Showing papers on "Peening published in 1979"

Surface residual stresses, surface topography and the fatigue behavior of Ti-6AI-4V

Abstract: Fatigue tests have been conducted on Ti-6Al-4V from 293 to 589 K to determine the influence of surface residual stresses and surface topography on low and high cycle fatigue properties. Four types of machined surfaces as well as shot peened surfaces were included in the investigation. It was found that surface residual stresses play a key role in controlling the development of microcracks and, therefore, overall fatigue lives at both room and elevated temperature. X-ray measurement of the stability of surface residual stresses under thermal activation and/or cyclic loading demonstrated that, for the conditions studied, cyclic loading was primarily responsible for residual stress decay. In addition, the magnitude of the decay was dependent on the relationship between the sign of the residual stress and the sign of the imposed mean strain. Finally, it was demonstrated that the sharpness of machining grooves is more important than their depth in controlling fatigue resistance.

Subsurface crack initiation during fatigue as a result of residual stresses

Abstract: — The influence of shot peening on the bending fatigue strength of hardened specimens of a carbon steel is reported. Effects of residual compressive stresses after shot peening, as a function of distance from the surface, are discussed along with the evidence of scanning electron micrographs from fractured specimens. Subsurface crack initiation is reported at all stress amplitudes below a threshold value of 1100 N/mm2. Assuming that the fatigue strength is enhanced locally due to compressive residual stresses the experimental results can be explained with the aid of the Goodman relationship.

Shot peening to prevent the corrosion cracking of austenitic stainless steels

Abstract: Rockwell International and Metal Improvement Company have conducted a joint test program to develop shot peening as a technique for preventing corrosion cracking in austenitic stainless steels Initial laboratory-scale tests demonstrated the feasibility of preventing stress corrosion cracking by shot peening to impose compressive stresses on the surface of the work pieces Conventional U-bend test specimens, when peened, survived 1000 h tests in the boiling 42 pct magnesium chloride stress corrosion test Unpeened reference specimens commonly fractured within one or two hours in this test Component tests were conducted to demonstrate the practicality of the peening process for sizes and shapes that typify components in a reactor piping system Pipe sections and cold worked, hexagonal tubes were tested In all components, unpeened sections developed stress corrosion cracks within a few hours in the magnesium chloride test; in contrast, the shot peened surfaces survived hundreds of hours It was discovered at Rockwell International that intergranular corrosion can be prevented in austenitic stainless steels by severe shot peening prior to exposure to sensitizing temperatures For this purpose, the surfaces must be severely cold worked by the shot peening to break up surface grains and grain boundaries Two nondestructive testing techniques show promise as methods for measuring the stresses or cold work imparted on the surface of the work piece by peening In one method, eddy currents are used to measure differences in electrical properties induced by cold working of metals Another is a magnetic technique which measures the changes in magnetic properties due to the transformation of austenite to ferrite by cold working

Effect of residual stresses of shot peening on the fatigue behaviour of a high strength steel

Abstract: — The effects of shot-peening residual stresses on bending fatigue behaviour of welded plate and surface-flawed plate were investigated. The results show that shot peening residual stresses may significantly increase fatigue strength as well as the threshold stress- intensity factor range of a surface-flawed plate. This paper presents a simple analytical method for determining the residual stresses. The calculated values are essentially in agreement with the experimental results.

Hardening method for surface of turbine blade

Abstract: PURPOSE: To prevent the erosion due to drain and the stress corrosion cracking of turbine blade, by flame hardening the surface of an erosion-preventive layer of a turbine blade, then by tempering said surface at a specific temp., and by shot peening it. CONSTITUTION: Erosion-preventive layer 13 in the range of L 2 length from the steam inlet side top end, which is liable to be eroded by drain, of a turbine blade 7 is flame hardened at 1,000W1,600°C temp. using a heating burner A. Then it is tempered at 500W600°C temp. for about 3hr for the purpose of the regulation of hardness and uniformalization of the distribution of carbide. The erosion-preventive layer has 600W700 Vickers hardness. Finally compressive stress is given to the surface by shot peening. COPYRIGHT: (C)1981,JPO&Japio

Fatigue research with discriminating specimens

Abstract: When more than one variable has an effect on fatigue life, a test with a suitably designed specimen can discriminate between theories of interaction as to their correctness. A small number of tests can determine the interaction coefficient. This paper discusses the application of such specimens to discriminate between three theories for out-of-phase torsion and bending. It also shows applications of such specimens to determine the increase of bending fatigue strength by peening, to determine the mean stress effect on bending fatigue, and to discriminate between the maximum shear stress and the octahedral shear stress as criteria for in-phase bending and torsion. The advantages of discriminating specimens are explained.

Method of treating ingot moulds.

Abstract: To overcome various problems associated with moulding of steel, the moulds (5) are shot peened in between casts using an air-blast system which incorporates a compressor (4), a shot recovery and supply system (2), a dust collector and control section (3, 3 min ) and a peening/cleaning station (1) which has a nozzle assembly (9) arranged to traverse the length of a mould (5) whilst rotating and simultaneously firing shot at the interior mould surfaces to achieve a peening effect.

Pressure pipe made of zirconium alloy

Abstract: PURPOSE:To provide a pressure pipe made of Zr alloy used for heavy water reactors or the like with a protective oxidized film on the surface of the body maintaining residual compressive stress through a hot water autoclave treatment at a temperature lower than that of relaxation following peening of the surface. CONSTITUTION:After a drawing of the body of a pressure pipe, a shot peening is applied to smooth fine cracks on the surface thereof employing a steel ball or the like while a residual compressive stress is given up to about 1 mm under the surface. Then, the body of the pipe is inserted into a hot water autoclave and retained for about 5 hours at a temperature below 400 deg.C under which a creep deformation is hard to take place whereby a protective oxidation film 3 is formed on the surface of the body. This makes the residual compressive stress by the peening larger than the stress W' when an inner pressure P is applied on the body of the pipe. Consequently, the inner surface thereof is invariably subjected to a compressive stress allowing hydride 2 to be parallel to the stress thereby minimizing the possibility of flucture due to a delay in hydrogen. In addition, oxidation by cooling water can be prevented.

Fatigue properties of welded roller-quenched and tempered (rq) steels

Abstract: Axial fatigue tests were performed on unwelded and welded roller-quenched and tempered carbon and alloy steels in order to study the effect of stress ratio, weld geometry, base metal tensile strength, and weld peening on the fatigue resistance of submerged-arc transverse butt welds in 3/4-inch-thick plates. Test results showed that the constant amplitude long-life fatigue resistance of transverse butt welds with reinforcement intact was insensitive to stress ratio and was primarily a function of stress range. The fatigue resistance of transverse butt-welded constructional steels with reinforcement intact was practically independent of tensile strength. Reinforcement removal, however, increased fatigue resistance to that of the unwelded base material at long lives. Doubling weld reinforcement height reduced the fatigue strength of transverse butt welds at two million cycles by about 67%. Neither short nor hammer peening of transverse butt welds with reinforcement intact significantly improved fatigue resistance. Improvement in transverse butt weld fatigue strength was best achieved by removing weld reinforcement, i.e., by reducing mechanical notch severity; this restored the pulsating tension fatigue strength to that of the unwelded material at lives greater than 400,000 cycles.