Maximum Tensile Residual Stress Research Articles

Numerical Analysis of Residual Stress for Copper Base Brazed Stainless Steel Plate-Fin Structure

Copper base stainless steel plate-fin structure has been widely used as a heat exchanger in many fields. The nonlinear thermal reaction on the residual stress in brazing process of the plate-fin structure was studied in this paper. A finite element model (FEM) was proposed to simulate the heat transfer and the sequential residual stress generated in the plate-fin and filler metals based on thermal elastic-plastic theory. By the stress distribution in four paths marked in the structure obtained from FEM results, it is found that the maximum residual tensile stress occurs in the brazed joint next to the plate side and a crack would initiate in this region. Also, the first principle stresses of reference nodes were calculated and the conclusion is consistent with the simulation results. These results would provide some constructive instructions in the practical brazing procedure.

The effects of laser peening and shot peening on fretting fatigue in Ti–6Al–4V coupons

This paper describes testing of Ti–6Al–4V coupons in fretting fatigue and compares the effects of mechanical surface treatments on performance. Fretting fatigue tests were performed using a proving ring for fretting load, bridge-type fretting pads, and applied tension–tension cyclic fatigue stress. As-machined (AM), shot peened (SP), and laser peened (LP) coupons were evaluated, and data generated to compare residual stress, surface condition, lifetime, and fractographic detail encountered for each. Near-surface residual stress in SP and LP coupons was similar. The layer of compressive residual stress was far deeper in LP coupons than in SP coupons and, consequently, subsurface tensile residual stress was significantly greater in LP coupons than in SP coupons. SP coupons exhibited a rough surface and had the greatest volume of fretting-induced wear. LP coupons exhibited a wavy surface and had a small volume of wear localized at wave peaks. SP coupons had the greatest fretting fatigue lifetime, with significant improvement over AM coupons. Lifetimes of LP coupons were similar to those for SP coupons at high fatigue stress, but fell between AM and SP coupons at lower fatigue stress. Fractographic evaluation showed that fractures of AM samples were preceded by initiation of fretting-induced cracks, transition of a lead fretting crack to mode-I fatigue crack growth, and crack growth to failure. SP and LP samples exhibited behavior similar to AM samples at high fatigue stress, but in coupons tested at low stress the lead crack initiated subsurface, near the measured depth of maximum tensile residual stress, despite the presence of fretting-induced cracks. The level of fatigue stress above which lead cracks were initiated by fretting was higher for LP than for SP, and was predicted with good accuracy using an analysis based on linear elastic fracture mechanics, the fatigue crack growth threshold stress intensity factor range, and superposition of measured residual stress and applied fatigue stress.

ワイヤークラスプの屈曲操作により生じる残留応力と曲げ特性の検討

The purpose of this study was to assess the influence of residual stress produced after the bending manipulation of a straight wire on flexibility and permanent deformation of wrought-wire clasps. A three-dimensional finite element model of a straight wire (12 mm in length and 1.0 mm in diameter) was created. Elastic and plastic properties of a commercial Co-Cr straight wire measured by means of tensile test were input into the program. We simulated the bending of the clasp shoulder and clasp arm to an angle of 90 degrees or 120 degrees and subsequent unloading processes with spring-back phenomenon. The maximum residual tensile stress appeared at the inside of the bending angle after unloading of the bending force. Thereafter, the clasp models were deflected 0.25, 0.50 mm, and 0.75 mm at the tip to simulate the removal and insertion of a denture. The maximum tensile stress at the inside corner of the bending angle under the deflection was considerably higher than the residual stress before deflection. The stress increase by the deflection was larger at the shoulder than the arm. The load required for deflection was larger in the models with the arm of 120 degrees angle than models with the arm of 90 degrees angle. The results suggest that the permanent deformation of wrought-wire clasps is likely to initiate at the clasp shoulder, while the clasp flexibility is dependent on the bending angle of the clasp arm.

Solid State Bonding of Carbon Material to Copper with Nickel Insert

Carbon material/nickel/copper system was heated under a compressive stress of 13 MPa in a vacuum at 1073 K for different keeping times, and the bending strength of the joint, the microstructure, hardness and carbon concentration near the joining interface were examined. Thermal stress induced in the joint was estimated by a finite element method. In carbon material/copper system solid state bonding is difficult. However, good solid state bonding becomes feasible when nickel is used as an insert metal. Axisymmetric thermoelastic finite element analysis reveals that the maximum tensile thermal stress is induced on the surface of carbon material near the joining interface, and it decreases with increasing nickel thickness. The maximum residual tensile thermal stress in practical joints is less than the maximum tensile thermal stress calculated by finite element method because the thermal stress is released. [doi:10.2320/matertrans.H-MRA2008819]

Simulation of welding residual stresses in resistance spot welding, FE modeling and X-ray verification

In the present study, an electro-thermo-mechanical model is utilized to predict electrical potential, temperature and residual stress distributions during different stages of resistance spot welding. In order to improve accuracy, material properties including physical, thermal and mechanical properties supposed to be temperature-dependent. The employed model is capable of considering the effects of welding parameters such as heat input and welding time on residual stress distribution. The model results are then compared with the measured residual stresses and good agreement is observed. Predictions show that maximum tensile residual stresses are located at the weld center while they are reduced towards the nugget edge.

