Showing papers on "Fatigue limit published in 1969"

Fatigue failure in denture base polymers

Abstract: Although well-fitting dentures of adequate thickness seldom exhibit fatigue failure in service, a very small percentage of the millions of denture wearers have well-fiting dentures. Fatigue failure is a very real problem in these dentures, in the well-fitting single upper denture occluding against natural lower teeth, and in all dentures with soft liners. We can make dentures more resistant to fatigue failure by using a few precautions. First, the heat-curing resins are much more resistant to this failure; therefore, use of a heat-curing acrylic resin is indicated. Second, fine-polymer beads increase fatigue strength many times, so a fine-grained polymer should be used. Finally, stress concentrators should be avoided. Most important would be the elimination of sharp surface contours, such as deep notches for low frenum attachments, and prominent rugae patterns. A prominent frenum attachment has little function and is not beneficial to the completely edentulous individual. It is a simple procedure to eliminate the frenum at the time of extraction of the anterior teeth. Any particle acts as a stress concentrator; therefore, acrylic dentures should be fabricated in a relatively dust-free atmosphere such as that used for porcelain work. Fibers and the surface defects that they produce act as stress concentrators, and this should be recognized if a material with fibers is used. Rayon or nylon fibers are used commercially. 20 The use of acrylic fibers should correct this weakness.

Fatigue strength of welded structures

Abstract: IIW Recommendations for the Fatigue Assessment of Welded Structures By Notch Stress AnalysisFatigue Design of Welded Joints and ComponentsRecommendations for Fatigue Design of Welded Joints and ComponentsIIW Guidelines on Weld Quality in Relationship to Fatigue StrengthThe Fatigue Strength of Transverse Fillet Welded JointsFatigue Life Analyses of Welded StructuresBibliography on the Fatigue of Welded StructuresIIW Recommendations for the HFMI TreatmentFracture and Fatigue of Welded Joints and StructuresDesign and Analysis of Fatigue Resistant Welded StructuresApplication of the Local Approach to the Fatigue Strength Assessment of Welded Structures in ShipsFatigue Analysis of Welded ComponentsStress Determination for Fatigue Analysis of Welded ComponentsA Method for Obtaining Conservative S-N Data for Welded StructuresFatigue Strength of Welded StructuresAnalysis of Welded StructuresFatigue Assessment of Welded Joints by Local ApproachesDesign, Fabrication and Economy of Welded StructuresFatigue strength of welded ship structuresStructural HotSpot Stress Approach to Fatigue Analysis of Welded ComponentsImproving the Fatigue Life of High Strength Steel Welded Structures by Post Weld Treatments and Specific Filler Material (FATWELDHSS)Fatigue Testing of WeldmentsFatigue Assessment of Welded Joints by Local ApproachesFatigue Strength of Welded Steel StructuresThe Welding Engineer’s Guide to Fracture and FatigueDesign and Analysis of Fatigue Resistant Welded StructuresFourth International Conference on Advances in Steel StructuresFatigue Strength of Welded Joints and Fatigue Strength of Welded Joints: A Review of the Literature to July 1, 1936Evaluation of Fatigue Strength of Welded Steel StructuresFatigue Strength of Welded StructuresFatigue Analysis of Welded Structures Using the Finite Element MethodCumulative Damage of Welded JointsFatigue of Welded StructuresFatigue of Welded Steel StructuresIIW Recommendations On Methods for Improving the Fatigue Strength of Welded JointsFatigue strength of welded connections in round bar steel structuresTechniques for Improving the Fatigue Strength of Welded StructuresThe Influence of Residual Stresses on the Fatigue Strength of Welded Steel StructuresFatigue Strength of Welded StructuresHeat Treatment of Welded Structures

Effects of Cycle Frequency on Fretting Fatigue Life of Carbon Steel

Abstract: The bending and twisting fretting fatigue tests of carbon steels are carried out and the effects of cycle frequency are studied in comparison with the corrosion fatigue. The behaviors of the frictional force with progress of fretting cycles are observed. The results obtained are as follows : The fretting fatigue strength is decreased with lower frequency. The fretting damage is saturated in the early period of the total fatigue life, and the subsequent crack propagation period constitutes the most part of the life. The lower the frequency is, the shorter the saturation period. The frictional force increases initially and then decreases after showing a peak value. These changes at various frequencies well correspond to the extents of the fretting damage. Consequently, this shows that the fretting damage is attributed to cracks initiated under the frictional stresses at the initial stage simultaneously applied with the repeated stresses in the surface layers. The fretting corrosion without the repeated stresses hardly reduces the fatigue strength though the depth of wear scars is the same as that under fretting fatigue. The greater reduction of the fatigue strength by fretting under bending than under twisting may be also explained with the combined stresses.

