bluuebunny/crossref_metadata_2025_split huggingface dataset:
FATIGUE AT NOTCHES SUBJECTED TO REVERSED TORSION AND STATIC AXIAL LOADS
Authors: Brown M. W. , Hay E. , Miller K. J. 
Published: April 2007

AbstractReversed torsion with and without a superimposed end load has been applied to 1% Cr‐Mo‐V steel specimens containing sharp notches. Crack propagation was monitored by a sensitive d.c. potential drop system that measured crack depths between 25 μm and 0.6 mm from the root of the notch.Stress intensity factors do not satisfactorily correlate all the crack growth data but a strain intensity factor which is a function of material properties and notch plastic zone size shows a significant improvement and provides a single upper bound solution for both ambient and elevated temperatures. This solution permits designers to make safe lifetime assessments.At room temperature cracks initially propagate by mode II along the surface, and mode III radially but at low stresses crack growth is continued by mode I propagation. At higher stresses a transition to mode I cracking is avoided. Elevated temperature causes a brittle layer to form and in this case cracks initially propagate by mode I which then translates to mode III cracking at high stresses.Mode III thresholds are significantly higher than mode I thresholds but a constrained shear strain zone, as found at the root of notches subjected to torsion, permits the initiation and generation of a mode III crack. The application of an axial load enhances the mode III crack propagation rate since this increases the effective crack tip intensification factor.
INFLUENCE OF TEMPERATURE ON FATIGUE CRACK GROWTH BEHAVIOUR OF STEELS AT ULTRASONIC FREQUENCY
Authors: PuškÁr A. , Várkoly L. 
Published: April 2007

AbstractFatigue crack growth rates have been measured at 22 kHz for two types of carbon steel, between 20 and 500°C under symmetrical push‐pull loading. The crack length was determined from the decrease in the resonant frequency of the specimen. For ČSN 412013 steel, an increased crack propagation resistance was observed between 250 and 300°C. The values of the constants C and n in the Paris equation, and Ka,th are dependent on temperature. The fatigue crack growth rate and C both increase with temperature, while n and Ka,th decrease with increasing temperature. Electron scanning and light microscopy have shown that intercrystalline fracture does not occur in ČSN 415313 steel at elevated temperature. Intercrystalline fracture was observed for specimens fatigued at 20°C and also in ČSN 412013 steel at temperatures of 200 and 500°C. The width of the plastic zone and the height of the surface relief around the fatigue crack increased with temperature.
FATIGUE LIFE PREDICTION IN BENDING FROM AXIAL FATIGUE INFORMATION
Authors: Manson S. S. , Muralidharan U. 
Published: April 2007

AbstractBending fatigue in the low cyclic life range differs from axial fatigue due to the plastic flow which alters the linear stress‐strain relation normally used to determine the nominal stresses. An approach is presented in this report to take into account the plastic flow in calculating nominal bending stress Sbending based on true surface stress. For a given surface strain εS, hence the surface life (NS), an equation is derived to express Sbending in terms of axial fatigue stress (Saxial), involving material constants c, b, NT which are obtained from axial fatigue information and f1 and f2 which are functions of strain hardening exponent and depend on the geometry of cross‐section. These functions are derived in closed form for rectangular and circular cross‐sections. The nominal bending stress and the axial fatigue stress are plotted as a function of life (NS) and these curves are shown for some materials of engineering interest.
CRACK GROWTH BEHAVIOUR OF FATIGUE MICROCRACKS IN LOW CARBON STEELS
Authors: Suh C. M. , Kitagawa H. 
Published: April 2007

AbstractThe behaviour of low carbon steels has been studied, in particular the initiation and growth of the major crack which led to final fracture of smooth specimens, via surface replica and photomicrograph techniques. From this study, the fracture process and fatigue life prediction characterized by the growth of surface microcracks have been analysed by a new approach unifying the conventional approaches based on the final fracture of materials with the fracture mechanics approach. Knowledge of fracture parameters is critical for non‐destructive inspection during service life and the application of fracture mechanics to life prediction and assessment.
FRACTOGRAPHIC ANALYSIS OF CRACK GROWTH AND SHEAR LIP DEVELOPMENT UNDER SIMPLE VARIABLE‐AMPLITUDE LOADING
Authors: Ling M. R. , Schijve J. 
Published: April 2007

