Improvement Of Fatigue Properties Research Articles

Improvement of fatigue properties of poly(methyl methacrylate) bone cement by means of plasma surface treatment of fillers

Improvement of fatigue properties of poly(methyl methacrylate) bone cement by means of plasma surface treatment of fillers

The effect of interfacial state on electrical properties of PZT-electrode system for applying to nonvolatile memory devices

The ferroelectric property of Pb(Zr x Ti 1 − x )O 3 (PZT) films have been reported to be greatly dependent on the interfacial state between PZT and electrode. However, the interfacial state of this system is not studied well and much is not known. In this study, we investigated the effect of phase, compositional and interfacial states of PZT-Pt bi-layered thin film system on its electrical properties using X-ray diffractometer, X-ray photoelectron spectroscopy, Auger electron spectroscopy and Rutherford backscattering spectrometry. The improvement of fatigue property after the post-anneal could be explained based on the space charge layer model. During the post-anneal, the decomposition of α-PbO 2 phase was observed. This compensates the loss of Pb and O in PZT near the interface which can cause space charge accumulation and fatigue. And also the reduction of Pt oxide was observed which induces the ideal interface state.

Effect of casting technique on fatigue properties of hot isostatically pressed Al-10Mg castings

The fatigue properties of Al-1OMg (wt-%) castings have been shown to be improved by hot isostatic pressing (hipping) with a level of improvement highly dependent on the initial quality of the castings. Only castings with low oxide inclusion levels were found to show a significant improvement infatigue propertiesjollowing hipping. To reduce the oxide inclusion content a casting technique has been developed in which the molten aluminium is tapped from the bottom of an induction melting furnace. The average fatigue life (at a test stress amplitude of 106 MN m−2) increased from 213×103 to 1016×103 cycles following adoption of the bottom tapping technique. Hipping of the bottom tapped castings produced a further increase in the average life to at least 15×106 cycles. These substantial improvements in fatigue properties can be attributed to a reduction in the size and quantity of oxide inclusions in the bottom tapped castings. Unless the oxide inclusion content of the castings can be maintained at a sufficiently low level the optimum properties will not be obtained after hipping and the repeatability in the mechanical properties of hipped castings, necessary for confidence in design, will be poor.MST/3186

Effect of strontium modification on near- threshold fatigue crack growth in an Al-Si-Cu die cast alloy

The effects of strontium modification on microstructure and fatigue properties in a die cast com-mercial aluminum-silicon alloy are demonstrated. Strontium additions of 0.010 and 0.018 wt pct drastically change the morphology of the eutectic silicon. The influence of these microstructural changes on fatigue properties is evaluated through fatigue crack growth testing. Examination of the fracture surfaces and the crack path establish distinct fatigue fracture modes for the modified and unmodified eutectic structures. Changes in fracture mode and crack path are correlated to the mi-crostructure changes. A higher energy fracture mode and increased crack path tortuosity explain the observed improvement in fatigue properties for the modified alloys. Strontium modified alloys exhibit a 10 to 20 pct higher fatigue crack growth threshold compared to an unmodified alloy for testing at a load ratio of 0.5. No difference was observed for testing at a load ratio of 0.1.

Improvement of fatigue property of AI/CFRP hybrid composite material by residual stress control: Haga, O., Koyama, H., Kawada, K. and Ogawa, K. J. Soc. Mater. Sci. Jpn Mar 1992 41, (464), 734–739 (in Japanese)

Improvement of fatigue property of AI/CFRP hybrid composite material by residual stress control: Haga, O., Koyama, H., Kawada, K. and Ogawa, K. J. Soc. Mater. Sci. Jpn Mar 1992 41, (464), 734–739 (in Japanese)

