Showing papers on "Peening published in 1992"

Intrinsic stress in sputter-deposited thin films

Abstract: A review of the sputtered film stress literature shows that the intrinsic stress can be tensile or compressive depending on the energetics of the deposition process. Modeling studies of film growth and extensive experimental evidence show a direct link between the energetics of the deposition process and film microstructure, which in turn determines the nature and magnitude of the stress. The fundamental quantities are the particle flux and energy striking the condensing film, which are a function of many process parameters such as pressure (discharge voltage), target/sputtering gas mass ratio, cathode shape, bias voltage, and substrate orientation. Tensile stress is generally observed in zone 1-type, porous films and is explained in terms of the grain boundary relaxation model, whereas compressive stress, observed in zone T-type, dense films, is interpreted in terms of the atomic peening mechanism. Modeling of the atomic peening mechanism and experimental data indicate that the normalized moment...

An analysis of stress concentrations caused by shot peening and its application in predicting fatigue strength

Abstract: — In order to calculate the stress concentration caused by shot-peening dents, three simplified models, namely a one-pit model, a seven-pit model and a pit-loop model, are proposed in this paper. By using a finite element program for automatic dynamic incremental non-linear analysis, the stress concentration coefficients based on these models are calculated for different pit parameters and different stress fields. When considering the stress concentration and residual stress field produced by shot peening, a modified Goodman formula is proposed and used for forecasting the fatigue strength of peened specimens having the fatigue sources at the surface. The forecasted results were verified by peening followed by fatigue tests on 40Cr steel.

Water jet peening device

Abstract: PURPOSE:To increase the peening efficiency by providing control means to control at least either side of a nozzle processing surface distance or a water injection pressure so as to make the frequency property of a nozzle to an optimum value of the frequency property. CONSTITUTION:In the water 2, the water 14 fed at a high pressure from a high pressure pump 12 is injected into the water 2 from a nozzle 4, to hit against the surface 3 of a work piece in the water 2, so as to improve the stress condition of the work piece. In this case, depending on the detecting output from a shock pulse detecting sensor 5 installed to the nozzle 4, the vibration frequency property generated to the nozzle 4 is analyzed by a frequency analysis means 7. The deflection between the resaltant frequency property and a preset optimum frequency property value is found, and at least either side of a nozzle processing surface distance L or a water injection pressure is controlled to make the frequency property of the nozzle 4 to the optimum frequency property value by control means 9 and 10.

Method for protecting a metal surface

Abstract: Protection of a metal surface is carried out by applying a coating of vitreous enamel to the surface so that the enamel forms a strong bond with the metal and then spraying a coating of an atomized protective metal on the enamel. Preferably a peening operation is carried out on the surface of the sprayed metal simultaneously with or immediately after the spraying of the metal. The method is particularly advantageous in protecting steel marine structures against corrosion and, where the protective metal is cupro-nickel, fouling by marine creatures. The vitreous enamel forms an electrically insulating layer preventing galvanic action between the steel and the cupro-nickel in the presence of sea water.

Surface modification by means of laser melting combined with shot peening: A novel approach

Abstract: Among the available laser applications laser surface melting has turned out to be a powerful technique for the production of wear-resistant layers. Despite the advantages of this process, laser surface melting results in tensile stresses which may assist crack propagation. In this paper it will be shown that shot peening can overcome this drawback effectively. It turned out that a preceding laser treatment of an eutectic aluminium-silicon alloy is able to amplify considerably the effectiveness of the shot peening treatment. In particular the maximum attainable hardness and compressive stress increase upon increasing the quench rate, i.e. upon increasing the laser scan velocity. The high concentration of silicon in solid solution turned out to be the main reason for the enhanced mechanical performance, not only directly through solid solution hardening, but also by precipitation hardening and by a higher dislocation density. The latter contribution is affected indirectly by a changed cross slip behavior.

Effect of shot peening on fatigue behavior in al-alloys

Abstract: The individual contributions of residual compressive stresses, high dislocation densities, and surface roughness that are induced by shot peening to the improvement of fatigue life of Al 2024 are assessed. Stress amplitudes to number of fatigue cycles (S-N) curves and microcrack propagation (da/dN-ΔK curves) are determined for both underaged (T3) and peak-aged (T6) conditions. The fatigue behavior of the electropolished (which is also the reference condition), shot peened, shot peened and stress relieved, shot peened and polished, and shot peened, stress relieved, and polished condition is evaluated in fatigue tests.

Process for forming a bearing surface for aluminum alloy

Abstract: A process for forming a bearing surface on an aluminum alloy article including the steps peening the surface, anodizing the surface, and washing the anodized surface with a boehmite inhibiting agent.

