Showing papers on "Peening published in 1987"

The effect of residual stresses induced by shot‐peening on fatigue crack propagation in two high strength aluminium alloys

Abstract: — The crack initiation lives of peened specimens of aluminium alloys 7010 and 8090 are shorter than those of unpeened specimens. This is caused by the acceleration of crack initiation due to stress concentration in the rough peened surface, especially at fold-like defects. The crack growth rate in peened specimens is significantly reduced with increasing ΔK, i.e. with increasing crack length. At a crack length of approximately 0.3 mm this trend is reversed and the crack growth rate rapidly increases and attains the same level of crack growth rate as that in unpeened specimens. The point of smallest crack growth rate roughly corresponds to the point of maximum residual stress. The crack growth rate in a peened specimen has been modelled by assuming the effect of residual stress reduces to the equivalent stress ratio. The predicted results agree well with the experimental data.

Analyse des surfaces grenaillées: fissuration, rugosité et contraintes résiduelles

Abstract: The study of superficial cracks of shot peened surfaces in terms of coverage rate, material nature and ball diameter shows the relation between cracks and dynamic behaviour of the sample surface during the impact. The shot peened layers are not deformed quickly enough under the shock.For the different shot peened steels, the fracture of superficial layers appears for materials such as 35CD4 (SAE 4135) and E460 which are more sensitive than others of high mechanical strength. The roughness of E460 and its cracks increase with coverage rate. In case of a long shot peening exposition, the cracks are deeper and the superficial residual stresses decrease, hence the exterior loading to enable the propagation of the surface default is small.The classical fracture mechanics could not be applied for short cracks (10 im) and the mechanical characteristics of the hammered layer are unknown. We shall describe how difficult is the prediction of noxiousness of cracks using our actual knowledges.

Improvement of material quality of metal for welding austenitic stainless steel

Abstract: PURPOSE:To prevent the segregation of a weld metal, to fine the crystal grains and to improve the material quality thereof by welding an austenitic stainless steel and imparting specific deforming work to the solidified weld metal in the temp. region above the recrystallization temp. CONSTITUTION:The weld metal is imparted >=10% strain working while the weld metal is in the temp. region above the recrystallization temp. thereof after solidification in welding of the austenitic stainless steel. The weld metal is otherwise imparted >=5% strain working in the temp. region below the recrystallization temp. and is then heated to the recrystallization temp. or above. The above-mentioned strain working is preferably applied uniformly to the weld metal part by means such as peening. Random and fine crystal grains of the weld metal are thereby formed and the microsegregation is prevented, by which the weld metal having the excellent corrosion resistance and mechanical properties is obtd.

The effect of shot-peening intensity on the fatigue and fretting-fatigue behaviour of an aluminium alloy

Abstract: Shot-peening can produce surface imperfections and these become more severe at higher intensities of shot-peening, with a possibility that fatigue performance may be impaired. Specimens of aged Al-4Cu-lMg alloy (2014A) were shot-peened to three levels on the Almen scale, 12–16A, 16–20A, and 8–10C. S-N curves in fatigue and fretting-fatigue were determined in rotating-bending. In high-cycle fatigue and fretting fatigue the lowest level of peening gave the greater increase in fatigue life. In low-cycle fatigue the highest level of peening gave the greater increase in fatigue life. In fatigue the intermediate level of peening gave results similar to those of the high level peening, whereas in fretting-fatigue the results were similar to those of the low level peening. These results are explained in terms of the surface damage observed in the scanning electron microscope. All the treatments gave some improvement in fatigue and fretting-fatigue performance compared with unpeened specimens.

Titanium‐oxide films made by rf diode sputtering from a compound target

Abstract: This paper describes thin‐film stress, stoichiometric ratio, deposition rate, and refractive index of an rf‐sputtered titanium‐oxide dielectric film. High compressive stresses (1010 dyn/cm2) were obtained, which can be correlated to the argon sputtering gas incorporation and peening effect. The process dependencies of the stoichiometric ratio, deposition rate, and refractive index are also described.

Shot peening for Ti-6Al-4V alloy compressor blades

Abstract: A text program was conducted to determine the effects of certain shot-peening parameters on the fatigue life of the Ti-6Al-4V alloys as well as the effect of a demarcation line on a test specimen. This demarcation line, caused by an abrupt change from untreated surface to shot-peened surface, was thought to have caused the failure of several blades in a multistage compressor at the NASA Lewis Research Center. The demarcation line had no detrimental effect upon bending fatigue specimens tested at room temperature. Procedures for shot peening Ti-6Al-4V compressor blades are recommended for future applications.

