Showing papers on "Peening published in 1996"

On the fly laser shock peening

Abstract: An on the fly method of laser shock peening a gas turbine engine part by continuously moving a metallic gas turbine engine part while continuously firing a stationary laser beam, which repeatably pulses between relatively constant periods, on a portion of the part with sufficient power to vaporize material on the surface of the portion of the part with the pulses around laser beam spots formed by the laser beam on the surface and form a region having deep compressive residual stresses extending into the part from the laser shock peened surface. Flowing a curtain of water over the surface upon which the laser beam is firing while moving the part until the laser shock peened surface is completely covered by laser beam spots at least once. The surface may covered by a paint which is then the material used to produce the plasma or the surface may be unpainted and the metal of the part is used to produce the plasma. The part such a fan or compressor blade may be moved linearly to produce at least one row of overlapping circular laser beam spots having generally equally spaced apart linearly aligned center points.

Laser shock peened gas turbine engine fan blade edges

Abstract: Gas turbine engine fan blade with a metallic airfoil having a leading edge, a trailing edge, and a radially outer tip, and at least one laser shock peened surface located along the leading edge with a region having deep compressive residual stresses imparted by laser shock peening (LSP) extending into the airfoil from the said laser shock peened surface.

A technique to prevent or divert cracks

Abstract: Gas turbine engine static component with a metallic panel section, either linear or curved, that is susceptible to cracks initiated by features on the component has an elongated laser shock peened region having deep compressive residual stresses imparted by laser shock peening (LSP) disposed between the feature and a portion of the panel section, which is to be protected from failure, such that the laser shock peened region diverts cracks that propagate from the feature away from the portion of the panel section. The laser shock peened region preferably extends through the component and is may be formed by simultaneously laser shock peening first and second laser shock peened surface areas to form the laser shock peened region.

Thin Palladium Film Formation on Shot Peening Modified Porous Stainless Steel Substrates

Abstract: The rapid development of catalytic membrane reactors requires materials with a higher permeability and a better mechanical stability than the current thick membranes. Pd-based composite membranes supported on porous stainless steel offer such an alternative. However, commercially available porous stainless steel materials have to be further worked to reduce the surface pore sizes and ensure the formation of thin Pd films in an impervious form. In this work, a shot peening treatment was performed on the surface of a porous stainless steel to modify its surface pore size. Substrates with effectively reduced surface pore sizes were obtained under mild peening conditions. The permeation behavior of the substrates was examined using argon as the permeation gas. Impervious thin palladium films were deposited on the modified porous substrate surface by electroless plating. Hydrogen permeability through the resulting membranes was found to be comparable to that of pure palladium sheets, while the permeation flux was significantly enhanced due to the use of the thin Pd membrane.

Current applications of x-ray diffraction residual stress measurement

Abstract: A brief theoretical development of x-ray diffraction residual stress measurement is presented emphasizing practical engineering applications of the plane-stress model, which requires no external standard Determination of the full stress tensor is briefly described, and alternate mechanical, magnetic, and ultrasonic methods of residual stress measurement are compared Sources of error arising in practical application are described Subsurface measurement is shown to be necessary to accurately determine the stress distributions produced by surface finishing such as machining, grinding, and shot peening, including corrections for penetration of the x-ray beam and layer removal Current applications of line broadening for the prediction of material property gradients such as yield strength in machined and shot peened surfaces, and hardness in steels are presented The development of models for the prediction of thermal, cyclic, and overload residual stress relaxation are described X-RAY DIFFRACTION (XRD) STRESS MEASUREMENT can be a powerful tool for failure analysis or process development studies Quantifying the residual stresses present in a component, which may either accelerate or arrest fatigue or stress corrosion cracking, is frequently crucial to understanding the cause of failure Successful machining, grinding, shot peening, or heat treatment may hinge upon achieving not only the appropriate surface finish, dimensions, case depth or hardness, but also a residual stress distribution producing the longest component life The engineer engaged in such studies can benefit by an understanding of the limitations and applications of XRD stress measurement This paper presents a brief development of the theory and sources of error, and describes recent applications of material property prediction and residual stress relaxation Application of XRD stress measurement to practical engineering problems began in the early 1950's The advent of x-ray diffractometers and the development of the plane-stress residual stress model allowed successful application to hardened steels (1,2) The development of commercial diffractometers and the work of the Fatigue Design and Evaluation Committee of the SAE (3) resulted in widespread application in the automotive and bearing industries in the 1960's By the late 1970's XRD residual stress measurement was routinely applied in aerospace and nuclear applications involving fatigue and stress corrosion cracking of nickel and titanium alloys, as well as aluminum and steels Today, measurements are routinely performed in ceramic, intermetallic, composite, and virtually any fine grained crystalline material A variety of position sensitive detector instruments allow measurement in the field and on massive structures The theoretical basis has been expanded to allow determination of the full stress tensor, with certain limitations

X-Ray Study on Deformation and Fracture of Solid. Effects of Water Jet Peening on Corrosion Resistance and Fatigue Strength of Type 304 Stainless Steel.

