bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel strategy to stop cigarette smoking by surgical patients: Pilot study in a preadmission clinic
Authors: Haile Melanie J. , Wiggers John H. , D. Spigelman Allan , Knight Jenny , Considine Robyn J. , Moore Karen
Published: March 2003

Background:  Evidence‐based guidelines suggest that all services, wards and clinics within hospitals consider smoking status a vital sign and routinely provide cessation care. Despite this, such opportunities are currently under‐utilized. The aim of the present pilot study was to determine the potential effectiveness, feasibility and acceptability of computer delivery of smoking cessation advice to surgical preadmission patients.

Methods:  All smokers attending a non‐cardiac surgical preadmission clinic at the John Hunter Hospital, New South Wales, completed a brief computerized smoking cessation intervention programme. Nine months following completion of the programme, patients completed a follow‐up telephone interview that assessed their smoking status and the acceptability of the programme.

Results:  At follow up, 22 of the 37 participants (60.0%) reported that they had stopped smoking prior to their surgery 9 months previously. Of the 37 participants at follow up, five reported that they were no longer smokers at that time, a cessation rate of 13.5%. Among those patients still smoking, a trend toward smoking fewer cigarettes was evident. Of the 56 smokers at baseline, all completed the computerized smoking cessation programme, with an average completion time of 21 min. A large majority of the smokers (80%) and non‐smokers (88%) found that the provision of smoking cessation advice by the computer was appropriate and acceptable. Extrapolation of the results to a full year suggests a cost per quitter of $443.

Conclusions:  An interactive computerized smoking cessation programme is an acceptable and feasible method of routinely encouraging surgical preadmission clinic patients to stop or reduce their smoking. Further development and testing of the efficacy of this approach is required.
Wound blisters post hip surgery: A prospective trial comparingdressings
Authors: Lawrentschuk Nathan , Falkenberg Michael P. , Pirpiris Marinis
Published: March 2003

Introduction:  Wound blisters are formed in the epidermis adjacent to surgicalincisions and are a significant cause of morbidity following hipsurgery. This study was designed to compare two commonly used primarydressings, namely a nonadherent absorbable (NAA) dressing and paraffintulle gras (PTG). Monitoring for the subsequent development of woundblisters in the epidermis adjacent to the surgical incision wasthen undertaken.

Methods:  The present study was performed in the setting of a prospective,randomised trial of 50 consecutive patients undergoing hip surgery.It was assumed there would be no difference in the development ofblisters between the dressing groups. The alternative hypothesiswas that PTG would, because of its properties, provide less frictionin the epidermis and contribute to fewer wound blisters.

Results:  A statistically significant difference (P = 0.0028)between the two dressing groups was observed with the NAA group developingblisters in 17 (64%) patients and the PTG group in onlytwo (8%) of the patients.

Conclusion:  The present study would suggest that PTG produces fewer woundblisters following hip surgery when compared to the NAA type asa primary dressing.
A RELIABILITY‐BASED MODEL TO PREDICT SCATTER IN FATIGUE CRACK NUCLEATION LIFE
Authors: Tryon RG , Cruse TA
Published: March 2003

This paper investigates the scatter inherent in the early stages of fatigue life. A probabilistic fatigue model is proposed which relates the microstructural heterogeneity to the scatter in crack nucleation life. The crack nucleation life is defined as the number of cycles necessary to develop a crack with a length equal to the grain size. The model assumes homogeneity at the level of the grain size. A fracture mechanics‐based microstructural model is used to describe the response of the grains. The primitive random variables which drive crack nucleation are identified and recent developments recorded in the literature are used to describe their statistical characteristics. First order reliability methods are used to predict the statistical distribution of fatigue crack nucleation life. Comparisons are made with trends in experimental observations.
ANALYSIS OF FREE‐EDGE STRESS AND DISPLACEMENT FIELDS IN SCARF JOINTS SUBJECTED TO A UNIFORM CHANGE IN TEMPERATURE
Authors: Qian ZQ , Akisanya AR
Published: March 2003

The role of free‐edge stresses in controlling the initiation of failure from the interface corner of a scarf joint subjected to a uniform change in temperature is examined. In general, the stress field can be expressed by σij = Hrλ−1 + σij0 , where r is the radial distance from the interface corner, λ − 1 is the order of the stress singularity, H is the intensity of the singularity, and σij0 is a non‐singular constant stress. A combination of the finite element method and a path‐independent integral is used to evaluate the magnitude of H for two joint configurations: (i) a scarf joint between two long bi‐material strips; and (ii) a scarf joint consisting of a thin elastic layer sandwiched between two substrates. The magnitude of H is linearly dependent on a non‐dimensional constant function a; the magnitude of a decreases with increasing level of mismatch in the elastic properties of the bonded materials. A comparison between the values of H evaluated by the path‐independent integral method and the commonly used extrapolation method indicate that the extrapolation method could be in error by as much as 25%.
A FIBRE STRESS‐BASED PARAMETER FOR THERMOMECHANICAL FATIGUE LIFE PREDICTIONS OF TITANIUM MATRIX COMPOSITES
Authors: Johnson  , Calcaterra
Published: March 2003