Microstructure and mechanical properties of magnesium alloy AZ31B laser beam welds

Microstructure and properties of a Mg AZ31B laser beam weld without filler are studied using electron microscopy, X-ray diffraction and mechanical tests. The microstructure of the weld is characterized by a narrow heat affected zone, columnar grains and precipitate coarsening in the fusion zone. Texture in the fusion zone is significantly different from the texture of the base material. The residual stress distribution observed is similar at the top and the bottom of the weld, maximum tensile residual stress values are observed in the fusion zone. Tensile tests reveal differences in the mechanical behavior of the fusion zone and the parent material, which can be related to the differences of texture and the resulting deformation mechanisms.

Effect of Rounded Cutting Edge Radius on Residual Stress within Machined Sublayer

A coupled thermal-mechanical model of plane-strain orthogonal metal cutting with continuous chip formation is developed to investigate the residual stresses in the finished workpiece. Deformation of the workpiece material is treated as elastic-viscoplastic with isotropic strain hardening, and the numerical solution accounts for coupling between plastic deformation and the temperature field, including treatment of temperature-dependent material properties. Automatic continuous remeshing and adaptive meshing technique are employed to achieve chip separation at the tool tip region and a satisfactory solution. The finite element model is well validated by comparing values of the predicted cutting forces and residual stresses with experimental results. Based on the established finite element model, the effect of rounded cutting edge radius on residual stress distribution is analyzed. The results show that altered cutting edge radius clearly produced significant changes in residual stresses. The maximum tensile residual stress and its penetration depth decrease as the cutting edge radius increases.

A Comparative Study of Microstructure and Residual Stresses of CMT-, MIG- and Laser-Hybrid Welds

Recently a new welding technique, the so-called ‘Cold Metal Transfer’ (CMT) technique was introduced, which due to integrated wire feeding leads to lower heat input and higher productivity compared to other gas metal arc (GMA) technique. Here microstructure formation and residual stress state in aluminum CMT welds are characterized and compared to those produced by pulsed MIG- and Laser-hybrid techniques. The results show a small heat affected zone (HAZ) in the MIG weld, the HAZ in the CMT and the laser hybrid welds was not visible by optical and scanning electron microscopy. Compared to the MIG welding the CMT process appears to introduce slightly smaller maximum tensile residual stresses into the weld.

Fracture of composite alumina/yttria-stabilized zirconia joints

Four-point bend tests have been performed on samples consisting of yttria-stabilized zirconia containing 0–80% alumina joined by plastic deformation to the same or different composition. The fracture strength of joints between the same composition was equal to the strength of the monolithic material. Fracture of joints made between different compositions occurred at the position of maximum tensile residual stress, as determined by finite-element analysis, not at the interface. Measured strengths were in accord with fracture mechanics and the calculated residual stresses.

Calculation of Thermal Stresses in Mo-Ti FGM with a Continuous Change of Composition

In the present paper, a kind of Mo-Ti system functionally graded material with a continuous change of composition was formed via particle settling method at first, and then it was desified by hot-press under 1473K-30MPa-1h. Finally, by using an axisymmetric finite element method, the fabricated thermal stresses in a disk-shaped Mo-Ti FGM were calculated. The results showed that the thermal stresses changed continuously with the smooth variation of graded composition. The residual tensile stresses in the Mo-Ti FGM with a continuously changed composition were located in the medial region of graded layer and the radial compressive stresses distributed in the Mo- and Ti-rich sides. The calculated maximum residual tensile stresses in the Mo-Ti FGM were much lower than the bending strength of Mo-Ti alloys, which demonstrated that during fabrication no damages occurred in the Mo-Ti FGM with continuously graded composition.

