Electrical resistivity of fatigued copper crystals

Electrical resistivity of fatigued copper crystals

experimentally examined. In the form-rolling operation, lap defects at the tips of formed teeth can be prevented by increasing the infeed rate of roll...

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experimentally examined. In the form-rolling operation, lap defects at the tips of formed teeth can be prevented by increasing the infeed rate of roller dies and the heating depth of the blank before rolling. Lap and sinking defects at the roots of formed teeth can also be minimized by reducing the amount of metal flow in facewidth directions, increasing the rolling temperature and the tip radii for the roller die teeth as well as optimizing the indentation of the roller dies and improving lubrication. Short time reheating of formed gears at appropriate temperature is also found effective in refining the size of austenite grains formed during carburizing end to increase the bending fatigue strength of carburized and quenched gear teeth. 11 refs.

Influence o f surface rolling o n t h e f a t i g u e p r o p e r t y o f 3 5 C r M o V high strength steel. Lu, Y. and Wang, Y. Mater. Mech. Eng. (China) 13, (3), 4 6 - 5 1 , J u n e 1989 (in Chinese) The influence of surface rolling on the fatigue properties of 35CrMoV high strength steel is investigated. A special device which can accurately give rolling forces was designed. The test results show that an optimum fatigue property exists when the rolling force is increased adequately; it is due to the combined actions of surface hardening factors and surface detrimental cracks. According to fracture mechanics analyses, it can be considered that surface cracks are the primary factors which lower fatigue strength of specimens and components. Graphs, photomicrographs.

A n e w r o f i n i n g p r o c a s s for improving contact f a t i g u e o f bearing steel.

He, J., Huangfu, Q., Wang, C. and Wan, Y. Iron Steel (China) 23, (12), 5 8 - 6 1 , Dec. 1968 (in Chinese)

The effect of oxygen content and non-metallic inclusions in bearing steel on contact fatigue is discussed. The contact fatigue tests were carried out on bearing steels produced by three different processes. The results show that the bearing steel produced by the low basicity slag-Ar-blowing process gives better contact fatigue. The process has already been adopted in production. Graphs. 5 ref.

Joining Designing against f a t i g u e failure. Maddox, S.J. Met. Mater.5, (12), 727-731, Dec. 1989 Fatigue is the major cause of service failure in welded constructions, but it can be avoided by good design, The basic principles are described which govern the form of most modest fatigue rules for welded joints, and the present state of design codes related to welded components and structures is reviewed. The most recent codes and standards comply with a number of basic principles which have become internationally accepted as a sound basis for fatigue design rules. Graphs, photomicrographs. 21 refs.

Parameters affecting t h e r m a l f a t i g u e behavior of 60Sn-40Pb solder joints. Frear, D., Grivas, D. and Morris Jr, J. W. J. Electron. Mater. 18, (6), 671-680, Nov. 1989 Solder joints in electronic packages experience cyclical thermally induced strain when temperature fluctuations are encountered in service. This study investigates three parameters that affect the microstructure and therefore the thermal fatigue behaviour of 60Sn-4OPb solder joints. These parameters are: the effect of a tensile component in thermal fatigue, solder joint thickness variations, and hold time variations at the elevated temperature portion of the thermal cycle. Solder joints were thermally fatigued in a tension/compression deformation mode. Cracks developed both in the interfacial intermstallic layer (early in thermal fatigue) and in the coarsened regions of the microstructure of the solder joint (after many more cycles). The effect of joint thickness on solder joints thermally fatigued in shear was also explored. Solder joint thickness was found not to significantly affect fatigue lifetimes. The effect of an increase in the hold time at the elevated temperature portion of the thermat fatigue cycle was also investigated. It was found that time spent at the high temperature end of the fatigue cycle does not determine solder joint lifetime, rather it is the combination of the amount of deformation induced during thermal fatigue in concert with the elevated temperature. 20 refs. Fatigue life e s t i m a t i o n o f adhesive b o n d e d shaft joints. Imanaka, M.,

Electdcal

resistivity

o f f a t i g u e d copper crystals.