Randschichtzustände von normalisiertem und vergütetem 42 CrMo 4 nach konsekutiven Kugelstrahl- und Festwalzbehandlungen

Abstract: Die Randschichteigenschaften von normalisiertem und vergutetem 42 CrMo 4 nach konsekutiven Kugelstrahl- und Festwalzbehandlungen werden vorgestellt und diskutiert. Kugelgestrahlte bzw. festgewalzte Proben weisen insbesondere im normalisierten Zustand charakteristische Unterschiede in den randnahen Versetzungsstrukturen sowie in der Dicke der beeinflusten Randschicht auf. Bei einer konsekutiven Anwendung beider Verfahren wird ein deutlicher Reihenfolgeeinflus festgestellt. Das zuletzt angewandte Verfahren bestimmt dabei die in der Randschicht vorliegende Mikrostruktur. Near surface materials states of normalized as well as quenched and tempered SAE 4140 after consecutive shot peening and rolling treatments The near surface states of normalized as well as quenched and tempered SAE 4140 after consecutive shot peening and rolling treatments are presented and discussed. Especially in the normalized state separately shot peened or rolled specimens reveal characteristic differences in the near surface dislocation structures and in the thickness of the subsurface areas influenced by the mechanical treatments. In case of the consecutive application of shot peening and rolling, a sequence effect occurs in such a way that the finally applied surface treatment determines the microstructure of the very surface and the subsurface materials layers.

A Study on Peening by Submerged Ultra-High-Speed Water-Jets

Abstract: To clarify cavitation behaviours of submerged high-speed water-jets, systematic experimental studies were carried out by using a flow visualization technique. The cavitation behaviours were studied for both the free jet and the impinging jet at various stand-off distances x from the outlet edge of the nozzle. Effects of the injection pressure P 1 and the nozzle structure on the behaviours were also examined. The behaviours of the jets are largely dominated by explosive cavity clouds and by remarkably developed vortex cavitation. Therefore the structure of the submerged jet differs from that of jet in still air. The distribution of impulsive pressure P sh , which is measured by pressure sensitive films, clearly shows the existence of two pressure peaks along the jet. At the stand-off distance where P sh shows the “1st peak,” the impinging jet results in the severe erosion on the ambient solid surfaces. Because of this, the performance of cutting- or drilling- fabrications is considered to be remarkably improved when jet impinging is conducted at x 1 of the “1st peak.” On the other hand, at x 2 of the “2nd peak” downstream from the “1st peak,” numerous pressure pulses are produced on the solid surfaces, but mass loss due to cavitation erosion is barely detected. Clearly, x 2 of the “2nd peak” is believed to be suitable for precise peening fabrications.

Effect of Shot Peening on Delayed Fracture of High Strength Steel.

Abstract: A study was made on the effect of shot peening on delayed fracture of high strength steel at a level of 1300MPa and 1400MPa. To investigate this effect, three types shots, having different hardness and mean diameter, were prepared to make the different residual stress distribution in the bending type specimen. Using these shots, specimens were peeved by an air type shot peening device. It was confirmed that the delayed fracture resistance of each shot peened specimen was improved compared with those of as quenched and tempered specimens due to an increase in compressive residual stress. By measuring the displacement of moment arm, it was found that this result was caused mainly by a prolonged incubation period to crack initiation, the reason of which would be that the compressive residual stress defended hydrogen entry in metal.

