Consideration Of Residual Stresses Research Articles

Microscopic cracking simulation of nanocomposite ceramic tool materials under the consideration of residual stress

In this paper, the numerical simulation of crack propagation in microstructures of Al2O3/SiCn nanocomposite ceramic tool materials is carried out by means of a micromechanical model based on the Voronoi tessellation and the cohesive element theory in order to explore the relationship between microstructure morphologies and mechanical properties. The residual stress initiated due to the mismatch of thermal expansion coefficients and elastic modulus between matrix grains and nanoparticles is considered in the simulation. The effects of microstructure types and nanoparticle volume content on the residual stress field and the fracture behavior are analyzed, respectively.

Study on the Steel Rail Rolling Contact Stress with Consideration of Initial Residual Stress

Based on ANSYS/LS-DYNA explicit analysis software, this paper established the three-dimensional finite element model of wheel/rail rolling contact in curve negotiation with consideration of the residual stress impact after rail straightening process. It used the dynain file method to apply the initial resid- ual stress to the rails, and conducted numerical simulation to the process of dynamic wheel/rail rolling contact under the operation condition which is corresponding to the setting of taking velocity and axle load as the varia- bles. The simulation results can show that with the increase of velocity, the equivalent stress on the outer rail railhead and at the rail web will increase accordingly; the equivalent stress on the inner rail railhead and at the rail web will decrease accordingly; and the equivalent stress on the rail flange will be basically the same. With the increase of axle load, all the equivalent stress on the railheads and rail web of the inner rail and the outer rail will increase accordingly while the equivalent stress on the rail flange will be basically the same.

Experimental investigation on variation of machined residual stresses by turning and grinding of hardened AISI 1053 steel

Residual stresses in machined surfaces are of great importance to the service life of a component under various loading conditions. In many cases, the material damage initiates from the weakest spot with the least compressive stress in the component surfaces. This situation leads to the consideration of residual stress moving beyond the traditional thinking of single or average values to the inclusion of variation of stress values on different measurement points. In this paper, we experimentally investigated the surface and in-depth residual stresses in hardened AISI 1053 steels machined using hard turning and surface grinding processes. Cubic boron nitride (CBN) cutting tools were used in both processes. The effects of depth of cut and number of passes were also studied. It was found that both processes produce a significant amount of compressive stress on the machined surfaces, as well as steep stress gradients underneath the surfaces. Compared with hard turning, surface grinding produces higher magnitudes of average compressive residual stresses, but it also generates up to 14 times higher scattering of residual stresses, indicated by the standard deviation of the residual stress measurements. As a result, the benefits of a highly compressive average residual stress will be offset by highly scattered individual measurements. The stochastic nature of abrasive grit distribution and orientations in grinding wheels is believed to be the contributing factor for the significant scattering. Meanwhile, for hard turning, the variation of surface and in-depth residual stresses greatly increases, up to 3.8 times, with a larger depth of cut and the use of multiple passes; however, this trend is less significant for surface grinding.

Consideration of residual stress and geometry during heat treatment to decrease shaft bending

In automotive industry, heat treatment of components is implicitly related to distortion. This phenomenon is particularly obvious in the case of gearbox parts because of their typical geometry and precise requirements. Even if distortion can be anticipated to an extent by experience, it remains complex to comprehend. Scientific literature and industrial experience show that the whole manufacturing process chain has an influence on final heat treatment distortions. This paper presents an approach to estimate the influence of some factors on the distortion, based on the idea of a distortion potential taking into account not only geometry but also the manufacturing process history. Then the idea is developed through experiments on an industrial manufacturing process to understand the impact of residual stress due to machining on shaft bending and teeth distortion during heat treatment. Instead of being measured, residual stress is being neutralized. By comparing lots between each other, connections between gear teeth geometry and manufacturing steps before heat treatment are obtained. As a consequence, geometrical nonconformities roots can be determined more easily thanks to this diagnosis tool, and corrective actions can be applied. Secondly, the influence of product geometry on bending is experimentally considered. Moreover, metallurgical observations enable to explain the influence of workpieces geometry on shaft bending. Thanks to the obtained results, process and product recommendations to decrease shafts bending are proposed.

