Conventional Shot Peening Research Articles

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.

The influence on gear surface properties using shot peening with a bimodal media size distribution

New technologies developed for automotive engines also have highlighted the transmission torque capacity as restriction factor in the development of enhanced vehicle dynamics performance. Generally, the restriction is defined by the lifetime of the first speed gear. At the end of the gear manufacturing process, shot peening is used to induce compressive residual stresses and further increase fatigue life. This research verified the influence of introducing a bimodal media size distribution into the shot peening process. The proposal is supported by the independent effects of each media class. A higher compressive residual stress can be obtained from larger spheres. And the use of a lower diameter media class improves the surface homogeneity. The bimodal distribution was defined with a probabilistic approach over plasticity and contact stress theories. The experimental validation scope includes a topography analysis and residual stress profile measurements. The results showed mixtures combining up to an increase of 30.9% in the compressive residual stresses without jeopardising the surface quality. The collected data supported the expectation for improving the gear lifetime. It also represented the validation of a new peening process. An improvement in the product properties can be achieved in comparison to the parts produced using conventional shot peening; additionally, a lower process lead time is required in comparison to that for dual peening.

Ultrasonic shot peening

This paper gives a brief overview of published results pertinent to ultrasonic shot peening, a relatively new method to introduce severe plastic deformations in the surface of materials and obtain nanosized grains. Among reported benefits are increased surface hardness and fatigue resistance, and possibility to perform nitriding at lower temperatures and in shorter times. Being a new technology, there is a lack in available literature on ultrasonic shot peening. For that reason, some of the results published for conventional shot peening are also presented. We believe, however, that the results selected here are transferrable to ultrasonic shot peening, or at least can serve as a reference point for this process.

Surface layer investigation of duplex stainless steel S32205 after stress peening utilizing X-ray diffraction

Residual stresses and micro-hardness of duplex stainless steel S32205 after stress peening are measured and domain sizes and microstrain are calculated. The results show that stress peening can significantly improve the compressive residual stresses and micro-hardness in both austenite and ferrite, and the former is affected by both the prestress and the measurement directions. Microstructure investigation reveals that material deformation is enhanced after stress peening, and smaller domain sizes and higher microstrain are introduced. The compressive residual stress enhancement by stress peening in ferrite is more than that in austenite under the same stress peening, which is due to the more elastic deformation recover in ferrite. Therefore, the difference of residual stresses between ferrite and austenite can be narrowed down by conducting appropriate stress peening. Based on these investigations, it is concluded that stress peening is superior to conventional shot peening treatment to improve the surface properties of duplex stainless steel.

Finite Element Analysis of the Variation in Residual Stress Distribution in Laser Shock Peening of Steels

Laser shock peening (LSP) is a surface treatment technique similar to conventional shot peening. The laser induced plasma causes plastic deformations and compressive residual stresses that are useful for developing improved properties in the fields of resistance to fatigue, wear or stress corrosion cracking. The actual distribution of residual stresses is extremely important while designing for improved fatigue life using laser shock peening, as fatigue cracks would initiate from the weakest point in the structure. In this paper, the variations in distribution of residual stresses due to laser shock peening are studied with a focus on two materials, annealed 1053 and hardened 52100 AISI steels. A 3D finite element model was developed to study the actual distributions of the residual stresses due to laser shock peening. The effect of hardness on the distribution of the residual stresses and the presence of tensile residual stresses in the surrounding regions of the impact is analyzed. Much larger variations in the residual stress distributions were observed in case of the 1053 steel as compared to hardened 52100 steel. A comprehensive analysis of the simulation results was performed in order to address and explain this behavior. It was observed that the extent of overlap would also affect the variations in the residual stress distributions. The tensile residual stresses present in the areas surrounding the shocked region were also analyzed based upon the extent of overlap and the hardness of the material. It was observed that the ratio of peak tensile to compressive residual stresses developed in 1053 steel was much higher as compared to that in the hardened 52100 steel.

