Showing papers on "Peening published in 2005"

A self-closed thermal model for laser shock peening under the water confinement regime configuration and comparisons to experiments

Abstract: Laser shock peening (LSP) is emerging as a competitive alternative technology to classical treatments to improve fatigue and corrosion properties of metals for a variety of important applications. LSP under a water confinement regime (WCR) can produce plasma pressures on the target surface four times higher and two to three times longer than those under direct regime configurations. However, most of the published thermal models for LSP under WCR are not self-closed, and have free variables which have to come from experimental measurements under the same conditions. In this paper, a self-closed thermal model for LSP under WCR configurations is presented. This model has considered most of the relevant physical processes for laser ablation and plasma formation and expansion, and there are no free variables in the model. The simulation results for pressures from the model are compared with the available experimental results in literature under a variety of laser-pulse conditions, and good agreements are found.

Wave-solid interactions in laser-shock-induced deformation processes

Abstract: A model was developed for material deformation processes induced by laser-generated shock waves. The processes include laser peen forming (LPF) and laser shock peening (LSP) of metals. Numerical solutions of the model using finite element method were implemented in two steps: (1) explicit step, devoted to shock wave propagation, and (2) implicit step, calculating relaxation of material. A series of LPF and LSP experiments was conducted to validate the model. The residual stress measurements by synchrotron x-ray diffraction and deformation measurements by profilometry showed that the experimental and numerical results were in good agreement. It is the first time to numerically and experimentally study the novel process of micro-scale LPF. An important aspect of the work is that the numerical results were further analytically explored to gain improved understanding of wave-solid interaction including shock wave attenuation and shock velocity variation.

The modelling of residual stresses due to surface peening using eigenstrain distributions

Abstract: The beneficial effect of surface peening (including shot peening, laser shock peening, low plasticity burnishing, etc.) on fatigue resistance of structural alloys is well documented and widely used in industry to improve component life. It is perhaps the most widely used technique that relies on the introduction of residual stresses into the component by direct mechanical means. The resulting stress states are usually evaluated experimentally by X-ray diffraction or other stress measurement techniques. In order for shot peening operations to be effective and reliable, the process of introducing residual stresses and strains into peened components must not only be controlled but also be predictable and quantifiable.The present paper establishes a framework for predictive modelling of the residual stress states due to surface peening. Firstly, uniform (within planes parallel to the surface) plastic deformation of the surface layer taking place during shot peening of a thin plate is simulated using the conce...

High-Speed Observation of a Cavitating Jet in Air

Abstract: The use of cavitation impact is a practical method for improving the fatigue strength of metals in the same way as shot peening. In the case of peening using cavitation impact, cavitation is produced by a high-speed submerged water jet with cavitation, i.e., a cavitating jet. A cavitating jet in air was successfully generated by injecting a high-speed water jet into a low-speed water jet injected into air using a concentric nozzle. In order to investigate the various appearances of cavitating jets in air, an observation was carried out using high-speed photography and high-speed video recording. In this study, periodical shading of the cavitation cloud was observed and the frequency of the shading was found to be a function of the injection pressure of the low-speed water jet. Unsteadiness of the low-speed water jet, which is related to the periodical shading of the cloud, was also observed.

Effects of fretting fatigue on the residual stress of shot peened Ti–6Al–4V samples

Abstract: X-ray diffraction residual stress measurement has been utilized as nondestructive tool for the characterization of fretting fatigue damage in shot peened samples of Ti–6Al–4V. Prior to fretting fatigue damage, compressive residual stresses were found to be uniform over the entire face of the sample and independent of the measurement direction. After fretting fatigue, inside and in the vicinity of the fretting damage zone large relaxation of compressive residual stress was observed. An anisotropic residual stress distribution has been observed in the fretting fatigue damaged region. Residual stress measurements in interrupted fretting fatigue experiments showed that the relaxation of residual stress increases as the number of fretting fatigue cycles increase. The results are discussed in the light of their importance in establishing X-ray diffraction residual stress measurement technique as a nondestructive tool to characterize fretting fatigue damage.

Fatigue strength improvement of gears using cavitation shotless peening

Abstract: Peening, using cavitation impacts induced by bubble collapse, represents a novel surface enhancement technique for machine parts without involving conventional shot peening blasting. This is known as cavitation shotless peening, CSP. The improvement in the fatigue strength of a spur gear after CSP has been demonstrated. The fatigue strength of a gear treated with CSP was improved by about 60%, compared with that of a non-peened gear.

