Shot Peening Conditions Research Articles

Influences of Fine Particle Shot-Peening on Surface Durability of Austempered Ductile Iron.

For Austempered Ductile Iron (ADI) gears, a shot-peening is utilized to improve the bending fatigue strength. However, under some shot-peening conditions, the increase of surface roughness by shot-peening may deteriorate the surface durability of ADI gear. The authors in this paper investigate the influence of the fine particle shot-peening on surface durability of ADI (austempering temperature 375°C) roller using a disk machine with rolling and sliding. The results are summarized as follows : (i) After the fine particle shot-peening, the hardness and compressive residual stress near the surface are risen. Furthermore, the surface roughness is smaller than that after the conventional shot-peening. (ii) The surface durability of ADI roller with the fine particle shot-peening is superior to that of ADI roller with the conventional shot-peening. Consequently, if a shot-peening is applied to improve the bending fatigue strength of ADI gear, the fine particle shot-peening is available to prevent the deterioration of the surface durability.

ショットピーニング材の残留応力分布に及ぼすピーニング粒形状の影響

New shot peening method, which gives larger residual stress and smaller transformation than usual method, is required. In this study, residual stress distributions due to two shot peening conditions were measured by inherent strain method. One shot peening condition was using steel grid which was angular shape. Another was using steel shot which was spherical shape. Residual stress by steel grid was larger than that by steel shot. And inherent strain by steel grid existed on narrower zone than that by steel shot. Moreover, deflection of specimen by steel grid was smaller than that by steel shot. As results, it has been recognized that shot peening using steel grid was very useful. And residual stress distribution can't be estimated by deflection of specimen, on the other hand, inherent strain method is effective to estimate residual stress distribution due to shot peening.

Influence of Shot-Peening on Surface Durability of Austempered Ductile Iron.

For austempered ductile iron(ADI)gears, shot-peening is utilized to improve the bending fatigue strength. However, in some shot-peening conditions, the increase of surface roughness by shot-peening may deteriorate the surface durability of ADI gear. The authors in this paper investigate the influence of shot-peening on surface durability of ADI(austempering temperature 375°C)using a disk machine with rolling and sliding. The results are summarized as follows : (i)Under the shot-peening condition in this paper, the surface durability of ADI is deteriorated. (ii)We obtain that the increase of surface roughness by the shot-peening may cause the deterioration of surface durability. The above expectation is confirmed by testing test pieces polished after the shot-peening. (iii)When the shot-peening is used for ADI gears, the increase of surface roughness must be controlled as possible.

Theoretical Prediction of Residual Stress Produced by Shot Peening and Experimental Verification for Carburized Steel

Simplified theoretical formulae based on shot peening parameters and materials properties have been developed to predict the maximum and the peak depth of the compressive residual stress produced by shot peening. These formulae are based on the motion equation for a shot and the analytical model proposed by Li, who utilized the Hertz theory of elastic contact and a simplified elasto-plastic theory. Experimental verifications were carried out under various shot peening conditions. Shots were made of cast steel, fused Zirconia, and glass, each having its own range in diameter. Actual residual stress distributions were measured by the X-ray diffraction method. The maximum and peak depth of the compressive residual stress predicted by the proposed formulae agreed well with the experimental values in a wide variety of shot peening conditions.

浸炭窒化歯車鋼の面圧強度向上に関する研究 ショットピーニング処理とバレル研磨処理の影響

When the shot peening process is employed in order to improve the bending fatigue strength of a gear tooth, there is a fear that the surface durability of the shot peened surface may reduce because of degradation of its surface roughness. In this study, the surface durability of the carbo-nitrided steel rollers besides the carburized ones was investigated using a highly loaded two rollers contact fatigue testing machine. It was confirmed that only the shot peening could scantly improve the surface durability because it is very hard to smooth the surface roughness by control of the shot peening conditions. Then, the barreling process was employed to improve the surface roughness, and it was clarified that the surface durability of shot peened rollers was remarkably improved by the barreling process. Also, it was shown using the D-value that the pitting limit increases and amount of wear decreases appreciably when the surface roughness becomes small. Pitting occurred on two kinds of case-hardened steels in the present experiments have always originated at the surface with/without shot peening process. The crack for pitting has rapidly propagated in the inside where a fatigue will be produced by a repeated shear stress, and a large pit (spalling) has immediately occurred all over the face width.

