Showing papers on "Peening published in 1995"

Effect of shot peening on residual stress and fatigue life of a spring steel

Abstract: This study describes shot peening effects such as shot hardness, shot size and shot projection pressure, on the residual stress distribution and fatigue life in reversed torsion of a 60SC7 spring steel. There appears to be a correlation between the fatigue strength and the area under the residual stress distribution curve. The biggest shot shows the best fatigue life improvement. However, for a shorter time of shot peening, small hard shot showed the best performance. Moreover, the superficial residual stresses and the amount of work hardening (characterised by the width of the X-ray diffraction line) do not remain stable during fatigue cycling. Indeed they decrease and their reduction rate is a function of the cyclic stress level and an inverse function of the depth of the plastically deformed surface layer.

Laser shock peening for gas turbine engine vane repair

Abstract: A wide gap braze repair, particularly for a gas turbine engine vane or a component in the hot section of the engine. The repair is characterized by a braze filled void in a damaged area of the component, a laser shock peened surface over the repaired area of the braze filled void, and a region of deep compressive residual stresses imparted by laser shock peening (LSP) extending from the laser shock peened surface into the repair.

Correlation of Almen arc height with residual stresses in shot peening process

Abstract: The deformations of shot peened Almen strips constrained on Almen blocks with increasing shot peening time, and their subsequent changes after the fixing screws are removed, are experimentally investigated and modelled. Deflection of the constrained Almen strips appears, principally in the transverse direction, as soon as the first passes of peening are applied. The curvatures and the residual stress change with increasing peening time. Removing the screws results in a significant deflection and a great relaxation of residual stress in the longitudinal direction only. A model is proposed to calculate the deformation and the residual stresses in the constrained and free strips. A new problem arises in the evaluation and interpretation of the Almen intensity scale.MST/3113

Laser generation of stress waves in metal

Abstract: Laser-shock surface treatment can create plastic strains and induce compressive residual stresses in metals. This process consists in irradiating a metallic sample with a short but intense laser pulse. As a consequence, a high temperature and pressure plasma is created at the sample surface. An elastic-plastic wave is then propagating in the sample creating plastic strains. This paper presents the effects of laser-induced stress waves on the residual stresses of a standard steel: the surface residual stress induced is approximately 0.6 times the compressive yield strengh of the material for a plastically affected depth of one millimeter.

The surface performance of shot peened and ion implanted NiTi shape memory alloy

Abstract: Equiatomic NiTi shape memory alloy in austenitic and martensitic forms has been modified by shot peening with glass media and by N+ ion implantation. The effect upon microstructure, surface hardness and coefficient of friction was measured, along with the effect of the two treatments upon the shape memory behaviour. Examination using transmission electron microscopy (TEM) showed amorphous regions within the surfaces treated by both peening and ion implantation. In addition, peened and ion implanted samples showed similar increases in surface hardness and reduced surface friction coefficient. Differential scanning calorimetry showed that both surface treatments had no effect upon the bulk shape memory phase transformation behaviour.

Laser shock peening surface enhancement for gas turbine engine high strength rotor alloy repair

Abstract: A metallic article and method for producing such an article, having a metallic substrate, at least one metallic layer sprayed onto a laser shock peened surface area of the substrate, and a region having deep compressive residual stresses imparted by laser shock peening extending into the substrate from the laser shock peened surface. The metallic substrate and or layer may be made from an alloy such as a Cobalt or a Nickel based superalloy. The substrate may be made from Nickel Base forgings or Titanium base forgings. An exemplary embodiment of the present invention is a gas turbine engine rotor component such a disk and, more particularly, a turbine disk suitable for use in a hot section of a gas turbine engine. The invention may be used for new or refurbished parts to restore dimensions of the component and, in particular, radial dimensions.

Distortion control for laser shock peened gas turbine engine compressor blade edges

Abstract: A method for counteracting distortion of the airfoil caused by laser shock peening a gas turbine engine compressor metallic airfoil along its leading and/or trailing edge to form laser shock peened surfaces extending radially along at least a portion of the edges with a region having deep compressive residual stresses imparted by laser shock peening (LSP) extending into the airfoil from the laser shock peened surfaces.

Suitable Region of High-Speed Submerged Water Jets for Cutting and Peening.

