Showing papers on "Peening published in 2001"

Laser shock peening on fatigue behavior of 2024-T3 Al alloy with fastener holes and stopholes

Abstract: The effect of laser shock peening on the fatigue behavior of 2024-T3 aluminum alloy with a fastener hole, multiple crack stopholes and single-edge notch was investigated. Laser shock peening (LSP) was performed under a ‘confined ablation mode’ using a Nd:glass laser at a laser power density of 5 GW cm−2. The fatigue crack initiation life and fatigue crack growth rates of the Al alloy, with different preexisting notch configurations, were characterized and compared with those of the unpeened material. The results clearly show that LSP is an effective surface treatment technique for improving the fatigue performance of Al alloys having various preexisting notch configurations.

Peening action and residual stresses in high-velocity oxygen fuel thermal spraying of 316L stainless steel

Abstract: 316L stainless steel powder was sprayed by a high-pressure high-velocity oxygen fuel (HVOF) process. Effects of powder size and the pressure in the combustion chamber on the velocity and temperature of sprayed particles were studied by using an optical instrument, first, at the substrate position. A strong negative correlation between the particle temperature and the diameter was found, whereas the correlation between the velocity and the diameter was not significant. The pressure in the combustion chamber affected the velocity of sprayed particles significantly, whereas the particle temperature remained largely unchanged. In-situ curvature measurement was employed in order to study the process of stress generation during HVOF spraying. From the measured curvature changes, the intensity of peening action and the resultant compressive stress by HVOF sprayed particles were found to increase with the kinetic energy of the sprayed particles. The results were further used to estimate the stress distribution within the coatings. X-ray stress measurement revealed that the residual stress on the surface of the HVOF coatings is low and often in tension, but the stress inside the coatings is in a high level of compression.

The Effect of Low Plasticity Burnishing (LPB) on the HCF Performance and FOD Resistance of Ti-6AI-4V

Abstract: Low Plasticity Burnishing (LPB) has been developed as a rapid, inexpensive surface enhancement method adaptable to existing CNC machine tools. LPB produces a deep layer of compression with minimal cold work of the surface, comparable to laser shock peening (LSP), but can be incorporated into manufacturing operations at lower cost. Minimizing cold work during surface enhancement has been shown to improve both thermal stability at engine temperatures and resistance to overload relaxation accompanying foreign object damage (FOD). Recent research leading to the development of a practical LPB demonstration facility and tooling is described. The mechanism for compressive residual stress development during LPB has been studied with elastic-plastic finite element modeling. DOE methods have been utilized to optimize compressive magnitude and depth with minimum cold work. Using optimum burnishing parameters, compression on the order of the material yield strength can be achieved to depths exceeding 0.040 in. (1mm) with low cold work. Residual stress and cold work distributions developed by LPB in Ti-6Al-4V are compared to traditional shot peening and LSP. The compressive layer produced by LPB is shown to be resistant to both thermal and overload relaxation. After exposure to engine temperatures, the high cycle fatigue (HCF) strength at 2x10

Device for ultrasonic peening of metals

Abstract: A device for ultrasonic peening of metals is intended for strengthening and relaxation treatment of metal surfaces with an ultrasonic oscillation and includes an ultrasonic generator (1) having the optimized power of from 0.2 to 0.5 kW, a piezoelectric transducer with an ultrasonic velocity transformer (6) and a set of readily replaceable heads with striking tools (pins). Various sizes and arrangements of the tools allow for ultrasonic peening of parts of complicated configuration fast and efficiently. In the device, drop-wise cooling and lubrication of striking tools, as well as of treatment area are provided.

Surface Modifications in Aerospace Applications

Abstract: The long service life, often in harsh environmental conditions, and the stringent requirements of lightweight design make surface modification an essential part of materials technology for aerospace applications. Six contemporary developments are described, which are representative of advances in corrosion protection, fatigue life extension, metal matrix composite (MMC) based new design, and enhanced temperature capabilities by ceramic protective coatings. Coatings and corrosion inhibitors for aluminium skinned aircraft provide survivability, corrosion protection, and cosmetic appearance. Environmental concern on the presently used chromate have led to developments of self-priming topcoats, flexible primers, e.g. based on self-assembling silane molecules, temporary and multifunctional coatings. Fatigue life of titanium parts is shown to be enhanced by laser shock peening introducing compressive surface stresses. Preventing the onset of fatigue cracking from surfaces of titanium alloys and titanium...