Mathematical Modeling of Ultra-High-Pressure Waterjet Peening

Abstract: Waterjet peening is a recent promising method in surface treatment. It has the potential to induce compressive residual stresses that benefit the fatigue life of materials similar to the conventional shot peening process. However, there are no analytical models that incorporate process parameters (i.e., supply pressure, jet exposure time, and nozzle traverse rate, etc) to allow predicting the optimized peering process. Mathematical modeling of high-pressure waterjet peening was developed in this study to describe the relation between the waterjet peening parameters and the resulting material modifications. Results showed the possibility of using the proposed mathematical model to predict an initial range for effective waterjet peening under the variation of waterjet peening conditions. The high cycle fatigue tests were performed to validate the proposed model and fatigue test results showed good agreement with the predictions.

Overview of Low Plasticity Burnishing for Mitigation of Fatigue Damage Mechanisms

Abstract: Surface enhancement technologies such as shot peening (SP), laser shock peening (LSP), and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue strength must be retained in service. LPB provides thermally stable compression and can be performed in conventional machine shop environments on CNC machine tools. LPB enables the extension of component service lives fatigue limited by various damage mechanisms including foreign object damage (FOD), corrosion fatigue, pitting, and fretting. The thermal and mechanical stability of the compressive layer are briefly reviewed. The LPB process, tooling, and control system are briefly described. Four representative applications are presented: thermal stability in IN718, improved damage tolerance in Ti-6-4 fan blades, mitigation of fretting fatigue damage in Ti-6-4, and improved corrosion fatigue in 17-4PH stainless steel.

The effect of shot peening coverage on residual stress, cold work, and fatigue in a nickel-base superalloy

Abstract: The goal of this work was to determine effects of shot peening (SP) coverage on the compressive residual stress magnitude, depth, and relaxation of residual stresses due to thermal exposure, as well as fatigue strength of IN718, a nickel -base superalloy. The residual stress-depth profiles (both depth of compression and magnitude) for coupons shot peened to different coverage levels of 82 % (0.2T where T = time to achieve full area coverage) to 400% (4T) show a slight trend of increased depth of compression with increase in coverage. Though having similar residual stress distributions, the coupons exhibited markedly different cold work distributions. While 82% (0.2T) coverage resulted in less than five percent cold work, increasing coverage to 400% (4T) resulted in cold work as high as thirty -five percent. The heavily cold worked surfaces of the higher coverage coupons exhibited significant relaxation of surface residual stresses, accompanied by corresponding reduction of cold work upon thermal exposure at 525 °C for 10 hours. In contrast, the low cold work associated with lower SP coverage resulted in little relaxation of residual stresses under the same conditions. These observations were consistent with findings in other alloy systems. High cycle fatigue (HCF) performance at 525°C showed little dependence on peening coverage. Even with deeper compression achieved through low plasticity burnishing (LPB), the 525C fatigue performance of IN718 was only marginally improved. There may be other controlling elevated temperature fatigue mechanisms, such as oxidation, operating here that do not depend on residual stresses. HCF behavior at room temperature for the LPB treatment was significantly better than for SP treatment.

Effect of high-velocity oxygen-fuel thermal spraying on the physical and mechanical properties of type 316 stainless steel

Abstract: Data on the microstructural, physical, and mechanical characteristics of high-velocity oxygen-fuel (HVOF)-sprayed type 316 stainless steel coatings are presented and compared with properties of wrought 316 stainless steel. Coatings were prepared at three different spray particle velocities; coating characteristics are presented as a function of velocity. The coatings had relatively low porosity and oxide contents and were significantly harder than annealed, wrought 316 stainless steel. The hardness difference is primarily attributed to high dislocation densities resulting from peening imparted by high-velocity spray particles. The coating hardness increased with increasing spray particle velocity, reflecting increased peening effects. The elastic modulus of the coatings was essentially identical to wrought material. The mean coefficient of thermal expansion of as-sprayed coatings was lower than wrought material, but the expansion of annealed coatings matched the wrought behavior.

Comparison of the hole-drilling and X-ray diffraction methods for measuring the residual stresses in shot-peened aluminium alloys:

Abstract: The incremental blind hole-drilling and the X-ray diffraction methods were used to measure the residual stress field introduced by shot peening in aluminium alloy 6082-T5 plates. Two peening treatm...