Application of hard shot peening to automotive transmission gears

Abstract: Although shot peening is an old technology, it has been revived in the Japanese automotive industry as a means to enhance the fatigue durability of steel components Particular emphasis is on the application of "hard shot peening" "Hard shot peening" is a high intensity peening technology which results in a higher magnitude of compressive residual stress and, therefore, greater fatigue resistance than conventional shot peening The first area of development was in high performance carburizing steels suitable for hard shot peening Desirable traits were enhanced by reducing the carburizing anomalies resulting from intergranular oxidation and by the enhancing case toughness Further improvement of fatigue resistance has been accomplished by dual peening, first with hard shot followed by smaller diameter steel shot at a lower intensity This paper also describes the development of long life shot media for hard shot peening THE DEVELOPMENT of high fuel efficiency vehicles is an urgent need in the automotive industry, especially with CAFE regulations becoming stricter One approach is to reduce the weight of automotive parts to achieve greater fuel economy To achieve this, two methods are effective; the application of lighter materials and the downsizing the parts by strengthening of the steels used There are many techniques to obtain higher strength such as alloying, the application of clean steels, high quality heat treatment, and introducing residual stress by shot peening Among these methods, shot peening is gaining increased use as one of the most cost effective ways to enhance fatigue durability Shot peening is a cold working process performed by projecting hard particles onto the surface of parts which results in residual stress[l]-[3]* Even though it is an old technology, new developments are occurring in "hard shot peening" "Hard shot peening" is defined as a high intensity peening with an arc height larger than O6mmA and using hard shot media such as HV550 or higher It is well known that hard shot peening provides high compressive residual stress in a thin surface layer and results in remarkably high fatigue strengths[4]-161 In spite of its benefits, there remains several problems to be solved in hard shot peening The surface of a workpiece becomes roughened[7] and the life of the shot media decreases This paper will present a study on high performance carburizing gear steel suitable for hard peening, shot peening technologies to obtain higher fatigue strength and long life shot media APPLICATION OF HARD SHOT PEENING NEW STEELS FOR HARD SHOT PEENING-Although shot peening is beneficial, it is important to reconsider the materials being peened to obtain a higher fatigue strength The surface of a part becomes roughened by the high energy projection of hard particles and the surface roughness is influenced by the material being peened This roughening is accelerated by the existence of carburizing anomalies Intergranular oxidation is one of these defects which occurs at prior austenite grain boundaries during the carburizing process with an endothermic atmosphere It depletes oxide forming alloying elements adjacent to the grain boundary, which results in a local decrease in the hardenability and promotes the forming of soft transformation products on quenching Because they are oxide formers, silicon, manganese and chromium are also hardenability increasing elements Another disadvantage of hard shot peening, the decrease in toughness of peened parts, is caused by the decomposition of retained austen*Numbers in parentheses designate references at end of paper ite to martensite and work-hardening It is inevitable as long as conventional carburizing steels are used It is, therefore, important to select the optimum carburizing steel in the application of hard shot peening High performance gear steel, DSG1, is one of the candidates The fundamental properties of DSGl have already been published[8][9] The chemical composition of DSGl is shown in Table 1 This steel is characterized by decreased intergranular oxidation and soft transformation products by reducing its silicon content to less than 015% Furthermore, case toughness is improved by reducing the grain boundary embrittling element phosphorus and by increasing the molybdenum content up to 04% Table 1 Chemical composition of DSGl steel fwt X') MECHANICAL PROPERTIES OF DSGl Steel

Water jet peening method and device therefor

Abstract: PURPOSE: To improve the tensile residual stress of metal material by vibrating a nozzle at high-frequency in water, generating a vibration-induced cavity near the nozzle wall surface and colliding the vibration-induced cavity against the surface of the metal material by high-speed injected water stream including the cavity. CONSTITUTION: In a water jet peening method for reducing the surface tensile residual stress of the metal material by colliding the high speed injected water stream including the cavity against the surface of the metal material dipped in the water from a nozzle 3 provided with an orifice part for accelerating the flow speed and a horn-like injection hole followed to the orifice in the water, the high-frequency vibration is applied to the nozzle to vibrate it and the vibrating induced cavity is generated near the nozzle wall surface, and the above vibration-induced cavity is collided against the surface of the metal material by the high speed injected water stream including the cavity. COPYRIGHT: (C)1993,JPO&Japio

Development of the Neutron Diffraction Technique for the Determination of Near Surface Residual Stresses in Critical Gas Turbine Components

Abstract: Near surface residual stresses contribute significantly to the life of structural engineering components. A method of producing compressive residual stresses in the surface region of components to give improved resistance to fatigue fracture is shot peening. Neutron diffraction methods are successfully being used to determine through thickness engineering strains in polycrystalline materials. In this paper the results are reported of measurements that have been made on shot peened samples of a nickel superalloy. Good instrumental characteristics, sample positioning in the beam and the correction of near surface data have resulted in the accurate determinations of the residual stress fields. It is observed that the stress profile has a characteristic shape irrespective of material or of the peening intensity employed, and also that the distribution of stresses balancing the surface compressive field results in a peak tension of approximately one third of the maximum surface compression.

Hot peening method for carburized steel

Abstract: PURPOSE:To improve the fatigue strength of a steel member and to prevent the breakage of corners by subjecting a steel member having corners, such as gear, after carburizing, quenching, and tempering to two-stage shot peening of different high hardness shots. CONSTITUTION:The surface of parts made of steel having corners, such as gear, used for machinery is carburized and subjected to quench-and-temper treatment, by which the strength of the corners is improved. Further, in order to improve the fatigue strength of the corners, shots having >700 hardness HV and also having relatively large grain size of 0.6-1.2mm are sprayed onto the surface of the gear to perform first shot peening. Then, annealing is done at 100-200 deg.C, and second shot peening is performed by using shot grains of >=700 hardness HV and 0.1-0.5mm grain size. By this method, proper compressive residual stress distribution can be formed in the gear, and the gear improved in fatigue strength and free from breakage of corners can be obtained.