The influence of coatings on subsurface mechanical properties of laser peened 2011-T3 aluminum

Abstract: High power Q-switched laser systems are currently being developed for use in a process known as laser shock processing or “laser peening” which results in significantly improved fatigue properties in aluminum components. An ablative, sacrificial coating such as paint or metal foil is used to protect the aluminum component from surface melting by the laser pulse, which adversely affects fatigue life. This paper, using nano-indentation, analyzes the effect of the paint and foil coatings on the shock wave propagation into the aluminum specimen and the resulting change in mechanical properties versus depth. Near the surface, hardness was found to be increased by the laser peening, however this process decreased the measured elastic modulus. The laser pulse energy density and properties of the foil including its adhesion to the aluminum alloy were found to influence the change in surface mechanical properties.

Method for extending the life of attachments that attach blades to a rotor

Abstract: A method for extending the life of the attachments that attach blades to rotors, particularly for aerojet engines. Such a method is notable in that it employs intensive ultrasonic peening of the grooves and of the roots of the blades, this peening being performed with an Almen intensity at least equal to F8A, so as to increase the compressive prestress in the contact surfaces without increasing the roughness of these surfaces.

Method and apparatus for peening tops of cooled blades

Abstract: A method for peening the tops of cooled blades which include cooling air passage orifices. Peening is performed by means of the mobilization of a plurality of beads in a sealed chamber containing at least one blade tip. Said plurality of beads is mobilized by the active surface of a sonotrode which delimits part of said chamber. Said beads have a diameter greater than that of said cooling air passage orifices.

Gas turbine engine rotor blades

Abstract: A component for a gas turbine engine having at least one surface, that has been treated by ultrasonic hammer peening so as to provide a region of deep compressive residual stress in the treated region.

Method and apparatus for peening

Abstract: A mask for masking a corner of a metal component during peening. The component has a first surface defining an opening in the component and a second surface intersecting the first surface of the component at the corner. The mask includes a plug sized and shaped for insertion in the opening adjacent to the corner to cover the corner during peening. Further, the mask includes a rim surrounding at least a portion of the plug sized and shaped for surrounding at least a portion of the opening to cover the corner during peening thereby preventing the corner from being peened.

Method and apparatus for ultrasonic peening of annular recesses for the attachment of blades to a rotor

Abstract: The invention relates to a method for the ultrasonic peening of annular recesses for the attachment of blades to a rotor rim, these recesses including a blade introduction opening. According to the method, a plurality of beads is placed on a vibratory surface of a sonotrode, arranged in an intermediate position in a sleeve having opposed closing-off means capable of sliding in the recess, the introduction opening is placed facing the sonotrode, the sonotrode and the sleeve are moved together toward the introduction opening into a peening position in which the closing-off means face the recess ends opening into said opening, then the rotor rim is turned about its axis so as to bring the closing-off means into a first end of the recess so as to form a closed chamber containing the beads. The rim is turned and the vibratory surface is vibrated to mobilize the beads within the chamber, thereby peening the recess.

Laser search peening for exfoliation corrosion detection

Abstract: An exfoliation corrosion detection method which enables rapid detection and evaluation of hidden exfoliation corrosion on aircraft with related cost savings. Pressure exerted on the surface by the laser created plasma generates a pressure pulse or shock wave that propagates into the part. When the stress in the shock wave is above the dynamic elastic limit of the material, the surface material yields plastically. This plastic strain creates compressive residual stresses in the surface, thereby enabling detection of exfoliation corrosion, if present.

The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel

Abstract: Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.

Transverse ultrasound peening of blades on a rotor

Abstract: The invention concerns a method for transverse ultrasound peening of blades (2) on a rotor which consists in driving in rotation the wheel (3) bearing the blades (2) about its geometrical axis (6) arranged substantially vertically and in causing the blades (2) to pass through a mist of microbeads produced by a vibrating surface (20) in an active chamber (12) arranged laterally relative to the wheel. The active surface (20) is located beneath the path of the blades (2). Preferably, the active chamber (12) comprises a second vibrating surface above the path of the blades (2). The invention also concerns a machine for implementing said method.

