Peening Applications Research Articles

Mechanical Properties and Fatigue Life Evaluation under High Temperature and Shot Peening Application using AA7001

In some applications, AA7001 may be subjected to high temperature and fatigue. This interaction leads to varying the mechanical and fatigue properties of the above alloy. This work deals with the effects of tensile properties and constant fatigue amplitude performance. Aluminum alloys have a low specific strength, are simple to produce, and are lightweight, which has made them popular in the construction, automotive, marine, and aviation industries. The history of stress and temperature applied to the component has a significant impact on the time-dependent process of creep and strain damage. The purpose of this research is to investigate the behavior of AA7001-T6 when two phenomena, high temperatures creep and fatigue, are combined. Compared to the fatigue life interaction employing shot peening thereby, the fatigue lifetimes were The influence of shot peening on the mechanical and fatigue characteristics of AA7001-T6 was investigated utilizing four different temperatures, including RT, SP+RT, 330°C, and SP+330°C. It has been observed The application of 330°C to the tensile process lowered the ultimate tensile strength of UTS and YS by 21.9 % and 22.3 %, respectively. Shot peening improved the aforesaid percentage, lowering it to 19.2 % and 19.7%, respectively. At a stress level of 400MPa, fatigue life was lowered by 18.18 % owing to an increased temperature of 330°C, and this percentage was reduced to 10.16 % due to creating the compressive residual stresses (CRS) (SP). At (RT), the fatigue strength (endurance fatigue limit) was 229 MPa, but after Shot Peening, it improved to 237 MPa. At 330°C, shot peening increased the improved fatigue limit from 217MPa to 229MPa, resulting in a 5.24 % improvement.

Identification of Johnson-Cook material model parameters for laser shock peening process simulation for AA2024, Ti–6Al–4V and Inconel 718

This paper addresses the identification of Johnson-Cook material model parameters for the simulation of high strain rate processes such as laser shock peening. A combined numerical and experimental approach is described for the identification of the material parameters for AA2024-T3, Ti–6Al–4V, and Inconel 718 alloys. Validation of the parameters was performed based on depth-resolved residual stress profile evaluation after both experimental and numerical laser shock peening application. However, it has been observed that the strain rate-dependent coefficient identified at low strain rates is insufficient for accurately representing the behavior of the Ti–6Al–4V alloy. Consequently, there is a need to identify and determine the appropriate parameter specifically tailored to the strain rates that are relevant to the intended application of the material. The outcomes of this study provide significant insights into the accurate identification of Johnson-Cook material model parameters for laser shock peening simulations. The findings emphasize the critical importance of considering the strain rate-dependent coefficient C in the Johnson-Cook material model to enhance the accuracy and precision of representing material behavior in simulation efforts.

Prior Aggressive Corrosion and Fatigue of AA6063-T6 under Shot Peening Application

The mechanical and constant fatigue behavior of AA6063-T6 exposed to aggressive 3.5 wt.% NaCl solution corrosion has been investigated. The selected alloy used in this work is typically employed in structured components like aircraft spars. Some tensile and fatigue specimens were hardened using shot peening (SP) treatment for 10 mins, shot peening time. The experimental results revealed that the (UTS) and (YS) were reduced by 10.88% and 9% respectively due to corrosion while ductility increased from 12.5% to 14%. SP treatment improved the above reduction percentage to 8.17% for (UTS) and 7.53% for (YS). Corrosion-fatigue had a significant impact on fatigue life as well as strength at lower stress levels, but had no influence at higher stress levels. The endurance fatigue limit (EFL) reduced to 62.64 MPa and raised to 64 MPa due to corrosion when using (SP) treatment

Tailoring of residual stresses by specific use of defined prestress during laser shock peening

The aim of the present study is to tailor laser shock peening-induced residual stresses by applying defined prestress. For this purpose, elastic prestress is introduced during laser shock peening application and subsequently released. The influence of prestress on the resulting residual stresses is investigated experimentally by a four-point bending device that allows prestressing of the specimen during laser shock peening. Furthermore, a semi-analytical model of laser shock peening, extended by a contribution accounting for the prestress, is used to determine the prestress—residual stress relationship. A linear relation between prestress and compressive residual stress is found when the resulting compressive residual stresses are in the range of 20 % – 100 % of the yield strength. Generally, tensile prestress leads to a higher magnitude and penetration depth of resulting compressive residual stress after laser shock peening. As a proof of concept, prestress was used to alter a non-equibiaxial residual stress profile into an equibiaxial one, demonstrating the applicability of prestress as an effective tool for residual stress design.

