Papers by Keyword: Shot Peening

Abstract: Shot peening is one of the most powerful mechanical peening techniques applied in surface engineering to improve the mechanical properties of metal alloys by introducing compressive residual stresses. During shot peening process, surface integrity, such as microstructures, surface roughness, hardness and residual stress can be varied by adjusting the operating parameters of shot peening. To facilitate the understanding of the microstructure and properties variation, in our latest work, shot peening with high coverage percentage has been employed to create severe plastic deformation on stainless steel 304 (SUS304). Morphological and topological study on the shot peened coupons were carried out using microscopes and 3D optical profiler. Residual stress depth profiling was evaluated using X-ray diffraction technique. Microstructures, phase distribution and crystal orientation were analyzed by electron backscatter diffraction technique. The results show that phase transition γ - α’ and grain refinement occur during this mechanical peening process. A nanocrystalline layer with preferred orientation formed near the surface, and dislocations accumulated within sub-surface area, which can be attributed to the high energy input from the peening process. The maximum compressive residual stress, which is around 1000-1200 MPa, occurred beneath the top surface. All these findings will provide guideline for surface engineering at various scales and designing of the surface enhancement process via mechanical peening for achieving optimum surface integrity of metallic alloys.

Abstract: Compressive residual stress below the surface of material could increase fatigue life as it encounters the tensile loading applied on the material during operation. Shot peening process is a common surface treatment to introduce this stress. This study will investigate on how to introduce the same amount of residual stress by simulation using FEM as introduced in experimental shot peening process. Actual shot peening process was done using a particular sets of parameters and FEM with single shot is used to simplify the simulation procedure. Result shows that using a single shot simulation could also introduce the equivalent amount of residual stress as in the experimental multi-shots shot peening process. This value could be used in further study to study the relaxation of the stress after load is being applied.

Abstract: Widely used in thermal production quenching surroundings, gas atmospheres and working mixtures for shot peening are considered. Features of materials at their use are presented and recommendations for more effective application are given. The change of quenching surroundings cooling capacity on the water-soluble polymer basis after an annual operation is shown. Hardening oils during operation are exposed to oxidation and viscosity index change, what affects on the quenched products properties. For endothermic atmospheres that are used in the parts chemical-thermal treatment the composition improvements are required. Working mixtures for shot peening must have a certain composition, properties and sizes, depending on the tasks to be solved.

Abstract: The fatigue life of 7050 Al alloy samples after different surface treatments, i.e., as-machined, anodizing, shot peening, and shot peening followed by anodizing, had been tested. The shot peening treatment specimens presented the longest average fatigue life. The fatigue life of anodizing treatment specimens decreased by 69.3% and 78.8% at 215 MPa and 260 MPa stress levels than as-machined ones. Introducing the shot peening treatment before anodizing can increase the fatigue life by 220% / 296.9% at 215 MPa/260 Mpa than that only treated by anodizing. The effect of the surface treatments on the fatigue life were studied by performing surface morphology investigation, residual stress measurements and fracture surface analysis.

Abstract: The effects of peening conditions on the surface characteristics and fatigue life of titanium alloy was investigated using microshot peening, ultrasonic shot peening, and multiple shot peening. The use of microshot peening technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. The ultrasonic shot peening that uses media of several millimeters in size with ultrasonic vibration has attracted attention as a means to reduce the surface roughness. In the present study, an air-type and an ultrasonic type machine were used. In the microshot peening process, the media used was high-carbon cast steel and the hard powder, with an average diameter of 0.1 mm. The workpiece was commercial titanium alloy Ti-6Al-4V. In the microshot peening (MSP), work hardening was evident to the depth of approximately 0.3 mm from the surface. This depth was approximately three times the diameter of the media. However, the influence of the peening time on the hardness distribution was not great. In the ultrasonic shot peening (USP), work hardening was deeper in the material. This is because the diameter of the media used for ultrasonic machining was large. On the other hand, in the combined shot peening (CSP), a degree of hardness was higher at the top surface. However, the hardness patterns and values were pretty much identical to ultrasonic shot peening. The fatigue limit was thought to be greater in the microshot peening experiment because the work-hardened layer was formed near the workpiece surface.