The calculation of elevated temperature cyclic life considering low cycle fatigue and creep

Abstract: Cyclic life calculations of materials sujected to isothermal stress considering fatigue and creep

The influence of specimen size, polycrystal grain size, and yield point behaviour on the fatigue strength of low-carbon steel☆

Abstract: I t is shown, by comparison of fatigue and yield strength results previously reported for several materials, that a rational explanation can be given of the seemingly complicated manner in which the fatigue properties of annealed low-carbon steel depend on the number of grains in a specimen cross-section, the polycrystal grain size and the yield point behaviour This dependence varies according to whether the fatigue stress is greater than, equal to, or less than the yield stress of the same material

The development of a calculation method for the fatigue strength of lugs and a study of test results for lugs of aluminium

Abstract: This report treats single, symmetric, longitudinally loaded lugs, fitted with a non-interference pin. A calculation method for fatigue strength, which takes the shape and size of the lug into consideration, has been devised. With varying parameter values, substituted into assumed relations which are partly verified empirically, test results are reduced to refer to a ‘reference lug‘ of a defined shape and size. The method is presented, its background is related and it is applied to approximately 900 lugs, for which test results were available. These lugs represent two main groups of aluminium alloys, Al-Cu-Mg and Al-Zn-Mg-Cu, which are divided into 8 subgroups. About 400 of the lugs represent aluminium alloy of the 2024 type. This number allowed, to some extent, a statistical analysis of the test results. The size effect has been investigated in a special test series with lugs of aluminium 7079-T6 (Saab 3624). The pin diameters were 5, 10, 20, and 40 mm. Results from this test series have also been studied with respect to the scatter in fatigue strength.

The effect of secondary bending on the fatigue strength of 2014-T3 Alclad riveted joints

Abstract: Six types of riveted specimens including lap joints and single and deuble strap joints have been compared both, in constant-load-amplitude tests and in programme tests. In the programee tests, based on a gust load spectrum, the endurance of the double strap joint specimens was about three times as long: as that of the single lap joint and the single strap joint with low secondary bending stresses, and it was about ten times as long as the endurances of the joints with severe secondary bending stresses. The fatigue strength for N - 10 7 load cycles decreased by severe secondary bending in the specimens to about half the strength of the double strap joints. The relation between the calculated bending stresses and the fatigue strength was analysed with respect to design aspects.

Torsional Fatigue and Bending Fatigue of Electropolished Low Carbon Steel Specimens

Abstract: Rotating bending and torsional fatigue tests of plain and notched steel specimens with electropolished surfaces were carried out. The main results obtained are as follows. (1) The maximum shear stresses in the crack initiation limit of torsional fatigue are determined only by the stress gradient X independently of the notch depth as in the case of bending fatigue. (2) When the values of X are equal, the maximum shear stress in the crack initiation limit of torsional fatigue is about 1.2 times that of bending fatigue. (3) The surface states of notch roots after 107 cycles of the limit stress for crack initiation in torsional fatigue are similar to each other irrespective of the maximum stress repeated on the notch root, as in the case of bending fatigue. The fatigue damages at the crack initiation limit under torsional stresses are severer than the ones under bending stresses. (4) The mechanism of non-propagation of a crack in torsional notched specimens is different from that in bending notched specimens.

Impact fatigue of an alumina ceramic

Abstract: A new type of pendulum impact apparatus is described for determining single and repeated impact strength of ceramics, It has been demonstrated that specimens of a “Sintox” alumina ceramic exhibit fatigue behaviour, having a high stress plateau followed by progressively increasing endurance with decrease in applied impact energy. A fatigue limit, at least from the engineering view point, has been drawn at high endurances (105 impacts). The influence of environment (static fatigue) and/or plastic deformation to explain the fatigue behaviour is suggested.

