Effect Of Compressive Residual Stress Research Articles

Effect of residual stress on corrosion sensitivity of carbon steel studied by SECM

The effect of compressive residual stress on the reactivity of carbon steel in a neutral chloride solution was investigated by means of potentiodynamic polarization and local electrochemical measurement with scanning electrochemical microscope(SECM). Meanwhile, X-ray diffraction, as a nondestructive technique, was employed to determine the levels of residual stress in near-surface layers of carbon steel specimen. The results show that the residual stress existed in the specimen fell into the category of compressive residual stress which was inversely proportional to the corrosion sensitivity of carbon steel specimen. By using I−/I3− couple as a redox mediator in the current feedback mode of SECM measurements, the Faradaic current on Pt tip, which was relevant to the rate of the I3− ion reduction, fell with the increase of compressive residual stress. The correlation between compressive residual stress and heterogeneous electron transfer rate has been proposed based on the inference of the localized electrochemical reactions occurred on the specimen surface.

Influence of the T-stress on the Crack Bifurcation Phenomenon in Ceramic Laminates

The main goal of ceramic laminates designed with residual stresses is to increase the fracture energy of the system during fracture through energy dissipating mechanisms such as crack deflection or crack bifurcation.The angle of crack deflection from the straight propagation direction is influenced mainly by level of the residual stresses in the laminate layers, which was investigated in previous works of the authors. Another key factor playing role in the crack deflection and presence of the crack bifurcation phenomenon is the thickness of the layer to which the crack propagates. This factor has not been studied yet and will be thus essence of this contribution where the combined effect of compressive residual stresses and layer thickness is numerically investigated. Three different multilayer designs of Al2O3-ZrO2 based ceramic materials are modelled using a non-periodic and symmetric architecture (i.e. layers of a given material may not have the same thickness within one specimen, but they are symmetrically distributed with respect to the laminate mid-plane). The volume ratio of both material constituents is kept constant, so that the residual stresses in the different laminates remain unchanged. Varied is only the thickness of the second compressive layer (where the bifurcation phenomenon is observed). A crack terminating perpendicularly on the first interface with the compressive layer is considered as the initial state before application of the four point bending. Using the fracture criterion, based on the Finite Fracture Mechanics, the angle and type of crack propagation (single crack deflection/bifurcation) is investigated. In these cases, the level of the T-stress (in the vicinity of the crack tip) can play a role as a second parameter in the fracture criterion (next to the generalized stress intensity factor) and as a consequence can this term influence the predicted crack propagation behaviour.

Fatigue Strength of Laser Hardened 42CrMo4 Steel Considering Effects of Compressive Residual Stresses on Short Crack Growth

The paper contains results of a study aimed at an experimental evaluation of fatigue resistance and initiation mechanisms of heat treated and laser hardened 42CrMo4 steel. Experiments were performed using quite small specimens of 8 x 8mm cross section, under three point bend fatigue loading. Two different parameters of laser hardening were used, one of them resulted in considerable longitudinal residual stresses – surface speed of laser beam 4mm/s. Results of fatigue tests of basic reference material, just heat treated, were characteristic by a surprisingly high scatter, particularly in the region near fatigue limit. Fractographical analyses indicated that this scatter was connected with presence of surface or subsurface defects, mostly inclusions, even quite large, which in some cases caused fatigue crack initiation. Compressive residual stresses after the laser treatment, dependent on laser treatment parameters, improved fatigue strength and reduced the scatter, likely due to short crack retardation in the compressive residuals stress field. Further analyses were carried out using Murakami method of evaluation of fatigue life of materials containing defects. The Murakami model of fatigue limit evaluation of specimens containing defects was just slightly conservative, when applied to specimens just conventionally heat treated, but quite strongly conservative particularly in case of laser surface hardening with high longitudinal compressive residual stresses. The results indirectly confirm significant beneficial effects of compressive stresses induced by laser hardening on fatigue resistance caused by retardation or arrest of short fatigue cracks emanating from microstructure defects.

Strengthen Experimental Study of High Strength Steel 40CrNi2Si2MoVA Based on Laser Shock Processing

40CrNi2Si2MoVA high-strength steel is widely used in aircraft industry because of its unique combination of ultrahigh strength with high fracture toughness. However, 40CrNi2Si2MoVA is vulnerable to both corrosion fatigue and stress corrosion cracking failures with catastrophic consequences for aircraft. The high strength steel 40CrNi2Si2MoVA is enhanced and strengthen by usage of laser shock processing (LSP) with a optimal shock processing parameters, and after a series of comparion experiment in different overlap rate,the surface compressive residual stress in the testing specimen is measured and compared, and the experiment results show that the specimen surface has-962MPa compressive residual stress. Finally, the enhanced effect of compressive residual stress in surface of specimen by laser shock is discussed. The results of laser shock processing has a guiding significance to the engineering applications of high strength steel.