Fatigue assessment of welds joining corrugated steel webs to flange plates

This paper presents an analytical approach for the fatigue assessment of welds joining corrugated plates to flange plates. The failure mode, stress distribution and fatigue strength of such welded joints have been examined through experimental tests and finite element analyses. As the stress concentration at the external weld line of the transition curvature is very critical for the fatigue life assessment, the study of such geometric effect has been performed and its resultant stress characteristics are discussed. The results show that, for the stress concentration at the fatigue critical point of the transition curvature, the influence of the corrugation/curvature angle is more significant when the ratio of the curvature radius to the corrugation depth is smaller, and vice-versa. The S–N curve of referred cruciform joint details can be regarded as the lower bound in contrast to the fatigue strength of welded joints with varying corrugation angle. Allowing for the combined stress condition, the proposed analytical approach is demonstrated to be appropriate for the fatigue assessment of the welded joint with the corrugated plate. The consideration of residual stress in the proposed analytical model is also discussed in theory.

Life assessment methodologies incoroporating shot peening process effects: mechanistic consideration of residual stresses and strain hardening Part 2 – approaches to fatigue lifing after shot peening

Shot peening is a well known process applied to components in order to improve their fatigue resistance. In recent years, there has been an increasing interest in including the effects of the shot peening process in life assessment models since this would allow a reduction in conservatism compared to those in current application. Part 1 of this review dealt with the effects of the shot peening process (surface roughening, strain hardening and compressive residual stresses) and the resulting effect on component fatigue life. This part of the review considers how this effect on component fatigue life can be incorporated into life assessment modelling approaches with discussion of the relative merits of each approach. The paper concludes with a flow chart demonstrating a possible route for the inclusion of shot peening effects within industrial component life assessment frameworks.

Life assessment methodologies incoroporating shot peening process effects: mechanistic consideration of residual stresses and strain hardening Part 1 – effect of shot peening on fatigue resistance

Shot peening is a well known process applied to components in order to improve their fatigue resistance. In recent years, there has been an increasing interest in including the effects of the shot peening process in life assessment models since this would allow a reduction in conservatism compared to those in current application. The present paper seeks to review firstly the effects of the shot peening process (surface roughening, strain hardening and compressive residual stresses) and how the magnitude of these effects can be determined both experimentally and numerically. The reasons for the beneficial effect of shot peening on fatigue resistance are reviewed; this includes consideration of how different operating conditions can affect the magnitude of the benefit. The second part of the review details the life assessment approaches which have been developed to date incorporating these effects and seeks to identify the areas in which further development is still required before the models can be applied in structural integrity assessments.

Laser shock processing with two different laser sources on 2050‐T8 aluminum alloy

PurposeThe purpose of this paper is to conduct a comparative study of the surface modifications induced by two different lasers on a 2050‐T8 aluminum alloy, with a specific consideration of residual stress and work‐hardening levels.Design/methodology/approachTwo lasers have been used for Laser shock peening (LSP) treatment in water‐confined regime: a Continuum Powerlite Plus laser, operating at 0.532 mm with 9 ns laser pulses, and near 1.5mm spot diameters; a new generation Gaia‐R Thales laser delivering 10 J‐10 ns impacts, with 4‐6mm homogeneous laser spots at 1.06 mm. Surface deformation, work‐hardening levels and residual stresses were analyzed for both LSP conditions. Residual stresses were compared with numerical simulations using a 3D finite element (FE) model, starting with the validation of surface deformations induced by a single laser impact.FindingsSimilar surface deformations and work‐hardening levels, but relatively lower residual stresses were obtained with the new large 4‐6 mm impact configuration. This was attributed to a reduced number of local cyclic loadings (2) compared with the small impact configuration (4). Additionally, more anisotropic stresses were obtained with small impacts. FE simulations using Johnson‐Cook's material' behavior were shown to simulate accurately surface deformations, but to overestimate maximum stress levels.Research limitations/implicationsThis work should provide LSP workers a better understanding of the possible benefits from the different LSP configurations currently co‐existing: using small (<2 mm) impacts at high‐cadency rates or large ones (>4‐5 mm). Moreover, experimental results and simulated data had never been presented on 2050‐T8 Al alloy.Originality/valueAn experimental (and numerical) comparison using two distinct laser sources for LSP, has never been presented before. This preliminary work should help LSP workers to choose adequate sources.

