Stress Cycle Frequency Research Articles

Fatigue performance of hydraulic asphalt concrete under uniaxial constant-amplitude tensile cycle loading

The fatigue properties of hydraulic asphalt concrete (HAC) have significant impact on the impervious performance and safety of HAC embankment dam. Therefore, this study investigated the fatigue performance of HAC, including fatigue deformation, tensile failure mode and fatigue life, and proposed a model for predicting HAC fatigue life considering stress level, cycle frequency, and failure probability. For these purposes, a constant-amplitude continuous cyclic tensile test was conducted on dumbbell-shaped HAC samples at different stress levels and cyclic frequencies. The results indicated that the failure strains of HAC at different fatigue tensile loading conditions was as high as 4.6 %, which is about 2 times the monotonic tensile strain. The failure surface of the HAC sample has a larger proportion of aggregate fracture with increasing stress level and cycle frequency. In addition, the fatigue life increases significantly with the cycle frequency. Specially, at the stress level of 0.5, the maximum fatigue life can reach up to 4365 cycles with a frequency of 5 Hz, about 10 times greater than that with a frequency of 0.5 Hz. Finally, the predection model proposed based on the double logarithmic fatigue equation can accurately predict the fatigue life of HAC.

Effect of Cyclic Stress Frequency on Corrosion Electrochem-ical Behavior of MS X65 Pipeline Steel in H2S Containing Medium

Effect of Cyclic Stress Frequency on Corrosion Electrochem-ical Behavior of MS X65 Pipeline Steel in H2S Containing Medium

Probabilistic fatigue assessment of monitored railroad bridge components using long-term response data in a reliability framework

Fatigue is a primary concern for railroad bridge owners because railroad bridges typically have high live load to dead load ratios and high stress cycle frequencies. However, existing inspection and post-inspection analysis methods are unable to accurately consider the full influence of bridge behavior on the fatigue life of bridge components. Reliability-based fatigue analysis methods have emerged to account for uncertainties in analysis parameters such as environmental and mechanical properties. While existing literature proposes probabilistic fatigue assessment of bridge components, this body of work relies on train parameter estimates, finite element model simulations, or controlled loading tests to augment monitoring data. This article presents a probabilistic fatigue assessment of monitored railroad bridge components using only continuous, long-term response data in a purely data-driven reliability framework that is compatible with existing inspection methods. As an illustrative example, this work quantifies the safety profile of a fracture-critical assembly comprising of six parallel eyebars on the Harahan Bridge (Memphis, TN). The monitored eyebars are susceptible to accelerated fatigue damage because changes in the boundary conditions cause some eyebars to carry a greater proportion of the total assembly load than assumed during design and analysis; existing manual inspection practices aim to maintain an equal loading distribution across the eyebars. Consequently, the limit state function derived in this article accounts for the coupled behavior between fatigue and relative tautness of the parallel eyebars. The reliability index values for both the element (i.e. individual eyebars) and system (i.e. full eyebar assembly) reliability problems are assessed and indicate that under the conservative assumption that progressive failure is brittle, first failure within the parallel eyebar system is generally equivalent to system failure. The proposed method also serves as an intervention strategy that can quantify the influence of eyebar realignment on the future evolution of the reliability index.

Effect produced by corrosive environment on fatigue resistance of automotive structural steel

We have studied the influence of corrosive environment on the mechanism of changes in fatigue resistance of automotive structural steels. Analysis of the experimental data has shown that the fatigue resistance of metal materials in corrosive environments is reduced significantly with the increased time of testing. This, in turn, causes a continuous decrease in fatigue curves in the multi-cycle area without reaching the endurance limit. We have identified the factors affecting the resistance to fatigue failure: the medium and its aggressiveness; stress cycle frequency, shape and asymmetry. The presence of a corrosive environment makes it problematic to determine the moment of origin of a macro crack, necessary for the analytical assessment of the time before its appearance. The proposed use of the current sag curves under the sample cyclic loading will allow to fix the moment of the crack origin and to determine the speed of its subsequent propagation. This allows to optimize the choice of structural materials for machines taking into account the operating conditions and to justify the technological manufacturing process in order to reduce material consumption, increase durability and maintainability.