Titanium Matrix Composites (TMCs) are envisioned for use in the next generation of advanced aircraft and their engines. To ensure a smooth transition to industry, fatigue life prediction methodologies, which can account for random variations in mechanical and thermal loads, must be developed. To facilitate the development of such a model, fatigue testing has been conducted at Georgia Tech. on [0/ ± 45/90]s and [90/ ± 45/0]s laminates of SCS‐6/Timetal 21S. The tests were done at temperatures of 400, 500 and 650 °C, with hold times of 1, 10 and 100 s superimposed at the maximum stress. The purpose of the tests was to separate the effect of time‐dependent deformation from the effect of environmental degradation. Using the results of these tests, and results generated at NASA–Lewis Research Center (LeRC) and the US Air Force’s Wright Laboratory, a model has been developed which is based on the stress in the load‐carrying fibres. The stress is modified by an effective stress concentration factor that is due to matrix cracking and a factor that includes the effect of hold times. It is a single term model that is intended for treating any variations in mechanical and thermal loads. Verification of this model is achieved by predicting fatigue lives for specimens subjected to spectrum loads performed at NASA–Langley Research Center (LaRC) and vacuum tests completed at Georgia Tech. The model is compared to five methodologies previously developed for life prediction, and is shown to have significantly better predictive power while reducing the number of empirical constants and curve fitting parameters necessary to collapse the data.
A STATISTICAL INVESTIGATION OF THE FATIGUE LIVES OF Q235 STEEL‐WELDED JOINTS
Authors: Zhao  , Gao  , Sun
Published: March 2003

An investigation into the fitting of six assumed distributions (three‐parameter Weibull, two‐parameter Weibull, extreme minimum value, extreme maximum value, normal and lognormal distributions) of 23 groups of fatigue life data for Q235 steel‐welded joints is performed in terms of linear regression analyses. The results reveal that the fatigue life distribution shapes mostly tend to be positively skewed. Therefore, the extreme minimum value and normal distributions are not the most appropriate distributions to assume for a fatigue life evaluation. The three‐parameter Weibull distribution may give misleading results in fatigue reliability analyses because the shape parameter is often lesss than 1. This means that the hazard rate decreases with fatigue cycling. This is contrary to the general understanding of the behaviour of welded joints. Reliability analyses may also be affected by slightly non‐conservative evaluations in tail regions of the three‐parameter Weibull distribution. The two‐parameter Weibull distribution does not give as good a fit as either the extreme maximum value distribution or the lognormal distribution. On the other hand, the extreme maximum value and lognormal distributions can be safely assumed in reliability analyses due to the good total fit effects and the conservative evaluations in tail regions. In addition, the extreme maximum value distribution is in good agreement with the general physical understanding of the structural behaviour of welded joints.
INFLUENCE OF INTERMEDIATE LOADING RATES AND TEMPERATURE ON THE FRACTURE TOUGHNESS OF ORDINARY CARBON–MANGANESE STRUCTURAL STEELS
Authors: Lorentzon  , Eriksson
Published: March 2003

Three‐point bend and compact tension specimens, taken from beam sections of modern and older ordinary C–Mn structural steels, were tested at intermediate loading rates at room temperature and −30 °C. The experimental work, except the loading rates used, was performed according to ASTM E‐813. In order to investigate transferability of data, full‐scale beam sections were also tested at intermediate loading rates. The fracture toughness of C–Mn structural steels depends strongly on the loading rate, and decreases rapidly with increasing loading rate at and just above the maximum prescribed in ASTM E‐813. Fracture toughness data for structures exposed to intermediate loading rates indicate the requirement for testing at appropriate loading rates. The behaviour of full‐scale structural elements subjected to intermediate loading rates can, provided certain conditions are fulfilled, be predicted from data obtained from small laboratory specimens.
A MODIFIED STRIP‐YIELD MODEL FOR PREDICTION OF PLASTICITY‐INDUCED CLOSURE IN SURFACE FLAWS
Authors: Daniewicz
Published: March 2003

A slice synthesis methodology is developed and used to construct a modified strip‐yield model for the semielliptical surface flaw, enabling prediction of plasticity‐induced closure along the crack front and subsequent fatigue crack growth. A mathematical description of the model is presented. Slice synthesis methodologies have previously been limited to stress intensity factor and elastic crack displacement computation. Predictions of flaw shape evolution under cyclic loading are compared with experimental data for aluminium alloy specimens under uniform constant amplitude loading withR = 0.1, 0.3 and 0.6. Model predictions are shown to correlate well with experimental data. An empirical correlation of relative crack opening stress with appliedRratio from the literature is shown to underestimate the level of closure at the deepest point of penetration when compared with the model predictions.
INFLUENCE OF SURFACE DEFORMATION AND ELECTROCHEMICAL VARIABLES ON CORROSION AND CORROSION FATIGUE CRACK DEVELOPMENT
Authors: Akid  , Dmytrakh
Published: March 2003