Assessment of the allowable design stresses and the corresponding fatigue life

Abstract: Variable amplitude tests for determining the allowable stresses of structural components or sub-assemblies subject to statistically varying loads with constant mean load are meaningful and economically feasible only if they are restricted to one of the generally encountered types of frequency distribution. A Standard Distribution of stress amplitudes, approximating very closely the distribution of level-crossings in a stationary Gaussian process as well as a cumulative frequency distribution of causative nature, appears to be appropriate for this purpose. It will be shown that the determination of the allowable stresses for any other type of frequency distribution, which can be synthesized by summing several Standard Distributions, does not present any greater difficulties than the application of the Miner hypothesis; the procedure, first outlined more than ten years ago, moreover gives a higher degree of reliability. An example of determining the allowable stresses is given for the aluminium alloy 2024-T3, varying the two important variables stress concentration factor and stress ratio over a range of Kt= 1.8 to 4.5 and R = − 1.0 to +0.33. The fatigue strength evaluation is described for a composite stress spectrum with constant mean stress.

The cyclic stress behaviour of a 355 stainless steel 2024-T8 aluminium alloy

Abstract: The push-pull fatigue behaviour of a 355 stainless steel 2024-T8 aluminium alloy composite, has been studied at constant stress. The S-N curve shows a fatigue strength of 20 kg/mm2. Microhardness measurements reveal that little fatigue hardening takes place within the matrix; also, hardness numbers are similar in fatigued specimens, irrespective of the applied stress amplitude. The increase in damping capacity for increasing stress amplitudes, is attributed to increased delamination at the fibre-matrix interface, in the early fatigue stages. This result is also confirmed by optical microscopy. It is inferred that the sequence of failure weakness in the composite is: fibre-matrix interface, matrix and, finally, fibres. A fatigue strength/tensile strength ratio of 0.16 for this material is noticeably low, but fatigue properties of the composite can be improved by enhancing the fibre-matrix bonding.

Modern Design of Concrete Pavements

Abstract: Traffic studies on modern pavements and stress analysis with influence charts show that the critical stress location has changed from outside edges and corners to transverse joint edges Design charts for the critical transverse edge stresses are presented and their use is shown in a design problem Analysis of restrained contraction and warping stresses shows that these stresses do not influence thickness design The new procedure reflects review of past and current fatigue research The review justifies continued use of an endurance limit for concrete and a revised fatigue curve Methods are presented for estimating total traffic, truck traffic, and the single and tandem axle loads needed for design A comparison of alternate designs shows how the new procedure can be used to get low annual costs

Measurement of the strain-dependent damping of metals in axial vibration

Abstract: The internal vibration-damping characteristics of metallic materials at stress levels of engineering interest have been measured by exciting resonant longitudinal vibration in bar specimens and observing the consequent temperature rise. The method has proved suitable for all stress levels from a few hundred lbf in−2 to stresses near the fatigue limit, and for the range of specific damping capacity encountered in most ferrous and non-ferrous materials. There are no extraneous effects from damping not inherent in the material itself. The present paper describes the apparatus and techniques used, and summarizes the results of a few typical measurements. Detailed results obtained by this method are to be published separately.

Theoretical calculation of strength at stress concentration

Abstract: The mechanism of stress and strain concentration at fatigue loading is governed by two fundamental effects. Within the yield range of ductile materials the macro-support effect predominates, which can be represented by the results of a nonlinear theory derived by the author [1, 2, 4]. Within the high-cycle fatigue range the micro-support effects predominate, which can be described by the author's theory of mean stress value originally derived in connection with the calculation of sharply curved notches [1, 3, 4]. This theory introduces a material constant of length dimension. Taking the two effects into account, an approximate preliminary calculation of the fatigue strength of notched construction parts is possible [4].

Method of induction hardening for improving fatigue strength of boundary of heated zone

Abstract: Residual tensile stresses are reduced in a locally casehardened steel object by cooling the boundary zone adjacent the area to be hardened during induction heating.

The Effect of Inclusion Size and Distribution on Fatigue of 2024-T4 Aluminum.