Investigation for Different Peening Techniques on Residual Stress Field of SiCw/Al Composite

In order to improve the residual stress field of SiCw/Al composite after conventional shot peening, modified warm peening, stress peening, and compound peening were carried out on SiCw/Al composite specimens and residual stress fields of those specimens were investigated via x-ray measurement. Results show conventional peening can improve residual stress field of SiCw/Al composite but the improvement has a limit. Compared with conventional peening, modified warm peening can increase the maximum residual stress, the depth of compressive residual stress layer and improve stability of residual stress field whereas stress peening can increase all characteristic parameters of residual stress field efficiently. Compound peening combines the positive effects of modified warm peening and stress peening, and has the most strengthening effects.

Surface mechanical properties of S30432 austenitic steel after shot peening

The surface yield strength of S30432 austenitic steel after conventional and dual shot peening treatments has been investigated by means of X-ray stress analysis. The results showed that the proof stress σ0.2 of the shot peened surface increased to around 830MPa and 940MPa after conventional and dual shot peening, respectively. While for the bulk S30432 austenitic steel, the yield strength was 268MPa. The strengthen mechanism was discussed in terms of microstructure by X-ray line profile analysis method. The results revealed that the refined domain size and high micro-strain were induced in the deformed surface layer. This changed microstructure was mainly responsible for the high yield strength of shot peened surface. The surface yield strength of the material surface can be obtained from the proposed X-ray stress analysis method. Therefore, this method can be considered as a complementary approach in investigating the microstructural hardening effect of SP treatment.

Effect of prestress state on surface layer characteristic of S30432 austenitic stainless steel in shot peening process

Residual stress and microstructure on surface deformed layer of S30432 austenitic stainless steel after shot peening with different prestress states were investigated. The domain size and micro-strain in the deformed layer were analyzed by Voigt method. The results showed that the compressive residual stress and microstructure were improved significantly after stress shot peening. The values of compressive residual stress depended on both the prestress state and the measurement directions. Microstructure investigations revealed that smaller domain size and higher micro-strain were induced compared with the conventional shot peening. And the variations of microstructure were mainly influenced by the values of prestress state. Based on these investigations, it is concluded that stress shot peening is superior to conventional shot peening and it is an effective method to improve the surface properties of S30432 austenitic stainless steel.

Effect of the impact energy of various peening techniques on the induced plastic deformation region

In order to clarify the relationship between the depth of dimples and the plastically deformed region beneath the surface induced by shot peening and compare the characteristics of various peening methods in terms of single impact energy, the plastic deformation regions induced by single impact at various peening techniques were visualized using Fry's etching method. The relationships between impact energy and both the dimple size and plastic deformation region in the high shot speed range (∼50m/s) were clarified, and the relationships were found to be different from those in the low speed range (∼25m/s). The plastic deformation zones induced by cavitation and laser peening were also studied in order to understand their features. The results showed that the ratio of the plastic deformation region to dimple depth induced by cavitation peening and laser peening was more than 3 times larger than that induced by conventional shot peening, though the plastic deformation volumes induced by cavitation and laser peening were smaller than that induced by conventional shot peening.

Effect of stress peening on surface layer characteristics of (TiB + TiC)/Ti–6Al–4V composite

Residual stresses and microstructure on surface layer of (TiB + TiC)/Ti–6Al–4V are investigated after stress peening. The values of domain sizes and microstrain of surface deformation layers are calculated from the integral breadth of diffractive peaks via Voigt method. The results show that the compressive residual stresses and microhardness are improved significantly after stress peening, and the variations of residual stresses are affected by both the prestresses and the directions of measurement. Microstructure investigations reveal that, the deformation amount increase after stress peening, and smaller domain grain sizes and higher density dislocations are introduced. The changes of microstructures are mainly influenced by the values of prestresses. According to these investigations, it is can be found that the stress peening is superior to the conventional shot peening treatments and it is an effective method to improve the surface properties of (TiB + TiC)/Ti–6Al–4V composite.

Investigation of the Process Capability of Water Cavitation Peening and Shot Peening Processing

Water cavitation peening (WCP) with aeration is a recent potential method in the surface enhancement techniques. In this method, a ventilation nozzle is adopted to improve the process capability of WCP by increasing the impact pressure, which is induced by the bubble collapse on the surface of components in the similar way as conventional shot peening(SP). In this paper, the process capability of water cavitation peening and shot peening is investigated, The residual stresses in the near-surface and surface morphologies of spring steel SAE 1070 was characterized by X-ray diffraction (XRD), optical microscopy (OM). After peening treatment, changes in surface morphologies, as well as residual stress with the different peening duration were recorded. The obtained results indicate that the WCP processing had a better surface finish than SP processing.

