Showing papers on "Peening published in 1986"

Relaxation of shot peening induced compressive stress during fatigue of notched steelsamples

Abstract: This paper presents an experimental investigation of the surface residual stress relaxation behaviour of a shot peened 0.4% carbon low alloy steel under fatigue loading. A round specimen with a circumferential notch and a notch factor Kt = 1.75 was fatigue loaded in both shot peened and ground conditions. Loading conditions included axial fatigue with stress ratio R = −1 and R = 0 and also R = −1 with an additional peak overload applied at 106 cycles. Plain unnotched shot peened specimens were also fatigue loaded with stress ratio R = −1. The results show how the relaxation is dependent on load level, how the peak load changes the surface residual stress state, and that relaxation of the smooth and notched conditions is similar. Two different shot peening conditions were used, one with Almen intensity of 30–35A (mm/100) and another of 50–55 A (mm/l00).

Manufacture of high-strength gear

Abstract: PURPOSE: To increase the bending fatigue strength by conducting surface hardening with carbo-nitriding process, and then performing shot-peening with grain hardness and peening time set in specified conditions. CONSTITUTION: After coarse tooth cutting, a finish tooth processing is performed, wherein each tooth flank is formed in a smooth curvature with fillet radius more than 1mm, and surface hardening is carried out with carburizing or carbo-nitriding. Thereafter shot peening is made using impeller type or air stream nozzle type under the conditions with the grain hardness over H v 550 and peening time between 3 and 7min. COPYRIGHT: (C)1987,JPO&Japio

Evaluation of sputter ion plated CoCrAlY and NiCrAlTi coatings for gas turbines

Abstract: This paper highlights the potential of a simple dc sputtering process to deposit the complex MCrAlY overlay compositions onto the hot end components of gas turbines. Particular advantages of sputter ion plating technology include good control of coating composition, no need to rotate the components to be coated, and deposition in a clean environment. The effect of peening on coating microstructure and the subsequent oxidation behavior of the coating has been examined for a range of MCrAlY compositions. Peening serves to eliminate leader defects from the surface layers by compaction of the coating and also affects the oxide‐growth mechanisms. The surface roughness of the sputter ion plating coatings, both as deposited and after glass bead peening, increases with that of the substrate and compares favorably with published values for electron beam evaporated coatings. For coatings tested between 1020 °C and room temperature in a heat treated and peened condition, fatigue cracks occurred after 100–150 cycles, while for peened and heat treated coatings, the time to crack initiation was extended to 800 cycles. Results from engine endurance trials are also summarized.

Kugelstrahlen zur Verbesserung der Schwingfestigkeit von Bauteilen

Abstract: Das Kugelstrahlen ist ein seit uber 50 Jahren bekanntes Verfahren zur Verbesserung der Schwingfestigkeit von Bauteilen. Es wurde ursprunglich in der amerikanischen Kraftfahrzeugindustrie entwickelt, wird aber in der Zwischenzeit von praktisch allen Industriezweigen angewandt, bei denen schwingende Beanspruchungen auftreten. Nach einer kurzen Schilderung der historischen Entwicklung des Kugelstrahlens wird das Verfahren selbst sowie die erforderlichen Kontrollmasnahmen in der Fertigung erklart. Sodann wird geschildert, das das Kugelstrahlen Druckeigenspannungen erzeugt und warum diese die Schwingfestigkeit verbessern. Danach wird diskutiert, welche Bauteile und Werkstoffe kugelgestrahlt werden konnen und wo die Grenzen des Kugelstrahlens liegen (z.B. bei erhohten Temperaturen). Auch andere Anwendungen des Kugelstrahlens, die nicht die Schwingfestigkeit betreffen (z.B. die Verbesserung der Spannungskorrosionsempfindlichkeit) werden erwahnt. Das letzte Kapitel enthalt eine Anzahl weiterer Beispiele uber die Verbesserung der Schwingfestigkeit kugelgestrahlter Bauteile. Shot Peening to Improve the Fatigue Strength of Components Shot peening has been used by industry for more than fifty years to improve the fatigue strength of components. It was originally developed by and for the US automobile industry; nowadays it is being employed by practically all branches of industry where fatigue loaded structures occur. After a short description of the historical development of shot peening the process itself is described as well as the necessary control specifications. It is explained that shot peening induces residual compressive stresses and why these improve the fatigue strength. The components and materials which can be shot peened to advantage are discussed next, as well as the limitations of shot peening (i.e. increased temperatures etc.). Other applications of shot peening (i.e. improvement of stress corrosion sensitivity) are mentioned. The last section contains a number of further examples on the use of shot peening to improve the fatigue strength of components.

