Plasticity-induced compressive residual stress effects in fatigue and corrosion fatigue
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Corrosion Fatigue
Goodman relation
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An experimental investigation was made to determine the effect of the initial or residual stress state on rolling element fatigue life. This was done by simulating a residual stress by a mechanically applied static stress. Hoop-shaped specimens were statically stressed in both a tangential direction and a transverse direction to simulate either a biaxial tension or biaxial compression stress state and then subjected to repeated rolling contact until failure occurred. The results showed the rolling element fatigue properties for the compression state is not significantly better than the “zero” stress state, contrary to widely held opinion, and that the tensile state is detrimental to fatigue properties as expected.
Tension (geology)
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Surface integrity is a subject covering the description and control of the many possible alterations produced in the surface of a component during manufacturing. Surface integrity is evaluated by measuring the influence of machined surface layers on component reliability. This is accomplished primarily through fatigue testing under both low-cycle and high-cycle conditions. Considerable data have been developed permitting definition of characteristic changes in fatigue strength of a variety of high-strength structural alloys as a function of several different metal removal methods and also variations within these methods. High-cycle fatigue data have been developed in the cantilever bending mode at temperatures ranging from ambient to 1400 F. Low-cycle fatigue data have been obtained in four-point bending over the same temperature range following the development of a specialized testing technique. Data are presented showing fatigue behavior of Inconel 718, René 80, and René 95 using specimens finished by variations of grinding, turning, electrochemical machining, and electrical discharge machining.
Surface Integrity
Inconel
Fatigue limit
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Fatigue limit
Titanium alloy
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The plastic strain energy required for failure in low-cycle biaxial fatigue is estimated using the energy in uniaxial fatigue and assumptions from the theory of plasticity. A criterion for high-strain multiaxial fatigue of the form Δε¯pΔσ¯=KNƒc is developed, where the equivalent stress amplitude Δσ and the equivalent plastic strain amplitude Δεp are based on the von Mises yield function of plasticity. The parameters K and c are assumed to depend on the mechanical properties of the material and to be functions of the stress ratio. These functions can be evaluated from uniaxial fatigue data and are compared with tests performed on thin-walled tubes of mild steel at different stress ratios. The proposed criterion seems to yield a promising approach for the low-cycle fatigue analysis of metals under biaxial states of stress.
Low-cycle fatigue
Strain (injury)
Goodman relation
Strain energy
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A theoretical analysis of uniaxial cumulative fatigue damage is presented together with a large number of experimental results on unnotched specimens of A-201 and A-517 steels. The theory developed permits the prediction of fatigue curves for stress-controlled conditions with zero or positive mean stress as well as the evaluation of the damage accumulated during a fatigue test and hence the prediction of the remaining life of a specimen. Theory is in good agreement with the experimental results as well as with published data on other materials. The development may be extended to other types of tests such as strain-controlled or random loading conditions.
Vibration fatigue
Goodman relation
Stress–strain curve
Fatigue limit
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For pure rolling fatigue conditions, the effect of microstructural changes and internal stresses due to grinding and fatigue processes itself was studied. Using Sachs’ method, the field of internal stresses was determined and it has been shown that its evolution is correlated with microstructural changes. These microstructural changes lead to changes in mechanical properties, especially to the reversible strain limit stress (R.S.L.S.) which has been determined in each point of the subsurface contact. Assuming a given relation between R.S.L.S. and fatigue limit, and using fatigue criterion which includes R.S.L.S., the effect of internal stresses, microstructural evolution, and Hertz stresses was analyzed. It has been found that the grinding internal stresses have no significant effect. On the contrary, the R.S.L.S. value was strongly reduced by grinding thermal effect in subsurface region, and was also strongly changed by the fatigue process. Finally, this analysis method was used to determine the best field of internal stresses necessary to minimize the fatigue damage.
Internal stress
Fatigue limit
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Open link lifting chain is routinely proof loaded during manufacture. However, the effect of residual stresses imposed by this operation on the fatigue strength of the chain has not been quantitatively investigated. This paper discusses the results of constant amplitude fatigue tests on open link chain segments which have received proof loading at various levels. The chain was initially heat treated to relieve manufacturing residual stresses and then proof loaded at levels ranging from 0 to 82 percent of its break strength. Tests were performed at two different mean loads and four different load amplitudes. Failure site trends are noted as a function of applied loading and are correlated with results of a finite element stress analysis. Residual stresses are estimated using strains measured from strain gages placed at critical locations on individual links during the proof load operation. Residual stress estimates are used with standard fatigue damage parameters to estimate the fatigue life of the chain and predictions are compared to data. Proof loading was shown to substantially increase the fatigue life of the chain. Residual stresses can explain the increase in fatigue life. Neuber’s rule demonstrated the ability to model the data trends.
Chain (unit)
Fatigue limit
Vibration fatigue
Residual strength
Strain gauge
Goodman relation
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An energy-based framework is developed for welded steel and AL6061-T6 for assessment of nonlinear evolution of fatigue damage accumulation along fatigue life. The framework involves interrogation at continuum using a newly developed experimental procedure to determine the cyclic damaging energy to reveal that the accumulated fatigue damage evolves nonlinearly along cycle in case of low cycle fatigue but has somewhat linear relationship with cycle in case of high cycle fatigue. The accumulated fatigue damage is defined as the ratio of the accumulated cyclic damaging energy to the fatigue toughness, a material property and hence remains the same at all applied stress ranges. Based on the experimental data, a model is developed in order to predict cyclic damaging energy history at any applied stress range. The predicted fatigue damage evolution from the energy-based model are found to agree well with the experimental data.
Vibration fatigue
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This chapter contains sections titled: Introduction Drastic differences between the fatigue of composites and metals Notch effect on fatigue strength Effect of a stress on composite fatigue Fatigue after impact Fatigue damage criteria Conclusion Bibliography
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