This paper presents experimental data for a 0.2%C steel/artificial seawater system showing the influence of shear loading on corrosion response, via measurements of electrochemical variables, e.g. anodic/cathodic Tafel slopes and polarization resistance. Based on the results of these tests, several corrosion fatigue tests were conducted at different stress levels under potentiostatic control. Analysis of the results shows there to be a dependence of corrosion rate on the ratio of applied/yield strain and test frequency. In addition, the corrosion current associated with corrosion fatigue (CF) damage appears to be dependent upon the crack size, which in turn shows a relationship with fatigue crack growth rate. This paper sets out to determine the influence of stress on electrochemical parameters, i.e. free corrosion potential,Ecorr , polarization resistance,Rp , anodic,τaand cathodic,τcTafel constants. Based upon these results, it is found that a simple linear relationship between stress and corrosion damage does not exist. Furthermore, analysis of the corrosion current fluctuations during corrosion fatigue crack growth shows a minimum current coincident with the point at which a crack is growing at its slowest rate.
R‐CURVE TESTING AND ITS RELEVANCE TO STRUCTURAL ASSESSMENT
Authors: Schwalbe  , Heerens
Published: March 2003

Crack growth resistance can be substantially affected by the constraint conditions of a structural member which in turn are mainly a function of geometrical variables and the degree of plasticity. Standardized test methods are restricted to high constraint conditions as represented by deeply cracked bend‐type specimens and may hence lead to conservative structural assessments. It is demonstrated that adjusted testing can be used to reduce the degree of conservatism. Due to rapidly increasing computer capabilities, a combination of conventionalR‐curve testing with micromechanical models emerges as an accurate tool which may permit routine evaluations of practical situations in the near future.
HIGH‐CYCLE FATIGUE BEHAVIOUR OF SPHEROIDAL GRAPHITE CAST IRON
Authors: Yaacoub Agha H , Béranger A.‐S. , Billardon R , Hild F
Published: March 2003

An expression for the cumulative failure probability of a structure is proposed for cyclic loading conditions. This expression is dependent on an initial flaw distribution and a microcrack propagation law. Two sets of experiments were carried out on specimens made of spheroidal graphite cast iron. These specimens are tested under cyclic tension with two different load ratios. The initial flaw distribution is experimentally identified from microscopic observations. The crack propagation law parameters are identified from experimental results obtained with a load ratio R = 0.1. The expression for the failure probability is then used to predict experimental data obtained with a load ratio R = −1.
FATIGUE CRACK GROWTH BEHAVIOUR OF METALLIC BIOMATERIALS IN A PHYSIOLOGICAL ENVIRONMENT
Authors: Nakajima Masaki , Shimizu Toshihiro , Kanamori Toshitaka , Tokaji Keiro
Published: March 2003

Fatigue crack propagation (FCP) in Ringer's solution has been studied on four metallic biomaterials, i.e. pure titanium (TP35H), stainless steel (SUS304), dual‐phase stainless steel (SUS329J4L), and titanium alloy (Ti–6Al–4V). For TP35H and SUS329J4L, the crack growth characteristics in Ringer's solution were almost the same as those in room air in the entire ΔK region examined, and thus the effect of Ringer's solution was not observed. The crack growth rates of SUS304 were enhanced in Ringer's solution in the region of ΔK ≥ 25 MPa m as compared to room air, while below this ΔK level they were similar in both environments. Also in Ti–6Al–4V, similar crack growth behaviour in Ringer's solution was found. From the comparison among the da/dN–ΔK relationships of the four materials in Ringer's solution, TP35H exhibited the fastest growth rates and then Ti–6Al–4V, SUS304, SUS329J4L in the order of decreasing growth rate. On the contrary, if the data were plotted in terms of ΔKeff /E, Ti–6Al–4V and TP35H showed superior crack growth resistance to the stainless steels.
Measurement of fatigue crack growth in large compact tension specimens using an AC magnetic field method
Authors: Austin J.
Published: March 2003

Fatigue crack growth rate data are required in order to carry out a numerical analysis of the fatigue performance of complex structural components. These data are obtained by measuring crack growth in standard fracture mechanics specimens. A new method for measuring fatigue crack growth in compact tension specimens has been developed. The technique is based on the measurement of the surface magnetic fields produced when passing a high‐frequency alternating current through the specimen. Fatigue crack growth data recorded using this method indicated an accuracy of ±0.02 mm when compared with optical measurements. The technique is suitable for computer‐controlled operation and could easily be applied to other standard specimen geometries.
Three‐dimensional calculations of high cycle fatigue life under out‐of‐phase multiaxial loading
Authors: Akrache  , Lu
Published: March 2003

In this study, we investigate the prediction of fatigue life at a high number of cycles (>5 × 104 cycles) for three‐dimensional structures. An approach has been developed that includes the results of fatigue tests in a program using the finite element method. Numerical fatigue life calculations using three fatigue criteria were conducted to predict S–N curves. To complete the study and validate this approach, tests were carried out on FGS 700/2 cast iron with different geometrical structures and different fatigue loadings.
Fracture mechanisms and fracture mechanics at ultrasonic frequencies
Authors: Stanzl‐Tschegg
Published: March 2003

