DOCSLIB.ORG

Peening Weld Surfaces with Steel Shot Induces Compressive Stresses That Raise Resistance to Fatigue and Corrosion

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Peening Weld Surfaces with Steel Shot Induces Compressive Stresses That Raise Resistance to Fatigue and Corrosion Peening weld surfaces with steel shot induces compressive stresses that raise resistance to fatigue and corrosion. By Tom Floyd hot peening improves Testing shot-peened parts, re- Built-in compressive stresses property performance searchers have demonstrated that raise resistance to stress corrosion of welds and weld- peening raises fatigue resistance of by counteracting tensile stresses. mentsS by cancelling residual tensile fillet welds in carbon steel and butt Stress corrosion occurs when tensile stresses that develop in surfaces as welds in constructional alloy steel stresses break up oxide layers that welds cool and replacing them with by 20 to 40 percent, and can double normally protect surfaces of chro- compressive stresses. Compressive fatigue resistance of butt welds in mium-containing alloys. Though stresses raise resistance to fatigue, aluminum plate and 18-percent Ni bare metal re-oxidizes to form fresh stress corrosion, and intergranular maraging steel. Researchers at Rock- oxide coatings, recurring cycles of corrosion. well International (Atomic Di- tensile stresses continually rupture A cold-working process, shot vision) found that shot peening pre- these layers. peening bombards a metal work- vents stress corrosion cracking of As for intergranular corrosion, piece with spherical pellets, com- weldments in austenitic stainless characteristic of stainlesses sensi- monly steel shot. Each impact steel. tized at weld temperatures, peening stretches and densifies surface lay- Fatigue resistance improves be- before welding helps to prevent it ers. Because subsurface material re- cause, when service imposes tensile by breaking up surface grains. This mains unstretched, it exerts an op- stresses in a part, the built-in com- action provides a multitude of nu- posing force, trying to restore the pressive stresses counteract them. cleation sites for chromium carbides surface to its original area. This This action keeps surface stresses in that would otherwise grow prefer- force, compressive stress, preloads compression, allowing the part to entially in grain boundaries, leav- the metal surface against tensile withstand fatigue cycling for long ing chromium-depleted zones sen- loading stresses. periods. sitive to corrosion. PEENING DEVELOPS COMPRESSIVE STRESSES Peened surface 1 Stress Tension 0 Compression ---------- 68 WELD1NG DESIGN & FABRICATION SEPT 85 Controls for peening Operators consider expected ser- LOADS ALTER STRESS DISTRIBUTION vice conditions when determining Peened surface how deep compressive stresses I +-Tension 0 Compressions- , should run beneath surfaces. Shal- low peening, to 0.008 inch, suffices to counteract tensile stresses built up by simple bending and to fore- stall stress corrosion cracking. To combat tensile stresses imposed by complex bends and torsion, and to handle fretting fatigue, peeners rec- ommend compressive depths to 0.015 inch. To adjust depth of compression, operators adjust the energy at which pellets strike work surfaces. They measure kinetic energy on the Al- men Intensity Scale, running tests with Almen strips, of cold-rolled SAE 1070 spring steel hardened and tempered to Rc 44 to 50. Measuring 314 by 3 inches, Almen strips come in three thicknesses: 0.031 inch (N strips, for thin work), 0.051 inch (A strips, for most jobs), and 0.094 inch (C strips, for heavy parts). To run an Almen test, the operator clamps the strip to a jig, called an Almen block, then tightens four screws at corners to hold the strip <I-& u- -..-:I.:--- I.L- ::- LL--..-& llai. I le YUD~LIU~~DLlle jllj VAL-- ule pa1 L, such that the test strip lies along the section of interest, say the surface of PEENING INTENSITY a butt weld. Then the operator starts PREDICTS COMPRESSION DEPTH a peening run, stopping the action periodically to inspect the strip. As peening proceeds, com- pressive stresses build up on the ex- posed side of the Almen strip, bow- ing it to a maximum curvature, called saturation. Curvature is mea- sured with an Almen Gage, a dial gage scaled in mils. The operator records the corresponding arc height-an intensity of 10A means that an A strip is saturated with an arc height of 0.010 inch. Almen intensities relate to com- pression depth, which varies with material and hardness. As the graph shows, an Almen intensity of 6C (0.006 inch on a C strip) corresponds to compression depths of 0.012 inch for steel at Rc 52, 0.015 inch for ti- tanium-6Al-4V, and 0.022 inch for steel at Rc 31. 