Predicting welding residual stresses in a dissimilar metal girth welded pipe using 3D finite element model with a simplified heat source

Dissimilar metal welds are commonly used in nuclear power plants to connect low alloy steel components and austenitic stainless steel piping systems. The integrity assessment and life estimation for such welded structures require consideration of residual stresses induced by manufacturing processes. Because the fabrication process of dissimilar metal weld joints is considerably complex, it is very difficult to accurately predict residual stresses. In this study, both numerical simulation technology and experimental method were used to investigate welding residual stress distribution in a dissimilar metal pipe joint with a medium diameter, which were performed by a multi-pass welding process. Firstly, an experimental mock-up was fabricated to measure the residual stress distributions on the inside and the outside surfaces. Then, a time-effective 3-D finite element model was developed to simulate welding residual stresses through using a simplified moving heat source. The simplified heat source method could complete the thermo-mechanical analysis in an acceptable time, and the simulation results generally matched the measured data near the weld zone. Through comparing the simulation results and the experimental measurements, we can infer that besides the multi-pass welding process other key manufacturing processes such as cladding, buttering and heat treatment should also be taken into account to accurately predict residual stresses in the whole range of the dissimilar metal pipe.

Strain-energy function and three-dimensional stress distribution in esophageal biomechanics

Knowledge of the transmural stress and stretch fields in esophageal wall is necessary to quantify growth and remodeling, and the response to mechanically based clinical interventions or traumatic injury, but there are currently conflicting reports on this issue and the mechanical properties of intact esophagus have not been rigorously addressed. This paper offers multiaxial data on rabbit esophagus, warranted for proper identification of the 3D mechanical properties. The Fung-type strain-energy function was adopted to model our data for esophagus, taken as a thick-walled (1 or 2-layer) tubular structure subjected to inflation and longitudinal extension. Accurate predictions of the pressure–radius–force data were obtained using the 1-layer model, covering a broad range of extensions; the calculated material parameters indicated that intact wall was equally stiff as mucosa–submucosa, but stiffer than muscle in both principal axes, and tissue was stiffer longitudinally, concurring our histological findings (Stavropoulou et al., Journal of Biomechanics. 42 (2009) 2654–2663). Employing the material parameters of individual layers, with reference to their zero-stress state, a reasonable fit was obtained to the data for intact wall, modeled as a 2-layer tissue. Different from the stress distributions presented hitherto in the esophagus literature, consideration of residual stresses led to less dramatic homogenization of stresses under loading. Comparison of the 1- and 2-layer models of esophagus demonstrated that heterogeneity induced a more uniform distribution of residual stresses in each layer, a discontinuity in circumferential and longitudinal stresses at the interface among layers, and a considerable rise of stresses in mucosa, with a reduction in muscle.

The effects of residual stresses on the fatigue life of 5083-O aluminum alloy spot welded joints

In this study, resistance spot welding (RSW) process of 5083-O Aluminum alloy has been simulated numerically using an axisymmetric model of electrodes and sheets, and then the effects of residual stresses have been investigated on the fatigue life of the joints. All process parameters except electrode clamping force have been considered to be constant during RSW. Three different electrode force level have been considered and then dimensions of nuggets, HAZ and gaps have been obtained numerically. Three kinds of spot welded models with three different gap values between sheet joints have been simulated using Ansys code. Non-linear analysis was performed to obtain the local stress and strain ranges and then, Morrow equation with particular consideration of residual stress and gap distance effects has been applied to estimate fatigue lives. The results show that, with increasing the electrode force, the gap values between sheet joints increase. The results also reveal that the center region and the roots of nuggets have surrounded by the relatively large amounts of tensile residual stresses and also increasing the electrode force, reduce the amounts of residual stresses. The comparison between numerical results of fatigue lives and experimental data provided good agreement between numerical predictions and experiments.

Friction stir welding of aluminium alloys

<title/>The comprehensive body of knowledge that has built up with respect to the friction stir welding (FSW) of aluminium alloys since the technique was invented in 1991 is reviewed. The basic principles of FSW are described, including thermal history and metal flow, before discussing how process parameters affect the weld microstructure and the likelihood of entraining defects. After introducing the characteristic macroscopic features, the microstructural development and related distribution of hardness are reviewed in some detail for the two classes of wrought aluminium alloy (non-heat-treatable and heat-treatable). Finally, the range of mechanical properties that can be achieved is discussed, including consideration of residual stress, fracture, fatigue and corrosion. It is demonstrated that FSW of aluminium is becoming an increasingly mature technology with numerous commercial applications. In spite of this, much remains to be learned about the process and opportunities for further research and development are identified.