Basinski, Z.S. and

Basinski, S. J. Acta Metall. 37, (12), 3275-3281, Dec. 1989 Measurements made during fatigue at very low temperatures show that electrical resistivity saturates with the flow stress. The nat crystal defect content therefore roaches an equilibrium value. Isochronal anneal of the fatigued crystals shows no reduction of resistivity < 80 K, and < 4% reduction at 100 K. The fundamental fatigue mechanism operating at low temperature is thus unlikely to involve point defect recovery processes. The resistivity then decreases with increasing anneal temperature; at 300 K approx 40% remains. There is no correlation between resistivity anneal data and PSB profile shapes. Dislocation density in PSB walls, calculated from resistivity, exceeds that for which description in dislocation terms is valid; the material is dislocation-saturated. Such PSB wall material should behave as a perfect sink for dislocations, providing a natural explanation for fatigue saturation. Single crystals of Cu are studied. 23 refs.

Effects o f t e m p e r a t u r e g r a d i e n t and growth rate on the morphology and f a t i g u e properties o f MAR-M246(Hf). Schmidt, D.D., Alter, W.S., Hamilton, W.D. and Parr, R.A. NASA Marshall Space Flight Center Report No N89-29528/1/XAB Aug. 1989, 25 pp MAR-M246(Hf) is a Ni base superalloy used in the turbopump blades of the Space Shuttle main engines. The effects are considered of temperature gradient (G) and growth rate (R) on the microstructure end fatigue properties of this superalloy. The primary dendrite arm spacings were found to be inversely proportional to both temperature gradient and growth rate. Carbide and ?-~ morphology trends were related to G/R ratios. Weibull analysis of fatigue results shows the characteristic life to be larger by a factor of ten for the low gradient/fast rate repairing of G and R, while the reliability (13) was lower.

Precipitation s t r e n g t h e n i n g and its influence on t h e mechanical behaviour o f cysiically d o f o r m e d A I - L i alloys. Gudladt, H.-J., Lendvai, J. and

Schneider, J. Acta MetalL 37, (12), 3327-3333, Dec. 1989 The strengthening contribution of 5' precipitates in AI-Li alloys was determined from low cycle fatigue tests under plastic strain control performed on single-crystal and polycrystalline specimens. For underagad specimens the experiments show a plateau in the stress response for the first 10-100 cycles, which is independent of the plastic strain amplitude. These stress levels were compared with theoretical estimates of particle strengthening due to internal order where the volume fraction f and the mean particle radius r were the variables. Results of monotonic tests collected from the literature were also included in the analysis. Good agreement between theory and experimental results obtained from both cyclic and monotonic testing can be reached by assuming a specific antiphase boundary energy of 165 mJ m -z for the (111) planes. Aluminium alloy AI-8.4Li was studied. 31 refs.

Kishimoto, W., Okita, K., Nakayama, H. and Nagai, H. Int. J. Fract. 41, (3), 223-234, Nov. 1989

Fatigue tests and analytical investigations of adhesive bonded shaft joints were conducted to propose the estimation method of fatigue strength. Two kinds of adhesive bonded joint were studied: one, shaft joints connected with adhesive coupling, the other, adhesive joints of thin wall tubes to obtain standard fatigue stength. Both pulsating tensile and torsional fatigue tests were conducted with each adhesive joint. Furthermore, the stress distributions under tensile and torsional load conditions were analysed by the finite element method. Based on the analytically computed maximum normal shear stress in adhesive layer, fatigue strength of the shaft joints was standardized and compared with that of adhesive joints of thin wall tubes. As a result, it is confirmed that the maximum normal and shear stresses are key parameters for estimating fatigue strength under pulsating tensile and torsional load conditions, respectively. Furthermore, this study indicates an improved method of estimating fatigue strength by using tapered coupling in order to reduce the stress concentration at the end of the adhesive layer. The material mentioned was Inconel 718. 7 refs.