Formation of thermally sprayed film having superior wear and corrosion resistance and durability

Abstract: PURPOSE:To improve the wear and corrosion resistances and durability of a thermally sprayed film by increasing the density of the film by peening. CONSTITUTION:Satisfactory malleability and ductility are provided to a thermally sprayed film by heating or other method and many steel shots are hit against the film to heat the film. By this beating, that is, peening, pores present among the constituent particles of the film are reduced. Thus, the wear and corrosion resistances and durability of the film are improved.

Surface thermomechanical treatment for metal product

Abstract: PURPOSE:To provide high surface hardness and fatigue strength, by spraying, at a specific speed, shots with small grain size having a hardness equal to or higher than that of product onto the surface of a metal product and by increasing the temp. in the vicinity of the product surface. CONSTITUTION:Shot peening spraying the shots of 40-200mu grain size having a hardness equal to or higher than that of product at >=100m/sec spray velocity is applied to the surface of a metal product, by which the temp., in the vicinity of the surface of the layer to be worked, of the product is elevated to the A3 transformation point or above. In the above process, two stages of heat treatment and shot peening are carried out by a single shot peening. In this way, the hardness and wear resistance at the product surface is improved and, at the same time, fatigue strength can be increased owing to the establishment of compressive residual stress due to shot peening.

Apparatus for securing metal tabs to file unit bodies

Abstract: A table supports a cardboard file unit body as it is manually slid edgewise forwardly, engaged against a fixed but adjustable side edge guide, into engagement with a fore-and-aft movable front edge guide and an air microswitch thereon that actuates a punch mechanism. After punch operation, the front edge guide moves forward, bringing the punched portion of the body between the wings of a metal tab waiting at a peening station. Arrival of the front edge guide at its forward position trips another air microswitch to actuate a tab peening mechanism. The tabbed body is then manually withdrawn rearwardly and a new tab is automatically fed rearward to the peening station from a stack of tabs in front of that station. The punching and peening mechanisms, front edge guide and tab feed slider are actuated pneumatically.

The effect of the surface working process on the fatigue strength of carburized steels.

Abstract: The effect of surface working (shot peening) and additional post working heat treatment on the fatigue properties of carburized steel with surface structure anomalies was evaluated through rotating bending fatigue tests. Smooth specimens with various surface roughness and notched specimens were gas carburized and shot peened. Some smooth specimens were tempered after shot peening to examine the effect of post working heat treatment. Hardness, residual stress and the amount of retained austenite near the surface of the carburized and shot peened specimens were measured. The fatigue strength of all of the shot peened specimens increased and was as much as 90% higher than that of carburized specimens. The smooth specimen tempered at 100°C after shot peening gave the highest fatigue strength among all samples tested in this study.

Deceleration of small crack growth by shot­ peening Ralentissement de la croissance de petites fissures par 'shot peening' Verlangsamung des Wachstums kleiner Risse durch OberfHkhenkugelstrahlen

Abstract: The effect of shot-peening on surface crack growth beha>,(Lour was observed in a mild carbon steel specimen with a relatively large hole notch under-'rotating bending stresses. A new damage curve based on crack propagation was proposed by quantifying fatigue damage by surface crack area. This damage function can follow crack growth behaviour well even in a surface treated specimen in which crack growth rate is affected strongly in the early stage of fatigue, and shows that the fatigue damage accumulation process can be expressed by a compound Wei bull function. Compressive residual stress in thin work-hardened surface layer decreased crack growth rate only when the crack was small, and the crack grew faster than in un peened specimens after crack length reached some extent. Shot-peening definitely increased both crack initiation and propagation period much more under lower stress level.

Fatigue Behaviour of Shot Peened Surfaces

Abstract: Peening is a technique commonly used to improve fatigue resistance, but it is not always appreciated that excessive peening may be detrimental to fatigue behaviour. The present work demonstrates this effect in three different alloys: a mild steel, stainless steel, and a commercial copper alloy. The dependence of fatigue behaviour on peening intensity is shown to reach a maximum beyond which high intensity peening reduces fatigue life; at very high intensities the fatigue life can be reduced below the unpeened value. This reduction in fatigue life is shown to coincide with an increase in surface roughness, as measured by the parameter Ra, and the onset of a distinct damage mechanism revealed by scanning electron microscopy. The varying effect of peening intensity in the different materials is related to their tensile, fatigue, and wear properties; a model is advanced to explain the observed behaviour, based on the change from an initiation dominated mechanism to a propagation dominated mechanism as...