Fatigue design of welded joints from the wrought magnesium alloy AZ31 by the local stress concept with the fictitious notch radii of rf = 1.0 and 0.05 mm

Investigations were carried out with three different types of MIG- and TIG-welded joints of the magnesium alloy AZ31(ISO-MgAl3Zn1): fully or partially penetrated butt welds, transversal stiffeners. The evaluation of the results showed that the local stress concept using the fictitious notch radius of r f = 1.0 mm can be applied to magnesium welded joints from plates with thicknesses t ⩾ 5 mm independently of the weld geometries. Design curves are proposed for different stress ratios, i.e. R = −1 as well as 0 and 0.5, which allow the consideration of residual stresses as well as load induced mean-stresses. The results also permit the suggestion of Δ σ = 28 MPa for r f = 1.0 mm as FAT-value in the IIW-Fatigue Design Recommendations. Further, the FAT-value Δ σ = 73 MPa is also derived for the fictitious radius of r f = 0.05 mm to be applied to welded thin magnesium joints ( t < 5 mm). These FAT-values are compared with data already known for steel and aluminium joints. A linear relationship between the FAT-values and the Young’s modulus is determined.

Effects of the Welding Residual Stress on the Grounding Damage Analysis of a Tanker

Vessels are rarely subjected to accidental loads such as the collision, grounding and stranding. But these accidental loads cause a lot of damages to hull structure including a large deformation, fracture, tearing and so on. In case of carrying dangerous goods such as crude oil, these accidents can induce a serious environmental pollution. All ocean-going vessels were made by welding. The welding residual stress is a significant shortcoming of welding remains at the hull structure, even though welding technology in shipbuilding field has provided a variety of advantages, e.g. remarkable shortening of the shipbuilding time. The aim of this paper is to investigate the effects of the residual stress in a grounding accident. When a ship runs aground against a sea-obstacle like a rock, this accident can be classified as a grounding. Among parameters of grounding accident scenarios such as the ship speed, the initial striking point, and loading conditions of the ship, only ship speed varies from 10 to 15 knots under ballast condition with/without consideration of residual stress(this sentence is not clear to the read). The initial striking point is at the bow of the center line of ship. A series of nonlinear numerical simulations with large deformation and fracture were carried out using LS-DYNA. As a result, two cases with residual stress have longer damage length. The difference seems to be relatively small, but not negligible.

Fatigue design of aluminium welded joints by the local stress concept with the fictitious notch radius of rf=1 mm

The investigations were carried out with three different types of MIG-welded joints of the two aluminium alloys AlMg4.5Mn (AW-5083) and AlMgSi1 T6 (AW-6082 T6) under fully reversed and pulsating axial loading. The evaluation of the results showed that the local stress concept using the fictitious notch radius of r f=1.0 mm can be applied to aluminium welded joints from plates with thickness t≥5 mm independently from the alloy and weld geometries (fully or partially penetrated butt welds, transversal stiffener). Master design curves are proposed for different stress ratios, i.e. R=−1, 0 and 0.5, which allow the consideration of residual stresses as well as load induced mean stresses. The results permit also the suggestion of Δ σ=70 MPa as FAT-value for the IIW-fatigue design recommendations.

Fatigue analysis of crankshaft sections under bending with consideration of residual stresses