A numerical procedure for shot peening optimisation by means of non-dimensional factors

Shot peening is widely used to improve the fatigue behaviour of mechanical components. The improved performances of shot peened components are generally put into relation with the residual stress field induced. The aim of the present paper is to define a calculation approach, based on FE analyses, able to predict, once the shot peening parameters are known, the residual stress profile. In this way, it is possible to optimise the results of shot peening by taking into account the applied loads. The possible application of a non-dimensional number to summarise the shot peening conditions was evaluated. It was also possible to express non-dimensional residual stress profiles (residual stresses/yield stress of the material) as a function of this non-dimensional number. The measurements carried out on shot peened specimens by means of a X-ray diffractometer allowed for critical analyses of the results.

Non-Destructive Method for Estimating Residual Stress Distribution in Component due to Shot Peening.

A non-destructive method is proposed for estimating residual stress distribution in an object part due to shot peening. The method involves measuring the eigen strain distribution in a small test piece made of the same material and peened under the same shot peening conditions as the object part using the layer removal technique. The residual stress distribution in the part is calculated from this eigen strain. An experiment was carried out to estimate axisymmetric residual stresses in a shot peened cylinder. The results measured directly from the cylinder show good agreement with the results predicted by the proposed method.

ショットピーニングにより浸炭焼入れ鋼に付与される残留応力の理論的予測と実験検証

Simplified theoretical formulae have been developed to predict the maximum and the peak depth of the compressive residual stress due to shot peening from the shot peening parameters and materials properties. These formulae put the base on the motion equation of a shot and the analytical model proposed by Li, who used a Hertz theory of elastic contact and a simplified elasto-plastic theory. For experimental verifications, several conditions of shot peening were carried out with the shots made of cast steel, fused zirconia and glass, which had three les distribvels of shot diameter respectively. The residual stresutions were measured by X-ray diffraction method. The predicted maximum and the peak depth of the compressive residual stress by the proposed formulae were agreed well with the experimental values in the wide range of shot peening condition.

Non-Destructive Method for Estimating Residual Stress Distribution in Component due to Shot Peening.

A Non-destructive method is proposed for estimating residual stress distributions in a component due to shot peening. The method involves measuring the inherent strain distribution in a small plate, made of the same material and peened under the same shot peening conditions as the component, by layer removal technique. The residual stresses in the component are estimated from the measured inherent strain in the plate. An experiment was carried out to estimate axisymmetric residual stresses in a shot peened shaft. The results measured directly from the shaft show a good agreement with the results predicted by the proposed method.

Experimental investigations and modelling of relaxation behaviour of shot peening residual stresses at high temperature for nickel base superalloys

Residual stresses induced by two shot peening conditions in nickel base superalloy Inconel 718 and their relaxation after different exposure times (10 and 100 h) at 600 and 650°C were evaluated by an X-ray diffraction technique. The behaviour of stress relaxation (effects of exposure time and applied temperature) is particularly analysed and discussed. A significant decrease of the initial stress values was observed in the first period of exposure time, followed by slowing down and then stabilisation. Experimental results showed that the maximum relaxation always occurred at the surface. It was also observed that a higher applied temperature produced greater relaxation, but had no significant effect on the pattern of the depth profile of stress. The relaxation mechanism is essentially interpreted by thermal recovery characterised by a rapid annihilation of the unstable crystalline defects in highly deformed materials. Complex changes of various microscopic magnitudes under high temperature are described by macroscopic magnitudes related to the plastic strains and associated residual stresses. An existing model is developed and actualised by integrating the limiting state of recovery and the integrated width of X -ray diffraction peaks in order to predict relaxation of the residual stresses. The relaxation predicted by the model agrees satisfactorily with the experimental results in the studied cases.