Performing fatigue tests at ultrasonic frequencies, e.g. 20 000 Hz, allows one to perform experiments beyond 109and 1010cycles within half a day or a week, respectively. The testing technique has led to the construction of fatigue machines of high technical standard. Use of the ultrasound technique to study the mechanisms of crack initiation in pure metal single crystals, in cast alloys with voids being crack initiation sites, and in complicated fibre‐reinforced laminates is reported. Likewise, use of ultrasonic loading to study the mechanisms of crack propagation is discussed, as well as LEFM principles; especially when these principles cannot be applied. It is shown how crack growth retardation with increasing crack length is attained in fibre‐reinforced laminates by the effect of fibre bridging. Additional experimental possibilities, e.g. random loading, variation of mean load, superposition of shear loads, variation of temperature and environment, and not only axial but also torsional loading at ultrasonic frequency, and recent research results are discussed.
A Weibull stress model to predict cleavage fracture in plates containing surface cracks
Authors: Gao  , Dodds Jr  , Tregoning  , Joyce  , Link
Published: March 2003

This study applies recent advances in probabilistic modelling of cleavage fracture to predict the measured fracture behaviour of surface crack plates fabricated from an A515‐70 pressure vessel steel. Modifications of the conventional, two‐parameter Weibull stress model introduce a non‐zero, threshold parameter (σw‐min ). The introduction of σw‐minbrings numerical predictions of scatter in toughness data into better agreement with experimental measurements, and calibration of this new parameter requires no additional experimental data. The Weibull modulus (m) and scaling parameter (σu ) are calibrated using a new strategy based on the toughness transferability model, which eliminates the non‐uniqueness that arises in calibrations using only small‐scale yielding toughness data. Here, the Weibull stress model is calibrated using toughness data from deep‐notch C(T) and shallow‐notch SE(B) specimens, and is then applied to predict the measured response of surface crack plates loaded in different combinations of tension and bending. The model predictions accurately capture the measured distributions of fracture toughness values.
An interpretation of theCtparameter for increasing load conditions
Authors: Lee J. H. , Kim Y. J. , Yoon K. B.
Published: March 2003

The prior assessment equations forCt , which is a well‐known fracture parameter for characterizing creep and creep–fatigue crack growth rates, have applicability to constant loading conditions only. However, crack growth due to creep can also occur under varying load conditions during a fatigue cycle when the loading (or unloading) rate is slow enough such that creep deformation can occur near the crack tip. Hence, the applicability of theCtparameter should be extended to varying load conditions.

In this study, a method of extending the use of theCtparameter to increasing load conditions is proposed. Based on the concept of Irwin’s effective crack size, new equations for estimatingCtunder increasing load conditions are derived and denoted as (Ct )r . Finite element analyses were also performed under various increasing load conditions. From the analysis, the variation of (Ct )rvalues during the load rise period is obtained and the difference between the (Ct )rvalue at the end of the load rise period and theCtvalue at the beginning of the succeeding load hold period is discussed. A generalized creep–fatigue crack growth model which employs (Ct )ras a parameter characterizing crack growth rate during the rise time is also discussed.
Crack profiles and corner point singularities
Authors: Pook
Published: March 2003

Crack profiles in the vicinity of a crack tip were investigated both theoretically by using standard displacement field equations, and by experiments using foam plastic models. Particular attention was paid to crack profiles in the vicinity of a corner point where a crack front intersects a free surface. Crack profiles for single‐mode and mixed‐mode cracks, calculated from standard displacement field equations, are incorrect in the vicinity of a corner point. The use of foam plastic models permits the visualization of crack profiles in the vicinity of a corner point. Strictly speaking, stress intensity factors have no meaning in the vicinity of a corner point, but for practical purposes it is possible to calculate representative values. Failure to take into account warping of an initially plane‐free surface, at a corner point, has led to some confusion in the finite element calculation of representativeKIIIvalues.
Bonded aircraft repairs under variable amplitude fatigue loading and at low temperatures
Authors: Vlot  , Massar  , Guijt  , Verhoeven
Published: March 2003

Bonded repairs can replace mechanically fastened repairs for aircraft structures. Compared to mechanical fastening, adhesive bonding provides a more uniform and efficient load transfer into the patch, and can reduce the risk of high stress concentrations caused by additional fastener holes necessary for riveted repairs. Previous fatigue tests on bonded Glare (glass‐reinforced aluminium laminate) repairs were performed at room temperature and under constant amplitude fatigue loading. However, the realistic operating temperature of −40 °C may degrade the material and will cause unfavourable thermal stresses. Bonded repair specimens were tested at −40 °C and other specimens were tested at room temperature after subjecting them to temperature cycles. Also, tests were performed with a realistic C‐5A Galaxy fuselage fatigue spectrum at room temperature. The behaviour of Glare repair patches was compared with boron/epoxy ones with equal extensional stiffness. The thermal cycles before fatigue cycling did not degrade the repair. A constant temperature of −40 °C during the mechanical fatigue load had a favourable effect on the fatigue crack growth rate. Glare repair patches showed lower crack growth rates than boron/epoxy repairs. Finite element analyses revealed that the higher crack growth rates for boron/epoxy repairs are caused by the higher thermal stresses induced by the curing of the adhesive. The fatigue crack growth rate under spectrum loading could be accurately predicted with stress intensity factors calculated by finite element modelling and cycle‐by‐cycle integration that neglected interaction effects of the different stress amplitudes, which is possible because stress intensities at the crack tip under the repair patch remain small. For an accurate prediction it was necessary to use an effective stress intensity factor that is a function of the stress ratio at the crack tip Rcrack tip including the thermal stress under the bonded patch.
Void growth and damage models for predicting ductile fracture in welds
Authors: Wilsius  , Imad  , Nait Abdelaziz  , Mesmacque  , Eripret
Published: March 2003