Abstract: : Two experiments were performed to determine the effect of inclusion size and distribution on the fatigue strength of 2024 aluminum. Rolled, 2024 Al sheet was shown to contain about twice as many inclusions larger than 10 microns in diameter in the center plane as at the surface. Bending fatigue tests, in which a zero to maximum tensile stress was applied to one surface of a flat specimen cut from the sheet, showed that when the center plane was made the tensile surface, the fatigue life was reduced to half that obtained with the original surface under tension. An experimental 2024 alloy was made from high purity constituents so that the number of inclusions larger than 10 microns was reduced by a factor of 10 over the commercial alloy. Comparative S/N curves were generated which showed that the fatigue strength of the experimental alloy was increased by 20% in the high amplitude load range and 10% in the low amplitude range. Fatigue lives were increased by a factor of 5. One sample was observed periodically during a test and it was established that crack initiation did not occur at the inclusions as it does in the commercial alloy. (Author)

Fatigue of notched Ti-8Al-1Mo-1V titanium alloy at room temperature and 550 deg F /560 deg K/ with flight-by-flight loading representative of a supersonic transport

Abstract: Load and temperature effects on fatigue strength of notched titanium alloy sheet for supersonic transport operation

Effect of molten Pb-Bi eutectic on the fatigue strength of steel

Abstract: 1. When steel is wetted by molten Pb-Bi eutectic, its fatigue strength is substantially reduced as a result of the penetration of the molten alloy into the steel (usually along the grain boundaries). 2. The harmful effect of molten Pb-Bi eutectic can be prevented by the formation of an oxide film on steel surface. And so, a continuous film of a tenancious chromium spinel is formed on steel 4Khl3 at 600°C; this film has a good resistance to cyclic loads, inhibits the wetting of steel by the molten alloy and, consequently, protects the specimens from the weakening action of this alloy.

Procurement and Analysis of Structural Fatigue Data

Abstract: The most common type of structural fatigue test program is the experimental construction of an S-N curve and may be divided into two phases: determination of the mean fatigue limit by the staircase method; and determination of the finite life region and its subsequent analysis by regression analysis. The bases for statistical design of experiments require both randomization and, generally, replication. Randomization in sampling of material, specimen assignment to stress levels, and test sequence minimizes the effects of possible bias due to uncontrolled variation in material, laboratory environment, and test procedures. Replication of tests at a given stress level to estimate variability in fatigue life is often impractical. The variability in life may be estimated from regression analysis and used to predict probability of survival at any stress level.

Fatigue strength of finger joints.

Abstract: : Specimens of two types of finger joints used for end-jointing dimension lumber were evaluated under cyclic loading at various stress levels. The relative fatigue strength of the joints in tension parallel to grain after 30 million cycles of load equalled about 40 percent of static strength. (Author)

Endurance and wear resistance of steels with vacuum-diffused coatings

Abstract: The fatigue strength and wear resistance of steels St. 3, P-1, EI-802, and EI-612 after vacuum-diffusion chromizing, siliciding and boriding was studied. It was shown that the wear resistance of carbon steels is increased more than 20-fold by boriding, being approximately doubled by chromizing, and increased 1.3 times by siliciding. Of the alloy steels, only steel EI-612 has its wear resistance increased by vacuum chromizing. The fatigue strength was reduced in every case by 20–50%.

Effect of Superimposed Stress of High Frequency on Fatigue Strength of Annealed Carbon Steel

Abstract: The behavior of the fatigue strength of annealed S 45 C carbon steel under composite stress consisting of rotating bending stress and superimposed stress of higher frequency was studied. The ratio of the frequency of superimposed stress to the frequency of rotating bending stress was selected as 11.6. It was observed that, when the ratio of superimposed stress to maximum stress was less than 0.2, the fatigue life was scarcely affected by the superimposed stress, but, when the ratio was more than 0.2, the fatigue life under composite stress was comparatively shorter than that under the stress of constant amplitude. The endurance limit was lowered by superimposing the stress of high frequency. The maximum decrease reached about 35 percent of the endurance limit under the stress of constant amplitude.

Estimation of corrosion fatigue strength by corrosion resistance and notch sensitivity of materials

Abstract: Corrosion fatigue tests of various materials have been carried out in 1% saline and in 0.3N hydrochloric acid, accompanied with the measurements of corrosion current and notch sensitivity. In corrosion fatigue the critical depth of pits from which fatigue cracks initiate is determined by the stress concentration of pits depending on the corrosion resistance of materials and by the notch sensitivity. Corrosion effects κ (the ratio of fatigue strength in air σ to that in corrosive media σc) are referred to the static and the dynamic corrosion resistance, which are indicated by the corrosion current density ic0 at the beginning of the tests and by the inclination s of the corrosion current-testing time curve respectively, and to the notch sensitivity which is obtained by fatigue tests in air with notched specimens. Finally Eq. (14), (κ-1)/η=K3K4√((e -1)/K1>√(i is obtained. (κ-1)/η is proportional to K3K4√(i for the same corrosive media irrespective of materials and of testing conditions. Test results show a linear relation between (κ-1)/η and √(i for the variety of materials, K3 and K4 being constant for the materials used in the present experiment. Thus, the meaning of the corrosion effect κ proposed by one of the authors is made clear. Besides sτT=K1 is obtained between the corrosion fatigue life τT and the dynamic corrosion resistance s, where the value of K1 is 4 in 1% saline and 2 in 0.3N hydrochroric acid.

