Showing papers on "Shot 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.

Shot peening system and method with velocity sensing

Abstract: Consistency in shot peening is obtained by a system using a force sensor to sense the reaction force from a shot peening gun. The reaction force is used to calculate the average velocity of the shot stream. Since the quality of effect of the shot peening process depends upon the square of the velocity of the shot and the mass of the shot, control of the shot velocity and mass flow rate is used to provide consistent shot peening results. Additionally, the force sensor is used to trigger an alarm and/or turn off the shot peening if the reaction force is too low such that a clogged nozzle or other malfunction is occurring.

Method of forming a fine grain structure on the surface of an aluminum alloy

Abstract: An aluminum alloy is provided which has a surface with a fine grain structure. It is produced by overaging an aluminum alloy and then cold working only the surface by shot peening or other surface working technique. The alloy is then heated so that the overaged, cold-worked surface recrystallizes into a fine grain structure.

Production of gear

Abstract: PURPOSE:To easily and surely produce the gear having excellent fatigue strength and pitting resistance by subjecting the gear to shot peening which project shot particles of specific particle sizes from the tip side toward the deddendum side prior to a surface hardening treatment after tooth working. CONSTITUTION:A rough shape material obtd. by cutting and forging of a material is subjected to the tooth working and is then subjected to the surface hardening treatment, such as carbonitriding, to obtain the gear 1. The formed teeth 2 are subjected to the shot peening prior to the above-mentioned surface hardening treatment after the tooth working in the above-mentioned process for producing the gear. The shot particle size is specified to a 0.2 to 0.6mm range, The direction for projecting the shot particles is so determined that the particles are directed from the tip side toward the deddendum side approximately along the surface of the teeth 2 as shown by arrow and the shot peening is executed while this direction is move in the tooth lead direction. Tip edges 3, shaving steps 4 and hobbing traces, etc., are removed or are changed to adequate shapes in this way, by which the fatigue strength and pitting resistance of the gear are additionally improved.

Residual stresses and fretting, crack initiation and propagation

Abstract: The effect of residual compressive stresses in the surface of a component on the resultant improvement in fatigue performance is well known. Fretting is a surface effect which causes local wear and is an efficient initiator of fatigue cracks. It also may cause a rise in surface temperature. The effect of residual stresses in cases of fretting is not so straightforward as in plain fatigue. Many of the usual methods of inducing compressive stresses in a surface also cause hardening, e.g. surface rolling, shot peening and nitriding. Increased surface hardness tends to reduce fretting wear. It is known, however, that in situations where the wear rate is high, the initiation of fatigue cracks by fretting is prevented. Some results are presented on the effect of shot-peening on the fretting wear of a carbon steel and an austenitic stainless steel. Experiments have been designed to separate the hardening effects and the compressive stress effects in the fretting fatigue of certain aluminium alloys and austenitic stainless steel. Surface roughening by shot-peening also has an effect on crack initiation in fretting fatigue of an aluminium alloy. Fading of compressive stresses under the influence of fretting is more rapid than in normal fatigue. Some results are given on the initiation and propagation of short fatigue cracks in a compressive stress field.

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.

Overview on the shot peening process

Abstract: Shot-peening is a cold working process which allow to increase the resistance of materials and parts against fatigue, fretting, stress corrosion cracking and other mechanical and conjoint mechanical and chemical behaviours It is largely used in the mechanical and aeronautical industry The technique consists of propelling at high speed small beads of particles (on steel, cast iron, glass or ceramics) against the part to be treated The size of the beads can vary from 01 to 13 mm The main advantage of this particular surface treatment is that it increases the fatigue life of mechanical parts subjected to dynamic stresses by generating compressive residual stresses on the surface of the material Industrial parts such as helical springs, rockers, welded joints, propeller, blades and other aircraft parts, transmission shafts torsion bars etc are always shot peend At a time when optimum characteristics are being demanded of mechanical components and structures, shot-peening is being increasingly chosen by engineers to meet such demand Therefore it is necessary to know the effect of the technological parameters of shot-peening upon the fatigue influencing parameters such as surface roughness, residual stresses and the work hardened depth

Shot-peening method and apparatus

Abstract: A method for controlling the flow in a shot-peening apparatus, comprising an auger having an inlet supplied with granular media via a hopper, the auger preferably being driven by a stepping motor, for advancing the media fed into the inlet at a precisely controlled rate to a discharge conduit. The motor is controlled by a computer to cause a programmed amount of flow to discharge from the discharge conduit. A proximity sensor, preferably of the capacitive type, is provided in the discharge conduit to detect if the discharge is blocked. The motor and auger may be replaced by a vibrating feeder.