Abstract: The effect of water jet peening (WJP) on the improvement of stress corrosion cracking (SCC) and fatigue strength was verified by performing SCC and fatigue tests. The SCC specimens employed were sensitized type 304 stainless steel simulating the heat affected zone in welded metal. The creviced bent beam (CBB) type SCC test was performed in high temperature water using the smooth and pre-cracked specimens. WJP remarkably improved the susceptibility of SCC for the smooth specimen, and cracks were not initiated when the applied strain was less than 0.3%. WJP was also confirmed to prevent SCC for the pre-cracked specimen. In the fatigue tests both smooth and pre-cracked plate specimens were subjected to cyclic bending loads in air at room temperature. The fatigue strength of smooth and pre-cracked specimens at a fatigue life of 107 cycles was increased by 1.1 and 2.4 times, respectively, in comparison with that of non-WJP specimens. This means that WJP was much more effective for the pre-cracked specimens. CBB and fatigue tests show that WJP is an effective technique for preventing SCC in the structural components of power plants.

Preloaded laser shock peening

Abstract: A method of laser shock peening a gas turbine engine article by loading the article such that a portion of the article to be laser shock peened is placed in a loaded condition while the portion is laser shock peened using a laser to fire a laser beam with sufficient power to vaporize material on a laser shock peening surface of the portion of the article to form a region in the portion having deep compressive residual stresses imparted by the laser shock peening process extending into the article from the laser shock peened surface. The loaded condition may be either in compression or preferably tension. The loaded article is continuously moved while continuously firing a stationary laser beam, which repeatably pulses between relatively constant periods, on a portion of the article with sufficient power to vaporize material on the surface of the portion of the article with the pulses around laser beam spots formed by the laser beam on the surface and form a region having deep compressive residual stresses extending into the article from the laser shock peened surface. Flowing a curtain of water over the surface upon which the laser beam is firing while moving the article until the laser shock peened surface is completely covered by laser beam spots at least once. The surface may coated with paint or tape which is the material used to produce the plasma or the surface may be unpainted and the metal of the article is used to produce the plasma.

Short crack growth behaviour under variable amplitude loading of shot peened surfaces

Abstract: The effect of variable amplitude loading on the initiation and propagation of fatigue cracks from shot peened and unpeened surfaces was investigated. The results confirm the well-known effect of shot peening, i.e. the increase of fatigue life in comparative tests under constant amplitude loading. Shot peening increases the time to crack initiation and also decreases crack propagation rate, particularly in the earlier stages of growth. Variable amplitude tests were of various kinds : (i) half-life at one stress level, followed by testing at the second stress level until failure, (ii) sequence loading at two stress levels, and (iii) a different number of overload cycles (1, 10, 100) following a given number of base amplitude cycles. The results of the two amplitude tests showed different behaviour depending on whether the first half-life cycles were of higher or lower stress levels. These results are explained in terms of crack density and crack coalescence. The extent of damage accumulation during block loading depends on the stress levels employed. The benefits of shot peening are compromised by high stress levels. Results from the overload tests showed that the interpretation of results is not straight forward. A combination of the theories of crack retardation and microstructural-fracture mechanics seems a necessary prerequisite in an explanation of the resultant behaviour.

Effect of shot peening on the fatigue and fracture behaviour of two titanium alloys

Abstract: The fatigue and fracture behaviour of two titanium alloys, the near-alpha IMI-685 and alpha-beta IMI-318, were studied in the machined and polished (MP) as well as the machined, polished and shot (glass-bead) peened (MPS) conditions. Glass-bead peening reduced the room-temperature as well as the high-temperature (450°C) fatigue life of alloy IMI-685 at high stress amplitudes, σa, approaching the proof stress, σps, of the material (LCF region). When the applied stress amplitude (0–770 MPa, HCF region) was comparable to the peen-induced peak longitudinal residual stress, σLP, i.e. (σLP/σa)=0.92, an improvement in the room-temperature fatigue life of IMI-685 was observed. When the (σLP/σa) ratio was less than this value, decreases in the fatigue life were seen. The room-temperature fatigue behaviour of IMI-318 at high stress amplitudes was similar to that of IMI-685. The decrease in the fatigue life of this alloy, at a stress amplitude (770 MPa) where improvement was observed for IMI-685, could be attributed to the higher relaxation of peen-induced residual stresses in IMI-318 compared with IMI-685. Glass-bead peening improved the hightemperature (450°C) fatigue life of IMI-685 at a low stress amplitude (465 MPa; (σa/σPS)=0.87). The crack-initiation sites in the MP and the MPS conditions were at the surface for both the alloys. However, fracture in the surface layers of the alloys appeared more brittle in the peened (MPS) rather than in the unpeened (MP) condition.