Viscoelastic finite element analysis of an all-ceramic fixed partial denture

In recent years metal-free ceramic systems have become increasingly popular in dental practice because of their superior aesthetics, chemical durability and biocompatibility. Recently, manufacturers have proposed new dental ceramic systems that are advertized as being suitable for posterior fixed partial dentures (FPDs). Reports indicate that some of these systems have exhibited poor clinical performance. The objective of this study was to use the viscoelastic option of the ANSYS finite element program to calculate residual stresses in an all-ceramic FPD for four ceramic–ceramic combinations. A three-dimensional finite element model of the FPD was constructed from digitized scanning data and calculations were performed for four systems: (1) IPS Empress ® 2, a glass-veneering material, and Empress ® 2 core ceramic; (2) IPS Eris™ a low fusing fluorapatite-containing glass-veneering ceramic, and Empress ® 2 core ceramic; (3) IPS Empress ® 2 veneer and an experimental lithium–disilicate-based core ceramic; and (4) IPS Eris TM and an experimental lithium–disilicate-based core ceramic. The maximum residual tensile stresses in the veneer layer for these combinations are as follows: (1) 77 MPa, (2) 108 MPa, (3) 79 MPa, and (4) 100 MPa. These stresses are relatively high compared to the flexural strengths of these materials. In all cases, the maximum residual tensile stresses in the core frameworks were well below the flexural strengths of these materials. We conclude that the high residual tensile stresses in all-ceramic FPDs with a layering ceramic may place these systems in jeopardy of failure under occlusal loading in the oral cavity.

Restrained shrinkage cracking: the role of shrinkage reducing admixtures and specimen geometry

Early-age cracking may occur in concrete elements if shrink-age is prevented by the surrounding structure. The risk of early-age shrinkage cracking in any given structure is influenced by many factors including the magnitude of shrinkage, rate of shrinkage, degree of stress relaxation, degree of structural restraint, and rate at which material properties develop. In addition to the aforementioned factors, this paper highlights the fact that shrinkage cracking is also influenced by geometry. This paper compares two series of experiments to better understand the role of specimen geometry. In the first series ring specimens of varying size were prepared to undergo the same rate of shrink-age and maximum strain development. Although the maximum residual tensile stress that developed was nearly identical for all geometries, the age at which cracking occurred varied with specimen thickness. In the second series of experiments the combined effect of moisture gradients and specimen geometry was investigated. In these experiments specimen thickness was varied while the surface area exposed to drying was maintained constant. The age of cracking was measured, as was the development of a moisture gradient. Again the influence of specimen size/geometry was apparent with smaller specimens cracking at an earlier age. This paper provides an explanation for this geometry dependence through the use of fracture mechanics concepts.

On the effect of the residual stresses on the crack opening displacement in a cracked sheet

The residual stress and displacement fields caused by localized plastic flow near a mode I crack tip in a sheet under plane stress conditions are investigated. The present study founds on the classical Dugdale scheme of the plastic flow localization. The residual stress field is considered to be induced by reversed plastic flow near the crack tip caused by an unloading. As it is found the residual stresses around the crack compress the crack tip, while the residual tensile stresses in a distant from the crack tip zone occur. It is shown the maximum residual tensile stresses can reach the significant value of the one third of the yield limit. The length of the compressed plastic zone and the residual displacement distributions are obtained. The exact formula for the residual crack opening displacement to estimate the crack closure is found. Then the next loading of the cracked plate is considered. It is shown that the second loading causes the origin of two plastic zones localized near the crack tip and at the point, where the maximum residual tensile stresses are concentrated. Again, according to the Dugdale scheme of the plastic localization, both the plastic flow zones are modelled as narrow stripes on the line extending the crack. To determine three non-dimensional parameters, characterizing the position of the segment-like plastic flow zones, a non-linear system of equations is obtained and analyzed. The exact formula for the crack opening displacement after a loading–unloading cycle is obtained. An asymptotic analysis (as the linear dimension of the distant plastic flow zone compared with the actual crack length is small) is given. It shows that the effect of the distant plastic flow zone appears as some complementary crack closure.

Mechanism of Formation of Exfoliations on the Surface of Rolls for Cold Rolling

We studied the phase composition and the distribution of stresses (residual and contact) over the depth of the surface layer of rolls for cold rolling. The results of this investigation are used to explain the mechanism of formation of exfoliations. Exfoliations appear in the zone of maximum residual tensile stresses on the boundaries of microinclusions of phases. The evolution of exfoliations passes through four stages: initiation of microcracks at a certain depth, formation of the main crack, its stable development, and final fracture. The crack-opening displacement is promoted by stresses and the decomposition of residual austenite under the influence of cyclic loads of rolling. The probability of formation of exfoliations can be lowered by optimizing the conditions of thermal treatment of the rolls.

Analytical Study on Fatigue Strength Reduction Factor of Small-Diameter Socket-Welded Pipe Joints

Four-point bending and rotating bending fatigue tests were conducted on socket-welded joints made of carbon, stainless, and Cr-Mo steels for clarification of the effects of diameter, welding pass sequence and post-weld heat treatment (PWHT) on fatigue strength. The results were evaluated quantitatively. Fatigue strength of socket-welded joints was found to strongly depend on weld pass sequences in fillet welds, this being possibly due to large change in residual stress distribution at roots and toes. The effects of residual stress were thus examined quantitatively by comparison of fatigue strength of PWHT stress-free specimens with that of as-welded specimens. By the modified Goodman’s method, the lowest S-N curve corresponding to maximum tensile residual stress and the highest S-N curve corresponding to maximum compression residual stress were obtained for different steels and diameters. Conventional S-N data of socket-welded joints were situated between these two limiting curves. Based on the lowest curve, fatigue strength reduction factors of socket-welded joints were proposed.