Determination of Sub-Surface Microstructure States by Micromagnetic NDT

Abstract: The functional behaviour of many components is determined by the intrinsic properties — residual stresses and microstructure — of sub-surface near zones. Therefore, in order to improve the static and dynamic mechanical properties of these surface near states, mechanical and/or thermal treatments such as laser hardening, inductive hardening, case hardening, nitriding, grinding and shot peening are applied. Depending upon the work-piece/component and the employed technique and machining parameters, the residual stress- and microstructure states will be changed between a few micrometers and several millimeters. To control the quality of these subsurface near states, metallographic inspections, x-ray methods and hardness measurements have been applied. Because all these conventional testing methods are expensive, time consuming and not suitable for real time control,1–4 there is a considerable need of nondestructive testing (ndt) methods. So far ndt procedures are mainly restricted to eddy current methods,5,6 ultrasonic techniques7,8 and — in the case of ferromagnetic materials — micromagnetic techniques1,9–11.

Improvement of strength of gear

Abstract: PURPOSE:To considerably improve the fatigue strength of a gear by aging the gear subjected to shot peening after carburization, hardening and tempering so as to convert the surface layer of the gear into a high density hardened layer. CONSTITUTION:A toothed gear is carburized, hardened and tempered. After the surface of the gear is subjected to shot peening, the gear is aged at 100-200 deg.C for 1-2hr. By this method, carbon penetrates into the interstices among the atoms in the surface layer work-hardened by the shot peening, so a high density hardened layer is formed and the fatigue strength of the gear can be considerably improved.

Surface treatment of titanium member

Abstract: PURPOSE:To improve the wear resistance and fatigue strength of a Ti member at a low cost by subjecting the surface of the Ti member to electroless Ni plating, annealing the member at a specified temp. and carrying out shot peening. CONSTITUTION:The surface of a Ti member is subjected to electroless Ni plating to uniformly and firmly form an Ni coating layer without causing hydrogen brittleness. The Ni coated Ti member is annealed at 250-450 deg.C. By this annealing, P, B, etc., are precipitated as Ni3P, Ni3B, etc., from the Ni coating layer to increase the hardness and to improve the wear resistance. The Ni coating layer is then subjected to shot peening to produce compressive residual stress. The occurrence and growth of fatigue cracks in the surface of the Ti member is inhibited and the fatigue strength is improved.

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.

Manufacture of high strength and toughness cast steel

Abstract: PURPOSE:To manufacture cast steel goods having superior fatigue strength and toughness, by applying composite treatment composed of carburization and austempering treatments to cast steel product, then applying compressive stress to surface part CONSTITUTION:Cast steel goods having compsn contg 02-08% C, 20-45% Si, <08% Mn, <005% P, <005% S, <10% Mo, <20% Ni, <10% Cr is subjected to composite treatment in which it is heated and carburization treated under existence of carburizing material, and austemper treated by lowering temp to 200-450 degC and holding for a fixed time By the treatment, inner part is made to bainite structure while leaving a large quantity of residual austenite structure at surface part Next, compressive stress is applied to surface of cast steel goods by shot peening or roll working, etc, to cause transformation induced by working of residual austenite structure at surface to martensite structure High strength and toughness cast steel goods comparable with forged steel is obtd

Residual stresses and X-rays

Abstract: Residual stresses can have significant effects on the fatigue lives of components and are particularly important in surface treatments such as shot peening. X-ray stress analysis provides a nondestructive method for measuring the residual stress in a shallow surface layer of material approximately 10 μm thick. Layer removal techniques such as electropolishing allow the evaluation of the residual stress profile through the material. Reliable and accurate dedicated X-ray stress analysers are available that enable measurements in less than 0.5 h analysis time. The X-ray technique is described and some examples are presented of its applications. Additionally, difficulties that have been experienced with this technique are discussed.

Deceleration of small crack growth by shot-peening

Abstract: L'influence du grenaillage sur le comportement de la croissance de fissures en surface a ete observee sur des specimens d'acier de construction au carbone avec une rainure perforee relativement grosse sous pliage rotatif

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.

Manufacture of surface hardened gear made of cast iron

Abstract: PURPOSE:To manufacture the titled gear, by applying austemper treatment, shot peening treatment to a gear blank made of spheroidal graphite cast iron, then forming wear resistant cover layer to form alloy layer between the blank and a cover layer. CONSTITUTION:A spur gear 1 is manufactured by using spheroidal graphite cast iron composed of a prescribed compsn., the gear 1 is heated at about 900 deg.C for about 1hr to austenitize, then gradually cooled to about 300 deg.C to apply austemper treatment, next, shot peening treated under conditions of about 0.40 arc height and about 200% coverage. Wear resistant material (TiN, etc.,) is thermally sprayed to tooth surface excluding addendum surface of the gear 1 to form the cover layer 2, then a diffused alloy layer 4 is formed between the layer 2 and the blank 3 by high frequency heating treatment. In this way, the gear 1 having remarkably improved wear resistance, pitching resistance and fatigue strength is manufactured.

