Showing papers on "Fatigue limit published in 1986"

Atlas of Fatigue Curves

Abstract: Contains more than 500 fatigue curves for industrial ferrous and nonferrous alloys. Also includes a thorough explanation of fatigue testing and interpretation of test results. Each curve is presented independently and includes an explanation of its particular importance. The curves are titled by standard industrial designations (AISI, CDA, AA, etc.) of the metals, and a complete reference is given to the original source to facilitate further research. The collection includes standard S-N curves, curves showing effect of surface hardening on fatigue strength, crack growth-rate curves, curves comparing the fatigue strengths of various alloys, effect of variables (i.e. temperature, humidity, frequency, aging, environment, etc.) and much, much more. This one volume consolidates important and hard-to-find fatigue data in a single comprehensive source.

Fatigue Analysis of Plain Concrete in Flexure

Abstract: This paper investigates fatigue strength of plain concrete subjected to flexural loading. This type of fatigue loading is of concern in the design of concrete bridges and concrete pavement slabs, since the flexural stresses in these structures can be critical. Both experimental and theoretical studies are conducted. The S‐N curves are generated from the test results and an equation is obtained by regression analysis to predict the flexural fatigue strength of concrete. A probabilistic approach is introduced to predict the fatigue reliability of concrete. The distribution of fatigue life of concrete under a given stress level was found, from the test data, to approximately follow the Weibull probability law. The method of obtaining the distribution parameters from S‐N relation for the flexural fatigue of concrete is also presented. The Weibull distribution is found to have more convincing physical features than the lognormal distribution, and may be appropriate to. describe the fatigue behavior of concrete.

Non‐damaging notches in fatigue*

Abstract: The fact that very small notches (cavities, holes, scratches, etc.) have no effect on the fatigue limit of metallic materials is well known. This paper presents both a qualitative explanation for the existence of non-damaging notches and a quantitative derivation of their critical sizes. The condition for a notch (characterized by the stress concentration factor Kt and the notch root radius ρ) to be non-damaging in a metallic material (characterized by a critical crack size l0) is (K2t− 1)ρ≤ 4.5 l0. The critical crack size can be expressed with good approximation in terms of the threshold stress intensity for fatigue crack growth and the plain fatigue limit. Therefore the above relation can be applied for an engineering evaluation of non-damaging notches. Test results obtained for copper and a pressure vessel steel demonstrate the applicability of the proposed method.

Evaluation of Fatigue Tests and Design Criteria on Welded Details

Abstract: A study is reported which attempted to compile and review all available fatigue data. It reevaluated the existing fatigue specificatios so that they more accurately reflected the current state of knowledge. The study developed a database for welded steel bridge details that includes details from all available sources. The study also analyzed the new data on an individual basis with respect to the existing AASHTO fatigue provisions to see if changes are required in the code because of the new test results. The AASHTO fatigue design curves were standardized with the increased database. The study provided new fatigue design specifications for use in national design codes that more accurately define the fatigue resistance of welded steel bridge details.

Fatigue life prediction for gaussian random loads at the design stage

Abstract: Fatigue life prediction under variable amplitude loading normally involves a two stage process of cycle counting and damage summation. This paper shows that for certain classes of strain history, predictions can be made directly from a knowledge only of the power spectral density of the strain history and conventional fatigue strength data.

Fatigue strength of sintered Si3N4 under rotary bending

Abstract: Etude de la resistance a la fatigue d'une alumine frittee soumise a un essai de flexion rotative. Examen des surfaces de rupture par MEB

Effect of Fatigue on Fracture Toughness of Concrete

Abstract: An experimental study utilizing 4‐point bending SENB specimens was carried out to determine the effect of fatigue on the fracture toughness of plain concrete. In addition to fourteen static tests of beams with a midspan precast notch, nine specimens with an initial precast notch of a depth to height ratio of l/d=0.20 were fatigued until a certain crack length was reached. Crack growth was successfully monitored by the CMOD compliance measurements. Independent surface crack length measurements by a hand‐held scope and observations of the crack front with the use of a fluorescent dye‐penetrant injected into the notch root were also performed. The fracture toughness, GIC, under fatigue appears to be higher than under static loading and shows an increasing trend with increasing crack length and number of loading cycles. The observed behavior is most likely related to the presence of a microcracking zone that evolves with fatigue.