OPTIMUM EXPANSION AND RESIDUAL CONTACT PRESSURE LEVELS OF HYDRAULICALLY EXPANDED TUBE-TO-TUBESHEET JOINTS

Tube-to-tubesheet joints in steam generators and other heat exchangers are now often assembled by means of a hydraulic expansion process that plastically deforms the tubes against the tubesheet and thus creates an interference residual contact pressure between the tube and the tubesheet as well as tensile residual stresses in the tube. A good understanding of both the residual contact pressure and the residual stresses is important for establishing the integrity of the expanded joint. The propose of this paper is to investigate the effect of the level of the expansion pressure on both the residual contact pressure an the maximum tensile residual stresses. A comparison between the 3-D and the axisymmetric Finite Element models for a triangular array tube patterns is presented. An analytical equation is proposed for determining the optimum expansion pressure that provides an acceptable level of residual contact pressure and maximum tensile residual stresses. A statistical technique is also carried out to confirm the validity of the proposed approach.

Effect of residual stress on fatigue behaviour of notches

The effects of surface-rolling-induced residual stresses on the endurance limit and the growth behaviour of short cracks were investigated for notched steel parts. Unlike the case of smooth specimens tested in laboratory conditions, the endurance limit of notches under axial loading was enhanced by surface rolling, but the improvement was limited owing to the detrimental effect of tensile residual stresses at a distance from the surface. The second fatigue origin, which was just ahead of the crack tip and destroyed the condition of slowed propagation rate of the short crack in the compressive residual stress field, would be produced at the position where the maximum tensile residual stress was acting. This effect could be effectively eliminated by tensile preloading in such a way that the tensile residual stresses were greatly released by plastic deformation and the short fatigue crack in the compressive residual stress field became non-propagating at the loading of endurance limit. The effect of compressive residual stress on growth behaviour of short fatigue cracks lies in two aspects: (a) increasing the crack closure effect; and (b) decreasing the maximum stress intensity factor. A predicted d a/dN versus ΔK eff curve based on this assumption agreed with the experimental results.

Effect of specimen geometry on fatigue of welded joints: Guha, B. Eng. Fract. Mech. (Sept. 1993) 46 (1), 35–39

The magnitude and state of residual stress has a great influence on the fatigue life of sheet metal joints used in the automobile and aircraft industries. The present study developed a parametric 3D finite element model for simulation of welding and post-weld loading on the specimen. Electro-thermo-mechanical analysis is utilized to estimate the residual stress distribution at the nuggets and their surroundings at different stages of welding and post-weld mechanical loading. The results show that at the end of post-weld loading, the maximum tensile residual stress location moves nearer to the edge of the weld nugget and the residual stress magnitude and distribution change. Also, residual stress have sufficiently effects on stress distribution at the weld joint due to mechanical loading. To accurately estimate the fatigue life of resistance spot-welded joints, moreover external stresses, residual stress and local strain hardening of the material near the edge must be considered.

A study of residual stresses in the surface hardening of a blade mould by high frequency induction heating

High frequency induction heating is a method of surface treatment which restricts the hardening area using the skin effect. Since the penetration depth of the magnetic field in the workpiece is dependent on the frequency, the required size of hardening area can be obtained by selecting an appropriate frequency. High frequency induction heating is able to harden a large area at once, in which the shapes of the coil and workpeice and the distance between them are important factors for the hardening area shape and the distribution of residual stresses. In this study, the transient heat flow and thermal stress were analysed for the high frequency induction surface hardening of a blade mould by using the modified two-dimensional finite element method. Besides the volume change in the phase transformation, the effect of transformation plasticity was also considered as an additional strain in the numerical analysis of the high frequency induction hardening process. The hardening area was fairly uniform in the mould surface except around the corner where the distance between the coil and workpiece was slightly larger than on the other parts. The thermal stress was induced mainly by the temperature gradient and martensitic phase transformation, while the latter was found to have a greater influence on the residual stress than the former. Simulation results revealed that compressive residual stresses occur in the hardening area, while the maximum tensile residual stress occurs near the boundary of the hardened zone.

Residual stresses in welded jumbo box columns

Abstract Eight full-scale welded jumbo box columns fabricated with different details are selected to examine the distribution and magnitude of residual stresses. It is found that the maximum tensile residual stresses can be as high as 1·1 Fy and the maximum compressive residual stress is 0·43 Fy, where Fy is the yield stress.