모델 불확실성을 고려한 레이저 피닝 구조물의 피로 수명 예측

In this paper, the fatigue life of a laser peened structure was predicted. In order to calculate residual stress induced by laser peening finite element simulation was carried out. Modified Goodman equation was used to consider the effect of compressive residual stress induced by laser peening in fatigue analysis. In addition, additive adjustment factor approach was applied to consider S-N curve model uncertainty. Consequently, the reliable bounds of the predicted fatigue life of the laser peened structure was determined.

Effect of Austenite Grain Size on the Fatigue Crack Growth and Arrest Behavior of Carburized Steel

The effect of austenite grain size on the fatigue crack growth and arrest behavior of carburized steel was studied. On the fatigue test of same stress amplitude, the fatigue crack initiation of fine austenite grain steels is delayed in comparison with coarse austenite grain steels, but the difference of crack initiation life between fine grain steels and coarse grain steels is very slight against 107 cycles. The improvement of crack arrest property is dominant for increasing fatigue limit by refinement of austenite grain size. The critical stress intensity factor for crack arrest under fatigue tests at the stress amplitude of the each fatigue limit of carburized steels is calculated by considering the effect of compressive residual stress. As a result, it becomes clear that the finer the austenite grain size, the larger becomes the critical stress intensity factor for crack arrest, and crack arrest property is improved remarkably by the refinement of austenite grain size.

Effects of compressive residual stress on bending propagation behaviour of fatigue crack

Testing for bending fatigue crack propagation under mixed-mode condition was carried out using fatigue and annealed slant pre-cracks with different slant angles, �, defined as the angle between loading and crack directions in a rectangular plate. As a result, bending fatigue crack from the fatigue pre-crack with � = 45 deg propagated under mixed-mode condition with mode I and II stress intensity factors KI and KII , while bending fatigue cracks from the fatigue pre-crack of � = 60 deg and from the annealed pre-cracks with both slant angles of � = 60 deg and � = 45 deg propagated under mode I crack behavior. Furthermore, the estimated fracture angles calculated by maximum tangential criterion using the stress intensity fac tors, KI and KII , are in good agreement with the measurement ones except the fatigue pre-crack of � = 45 deg at the initial premium propagation. That is to say fatigue crack propagation behavior was effected by compressive residual stress around pre-crack while the slant angleis smaller (such as � = 45 deg in this study). But the effect was disappeared ifbecame bigger (such as � = 60 deg.).

Effects of compressive residual stress on the morphologic changes of fibroblasts

Recently, the term tensotaxis was proposed to describe the phenomenon that tensile stress or strain affects cell migration. Even so, less attention has been paid to the effects of compressive stress on cell behavior. In this study, by using an injection-molded method combined with photoelastic technology, we developed residual stress gradient-controlled poly-L-lactide discs. After culturing NIH-3T3 fibroblasts on the stress gradient substrate, the cell distributions for high- and low-stress regions were measured and compared. Our results showed that there were significantly more cells in the low-compressive stress region relative to their high-stress analogs (p < 0.05). In addition, NIH-3T3 fibroblasts in the low-compressive stress region expressed more abundant extensive filopodia. These findings provide greater insight into the interaction between cells and substrates, and could serve as a useful reference for connective tissue development and repair.

The effect of residual stress on adhesion-induced instability in micro-electromechanical systems

Adhesion and residual stress play a critical role in the performance and reliability of MEMS (micro-electromechanical systems). The effects of residual stress on the pull-in instability of the micromechanical structure were examined using thin plate theory and energy criterion. It is shown that the critical gap between the film and the substrate is a function of the ratio of residual stress to bending rigidity and the adhesion energy. Such instability is mitigated by the presence of in-plane tensile residual stress in the film. But, it is aggravated by the presence of compressive residual stress. In addition, the effect of compressive residual stress is much more significant than tensile residual stress.

Transition of fatigue failure mode of Ni–Cr–Mo low-alloy steel in very high cycle regime

Transition of the fatigue failure mode in very high cycle regime was investigated based on the experimental results obtained under a fully reversed tension–compression test in air at room temperature using a hourglass shaped specimen of a Ni–Cr–Mo low-alloy steel, JIS SNCM439. A clear duplex S–N curve existed in an emery-polished specimen as a result of the change from surface-induced failure to internal-induced failure with GBF area. On the other hand, a smooth and continuous S–N curve appeared in a specimen treated by a shot-peening, even though the failure mode changed depending on applied stress amplitude level. An internal-induced failure without GBF area was observed on the fracture surface of the shot-peened specimen in addition to the above two failure modes. Stress amplitude for the transition of the failure mode was explained by considering an effect of compressive residual stress in the surface layer, and competing subsurface crack growth rate with surface one. A map for transition of failure mode was proposed through the experimental and theoretical investigation.

