Peening Conditions Research Articles

INFLUENCE OF SURFACE PROFILE MODIFIED WITH FINE SHOT PEENING ON SCUFFING IN ROLLING-SLIDING CONTACT ELEMENT

Recently, the gear is required of high strength, reliability, and surface damage resistance under severe service condition to achieve the weight saving and downsizing of a product. It is necessary to understand the influence of the surface profile on the scuffing resistance. The shot peening is able to form the arbitrary surface profile with the changes of peening conditions to the metal surface. When the effective surface profile will be found to increase the lubrication property, the metal surface will be obtained with both the surface strength and the surface lubricity. In this paper, the influence of surface profile with the fine shot peening, which is able to form the arbitrary surface profile, on the scuffing resistance in the rolling-slipping contact machine element was investigated. The scuffing test using the two cylinder rolling contact test machine was carried out. The test rollers processed with shot peening were used in the scuffing test.

Effects of shot peening pressure, media type and double shot peening on the microstructure, mechanical and tribological properties of low-alloy steel

The effects of different shot peening conditions such as pressure (from 68.9–551.6 kPa), media type (media S230 and S110) and double shot peening on the microstructure, mechanical and tribological properties of shot peened AISI 4340 low-alloy steels, were systematically investigated. Their surface topography, hardness and roughness were analyzed by scanning electron microscopy, a Vickers micro-hardness tester and surface profilometer, respectively, while the cross-sectional sub-surface structures of the as-received and shot peened samples were characterized by means of optical microscopy and nanoindentation. The tribological properties were determined by using a ball-on-disc micro-tribological tester. It was shown that shot peening pressure and media type had a significant effect on the surface roughness, hardness, microstructure, wear resistance and friction of the shot peened AISI 4340 steel samples. It also indicated that the double shot peening process was a promising treatment, not only to reduce the surface roughness of the material after undergoing the first shot peening process with large media and high intensity, but to improve the tribological properties of the shot peened material.

Optimization of shot peening parameters by response surface methodology

Abstract In this study, the shot peening parameters which directly influence the arc height of the Almen strip and its characteristics are optimized within the context of Almen intensity, surface roughness and surface hardness via response surface methodology. Determination of the Almen intensity by trial and error method depending on the experience of the technician (measuring the arc height of Almen strips by changing the parameters repeatedly for each shot peening process) makes the optimization approaches valuable. The optimization is considered to perform by selecting surface roughness and surface hardness as the responses in order to classify the shot peening processes by taking into consideration of wide range of plastic deformation level. The effect of input parameters air pressure, shot diameter and peening duration on the Almen intensity, surface roughness and surface hardness is to be determined by using ANOVA regression analysis. Based on the estimated models, optimum peening conditions are introduced via response optimizer. The model adequacy is verified by the confirmation tests.

Synergetic effect of thicker nanocrystalline structure with high amount of strain induced martensite on surface characteristics of plasma nitrided austenitic stainless steel

Abstract Severe shot peening is a simple and effective method to synthesize nanocrystalline layer on metallic surfaces. A new reactor to synthesize thicker nanocrystalline layers on metallic surfaces by shot peening is presented. In this cylindrical reactor air enters inside the reactor tangentially, propels shots on the specimen to be shot peened and leaves the reactor after multiple rotations. Air vortex and very high turbulence formed inside the reactor dissipate heat generated during shot peening and thus suppress dynamic recovery which promotes formation of refined and thicker nanocrystalline structure on a metallic surface. Experiments were conducted on 5specimens of austenitic stainless steel with different shot velocities in the reactor. Characterization (X-ray diffraction profiles, cross-sectional optical micrographs, TEM and micro-hardness profiles) of shot peened surfaces showed that thicker nanocrystalline/nano-twinned layers were developed during all peening conditions used in the experiments. Microstrain in the lattice, dislocation density and volume fraction of strain induced martensite observed to increase with rise in shot velocity. Specimens with thicker nanocrystalline layers were prepared. These specimens contained high amount of strain induced martensite deep down the surface. Plasma nitriding of these pre-shot peened specimens were done at 425 °C and 500 °C for six hours. Presence of thicker nanocrystalline layer with high amount of martensite at the surface of austenitic stainless steel observed to have synergetic effect and significantly influenced kinetics of nitriding process leading to higher surface hardness and 6-fold thicker nitrided layers compare to untreated nitrided surface. Presence of nanocrystalline structure, however, also effects on precipitation of chromium nitrides during nitriding.