0.do2 0,004 0.006 0.008 0.010 Almen intensity (C strip), in. Peen all surfaces To raise fatigue resistance effec- SEPT 85 WELDING DESIGN 81 FABRlCATlQN To perform Peenscan inspection, the operator coats the part with fluorescent dye, which glows under black light (left). Peening I for 15 seconds (center) removes some of fhe coating, such that the part continues toglow hazily. Glowing stops after 1 minute of beening (right) to demonstrate 100-~ercentcover&e. With use, shot shatters, breaking Inspection has improved appre- up into sharp-edged fragments that ciably with the development of the nick surfaces. Since peening aims at Peenscan method, which takes the building uniform compressive place of tedious examination by stress into surfaces without abrad- magnifying lens. Peenscan in- ing material or introducing stress spectors use black-light projectors raisers, peening cannot tolerate bro- to determine coverage. They start by ken pieces of shot. We start all peen- coating the part with an alcohol- ing jobs with 100-percent round based fluorescent liquid, which shot, screened to remove broken dries rapidly leaving a thin film of pieces and sized to uniform di- fluorescent material, During runs, ameters. In modern peening ma- p eening gradually removes the chines, classifiers screen out broken film, causing the glow to fade out, as pieces continuously throughout viewed under black light. Complete peening runs. disappearance of the glow indicates 100-percent coverage. Recognized I Operal'ors shot-peen cra;ze-boom welds Peening today by military specifications (MIL-S- to help them resist fatigue in service. Late in the last decade, Peenama- 13165B: Shot Peening of Metal Parts), Booms, of ASTM A618 steel (70,000 tic Division, Metal Improvement Peenscanning eliminates the need lbl in. * tensile), go to draglines. Company, adapted microprocessors for 200-percent coverage in order to to run shot peening production be assured of complete peening. tively, peening must cover weld equipment. Microprocessors pro- Ceramic shot, another new devel- joints, including HAZs, com- gram machines, changing settings opment, gets the call when ferrous pletely-every square inch should to peen parts of different materials, contamination might be a draw- be dimpled overall. Inspectors con- shapes, and sizes. They set, automat- back, as when peening stainless ventionally determine 100-percent ically, all parameters, including steels. Harder than carburized steel, coverage by examining surfaces shot-impingement angle, Almen ceramic shot produces higher Al- thoroughly with a magnifying lens, intensity, air pressure, and motion men intensities and fractures less X 10 power. Some customers call for of the shot streams. The computer than steel shot. Zirconia-silica shot stores settings for repeat runs. It also will probably replace steel shot monitors parameters during peen- within 10 years. ing, and will shut the run down if a Peening shops have devised inno- To raise fatigue resistance effectively, parameter, such as air pressure, vative ways to peen out-of-the-way peening must cover part surfaces, strays out of the preset range. areas and corners of parts. They use determined by X 10 lens or black-light Microprocessor-based systems flexible lances to deliver shot adapt to statistical process control, around corners, and employ inter- inspection of fluorescent-coated parts. which will become simpler when nal shot deflectors to shot-peen in- computer-monitored parameters sides of welded pipe, replace Almen strips, a move 125-percent coverage, even 200-per- planned before the year 2000, Com- Tom Floyd is manager of metallurgy, cent coverage, to make sure that puters will also predict shot de- Cleveland Division, Metal improvement they will get 100-percent coverage. gradation as a function of Almen Company, subsidiary of Curtiss Wright The extra peening adds no benefits, intensity, type of shot, and target Corporation, 18683 South Miles Road, but costs more. hardness. Cleveland, Ohio 44228; (226) 662-8408. 70 WELDING DESIGN & FABRICATION SEPT 85 .