A unified theory for microstructural alterations in bearing steels under rolling contact fatigue

Three major types of microstructural alterations occurring under rolling contact fatigue, white etching areas (WEAs), dark etching regions (DERs) and white etching bands (WEBs), are modelled under a unified approach: dislocation-assisted carbon migration theory. Following our previous work on DERs and WEBs, a novel model is proposed to describe dislocation cell formation in WEAs. The proposed model yields predictions of WEAs appearance, agreeing with experimental observations. Bearing life can be estimated by the WEA appearance model. The three microstructural alterations models are combined and, for the first time, it becomes possible to predict the occurrence and the formation progress of WEAs, DERs and WEBs with a unified theory. Microstructural alteration maps are plotted as a function of number of cycles, temperature, contact pressure and stress cycle frequency. The models are validated by the experimental results reported over the last 50 years.

Accumulated damage process of thermal sprayed coating under rolling contact by acoustic emission technique

The accumulated damage process of rolling contact fatigue (RCF) of plasma-sprayed coatings was investigated. The influences of surface roughness, loading condition, and stress cycle frequency on the accumulated damage status of the coatings were discussed. A ball-ondisc machine was employed to conduct RCF experiments. Acoustic emission (AE) technique was introduced to monitor the RCF process of the coatings. AE signal characteristics were investigated to reveal the accumulated damage process. Result showed that the polished coating would resist the asperity contact and remit accumulated damage. The RCF lifetime would then extend. Heavy load would aggravate the accumulated damage status and induce surface fracture. Wear became the main failure mode that reduced the RCF lifetime. Frequent stress cycle would aggravate the accumulated damage status and induce interface fracture. Fatigue then became the main failure mode that also reduced the RCF lifetime.

A thermodynamic constitutive model for undrained monotonic and cyclic shear behavior of saturated soils

Based on a non-equilibrium thermodynamic approach, this paper has established a constitutive model for saturated soils different from the classical elasto-plastic model and other thermodynamics-based models. It does not require concepts such as yield surface and flow rule. Instead, through a quantitative description of the energy in the reversible and irreversible processes in materials, the constitutive relations have been obtained theoretically. Using the elastic potential energy function, the stress is expressed as a function of elastic strain. By introducing the granular entropy and locked energy concepts, the non-elastic strain evolution is determined according to the non-equilibrium thermodynamics. The model can describe many basic mechanical properties of saturated soils under monotonic and cyclic shear loadings, such as the stress state boundary, the critical state and especially the cyclic mechanical behavior. Based on this model, the paper simulates the cyclic undrained triaxial shear tests for saturated clays and analyzes the impact of factors that include cyclic stress ratio, OCR value and cyclic stress frequency. The simulation results are compared with experimental results in order to validate the model.

Cyclic Contact Fatigue of Dental Porcelain

The residual strength of dental porcelain discs were test after cycling fatigue compressive load in this study. Moreover, the effects of stress intensity and cycle frequency to the damage of porcelain were explored. The porcelain specimens were bonded to the epoxy resin blocks, with 12.5mm height. The cycling fatigue contact loads were subjected on the porcelain surfaces of the bi-layer composites with silicon nitride spheres of radius 2.5mm. The crosshead speed was 6mm/min. The top load value was varied from 10N-20N in every load cycles. The cycling number was from 50-300. After cycling test, the residual strength of all porcelain samples was measured by bi-axial bending test. Fractured pieces of the specimens were collected and examined with optical microscope and SEM. On the fracture surfaces of porcelain discs after bi-axial bending test, Hertz cone cracks were presented due to cycling fatigue load. The result showed that the residual strength of dental porcelain had negative correlation with the fatigue load values and cycles. When the fatigue load cycles were lower than 100, the residual strength of porcelain presented no significant different under 10 or 20N fatigue load. In contrary, when the fatigue load cycles were over 100, the residual strength of porcelain was much lower under 20N fatigue load than 10N fatigue load. Based on the limited results of this study, the conclusion could be drawn that the residual strength of porcelain under fatigue compressive stress was main determined by load cycles in the range of small load values. The porcelain could be destroyed after very few cycles if the load is up to a critical value.

Fatigue crack growth acceleration caused by irreversible hydrogen desorption in high-strength steel and its mechanical condition

In this paper, the influence of irreversible hydrogen on the fatigue crack growth in high-strength steel is discussed. The fatigue crack growth rate was accelerated by irreversible hydrogen, and the acceleration increased with a decrease in stress cycle frequency. However, the stress ratio did not influence the fatigue crack growth rate evaluated in terms of ΔKeff. The behavior of irreversible hydrogen under cyclic loading was visualized by a hydrogen microprint technique. This proved that irreversible hydrogen desorbed out from the trap site under cyclic loading. The mechanical condition for irreversible hydrogen desorption was investigated by stress analysis and EPMA analysis.