Fatigue life enhancement of aluminum alloy for aircraft by Fine Particle Shot Peening (FPSP)

Fine Particle Shot Peening (FPSP) enhances fatigue properties of aluminum parts for aerospace compared with conventional shot peening (SP). The features of FPSP process are small ceramic media and high velocity of the media flow. Fatigue life of aluminum alloy obtained by FPSP is around one order of magnitude longer than that by SP. And the superior fatigue property unchanged even after anodize for corrosion protection. FPSP creates fine dimples with small surface roughness and high compressive residual stress at very near surface, while SP forms large dimples and high compressive stress inside of the material. The fatigue crack occurred at the subsurface in case of FPSP, while at the surface in case of SP and machined. The fatigue crack initiation at the subsurface is the reason of superior fatigue life by FPSP.

Laser shock peening to improve the fatigue resistance of AA7050 components

PurposeLaser shock peening (LSP) is a process capable of introducing compressive residual stresses into a metallic component. The residual compressive stress field can extend deeper below the treated surface than that produced by conventional shot peening (SP). The effect of such deep compressive stress profile is expected to result in a significantly greater benefit in fatigue resistance after LSP compared to SP. The purpose of this paper is to examine this further.Design/methodology/approachResidual stress profiles have been determined by X‐ray diffraction and incremental centre hole drilling. They have been correlated with the respective LSP process parameters and the obtained fatigue behavior.FindingsA significant improvement of the fatigue life was found for an R ratio of 0.1. SP leads to a fatigue improvement of about 15 percent. For the same specimen geometry, a fatigue life improvement of about 25‐35 percent, depending on the load level, can be obtained after LSP. However, not only for the positive R ratio, where it is quite obvious, but also for the negative R ratios, R=−1 and −3, an increase of the fatigue life is generated by SP and LSP.Originality/valueA shown LSP has a high potential for extending the service life of metallic components at the design stage, but it may also be possible to apply this technique to in‐service aircraft to extend the service goals of existing structures.

Effects of laser peening on fatigue life in an arrestment hook shank application for Naval aircraft

Laser peening is evaluated relative to and in combination with other means of improving fatigue resistance in a particularly severe arrestment hook shank application for a carrier-based Naval aircraft. A large-scale test specimen was designed and manufactured from Hy-Tuf steel to geometrically simulate conditions in the arrestment hook shank, and fatigue tests were conducted on peened specimens under conditions of spectrum loading that simulate aircraft arrestments. Laser peening substantially increases the resistance to crack initiation relative to conventional shot peening. A change to a higher-strength steel, Ferrium S53, significantly increases the crack initiation life of both conventionally shot peened and laser peened specimens, with the latter exhibiting the highest levels of crack initiation life for all conditions evaluated in this test program. Proof loading at levels above the design limit load, conducted before the peening operation, substantially increases the crack initiation life of conventionally shot peened specimens. In contrast, proof loading does not provide additional improvements in the fatigue life of laser peened specimens since the depth of plasticity due to proof loading is similar in magnitude to the depth of residual compressive stress introduced by laser peening. Finally, limited test results suggest that repeated laser peening over the life of a component may maximize or even extend crack initiation life; however, a significant amount of testing would be required to determine the processing parameters that maximize the efficacy of this approach to extending fatigue life.

Finite Element Simulation of Shot Peening Coverage with the Special Attention on Surface Nanocrystallization

The present study aims to challenge the existing finite element models in terms of one of the most important practical parameters, i.e. coverage. Important models from the literature are re-simulated and their resulted treated surfaces are carefully examined. Result of this study shows that existing finite element models could not reflect the realistic coverage. A variable dimension symmetry cell is developed in order to acquire full coverage and at the same time not increasing the computational cost. This model can successfully simulate the surface nanocrystallization by severe shot peening in which the amount of coverage is much higher than conventional shot peening

Comparable Study on Water Cavitation Peening and Traditional Shot Peening of Almen Strips

Comparing with conventional mechanical shot peening (SP) technique, water cavitation peening (WCP) experiments of Almen strips were carried out on a self-manufactured equipment. The results show that WCP demonstrates a wide range of standoff distance (SD) that from the nozzle to the surface of the object. By measuring the colour changes of the Fuji pressure sensing film, over 110 MPa impacting pressure was detected, which is resulted from the bubbles blasting on the sample surface when the SD is from 65 to 100 mm under 40 MPa of operating pressure. 600 MPa compressive residual stress achieved on the suface of the Almen strips after WCPed for 32 min. The depth of the zone affected by the compressive residual stress is about 100 µm. The highest residual stress appears in the top surface layer, while in case of SP it appears in the subsurface. Compared to SP, WCP is capable to get rather smoother surface and cause less deformation of the testing sheet, simultaneously.