Ion implantation effects on fatigue properties of Fe-13Cr-15Ni alloys

Bend fatigue tests and microhardness measurements were carried out on eight complex Fe-13Cr-15Ni alloys based on the composition Fe-13Cr-15Ni-2Mo-2Mn-0.2Ti-0.8Si-0.06C, implanted simultaneously with 400 keV boron and 550 keV nitrogen ions to a dose of 2.3 × 10 16 ions cm -2 for each ion. For all eight alloys, the dual implantation improved the surface hardness but reduced the fatigue life. Optical microscopy revealed that the implantation suppressed surface slip band formation and slip band crack initiation. Transmission electron microscopy was used to characterize the near-surface microstructures. It is evident that the suppression of slip band formation promoted grain boundary cracking to relieve stresses developed in the grains, thus leading to a reduced fatigue life. A similar study of four simple alloys based on the ternary Fe-13Cr-15Ni indicated that while dual implantation improved fatigue life, up to 250% in one case, triple implantation with boron, nitrogen and carbon ions reduced fatigue life, again owing to a shift to grain boundary cracking. Improvement in fatigue properties of polycrystalline alloys by multiple ion implantation is thus limited by the presence of grain boundaries.

ばね鋼の曲げ疲れ強さに及ぼす超清浄化の影響

There is a recent tendency to develop a motorcars suspension coil spring that can be used under higher-stressed condition and to develop a valve spring having a higher-level of strength therefore creating better engine performance. Since there is a difference between the required fatigue strength level of suspension coil spring and valve spring steel, improvement of fatigue property is a common destination. In order to achieve this purpose, ultra clean steel is considered to be one of the effective methods.The degassing process for producing ultra clean steel satisfies the needs for low cost and mass production. Ultra clean steel is examined and tested as to the properties required for valve spring and suspension coil spring steel. The following results are obtained.(1) Ultra-Low-Oxygen steel (ULO steel) with oxygen content less than 15ppm is confirmed one of the effective means to realize a suspension coil spring satisfying 200kgf/mm2 high stress level.(2) ULO+UL·TiN steel produced by ultra low oxygen and ultra low TiN process exhibits almost the same endurance limit as the Vacuum Arc-furnace Remelted steel. Therefore, this steel is found to be applicable to high strength valve spring.

Structure-property relationships in graphitic cast irons

Some techniques used to study fatigue of cast irons are discussed and used to study the structure-property relationships in graphitic cast irons. A wide range of cast irons have been assessed to give a better understanding of the effects of metallurgical structure and graphite morphology on the fatigue behaviour of these materials. It is concluded that the ‘true’ fatigue strength reduction factor is one of the most significant parameters by which to consider improvements in fatigue properties. Increasing the amount of spheroidal graphite is suggested as a method of improving the fatigue properties of CG cast irons and yielding alloys with great potential importance.

Fatigue of nitrided En41B steel: effect of internal-stress distribution

AbstractThe axial fatigue properties of nitrided En41B steel specimens of differing diameters but with constant case depth have been studied. The tensile residual stress in the specimen core is increased as the case/core area ratio rises. No relaxation of these stresses was detected after stressing close to the fatigue limit, although at higher stress levels a 10% reduction was measured after 50% of the expected fatigue life. Significant improvements in fatigue properties were observed after nitriding; close to the fatigue limit the greatest improvement occurred in larger (5 mm dia.) specimens, but the smallest specimens (3 mm dia.) showed the greatest increase in fatigue strength at lives below 105 cycles. The mechanisms of failure were identified metallographically in each case; Yielding of the core occurs when the sum of the applied tensile stress and the axial core residual stress exceeds the yield stress of the non-nitrided material, and this leads to a redistribution of stresses between case and cor...

Microstructure and fatigue of a Ni,Cr, Al-TaC eutectic composite

The Ni,10Cr,5Al-TaC aligned eutectic has been heat treated subsequent to solidification to produce several microstructural conditions. High cycle fatigue tests have been conducted at 25 and 825°C, while creep tests were performed at 825 and 950°C. Experimental variables in the fatigue tests were stress level, test frequency, and environment. Post solidification heat treatments caused substantial improvements in fatigue properties at 825°C, but had little effect at room temperature. Elevated temperature fatigue lives were substantially reduced at low test frequencies in vacuum, accompanied by a shift from external to internal crack nucleation sites. Dislocation substructures produced in high temperature fatigue tests resembled those of creep specimens.