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.

Surface hardening method for carburized product

Abstract: PURPOSE:To obtain a carburized product having improved fatigue strength by carburizing and hardening a product at a specified carbon potential to produce a large amount of retained austenite in the uppermost layer and by transforming the retained austenite into martensite CONSTITUTION:When a product is carburized and hardened, it is held at the hardening temp at 100-120% carbon potential to produce a large amount of retained austenite only in the uppermost layer of the product having about 01mm thickness The uppermost layer is subjected to proper shot peening to transform the retained austenite into martensite by work induced transformation Thus, the residual compressive stress in the surface part of the product is increased and the strength and toughness under processing stress are improved

Steel wire for spring having excellent resistance to fatigue and its production

Abstract: PURPOSE:To easily produce a steel wire for springs having excellent resistance to fatigue by subjecting a wire contg. a small amt. of Cr as a steel wire for springs to a hardening treatment, then softening the surface layer of the wire by quick heating. CONSTITUTION:The steel products contg., by wt%, 0.3-1.0% C, 0.15-2.5% Si, 0.3-2.0% Mn, and =2.0mm diameter. The wire is then subjected to hardening and tempering treatments, by which the hardness is adjusted to >=500 Hv; thereafter, the surface layer part is heated to 500-700 deg.C for the treatment time of =10MHz. The hardness in the range of 10mum from the surface is adjusted to =100mum to >=500 Hv. The steel wire for springs having the excellent resistance to fatigue is produced without subjecting the wire to a surface treatment such as shot peening treatment and soft nitriding as in the conventional practice.

Surface machining method for water turbine runner

Abstract: PURPOSE:To increase fatigue strength of a water turbine runner, by a method wherein, by using a steel ball with a specified diameter, a region having compression residual stress exceeding a polishing amount needed after shot peening machining is held. CONSTITUTION:By using a steel ball with a diameter of 4-10mm, shot peening machining is applied on the root part of a water turbine runner to form a deep surface layer with a size of maximan 4mm having compression residual stress. After removal of the uneven part of a surface and a change of properties layer, which are produced resulting from shot peening, a sufficient next surface is caused to remain, and fatigue strength of the root part of the water turbine runner is improved, and this increases fatigue strength of the water turbine runner about ten times.

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.

Shot peening of crank shaft

Abstract: PURPOSE:To avoid injection of shot particles to a pin parallel portion and permit, in a short time and efficiently, shot peening of only a fillet portion by holding the pin portion of a crank shaft with a shot particle injection preventing device having a block construction. CONSTITUTION:Centering on the central axis A of a pin portion 1a, a jig which rotates a crank shaft 1 is attached to a journal 1c, and the crank shaft 1 is rotated centering on the central axis A. Understabilized state of this rotation, a shot particle injection preventing device 2 is attached along the vertical direc tion to the pin portion 1a. Next, when shot particles 6 are injected, injection of shot particles 6 to the pin parallel portion 1d of the crank shaft 1 is prevented by the shot particle injection preventing device 2, while shot peening on only the fillet portion 1e of the crank shaft 1 can be made in a short time.

Production of high-strength gear

Abstract: PURPOSE:To produce a gear having improved strength and toughness by forming residual austenite on the surface layer by carburization hardening in which carbon potential is specified then transforming only the extreme surface part of the residual austenite to martensite by strong working. CONSTITUTION:The carbon potential is controlled to a 1.0-1.2% range to form a large amt. of the residual austenite in the surface layer (about 0.4-0.5mm depth) of the gear when the gear is held at the hardening temp. in the carburization hardening treatment in the stage of subjecting the gear to carburization hardening. The gear is then subjected to physically strong working such as heavy-duty shot peening or heavy cutting (strong cutting) to transform only the residual austenite in the extreme surface layer part (about 0.1-0.2mm depth) to the strain-induced transformation type martensite. A large amt. of the austenite layer is thereby made to remain in the lower part (about 0.3-0.5mm depth) of the martensite layer so that said layer functions effectively to prohibit the progression of fatigue crack.

Improvement of the fatigue strength of welded high-strength steels

Abstract: The objective of the work is to promote the use of high-strength steels in offshore structures. In this connection laboratory tests were carried out in order to improve the fatigue strength of welded joints by means of weld posttreatment. TIG dressing and shot peening of the weld interfaces are discussed. Testing in air showed that both techniques appreciably prolong the service life. The fatigue behaviour in seawater is similarly improved by shot peening. The test results help to provide a better understanding of the advantages made possible by the use of highstrength steels.