Fatigue Strength of Shot Peened Carburized Steel

Abstract: The common problem of carburized steels is the reduction of the fatigue strength by the existence of surface structure anomalies and the sensitivity of the mechanically induced notches. In order to improve the surface origin fatigue fracture resistance, shot peening has been applied. The significance of the distribution of residual stresses and hardness within the shot peened surface layer of the specimen is discussed. Approaches to developing extremely high fatigue strength are presented.

Production of rim for alminum wheel

Abstract: PURPOSE:To prevent the crack generation in rolling by using the spiral shaping for the rim center axis of the weld zone together with a peening hardening in obtaining a product with rolling by making an annular blank body by welding a plate blank. CONSTITUTION:A plate shaped rim blank is prepared by cutting it so as to incline for the longitudinal direction of the coil from the coil stock manufactured from the rolling of a slab and so that the butt end thereof becomes spiral for the center shaft of the rim in winding. The both ends of this blank is subjected to butt welding after its winding annularly. The peening is then performed on the weld zone until the weld zone shows the work hardening in the refining state of H14 - H16 as regulated in JIS standards. A cold work is then performed on the rim into the necessary final shape with the rolling works of a spinning, ring rolling, etc., after forming the vicinity of the weld zone in a smooth surface by performing the trimming of residual part of excess metal.

Behavior of surface residual stress induced by shot peening (ii)

Abstract: Shot peening is used to produce work hardened layer and to induce compressive residual stress. Residual stress is induced by micro strain in a metal. As the characteristics of residual stress is not cleary confirmed, it is important to clear the behaviour of residual stress and to apply it's characteristics successfully. As shown in previous paper 1), even if shot peening conditions are constant, the residual stress on peened surface changes by the thickness of specimen and also changes by chemial etching non-peened surface. In order to clear the characteristics of surface residual stress, shot peening were run under several shot peening conditions and surface residual stress was measured by X-ray diffraction. The influences of the blasting angle and surface roughness for the surface residual stress were discussed and then the relationship of kinetic energy of a shot and critical thickness of specimen for surface residual stress were obtained.

Surface Treatment By Laser Generated Shock Waves

Abstract: Surface Treatment by Laser Generated Shock WavesPh. Bournot, D. Dufresne, M. Autric, P. Giovanneschi-TestudC. Coquerelle*Laser - Matter Interaction Group, Institute of Fluid Mechanics1, rue Honnorat - 13003 - Marseille - France*CMCM -SM Etablissement Technique Central de l'Armement16 bis Avenue Prieur de la Cate d'Or - 94114 - Arcueil CedexAbstractA study of surface treatment by laser generated shock waves was carried out on various materials. A plasmatrapping device enabled intense shock waves to be obtained with attenuated thermal effects. A hardening of50 % over 1 mm of thickness was obtained on aluminium samples.Amongst the different surface treatment techniques which seem the most promising is that using a highpower pulse laser. With the new technique it is possible to obtain intense shock waves over large surfaces ofwhatever form at the same time as attenuated thermal effects without creating bulk deformation. An experimen-tal study of surface treatment by shock waves generated by an Nd -YAG pulse laser (30 J, 25 ns) was carriedout on metals (aluminium, titanium, steel). To obtain high pressures (40 Kbar) with moderate energies andnot very high laser intensities (109 W /cm2), a containment device for the plasma resulting from the interac-tion and the easily vaporizable materials was used. A analysis showed a hardening of more than 50 % over asurface of 0.6 cm2 throughout the thickness of an aluminium sample (1 mm). No hardening effect was observedfor the other metals. These results were obtained without optimization of the trapping technique. Bettercontrol of this will enable a hardening effect to be obtained on other metals.IntroductionFor the ever greater performances required, mechanical components must satisfy often contradictory cons-traints, such as good mechanical resistance, lightness, good resistance to abrasion and wear. To obtain theselatter conditions, a surface treatment must be carried out most often on parts already machined. One solutionconsists of hardening a thin layer of the material by modifying its structure by shock. This can be obtainedby shock peening or by laser. Shock peening presents certain problems of homogeneity ; on the other hand, thetechnique using laser energy to generate a shock wave appears very promising. This technique has been thesubject of a preliminary study whose main results are presented in this paper.Creation of a high -energy shock wave by laser irradiationBy making a pulsed laser beam interact with materials, high -energy pressure waves are created in thematerial, through phenomena such as vaporization and the propagation of laser supported blast waves, detona-tion waves and combustion waves. However, due to air breakdown, the laser powers which can generally be usedare limited and the maximum pressures obtainable are around 0.5 GPa. This pressure limit is mainly due to thevapour and ambient air being moved as a result of the interaction. To obtain higher pressures (of severalGPa) necessary for significant changes in the material, this movement must be limited by trapping the plasmausing a layer of matter which is transparent to laser radiation. Studies carried out by B.P. Fairland andA.H. Clauer(1) have shown that pressures of 10 GPa can be obtained with a laser pulse of 109 W /cm2 and ofseveral tens of nanoseconds duration.Description of the experiments and the diagnosticsThe laser used in the experiments was a Nd : YAG laser emitting a maximum energy of 35 J for a pulse peakof 25 na full width half maximum. The beam was focused onto a surface of 0.3 or 0.6 cm2.The tests were carried out for energy densities between 40 and 110 J /cm2 and corresponding flux of