Effect of Decarburization on the Residual Stresses Produced by Shot Peening in Automotive Leaf Springs

The shot peening is used in the leaf springs manufacturing process for producing a compressive residual stress field (CRSF) at and near the surface that improves the fatigue resistance. The resulting CRSF is influenced by the surface ferrite thickness associated with the decarburization. Hence, this work aims to extend the knowledge on the influence of the decarburization on the CRSF for the given shot peening conditions. A study on the laboratory scale was conducted for an SAE 5160 steel grade used in the automotive industry. Next, specimens with different decarburization depths were treated using industrial shot peening, and the resulting CRSF was characterized. The CRSF was found to be influenced by the decarburization depth. It is assumed that the elastic deformation mechanism is predominant at low decarburization depths, followed by a zone in which both the elastic and plastic deformation have competing mechanisms that contribute to the CRSF, and at higher decarburization depths, the dominant mechanism is plastic deformation. The values for σsrs and σmcrs decrease as the decarburized depth increases, and suitable CRSFs were obtained below a decarburization depth of 120 µm in industrial leaves. Furthermore, the prediction based on expressions correlating the measured variables was good in these leaves.

Use of response surface methodology for shot peening process optimization of an aircraft structural part

The shot peening process causes the surface of metallic parts to become hardened by bombarding it with a stream of small particles called shots, generating compressive residual stress at the material surface and resulting in surface hardening. In the aerospace industry, proper selection and control of peening factors (parameters) is needed to ensure that the Almen intensity is within specifications and full surface coverage. In this study, the effects of four parameters (nozzle distance, pressure, impact angle, and exposure time) on Almen intensity and coverage are investigated. In order to systematically estimate the models of Almen intensity and coverage in terms of the four parameters, a Box-Behnken design with blocking is employed. Based on the estimated quadratic models, optimum peening conditions are determined using the desirability function approach. Additionally, in order to verify the validity of the optimal conditions obtained from experimental results, metallurgical analyses of the shot-peened aerospace structural part were conducted to examine the hardness, surface morphology, and residual stress.

Predicting the Peen Forming Effectiveness of Ti-6Al-4V Strips With Different Thicknesses Using Realistic Finite Element Simulations

This paper is intended to quantify the relationship between the peen forming effectiveness and various involved parameters through a realistic numerical study. For this purpose, a new finite element (FE) model is proposed with full geometry representation, random shots generation, and rate-dependent material law of kinematic strain-hardening. The mesh sensitivity and effects of boundary conditions are carefully examined. The FE model is validated by comparing the results with the experimental measurements. The proposed model is then used to investigate the effects of the peening intensity (represented as the shot velocity) and the strip thickness on the peen-formed deflection and the residual stress distribution for strips made of Ti-6Al-4V. Our results indicate the existence of a maximum convex deflection for different strip thicknesses. In addition, a reversed deflection (i.e., concaved curvature) is observed for severe peening conditions (i.e., thin strip under high peening intensity). Our simulations verify the previous proposition that a concaved curvature can be generated only when the whole cross section is plastically deformed.

3-D analysis of fatigue crack behaviour in a shot peened steam turbine blade material

Serial mechanical sectioning and high resolution X-ray tomography have been used to study the three-dimensional morphology of small fatigue cracks growing in a 12 Cr tempered martensitic steam turbine blade material. A range of surface conditions has been studied, namely polished and shot peened (with varying levels of intensity). In the polished (unpeened) condition, inclusions (alumina and manganese sulphide) played an important role in initiating and controlling early fatigue crack behaviour. When fatigue cracks initiated from an alumina stringer, the crack morphology was normally dominated by single stringers, which were always in the centre of the fatigue crack, indicating its primary role in initiation. Manganese sulphide inclusion groups however seemed to dominate and affect the crack path along both the surface and depth crack growth directions. The more intensely shot peened condition did not however evidence inclusion or stringer affected fatigue crack initiation or growth behaviour; sub-surface crack coalescence being clearly observed by both serial sectioning and computed tomography (CT) imaging techniques at a depth of about 150–180μm. These sub-surface crack coalescences can be linked to both the extent of the compressive residual stress as well as the depth of the plastic deformation arising from the intense shot peening process. Shot peening appears to provide a different defect population that initiates fatigue cracks and competes with the underlying metallurgical defect populations. The most beneficial shot peening process would in this case appear to “deactivate” the original metallurgical defect population and substitute a known defect distribution from the shot peening process from which fatigue cracks grow rather slowly in the strain hardened surface layer which also contains compressive residual stresses. A benefit to fatigue life in bending, even under Low Cycle Fatigue (LCF) conditions, has been observed in these tests if a sufficiently severe shot peening condition is applied in a constrained notch configuration.