The effect of HIPing on the fatigue and tensile strength of a case, porous-coated Co-Cr-Mo alloy.

Abstract: The process required to sinter porous Co-Cr-Mo alloys results in the formation of substrate porosity through carbide dissolution. Since hot isostatic pressing (HIPing) has been shown to eliminate casting porosity in the Co-Cr-Mo alloy, it is possible that it may be equally effective on pores that are generated from the sintering operation. The effect that HIPing a porous-coated Co-Cr-Mo material has on the fatigue and tensile properties was investigated. Fatigue testing was performed on sintered materials as well as sintered and HIPed materials, both with and without a porous coating. Further, the effect of varying coating thickness on the resulting fatigue strength of sintered and HIPed materials was studied. Light microscopy was performed in order to define the microstructural changes brought about by the various thermal cycles. Scanning electron microscopy was utilized to define the crack initiation process. The fatigue strength of uncoated "as sintered" materials was found to be reduced by 34% relative to the "as cast" condition. The same material that was HIPed revealed a fatigue strength slightly lower than the "as cast" condition. It was found that porous coatings created preferential sites for fatigue crack initiation. However, the presence of the coating did not further reduce the fatigue strength of "as sintered" materials because of the already low strength created by the sintering operation. Materials that were sintered exhibited a lowering in both tensile strength and elongation to failure relative to the "as cast" condition. The HIPing of sintered materials improved both fatigue and tensile properties relative to the "as sintered" condition.

The role of crack resistance parameters in polymer wear

Abstract: When polymers slide against a smooth metal counterface wear occurs via a combination of adhesive and fatigue processes. A relationship is derived to predict such wear rates from measurements of the fracture mechanics parameters characterising fatigue crack growth. The predictions are directly confirmed from wear and crack growth measurements with polymethylmethacrylate (PMMA) and polyethersulphone (PES) in different organic liquids. Supporting evidence is provided from wear and crack growth data on thermoplastics and on epoxy resins of varying cross-linking densities. In abrasive conditions against rough metal counterfaces, the most important material property controlling wear is the fracture toughness, KIc. A simple analysis suggests that the wear rate should be proportional to 1/KIc2 and this is confirmed experimentally for PMMA and PES in organic liquids and for cross-linked epoxies.

Relationship between fatigue strength and hardness for high strength steels.

Abstract: To make a quantitative analysis of the defect size for high strength steels, fatigue properties and fatigue fracture mechanism were examined for 3 different low alloy steels tempered at several temperatures. Fatigue strength was evaluated up to about 108 cycles under rotating bending at room temperature in dry air. Two types of S-N curves were found, the one has fatigue limit for medium strength steels fractured from the specimen surface, the other for higher strength steels has temporal fatigue limit because of the interior fracture in the long life region over about Nf=107. Fatigue strength would be predicted by the liner relation between the threshold stress intensity factor and the hardness of the materials. It is suggested that the defect size to originate the fatigue crack would have important role for high strength steels up to about HV600.

Mechanical Behavior and Processing of DS and Single Crystal Superalloys

Abstract: This article examines mechanical anisotropy of single crystals, cold work induced surface recrystallization on directionally solidified (DS) materials, and the effect of temperature gradient in a DS furnace on the fatigue strength of single crystals. It draws attention to the highly anisotropic creep behavior of some modern single crystal alloys showing, in particular, extremely poor creep resistance in the 〈111〉 orientation. Effects of surface recrystallization on the creep strength are evaluated. The present work incites further investigation on heat treatments and alloy chemistry modifications in order to reduce the effect of mechanical anisotropy. Great care should be taken during the “mechanical” handling of DS or single crystal components to avoid surface recrystallization. HIP’ing or high gradient solidification are shown to be two possible ways for enhancing the durability and the fatigue strength of single crystal superalloys. In certain liquid fuel rocket engine applications, where hydrogen embrittlement of single crystal turbopump blades can be of concern, both these techniques can be useful.