Quantitative Fracture Mechanics Approach to Fatigue Life Improvement by Shot Peening Application

Stress intensity factor has been a favorite tool in fracture mechanics due to its simplicity. Here, it is used to study the influence of the shot peening application in fatigue life improvement. Using a CT-specimen, the study of shot peening effect on fatigue life was performed. Here, the compressive residual stress is converted into residual stress intensity factor, Kres.. Together with the applied stress intensity factor, Kapl., the superposition principle can be used. The result of the investigation clarifies quantitatively what has been widely believed that one of the easiest ways to improve fatigue life is by perfecting the surface via shot peening. Compressive stresses are beneficial not only in postponing fatigue crack initiation but also in preventing the crack propagation, which lead to increasing fatigue strength.

Surface integrity and residual stress analysis of pulsed water jet peened stainless steel surfaces

Enhancement of the life of the engineering components is essential from the perspective of its performance, therefore, it is necessary to eliminate the negative effects that attenuates the life of these components. Numerous surface treatment methods are used at present out of which water jet peening process have been stated to overcome the shortcoming reported in other surface treatment methods like surface defects caused by the embedment of particles during shot peening, thermal effects caused by laser shock peening. It has been reported in studies that the technological modification of water jet technology, ultrasonically generated pulsed water jet (PWJ) can be used for the peening application but still the detailed study of parametric variations for the peening process is not clearly explained. The present work aims at reporting the effect of variation of parameters: jet pressure (40 MPa to 100 MPa), traverse speed of the nozzle (5 mm/s to 25 mm/s) and standoff distance (15 mm to 31 mm) during the ultrasonically generated PWJ peening process. The peened surface was quantified in terms of surface residual stress measurements, micro hardness and surface roughness measurements. The results indicate that the variations in the parameters shows significant changes in the surface residual stress enhancement and strengthening process. The lower pressure (40 MPa), lower traverse speed (5 mm/s) and higher standoff distance (31 mm) showed the maximum improvement in the surface residual stress (up to 540 MPa) and micro-hardness (up to 570 HV). The impact of the repeated pulses causes plastic deformation on the surface and sub-surface layers which results into the change in the microstructures of the affected area. The microstructural examination through field emission scanning electron microscopyshowed variations in these deformations under different parametric conditions. This study can give better understanding for the proper selection of the peening parameters for practical applications using ultrasonically generated pulsed water jet technology.

Shot Peening Modeling and Simulation for RCS Assessment

The application of shot peening to components and structures induces residual compressive stresses (RCS) on the surface. It has also been identified that fatigue, corrosion fatigue (CF) and stress corrosion cracking (SCC) are lifted by RCS. However, failures still occur in local areas of shot peened components under service conditions at stresses below the yield strength of the material. This calls for a real assessment of the distribution of stresses in the shot peened component for enhanced prediction of induced RCS. This report is the first part of an ongoing research aimed at establishing a simplified methodology for a realistic simulation of the shot peening process and the accompanying residual stress by combined DEM-FEM approach. In this paper, the authors have replaced the transient analysis used in past DEM-FEM approach with a simpler static structural analysis. The results obtained are validated with similar experimental results available in literature. This will serve as a reliable tool for more accurate analysis/prediction of the service life of shot peened components and for enhancement of shot peening application as a life-extension remedy to critical engineering components.

Novel Type Shot Peening Applications on Railway Axle Steel

In this study, novel type shot peening applications such as severe shot peening (SSP) and dual step peening -DSP- (severe shot peening followed by re-peening -RP-) have been applied to AISI 4340 railway axle steel. Microstructural and mechanical properties are compared with conventionally shot peened (CSP) ones. The new treatments influence thicker surface layer and improve mechanical properties (microhardness and fatigue) by the way of Almen intensity enhancement. Disadvantageously, SSP increase surface roughness to the values that can be hazardous to the expected fatigue life of critical machine parts. However, DSP reduces the values and new approaches could be designed for making surface roughness values comparable with CSP in the aspect of the experimental outputs.

Study and development of high peak power short pulse Nd:YAG laser for peening applications

Because short pulse Nd:YAG laser of nanosecond pulse-width and high peak power has a unique capability to improve the mechanical properties of metal parts, a study on the development of high peak power short pulse from Nd:YAG laser along with its peening application has been performed. The design scheme of laser and the characteristic of laser beam transmission are presented and discussed. A pulse energy of 25 J with 15 ns pulse-width and a maximum peak power of 1660 kW laser system which use one oscillation and eight amplifiers has been achieved. Laser beam has a max divergence angle of 0.03 mrad, a pulse-to-pulse pulse-width stability of ±0.1 ns, and the pulse-to-pulse energy stability factors of less than ±2.8%. A low value of divergence means an easier modification of a nearly hat-top laser beam intensity profile and an easier transmission of laser beam. To evaluate the performance of the laser system, several metal materials are processed. Laser peening quality and efficiency are analyzed by using an optical microscope, a transmission electron microscope, and an X-ray diffraction device. The processing results show that the performance of this laser system is excellent.