Influence of Irreversible Hydrogen and Stress Cycle Frequency on the Fatigue Crack Growth Property in High-strength Steel and Hydrogen Visualization

The influence of irreversible hydrogen on the fatigue crack growth in cold-drawn high-strength steel was investigated to clarify the mechanism of fatigue strength degradation by irreversible hydrogen. The fatigue crack growth rate was accelerated by irreversible hydrogen in low ΔKeff region, and the acceleration increased with a decrease in ΔKeff. Moreover, the fatigue crack growth rate under irreversible hydrogen charged condition increased as the stress cycle frequency decreased. The behavior of irreversible hydrogen under cyclic loading was visualized using a hydrogen microprint technique. It was proved that irreversible hydrogen desorbed out from its trap site under cyclic loading.

OS0723 非拡散性水素吸蔵条件下の疲労き裂進展特性に及ぼす繰返し負荷条件の影響(構造用材料の疲労挙動と寿命評価,オーガナイズドセッション)

This paper describes the influence of cyclic loading condition and irreversible hydrogen on the fatigue crack propagation properties in a cold drawn eutectoid steel wire. Fatigue crack propagation tests were conducted for virgin samples and irreversible hydrogen charged samples. In the low ΔK_<eff> region irreversible hydrogen accelerated the fatigue crack propagation rate. However, in the high ΔK_<eff> region, the fatigue crack growth rate was not influenced by irreversible hydrogen. To elucidate the mechanism of the acceleration of the crack growth rate by irreversible hydrogen, the influence of stress cycle frequency and stress ratio was investigated. In the case of irreversible hydrogen charged sample, crack growth rate at a lower stress cycle frequency of 1 Hz was higher than that at a higher stress cycle frequency of 10 Hz. As the stress ratio become large in order of 0.1, 0.2 and 0.4, the fatigue crack growth rate increased in the irreversible hydrogen charged sample. These results were similar to the case of diffusible hydrogen.

Influence of nanometre‐sized notch and water on the fracture behaviour of single crystal silicon microelements

The influence of a notch and a water environment on the quasi‐static and fatigue fracture behaviour was investigated in single crystal silicon microelements. The tests were conducted in smooth and notched microcantilever beam samples. Smooth specimens were prepared by micromachining (photo‐etching) of (110) silicon wafers. For some specimens, a nanometre‐sized notch was machined 100 μm away from the sample root by using a focused ion beam system. A machining condition was optimized, and the V‐shaped notch was successfully introduced. The radius of curvature of the notch, measured by an atomic force microscope (AFM), decreased with an increase in notch depth, and ranged from about 20 to 100 nm. Single‐crystal Si microelements deformed elastically until final failure, which was of a brittle nature. The maximum fracture strength of a smooth microcantilever specimen reached about 7.7 GPa, which was higher than that obtained in millimetre‐sized single crystal Si samples. However, the fracture strength decreased with an increase in notch depth, even though the notch depth was of the order of a nanometre. This means that a nanometre deep notch, which is often regarded as surface roughness in ordinary‐sized mechanical components, caused a decrease in the fracture strength of Si microelements. The fracture initiated at the notch, and then the {111} crack propagated in the direction normal to the sample surface. Fatigue tests were also conducted in laboratory air and in pure water at a stress cycle frequency of 0.1 Hz and a stress ratio of 0.1. In laboratory air, no fatigue damage was observed even though the surface was nanoscopically examined by an AFM. However, when the fatigue tests were conducted in pure water, the fatigue lives in water were decreased. Crack formation on the {111} plane was promoted by a synergistic effect of the dynamic loading and the water environment. Atomic force microscopy was capable of imaging the nanoscopic cracks, which caused failure in water.