This study reports on a numerical and experimental investigation of ductile tearing using a local approach to fracture. Two models have been analysed: (i) the Rice–Tracey (RT) void growth model; and (ii) the Rousselier continuum damage theory. The effects of the model parameters, including the mesh size, on the crack growth behaviour have been analysed, and a significant influence on both the J‐values and the slopes dJ/da has been noted. The crack propagation in an overmatched welded joint has also been investigated. For the RT model, crack propagation has been simulated using the release node technique. Because this method requires one to previously assign the crack propagation path, using such a model is somewhat restrictive. This problem vanishes when dealing with Rousselier’s model (and more generally with coupled models) because the elements which are damaged automatically give the crack path.
Contact fatigue of automotive gears: evolution and effects of residual stresses introduced by surface treatments
Authors: Batista  , Dias  , Lebrun  , Le Flour  , Inglebert
Published: March 2003

Helical gears from an automotive gearbox, previously subjected to the surface treatments of carbo‐nitriding and shot‐peening, were submitted to contact fatigue tests. The X‐ray diffraction technique was used to characterize the evolution of different mechanical and metallurgical parameters as a function of gear damage. Particular attention was paid to residual stress relief. A numerical model was developed to predict residual stress relaxation and estimate the most likely localization of contact fatigue crack initiation. The stress–strain laws of the surface‐treated layers were determined by means of two separate experimental methods, based on locally measured parameters. The Dang Van multiaxial fatigue criterion was used to analyse the failure of the gears, taking into account the effects of friction and roughness.
Crack interaction modelling
Authors: Meyer  , Diegele  , Brückner‐Foit  , Möslang
Published: March 2003

The growth characteristics of short fatigue cracks under axial loading were investigated using specimens of the ferritic–martensitic steel F82H‐mod. Interest focused on crack propagation due to coalescence, which proved to be the dominant mechanism of crack growth. Crack propagation due to coalescence under a certain loading state is strongly influenced by the microstructure of the material on the one hand and by the interaction of cracks on the other. This study deals with an elasto‐plastic fracture mechanics analysis of two interacting cracks neglecting the microstructural influence. Finite element calculations based on a Ramberg–Osgood model for the material properties were performed to quantify the interaction of two cracks in terms of an interaction functionY depending on the material and crack configuration. Finally, a neural network was trained to determine the interaction function for two cracks within the range of interest.
Modelling fatigue crack growth in shot‐peened components of Al 2024‐T351
Authors: De Los Rios E. R. , Trull M. , Levers A.
Published: March 2003

Microstructural fracture mechanics concepts are used to develop a model to incorporate shot‐peening effects into crack propagation laws and fatigue life predictions. Shot peening produces a residual stress which resists opening of the crack and also produces a work‐hardened layer within which the flow stress is raised. The model takes account of these effects to give an accurate prediction of the increase in fatigue life. The model was also used to derive the conditions for crack arrest, and the results are presented in the form of a fatigue damage map (FDM). The FDM can be used for the determination of safe loads in durability and maintainability analyses.
Mixed‐mode crack opening displacement measurements for small fatigue cracks growing in Astroloy at 20 °C
Authors: Davidson
Published: March 2003

Crack opening displacements were measured for small fatigue cracks in Astroloy being grown with uniaxial stress application under high‐cycle fatigue conditions. Four cracks were investigated including one that grew from 27 to 74 μm in three increments. Most of the cracks grew at an angle to the loading axis and all opened bimodally. Crack opening scaled with distance from the crack tip similar to an elastic crack, which allowed the calculation of a local stress intensity factor for both mode I and mode II. The proportion of mode II stress intensity factor was relatively large, varying as 0.06 < ΔKII /ΔKI < 0.42, with an average of ~0.3. Thus, uniaxial loading remote to the cracks resulted in a bimodal opening response on the scale of the cracks.
Effect of solidification cooling rate on the fatigue life of A356.2‐T6 cast aluminium alloy
Authors: Zhang  , Chen  , Poirier
Published: March 2003

The effect of the cooling rate during solidification on the fatigue life of a cast aluminium alloy (A356.2‐T6) is examined. The fatigue lives were determined for specimens removed from ingots with a gradient in cooling rates along their heights. Low‐ and high‐cycle fatigue tests were conducted under both axial loading and reciprocating‐bending conditions at a stress (strain) ratio (R ) of −1.0, 0.1 and 0.2. Results show that the fatigue life decreases by a factor of three in low‐cycle fatigue (R = −1.0) and by a factor of 100 in high‐cycle fatigue (R = 0.1) as solidification cooling rate decreases from ~10 to ~0.3 K s−1 , as indicated by measurements of the secondary dendrite arm spacings in the ingots. Fatigue cracks initiated from porosity in the material solidified at slower cooling rates. When pore size is below a critical size of ~80 μm, as a result of increasing the cooling rate, the fatigue cracks initiated from near‐surface eutectic‐microconstituent. When present at or near the surface, large oxide inclusions initiated fatigue cracks.
Mean stress effects on low‐cycle fatigue for a precipitation‐hardening martensitic stainless steel in different tempers
Authors: Lin  , Chu
Published: March 2003