Load more

Recommended publications
  • Controlled Shot Peening Preventing Failures
    MIC Services INNOVATORS IN TECHNOLOGY Metal Improvement Company Subsidiary of Curtiss-Wright Corporation Controlled shot peening Preventing failures Enhancing the performance of metals and materials www.metalimprovement.co.uk Controlled shot peening - preventing failures Metal Improvement Company (MIC) is a Component failure is often related to residual tensile stress global organisation specialising in metal and DESIGN CONSIDERATIONS - COST OF PERFORMANCE CRITERIA material surface treatments which enhance induced during manufacture. Subsequent severe working performance and extend the life of critical and/or unexpected conditions can eventually lead to Parameter selection - the choice of process have to be accurately and Intensity control components, enabling component designs to shot peening parameters is dependant repeatedly controlled. achieve their maximum potential. premature failure. on a variety of conditions: Shot peening intensity is the measure Controlled shot peening is different of the energy of the shot stream. It is Established in 1945, MIC has over 60 l knowledge of the application of the from most manufacturing processes in one of the essential means of ensuring operating divisions in Europe, USA, Canada Typical examples of premature failure are: The shot peening process - how it component that there is no non-destructive method process repeatability. The energy of the and Asia with on-site processing worldwide. works l component geometry to confirm that it has been performed shot stream is directly related to the We offer a quality controlled and cost l Metal fatigue to the proper specification. Techniques compressive stress that is imparted into l manufacturing method effective service, working in partnership to Controlled shot peening is the such as x-ray diffraction require the a component.
    [Show full text]
  • Shot Peening Overview
    H:\docs\training\SPO_08_28_2000.wpd Shot Peening Overview by Jack Champaigne Electronics Inc 1428 W. 6TH Street Mishawaka, In 46544 http://www.shotpeener.com Last Revised January 18, 2001 With special thanks to Metal Improvement Co for their technical contributions http://www.metalimprovement.com Shot Peening Overview 1. INTRODUCTION ............................................................... 3 1.1 Shot Peening Described ................................................... 3 1.2 Residual Stresses ....................................................... 3 1.3 Load Stress Profiles ...................................................... 6 2. MANUFACTURING PROCESSES - EFFECT ON FATIGUE LIFE .......................... 8 2.1 Beneficial Manufacturing Processes .......................................... 8 2.2 Detrimental Manufacturing Processes ........................................ 8 2.2.2ElectroDischargeMachining(EDM)....................................... 10 3. SERVICE EFFECTS REMEDIED BY SHOT PEENING ................................. 16 3.1CavitationDamage ..................................................... 16 3.2FrettingandFrettingFatigue .............................................. 17 3.3 Galling ............................................................... 18 3.4Pitting ............................................................... 18 3.5CrackArrest........................................................... 20 3.6StressCorrosionCracking................................................ 21 4. PRODUCTS BENEFITTING FROM SHOT PEENING
    [Show full text]
  • Improvement of Hardened Surface by Shot P
    IMPROVEMENT OF HARDENED SURFACE BY SHOT P M. Ohsawa, Honda R & D Co., LTD. T. Yonemura, Parker Netsushori Co., LTD. --ABSTRACT In the application of shot peening to automotive parts, this process has been the com- monly used. surface treatment for springs. Today, a tend among automobile manufacturers is to use this process for other parts, e. g. transmission gears, with the aim of in- creasing durabi 1 i ty . The authors have recent 1y conducted severa 1 experiments on the effect of this process on soft-nitrided parts which are now undergoing remarkable devel- opment, and on widely used plated parts after they have been case-hardened by carbu- rizing. These experirnen ts have proven that the fatigue strength of sof t-ni trided or casehardened surface is increased, and that reduction of the strength of hardened surf - face after plating is avoided, contributing greatly to reduction of the weight of such parts wi thou t loss of strength. KEYWORDS; Sof t-Ni triding, Tuff triding, Cr-plating, Residual stress, Fatigue strength. 1 OUTLINE OF TEST RESULTS 1-1 Effect of Shot peening on Sof t-Ni trided Parts Soft-ni triding which is also called as Gas Sof t-Ni triding, Liquid Ni triding known as Tufftride process has the features shown in Table 1 and is in wide use for various automotive parts. This treatment, however, may not be applicable to common carbon steel where high performance is desired because of shallow case depth and lower surface hardness. This paper deals with our observations on the effect of shot peening on sof t-ni trided steel to see how its mechanical properties are improved.