Effect of shot peening on the fatigue and fracture behaviour of two titanium alloys

The fatigue and fracture behaviour of two titanium alloys, the near-alpha IMI-685 and alpha-beta IMI-318, were studied in the machined and polished (MP) as well as the machined, polished and shot (glass-bead) peened (MPS) conditions. Glass-bead peening reduced the room-temperature as well as the high-temperature (450°C) fatigue life of alloy IMI-685 at high stress amplitudes, σa, approaching the proof stress, σps, of the material (LCF region). When the applied stress amplitude (0–770 MPa, HCF region) was comparable to the peen-induced peak longitudinal residual stress, σLP, i.e. (σLP/σa)=0.92, an improvement in the room-temperature fatigue life of IMI-685 was observed. When the (σLP/σa) ratio was less than this value, decreases in the fatigue life were seen. The room-temperature fatigue behaviour of IMI-318 at high stress amplitudes was similar to that of IMI-685. The decrease in the fatigue life of this alloy, at a stress amplitude (770 MPa) where improvement was observed for IMI-685, could be attributed to the higher relaxation of peen-induced residual stresses in IMI-318 compared with IMI-685. Glass-bead peening improved the hightemperature (450°C) fatigue life of IMI-685 at a low stress amplitude (465 MPa; (σa/σPS)=0.87). The crack-initiation sites in the MP and the MPS conditions were at the surface for both the alloys. However, fracture in the surface layers of the alloys appeared more brittle in the peened (MPS) rather than in the unpeened (MP) condition.

Rigid-Plastic Finite Element Simulation of Peening Process with Plastically Deforming Shot

To simulate not only plastic deformation of a workpiece but also that of a shot in a peening process, the effect of the interaction between the shot and workpiece in the collision is included in the dynamic rigid-plastic finite element method. In the formulation, the equilibrium equations of nodal forces are solved simultaneously with velocity boundary conditions at the interface between the workpiece and shot for sliding and non-sliding contacts. Axi-symmetric plastic deformation in peening of a circular workpiece with a single shot is computed. The calculated shapes of the workpieces and the shots are in good agreement with the experimental ones for plasticine workpieces and shots. It is shown that almost no plastic deformation of the shot occurs under actual shot-peening conditions for steel workpieces when the flow stress ratio of the shot to the workpiece is larger than two.

Examination of the effect of Shot-Peening Conditions on the Improvement of Fatigue Reliability of Meatl-Molded Austempered Ductile Iron.

An examination of the effect of shot-peening (SP) conditions on the improvement of fatigue reliability of metal-molded ADI was performed with a mesoscopic observation of fracture morphology. The main results obtained were as follows: (1) The 106 endurance limit could be improved with an increase of SP strength, but the endurance limit of 1.0mmA-Sp material was as high as that of 0.8-SP material. On the other hand, the 2×107 endurance limit as not improved with SP treatment. (2) The origin of fatigue cracks of metal-molded ADI as not the pores, since the cooling rate of metal-molded ADI was slower than that of sand-molded ADI. (3) The origin of fatigue cracks was transferred from the surface to the inside with an increase of SP strength, due to the effect of compressive residual stress induced by SP treatment. (4) Although the depth affected by SP treatment of 1.0-SP material was greater than that of 0.8-SP material. The influence of SP strength on the endurance limit of metal-molded ADI was only effective up to 0.8-SP strength because of the existence of a stress gradient.

ショットピーニングによる残留応力分布のシミュレーション

It is generally recognized that one of the reasons for improvement on fatigue durability by shot peening is surface compressive residual stress. And a shot peening condition decides a residual stress profile on surface layer. But, at this moment the method to confirm this profile is only measurement by X-ray difractometer. In this study, a simulation technique was applied to predict the residual stress distribution caused by shot peening. Firstly, the residual stress on shot peened plate specimens was measured by X-ray difractometer and the effect of shot peening condition on profile was confirmed. The equation to simulate the profile was obtained by the superposition method of simple three stresses, based on the equation that Y.F. Al-Obaid suggested. It was confirmed that the predicted stress profile shows good correspondence with the experimental value every shot peening condition of this experiment.

The Strengthening of Gears by Shot Peening. Optimization of Shot Diameter and Peening Angle for Gear Shape.

The optimum shot peening condition to improve fatigue strength for automobile transmission gears was investigated. Motion and clashing of shot particles were quantitatively described in relation to gear shape, and correlation with residual stress was investigated. Based on these results, computer simulation techniques for optimizing the shot peening conditions were proposed using the correlation between the fatigue strength and the residual stress which had been obtained in the previous work. Experimental results on the fatigue strength of gears coincided with the analytical prediction.