Effect of Yield Stress and Grain Size on Threshold and Fatigue Limit

Abstract: Experimental investigations have been carried out to study the effects of grain size and yield stress on fatigue limit and threshold stress intensity range. The relations between fatigue limit and grain size and yield stress and those between threshold stress intensity range and grain size and yield stress which were predicted according to the model proposed in the previous paper agreed quite well with the experimental data. The difference in the dependence of fatigue limit and threshold stress intensity range on yield stress was discussed based on the analytical relations between them.

Bending Strength of Carburized SCM420H Spur Gear Teeth

Abstract: For carburized spur gears of m = 5 which have effective case depths deff = 0.6, 0.9 and 1.3 mm as well as non-carburized gears and normalized gears, relations between the residual stress at the root and the hardness are made clear. Bending fatigue tests are carried out to obtain SN-curves of these gears. The effect of case depth on the fatigue limit is not very significant. Influences of the residual stress at the root surface, the surface hardness and the core hardness on the fatigue limit are quantitatively determined from the results of fatigue test and a formula which may be available to estimate the fatigue limit of spur gears is finally proposed as a function of these factors.

Fatigue behavior of continuous fiber silicon-carbide-aluminum composites

Abstract: Four lay-ups of continuous fiber silicon carbide (SCS2) fiber/aluminum matrix composites were tested to assess fatigue mechanisms including stiffness loss when cycled below their respective fatigue limits The lay-ups were 0 (sub 8), 0(sub 2)/ + or - 45 (sub 2s), 0/90 (sub 2s),and 0/ + or 45/90 (subs) The data were compared with predictions from the author's previously published shakedown model which predicts fatigue-induced stiffness loss in metal matrix composites A fifth lay-up, + or - 45 (sub 2s), was tested to compare shakedown and fatigue limits The particular batch of silicon-carbide fibers tested in this program had a somewhat lower modulus (340 GPa) than expected and displayed poor bonding to the aluminum matrix Good agreement was obtained between the stiffness loss model and the test data The fatigue damage below the fatigue limit was primarily in the form of matrix cracking The fatigue limit corresponded to the laminate shakedown for the + or - 45 (sub 2s) laminate

Effect of surface corrosion on glass fracture

Abstract: The nature of aqueous corrosion reactions on glass surfaces varies with glass composition and environmental conditions. We have shown how the physical effects of the various surface reactions can be incorporated into simple fracture mechanics models to predict measured crack velocity effects in silicate glasses. Reactions on glass surfaces are divided into four categories: 1) Bond rupture reactions — Crack tip bond rupture reactions in silica are modeled through a combination of theoretical and experimental surface reaction studies. The atomistic fracture model which we developed predicts both the stress dependence and environmental dependence of measured crack growth behavior in vitreous silica. 2) Alteration layer formation — Aqueous corrosion reactions alter the chemical composition and physical properties of glass surfaces. Sodium silicate glasses develop a surface tensile layer when exposed to aqueous environments. This tensile layer adds to the crack tip stress intensity to produce a low velocity plateau in the crack growth curve. Phase separated sodium-borosilicate glasses undergo selective leaching to produce a porous-reaction layer. The porous layer around the crack tip reduces the stress which is transferred to the crack tip to produce a fatigue limit. 3) Surface deposition — Preferential deposition of silica at the crack tip can increase the radius of curvature and reduce the crack tip stress concentration. Measured silica deposition rates predict the fatigue limit for soda-lime-silica glass. 4) Intermolecular surface forces — Attractive forces between surfaces decrease the crack tip stress and lead to crack healing. Crack healing measurements for vitreous silica and soda-lime-silica glass can be explained by the formation of hydrogen bonded linkages of surface adsorbed water molecules and electrostatic bonds between anionic surface groups.