Effect of Microshot Peening on Surface Characteristics of Spring Steel

Shot peening is a surface treatment that improves the performance of engineering components. In conventional shot peening, the medium consists of small spheres, which are usually made of high-carbon cast steel; the diameter of the spheres is in the range from 0.3 to 1.2mm. More recently, however, a new type of microshot has been developed to enhance the peening effect. The diameter of the spheres in the new medium is in the range from 0.02 to 0.15mm. In the present study, the effect of microshot peening on the surface characteristics of spring steel was investigated. The injection method of the microshot was of the compressed air type. The microshots of 0.1mm diameter were high-carbon cast steel and cemented carbide, and the workpiece used was the commercially spring steel JIS-SUP10. The surface roughness, hardness and compressive residual stress of the peened workpieces were measured. The surface layer of the workpieces was sufficiently deformed by microshot peening. A high hardness or residual stress was observed near the surface. The use of hard microshots such as cemented carbide was found to cause a significantly enhanced peening effect for spring steel.

ANALYSIS OF PNEUMATIC FINE PARTICLE PEENING PROCESS BY USING A HIGH-SPEED-CAMERA

In this study, the peening behavior of shot particles in a fine particle peening (FPP) process such as velocity and impact angles were analyzed by using a high-speed-camera. Results showed that the velocity of shot particles depended on a peening pressure; the higher the peening pressure, the higher the particle velocity. The particle velocity measured in this study was approximately 120 m/s; this was much higher than that of the conventional shot peening (SP) process. This was because the air resistance of shot particles in the FPP process was higher than that of shot particles in the SP process. In order to discuss the surface modification effect of the FPP process, commercial-grade pure iron treated by the FPP process was characterized by micro-Vickers hardness tester and scanning electron microscope (SEM). Thickness of hardened layer treated with higher peening pressure was much higher than that of the lower pressure treated one. The unique microstructure with stratification patterns, which was harder than that of the other part, was observed near the specimen surface. The reason for the microstructural changes by the FPP treatment was discussed based on the kinetic energy of shot particles.

Engineering the residual stress state and microstructure of stainless steel with mechanical surface treatments

Four mechanical surface treatments have been considered for the application to austenitic stainless steel structures. Shot peening (SP), laser shock peening (LSP), ultrasonic impact treatment (UIT) and water jet cavitation peening (WJCP), also known as cavitation shotless peening (CSP), have been applied to 8 mm thick Type 304 austenitic stainless steel coupons. This study considers the merits of each of these mechanical surface treatments in terms of their effect on the surface roughness, microstructure, level of plastic work and through thickness residual stress distribution. Microstructural studies have revealed the formation of martensite close to the treated surface for each process. Residual stress measurements in the samples show compressive stresses to a significantly greater depth for the LSP, UIT and WJCP samples compared to the more conventional SP treated sample.

Laser Shock Processing of 6061-T6 Al alloy with 1064 nm and 532 nm wavelengths

Laser Shock Processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results in the LSP concept for metal surface treatments in underwater laser irradiation at 532 nm and 1064 nm. The purpose of the work is to compare the effect of both wavelengths on the same material. A convergent lens is used to deliver 1.2 J/pulse (1064 nm) and 0.9 J/pulse (532 nm) in a 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG laser with spots of a 1.5 mm in diameter moving forward along the work piece. A LSP configuration with experimental results using a pulse density of 2500 pulses/cm 2 and 5000 pulses/cm 2 in 6061-T6 aluminum samples are presented. High level compressive residual stresses are produced using both wavelengths. It has been shown that surface residual stress level is comparable to that achieved by conventional shot peening, but with greater depths. This method can be applied to surface treatment of final metal products.