Increased Fatigue Strength of Powder Forged Connecting Rods by Optimised Shot Peening

AbstractShot peening is a surface treatment commonly used to improve the fatigue life of aircraft, automotive, and other highly stressed structural components. This improvement is attributed to the formation of compressive residual stress in the surface layer of the material by the impingement of spherical media (shot). The compressive residual stress usually decreases the tensile stress created in the component by ‘in service’ external forces and, therefore, increases the fatigue strength of the part. To quantify the improvement resulting from shot peening, the fatigue behaviour of powder forged connecting rods and laboratory test bars from the base material (2%Cu steel), in both the stress free (unpeened) and surface treated (shot peened) condition, were compared. Fatigue data were correlated with the residual stress generated at the surface. The stress magnitude and depth were determined using X-ray diffraction analysis. Optimum processing parameters for shot peening were also determined. Results show ...

Rigid-Plastic Finite Element Simulation of Peening Process with Plastically Deforming Shot.

To simulate not only plastic deformation of a workpiece but also that of a shot in a peening process, the effect of the interaction between the shot and workpiece in the collision is included in the dynamic rigid-plastic finite element method. In the formulation, the equilibrium equations of nodal forces are solved simultaneously with the boundary condition for velocity at the interface between the workpiece and shot. Both sliding and non-sliding contacts in the interface are dealt with, and the law of Coulomb friction is assumed for the sliding contact. Axi-symmetric plastic deformation in peening of a circular workpiece with a single shot is computed. The calculated shapes of the workpiece and the shot are compared with the experimental ones for the workpiece and a shot made from plasticine whose flow stress is controlled by temperature. It is shown that almost no plastic deformation of the shot occurs under actual shot-peening conditions for steel workpieces when the flow stress ratio of the shot to the workpiece is larger than two.

Thermomechanical relaxation of residual stress in shot peened nickel base superalloy

The thermal and thermomechanical behaviour of the relaxation of the residual stresses of a shot peened Astroloy superalloy under tensile cyclic loads has been evaluated by X-ray diffraction and investigated. The stress relaxation under purely thermal conditions (550 and 650°C) and thermomechanical conditions (pulsating tensile loading at 650°C) as afunction of the exposure time is presented. The purely thermal relaxation is interpreted by annihilation and reorganisation of the crystalline defects induced by shot peening, whereas the mechanical relaxation is linked to cyclic plasticity of materials. In consequence, the thermomechanical relaxation is essentially due to the complex mechanism of the concurrent thermal and mechanical effects. A model is used to predict the residual stresses induced by the specified shot peening conditions and their relaxation under the specified thermal/thermomechanical conditions.MST/1963

Thermomechanical relaxation of residual stress in shot peened nickel base superalloy

AbstractThe thermal and thermomechanical behaviour of the relaxation of the residual stresses of a shot peened Astroloy superalloy under tensile cyclic loads has been evaluated by X-ray diffraction and investigated. The stress relaxation under purely thermal conditions (550 and 650°C) and thermomechanical conditions (pulsating tensile loading at 650°C) as afunction of the exposure time is presented. The purely thermal relaxation is interpreted by annihilation and reorganisation of the crystalline defects induced by shot peening, whereas the mechanical relaxation is linked to cyclic plasticity of materials. In consequence, the thermomechanical relaxation is essentially due to the complex mechanism of the concurrent thermal and mechanical effects. A model is used to predict the residual stresses induced by the specified shot peening conditions and their relaxation under the specified thermal/thermomechanical conditions.MST/1963

Finite element analysis of peening process with plasticity deforming shot

To simulate not only plastic deformation of a workpiece but also that of a shot in peening processes, the effect of the interaction between the shot and workpiece in the collision is included in the dynamic viscoplastic finite element method. In the formulation, the equilibrium equations of nodal forces and the boundary condition for displacement are simultaneously satisfied under a sliding condition at the interface between the workpiece and shot. Axi-symmetric plastic deformation in peening of a circular workpiece with a single shot is computed. The calculated shapes of the workpiece and the shot are compared with the experimental ones for the workpiece and the shot made from plasticine whose flow stress is controlled by the temperature. It is shown that almost no plastic deformation of the shot occurs under actual shot-peening conditions for steel workpieces when the flow stress ratio of the shot to the workpiece is larger than two.