Effects of brush electroplating and shot peening on the fatigue strength of a medium strength steel

Abstract: — Brush electroplating causes a marked reduction in the fatigue strength of the base steel. For the medium carbon steel reported in this paper, the fatigue limit is reduced 28.6% by nickel brush electroplating. A large number of short cracks are found in the nickel coating, and the coating usually suffers a high value of internal tensile stress. These are two reasons that cause the loss of fatigue strength. Shot peening has been used to minimize the loss of fatigue strength caused by brush electroplating.

The Development of New Type Almen Strip for Measurement of Peening Intensity on Hard Shot Peening

Abstract: 高硬度材料の疲労強度は, おもに残留応力に支配され疲労強度を向上させるためには表面層の圧縮残留応力を高める必要がある. このため, アークハイトが0.6mmAを越えるような高い投射エネルギーで処理するハードショットピーニングが注目されている. この処理により, 従来のショットピーニングに比べ部材の疲労強度をさらに25%向上させることが報告されている. 一方, ピーニング強度を評価するアークハイト値は通常, 硬度がHRC44-50であるアルメンストリップA片を用いて測定される. しかし, ハードショットピーニングにおいて, A片で測定されたアークハイト値が部材の残留応力の大きさと一致せず, ピーニング効果の尺度としては不適切と指摘されている. そこで本研究では, ハードショットピーニングに適した基準片を検討するために, アルメンストリップC片と硬度がHRC60の高硬度基準片を準備した. それらの基準片を使用して, 残留応力とアークハイト値の関係を求めた結果, 高硬度基準片で測定されたアークハイト値は部材の最大圧縮残留応力値および圧縮残留応力の生じている範囲の大きさに良く対応していることが明らかになった.

Shot peening method of carburized gear

Abstract: PURPOSE:To assure the sufficient bending fatigue strength of the dedendum of a gear and to obtain excellent pitting resistance by forming a carbide on the surface of the gear after molding, subjecting the surface to shot peening, increasing the temp. to the Acm3 transformation point or above and holding the gear at this temp. for a short period of time. CONSTITUTION:After a gear blank material is molded by cutting or forging to a gear shape, the blank material is subjected to a carburization hardening and tempering heat treatment. A small amt. of the carbide 1a is formed in the range of about 100mum depth from the surface on the pitch circle of the gear 1 by this carburization heat treatment. This gear 1 is then subjected to the shot peening treatment. Short peening particles 4 of the sufficient size falling onto the bottom parts of the gear 1 are used at this time. The temp. on the pitch circle of the gear 1 is raised up to right above the Acm3 transformation point by utilizing the heat generated by the deformation, etc., when the shot peening is executed. The gear is held at this temp. or about >=3 minutes. The shot peening treatment is thereafter stopped and the gear 1 is cooled with water.

Water jet peening method for underwater structure

Abstract: PURPOSE:To remove any precipitated deposit from a steel surface or peening objective surface by dispersing and floating the precipitated deposit in the water as a minute grain group with a jet spouting at a lower velocity than a high speed water jet available in peening operation, and further drawing in the dispersing and floating grain group underwater through a flow of suction water CONSTITUTION:In advance of peening execution of works by means of high speed water injection, a precipitated deposit such as an oxidic scale or the like to be accumulated on the surface of an underwater structure or peening objective surface is dispersed and floated as a minute grain group in the water by a jet 12 spouting at a lower velocity than a high speed water jet 7 available in the peening In addition, the dispersed and floated grain group in the water is drawn in by suction water 11 and discharged to the outside of the underwater structure, through which the precipitated deposit is removed from a steel surface or peening objective surface

Method for gas-nitriding small article

Abstract: PURPOSE:To gas-nitride a small article such as a shot for peening. CONSTITUTION:A circular dish 12 for inserting a material to be treated is arranged at an angle of 60-85 deg. to a vertical rotating shaft 4 provided at the center of a cylindrical retort 3 in a vertical gas-nitriding furnace, and a small article is placed on the dish, vertically fluttered and shaken with the dish 12 being rotated or not by the rotating shaft 4 and gas-nitrided.