On stress distribution and fatigue strength of a single elliptical spotwelded lap joint under tension-shear load. Ho Bae Dong, Niisawa, J. and Koiso, A. Int. J. Veh. Des. 10, (3), 284-294, 1989 Stress distributions in a single elliptical spot-welded lap joint under tension-sheer load were investigated by the finite-element method. It was found that the maximum axial stress at the nugget edge of a laterally long elliptical nugget is lower than that of round nuggets with the same area. Using the maximum axial stress at the nugget edge as the fatigue strength, S-N curves of specimens with various dimensions and nugget ellipticities converge to nearly one line. 1 ref.

Evaluation of the fatigue strength of spot-welded assemblies taking into account t h e effect o f residual stresses. Le Duff, J. A., Masalski, D. and Duchanois, G. Soudage Tech, Connexes 43, (11-12), 15-30, Nov.-Dec. 1989 (in French) Following identification of the various parameters affecting the fatigue strength of spot-welded assemblies, tests on 8 mm rectangular single or multi-spot welded E24-3 steel plates of various dimensions are reported. The methods used to measure the joining stresses between welds in multi-spot welding and the residual welding stresses around a molten core in the fatigue crack propagation zone are described, followed by fatigue tests on as-welded and thermally stress-relieved test-pieces to examine crack initiation and propagation. Models evolved from the detailed results presented for the fatigue behaviour of spot-welded assemblies confirm the Wohler curves for these assemblies as valid parameters. It is concluded that (i) the crack propagation phase represents the fatigue life, (ii) the fatigue life is the same for the as-welded state as after stress relieving and (iii) the essential parameters affecting fatigue life are associated with the plate dimensions and the diameter, number and disposition of the welds and the distances between them. Graphs. 4 refs.

Copper single crystal PSB morphology b e t w e e n 4 . 2 - 3 5 0 K. Basinski,

Metallurgical methods for t h e differentiation b e t w e e n cold cracking and f a t i g u e cracking in a h i g h s t r e n g t h l o w alloyed steel w e l d e d structure.

Z,S. and Basinski, S.J. Acta Metall. 37, (12), 3263-3273, Dec. 1989

Ceqak, H., Horn, H. and Seibold, A. Prakt. Metallogr. 21, (10), 529-544, Oct. 1989

For fatigue at temperatures from 4.2-350 K, crystals in saturation comprise PSB and matrix regions; however, details of PSB morphology are tempereture-dependent. There are three main types of profile: Type h at very low temperatures, mildly bulged PSBs comprising smooth extrusions; Type Ih from approx 15-250K, triangular bulges reaching > 10 p,m in height; Type IIh > 300 K, non-bulged PSBs comprising both intrusions and extrusions. Transition regions with PSBs of mixed character are found between the distinct types. Room temperature is near the end of a transition region; PSB morphology therefore depends on fatigue conditions. PSB profile development is indepenent of fatigue environment; crack propagation is environment dependent. There is no correlation between PSB morphology and point defect mobility. 29 refs.

During in-service inspection, extensive cracks were found in the region of stiffeners to the supporting rings of a penstock that was part of a pumped storage plant and had been in service for about five years. The material of construction was a high strength, quenched and tempered, low temperature toughness steel Aldur 58/72, a steel similar to StE 580 V. A failure analysis determined that the cracks were a result of the fabrication process. Such cracks are known as cold cracks. The cause of cracking is interaction of the microstructure formed on welding, the hydrogen content of the welding consumable on the surrounding environment, and the internal stresses and welding parameters chosen. The cracks formed directly during welding or as delayed cracking thereafter and were present during subsequent stress relief heat treatment at approx. 530 °C. Photomicrographs. 9 refs.

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Int J Fatigue September 1990