Microstructure evolution and mechanical behavior of severe shot peened commercially pure titanium

Severe plastic deformation methods such as equal channel angular pressing (ECAP), high pressure torsion (HPT) and constrained groove pressing (CGP) have been increased in importance due to superior mechanical properties evolution and nanostructured grains build up. Besides, severe shot peening has been using as a severe plastic deformation method in recent years and applied converting microstructure to nanostructure just below the surface. Not only enhancement of fatigue, fretting fatigue and corrosion strength of materials but also altering the surface microstructure gathers much interest for severe shot peening application. In this study, severe shot peening with different Almen intensities (A28–30, A30–32, A32–34, A34–36, C4–6, C6–8, C8–10) was performed on commercially pure (CP) titanium (grade 2) and the specimens surfaces were investigated according to Almen intensity (plastic deformation rate). Also mechanical properties such as hardness and elastic modulus have been investigated by performing nanoindentation tests. Results have shown the work hardened layer is approximately 160 μm and has nanograin size distributions with much higher nanohardness and elastic modulus with compared to those of inside the bulk material.

The Role of Shot Peening in Increasing X70 Steel Fatigue Properties

The paper presents the authors' results of experimental examination of pipeline steel X70 fatigue properties before and after shot peening application, including relaxation of residual stresses during rotating bendi ng fatigue loading (f 30 Hz, T 20 5 °C, R 1). The obtained results confirmed the positive effect of surface hardening realized by shot peening. The fatigue properties incl. fatigue limit were higher after shot peening and this effect was visibly higher for notched specimens than for smooth specimens. During rotating bending fatigue loading the residual stresses in subsurface layers relaxes which decreases the strengthening effect after a certain number of cycles.

About the role of residual stresses and surface work hardening on fatigue ΔK th of a nitrided and shot peened low-alloy steel

Nitriding and shot peening are surface treatments widely used to improve the fatigue strength of mechanical and structural components. Both treatments enhance the mechanical properties of the surface layer of material: nitriding mainly by means of chemical transformations and formation of a very hard case, shot peening mainly due to compressive residual stress field in the sub-surface layer of material. The combined application of nitriding and shot peening has not been adequately investigated in literature and the known data do not allow to define a general criterion to assess if and when shot peening application after nitriding can be useful. In this paper the effect of nitriding plus shot peening on fatigue strength of a low-alloy steel is investigated by means of experimental tests carried out on specimens containing a micro-hole, acting as a pre-crack. To analyse the role played by shot peening induced residual stresses, a series of specimens was heat-treated after shot peening, being the aim the partial removal of residual stresses without strongly modifying the mechanical properties of the surface layer of material. After a critical discussion of the results in terms of residual stress, micro-hardness trend and fatigue strength, an original fracture mechanics based approach is proposed to predict the threshold value of the stress intensity factor of nitrided and shot peened steels. The results are in good agreement with the experimental evidence.

Computer modelling of interference effects in erosion testing: effect of plume shape

A computer model that simulates the interference between rebounding and incident streams of spheres has previously been developed by three of the present authors. The model can accommodate a wide variety of incident particle, target surface, and blasting process parameters making it suitable for application to erosion testing, blast cleaning, and shot peening applications. In this paper, the algorithm that controls the angular distribution of the particles as they leave the nozzle (i.e. the shape of the plume of particles leaving the nozzle) is modified to simulate experiments performed by Shipway and Hutchings. Comparisons between the modified model and experimental data in the literature revealed good agreement. The modified model was then used to predict the critical flux for significant interference effects, an important parameter in erosion testing, as a function of both incident particle and blasting nozzle parameters. The results are presented in dimensionless form, so that the critical flux can be determined under a wide variety of experimental conditions. The results of the present study may have important applications in erosion testing, blast cleaning, and shot peening applications.

浸炭焼入鋼の衝撃疲労強度におよぼす合金元素とショットピーニングの影響

Impact fatigue tests were carried out using various kinds of carburized steels. It was shown that internal oxidation was remarkably reduced with decreasing Si and Mn contents, and resulted in higher impact fatigue strength. The effects of residual stress, retained austenite, hardness near the surface, and fatigue fracture toughness were investigated. The difference of the fatigue strength in various carburized steels could be explained in terms of those effects.The effect of shot peening application to carburized steel was investigated using JIS standard type steels. As a result, high cycle impact fatigue strength increased 40 to 60% gain by shot peening. This improvement was caused by increase of hardness near surface and compressive residual stress. On the other hand, low cycle fatigue strength showed no gain. For this phenomenon, it was suggested that decrease of the amount of retained austenite by shot peening showed negative effect for fatigue strength. Further, the difference of the fatigue strength in shot peened steels was very slightly. For this reason, it was considered that the life of shot peened steel was influenced by releasing its compressive residual stress rather than the effect of alloying elements.