Method for reinforcing member

Abstract: PURPOSE:To improve fatigue strength to the position by applying surface hardness treatment, shot-peening, grinding process after beforehand executing rough working for which the ground thickness becomes the specific value, after shot- peening at the position which is a problem on the strength in a member. CONSTITUTION:After executing outer peripheral grinding to the outside diameter considering the following grinding thickness to a round bar raw material 11, to the part of an oil hole 11b, the rough working is beforehand executed so that the grinding thickness after shot-peening goes to <=50mum the axial directional length of e.g. about three times of diameter of this oil holes 11b to form the rough working part 11c making a little small diameter. Further, by working along the shape of center hole 11a, the center hole 11a is formed and also the oil hole 11b is opened to the diameter direction at the center of the above- mentioned rough working part 11c. Successively, after executing surface hardening treatment of carburized quenching and tempering to a hollow raw material 11, the shot peening is executed and grinding work is applied to obtain the member 12 having the center hole 11a and the oil hole 11b.

SURFACE LAYER INDUCED BY SHOT-PEENING AND ITS ROLE IN IMPROVEMENT OF FATIGUE STRENGTH OF 40Cr STEEL

Abstract: In this paper shot-peening and fatigue tests were carried out with specimens of 40Cr steel. The microstructure changes and residual stress fields produced by shot peening were determined by X-ray diffraction. From the test results it is concluded that the microstructure changes occur only within the compressive residual stress (CRS) zone, and that when the fatigue sources are localed in subsurface layers of specimens, the fatigue strengths of specimens are mainly controlled by the internal fatigue strength (IFS) of materials. Finally a characteristic curve of metal materials, local fatigue strength curve, was given, the curve is independent of peening conditions.

Improving the Fatigue Strength of Welded Joints by Shot Peening

Abstract: It was found that the effect of shot peening for a welded portion appeared greater for the lower stress-range and especially for the high-strength steel. The major factor is residual stress, and it seems that the created residual stress becomes larger especially for the high-strength steel. It was understood that the life calculation could be corrected by relating it to the S-N gradient.

The Effects of Surface Treatment on Torsional Fatigue Failure in Recoil Springs

Abstract: : Two different steels, AISI 4150H and maraging 250, were tested in torsional fatigue to failure. Both materials were prepared with three surface conditions: (1) as-machined (machining grooves left on the outside surface); (2) as-polished; and (3) polished and shot peened. All specimens converge at low cycle life (about 1,000 cycles), but at lower torsional stresses, the greatest improvement in fatigue life is shown by the shot peened specimens, followed by the as-polished specimens. This is true for both materials. The 4150H steel shows the greatest fatigue lives on the torsional S-N curves, but the maraging 250 displays the greatest degree of improvement throughout the range of surface conditions.

Eddy current characterization of magnetic treatment of materials

Abstract: Eddy current impedance measuring methods have been applied to study the effect that magnetically treated materials have on service life extension. Eddy current impedance measurements have been performed on Nickel 200 specimens that have been subjected to many mechanical and magnetic engineering processes: annealing, applied strain, magnetic field, shot peening, and magnetic field after peening. Experimental results have demonstrated a functional relationship between coil impedance, resistance and reactance, and specimens subjected to various engineering processes. It has shown that magnetic treatment does induce changes in a material's electromagnetic properties and does exhibit evidence of stress relief. However, further fundamental studies are necessary for a thorough understanding of the exact mechanism of the magnetic-field processing effect on machine tool service life.

Improved high-intensity rotary peening particle support and method of making same

Abstract: Previously known peening particle supports (10) fail under cyclic stresses encountered during peening operations. An improved high-intensity rotary peening particle support (10) of the type having a plurality of peening particles (20) metallurgically secured to an exposed face thereof is presented, the support having a base composition consisting essentially of from 0.08 to 0.34 weight percent carbon, the balance iron, and a Ni-enriched layer which provides a hard, wear resistant surface. A method of producing such a support is also described, the method including cold forming a peening particle support (10) base composition as described, stress relieving, metallurgically joining peening particles (20) to an exposed face of the support, austenitizing, quenching, and tempering the support (10) to form a support (10) having a Ni-enriched layer which is harder than the base composition.

Protection of metal surfaces against corrosion.

Abstract: Protection of a metal surface is carried out by applying a coating of vitreous enamel to the surface so that the enamel forms a strong bond with the metal and then spraying a coating of an atomized protective metal on the enamel. Preferably a peening operation is carried out on the surface of the sprayed metal simultaneously with or immediately after the spraying of the metal. The method is particularly advantageous in protecting steel marine structures against corrosion and, where the protective metal is cupro-nickel, fouling by marine creatures. The vitreous enamel forms an electrically insulating layer preventing galvanic action between the steel and the cupro-nickel in the presence of sea water.