Relaxation of peening residual stresses due to cyclic thermo-mechanical overload

Abstract: Shot-peening induced residual stresses can be relaxed due to cyclic loading. This relaxation plays an important role in determining the fatigue life of the peened components. It is therefore the purpose of this study to conduct comprehensive three-dimensional dynamic elasto-plastic finite element analysis of the joint peening treatment and relaxation process. In this regard, a novel symmetry cell is developed and used to model the multiple impact indentations resulting from multiple impingements of a cluster of shots. The model was further extended to integrate the relaxation resulting from cyclic loading at stresses above the yield strength of the material. This integrated model accounts for the main features of both stages by considering strain-rate effects, shot and target inertia and the dependence of the mechanical properties of the target material on temperature. A wide spectra of cyclic mechanical and thermal loads as well as their combinations is considered and the resulting relaxed residual stress field is determined. As an application, the model was used to predict the residual stress relaxation in a high-strength steel target made from AISI 4340 under different peening and thermomechanical cyclic overload.

System and method for monitoring laser shock processing

Abstract: A method and system for monitoring laser shock peening of a work piece. A line spectrum is obtained from radiation emitted by a plasma produced by a laser shock peening process. The shape of the line spectrum about its emission peak is compared to a defined line shape to verify proper operation of the laser shock peening process. The line shape may be a Lorentzian line shape corresponding to a desired line shape. The line shape may a Gaussian line shape corresponding to an undesired line shape. The system can also detect the failure mode that occurs when the opaque layer is broken through by detecting the plasma spectral component produced by the work piece material, along with the plasma produced by the opaque layer.

Effectiveness of Shot Peening in Suppressing Fatigue Cracking at Non-Metallic Inclusions

Abstract: The fatigue lives of modern powder metallurgy disk alloys can be reduced by over an order of magnitude by surface cracking at inherent non-metallic inclusions. The objective of this work was to study the effectiveness of shot peening in suppressing LCF crack initiation and growth at surface nonmetallic inclusions. Inclusions were carefully introduced at elevated levels during powder metallurgy processing of the nickel-base disk superalloy Udimet 720. Multiple strain-controlled fatigue tests were then performed on machined specimens at 427 and 650 °C in peened and unpeened conditions. Analyses were performed to compare the low cycle fatigue lives and failure initiation sites as a function of inclusion content, shot peening, and fatigue conditions. A large majority of the failures in as-machined specimens with introduced inclusions occurred at cracks initiating from inclusions intersecting the specimen surface. The inclusions could reduce fatigue life by up to 100X. Large inclusions had the greatest effect on life in tests at low strain ranges and high strain ratios. Shot peening can be used to improve life in these conditions by reducing the most severe effects of inclusions. Introduction The low cycle fatigue (LCF) lives and predominant failure modes of powder metallurgy (PM) nickelbase superalloy compressor and turbine disks can be influenced by material processing details including powder characteristics, consolidation, extrusion, forging, heat treating, and machining processing

Countering laser shock peening induced airfoil twist using shot peening

Abstract: A gas turbine engine blade is laser shock peened by laser shock peening a thin airfoil of the blade, forming a laser shock induced twist in the airfoil, and shot peening a portion of the airfoil to counter the laser shock induced twist in the airfoil. The shot peening may be performed before or after the laser shock peening. The shot peening may be applied over a laser shock peened surface formed by the laser shock peening. The shot peening may be performed asymmetrically on asymmetrically shot peened pressure and suction side areas of pressure and suction sides, respectively, of the airfoil. A shot peened patch near a blade tip may be formed on one of pressure and suction sides of the airfoil wherein the airfoil extends radially outwardly from a blade platform to the blade tip of the blade.

Measurement of laser peening residual stresses

Abstract: Laser peening is an emerging surface treatment for metals that imparts compressive residual stress near the surface by introducing cold work The present paper describes two residual stress measurement techniques that are well suited for the measurement of residual stresses induced by laser peening Since residual stress is a key outcome of the laser peening process, its measurement is an important process diagnostic The two residual stress measurement techniques described are the slitting method and the contour method In the present research, the slitting method is used to establish relationships between various laser peening parameters (irradiance, pulse duration, number of layers, etc) and the residual stress profile (residual stress versus depth) in flat plate coupons that have been uniformly peened on one surface This helps to identify an effective set of laser peening parameters for the given material Next, laser peening is applied to a specimen(s) with representative geometry and the c

Lebens- und Restlebensdauerverlängerung geschweißter Windenergieanlagentürme und anderer Stahlkonstruktionen durch Schweißnahtnachbehandlung