    [Show full text]
  • Effect of Shot Peening on Fatigue Strength of Maraging Steel
    Transactions on Engineering Sciences vol 39, © 2003 WIT Press, www.witpress.com, ISSN 1743-3533 Effect of shot peening on fatigue strength of maraging steel N. ~awa~oishi',T. ~a~ano~ & M. ~ori~arna~ I Faculty of Engineering, Kagoshima University,Kagoshima, Japan 2 Miyakonojyo National College of Technology, Miyakonojyo, Japan Abstract Rotating bendmg fatigue tests were carried out for a shot-peened maraging steel in order to investigate the effects of shot peening on the fatigue strength and the fracture mechanism focusing on the effect of surface roughness. Fatigue strength was markedly improved by shot peening because of hardening and generation of compressive residual stress in the surface layer. The origin of fatigue fracture changed from the specimen surface at high stress levels to an inclusion in the interior of specimen at low stress levels. And at the middle stress levels, both fracture modes were observed. Consequently, the shape of the S-N curve of shot- peened specimen was complex, corresponding to the change of fracture mode. In the region where surface fracture occurs, polishing the specimen surface and double shot peening using superhard fine particles were effective to improve the fatigue strength through the decrease in stress concentration due to smoothening the specimen surface. Transactions on Engineering Sciences vol 39, © 2003 WIT Press, www.witpress.com, ISSN 1743-3533 100 Surface Twatment V1 1. Introduction Maraging steel is an ultra-high strength steel which has both high tensile strength and high ductility [1],[2]. However, fatigue strength is relatively low in comparison with the hgh static strength [3]. Therefore, the study on the improvement of fatigue strength of maraging steel is important.
    [Show full text]
  • United States Patent [191 [111 4,354,371
    UnitedO States Patent [191 [111 4,354,371 Johnson [45] Oct. 19, 1982 [54] METHOD OF PRESTRESSING THE 4,214,923 7/1980 Price ............................... .. 29/421 R WORKING SURFACES 0F PRESSURE 4,230,426 10/ I980 Avery . .. 72/53 ERS 0R ERS Primary Examiner-Gene Crosby [75] lnventol‘l Daniel E- 30111180111 Dallas, TBX- Attorney, Agent, or Firm—Stephen A. Roen; Arthur L. [73] Assignee: Metal Improvement Company, Inc., Fredenck - Paramus, NJ. [57] ABsTRAcr [21] Appl‘ No" 200,767 A method of prestressing the working surface of pres 2 Filed; Oct, 27 1980 sure chambers or cylinders comprising the steps of ?rst [2 1 ’ s h o t peemng' th eir' wor king sur races t o rorm compres [gé] clci3 ............................................ "hr/1325161115 sive residual stresses’ and then applying ?uid pressure at [ 1 .' ' ' """""""""""""""""" " ’ a predetermined magnitude to cause tensile stresses in [58] Field of Search ................. .. 72/53, 40, 61; 148/4, the working surfaces The magnitude of compressive 148/141; 29/421; 51/319 residual stresses established on their outer working sur [55] References Cited faces 'is made substantially equal to the tensile stress U_s_ PATENT DOCUMENTS applied to these surfaces during the pressure phase of 454 592 6/1891 Jackson 72/61 the process‘ 3,4ss1073 12/1969 Burney .. 4,034,585 7/1977 Straub ................................... .. 72/53 6 Claims, 2 Drawing Figures 4,354,371 1 2 the plastic from the elastic zone in said substrate. This .METHOD OF PRESTRESSING THE wouxnwc tension component, unless neutralized, can produce SURFACES or PRESSURE CHAMBERS on microscopic fractures in the internal surface of the CYLINDERS chamber wherein defects exist therein.