Abstract: In order to establish useful techniques of cutting, drilling, peening and flushing by high-speed submerged water jets, we systematically observe the eroded surface on aluminum-alloy specimens in relation to the characteristics of cavitating jets, especially for the impinging jet through lucite specimens, for several types of nozzles. The impulsive pressures induced by the cavitating jets are also measured by means of pressure-sensitive film. It is concluded that the erosion characteristics are quite different in two typical standoff distances, i. e., the 1st and the 2nd peak. Cylindrical, small and deep pits predominantly occur at the 1st peak, while small lots of plastic deformations predominantly occur in the 2nd peak. Therefore, the 1st peak is suitable for cutting, while the 2nd peak is suitable for peening.

Method and apparatus for laser shock peening

Abstract: A method and apparatus for laser shock peening a portion of a surface on a workpiece with a laser beam directed through a curtain of water confined to the surface by a confining device that confines the water curtain on the surface essentially without any air gaps between the surface and a transparent wall of the confining device. The confining device may also incorporate a back pressure mechanism for producing a back pressure in the curtain of water over the surface such as a nozzle shaped portion of the transparent wall through which the continuous water curtain is introduced by a water nozzle. Automated mechanisms such as robotic arms may be used for positioning the confining wall a predetermined distance away from the surface portion and optionally a water supply nozzle to provide the curtain of water over the surface.

Laser induced shock waves as surface treatment for 7075–t7351 aluminium alloy

Abstract: A novel mechanical surface treatment using laser induced shock waves has been applied to the wrought aerospace aluminium alloy 7075–T7 351 to improve its fatigue behaviour. Optimisation of the shock parametersand mechanical effects produced by the treatment have been investigated and fatigue performance is compared with that of conventionally shot peened specimens. It is shown that use of a one-dimensional Lagrangian hydrodynamic shock wave analysis code allows the attenuation of shock waves to be simulated and the depth of the plastically affected zone to be predicted. An analytical model developed to predict residual stress levels gave good agreement with experimental values. The fatigue limit of laser shocked specimens was found to be higher than that following shot peening. This large increase (22%) appeared to result from the high levels of residual stress and the greater extent of the stress field in the laser treated specimens and, most importantly, from the preservation of the surface cond...

Surface modification by laser induced shock waves

Abstract: Laser shock surface treatment is a recently developed process designed to improve component fatigue life in a manner similar to conventional treatments such as shot peening. Irradiation with a short, intense laser pulse can be used to induce plastic strains and compressive residual stresses in metallic substrates. At laser energy densities above the threshold for melting and evaporation a hot plasma can form, expansion of which will induce a shock wave in the substrate, creating plastic strains. The effect of laser induced stress waves on residual stress, micro hardness, and surface quality of a standard steel have been investigated.

Simulation of Residual Stress Distribution on Shot Peening.

Abstract: It is generally recognized that one of the reasons for improvement on fatigue durability by shot peening is surface compressive residual stress. And a shot peening condition decides a residual stress profile on surface layer. But, at this moment the method to confirm this profile is only measurement by X-ray difractometer. In this study, a simulation technique was applied to predict the residual stress distribution caused by shot peening. Firstly, the residual stress on shot peened plate specimens was measured by X-ray difractometer and the effect of shot peening condition on profile was confirmed. The equation to simulate the profile was obtained by the superposition method of simple three stresses, based on the equation that Y.F. Al-Obaid suggested. It was confirmed that the predicted stress profile shows good correspondence with the experimental value every shot peening condition of this experiment.

Laser shock peened gas turbine engine blade tip

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

Eddy current measurement of residual stresses induced by shot peening in titanium Ti-6Al-4V

Abstract: An experimental investigation of the feasibility of using eddy current technology to nondestructively determine the residual stresses induced by shot peening in Ti-6Al-4V plate was undertaken. Because of the extremely small magnitude of the shot peening-induced conductivity changes, strict noise control was vital and was achieved by mechanical and thermal isolation of the apparatus. This was accomplished by modifying the instrument to improve temperature isolation of several key internal components and also by physically and electronically isolating the experimental apparatus. Results indicate that residual stress can be clearly determined for material shot peened to a depth of 0.3 mm (0.012 in.) or more with an experimental variation of less than 3 ppm.