The instrumentation and control of a wet peening process

Abstract: Describes a measurement system capable of monitoring slurry flow rates in both conducting and non-conducting fluids. The system uses two separate transducers, based on different principles, to cover the two types of fluid. The correct transducer is automatically selected by the computer, which controls the measurement system. Experimental results are presented for slurries based on two different sizes of solid particles over a range of plant operating conditions.

Effects of weld shape and residual stress on fatigue strength of fillet welded joint.

Abstract: X-ray stress measurement, calculation of stress concentration factor by FEM, fatigue test, etc. were performed to confirm the effects of weld shape and residual stress on fatigue strength of mild steel non-load-carrying cruciform fillet welded joint.The results obtained are summarized as follows:1) A relief of residual stress at the toe by cutting off the large size cruciform fillet welded joint specimen to the small size specimen was about 40%, but the fatigue strengths of both cutting off small size specimen and as welded same size specimen were almost the same. Such a degree of relieving of residual stress by cutting off, therefore, can be considered to have no effect on the fatigue strength.2) By FEM analysis in the case of axial tension load, the following became clear: Stress did not flow into the rib (cruciform plates) outside fillets, and the stress concentration factor was less than 1.0 constantly at the weld root (tip of slit parallel to the direction of axial load), and on the other hand, was 1.7-2.3 at the weld toe.3) Using the stress concentration factor in profile of weld toe fatigue fractured pracitcally, and assuming the failure probability, it was found that the fatigue strength of mild steel cruciform fillet welded joint at 2 X 106 cycles could secure about 118MPa {12 kgf/mm2} at failure probability p=5%.4) It is possible to consider that a fatigue life of peened specimen is improved owing to compressive residual stress and work hardeness (increase of yield point), and decreased owing to increase of surface roughness (5-8 times that of before treatment; Rmax=1518 jem) caused by peening and that the synthetic effect of the former two exceeds the negative effect of the latter, and fatigue ilfe is improved after all.The effect of compressive residual stress decreased with increasing applied stress, and became uncertain at the applied stress over yield point.5) By re-peening before or after a initiation of small crack (1, is about 0.5 mm) fatigue strength was improved additionally. We may expect improving fatigue strength in the practical welded structure, therefore, by a practical application of re-peening.

High temperature high pressure steam turbine and its welding method

Abstract: PURPOSE:To enable the use of the steam of high temp. and high pressure by constituting the inner part casing and main steam pipe with austenitic stainless cast steel and by forming the structure of welding heat influence part in a fine recrystallized structure. CONSTITUTION:The welding of a main steam pipe becomes of the welding structure of austenitic stainless cast steel each other due to its being austenitic stainless cast steel. The whole face of the beveling surface on which welding heat is applied is first subjected to a plastic work in the execution of welding. The chisel peening method using the compressed air or shot peening method is preferable for the plastic work. The groove part is then subjected to build up welding 9 in about 2-5 layers after subjecting the beveling face to the plastic work. After the build up welding of the groove a joint welding 10 is executed. After the welding the annealing treatment for stress removel is executed at the prescribed temp. The structure of the welding heat affected zone being subjected to the peening treatment shows a fine recrystallized structure.

Surface treatment of metallic material and titanium alloy or the like

Abstract: PURPOSE:To increase the thickness of a residual compressive stress layer and to increase the residual compressive stress value by subjecting a metallic material to a peening treatment, heat treatment and peening treatment and subjecting further repeatedly the material to the heat treatment and the peening treatment. CONSTITUTION:The metallic material is subjected to the peening treatment under the condition of about 0.20mmA arc height value to increase the thickness of the residual compressive stress layer. The material is subjected to the heat treatment at 100-300 deg.C to fix the movable dislocation of the residual compressive stress layer after the above-mentioned 1st stage of the treatment and thereafter the material is subjected to the 2nd stage of the treatment for age hardening. The material is subjected to the peening treatment under the condition of the arc height value lower than in the 1st stage to increase the residual compressive stress value on the surface of the residual compressive stress layer as the 3rd stage. The material is subjected to the 2nd stage of the heat treatment and the 3rd stage of the peening treatment repeatedly successively to the above. The residual compressive stress layer having the excellent residual compressive stress distribution is formed by the above-mentioned method, by which the fatigue resistant characteristic, stress corrosion resistance characteristic, etc., of the metallic material are improved.

Improvement of the fatigue strength of aluminum alloy castings by shot peening and clarification of the improving factor.

