Showing papers on "Shot peening published in 1970"

Machining of High Strength Steels with Emphasis on Surface Integrity.

Abstract: : As the strength level of High strength steels increases, fatigue and stress corrosion resistance exhibit a marked increase in sensitivity to surface conditions produced in machining. There are several significant surface alterations produced in machining which can seriously affect fatigue and stress corrosion resistance. These include untempered martensite, overtempered martensite, plastic deformation, cracks, tears, laps, burrs, spattered or redeposited metal, and residual stress. The effect of machining conditions on the formation or avoidance of these surface alterations is discussed in detail. Machining relationships and recommendations are given for chip removal operations, abrasive operations, as well as nonconventional operations, to minimize surface alterations. To maintain high surface integrity in milling, turning, drilling, etc. machining conditions are selected to provide long tool life. In addition, tools must be kept sharp, that is, tools must be changed frequently to minimize metallurgical alterations within the surface layer. In grinding, low wheel speeds, light down feeds, together with the use of highly active cutting oils are necessary to minimize surface alterations. Post-operative machining processes, such as heat treatment and shot peening are often needed to obtain desirable surface conditions. Rigid inspection techniques and often repair procedures are required to insure proper surface integrity. Particular attention is given to the problem of drilling and reaming holes with high surface integrity in high strength steels. (Author)

Apparatus for shot-peening turbine blades

Abstract: A turntable having a number of pairs of apposed resilient gripping members mounted on nested ring members, one of the rings having its axis eccentrically translatable relative to the other, the translatable ring being pressure-biased in one direction transversely to its axis so that the space between the rings is greater at one end of a diameter to allow loading of workpieces between gripping members, the space closing with rotation of the rings to provide a firm grip of the workpieces passing through a subsequent peening zone, a portion of each workpiece being exposed to peening action and a portion shielded therefrom.

Shot peening apparatus

Abstract: A shot peening apparatus includes a bank of a plurality of commonly mounted centrifugal shot throwing wheels and also includes a free moving centrifugal shot throwing wheel.

Shot peening method

Abstract: Metal sheets are peen formed by projecting peening shot from centrifugal shot throwing wheels against the sheet passing thereunder. The centrifugal shot throwing wheels are also used for saturation peening metal objects.

A Survey Of Surface Treatments To Improve The FrettingFatigue Resistance Of Ti-6Al-4V

Abstract: The effects of surface modification treatments such as shot peening, ion implantation (carbon and nitrogen), surface lubrication (soft coating), laser gas nitriding and various combinations thereof, on the fretting fatigue resistance of Ti-6Al-4V have been investigated. The best of these surface treatments appears to be shot peening. While ion implantation improves the base metal fretting fatigue resistance to some extent, the fretting fatigue life of shot peened Ti-6Al-4V is reduced by the ion implantation treatment or the application of a soft coating. The fretting fatigue life of laser nitrided Ti-6Al4V is inferior to that of the base metal and this occurs as a result of the inferior surface finish and brittle nature of the nitrided surface.

Effect Of Shot Peening And Post-peeningheat Treatments On The Microstructure, Theresidual Stresses And Hardness, Corrosionand Deuterium Uptake Resistance OfZr-2.5Nb Pressure Tube Material

Abstract: The effect of shot peening and post-peening heat treatment on the microstructure, the residual stresses, hardness, corrosion and deuterium uptake behaviour of Zr-2.5Nb pressure tube material has been evaluated. Shot peening produced a heavily cold-worked microstructure, with the original grain structure completely obliterated by the shot-peening process. Shot peening also caused a change in the texture of this material. Heat treating shotpeened specimens at temperatures from 670 to 770 K caused recrystallization of the cold-worked surface layers and breakup of the grain-boundary 0-phase network. The recrystallization is accompanied by precipitation within the a-Zr grains of fine uniformly distributed Nb-rich 0-phase particles and the reduction in the Nb supersaturation of the a-Zr phase from =1.5 to =0.5 at.% Nb. Shot peening produced an improvement in the corrosion and deuterium uptake resistance of Zr-2.5Nb pressure tube material. The improved corrosion and deuterium uptake resistance was attributed to the intense cold work and to microstructural changes produced by shot peening and post-peening heat treatments.