Abstract: Various impact analysis models have been used for analytical prediction of peeningresidual stress. In this paper, a new approach based on finite element (FE) analysis was proposed topredict the peening residual stress through single indentation analysis using the dent profilegenerated on a shot-peened surface. Three analysis models (rigid, elastic, and plastic shots) werecompared each other, and the dent obtained in the plastic shot impact analysis model showed a dentprofile almost identical to that of the experimentally obtained dent. A rigid indenter modelconstructed using the dent profile obtained by dynamic impact analysis, and it integrated into thesingle indentation analysis model. The FE surface residual stress obtained in the center of the dentof the indentation analysis model was found to be almost identical to the surface residual stressmeasured by X-ray diffraction (XRD), thus verifying the validity of the proposed single basicindentation FE model based on impact analysis.

Abstract: As shot peening is widely used to improve the crack resistance of various metals, it isimportant to have an accurate method to calculate the compressive residual stress produced by thisprocess. To this end, this paper presents a finite element (FE) model that includes an indenterdesigned from a dent profile. The results of compressive residual stress obtained by using thisindenter model and a normal shot impact model are compared. The indentation FE solution with anunmodified indenter is close to that obtained using the rigid shot (RS) impact model. The solutionfor the indentation FE model with a modified indenter closely matches that for an elasticdeformable shot (EDS) impact model. These results confirm the effectiveness of the indentation FEmodel based on the dent profile. This model can replace the present impact FE models to calculatethe compressive residual stress produced by shot peening.

Abstract: Plastic deformation can induce surface modification, such as shot peening (SP) on workpiece surface is the hot issue of recent scientific research. SP is the efficient way to improve mechanical behavior of specimens by inducing sever plastic deformation on their surface. Nevertheless, this surface treatment induced complex microstructural evolutions such as grain refinement, will enhance the corrosion resistance of specimens. In this work, the microstructure and properties of 34CrMo4 alloy of before and after SP for 20 min have been investigated. The evolution of microstructure and properties were analyzed from the surface and cross-section. The microstructure morphology at the different depth was determined by optical microscope. The results show grain size is increasing with the depth, and the microhardness and compressive residual stress decrease gradually. In terms of corrosion resistance, the 50 μm depth specimen has the best property than other depth, which the potential and corrosion current density are-0.484 V and-5.72 Acm^-2, respectively. The maximum polarization resistance is 2055 Ωcm² by capacitive arc radius of electrochemical impedance spectroscopy.

Abstract: Aluminum-magnesium-silicon alloys have been widely used as extruded products due to its mechanical strength and high ductility. The effects induced by shot peening has been extensively used in materials that have potential for structural applications. In this context, the purpose of this study was to evaluate the residual stress induced by shot peening of extruded aluminum alloy 6082. Initially, the effect of heat treatments such as solution treatment and ageing of this alloy was studied. The residual stress measurements were carried out using x-ray diffraction. The microstructure of the alloy was studied by optical microscopy. The crystallographic texture was determined using x-ray diffraction and back-scattered electron diffraction. The heat treatment sequence that resulted in the highest hardness of Al alloy 6082 was solution treatment at 560oC for 30 min, followed by ageing at 185oC for 5 h. The residual stress in compression of the extruded alloy’s surface increased by 87.38%, from-66.6 to-124.8 MPa, caused by shot peening. The residual stress profile indicated an increase in its value up to a depth of 86 μm, beyond which the values obtained were unreliable. The extruded section revealed accentuated crystallographic texture in the (111) plane parallel to the cross-section and in the (200) and (220) planes oriented preferentially in the longitudinal direction to extrusion and perpendicular to the (111) plane.

Abstract: High-pressure gas containers must be able to withstand high internal pressures because they store compressed gases. Otherwise, cracks or defects may lead to an explosion, which may in turn lead to a large-scale disaster. Therefore, accurate analysis of the causes of cracks or defects and various techniques for detecting cracks or defects are needed. In this research, we analyzed the failure mechanism of a high-pressure gas container through fractography using scanning electron microscopy and optical microscopy and through measurements of their mechanical and chemical properties.