Enhancing surface layer properties of an aircraft aluminum alloy by shot peening using response surface methodology

Abstract Shot peening leads to local plastic deformations in the near-surface regions, which result in the development of residual stress and the improvement of surface hardness in the aerospace structural components. These properties can be enhanced by careful selection of the peening parameters. 2124-T851 aluminum alloy is widely used in the aerospace industry due to its high specific static strength. In this study, a response surface methodology is presented to optimize the surface properties of microhardness and residual stress. The effects of four peening parameters (nozzle distance, pressure, impact angle, and exposure time) on microhardness and residual stress are investigated. Box–Behnken design, a popular second-order response surface design, is employed to systematically estimate the empirical models of microhardness and residual stress in terms of the four parameters. Based on the estimated models, optimum peening conditions are recommended by using the desirability function approach, which is the most popular technique for optimizing multiple responses. Additionally, to verify the validity of the optimal conditions obtained from experimental results, metallurgical analyses of the shot-peened aluminum alloy were conducted with respect to hardness, residual stress, surface morphology, X-ray diffraction analysis, and surface roughness.

Effect of Shot Peening Coverage on Fatigue Strengths of Steels and Aluminum Alloy

The relations between shot peening coverage and fatigue strength in the quenched-tempered and annealed medium-carbon steels and aluminum alloy A7075-T6 were experimentally studied using a rotating bending fatigue testing machine. It was found that the fatigue strengths of the annealed steel and aluminum alloy were increased by shot peening. On the other hand, the fatigue strength of the quenched-tempered steel were not increased by shot peening. Same shot peening condition causes the positive effect and the negative effect depending on the type of material. Moreover, the valuable coverage might depend on the type of material. More detailed work is necessary to resolve the issue.

Surface topography and the impact on fatigue performance

Areal characterization was applied to plain fatigue specimens manufactured from a nickel-based superalloy, Alloy 720Li, to determine the impact of machined/finished surface topography on fatigue performance of this material. Samples were subjected to fatigue testing in the as-turned and shot peened conditions to study the interaction between residual stresses and topography in influencing the fatigue performance. The turning process was deliberately manipulated to produce three distinct finishes which were subsequently given an identical shot peening, resulting in six grades of surface topography. Surface topography was found to influence fatigue even in the presence of peened compressive residual stresses by promoting crack initiation at valley sites. Both the roughness amplitude and spatial characteristics of the surface were found to be important when correlating to fatigue performance.

Effect of High-Frequency Mechanical Peening Conditions on Increase in the Fatigue Resistance of Butt-Welded Joints

A procedure is proposed for the determination of the endurance limit of butt-welded joints of low-carbon steels under different high-frequency mechanical peening conditions from the maximum depth value of plastically deformed layer using experimental microhardness measurement data.

Effect of shot peening coverage on fatigue limit in round bar of annealed medium carbon steel

Shot peening is an effective and economical technique for improving the fatigue strength of metallic components by inducing compressive residual stress and hardening the layer near the surface. The effect is generally evaluated by main two parameters: coverage and peening intensity. However, the valuable coverage for improving the fatigue strength depends on the shape of the target material. In this study, the effect of coverage on fatigue limit in round bar of annealed medium carbon steel was experimentally studied. The fatigue limits for shot peened round bar specimens with 140–2300% coverage increased 14–25% by comparing those for non-peened round bar specimens. The valuable range of coverage was 280–60% in the used material and shot peening condition for improving the fatigue limit in short time. The result indicates that the valuable coverage of the round bar material is higher than full coverage to improve the fatigue limit of the material due to the effect of incident angle on round bar, even though the degree depends on the materials and shot peening conditions.

Numerical Simulation of One Pulse Power Laser Shock Peening

Laser shock peening (LSP) is a novel technology of surface treatment. LSP utilizes a short laser pulse with high energy density, which induced a high pressure stress wave propagation and residual compressive stress on material surface. The effects of LSP of SAE9310 steel with a laser pulse of 14.2J at 2.9mm square beam have been studied by finite element method. The underlying formulation is based on Lagangian elastoplastic materials model. The propagation of shock wave, residual stress and plastic strain are simulated. The simulations show that the residual stress is mainly in the radial direction of the workpiece, and nearly zero in the longitudinal direction. The plastic strain remains on the processed surface dominantly. Divergences between theoretical and experimental residual stress occur due to the simplification of shock peening conditions.