    [Show full text]
  • Laser Peening Fact Sheet
    Hepburn and Sons LLC “Trusted advisors to the American Maritime Industry” TECHNOLOGY FACT SHEET – Laser Shock Peening TECHNICAL CHALLENGE 10X Compressive residual stress • Aluminum shipbuilding on the rise in the Navy, leading to benefits over other peening materials problems like stress corrosion cracking (SCC) and methods and treatments sensitization • Repair yards tasked with these substantial repairs • Aluminum repair has significant rework, as it is difficult to work with • Welding repairs impart large stresses on and deform the 48X aluminum SCC on aluminum ship Lifetime extension of • Flame straightening not permitted on marine grade aluminum superstructure sensitized aluminum when laser shock peened versus • Common aluminum forming methods are laborious, costly, and no treatment time-consuming TECHNOLOGY OVERVIEW • High-energy pulsed laser directed at material surface to generate pressure pulses • Shock wave plastically yields and cold works the 1-5 mm material to generate deep compressive stresses Range of compressive residual stress depth as a • Residual stress layers are orders of magnitude result of laser shock peening deeper than that achievable with shot peening • Highly predictive and deterministic stress Laser peening a metal surface profiles • Used successfully in the aerospace industry for nearly 20 years • Significantly improves aluminum lifespan • 20 years Arrests crack growth and mitigates stress Length of time that laser corrosion cracking shock peening has been successfully used in the • Mitigates aluminum sensitization
    [Show full text]
  • Laser Peening for Prevention of Fatigue Failures
    LASER PEENING FOR PREVENTION OF FATIGUE FAILURES David F. Lahrman Peter A. Gaydos LSP Technologies, Inc. United States ABSTRACT Laser peening is an innovative commercially-available surface enhancement process for increasing the fatigue life of metal components. The process produces deep residual compressive stress into treated surfaces, typically five to ten times deeper than conventional metal shot peening. These deep compressive residual stresses inhibit the initiation and propagation of fatigue cracks. Laser peening has been particularly effective in increasing the resistance to fatigue crack propagation initiated from foreign object damage in titanium alloy fan and compressor blades of aircraft gas turbine engines. [1,2,3,4] However, the potential application of this process is much broader, encompassing automotive parts, orthopedic implants, tooling and dies, and others. Significant progress has been made to lower the cost and increase the throughput of the process, making it affordable for numerous applications. This paper reviews the status of laser peening technology, material property enhancements, and potential applications. KEYWORDS Laser shock peening, fatigue, life, residual stress, surface, enhancement HOW LASER PEENING WORKS Laser peening drives a high amplitude shock wave into a material surface using a high energy pulsed laser. The effect on the material being processed is achieved through the mechanical “cold working” effect produced by the shock wave, not a thermal effect from heating of the surface by the laser beam. The laser system is a high-energy, pulsed neodymium-glass laser system having a wavelength of 1.054 µm. The laser peening system produces very short laser pulses, selectable from 8 to 40 nanoseconds, with a pulse energy of up to 50 joules.
    [Show full text]
  • Finite Element Modelling of Shot Peening and Peen Forming Processes and Characterisation of Peened Aa2024-T351 Aluminium Alloy
    UNIVERSITE´ DE MONTREAL´ FINITE ELEMENT MODELLING OF SHOT PEENING AND PEEN FORMING PROCESSES AND CHARACTERISATION OF PEENED AA2024-T351 ALUMINIUM ALLOY ALEXANDRE GARIEPY´ DEPARTEMENT´ DE GENIE´ MECANIQUE´ ECOLE´ POLYTECHNIQUE DE MONTREAL´ THESE` PRESENT´ EE´ EN VUE DE L'OBTENTION DU DIPLOME^ DE PHILOSOPHIÆ DOCTOR (GENIE´ MECANIQUE)´ SEPTEMBRE 2012 © Alexandre Gari´epy, 2012. UNIVERSITE´ DE MONTREAL´ ECOLE´ POLYTECHNIQUE DE MONTREAL´ Cette th`eseintitul´ee : FINITE ELEMENT MODELLING OF SHOT PEENING AND PEEN FORMING PROCESSES AND CHARACTERISATION OF PEENED AA2024-T351 ALUMINIUM ALLOY pr´esent´ee par : GARIEPY´ Alexandre en vue de l'obtention du dipl^ome de : Philosophiæ Doctor a ´et´ed^ument accept´eepar le jury d'examen constitu´ede : M. GOSSELIN Fr´ed´eric, Doct., pr´esident M. LE´VESQUE Martin, Ph.D., membre et directeur de recherche M. BOCHER Philippe, Ph.D., membre et codirecteur de recherche M. CHAMPLIAUD Henri, Ph.D., membre Mme ROUHAUD Emmanuelle, Ph.D., membre iii A` ma famille iv ACKNOWLEDGEMENTS I would like to first thank Pr. Martin L´evesque and Claude Perron for their guidance and trust throughout this project. Your confidence allowed me to explore hypotheses that made my work interesting, challenging and, I hope, useful. I would also like to thank Pr. Philippe Bocher at Ecole´ de Technologie Sup´erieure for welcoming the computer savvy mechanical engineering student I was in his group and introducing me to the fascinating field of materials science. The time and expertise provided by the National Research Council Canada - Aerospace is also greatly appreciated. I would like to thank Simon Larose for his generous help and advice and well as Christian Corbeil and Xavier Pelletier for their support.