The objective of this study is to investigate the effects of mean stress and ageing treatment on the low‐cycle fatigue (LCF) behaviour of a precipitation‐hardening martensitic stainless steel (PHMSS). Uniaxial LCF tests were conducted under strain control with three strain ratios, R = −1, 0 and 0.5 on specimens heat‐treated to three different tempers, i.e. solution‐annealed (SA), peak‐aged (H900) and overaged (H1150) conditions. Experimental results indicated that under a strain ratio of R = −1, specimens in H900 temper exhibited longer LCF lifetimes than those in SA and H1150 tempers. However, this advantage for H900 over SA and H1150 tempers disappeared at higher strain ratios (R = 0 and 0.5) due to the greater sensitivity to mean stress effects in H900 temper. For a given temper at high strain amplitudes, the LCF lifetimes under the three applied strain ratios did not show significant differences as a result of the mean stress relaxation effect. However, at low strain amplitudes, cyclic loading at R = −1 generated longer LCF lifetimes in comparison to R = 0 and 0.5 due to the absence of detrimental tensile mean stress. LCF lifetime data obtained for the given PHMSSs under various combinations of strain ratio and heat treatment were well correlated with a strength‐normalized Smith–Watson–Topper (SWT) parameter in a log–log linear model.
The effect of microstructure on the morphology of fatigue cracks in UDIMET® 720
Authors: Brooks* R. R. , Rainforth W. M.
Published: March 2003

The low cycle fatigue (LCF) behaviour of four variants of UDIMET®720 was investigated. The materials comprised a fine grained (approximately 10 μm), powder processed material with a fine bimodal distribution (∼20 and 80 nm) of secondaryγ′; the same material, but with enlarged secondaryγ′ (∼480 nm); a coarse grained powder processed material (grain size ∼62 μm) and finally a cast and wrought material with a similar microstructural scale to the fine grained powder processed alloy, but with reduced interstitial element content. LCF testing was undertaken on corner notched square section specimens at 20, 300 and 600 °C with a frequency of 0.25 Hz, a cyclic stress range of 500 MPa and anRratio of +0.1. At 20 and 600 °C fracture was found to be macroscopically flat for all materials. However, at 300 °C, significant shear fracture was observed in the two materials that had a fine grain size and a fine secondaryγ′ size, leading to a characteristic ‘tear‐drop’ appearance. Only minor shear fracture was observed in the coarse grained and enlarged secondaryγ′ materials. Tensile tests indicated that weak dynamic strain ageing occurred in all materials at 300 °C. The fine grained powder processed U720 also exhibited dynamic strain ageing at 600 °C, but this was not the case for the coarse grained or cast and wrought materials. The origin of the shear fracture are discussed and related to the microstructure.
Fatigue crack growth rates under sequential mixed‐mode I and II loading cycles
Authors: Wong S. L. , Bold P. E. , Brown M. W. , Allen R. J.
Published: March 2003

One common mode of failure that occurs in rolling bodies such as gears, bearings and rails is due to the fatigue process. Several research workers suggest that rolling contact fatigue cracks are subjected to mixed mode I and II loading cycles. It is believed that the correct modelling of loading cycles can help us to study the mechanics of crack growth because fatigue comprises a major safety consideration in the design process. Experiments have been performed under nonproportional mixed‐mode I and II loading cycles with fixed degrees of overlap, so that coplanar cracks were produced. Three empirical crack propagation laws have been established which are related to both mode I and mode II effective stress intensity factor ranges.
Creep‐damaged pipe steels probed with positron spectroscopy
Authors: Somieski B. , Krause‐Rehberg R.
Published: March 2003

Using positron lifetime spectroscopy (POLIS) the degree of damage in creep‐influenced pipe steels was found to decrease with depth, as measured from the physical surface of the samples. Ultrasonic measurements were revealed to mostly note the differences in internal stresses, not in the microstructure. A critical limit of 160 ps average positron lifetime was determined at about 80% of material lifetime consumption in a creep experiment, independent of the material or the creep test parameters. The results suggest the technique of positron lifetime spectroscopy as a method for non‐destructive monitoring of creep damage.
The role of T‐stress in brittle fracture for linear elastic materials under mixed‐mode loading
Authors: Smith D. J. , Ayatollahi M. R. , Pavier M. J.
Published: March 2003

The purpose of this paper is to revisit the maximum tensile stress (MTS) criterion to predict brittle fracture for mixed mode conditions. Earlier experimental results for brittle fracture of polymethylmethacrylate (PMMA) using angled cracked plates are also re‐examined. The role of the T‐stress in brittle fracture for linear elastic materials is emphasized. The generalized MTS criterion is described in terms of mode I and II stress intensity factors, KI and KII and the T‐stress (the stress parallel to the crack), and a fracture process zone, rc . The generalized MTS criterion is then compared with the earlier experimental results for PMMA subjected to mixed mode conditions. It is shown that brittle fracture can be controlled by a combination of singular stresses (characterized by K ) or non‐singular stress (T‐stress). The T‐stress is also shown to have an influence on brittle fracture when the singular stress field is a result of mode II loading.
Branch crack development from the flank of a fatigue crack propagating in mode II
Authors: Doquet V. , Frelat J.
Published: March 2003