Induced stress relationships for wing skin forming by shot peening

Abstract: Shot peening has been used to provide fatigue resistance and form to airplane wing skins for many years. In the past, the peening intensities used to form these wing skins were obtained through the use of geometric relationships along with trial and error testing. A computer model was developed to model shot peening, which could eliminate the trial and error phases of the existing process. The computer model is used to determine the peening intensities across the wing skin and the initial size of the skin (flat pattern). To support such a computer model, we have developed in this paper relationships among the thickness of the material, the stress induced into the aluminum, and the intensity of the shot peening (shot wheel revolutions per minute, rpm). Asimple induced stress theory is proposed. Results for a cylindrical wing skin utilizing the new relationships are included.

Effects of precoating surface treatments on fatigue of Ti-6A1-4V.

Abstract: Grit blasting is a common procedure of roughening surfaces to promote physical attachment of porous coatings, but it has been shown to reduce fatigue strength. Shot peening is known to increase fatigue strength by inducing compressive surface stresses; however, it is not known how subsequent grit blasting affects these benefits. This study examines the endurance limits, Se, of ELI grade Ti-6A1-4V specimens under rotating cyclic bending, including polished (control); belted and beaded; belted, beaded, and grit blasted; and belted, beaded, shot peened, and grit blasted. Belting and beading resulted in a slight increase in Se, grit blasting caused a 15% reduction in Se from polished. Fifty percent of this reduction was recovered when shot peening preceded grit blasting, suggesting that residual compressive surface stresses, induced by peening, were not eliminated by the blast process. Roughness averages and RMS values did not correlate with Se trends. SEM results showed classical fatigue fractures, consistent with surface crack initiation.

Reducing edge effects of laser shock peening

Abstract: Laser shock peening/processing (LSP) has been used to strengthen fatigue-critical areas in metal parts. Notwithstanding the advantages, one negative effect of LSP occurs at the boundary of the LSP-treated area. In LSP, the laser pulse induces a compressive stress in the material in the area on the surface (and to some extent in the subsurface) of the laser spot. Because the net residual stress in the material must be zero, compensating tensile residual stresses can be created in a boundary region surrounding the laser spot. This region of tensile stress at the surface of the part may be the site of further failure in the specimen if it is not reduced to an acceptable level. The tensile stresses may be reduced by further laser shocking the specinem surface in the boundary region with lower-energy pulses. Since lower energy fluence generally gives lower compensating tensile stress, this secondary LSP essentially reduces or eleminates the tensile compensating region caused by the primary laser shocking and replaces it with a lower compensating tensile region associated with the secondary shocked region further out from the fatigue-critical area.

Prediction of Improvement in Fatigue Strength by Shot Peening and Selection of Most Effective Peening Condition.

Abstract: Shot peening is one of the most effective treatments for improving the fatigue strength of transmission gears. As is well known, the improvement of fatigue strength is caused by the compressive residual stress. Fatigue crack propagation in the residual stress field was analyzed by the fracture mechanics approach, and the method for prediction of fatigue strength in terms of S-N diagrams is shown. Analytical prediction in accordance with the experimental results showed extreme delay of the crack propagation in the residual stress field, and also showed several possibilities for improving the fatigue strength by controlling the residual stress distributions.