AbstractFatigue crack growth experiments were carried out on 2024‐T3 sheet specimens, loaded under simple variable‐amplitude load sequences, including blocks of overload cycles or underload cycles and blocks of low amplitude cycles. The purpose was to study interaction effects by analysing striation measurements and shear lip developments. The striations clearly demonstrate delayed retardation. Shear lip measurements indicate significantly slower crack growth rates if the percentage shear lip increases from zero (no shear lips) to 100% (fully in the shear mode). The significance of incompatible shear lips during variable‐amplitude loading is discussed. The test results are evaluated with relation to interaction mechanisms and the meaning by cycle‐by‐cycle prediction models.
THERMAL FATIGUE UNDER MULTIAXIAL STRESSES
Authors: Junyi Feng , Mengxin Bian , Zijou Dang 
Published: April 2007

AbstractThermal fatigue under multiaxial stresses has been investigated. Circular cylindrical specimens were tested under thermal fatigue which was in‐phase with axial mechanical fatigue loading. The axial forces on the specimens were varied throughout the test programme, but all the temperature cycles were identical, so various biaxial stress and strain ratios were obtained. Straight thermal fatigue cracks occurred in different directions and also net‐like crazes in various patterns were observed on the surfaces of the specimens. The transient temperature, stress and strain fields have been calculated with a thermal elasto‐plastic Finite Element Method. Comparing test results with calculations, it appears that the patterns of thermal fatigue cracks are dependent on the stress state and the plastic strain state, not on the strain state. The direction of cracks is perpendicular to the maximum principal stress and the maximum plastic strain. Net‐like thermal fatigue crazes will occur when one principal stress is about the same as the other one and one plastic strain component is approximately equal to another.
FATIGUE CRACK INITIATION AND GROWTH BEHAVIOR OF Cu‐16 at.% A1 SINGLE CRYSTALS
Authors: Hong Sun Ig , Laird Campbell 
Published: April 2007

AbstractIn an attempt to understand the fatigue crack initiation and growth behavior of planar slip alloys, studies have been carried out in strain control on Cu‐16 at.% A1 single crystals oriented for easy glide. Alloy single crystals of Cu‐16 at.% A1 do not show saturation like copper crystals, but harden slowly and steadily throughout life, for the whole range of amplitudes applied. Cracks, the initiation and growth of which were studied by the sharp corner technique, were found to initiate when the peak stress reached 32 MPa irrespective of strain amplitude. The distribution of crack sizes in Cu‐16 at.% A1 single crystals was found to be more skewed to small cracks than that of copper. This behavior is attributed to the frequent migration of the bands of localized slip in this material. The fatigue lives of this alloy at low strain amplitudes (ypm < 6‐7 × 10−3) were found to be longer than those of copper single crystals because the strain is distributed more homogeneously than in copper. At high strain amplitudes, however, they become shorter because of the higher peak stress. The fatigue lives of Cu‐A1 crystals are predicted from those of copper on the basis of the different volume fractions of localized strain in the two materials; the prediction agrees well with the actual lives of Cu‐Al crystals. By geometrical consideration of secondary slip planes with respect to a primary crack, it was found that the critical system (A6) is most favored for secondary cracking adjacent to a primary crack.
POP‐IN AND CRACK ARREST IN AN HY80 WELD
Authors: Sumpter J. D. G. 
Published: April 2007

AbstractIt is generally thought that, when a material is in its brittle to ductile transition, it is more difficult to design for crack arrest than to prevent crack initiation (cleavage). This report shows that this is not always true for weldments. Comparison is made between compact crack arrest (CCA), Ka, and crack tip opening displacement (CTOD), KJc, toughness for the same HY80 weld. The value of Ka is shown to be much higher than the minimum KJc for pop‐in fracture initiation. It is considered that the results support the conclusion of Japanese research workers (Arimochi and Isaka) that small pop‐ins (in the CTOD test) propagate and arrest without load drop. It follows that prediction of structural failure for weldments need not be based on minimum pop‐in toughness from CTOD tests.
MODELLING RESIDUAL STRESSES AND FATIGUE CRACK GROWTH AT COLD‐EXPANDED FASTENER HOLES
Authors: Clark G. 
Published: April 2007