Low cycle corrosion fatigue (LCCF) behaviour of zircaloy-2 in an environment containing iodine in constant displacement mode test

Zircaloy-2 sheet materials of thickness 2 mm have been tested in an air, ethanol and ethanol-containing-iodine (at 0.1 vol%) environment at different loading frequencies between 0.1 and 0.3 Hz in a tension-tension, constant displacement type fatigue machine at maximum load ( P max) = 0.1 and 0.15 breaking load (BL) and initial stress ratio, R(= minimum stress maximum stress = σ min σ max ) = 0.1 . Susceptibility, as was determined by crack velocity (CV) and number of cycles to failure criteria, has been indexed as: ethanol + iodine > ethanol > air. Increased susceptibility was accompanied by an increasingly brittle fracture mode. Crack velocity increased with increasing P max and stress cycle frequency. Irrespective of the test variables used, flattening out of the P max vs number of cycles to failure curve at p TH was postulated as the threshold condition, concomitant with the observed transition in the fracture mode brittle-ductile. Tests in air had revealed a continuously sloping downward crack progression curve with an increasing number of cycles, while P max had decreased continuously. The fracture mode was microvoid coalescence (MVC).

Periodic strain burst behaviour of Al0.87 Mg alloy in cyclic creep at intermediate temperatures

Intermediate-temperature cyclic creep of Al0.87% Mg alloy under different cyclic peak stresses was studied. In the secondary creep stage, periodic strain bursts occurred only in a certain region of both stress and temperature. The threshold stress of strain burst appearance was found to be almost independent of temperature, but its temperature range for a constant stress decreased with increasing applied stress. The period of strain bursts decreased with increase in both stress and temperature, whereas their amplitude changed with stress only. The average creep rate during strain bursts was observed to be more sensitive to both stress and temperature than that during conventional creep. A new model on strain bursts is proposed based upon the strain equation in terms of mobile dislocation density and also the collective motion of pile-up dislocations in front of forest dislocations under concentrated stress. Relationships of strain burst period and amplitude with (i) temperature, (ii) cyclic peak stress, (iii) average creep rate and finally (iv) cyclic stress frequency have been deduced and also verified by the experimental results.

人工海水中における耐海水二相ステンレス鋼溶接材の腐食疲労き裂進展特性

The corrosion fatigue (CF) crack growth behavior of a duplex (α and γ phases) stainless steel, SUS329J1, weldment has been investigated in ASTM synthetic seawater (SSW) at the free corrosion potential and the cathodically charged potential of -957mV vs. Ag/AgCl. The tests were conducted with a sinusoidal load at stress ratios of 0.1 and 0.8 with stress cycle frequencies of 0.17Hz and 10Hz. The CF crack growth rate of the weld metal in terms of stress intensity factor range, ΔK, was considerably lower than that of the base metal, since a crack opening load was increased by the compressive residual stress by welding. In air tests, the crack growth rate of the weld metal in terms of the effective stress intensity factor range, ΔKeff, or a modified one, ΔKcont, was larger than that of the base metal, because the acceleration of the growth rate by nonmetallic inclusions in the former is more prevailing than in the latter. At low ΔKcont at the free corrosion potential, the crack growth rate of the weld metal, which was accelerated by the inclusion and hydrogen embrittlement (HE), was higher than that of the base metal, which was accelerated by dissolution. On the other hand, at high ΔKcont at f=0.17Hz of R=0.1 at the free corrosion and the cathodically charged potentials, the growth rate of the weld metal was lower than that of the base metal, since the base metal with lower area ratio of γ phase was more sensitive to HE than that of the weld metal.

Mechanical Conditions Dominating Cyclic Stress Corrosion Cracks of High-Strength Steel under Combined Cyclic/Static Multiaxial Loads

Cyclic stress corrosion cracking (SCC) tests of smooth specimens under combined cyclic/static tensile and torsional loads were conducted on a 4135 high-strength steel in 3.5% NaCl solution at 298 K. The stress waveform was triangular at a stress cycle frequency of 0.1 Hz. Two series of loading patterns were employed; multiaxial cyclic load tests under in-phase cyclic tension and torsion (tensile stress ratio, Rσ, of zero, and torsional stress ratio, Rτ, of zero), and multiaxial cyclic-static tests in which one of the two applied loads was cyclic and the other static, i.e., (Rσ=0, Rτ=1) or (Rτ=1, Rτ=1). The combined stress ratios of τmax/σ<max> were selected as 0, 1/2, 1, 2, and infinity. In the case of multiaxial cyclic load tests, a cyclic SC crack normal to the maximum principal stress was initiated at the bottom of the corrosion pit. In this case, the life of cyclic SCC was dominated by the maximum principal stress, σ1, max, which equaled the maximum principal stress range, 1, max. In the case of multiaxial cyclic-static loads a cyclic SC crack normal to the maximum tensile stress range was initiated at the bottom of the corrosion pit, provided that the static tensile load in the plane of the maximum tensile stress range was relatively small. IN this case, the life of cyclic SCC was dominated by the maximum tensile stress range, n, max. In either case, the mechanical condition dominating crack initiation at the bottom of the corrosion pit was determined by the stress intensity factor range, K1FSCC, calculated on the assumption that the spherical corrosion pit was a sharp surface crack.