Ambient temperature crack growth in titanium alloys and its significance for aircraft structures

Modern technology places great demands on structural material performance. Until the 1950s, structures were invariably designed according to safe-life principles, for which a crack-free service life was required and assumed. However, the tendency to much longer utilisation of aircraft, and latterly the introduction of high strength materials, have focused attention on damage tolerant design in which allowance must be made for possible cracking and its certain detection before catastrophic failure. Especially for high strength materials is this change in philosophy necessary, because the improved static strengths (and hence potentially increased structural efficiency) rarely result in comparable improvements in fatigue properties, and are usually accompanied by a decline in fracture toughness and in greater susceptibility to environment-induced cracking.

Low cycle fatigue, fatigue crack propagation and substructures in a series of polycrystalline Cu-Al alloys

Low Cycle Fatigue (LCF) on smooth hour glass specimens and Fatigue Crack Propagation (FCP) studies on Single Edge Notch (SEN) specimens were carried out at room temperature on four Cu-Al polycrystalline alloys to investigate the effects of Stacking Fault Energy (SFE) and mechanical property variations on fatigue characteristics. Significant improvements in fatigue properties were observed for alloys of low SFE. A microhardness technique was used to delineate the fatigue plastic zone ahead of stopped cracks at several stress intensity ranges for all the alloys. Planar slip was associated with a less than a second power dependence of plastic zone size on the stress intensity range. Transmission Electron Microscopy (TEM) was used to observe the substructures that developed both in LCF at different strain ranges and also ahead of fatigue cracks at different stress intensity ranges. Fractography was carried out to study the micromechanisms of crack propagation using a two stage replication technique. The experimental results were in good agreement with a theoretical model for FCP developed previously by the authors which incorporates mechanical and microstructural variables.

Improvement of Fatigue Properties of Springs made of 17-7 PH Stainless Steel Wire by means of Low Temperature Cyaniding

Improvement of Fatigue Properties of Springs made of 17-7 PH Stainless Steel Wire by means of Low Temperature Cyaniding

Effect of Highly Polarizable Ions on the Strength Retention of Glass Fibers

An investigation has been made of the possibility that polarizable ions in the surface of glass might retard the hydrolytic stress corrosion considered responsible for the gradual loss of strength of glass fibers under stress (static fatigue). Techniques were developed for simul taneous testing of large groups of glass fibers in bending. Fatigue tests covering the loss of strength over seven decades of log time were carried out. Fibers drawn from a specially prepared glass in which the highly polarizable Pb ++ ion was substituted for Ca++ and Mg++ in "E" glass were compared with "E" glass control fibers. The Pb-containing glass showed no significant improvement in fatigue properties.

On the Fatigue Strength of High Cr Steels Nitrided in the Salt Bath

The salt-bath nitriding is used widely today because it has an advantage of shorter treating time than the conventional nitrding process. We studied the effect of this process on the improvement in fatigue properties of high Cr steels, and clarified various features of hardened case by metallographic and X-ray diffraction tests.The results obtained are as follows:(1) The extremely hard compound layer produced in the surface of austenitic high Cr steel (SEH 4 or 21-4N) during the salt-bath nitriding at 570°C contains a large amount of Cr-nitrides and Cr-carbides. In ferritic high Cr steel (SEH 3), however, the formation of Cr-compound is less than in austenitic one, and it is found by X-ray diffraction analysis that the lattice in surface zone is distorted considerably after this treatment.(2) The salt-bath nitriding improves remarkably the rotating bending fatigue strength of SEH 3. But this process is not so effective for the improvement of fatigue strength of SEH 4 or 21-4 N.(3) In the welds of SEH 3 and SEH 4, in which the rupture occurs usually in SEH4 side during the fatigue test, the fatigue behavior of the welds before and after the nitiriding is almost equal to that of SEH 4 base material. On the other hand, it is found that this process is not always effective for improving fatigue characteristics in the welds of SEH 3 and 21-4 N, in which the rupture occurs usually in the weld zone.(4) Tufftride process which employs the salt-bath consisting mostly of potassium cyanide and cyanate has a more pronounced effect on the improvement in fatigue strength of high Cr steels than the domestic process.