a good correlation between the DHD measurement results and the FE results in the as-welded condition. The results highlighted the generation of high residual stresses due to repair welding. After APWT, there were noticeable differences between the measurements and the FE predictions. The study also demonstrated the feasibility of performing an APWT procedure on components and its significant effect on the redistribution of residual stresses. In particular, it was demonstrated that APWT promoted a finite volume of compressive stresses near the critical area of the header, thus providing increased confidence in the component integrity.

Residual Stress Evaluation of AA2024-T3 Friction Stir Welded Joints

The main aim of this study was to evaluate the residual stress field in friction stir welded joints of 2024-T3 aluminum alloy plates using the slitting method. This is based on the fact that when a cut, simulating a growing crack, is incrementally introduced into a part, residual stresses are relieved on the slot surfaces created, causing the part to deform. Such deformation can be measured by strain gages attached to specific regions of the part and the residual stress profile that originally existed can be evaluated. Cuts were introduced by wire electro discharge machining (WEDM), in finishing mode, either perpendicularly or longitudinally to the weld nugget, in 3.2 × 60 × 120 mm3 rectangular testpieces. For the longitudinal testpieces, the slot was introduced in two different positions: on the center of the weld nugget and 5 mm distant from the weld center line, in order to sample the thermomechanically/heat affected zone. The residual stress intensity factor, K r, was calculated using a fracture mechanics approach and the inverse weight function method was employed to obtain the initial residual stress profile. Residual stress redistribution profiles ahead of the slot tip could also be derived using the inverse weight function method. However, for cracked components subjected to compressive residual stress fields, when the crack faces are in contact, a non-linear problem arises and the zero displacement condition has to be taken into account in order to provide a more accurate solution of the residual stress field.

Basic Materials Studies of Lanthanide Halide Scintillators

AbstractCerium and lanthanum tribromides and trichlorides form isomorphous alloys with the hexagonal UCl3 type structure, and have been shown to exhibit high luminosity and proportional response, making them attractive alternatives for room temperature gamma ray spectroscopy. However the fundamental physical and chemical properties of this system introduce challenges for material processing, scale-up, and detector fabrication. In particular, low fracture stress and perfect cleavage along prismatic planes cause profuse cracking during and after crystal growth, impeding efforts to scale this system for production of low cost, large diameter spectrometers. We have reported progress on basic materials science of the lanthanide halides. Studies to date have included thermomechanical and thermogravimetric analyses, hygroscopicity, yield strength, and fracture toughness. The observed mechanical properties pose challenging problems for material production and post processing; therefore, understanding mechanical behavior is key to fabricating large single crystals, and engineering of robust detectors and systems. Analysis of the symmetry and crystal structure of this system, including identification of densely-packed and electrically neutral planes with slip and cleavage, and comparison of relative formation and propagation energies for proposed slip systems, suggest possible mechanisms for deformation and crack initiation under stress. The low c/a ratio and low symmetry relative to traditional scintillators indicate limited and highly anisotropic plasticity cause redistribution of residual process stress to cleavage planes, initiating fracture. Ongoing work to develop fracture resistant lanthanide halides is presented.

Effect of weld clip design on thermally induced angular misalignment in laser welding based optoelectronic packaging

Thermally-induced angular misalignment of fiber collimators in the laser packaging of optical devices is studied experimentally and numerically in this study. A novel design of arch-shaped weld clips is proposed and tested; after sustaining 10 consecutive accelerated thermal cycles, the proposed clips have been demonstrated to significantly lower angular misalignment, from the original error of 0.023° for a traditional saddle-shaped weld clip, to an improved 0.01°. A non-linear thermal–mechanical coupled finite element analysis (FEA) has also been used to simulate the variation of thermal stresses, the distribution of residual stresses, as well as the accumulated angular misalignment in the package. The results of the simulation have been found to be in full agreement with the experimental measurements. The calculation further indicates that the saturated angular shift is 0.043° for the proposed weld clip, dramatically improved from the 0.065° angular shift for a conventional saddle-shaped clip. The major angular misalignments come from the redistribution of residual stresses in solidification shrinkage, as well as the thermal stresses induced by temperature fluctuation within the package.

Residual stress redistribution within high-temperature coatings due to surface cracks

Residual stress is one of the important mechanical properties of high-temperature coatings and it will be redistributed if the physical discontinuities are presented. The objective of this theoretic study was to investigate the residual stress redistribution within a high-temperature ZrO 2/NiCoCrAlY coating due to the presence of surface crack. Results indicated that the shape and dimension of crack had significant influences on the magnitude and distribution of the residual stresses within coatings. When the surface crack was absent, there was a remarkable stress concentration near the edge of the coating. However, the location of the stress concentration may be changed due to the presence of surface crack. The effect of multi-surface crack on the residual stress redistribution within the coating was also discussed.

Influence of Residual Stress Redistribution on Fatigue Crack Growth and Damage Tolerant Design

The safe operation of many structures and components is ensured through the operation of damage tolerant design and evaluation. Substantial residual stresses can exist in many systems and it is important that these are incorporated in damage tolerance calculations of fatigue crack growth. Recent improvements in non-destructive measurement techniques and in the application of weight or Green’s functions methods of including residual stress fields into stress intensity factor (SIF) calculations have enabled predictions of the effects of residual stresses on fatigue crack propagation to be made more readily. Two examples from the aerospace industry, structures containing (i) cold expanded holes and (ii) fusion welds are used to show that presently, although final crack growth lives can be accurately predicted, the details of crack growth are not well represented with initial growth typically being underestimated and later growth being over estimated. It is shown that this is most likely to be due to residual stress redistribution. and that this must be built into fatigue life prediction models if accurate damage tolerance based procedures are to be developed for components and systems containing substantial residual stresses.