The propagation of fatigue cracks in mode II often leads to the development of a branch starting from a crack flank, some distance behind the tip and not to the expected bifurcation at the crack tip. This type of branch is suggested to initiate by decohesion along a secondary slip plane and to grow in mode I due to the tensile component of the mode II stress field. Finite element calculations are performed to evaluate the stress intensity factors for the main crack and the branch as a function of the position of the latter. It is shown that the branch has a substantial shielding effect on the main crack and generates contact forces along its flanks. The simultaneous and competitive growth of the main crack and the branch in fatigue is simulated step by step using kinetic data for mode II and mode I obtained for a maraging steel.
Size‐scale and slenderness influence on the compressive strain‐softening behaviour of concrete
Authors: Carpinteri A. , Ciola F. , Pugno N. , Ferrara G. , Gobbi M. E.
Published: March 2003

In this article the compressive mechanical behaviour of quasi‐brittle materials is analysed by means of experimental tests and by using an ad hoc algorithm for numerical simulations based on the Pseudo‐traction and the Boundary‐element methods. The experimental analysis is carried out on specimens with three different size‐scales, three different values of slenderness and two boundary conditions. The numerical analysis was carried out by taking into account the initial random crack distribution, considering the mutual crack interaction, the crack–boundary interaction and the internal friction between the faces of the cracks. The numerical results, in good agreement with the experimental data, highlight the characteristic strain‐softening behaviour of quasi‐brittle materials, and the influence of size‐scale and slenderness on the structural response. By observing the evolution of the crack patterns, it is possible to emphasize, both experimentally and numerically, the transition from crushing to splitting collapse by increasing the specimen slenderness, as well as the transition from ductile to brittle behaviour by increasing the specimen size‐scale.
An application of theJ‐Qmodel for estimating cleavage stress in the brittle‐to‐ductile transition
Authors: Miranda C. A. J. , Landes J. D.
Published: March 2003

A recent model was proposed by the authors to predict cleavage failure for steels based on a weak link mechanism and a crack tip stress field modified for planar constraint by theJ–Qtheory. The model uses the distribution of toughness results at a single temperature to predict a toughness distribution at a different temperature and/or geometry. In this model a material cleavage stress is needed to predict when the weak link fracture is triggered. This cleavage stress is a key input for the application of the model but it is not a property that is routinely measured and it is hence not available for most steel alloys. In this paper, a method to estimate the average value of the cleavage stress is presented, based on a characteristic of the model to predict cleavage failure. Examples of cleavage stress are given for several steels and these results are used to predict the toughness distributions for structural component models.
A high‐cycle fatigue apparatus at 20 kHz for low‐cycle fatigue/high‐cycle fatigue interaction testing
Authors: Matikas T. E.
Published: March 2003

High‐cycle fatigue (HCF) failures in aircraft engines are attributed to material damage states, created during processing or by in‐service loading and environmental conditions, and then propagated to failure by HCF loading. The loading configuration experienced by aircraft engine turbine blades consists of an axial load caused by the centrifugal acceleration during rotation combined with the tensile and compressive loads caused by the natural vibrations of the blades themselves. To simulate these loading conditions a new testing apparatus was developed that is capable of providing interactive low‐cycle fatigue/high‐cycle fatigue (LCF/HCF) loading, in ratios (of magnitude and frequency) that give a realistic simulation of the actual flight loads experienced by engine components. This testing apparatus is based on a HCF cell operating at 20 kHz. The cell can also be integrated to a servo‐hydraulic load frame, which provides a second fatigue cycle. The objective of this study was to demonstrate the capabilities of the new HCF apparatus via thermographic measurements and by performing LCF/HCF interaction tests.
Fatigue crack growth analysis of 2024 T3 aluminium specimens under aircraft service spectra
Authors: Kermanidis AL. TH. , Pantelakis SP. G.
Published: March 2003

The fatigue crack growth behaviour of 2024 T3 aluminium was investigated experimentally. The fatigue experiments were performed under constant stress amplitude, constant amplitude with single and multiple overloads and aircraft service spectra. The fatigue spectra used correspond to the air‐to‐air, air‐to‐ground and instrumentation and navigation flight phases. They were applied for different stress levels. In total 11 different random flight service spectra were examined. The retardation effects caused by the overloads on the fatigue crack growth behaviour and the fatigue crack growth under aircraft service spectra were predicted using an in‐house‐developed code. The code makes use of the strip plastic zone approximation to account for material hardening effects along the path of prospective crack growth. Crack growth is treated incrementally and corresponds to failure of material elements ahead of an existing crack after a certain critical number of fatigue cycles. For the simulation of irregular service spectra by equivalent sequences of distinguished stress cycles a modified rainflow counting method is utilized. Spectrum simulation accounts also for non‐linearity in fatigue damage accumulation and load sequence effects. The computed fatigue curves fit well with the experimental results.
Microstructural effects on crack closure and propagation thresholds of small fatigue cracks
Authors: Akiniwa Y. , Tanaka K. , Kimura H.
Published: March 2003