Notch effect in low cycle fatigue

Abstract: Consideration of results of different type of fatigue tests made on unnotched and circumferentially notched steel bar specimens showed that in order to clarify notch effect in low cycle fatigue, it is necessary to distinguish fatigue lives for crack initiation and for fracture. Fatigue life for crack initiation can be regarded as function of peak value of effective strain range at notch, but crack propagation after crack initiation is almost independent of notch; so-called fatigue notch factor i.e. fatigue strength reduction factor due to notch effect is discussed in various aspects of fatigue curves at low cycle region.

Investigation of Low Cycle Fatigue at Elevated Temperatures : (Factors Which Govern Number of Strain Cycles to Failure)

Abstract: In order to clarify how the number of strain cycles to failure is influenced by temperature and frequency of straining in low cycle fatigue, it is necessary to observe the process of the fatigue failure. To obtain the knowledge of the process, crack appearances existing on the failed specimens were compared with each other. Fatigue tests were carried out in a push-pull testing machine on the AISI 321 stainless steel under various temperatures and frequencies of straining conditions. According to the results, the crack appearance does not depend on the temperature and frequency of straining conditions but on the plastic strain range. If fatigue tests are carried out in the same plastic strain range but at different temperatures and frequencies of straining conditions, similar distributions of crack density from the outer surface to the interior of specimens are always observed in the failed specimens. Thus, it is concluded that in low cycle fatigue the behaviour of fatigue cracks is governed primarily by the plastic strain range and it is deduced that the rate of fatigue process depends on temperature, strain rate, and plastic strain energy per cycle.

Apparatus for improving the torsional fatigue strength of crankshafts

Abstract: Crankshafts frequently have low torsional fatigue strength in the region of the oilholes on the main bearing surfaces when inductively hardened. The invention provides a method and apparatus for producing hardened zones which increase in depth along the main bearing surface towards the oilhole, which oilhole is preferably hardened along its whole length, whereby the torsional fatigue strength is improved.

Effect of stress biaxiality on the high-strain fatigue behavior of an aluminum-copper alloy

Abstract: Although there is now a considerable volume of high-strain (<105 cycles) fatigue data for uniaxial tension-compression and simple-bending conditions, relatively little information is available regarding the effects of stress and strain biaxiality. A method which has been used to study the effects of biaxiality on longlife fatigue strength is to subject thin-walled tubes to repeated internal pressure and an end load which is in phase with, and a linear function of, the pressure. The object of the present research was to use this method to study the influence of stress biaxiality on the high-strain fatigue behavior of a high strength, aluminum-4% copper alloy at room temperature. From a continuum-mechanics point of view, this material is completely elastic after the first few load cycles. Cylinder results for hoop to axial stress ratios of 2:1, 1:1, 1:2 and 2: −1 suggest that fatigue failure of this material in the life range 103 to 105 cycles is primarily dependent on the maximum range of tensile stress. This conclusion and a study of fracture surfaces led to the use of linear-elastic fracture mechanics to interpret the fatigue and brittle fracture behavior of these cylinders.

X-Ray Study of Surface Residual Stress Produced in Fatigue Process of Annealed Metals

Abstract: Changes in surface residual stress during fatigue process of annealed specimen are investigated adopting X-ray stress measurement. It is found that in torsional fatigue a tensile residual stress appears in the early stage of fatigue process, which is insensitive to the alternation of applied stress range. Meanwhile in bending fatigue, the residual stress produced during stress alternations is fairly dependent on the range of applied stress. For instance, in the case of completely reversed bending fatigue, compressive residual stress is produced at the early period of fatigue process. Considerations are made on the mechanism of the changes in residual stresses, in connection with the behavior of microscopic lattice defects during fatigue process. The effect of residual stress on fatigue life is also discussed.