AbstractThis paper describes a model developed for predicting residual stresses and crack growth in residual stress fields, and the application of the model to crack growth from cold‐worked fastener holes in thick section aircraft components. Comparison with experimental results demonstrates that the model can provide useful predictions of critical crack length, and a capability for correctly predicting the maxima and minima in the crack growth rate for cracks from cold‐expanded holes. It also permits the observed asymmetry in cracking from cold‐worked fastener holes to be better understood.
SHORT FATIGUE CRACK GROWTH BEHAVIOUR OF A LOW CARBON STEEL UNDER CORROSION FATIGUE CONDITIONS
Authors: Akid R. , Miller K. J. 
Published: April 2007

AbstractThe effect of an aqueous chloride environment upon the development and growth of short fatigue cracks from smooth specimen surfaces has been studied under fully reversed torsional fatigue loading conditions. Crack initiation and growth has been monitored using a plastic replication technique enabling a full history of cracking characteristics to be recorded. Corrosion fatigue conditions were achieved by complete immersion in a 0.6 M NaCl solution, of nominal pH value 6.0, with specimens corroding at the free corrosion potential. Variations to these conditions were obtained by the addition of concentrated hydrochloric acid enabling test solution pH values to be altered, typically pH values of 3.5 and 2.0 were obtained. Further information regarding the effects of the environment on the early stages of crack development were obtained by conducting two stage alternate immersion type testing conditions. Evaluation of these effects through previously established Elastic‐Plastic Fracture Mechanics models shows that the environment plays a major role during the early stages of microstructure‐dominated crack growth particularly as cracks approach major barriers to propagation and at decreasing levels of applied shear stress.
CRACK‐FOLLOWING FOR ACCURATELY DETERMINING FRACTURE TOUGHNESS
Authors: Whitehead R. D. 
Published: April 2007

AbstractCurrent standard fracture‐mechanics methods encourage sudden, explosive and total testpiece fracturing in which one catastrophic event produces one set of measurements. By demanding conformance to the overall elasticity requirement while relaxing thickness and crack‐length specifications and following a slow crack‐growth sequence, series of simultaneous measurements were made on single testpieces. From these measurements independent values of the Mode‐I critical stress‐intensity factor and strain‐energy release rate were determined. Polyethersulphone injection‐moulded discs were prepared as round‐compact testpieces. The crack grown from a chevron‐notch was propagated under control, slowly. A large number of measurements were made as the crack extended. The fractures were smooth, square to the body of each disc and had a stable crack path across the diameter. The independent fracture‐toughness values were small but their derived modulus agreed well with directly measured values of Young's modulus, thus confirming the elastic integrity of the test.
FATIGUE CRACK PROPAGATION CHARACTERISTICS OF GLASS FIBRE REINFORCED POLYCARBONATE IN HOT DISTILLED WATER
Authors: Murakami Ri‐ichi , Noguchi Shinji 
Published: April 2007

AbstractThe fatigue crack propagation behaviour of polycarbonate and glass fibre reinforced polycarbonate was studied in hot distilled water. The effects of temperature, distilled water and glass fibre content on fatigue crack growth rate were determined. In distilled water at 333 K, the fatigue crack growth rate decreased with increasing glass fibre content. A melting was observed of the adhesive bond between the glass fibres and the matrix. It was evident that the fracture morphology closely relates to the fatigue crack growth rate which depends on the ΔK parameter rather than the Kmax parameter when the materials are tested in hot distilled water.
A STUDY OF SPECIMEN SIZE ON J‐R CURVE BEHAVIOUR
Authors: Jones R. L. , Gordon J. R. , Challenger N. V. 
Published: April 2007

AbstractThis paper presents results from an experimental programme to study size effects in J‐R curves. Results are presented from unloading compliance R curve tests on different sized single edge notch bend specimens of nickel aluminium bronze and compared with previously published R curve data on a Ti3A1‐2.5V titanium and an HY 100 steel alloy. The crack growth resistance was measured in terms of the standard fracture resistance J, J corrected for crack growth and the J modified parameter proposed by Ernst. It was observed that following a region of size independence small specimen J‐R curves could fall either above or below the large specimen curve. It was found that although the limit to J controlled crack growth could be extended the limit is not unique but dependent on material type.
INTERACTION OF OVERLOADS ON FATIGUE CRACK GROWTH FOR 40CrNi STEEL
Authors: Yang Shuilong , Li Hua 
Published: April 2007