Effect of shot peening on fretting fatigue of Ti811 alloy at elevated temperature

The effects of compressive residual stress, surface roughness, microstructure hardening induced by shot peening (SP) on the fretting fatigue (FF) resistance of Ti811 titanium alloy at elevated temperature were evaluated. The results show that SP improves the FF resistance of Ti811 alloy at 350 °C, but decreases the resistance at 500 °C. Compressive residual stress is the predominant factor in improving the FF resistance of the alloy at 350 °C. Compressive residual stress induced by SP arrests crack growth. Microstructure hardening due to SP has a minor effect on FF resistance. Surface roughening induced by SP is detrimental to the FF resistance of the alloy at both 350 and 500 °C, as microcracks initiate easily in the roughened surface under these conditions.

Axial Loading Fatitgue Properties of Low Alloy Steel, SNCM439, in Very High Cycle Regime

In order to study the fatigue properties of low alloy steel, JIS SNCM439, under axial loading condition in very high cycle regime, fatigue test under the stress ratio of -1 was carried out in air at room temperature using the hourglass shaped specimen. From the experimental results, clear duplex S-N curve existed in this material ; that is, there were two curves composed of a surface inclusion-induced fracture mode and a subsurface inclusion-induced fracture mode with granular bright facet (GBF) area in the vicinity of inclusion. Roughness of the GBF area was about 2 times larger than the area outside the GBF in the fish-eye zone relating to the size and distribution of carbide particle in the matrix. An appearance of the dual-stage S-N behavior was related to the difference of threshold for crack initiation and crack growth rate between surface inclusion and subsurface inclusion. Stress amplitude for transition of the fracture mode was explained by considering an effect of compressive residual stress on the surface layer. From the evaluation of fatigue life based on the estimated subsurface crack growth rate from the S-Ndata, effect of inclusion size on the dispersion of fatigue life was explained, and S-N curve for subsurface inclusion-induced fracture depended on the inclusion size was provided.

Influence of thermal and mechanical surface modifications induced by laser shock processing on the initiation of corrosion pits in 316L stainless steel

Pure mechanical and thermo-mechanical laser shock processing treatments have been carried out on an AISI 316L stainless steel. Surface properties, mostly mechanical and metallurgical modifications, were analysed at different scales: a local scale using the nano-indentation technique and AFM analysis, and a more macroscopic scale, using microhardness, optical microscopy and residual stress determinations. After a pure mechanical laser-peening treatment, a significant improvement in the pitting corrosion resistance (+0.1 V) was observed in 0.05 M NaCl. This improvement was attributed to the combined effects of compressive residual stresses and work-hardening, and, in turn, to a mechano-electrochemical phenomenon by which a modification of cathodic reactions occurs during electrochemical tests. For the surface treated by thermo-mechanical laser peening (combination of a surface ablation and shock waves), a tendency for decreasing resistance against pitting corrosion was shown, and attributed to the processing-specific surface texture (ablation craters), which made the material susceptible for the creation of occluded cells.

Fatigue life assessment and comparison of two types of bridge-mounted welded aluminum light pole support structures

The primary objective of this work was to perform fatigue life assessment for two types of mounted bridge aluminum light poles, which can lead to a better understanding of the structural behavior of both types of details, currently used as secondary structural elements mounted on various bridges and highways. Included in this study are shoe base and through plate socket connection details. Fatigue tests showed a relatively low life for through plate details as compared with the shoe base connections at the same stress range. Fracture mechanics studies indicated that lower bound design curves could be predicted using higher stress ratio fatigue crack growth data superimposed with the effect of compressive residual stresses at the surface of the tubes. Parametric studies demonstrated the importance of base plate thickness on the through thickness bending of the tube wall, which can be extremely effective on mounted bridge poles due to open terrain wind dynamic loads. A research study revealed that shoe base...

Effect of residual stress on stress intensity factors of fretting fatigue cracks

The effect of compressive Residual Stress (RS) on the Stress Intensity Factors (SIFs) of fretting fatigue cracks was studied using semi-analytical methods. The fretting fatigue of a half-plane in contact with a flat rounded pad was taken into consideration, and RS such as those created by shot-peening were added to the model. Studies of several RS profiles were accomplished to consider the effect of changes in RS caused by stress relaxation during service or pretreatment and manufacturing discrepancies regarding parameters. The distribution of dislocations method was applied to the calculation of the SIFs of these cracks and was shown to be capable of dealing with these kinds of problems. It will be used effectively in future studies. In order to evaluate the stress state in the half-plane, contact mechanics calculations were accomplished without considering the presence of a crack, and the final results showed that this simplification does not create noticeable difficulties.