Numerical modeling of a wing skin peen forming process

Abstract: For many years shot peering has been used to provide fatigue resistance and form to airplane wing skins at the Boeing Commercial Airplane Company. In this process, the peening intensities used to form a new wing skin have been obtained through the use of approximate geometric relationships, along with a considerable amount of trial and error testing. This paper describes a numerical model that has been applied to replicate the shot peening process used at Boeing. The model is used to predict peening intensities and the initial size of the skin (flat pattern) given an arbitrary aerodynamic contour requirement. Discussion focuses on the finite element method and special optimization techniques used in the approach.

Method for ceramic peening of orthopaedic titanium alloy implants

Abstract: A method of preparing fretting wear resistant titaniumbase alloy orthopaedic implants includes the steps of shot peening the surface of the implant with spherical ceramic beads of a selected size and density, and with selected intensity such that the fretting wear resistance of the implant is increased and wherein the implant surface is uniformly peened to create a compressively-stressed region within the surface of approximately 100-300 microns depth.

Laser shock peened gas turbine engine intermetallic parts

Abstract: An intermetallic article such as a gas turbine engine component and method of manufacture thereof includes a region having compressive residual stresses imparted by laser shock peening (LSP) extending into the article from a laser shock peened surface. One embodiment includes a turbine or compressor blade with an intermetallic airfoil having a leading edge and at least one laser shock peened surface extending radially along at least a portion of the leading edge with a region having compressive residual stresses imparted by laser shock peening (LSP) extending into the intermetallic airfoil from the laser shock peened surface.

Crack arresting structure

Abstract: In a crack arresting structure the crack arresting feature is located in the transition from one thickness to another, or a region of increased thickness can be intentionally introduced for the purpose of inhibiting crack growth propagation. The crack arresting feature comprises two different structural configurations. These structures include a thickness transition region where a portion of the structure is plastically deformed at or immediately adjacent to the thickness transition region. Alternatively, an overhang is provided where an appendage to the thicker part extends back over the thinner part at a thickness transition region. A high strength fiber or wire, preferably of non-constant cross-section may be inserted into a gap underneath the overhang and held in place by crimping due to plastic deformation. Fiber or wire reinforced interface may be adhesively bonded into place prior to or in lieu of deformation or crimping. The plastic deformation is preferably accomplished by strip or localized coining of the part by feeding the part through rollers or by other means such as localized shot peening, or laser shock peening or other suitable methods which apply high local stresses and result in a local thickness reduction at or adjacent the thickness transition point (or on either or both sides thereof). This results in a local compressive residual stress region, which has been shown to impede or even turn crack growth.

Trowel having imposed blade stresses and method of manufacture

Abstract: A trowel and related method of manufacture in which residual stresses are intentionally imposed upon the bottom working surface and/or the top mounting surface of a trowel blade Stresses can be imposed, for example, by glass bead peening, shot peening, rolling, and/or brushing the metal trowel blade Stresses are built up to a working stess level that remains substantially constant with further use of the trowel against abrasive, spreadable surfaces Imposed stresses on the top and bottom surfaces can also be used to vary the resulting curvature of the blade

Laser shock peened bearings

Abstract: A bearing element having a metallic body with a bearing contact curved surface portion, at least one laser shock peened surface encompassing at least a portion of the contact surface portion, and a region having deep compressive residual stresses imparted by laser shock peening (LSP) extending into the body from the laser shock peened surface. The present invention may be used for rolling elements such as ball bearing elements or elongated roller elements and for static elements such as races which may be singular or split and may have circumferentially spaced oil feed passages radially disposed therethrough.

Method of reducing relative ultimate moment at predetermined braking points

Abstract: The component is stressed, at least in torsion. A variety af methods may be used to carry out the cold working, including impact deformation, cold rolling and blast peening, by e.g. ball, shot or grit peening. Before the cold deformation, the component is hardened, at least in the region of the intended breaking point. The breaking point is located in regions of higher stiffness. The use of a procedure as described, in a tripod link shaft implementation.

Rigid-Plastic Finite Element Simulation of Peening Process with Plastically Deforming Shot

Abstract: To simulate not only plastic deformation of a workpiece but also that of a shot in a peening process, the effect of the interaction between the shot and workpiece in the collision is included in the dynamic rigid-plastic finite element method. In the formulation, the equilibrium equations of nodal forces are solved simultaneously with velocity boundary conditions at the interface between the workpiece and shot for sliding and non-sliding contacts. Axi-symmetric plastic deformation in peening of a circular workpiece with a single shot is computed. The calculated shapes of the workpieces and the shots are in good agreement with the experimental ones for plasticine workpieces and shots. It is shown that almost no plastic deformation of the shot occurs under actual shot-peening conditions for steel workpieces when the flow stress ratio of the shot to the workpiece is larger than two.