The effects of stress cycle frequency and stress wave form on SCC crack growth in high-strength steel and automatic classification of mixed mode of intergranular and transgranular cracking.

The effects of stress cycle frequency and stress wave form on SCC crack growth in high-strength steel and automatic classification of mixed mode of intergranular and transgranular cracking.

人工海水中における耐海水２相ステンレス鋼の腐食疲労き裂進展挙動

The corrosion fatigue crack growth rate of dual-phase stainless steel SUS329J1 has been measured in synthetic sea water at various stress ratios and stress cycle frequencies under free corrosion and a cathodic potential. In air the roughness-induced wedge effect enlarges the region II in the load-strain hysteresis loop. In synthetic sea water, the corrosion products-induced wedge effect under free corrosion and the Ca and Mg deposites-induced wedge effect under a cathodic potential are conspicuous, thereby enlarging the region II and raising Kop. Under free corrosion the stress assisted dissolution accerelates the crack growth rate at a low ΔKeff. In addition, at a high ΔKeff at R=0.1 and f=0.17Hz the crack growth rate is much more accerelated due to hydrogen embrittlement. Under a cathodic potential, ΔKth is remarkably high. But the crack growth rate is much accerelated due to hydrogen embrittlement in terms of ΔKeff.

Ａｌ‐Ｚｎ‐Ｍｇ合金のモードＩ，モードＩＩ混合モード下のＳＣＣき裂進展挙動

SCC crack growth behavior under dynamic mixed mode loading conditions was investigated in a high-strength Al-Zn-Mg alloy immersed in 3.5% NaCl solution. Mode II dynamic loads including high frequency (30Hz) small vibratory loads at a high stress ratio of 0.95 (dynamic SCC) and low frequency (0.002-5Hz) variation at a stress ratio of 0.1 (cyclic SCC) were applied to specimens with superposition of static Mode I loads of KIS=10MPa·m1/2 larger than the crack opening stress intensity factor and KIS=30MPa·m1/2 larger than the Mode I static SCC threshold, KISCC. In the case of static and dynamic Mode II SCC tests, crack extension was not observed; oblique cracks at an angle of about 50-60 degrees against the direction of shear stress were initiated and propagated, which was dominated by Mode I intergranular dissolution. On the other hand, subcritical Mode II cyclic SCC crack extension was observed at high ΔKII levels with higher crack growth rates than dry air values. The enhancement of crack growth rate was dependent on the values of Mode I static loads and Mode II stress cycle frequency: the increase in crack growth rate from the dry air value at KIS=10MPa·m1/2 was larger than that at KIS=30MPa·m1/2, and had maximum at a stress cycle frequency of 0.1Hz. In the case of Mode II fatigue, transgranular failure including elongated dimples and slips was dominant, whereas transgranular dissolution in addition to those observed in Mode II fatigue existed. The fraction of transgranular dissolution fairly well corresponded with an enhancement of cyclic SCC crack growth rates.

Influences of stress cycle frequency and stress ratio on corrosion product-induced wedge effects.

The corrosion fatigue crack growth rate of a high tensile strength steel HT55 has been measured in 1% NaCl solution at various stress cycle frequencies and stress ratios to elucidate the corrosion product-induced wedge effect and dominating mechanical parameters for crack growth. The wedge effect is most effective at R=0.1, whereas it is less effective in the order of R=-1 and R=0.5. At R=-3, however, the wedge effect disappears, and the growth rate in 1% NaCl solution is higher than that in air. At f=50Hz and R=0.1 and 0.5 in 1% NaCl solution, the load strain hysteresis loop traces different paths during loading and unloading periods, resulting from viscosity of the corrosive solution remaining within cracks, but the load sharing capacity of the viscosity is negligibly small. Regions I and II in the hysteresis loop must be taken into consideration to explain uniquely the corrosion fatigue crack growth characteristics under various conditions, and a contributory stress intensity factor range ΔKcont is proposed as a difference between ΔK and ΔKret, deduced from the load range shared by regions I and II.