AbstractThis work was designed to improve the general understanding of loading sequence effects on fatigue crack growth and lead to the development of improved methods for predicting crack propagation behaviour. Two loading histories were selected (1) a baseline amplitude with periodic overloads or underloads, and (2) several overloads without interactive effects. The specimen used was of a Wedge Opening Loading type and the material was a low alloy high strength steel, i.e. 4OCrNi. It was found that the Linear Summation of Damage (LSD) assumption could be applied in predicting fatigue crack growth rate (FCGR) under periodic overloads or underloads within the scatterband of the constant amplitude data obtained using an Alternating Current Potential Drop technique for measuring crack length for multiple specimens with several load amplitudes. A discrepancy existed between the FCGR predicted from LSD and the one actually measured during several hundreds of loading cycles immediately following every non‐interactive overload of the latter loading history although the overload ratio was the same as that of periodic overloading. The causes of this phenomenon are discussed.
PARABOLIC CURVED CRACK FRONTS IN FRACTURE TOUGHNESS SPECIMENS OF PARTICULATE REINFORCED ALUMINIUM ALLOY METAL MATRIX COMPOSITES
Authors: Roebuck B. 
Published: April 2007

AbstractCrack front shapes in relatively thick fracture toughness specimens of Sic particulate reinforced metal matrix composites have been analysed. They were found to have a common shape, that of a parabola. This shape is thought to arise as a result of a distribution of residual stress across the test‐piece. A simple analysis is used to derive an expression for an effective crack length which can be used to calculate KIC values in specimens in which the crack fronts are excessively curved and do not meet relevant criteria for curvature in current standards for toughness testing of metallic materials.
SOME MECHANICAL CHARACTERISTICS OF NITROGEN STRUCTURAL STEELS
Authors: Minchev Kiril 
Published: April 2007

AbstractIn this paper, test conditions and microstructural factors have been investigated for newly developed nitrogen steels at load rates and test temperatures suitable for future operating conditions. Static tests have been carried out at ε∼ 10−4 s‐1 and dynamic tests at ε∼ 102 s−1. Different test temperatures enable fracture mechanisms and fracture toughness variations to be studied. Anisotropy of some characteristics in the initial (non‐heat‐treated) state, together with heat treatment effects and structural changes under two load rates have been analysed. Fracture appearance transition temperature (FATT) values have been obtained from absorbed energy and fracture surface crystallinity values. Using yield strength and fracture toughness data, an estimate has been made of critical crack lengths for unstable fracture.
EFFECTS OF CONSTITUENT SCALE ON STRESS TRANSFER AND MATRIX CRACKING
Authors: Karbhari V. M. 
Published: April 2007

AbstractThe fundamental aspect of composites is that of stress transfer from the matrix to the fibers, and a number of mechanisms derive from this basic consideration. A previous analysis, although relatively simple and elegant, has a basic flaw, in that it assumes that there is no adhesion between the fiber and the matrix at the fiber ends, leading to the sometimes erronous condition of no stress transfer through those points. In this paper a modified end condition that better describes stress transfer is investigated and applied in determining the development of fiber, matrix and interfacial shear stress distribution in the uncracked, singly cracked and multiple cracked matrix configurations, with emphasis on the effects due to constituent dimensions.
EFFECT OF CYCLE MEAN STRAIN ON SMALL CRACK GROWTH IN ALLOY 718 AT ELEVATED TEMPERATURES
Authors: Rosenberger A. H. , Ghonem H. 
Published: April 2007