Method for repairing metallic mold

Abstract: PURPOSE: To execute the repair of a metallic mold which can improve the reliability to the repaired part, by repeating build-up weldings and peenings to a cut-off part in plural times after cutting off the crack in the damaged part in the metallic mold and removing foreign matter. CONSTITUTION: For example, to a design part A in the metallic mold 1 developing the damage of crack (h), etc., the crack (h) and the surrounding part are cut off and the foreign matter (d) stuck to the surrounding part is removed to apply the pretreatment. The build-up welding is applied to the cut-off part (a) formed with this work e.g. with a copper welding rod 4 having the same quality as the metallic mold 1 by using a plasma welder 3. The peening is executed to the build-up welding part (m), by continuously hitting with an air- hammer 5. By this method, the hardness of the build-up part (m) is uniformized and the hardness degree is improved and fatigue strength is improved. This build-up welding and the peening are repeated at least one or more times. By this method, the build-up welding part (m) is formed to the desired thickness and as necessary, the surface is finished with a finishing tool 6.

X-Ray Study on Deformation and Fracture of Solid. Improvement of Residual Stress on Material Surface by Water Jet Peening.

Abstract: Cavitation bubbles are generated when highly pressurized water is jetted in water. Surface residual stress is improved remarkably due to the peening effect of extremely high pressure caused by the collapse of cavitation bubbles. This technique is called water jet peening (WJP). WJP is expected to be an effective preventive maintenance technique for the stress corrosion cracking in various components of power plants.Various specimens are water jet peened to evaluate the fundamental characteristics of WJP and to select the most appropriate conditions for the residual stress improvement.The test results show that WJP markedly changes the tensile residual stress caused by welding and grinding into the high compressive residual stress and prevents the stress corrosion cracking.

Fatigue Crack Repair of Steel Beams with Tapered Cover Plate Details

Abstract: The fatigue strength of beams with tapered cover plates was investigated both experimentally and analytically. The test specimens were precracked and then repaired with one of the following three methods: a friction type bolted splice plate connection, air-hammer peening along the weld toe, and a hybrid of the previous two called the partial bolted splice connection. Test results demonstrated that the bolted splice connection was the most effective repair method. Cracked cover plate ends repaired with a bolted splice connection, partial bolted splice connection, and air-hammer peening demonstrated an increase in fatigue life equal to categories B, C, and D of the American Association of State Highway and Transportation Officials (AASHTO) specifications, respectively. Air-hammer peening was found to be particularly effective if applied to noncracked cover plate ends, with an increase in fatigue life equal to category B′. An analytical model was developed to predict the propagation life of cracked cover pla...

Influence of shot-peening on short crack behaviour in a medium carbon steel

Abstract: — The results of research into short fatigue crack behaviour in shot peened, medium carbon steel specimens under reversed torsion are presented. Characteristic features of short crack growth were established on the basis of optical and electron-optical observations of the replicas and micro-sections of the samples. Surface crack growth analysis, supported by plots of crack development, crack growth rate and crack length distributions against cycle ratio show that significantly slower crack growth and lower crack densities occur in shot peened specimens than in non-treated samples. That results can be linked to the effect of grain distortion, the packing of laminar grains, a high dislocation density in the plastically deformed surface layer and the introduction of compressive residual stresses. A fractographic analysis of the fracture surfaces has assisted an understanding of the mechanisms of fracture in shot peened specimens.

Anti-gravity blast cleaning

Abstract: A shot peening method and apparatus enables low intensity peening at a velocity which is equal to or less than the minimum velocity required to assure conveyance of the media through the transport hose in pneumatic systems or the minimum velocity necessary to project a coherent shot stream in the case of wheel systems.

Part for gas turbine engine

Abstract: PROBLEM TO BE SOLVED: To realize durability against fatigue damage by providing a laser shock peened surface extending along the front edge and/or rear edge of a blade, and a region having deep compressive residual stresses imparted by laser shock peening and extending into the blade from the laser shock peened surface SOLUTION: A compressor blade 8 has a front edge part 50 extending along the front edge LE of an airfoil 34 from a platform 36 of the blade 8 to the blade tip 38 The front edge part 50 has a first width, and the front edge part 50 surrounds notches 52 and clefts that may be formed along the front edge LE of the airfoil 34 In order to oppose the fatigue damage of the blade 8 part, at least one of the pressure side 46 and suction side 48 is provided with a laser shock peened surface 54 and a prestressed region 56 having deep compressive residual stresses imparted by laser shock peening and extending into the airfoil 34 from the laser shock peened surface 54