Effects of the Load History on the Residual Stress Distribution in Welded Components

The lifetime of a welded component is finally influenced by the various service conditions. The stress redistribution effect of subsequent load histories is fundamental to the load-bearing capacity of a structure later in service. Since every welded structure additionally experiences external shrinkage restraint, the resulting structural loads are very important for mechanical assessment. Forward-looking development of materials furthermore requires particular consideration of in-service load histories and of their effects on the global structural loads of a construction under shrinkage restraint. Using a large-scale test facility, stress and residual stress investigations have been performed relating to the subject area of residual stress redistribution resulting from a simulated load history. Based on the presented results, which were all carried out with matching filler materials, further research work concerning the influence of the variation of the mismatch factor on the residual stress distribution has to be done.

Limited weld residual stress measurements in fatigue crack propagation: Part II. FEM‐based fatigue crack propagation with complete residual stress fields

ABSTRACTUsing a limited set of residual stress measurements acquired by neutron diffraction and an equilibrium‐based, weighted least square algorithm to reconstruct the complete residual stress tensor field from the measured residual stress data, the effect of weld residual stress on fatigue crack propagation is investigated for 2024‐T351 aluminium alloy plate joined by friction stir welding. Through incorporation of the least squares, complete equilibrated residual stress field into a finite element model of the Friction Stir Weld (FSW) region, progressive crack growth along a direction perpendicular to the welding line is simulated as part of the analysis. Both the residual stress redistribution and the stress intensity factor due to the residual stress field, Kres, are calculated during the crack extension process.Results show that (a) incorporation of the complete, self‐equilibrated residual stress field into a finite element (FE) model of the specimen provides a robust, hybrid approach for assessing the importance of residual stress on fatigue crack propagation, (b) the calculated stress‐intensity factor due to the residual stress field, Kres, has the same trend as measured experimentally by the ‘cut‐compliance method’ and (c) the da/dN results are readily explained with reference to the effect of the residual stress field on the applied stress intensity factor.

Surface Crack Propagation Analysis under Residual Stress Field

Stress intensity factors due to surface crack propagation were analysed by using the influence function method and inherent strain analysis of the residual stress fields caused by welding. The initial residual stress in a plate with a welded butt joint was calculated by using inherent strain analysis, and the redistribution of residual stress and the stress intensity factor due to crack propagation were analysed as changes in the structure’s shape. The stress intensity factor was also calculated by using an influence function database. The stress intensity factor in the residual stress fields due to crack propagation obtained by using inherent strain analysis completely agreed with that obtained by using the influence function method. The results of the crack propagation analysis were compared with the experimental results of a fatigue test. It was validated that both the inherent strain analysis and the influence function method were efficient for analysing stress intensity factors in residual stress fields caused by welding.

변동하중을 받는 Lower Control Arm의 잔류응력 변화

Vehicle components such as lower control arm are usually affected by heat during the welding process. As a result, residual stress is generated, which has much effect on mechanical performances such as crashworthiness and durability. In this study, the residual stress in lower control arm has been measured by the x-ray diffraction method and been analyzed by finite element methods. Heat transfer during seam weld process has been calculated and used in calculating thermal deformation with temperature dependent material properties. High residual stress has been found at vertical wall both by measurement and simulation. The simulation also showed the residual stress re-distribution when the component is subjected to cyclic loading condition.

Modelling the Redistribution of Residual Stresses at Elevated Temperature in Components

Abstract In this study the effects of high temperature relaxation on the residual stresses has been examined for T-plate and tubular T-joint geometries by numerical analysis using elasto-plastic-creep finite element modelling. It is shown that residual stresses are important, especially at the early stages of lifetime before the residual stresses relax rapidly. A sensitivity analysis was carried out by varying the creep properties and geometric constraint under plane stress and plane strain conditions. A comprehensive residual stress profile derived from measured residual stresses of a range of steels and different geometries that have been welded, cold bent, repair welded, or overloaded, was used as a ‘Master curve’ of the residual stresses. In all cases compared, it has been shown that the transverse measured residual stresses were tensile at the surface The stress intensity factor (SIF) estimates using the master curve profile for the T-Plate, and tubular T-joint geometries are lower compared to current case specific residual stress profiles used in R6 and BS7910 procedures but is still sufficiently conservative when compared with experimental measured residual stress data. It has also been shown that the numerically calculated residual stresses induced by overload in this study compare well at the surface with the master curve but decrease more rapidly with respect to crack depth compared to experimental values. Furthermore, by considering creep stress relaxation rates from the present FE calculations, it is shown that the peak surface residual stresses drop rapidly to about 50% at the relatively short duration of the first 1000 h. The SIF values of the predicted residual stresses are found to be lower than the experimentally measured data, and they are also found to be insensitive to stress relaxation in the through depth of the T-plate and tubular T-joint geometries. It was shown that the master curve gives an overall conservative SIF, though reduced, for the weld residual stresses as well as for residual stresses derived from overload. Furthermore, where redistribution of the residual stresses is concerned, it is shown that present profiles may all be unduly conservative in their SIF estimations.

Machining FGM: Residual Stresses Redistribution

Machining FGM: Residual Stresses Redistribution