Laser shock peening quality assurance by acoustic analysis

Abstract: A method for quality control monitoring of laser shock peening a surface of a production workpiece during which laser beam pulses form a plurality of corresponding plasmas An acoustic signal of each laser beam pulse during a period of time during a duration of each corresponding one of the plasmas is monitored and an acoustic energy parameter value for each of the acoustic signals for each of the corresponding laser pulses is calculated A statistical function value of the workpiece based on the acoustic energy parameter values is calculated and compared to a pass or fail criteria for accepting or rejecting the workpiece The criteria may be based on a pre-determined correlation of test piece statistical function data such as high cycle fatigue failure data of test pieces The statistical function value may be an average of the acoustic energy parameter values of the laser beam pulses

Multiple beam time sharing for a laser shock peening apparatus

Abstract: A multiple laser peening cell apparatus for receiving pulses of energy from a laser shock peening device is comprised of a first cell for receiving a first pulse of energy, a second cell for receiving a second pulse of energy, and a beam distribution means, for directing the first pulse of energy and the second pulse of energy. Also, a method of directing pulses of energy originating from a single source to multiple workpieces comprises the steps of creating a first pulse of energy, directing the first pulse of energy to a first workpiece located in a first laser peening cell, creating a second pulse of energy, and directing the second pulse of energy to a second workpiece located in a second laser peening cell.

Method of cleaning turbine component using laser shock peening

Abstract: A method of cleaning airfoils and related turbine engine components that have a crust-like debris deposited on the surface thereof. This method involves subjecting at least the portion of the component having the deposit of the crust-like debris to sufficient laser shock peening to cause the debris on the surface thereof to be loosened therefrom so that the loosened debris can be removed from the component. This loosened debris can then be removed from the component, such as by passing a cleaning fluid through the portion of the component that is subjected to the laser shock peening.

Self-Limiting Hardness Changes in Laser Peened 6061-T6 Aluminium

Abstract: Laser peening uses shock waves to modify and work harden the surface of metal components and weldments to improve mechanical properties such as fatigue and wear resistance, in particular with aluminium alloys. The literature has reported on a variety of property changes from laser peening aluminium alloys, which varied with the initial metallurgical state and laser generated shock wave pressures. This paper analyses the effect of laser peening repetitions (one and five repetitions) on hardness and elastic modulus versus depth on a 6061-T6 specimen for two laser generated shock wave pressures of 3·5 and 6 GPa. The higher shock wave pressure increased the hardness with both one and five repetitions, however, the lower shock wave pressure only increased the hardness with one repetition and not with five. The two mechanisms responsible for the self-limiting hardness changes are increases in the metal's Hugoniot elastic limit and changes in the metal's dynamic yield strength. These mechanisms limit fu...

Effect of shot peening on fatigue strength of 18%Ni maraging steel

Abstract: Rotating bending fatigue tests were carried out on an 18%Ni maraging steel to investigate the effect of shot peening on fatigue strength. Fatigue strength was increased markedly by shot peening. The increase in fatigue strength due to shot peening depended on shot size and stress level. Fracture mode changed from surface fracture in the short life region to interior fracture, i.e., fish-eye fracture, in the long-life region. In the middle-life region, however, cracks initiated from both the surface and the inside of the material individually coalesced and led to the final fracture. These results were discussed on the basis of the effects of shot size on surface roughness, the depth and magnitude of compressive residual stress and work hardening.

Analysis of Particle Velocity and Temperature Distribution of Struck Surface in Fine Particle Peening.

Abstract: This study examines numerical analysis of particle velocity and temperature distribution of struck material surface in fine particle peening. When the particle is accelerated using a direct-pressure type, the velocity of a 50 μm particle, just before striking the metal surface, was calculated to be 222 m/s. In applying air pressure, the acceleration of fine particles show significant increase compared to larger sizes. Moreover, the experimental values agree well with the calculated ones. On the other hand, the temperature distributions show the maximum surface temperature to be 1500 K and cools instantly.

Fatigue Behavior of Welded Diaphragm-to-Beam Connections

Abstract: The purpose of this study was to evaluate the fatigue strength of a particular welded diaphragm-to-beam connection. The connection consisted of wide flange diaphragm members welded directly to the web of a deeper main beam member. Cyclic tests were performed to determine the fatigue resistance of the detail and to evaluate three different repair methods. The repair methods investigated involved combinations of diaphragm removal, drilling holes at the beam crack tips, and peening the bottom flange weld toes. This study has shown that the web and bottom flange welds of nonstaggered diaphragms are more susceptible to fatigue cracking than comparable staggered diaphragm configurations. It was also found that the fatigue life of the detail is not greatly reduced because of the formation of web and bottom flange weld fatigue cracks, because cracks formed in the beam web at the end of the bottom flange diaphragm weld controlled the fatigue behavior. Moreover, the repair methods were found to be effective in significantly extending the cyclic life of the diaphragm detail.