    [Show full text]
  • Laser Peening Process and Its Impact on Materials Properties in Comparison with Shot Peening and Ultrasonic Impact Peening
    Materials 2014, 7, 7925-7974; doi:10.3390/ma7127925 OPEN ACCESS materials ISSN 1996-1944 www.mdpi.com/journal/materials Review Laser Peening Process and Its Impact on Materials Properties in Comparison with Shot Peening and Ultrasonic Impact Peening Abdullahi K. Gujba 1 and Mamoun Medraj 1,2,* 1 Department of Mechanical and Industrial Engineering, Concordia University, 1455 De Maisonneuve Blvd. W., Montreal, QC H3G 1M8, Canada; E-Mail: [email protected] 2 Department of Mechanical and Materials Engineering, Masdar Institute, Masdar City, P.O. Box 54224, Abu Dhabi, UAE * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +1-514-848-2424 (ext. 3146); Fax: +1-514-848-3175. External Editor: Douglas Ivey Received: 17 October 2014; in revised form: 18 November 2014 / Accepted: 27 November 2014 / Published: 10 December 2014 Abstract: The laser shock peening (LSP) process using a Q-switched pulsed laser beam for surface modification has been reviewed. The development of the LSP technique and its numerous advantages over the conventional shot peening (SP) such as better surface finish, higher depths of residual stress and uniform distribution of intensity were discussed. Similar comparison with ultrasonic impact peening (UIP)/ultrasonic shot peening (USP) was incorporated, when possible. The generation of shock waves, processing parameters, and characterization of LSP treated specimens were described. Special attention was given to the influence of LSP process parameters on residual stress profiles, material properties and structures. Based on the studies so far, more fundamental understanding is still needed when selecting optimized LSP processing parameters and substrate conditions.
    [Show full text]
  • Case Studies of Fatigue Life Improvement Using Low Plasticity Burnishing in Gas Turbine Engine Applications
    Case Studies of Fatigue Life Improvement Using Low Plasticity Burnishing in Gas Turbine Engine Applications Paul S. Prevhy Ravi A. Ravindranath ~revev~ambBa-research.com) ([email protected]) Lambda Research NAVAIR, 22195 Elmer Road 5521 Fair Lane Bldg: 106, Room: 202-G Cincinnati, OH 45227 Patuxent River, MD 20670-1534 Michael Shepard Timothy Gabb [email protected] @[email protected]@ Wright Patterson AFB NASA Glenn Research 2230 Tenth St., Ste. 1 21088 Brookpark, Bldg. 43, Room 231 WPAFB, OH 45433-7817 Cleveland, OH 44135-3191 ABSTRACT fatigue benefit of thermal stability at engine Surface enhancement technologies such as shot temperatures. (LSP), and low plasticity An order of magnitude improvement in damage e substantial fatigue life tolerance of LPB processed Ti-6-4 fan blade improvement. However, to be effective, the leading edges. compressive residual stresses that increase fatigue 0 Elimination of the fretting fatigue debit for Ti-6-4 strength must be retained in service. For successful with prior LPB. integration into turbine design, the process must be Corrosion fatigue mitigation with LPB in Carpenter affordable and eompatible with the manufacturing 450 steel. LPB provides thermally stable Damage tolerance improvement in 17-4PH steel. Where appropriate, the performance of LPB is compared to conventional shot peening after exposure to engine operating temperatures. INTRODUCTION LPB is a new method of surface enhancementCl-4 ] deep stable surface compressive residual compressive residual stress little cold work for improved fatigue, ,and stress corrosion performance even design. ed temperatures where compression from shot The x-ray diffraction based background studies of relaxes.[5] LPB surface treatment is thermal and mechanical stability of surface using conventional multi-axis CNC machine t enhancement techniques are briefly reviewed, unprecedented control of the residual stress demonstrating the importance of -g cold work.