Abstract: The employment of aluminum alloy castings for automotive parts is increasing every year, and recently some of them require relatively high fatigue strength. Under these circumstances, the improvement of their fatigue strength is an important problem to be solved.One of the authors has found that it is very hard to improve the strength, especially the fatigue limit of aluminum alloy castings, either by T6 treatment or by changing their chemical compositions. Although numerous literatures show that shot peening increases the fatigue strength of many metallic materials, few studies deal with aluminum alloy castings.In this study, the effect of shot peening on the improvement of the fatigue strength of aluminum alloy castings was examined first. Secondly, the improving factor of the fatigue strength of the shot peened castings was identified through the other experiments with the upset specimens of the castings, and finally an evaluation method for the fatigue limit of shot peened aluminum alloy castings was proposed. The following conclusions were derived from the present study:(1) The fatigue strength of aluminum alloy castings was able to be improved with shot peening.(2) The improving factor is a compressive residual stress at the surface layer resulting from shot peening, and the fatigue limit is evaluated by dealing with the residual stress as the mean stress during cyclic loading.(3) Hardening at the surface layer resulting from shot peening does not contribute to the improvement of fatigue strength in aluminum alloy castings.

A mechanical method for applying rapidly solidified metal coatings

Abstract: This paper describes a mechanical process of applying rapidly solidified (RS) metal coatings. The process comprises spraying a mixture of RS metal powder and peening particles at high velocity against the surface of substrates. By the impact of peening particles, the metal powder will be bonded to the surface and form a protective coating. Parts thus treated are expected to have not only improved corrosion resistance due to RS metal coating but increased fatigue strength by peening also. The apparatus and coating procedures are presented, and specimens of brass substrate coated with RS tin powder are shown as examples.

Eigenspannungsmessungen an unterschiedlich abgekohlten, kugelgestrahlten und torsionsschwellbeanspruchten Proben aus Federstahl

Abstract: Im Rahmen eines von der Arbeitsgemeinschaft Industrieller Forschungsvereinigungen geforderten Forschungsvorhabens wurden zahlreiche Torsionsschwellversuche an Rundproben mit 14 mm ∅ aus dem Werkstoff 55 Cr 3 durchgefuhrt Zur Interpretation der Schwingfestigkeitsergebnisse wurden Harte- und Kohlenstoffverlaufskurven in der Randschicht der einzelnen Probenvarianten aufgenommen und metallographische Untersuchungen vorgenommen [1] Um die Aussagefahigkeit der Schwingfestigkeitsergebnisse zu verbessern, wurde anschliesend ein reduziertes Programm zur Untersuchung der Eigenspannungszustande der wesentlichen Abkohlungsvarianten an Proben der gleichen Charge durchgefuhrt Uber die Ergebnisse dieser Eigenspannungsmessungen wird im folgenden ausfuhrlich berichtet, wobei zunachst einleitend die wichtigsten Parameter und Ergebnisse des Forschungsvorhabens zusammengefast dargestellt werden Residual Stress Measurements on Differently Decarburized, Shot Peened and Cyclic Torsional Loaded Specimens of a Spring Steel In addition to previous fatigue tests with the spring material 55 Cr 3, X-ray residual stress measurements were carried out on differently decarburized, shot peened and cyclic torsional loaded specimens It was shown that longer duration of decarburization leads to higher residual tensile stress in the surface zone for not peened specimens Shot peening, however, effects almost equal residual compressive stresses in the surface zone in spite of different starting conditions, with a slight decrease for specimens with a long duration of decarburization, which corresponds to the results of the fatigue tests By cyclic torsional loading with mean stress the residual compressive stresses due to shot peening are diminished in the axial and circumferential directions A main stress system is now to be found with an angle of 45° to axis, whereas the residual stresses in the s1-(tensile direction) retain their values, those in the s2-(compressive) direction are decreased distinctly

Quenching film-making method of polyamide series film

Abstract: PURPOSE:To enable static peening film-making of a polyamide series film through low electric current discharge which does not arrive in a streamer state, by providing an electrically-insulating coating on the surface of a cooling roll. CONSTITUTION:As for an elecrtrically-insulating coating, organic polymer materials such as fluorine series resin, acrylic series resin and polyester series resin or an electrically-insulating ceramic material such as Al2O3 are used by combining them, in a method making a polyamide series film, which has been molten, extruded and molded by die, adhere closely to a cooling roll by a static peening method and quenching. The quality of the material and a thickness of a coating layer are selected in consideration of terms that the coating layer is provided for dielectric breakdown voltage of more than 5kV and desirably further dielectric strength of more than 10kV in the first place. In this instance, a matter making apparent impression density less than 2muC/cm is a second reference in selecting the quality and thickness of the electrically-insulating coating. As for an electrode, a steel wire and tungsten wire whose diameter is 0.1-0.3mm are arranged above a position where the film contacts with the cooling roll and at a position 1-10mm away from the surface of the film.