Processing, thermal, and mechanical issues in shape deposition manufacturing

Abstract: An overview of Shape Deposition Manufacturing (SDM) is presented, detailing manufacturing, thermal and mechanical issues of concern in making it a commercially viable method for creating arbitrarily shaped three-dimensional metal parts. SDM is a layered manufacturing process which combines the benefits of solid freeform fabrication and other processing operations, such as multi-axis CNC machining. This manufacturing process mates possible the fabrication of multi-material layers, structures of arbitrary geometric complexity, artifacts with controlled microstructures, and the embedding of electronic components and sensors in conformal shape structures. To minimize cost, SDM is implemented using primarily commercially available hardware and CAD modeling and planning software. Important issues toward the production of high quality objects are the creation of inter-layer metallurgical bonding through substrate remelting, the control of cooling rates of both the substrate and the deposition material, and the minimization of residual thermal stress effects. Brief descriptions of thermal and mechanical modeling aspects of the process are also given. Because SDM involves molten metal deposition, an understanding of thermal aspects of the process is crucial. Current thermal modeling of the process is centered on the issue of localized remelting of previously deposited material by newly deposited molten droplets. Residual stress build-up is inherent to any manufacturing process based on successive deposition of molten material. Current mechanics modeling is centered on the issue of residual stress build-up and its potential effects, including part warping and debonding between deposited layers. Shot peening is an operation currently used to control residual stress effects and preliminary work studying its effects is also presented.* 1. Shape Deposition Manufacturing Process Description Shape Deposition Manufacturing (SDM) (refer to Fig. 1) is a layered manufacturing process which systematically combines the benefits of Solid Freeform Fabrication (SFF) (Le., quickly planned, independent of geometry, multi-material deposition, and component embedding), with other intermediate processing operations such as CNC machining (i.e., for accuracy and precision with good surface quality), thermal deposition (i.e., to produce fully dense structures), and shot peening (Le., for stress control) (Merz et al, 1994). Like conventional SFF processes, SDM builds shapes using a layered material deposition approach. After each layer (or layer segment) is deposited, however, the part may be transferred to other processing stations where additional operations are performed on that layer. The basic strategy is to first slice the CAD model of the shape to be fabricated into layers while maintaining the corresponding outer surface geometry information. Layer thickness varies depending on the part geometry. Each layer consists of primary material(s) (i.e., the material(s) forming the part being created) and complementary shaped * This wok has been supported by the Engineering Design Research Center, a NSF Engineering Research Center. sacrificial support structure material which is removed when the entire part is completed. Each material in each layer is then deposited as a near-net shape using thermal deposition as described below. The sequence for depositing the primary and support materials is dependent upon the local geometry and the material combinations and is also described below in more detail. After deposition, the layer is then precisely shaped to net shape with a 5-axis CNC milling machine or EDM, for example, before proceeding with the next intermediate processing operation or layer. The 5-axis machining eliminates the stair-step surface appearance common to conventional SFF technologies. Microcast 5-Axis CNC Mill ShotPeen Integrate Sensors Deposit • Shape • Control Stress • Embed Figure 1. Shape Deposition Manufacturing Internal residual stresses build up as each new layer is deposited due to differential contraction and thermal gradients between the freshly deposited molten material and the previously solidified layer. Internal stresses can lead to warping and to delamination. To control stress-induced warping, each layer is also shot-peened. Small round metal spheres (called 'shot') are projected at a high velocity against the surface in a blasting cabinet The complex state of stress in deposited layers makes difficult the evaluation of the effect of peening on the state of residual stress. It is clear, however, that peening imparts a compressive load which counters warping due to the net tensile load in die newly deposited top layer. Building shapes with deposition also permits pre-formed, discrete components or assemblies to be fully embedded within the growing structure. For example, sensors can be placed throughout the structure to provide feedback for subsequent deposition process control, and when the part is operational these sensors can provide feedback on part integrity and operational parameter status. 1.1 Adaptive Shape Decomposition In SDM there are several feasible sequences for depositing and shaping each layer. The basic sequence which we use for building a single-material part is described below and shown in Fig. 2. Variations of this sequence, which will be discussed later, may be required to improve overall process performance and part quality. Both Undercuts No under-cuts

Laser shock peened dies

Abstract: A die having a metallic block with a depression, the depression having at least one cross-sectional transition zone, at least one laser shock peened surface encompassing at least a portion of the zone, a region having deep compressive residual stresses imparted by laser shock peening (LSP) extending into the airfoil from the laser shock peened surface. The die has been found to be useful for cold rolling blanks such when the metallic block is a cold rolling die block. The die may be adapted for forming a gas turbine engine component, such as a compressor blade, having an airfoil such that the depression corresponds to the airfoil.

Increased Fatigue Strength of Powder Forged Connecting Rods by Optimised Shot Peening

Abstract: Shot peening is a surface treatment commonly used to improve the fatigue life of aircraft, automotive, and other highly stressed structural components. This improvement is attributed to the formation of compressive residual stress in the surface layer of the material by the impingement of spherical media (shot). The compressive residual stress usually decreases the tensile stress created in the component by ‘in service’ external forces and, therefore, increases the fatigue strength of the part. To quantify the improvement resulting from shot peening, the fatigue behaviour of powder forged connecting rods and laboratory test bars from the base material (2%Cu steel), in both the stress free (unpeened) and surface treated (shot peened) condition, were compared. Fatigue data were correlated with the residual stress generated at the surface. The stress magnitude and depth were determined using X-ray diffraction analysis. Optimum processing parameters for shot peening were also determined. Results show ...