Abstract: Die Bemessung von Windenergieanlagen und anderen vorwiegend nicht ruhend belasteten Stahlkonstruktionen wird masgeblich durch die Ermudungsfestigkeit kritischer Kerbdetails, insbesondere von Schweisnahten, bestimmt. Durch gezielte Anwendung geeigneter Schweisnahtnachbehandlungsverfahren kann die Ermudungsfestigkeit und damit die Lebensdauer dieser Kerbdetails deutlich erhoht werden. Am Institut fur Bauwerkserhaltung und Tragwerk der Technischen Universitat Carolo-Wilhelmina zu Braunschweig werden derzeit die Verfahren shot peening und ultrasonic peening naher untersucht. Beide Nachbehandlungsmethoden scheinen durch die Kombination von geometrischen und mechanischen Effekten deutliche Erhohungen der Ermudungsfestigkeiten geschweister Verbindungsdetails zu bewirken. Erste Ergebnisse aus Zugschwellversuchen bestatigen dies fur geschweiste Ringflanschsegmente. Das ultrasonic peening wurde daruber hinaus auf die Moglichkeit der Ertuchtigung bestehender Bauteile untersucht. Erste Ergebnisse zeigen, das bei Anwendung des Verfahrens an bis zum Ende der rechnerischen Lebensdauer vorgeschadigten Proben eine Anhebung der Restermudungsfestigkeit auf das Niveau von unmittelbar nach der Fertigung behandelten Bauteilen moglich ist. Life cycle extension of welded wind energy converters and other steel constructions by weld improvement techniques. The design of Wind Energy Converters and other dynamic loaded structures is significantly defined by the fatigue strength of critical notch details, especially welded joints. Weld improvement techniques seem to be promising to increase the fatigue strength and life time of those details. In context of presently conducted research activities by the “Institut fur Bauwerkserhaltung und Tragwerk” at the Technical University Carolo-Wilhelmina Braunschweig shot peening and ultrasonic peening are more detailed analysed. Both methods seem to produce by their combination of geometrical and mechanical effects a clear improvement of the fatigue strength of welded details. First results from fatigue tests confirm this for welded ring-flange-details. The ultrasonic peening was further more tested for the use for the rehabilitation of fatigue stressed existing structures. First results show that the use of the method for specimen which reached their calculated life time can improve the fatigue strength to the level of originally treated specimen.

Weldability of alloys with directionally-solidified grain structure

Abstract: A method of welding alloys having directionally-solidified grain structure. The methods improve the weldability of these alloys by creating a localized region of fine grain structure, wherein the welding occurs in these localized regions. The localized regions are formed by applying strain energy using a variety of different methods, such as by hammer peening, laser peening or sand blasting. Then, a heat treatment step may be used to create recrystallized grains having the fine grain structure. The region of fine grain structure provides better weldability.

Determination of residual stresses using laser-generated surface skimming longitudinal waves

Abstract: A laser-ultrasonic technique is described to non-destructively determine residual stresses in metals such as those produced by shot peening. The method is based on monitoring the small ultrasonic velocity change of the laser-generated surface skimming longitudinal wave (LSSLW) propagating just below the surface. The main advantage of using LSSLW is that the effect of surface roughness induced by shot peening is greatly reduced compared to using surface acoustic waves (SAW). To improve resolution in the measurement of small velocity changes, a cross-correlation technique is used with a reference signal taken on the same but unstressed material in similar conditions. Also, the low-frequency SAW can be used to correct the LSSLW results when affected by minute changes in the path length during the measurements. The validity of the approach is demonstrated by measuring quantitatively the near surface stress in a four-point bending experiment with different levels of surface roughness. Then, scanning results on properly and improperly laser shock peened samples are reported. In particular, the LSSLW velocity variations for the properly peened samples clearly show an increase in the laser-peened area well indicative of a compressive stress.

Drill bit having increased resistance to fatigue cracking and method of producing same

Abstract: The present invention relates to a roller cone drill bit that includes a bit body adapted to be rotated about a longitudinal axis, where the bit body has at least one leg depending therefrom, wherein the leg comprises a treated portion that provides a residual compressive stress, and a roller cone rotatably mounted on a journal. The treated portion treatment may comprise one selected from shot peening, laser-shock peening, and hammer peening. Further, the present invention relates to a method of manufacturing a roller cone drill bit that includes inducing a compressive stress, through plastic deformation, in at least a portion of at least one leg depending from a bit body. The inducing a compressive stress may comprise one selected from shot peening, laser-shock peening, and hammer peening.