Multiple Shot Analysis In Shot-peeningUsing Finite Elements

Abstract: A computer program OB AID has been used to analyze complex target plate and allows for dynamic loading due to impinging single and multiple shot. Theoretical model using three dimensional isoparametric finite element has been presented, in which a provision is made for the surface hardening and cyclic impact loading caused by multiple shots. Theoretical model agrees reasonably well with other models. INTRODUCTION Shot peening is viewed as a process involving multiple and progressively repeated impact. The object is to include compressive residual stresses in the surface of the target. A general form of residual stress in a typical shot-peening operation is shown in Figure 1. The impact of spherical shots, which usually takes place at a high velocity 100 m/sec, also causes plastic deformation which results in changes in the mechanical properties in the surface material. An extensive work has been carried out by several authors [1-12] to model the process. An attempt to modelize the process, in viewing as process involving multiple repeated impact. When shots impinge upon a target of elastic/plastic material and the impact velocity is sufficiently high, the target material below each impact undergoes local plastic deformation and, upon rebound, the rest of the elastic material tends to push the plastically deformed zone resulting in compressively applying numerous impacts over the whole surface, the target acquires a shallow layer of superficial compressive residual stress below which it develops smaller equilibrating tensile stresses. This paper attempts to present theoretical model using three dimensional isoparametric finite element, as will be seen, it surprisingly agrees reasonably well with other model. [1,2] THREE-DIMENSIONAL FINITE ELEMENT MESH GENERATION The finite element mesh for the target plate is shown in Fig. 2. In order to produce accurate residual stresses, it has been decided to divide the thickness of the target steel plate into nine layers (in the Y-direction). The plate thickness below the Transactions on Engineering Sciences vol 2, © 1993 WIT Press, www.witpress.com, ISSN 1743-3533

Superfinishing And Shot Peening Of Surfaces ToOptimise Roughness And Stress

Abstract: Residual stress and surface roughness significantly affect component performance For many years, Engineers have designated roughness constraints on drawings with little heed to residual stress Fortunately this is changing as industries become aware of the significance of each and both are designated in critical applications Superfinishing is developing as a post Shot Peening treatment in situations where metal to metal contact occurs, high temperature or fluid flow and/or optimum performance is required Consequently the combination of residual stress and roughness control are essential on certain applications

Laser shock processing of low carbon steel

Abstract: The effect of laser shock processing (LSP) on the microstructure and mechanical properties of the low carbon (0.04 wt % C) steel was studied. LSP was performed with a 1.054 ^m wavelength Ndrphosphate laser operating in a pulse mode (600 ps duration and up to 200 J energy with a 3 mm diameter beam) with power densities above 10* * W/cmA Shock waves were generated by volume expansion of the plasma formed when the material was laser irradiated. Maximum shock wave intensities were obtained by not using a plasma-confining overlay. When an energy-absorbing black paint coating was used, the specimen surface yielded LSP-induced deformation without melting. The maximum pressure we were able to generate was approximately 2.5 GPa. The rise-time was about 25 ns and a generally 140 ns decay of the laser-shock wave followed. Mechanical properties of material such as surface hardness and residual stress were improved through modifying the microstructure by shock waves. The microstructure of low carbon steel was shown to be strain rate dependent; high density dislocation arrays (~10Wcm.2) were generated by LSP due to high strain-rate deformation and dislocation cell substructures were produced by the low strain rate deformation of shot peening and cold rolling. Strengthening of low carbon steel was a function of dislocation density regardless of processing method.

Fatigue Performance Of A Shot PeenedHigh-strength Magnesium Alloy

Abstract: The effect of peening medium and Almen intensity on fatigue performance of the high-strength magnesium alloy AZ 80 was studied in air and in aqueous NaCl solutions. When tested in air, the fatigue life given Almen intensity was independent of the peening medium However, the Almen intensity had a very significant effect, causing dramatic improvements in fatigue life at low intensities while hardly any improvement was found at higher intensities. For tests in aqueous NaCl solutions, peening with glass beads was superior to steel shot, presumably due to iron contamination of the magnesium surface and its effect on the resistance to corrosion fatigue crack nucleation. Reducing the process-induced roughness by polishing after heavy shot peening markedly improves fatigue performance in air as well as in aqueous NaCl solutions. Transactions on Engineering Sciences vol 25, © 1999 WIT Press, www.witpress.com, ISSN 1743-3533

The Effect Of Shot Peening On The Stress Corrosion Cracking Resistance Of 304 Stainless Steel Immersed In Nacl Solution

Abstract: Corrosion can deteriorate the material as a result of reaction with its environment. It is one of the major problems encountered in industry and it does cost the world billions of dollars every year. Substantial savings can be obtained in many types of plants through the use of corrosion-resistant materials of construction. Pitting, corrosion and stress corrosion cracking can lead to catastrophic unexpected failures to many engineering applications. Resistance to stress corrosion cracking and pitting can be greatly increased by a cold working process called shot peening. The present experimental work aimed to evaluate the effect of shot peening on retarding pitting, and enhancing the stress corrosion cracking resistance of 304 stainless steel, in a sodium chloride solution (NaCl) at 60 o C. The results obtained indicated that shot peening is beneficial against corrosion fatigue. Also it is found from the results that increasing intensity and coverage of shot peening will lead to an increase in corrosion resistance.

Influence Of Shot Peening And High PressureWater Peening On Near Surface MicrostructureOf 316 Ti Stainless Steel

Abstract: Recent investigations on the influence of mechanical and thermal loading on the stability of residual stresses in surface layers have shown a different relaxation behaviour of shot peened and high pressure water peened specimens. For this reason a stainless steel of type 316 Ti (1.4571) after shot peening and also high pressure water peening was investigated with the aim to characterize the microstructure of near surface areas by TEM-investigations. With the presented experimental results the effect of peening processes can be evaluated.