Application of Indirect Laser Peening to SUS304 Stainless Steel

Indirect laser peening applied to the substrate of austenitic stainless steel with the sheet of similar material. Effects of indirect laser peening condition on the formation of the dimple and the residual stress were investigated in this paper. Shape of the dimple and distribution of the residual stress were measured by laser microscope and X-ray diffraction, respectively. It was observed by the microscope that clean substrate surface of as-received state kept after indirect laser peening because of protection by the sheet. However, fracture of sheet occurred slightly in high pulse energy condition. The diameter and the depth of the dimple by indirect laser peening increased with the increase of laser power. Efficiency of dimple formation decreased with the increase of pulse energy. Affective condition region of indirect laser peening with a combination between the substrate and the sheet of austenitic stainless steel may be limited below the laser power density of 10GW/cm2. It was confirmed that indirect laser peening induced compressive residual stress in the substrate. One of peak of compressive residual stress in residual stress distribution existed near the bottom of the dimple. Residual stress distribution which was produced by indirect laser peening may affect change of quasi bending modulus which was obtained by three-point bending test.

Shot Peening Induced Plastic Deformation in Cast Iron – Influence of Graphite Morphology*

Abstract Graphite morphology in cast iron strongly affects the mechanical properties such as: Young's modulus, tensile/compressive strength and cyclic mechanical behaviour. In this study, pearlitic compact graphite iron (CGI) and grey cast iron (GI) have been studied in a scanning electron microscope (SEM) before and after shot peening under different conditions. The plastic deformation behaviour of CGI and GI under different shot peening conditions has been analysed using electron backscattering diffraction (EBSD) and electron contrast channelling imaging (ECCI). EBSD and ECCI revealed that plastic deformation around graphite inclusions depends on the size and shape of the graphite. The different response of CGI and GI to shot peening is explained by the different damping properties of the graphite and the matrix capability for plastic deformation. n

D40 アルミニウム薄板への特殊レーザピーニングの適用条件に関する検討(GS1 一般セッション)

D40 アルミニウム薄板への特殊レーザピーニングの適用条件に関する検討(GS1 一般セッション)

Residual Stresses in Shot Peened Grey and Compact Iron

AbstractGrey cast iron and compacted graphite iron with a pearlitic matrix are investigated in this study after shot peening using twelve unique combinations of parameters, namely shot size, peening intensity and coverage, followed by residual stress measurements and evaluations. Cylindrical test samples were cut out from heavy truck cylinder heads and polished on the top flat surface to decrease effects from cutting. Residual stresses and the affected depth from the different peening conditions varied between −245 MPa to −565 MPa and from 280 μm to 770 μm in depth. Resultant surface compressive stresses decrease with increasing shot size, peening intensity or coverage whereas the affected depth increases with increasing intensity. The increased affected depth is a result from the increased extent and magnitude of plastic deformation. The compacted graphite iron was more affected by shot peening than the grey cast iron, meaning that the same shot peening parameters resulted in both higher compressive stresses and larger deformation depth.

Wear behaviour of low carbon steel after severe shot peening

In this study, the shot peening process which is a mechanical surface treatment was applied to AISI 1017 low carbon steel material. The free ball micro abrasion test was applied to the specimens following the peening process. The applied shot peening conditions expose the specimens to higher plastic deformation than traditional shot peening and the aim was to establish fine grain structures on the surface and right underneath the surface. Conventional characterization techniques, such as optical microscopy, scanning electron microscopy and transmission electron microscopy were used to study the microstructure of the fine-grained layer. Microhardness measurements were also performed across the fine grained layer. As a result of the microstructure studies, it was observed that dislocation was extended as a result of plastic deformation in a layer of size 40 μm on the surface of the specimen. It was observed that the hardness and stiffness of the specimen surface increased due to the peening intensity, and the wear durability increased as a result.

The Influence of Shot Peening Process on the Residual Stress and Microstructure in Deformed Surface Layer of S30432 Austenitic Stainless Steel

Shot peening is an important surface treatment which can induce compressive residual stress and refine micro-structure in the deformed surface layer. In this paper, the conventional shot peening, dual shot peening and triple shot peening have been applied to S30432 austenitic stainless steel. The residual stress and micro-structure in the deformed layer were investigated by X-ray diffraction method. The results revealed that a compressive residual stress field was induced in the deformed layer for all shot peening conditions. As the shot peening step increased, the compressive residual stresses increased in near surface layer, and then deceased faster in deeper deformed layer. In terms of microstructure, the domain size increased, while the micro-strain decreased with the depth increasing in the deformed layer. Compare with the effect of three different shot peening method, triple shot peenng is more effective to optimize the compressive residual stress, microstructure and micro-hardness of S30432 austenitic stainless steel.