In this paper, the influence of the residual stresses induced by the fillet rolling process on the fatigue process of a ductile cast iron crankshaft section under bending is investigated. The stress concentration near the fillet of the crankshaft section under bending without consideration of residual stresses is first investigated by a two-dimensional elastic finite element analysis. The plastic zone development and the residual stress distribution near the crankshaft fillet induced by the fillet rolling process are then investigated by a two-dimensional elastic–plastic finite element analysis. In order to use the two-dimensional finite element analysis to shed light on the residual stress distribution due to the three-dimensional rolling process, the rolling depth after the unloading of the roller in the two-dimensional finite element analysis is determined by the fillet surface profiles measured by the shadowgraphs taken before and after the fillet rolling process. After the rolling process, a bending moment is then applied to the crankshaft section. With consideration of the stresses due to the rolling process and the bending moment, the fatigue failure near the fillet is investigated based on a linear elastic fracture mechanics approach. An effective stress intensity factor, which combines the stress intensity factors due to the bending moment and due to the residual stresses, is defined. An effective stress intensity factor range is then approximated and compared to an assumed threshold stress intensity factor range to determine if the crack can continue to propagate for a given crack length. The results indicate that the four-bubble failure criterion only determines the crack initiation life for small cracks initiated on the surfaces of fillets. The four-bubble failure criterion does not indicate whether a fatigue crack initiated on the fillet surface can propagate through or arrest in the compressive residual stress zone induced by the rolling process.

Sputtering deposited TiNi films: relationship among processing, stress evolution and phase transformation behaviors

TiNi films were prepared by co-sputtering a Ti50Ni50 target and a Ti target under different process parameters. Stress in TiNi film on silicon substrate were evaluated using curvature method. A wide range of residual stress levels (either tensile or compressive) were found in the deposited films, depending significantly on Ti/Ni ratio, gas pressure, deposition temperature and/or annealing conditions. Stress evolution for as-deposited amorphous films during annealing process were systematically studied with the consideration of residual stress in as-deposited films; thermal stress; tensile stress due to densification crystallization; stress relaxation due to martensite transformation, etc. Upon heating, the crystallized TiNi films generated large tensile stresses when transforming from martensite to austenite, whereas during cooling, the stress relaxed significantly when austenite transformed back to the ductile martensite. The stress generation and relaxation behavior was significantly affected by film composition, deposition temperature and/or annealing temperature.

Fatigue Strength Evaluation on Resistance Spot Welds of the Vehicle Body

This article evaluates the fatigue stress–fatigue life relationship of spot-welded structures in the vehicle body, considering the residual stress effect. When a vehicle travels on an actual road, the resistance spot welds of the vehicle structure are exposed to complex loadings. Because fatigue strength in the resistance spot weld of a vehicle body can be determined by residual stresses, joint geometry, and loading state during driving, actual loading state must be estimated with consideration of residual stresses. In this study, fatigue stress–fatigue life relationship derived from residual stress was obtained by thermoelastic, plastic, finite-element analysis. Applied loading in resistance spot weld of the vehicle body was calculated by dynamic analysis. Assumptions regarding fatigue life were based on proposed methods.

多方向強化複合材料積層板の層内樹脂割れ解析手法の提案

A new analytical method for calculation of transverse lamina cracking in multidirectionally laminated composites has been proposed in the present paper. Both energy balance criterion and stress criterion have been applied simultaneously for evaluation of initiation and extension of transverse lamina cracks with special consideration of residual stress. A micro model of [ θ/90 ] s laminate with a transverse crack in 90 deg. layer has been numerically analyzed and the results have been applied to evaluate the stress distribution and the stiffness reduction of a multidirectional laminate. Mixed mode fracture criterion based on Mode I and II energy release rates and Hashin's stress criterion were used to predict the initiation and extension of transverse lamina cracks in the multi layers. The analytical results were compared with experimental results of the cross-plied and quasi-isotropic laminates. Effects of ply thickness and stacking sequence on behavior of transverse lamina cracking were well explained by the present method. The present method has been expected to be a useful analytical tool for damage tolerance design of laminated composite structures.

Finite element modelling of a submerged arc welding process

A multi-wire submerged arc welding (SAW) process has been modelled using a general purpose finite element package ABAQUS. The paper explains briefly the welding process and its application in thick wall linepipe manufacturing. Corresponding 2D and 3D finite element (FE) models of the SAW process are presented. FE analyses were carried out to investigate the heat transfer characteristics in the fusion and heat affected zones during welding. The effect of process parameters and weldment geometry have been evaluated with and without the consideration of residual stresses and strains induced from the forming processes prior to welding. Comparisons of FE predictions with experimental results are presented where it is appropriate. It is shown that the geometrical distortion and residual stresses and strains caused by welding can be minimised through process optimisation. It is therefore demonstrated that finite element analysis can be applied to better understand the SAW process and hence be a useful tool for future process development and control with the view of optimising product properties.