Retardation of Fatigue Crack Growth on AC4CH Cast Aluminum Alloy by Laser Peening

The effect of laser peening to retard fatigue crack propagation has been demonstrated through rotating bending fatigue tests conducted on pre-cracked AC4CH casting aluminum alloy. The apparent maximum stress intensity factor at the surface of laser peened specimens was nearly equal to four times of the threshold stress intensity factor of long surface fatigue cracks just starting the propagation on AC4CH. The increase of the threshold stress intensity factor was due to the effect of compressive residual stress introduced by laser peening. The three dimensional (3D) image of fatigue cracks was reconstructed by micro computed tomography ({mu}CT) using synchrotron radiation of SPring-8. The reconstructed images were used to visualize the crack propagation behavior inside the specimens, which could not be attained by usual replication technique. The 3D image of a laser peened specimen showed a legible plastic deformation on the surface of the specimen. (author)

The Effect of Compressive Residual Stress on the Fatigue Characteristics of Al6061

Recently, the steel parts used at the aerospace and automobile industries are required to be used high stress more than ever before in need of the weight down. Therefore, used material steel have to be a high stress, which is an indispensable condition in this field. At the consideration of parts design, high hardness of the lightweight parts has an benefit of saving fuel and material. In this study, the surface conditions are measured to know the influence on fatigue properties by shot peening. In this study, the optimum shot peening condition is investigated. Fatigue test was accomplished to investigate the effects of compressive residual stress by shot peening on fatigue characteristics. Test results show the fatigue characteristics were increased by optimum peening condition. But the fatigue characteristics were decreased by under peening or over peening condition.

Effect of Roller-Working on Fatigue Strength Improvement of Notched Structural Stainless Steel

In order to study the effect of plastic deformation on fatigue behaviors of plastically deformed specimen, bending fatigue tests had been performed on notched deformed stainless steel specimens. Also pulsating fatigue tests were done on notched non-deformed specimens to evaluate the influence of mean stress on fatigue behavior of notched non-deformed specimens. The result showed that according to increase of deformation value, the fatigue limits of these specimens also significantly increase. Fatigue limit of rolled specimen does not linearly increase with increase in plastic deformation value. Based on fatigue limit diagram, the effect of compressive residual stress on fatigue limit improvement of stainless steel is higher than that of work-hardening. In case of non-deformed specimen, when the compressive mean stress increases, the fatigue limit and the number of cycles to failure increase. In case of tensile mean stress, this kind of mean stress decreases the fatigue limit.

Stress Analysis of the Automobile's Coil Spring Including Residual Stresses by Shot Peening

Durability assessment for the suspension system of the vehicle is very important. In order to secure reliability on the results of durability assessment and fatigue design criterion, accurate stresses for the interesting component must be basically calculated. In this paper, numerical stress analyses for the automobile’s coil spring were performed. Residual stresses by shot peening were also analyzed. The effects of the stress analysis results on fatigue strength of the coil spring were discussed. From the results, fatigue durability of the shot peened coil spring could be considerably improved by the effects of compressive residual stress. However, being attacked by corrosive environments, it could decrease by corrosion fatigue degradation.

Fatigue limits prediction of surface treated materials

The fatigue limit prediction methodology for cyclical loading of surface treated material has been developed in this paper by material investigation. The change in surface layer properties caused by surface treatments was evaluated by compressive residual stress and strain hardening. A model based on the Crossland's criterion has been developed. The X-ray diffraction method of measuring is used. We adopted the rate between X-ray widths measurement of base material and treated one to quantify the strain hardening. The theoretical model gives a better approach of the mechanism of fatigue behaviour of surface treated material. It was demonstrated that the increasing effect of strain hardening on fatigue strength is more important than that of compressive residual stress. To validate the model, the proposed fatigue limit criterion is formulated in two cases of surface treatment methods: shot peening and nitriding. Comparison of predictions of this criterion against experimental fatigue limit data showed good agreement. The fatigue limit criterion predicts that the crack origin is located into the region under the surface hardened layer. This goes in concordance with experimental observations. An important property of this model is that it can be used to optimise the surface treatment parameters and to choose the suitable material. The model is an approach for predicting the effect of compressive residual stress and strain hardening on high cycle fatigue behaviour.