Water jet peening device and water jet peening method

Abstract: PROBLEM TO BE SOLVED: To provide a water jet peening device which can further shorten a time required for water jet peening.SOLUTION: A water jet peening device (WJP device) 1 has a seating member 2, and a slewing part 3 and injection nozzles 19, 20 which are attached to the seating member. A lifting device 12 is attached to the slewing part 3, and the injection nozzles 19, 20 are attached to a nozzle arm 16. The WJP device 1 is hung by a crane and is lowered in a reactor pressure vessel (RPV) 31, and the seating member 2 is seated on an in-pile instrumentation cylinder 32 which is welded to a bottom of the RPV 31. The nozzle arm 16 is lowered by the lifting device 12, and thereby the injection nozzles 19, 20 are lowered. The injection nozzle 19 is inserted into the in-pile instrumentation cylinder 32, and the injection nozzle 20 is disposed outside the in-pile instrumentation cylinder 32. High pressure water are injected from the injection nozzles 19, 20, and the WJP is installed on each of the inside surface and the outside surface of the in-pile instrumentation cylinder 32.

Influence of surface condition on the fatigue of an aluminum-lithium alloy (2090-T3)

Abstract: This report examines the axial fatigue life data of the shot peened and unpeened 2090-T3 aluminum-lithium alloy. The effect of shot peening on life was detrimental and insignificant at higher and lower stresses respectively. This life variation is discussed in terms of crack initiation and, subsequently, such shot peened induced surface characteristics as the surface roughness and the surface compressive residual stress. The former eases cracking at all stresses; the latter, on the other hand, offers an opposing effect which was noted to be most significant at low stresses and minimal at high stresses. The life was conceived to depend on the way these factors respond to applied stress.

Effect of Machining and Shot Peening on the Residual Stresses of Superalloy Turbine Discs

Abstract: It is well known that the field of residual stresses in the surface layer of a component greatly influences its fatigue behavior. The distribution of stresses is created by processes like welding, machining, thermal treatments.The object of the present study was to correlate the effect of operations like turning, broaching and shot peening with the residual stresses of a highly–stressed flight safety component like a turbine disc made in Inconel 718 superalloy.The residual stress distributions were measured with newly installed x–ray diffraction equipment, in which real engine components can be tested.Different machining parameters and tools were used, and other factors like deformations during processing and thermal conditions of the disc in service were taken into account.The final aim of the activity was to perform a manufacturing cycle which can minimize production costs and, at the same time, guarantee the highest possible quality level required in such a critical component.Copyright © 1995 by ASME

Random Approach to Peening Coverage in Ultrasonic Shot-Peening

Abstract: The so-called ultrasonic shot-peening is a new process using calibrated peening hard balls motioned by walls vibrating at 20000 Hz. As in conventional shot-peening, a fully peened surface coverage is required tor the process to be efficient. However, it is intricate to determine the coverage ratio experimentally. A statistical approach, issued from the Random Sets Theory, was used to establish relationships between coverage, impact superficial density and impact crater area. The random modelisation was tested with different materials treated by ultrasonic shot-peening. Individual crater diameter measurements and local repartition analysis were made using quantitative image analysis to test the model. Calculations provide the mean number of impacts everywhere on the surface for any coverage ratio. This statistical approach can also be applied to any impact treatment involving an impact flow.

Shot peening method

Abstract: A method and apparatus for controlling a shot peening operation includes the measurement of pressures at two different points in a compound gas shot peening system. By comparing these pressure levels with the pressures set forth in a table for a given mass rate of flow of shot, the peening operator can control the velocity of the shot particles applied to the workpiece, thereby controlling peening intensity.

Shot peened golf club head

Abstract: Metallic golf club heads are improved by a treatment which involves shot peening the exposed ball striking surface of the metal head without creating any noticeable change in appearance of the head. As a result of the shot peening treatment there is improved feel with minimal vibrational feel in the hands of the user when the user strikes a golf ball thus providing better control and increased distance of the shots.