The crack closure behaviour of microstructurally small fatigue cracks was numerically simulated by combining the crack‐tip slip band model with the plasticity‐induced crack closure model. A Stage II crack started to propagate from an initiated Stage I crack. When the plastic zone was constrained by the grain boundary or the adjacent grain with higher yield stresses, the crack opening stress increased with crack extension, and the effective component of the stress range decreased. The crack‐tip opening displacement range (ΔCTOD), first decreased with crack extension due to the development of the residual stretch, then increased until the tip of the plastic zone reached the neighbouring grain boundary. When the plastic zone was blocked by the grain boundary, ΔCTODbegan to decrease. The arrest condition of cracks was given by the threshold value of ΔCTOD. At the fatigue limit, the arrest of small cracks takes place just after the Stage II crack crosses the grain boundary when the grain boundary does not act as a barrier. Only when the grain boundary has a blocking strength and the yield stress of adjacent grains is not so high, the arrest of Stage II cracks takes place before the crack reaches the grain boundary. The fatigue limit decreases with the mean stress. The predicted relation between the fatigue limit and the mean stress is close to the modified Goodman relation.
S–N curve characteristics and subsurface crack initiation behaviour in ultra‐long life fatigue of a high carbon‐chromium bearing steel
Authors: Shiozawa K. , Lu L. , Ishihara S.
Published: March 2003

The S–N curve obtained from cantilever‐type rotary bending fatigue tests using hour‐glass‐shaped specimens of high carbon‐chromium bearing steel clearly distinguished the fracture modes into two groups each having a different crack origin. One was governed by crystal slip on the specimen surface, which occurred in the region of short fatigue life and a high stress amplitude level. The other was governed by a non‐metallic inclusion at a subsurface level which occurred in the region of long fatigue life and low stress amplitude. The inclusion developed a fish‐eye fracture mode that was distributed over a wide range of stress amplitude not only below the fatigue limit defined as the threshold for fracture due to the surface slip mode but also above the fatigue limit. This remarkable shape of the S–N curve was different from the step‐wise one reported in previous literature and is characterized as a duplex S–N curve composed of two different S–N curves corresponding to the respective fracture modes. From detailed observations of the fracture surface and the fatigue crack origin, the mechanisms for the internal fracture mode and the characteristics of the S–N curve are discussed.
Corrosive fatigue of structures with dimple holes under spectrum loading
Authors: SHEN H. , GUO W. , LU G.
Published: March 2003

ABSTRACT Experimental investigation and life prediction are made for structures with straight holes and dimple holes in both laboratory ambient conditions and 3.5% NaCl solution under spectrum loading. With the aid of acoustic emission, label loading and fractography technique, the crack‐growth data are obtained in both environments. Stress‐intensity factors for the corner crack emanated from the dimple hole are evaluated by three‐dimensional (3D) finite element (FE) method. Life prediction of the tested structures is made by using the modified FASTRAN‐II code on the basis of corresponding fatigue crack‐growth rate curves. It is shown that once the initial defect size a0 is determined by one set of test data, it can be used together with the 3D crack‐growth method in order to provide accurate life prediction in alternative structure and loading condition. By comparison, life prediction by the traditional local strain method is also made which is shown to be less reliable than the 3D crack‐growth method.
Fatigue tolerant design of steel components based on the size of large inclusions
Authors: YATES J. R. , SHI G. , ATKINSON H. V. , SELLARS C. M. , ANDERSON C. W.
Published: March 2003

Fatigue failures in high strength steel components often originate from large, brittle inclusions. The durability of the components is strongly dependent on the size of the inclusions and the magnitude of the local stresses caused by the applied loads. A successful design must consider both the size and the number of large inclusions as well as the stress distribution arising from the geometry and loading of the component. This paper presents a new approach to the safe fatigue design of steel components based on the size distribution of large inclusions in a component with a given stress distribution. The procedure is illustrated using the example of the stress distribution around a hole in a plate, with the size of large inclusions in a large volume of steel estimated by the Generalized Pareto Distribution (GPD) method. It is found that the single largest inclusion is unlikely to lie in a highly stressed volume, but that the more frequently occurring slightly smaller inclusions contribute more to the probability of a fatigue failure. Knowledge of the shape of the size distribution over a range of large sizes, not solely that of the largest size, is therefore essential. The new approach offers a quantitative measure of the improvement in durability to be expected from reduction of the design stress range of a component and from improvements in steel cleanness.
An engineering model for prediction of rolling contact fatigue of railway wheels
Authors: EKBERG A. , KABO E. , ANDERSSON H.
Published: March 2003

An engineering model for rolling contact fatigue (RCF) of railway wheels is developed. Three well‐known types of fatigue in wheels – surface‐initiated fatigue, subsurface‐initiated fatigue and fatigue initiated at deep material defects – are accounted for. Fatigue impact is quantified by three fatigue indices expressed in analytical form. The model can easily be integrated in a multibody dynamics code without significantly increasing computational demands. A powerful tool for optimizing train–track configurations with respect to fatigue performance should result. In this paper, theoretical foundations, benefits and limitations of the model are presented. An example of a postprocessing analysis of data from a dynamic simulation of train–track interaction is given.