The niku-lari method and the stress source method:application to residual stress distribution of shot peened plates

Abstract: This chapter discusses application of the Niku–Lari method and the stress source method to residual stress distribution of shot peened plates. In industry, shot peening represents a well-known process to improve the fatigue properties of metallic components. As only the surface is plastically deformed by this process, an inhomogeneous deformation takes place, which induces compressive residual stresses in a thin surface layer. These reduce the mean stresses in the surface so that the initiation and early growth of fatigue cracks is retarded. A well-known measure of the shot peening process is the so-called Almen-intensity, that is, the deflection that results when a plate of normed size, called Almen-strip, is shot peened. This chapter introduces a simple procedure to determine the average depth and the average magnitude of the compressive residual stresses. The method involves the shot peening of plates of different thickness under identical conditions. Niku–Lari's method to determine the residual stress profile is based on a measurement of the deflection variation that results if the shot peened layer is removed step by step.

Production of blanking die for very thin sheet

Abstract: PURPOSE:To compose the punch and die of almost zero clearance quickly and easily by disusing the machining of super high accuracy by removing the prescribed part of both members with its grinding after performing a peening around the die inlet by facing the punch to the die inlet. CONSTITUTION:The punch 1 and die 2 on which a prework is made are fitted to a press device 3. The clearance (c) of both members does not need super high accuracy but is made smaller as far as possible with the accuracy of an ordinary micrometer. A shot peening is then made on the peripheral part of the die hole on the surface of the die 2 as per the arrow mark A by slightly inserting to or separating from the inlet of the die 2 the tip of the punch 1, a rubber made tubular cover 4 is protected by fitting it to the outer periphery near the tip excluding the tipmost part of the punch 1. The inlet part of the die 2 is thus deformed B plastically, the surface of the die 2' is removed by grinding it upto D-D face and on the other hand the worn tip face of the punch 1' upto E-E, and a sharp blade is put respectively.

The effect of shot peening on transition SCC of Alloy 600 steam generator tubing

Abstract: Electrochemical caustic testing demonstrated shot peening to be an effective remedial measure for primary side transition stress corrosion cracking of mill-annealed Alloy 600 steam generator tubing Dye penetrant inspection and extensive metallographic examinations failed to detect any evidence of crack initiation on the shot peened ID surfaces of 17 transitions roller expanded to between 2% and 6% wall thinning and tested for at least 15 days Only three small cracks (0003'' deep or 6% throughwall) were observed in the roller expanded region of one transition in a tube specimen severely deformed to 11% wall thinning In contrast, all but two of the 11 non-shot peened transitions displayed numerous deep axial and circumferential intergranular cracks Shot peening retarded the propagation of precracks and showed no evidence of exacerbating OD cracking Sodium tetrathionate testing of sensitized (621/sup 0/C (1150/sup 0/F)/10 hours) Alloy 600 was shown to be a useful but conservative stress indexing test Shot peening at intensities of 301 to 601 significantly reduced the depth of stress-assisted intergranular attack A few deep cracks (ie, 50% throughwall) were observed in two out of six transitions shot peened to only 151 to 201 intensities However, at these lower intensities the voluminous IGA seenmore » in non-peened specimens was eliminated« less