AbstractThe influence of the cyclic compressive excursion on the fatigue crack growth behavior of small surface cracks in Alloy 718 at 650°C is experimentally studied. Test conditions were chosen to simulate the cyclic plasticity found at notch locations in high temperature structural components. During cycling, the crack lengths were continuously monitored using the direct current potential drop method while the near field crack mouth opening displacement and global cyclic stressstrain behavior were measured using a laser interferometry technique and mechanical extensometry, respectively. Two aspects related to cyclic compressive excursion have been studied; crack closure and crack tip plasticity. Attempts have been made to use several modified ΔK expressions as well as ΔJeff to account for the effects of closure and decrease crack tip plasticity. It was concluded that the compressive excursion is most prominent in this alloy in its effect on the global plasticity and the subsequent loss of constraint. Closure was not found to be significant in the consolidation of test data.
FATIGUE CRACK PROPAGATION BEHAVIOUR UNDER VARIABLE AMPLITUDE LOADING IN THE NEAR‐THRESHOLD REGION OF A HIGH‐STRENGTH LOW‐ALLOY STEEL
Authors: Hénaff G. , Petit J. , Journet B. 
Published: April 2007

AbstractThe near‐threshold behaviour of a high‐strength low‐alloy steel used in helicopter rotors under variable amplitude loading is investigated in ambient air and in vacuum. Strong sequence effects occur, in particular a high decrease in crack growth rates after overloads of 40% on maximum load while keeping the amplitude constant. A detailed study of the retardation phenomenon due to the overloads provides an explanation for the different behaviour observed in air and in vacuum and has laid the basis for a method of predicting crack propagation under helicopter loading spectra.
FRACTURE ASSESSMENT FOR SECONDARY LOADS
Authors: Hallbäck Nils , Nilsson Fred 
Published: April 2007

AbstractThe fracture assessment of structures subjected to secondary loading systems was studied by FEM‐analysis of a few illustrative two‐dimensional examples. The first example is an edge‐cracked plate with a thermal gradient. The FEM‐calculations revealed that a purely elastic analysis yielded J‐values that are in most cases considerably more conservative than the ones calculated from an elastic‐plastic analysis. The results were further compared with different engineering type non‐linear estimates. As a second example a crack emanating from a semi‐circular notch in a rectangular plate was chosen. The plate was subjected to uniaxial tension along its boundaries. It turned out that for the cases considered the J‐values were fairly close to those elastically predicted.
A MODEL FOR THE COMBINED EFFECTS OF STRESS RATIO AND GRAIN SIZE ON THE LEFM FATIGUE THRESHOLD CONDITION
Authors: Lal D. N. 
Published: April 2007

AbstractA long‐crack, fatigue‐threshold model which explains and predicts the commonly observed effects of stress ratio, R, and grain size, d, on δK0, is proposed. The inclusion of a grain‐size‐effect is an extension of a recently proposed model that examined the effect of the R ratio. The extended model is based on the hypothesis that near‐threshold, crack growth involves two micro‐mechanical processes of fracture; Kmax‐controlled submicroscopic cleavage, which predominates when the defect concentration is small, and δK‐controlled reversed shear which predominates when the defect concentration is large, both processes occurring in a critically stressed volume, Vc, ahead of the crack tip. Defect concentration in Vc is reduced by a low value of R and a coarse grain size and is increased by a high value of R and a fine grain size. Good agreement is shown to exist between predicted and experimental curves of δK0 versus R and δK0 versus grain size for several steels and aluminium alloys. In particular, δK0 is shown to have an upper and a lower bound value for a material. The model may be used as an alternative procedure for obtaining quick, approximate but conservative estimates of δK0 for practical design applications.
A MODEL FOR THE EFFECT OF A GASEOUS ENVIRONMENT ON THE LEFM FATIGUE THRESHOLD CONDITION OF STEELS
Authors: Lal D. N. 
Published: April 2007

AbstractUsing a different approach to those methods involving hydrogen‐embrittlement and crack‐closure mechanisms a previously developed model is extended to predict the commonly observed effects of yield strength and a gaseous environment on the long‐crack fatigue crack growth threshold. The model assumes the existence of two intrinsic thresholds namely an upper bound value and a lower bound value related to, respectively, Kmax‐controlled cleavage and δK‐controlled reversed shear mechanisms of crack growth in a critically stressed volume at the crack tip. This new development assumes that nascent hydrogen atoms, liberated from moisture in the environment, assist in reducing dislocation mobility thereby rationalizing experimental observations on low strength materials in moist laboratory air when compared to a dry inert environment. Quantitative predictions of fatigue thresholds in laboratory air and inert environments show good agreement with experimental data for several low and high strength steels. This alternative procedure may be found to be useful in practical design applications when reasonably fast and accurate estimates are required.