Influence of plastic deforamtion by shot peening and of cyclic loading on the properties of the surface layer of 30KhGSN2A steel

Abstract: 1. The high effectiveness of repeated surface hardening, revealed in an increase in cyclic life of the high-strength steel, is caused by the high amount and depth of penetration of the first order residual compressive stresses (in comparison with the first peening) and by the significant changes in phase composition and fine structure of the surface layer of the material. 2. Cyclic loading of the material occurring before repeated peening intensifies the processes occurring in the surface layer in plastic deformation of it (decomposition of residual austenite and the martensite phase with precipitation of carbide particles, relaxation of local microstresses and a reduction in deformation nonuniformity of the structure, an increase in dislocation density). All of these processes promote an increase in the resistence to microplastic deformation and in fracture toughness and, consequently, lead to an increase in the resistance to the origin and development of fatigue cracks.

Variation of surface residual stress induced by shot peening.

Abstract: Several experiments were run to determine the relations between shot peening variables (shot size, shot velocity, impact angle, peening time) and surface residual stress. The surface residual stress was measured by X-ray diffraction method. The results are as follows : (1) The surface residual stress increases with peening time and then approaches a saturated value (-350-400 MPa) before full coverage. (2) Surface residual stress after full coverage depends slightly upon the shot peening conditions. (3) Surface residual stress shows the size effect to the thickness for the thin sheet of specimen. (4) Residual stress induced in the affected layer exists together with the non-affected zone and falls to zero where the depth of affected layer equals to the thickness of specimen.

Method for measuring residual stress-imparing depth

Abstract: PURPOSE:To calculate a residual stress-imparting depth in a surface to receive peening treatment from the relation between preliminarily calculated strain quantity and the residual stress imparting depth, by adhering strain gauges to the surface to receive peening treatment of a pipe material and the surface opposite thereto and detecting strain quantity. CONSTITUTION:In performing peening treatment by projecting shots 2 to the outer surface of a pipe material 1 to be treated, a strain gauge 3 is adhered to the surface opposite to the surface to receive peening treatment, that is, the inner surface of the pipe material 1 and the strain quantity generated by peening treatment is detected by a strain gauge 4 while peening treatment is performed. The relation between strain quantity and a residual stress- imparting depth is preliminarily calculated and the residual stress imparting depth is calculated on the basis of the strain quantity detected by the strain gauge 4. By this method, the residual stress-imparting depth can be determined during the peening treatment. Therefore, peening treatment can be rapidly controlled according to necessity.

Improvements in or relating to bearings

Abstract: A process is described for the production of bearings for sustaining high loads, the bearings having indentations (14, 32) filled with soft overlay alloy (13, 33). The indentations are produced by peening or embossing. The peening is preferably performed with rounded ceramic shot of 0.25 to 0.5mm diameter. Indentations should preferably be between 0.01 and 0.05mm deep. In one embodiment a bearing is described having alloy comprising a steel-backed (10) aluminium-based bearing alloy (11) having a composition of, for example, Al-Sn20-Cul and a soft Pb-SnlO overlay (13) there also being an interlayer of 3 to 5 um of nickel (12) between the bearing alloy and the overlay. Bearing surfaces having a continuous overlay or a composite surface comprising randomly-shaped areas of bearing alloy and overlay may be produced.

Materials technology applied to nuclear accelerator targets

Abstract: The continuing requests for both shaped and flat, very low areal density metal foils have led to the development of metallurgical quality, high strength products. Intent of this paper is to show methods of forming structures on various substrates using periodic vapor interruptions, alternating anodes, and mechanical peening to alter otherwise unacceptable grain morphology which both lowers tensile strength and causes high stresses in thin films. The three technologies, physical vapor deposition, electrochemistry, and chemical vapor deposition and their thin film products can benefit from the use of laminate technology and control of grain structure morphology through the use of materials research and technology.

Rotary peening device

Abstract: A rigid peening spindle for rotopeening the inside wall of a tube is disclosed herein. Generally, the peening spindle comprises a rotatable housing insertable within a tube, a mandrel disposed within the housing and having a plurality of peening flappers connected thereto, and a pair of bearings for rotatably mounting the mandrel within the housing in an off-center orientation relative to the longitudinal axis of the housing so that the peening flappers rotate and orbit within the tube when the mandrel and housing are simultaneously rotated. The housing includes a cage formed from an open section and a ligment, and the mandrel is rotatably mounted within the housing so that the peening flappers may engage the inside wall of the tube through the open section of the cage. Finally, each of the bearings which rotatably mount the mandrel in an off-center manner preferably have an outer diameter slightly larger than the outer diameter of the housing so that they may engage the inside wall of the tube in a running engagement within fairly tight tolerances, and thereby control the stand-off distance between the peening flappers and the inside wall of the tube. The bearings are preferably made from a self-lubricating plastic material. The invention is particularly useful in rotopeening the interior walls of the heat exchange tubes of a nuclear steam generator in order to prevent stress corrosion cracking in the tubes.