    [Show full text]
  • Laser Peening Vs. Shot Peening: Engineering of Residual Stresses, Surface Roughness and Cold Working
    Laser Peening vs. Shot Peening: engineering of residual stresses, surface roughness and cold working 0. Higounenc1 1 Metal Improvement Company I Curtiss Wright Surface Technologies, Bayonne, France Abstract In Laser Peening (LP), compared to Shot Peening (SP), the magnitude of residual compressive stress at the surface is the same: about 60% of elastic limit; but the depth is much higher. In Low Cycle Fatigue (LCF) depth of residual compressive stress is beneficial because it does not only delay crack initiation, but also crack propagation. Depth of residual stress is also crit­ ical in Foreign Object Damage (FOO) and Crack Grow Rate (CGR) applications. Changes in surface roughness, as soon as cold work, are much more significant in shot SP compared to LP. Those changes can have a positive, or a negative influence depending on application and condition: HCF or LCF, deteriorating or non-deteriorating environment such as corrosion or FOO, fretting, surface contact fatigue. Thus, LP is complementary to SP in some specific applications such as LCF, FOO, CGR. The other advantage is the extremely high process control that allow more easily to take into ac­ count the credit of LP in the design .. Keywords: shot peening, laser peening, fatigue life, crack nucleation, crack propagation Introduction Laser Peening (LP) is a process in which an iintense beam of laser light (irradiance 2 to 1OGW/cm2) is directed on to a sacrificial ablating material placed on the surface of the com­ ponent to be treated. The light rapidly vaporizes a thin portion of the ablative layer, producing a plasma that is confined by the inertia of a thin laminar layer of water (-1 mm thick) flowing over the surface.
    [Show full text]
  • An Overview of Shot - Peening
    International Conference on Shot Peening and Blast Cleaning AN OVERVIEW OF SHOT - PEENING A Niku-Lari· IITT, France. ABSTRACT Controlled shot-peening is an operation which is used largely in the manufacture of mechanical parts. It should not be confused with sand blasting used in cleaning or descaling parts. Shot-peening is in fact a true machining operation which helps· increase fatigue and stress corrosion resistance by creating beneficial residual surface stresses. The technique consists of propelling at high speed ~mall beads of steel, cast iron, glass or cut wire against the part to be treated. The size of the beads can vary from 0.1 to 1.3 or even 2mm. The shot is blasted under conditions which must be totally controlled. The main advantage of this particular surface treatment is that it increases considerably the fatigue life of mechanical parts subjected to dynamic stresses. It has many uses in industry, particularly in the manufacture of parts as different as helical springs, rockers, welded joints, aircraft parts, transmission shafts, torsion bars, etc. At a time when the optimum characteristi_cs are being demanded of mechanical assemblies, shot-peening is a surface treatment method which is being increasingly chosen by engineers. However, shot-peening technology is yet to be fully perfected and the substantial changes produced in the treated material make it difficult at the present time to put the best conditions into practical use. KEY WORDS Residual stress, surface roughness, stress relaxation, Sh.at-size, Shot-velocity, Shot-hardness, Intensity, Fatigue. 1. THE TECHNOLOGY OF SHOT-PEENING 1.1 Shot-Peening Machines There are numerous types of shot-peening machines.
    [Show full text]