bluuebunny/crossref_metadata_2025 huggingface dataset:
FRACTURE MECHANICS OF PHYSICALLY SHORT CRACKS
Authors: Vasjutin A. N.
Published: April 2007

Mechanical Engineering Research Institute, Academy of Sciences of the U.S.S.R., Griboedova Str., 4 Moscow Centre, Moscow 101830, U.S.S.R.
FATIGUE CRACK INITIATION AND PROPAGATION IN A LOW‐CARBON STEEL OF TWO DIFFERENT GRAIN SIZES
Authors: Kage M. , Miller K. J. , Smith R. A.
Published: April 2007

Rotary bending fatigue tests were carried out using both plain and notched specimens of a low‐carbon steel with two different grain sizes (15 and 50 μm). The process of early crack development was observed by the replication method. The effect of grain size on crack development was studied.

The main conclusions were as follows. (1) Fatigue resistance, in terms of the relative positions of the S‐N curves, increases with decreasing grain size. This phenomenon is related to the number of cycles to propagate a crack to failure and the condition for the non‐propagation of a fatigue crack. (2) The size of a non‐propagating crack, which initiates below the fatigue limit, tends to become larger as grain size increases. (3) The difference in fatigue behaviour between small (15μm) and large (50μm) grain sized specimens is due both to a decrease in crack propagation rate and a smaller non‐propagating crack limit in the finer grained material.
A MODEL FOR PREDICTING CRACK GROWTH RATE FOR MIXED MODE FRACTURE UNDER BIAXIAL LOADS
Authors: Shlyannikov V. N. , Braude N. Z.
Published: April 2007

A model for predicting the crack growth rate of an initially angled crack under biaxial loads of arbitrary direction is suggested. The model is based on a combination of both the Manson–Coffin equation for low cycle fatigue and the Paris equation for fatigue crack propagation. The model takes into consideration the change in material plastic properties in the region around the crack tip due to the stress state, together with the initial orientation of the crack and also its trajectory of growth. Predictions of crack growth rate for any mixed mode fracture is based on the results of uniaxial tension experiments.
FATIGUE LIMIT MODEL FOR HARDENED STEELS
Authors: Gustavsson A. I. , Melander A.
Published: April 2007

A fracture mechanics‐based model is developed for the fatigue limit of hardened steels. In such steels, non‐metallic inclusions are known to initiate fatigue cracks. In this work, these inclusions are modelled as spherical voids and, as the fatigue process continues, fatigue cracks are thought to develop from these sites.

The growth or arrest of these cracks is analysed in terms of the effective stress intensity range and the corresponding effective threshold for crack propagation. Elasto‐plastic crack closure is evaluated by finite element calculations. The fatigue limit of a sample is defined in terms of crack arrest at all inclusions. Simple equations of the model are presented and compared to experimental data from the literature as well as to an earlier model by Murakami.
BIFURCATIONS AND INSTABILITIES IN FRACTURE OF COHESIVE‐SOFTENING STRUCTURES: A BOUNDARY ELEMENT ANALYSIS†
Authors: Cen Z. , Maier G.
Published: April 2007

The “cohesive‐crack model” is adopted, together with the hypotheses of small deformations and linear elasticity outside the process zone or “craze”, for the simulation of fracture processes in structures of concrete‐like materials. A “direct”, collocation, multidomain boundary element method is employed and shown to be computationally effective in the considered situations, which are characterized by non‐linearity on interfaces only. Iterative algorithms for the direction search and interface adjustment in propagation analysis and for the determination of the response to a craze‐tip advancement are developed and numerically tested. Softening as an instabilizing factor embodied in the cohesive‐crack model may give rise to path bifurcations (“equilibrium branching”), instability under load control and intrinsic (“snapback”) instability. These phenomena are analysed by the proposed boundary element procedure and discussed.
THE COMBINED EFFECTS OF STRESS RATIO AND YIELD STRENGTH ON THE LEFM FATIGUE THRESHOLD CONDITION
Authors: Lal D. N.
Published: April 2007

Abstract— Long‐crack (LEFM) fatigue threshold, Δ,K0 values are predicted which include the commonly observed effects of stress ratio, R, and yield strength, σy. It is assumed that the yield strength effect on threshold is indirectly related to grain size and so is not an independent variable. Two intrinsic thresholds of a material are invoked to explain the observations of higher ΔK0 values and a higher R‐ratio sensitivity of ΔK0 in low strength materials compared to high strength materials. The paper shows that ΔK0 is almost independent of both yield strength and stress ratio at high values of the stress ratio. Quantitative relations are developed to estimate curves of (i) ΔK0 versus R and (ii) ΔK0 versus σy. These curves show good agreement with experimental data for steels and aluminium alloys. A method is presented that may be used as an alternative procedure for obtaining quick and conservative estimates of ΔK0 for design applications.
AN ANALYSIS OF STRESS CONCENTRATIONS CAUSED BY SHOT PEENING AND ITS APPLICATION IN PREDICTING FATIGUE STRENGTH
Authors: Li J. K. , Mei Yao , Duo Wang , Renzhi Wang
Published: April 2007

Abstract— In order to calculate the stress concentration caused by shot‐peening dents, three simplified models, namely a one‐pit model, a seven‐pit model and a pit‐loop model, are proposed in this paper. By using a finite element program for automatic dynamic incremental non‐linear analysis, the stress concentration coefficients based on these models are calculated for different pit parameters and different stress fields. When considering the stress concentration and residual stress field produced by shot peening, a modified Goodman formula is proposed and used for forecasting the fatigue strength of peened specimens having the fatigue sources at the surface. The forecasted results were verified by peening followed by fatigue tests on 40Cr steel.
MONITORING FATIGUE OF A NICKEL‐BASE SUPERALLOY AT POSITIVE AND NEGATIVE STRESS RATIOS USING AN OPTICAL SYSTEM
Authors: Healy J. C. , Grabowski L. , Beevers C. J.
Published: April 2007

Abstract— This paper describes the use of an optical crack monitoring system designed to examine the growth behaviour of short/long fatigue cracks in Waspaloy at room and elevated temperature. Its use at 19 and 500°C is demonstrated at stress ratios of 0.1 and ‐1. Fatigue crack formation was associated with slip band cracking at both R= 0.1 and R= ‐1. At 19°C short crack growth at R= ‐1 and R= 0.1 could not be normalized by adopting a positive stress approach. The compressive part of the fatigue cycle at R= ‐1 contributed to short crack growth at 19°C and long crack growth at 500°C.
THREE‐DIMENSIONAL SHAPE OPTIMIZATION OF A BAR WITH A RECTANGULAR HOLE
Authors: Mattheck C. , Erb D. , Bethge K. , Begemann U.
Published: April 2007

Abstract— A cylindrical bar subjected to bending has a rectangular hole for functional reasons. The initial design failed occasionally due to fatigue cracks originating at the corners of the hole under service conditions. Therefore, a shape optimization was performed using CAO (computer‐aided optimization) based on the computer‐simulation of biological growth. A significant reduction of large notch stresses was achieved.

Prototypes manufactured with the shape‐optimized design endured 40 times longer in a fatigue test than the previous design. The example demonstrates that the CAO method is a very powerful and straightforward method for the designer who wants a light‐weight and fatigue‐resistant design.
DETERMINATION OF THE POSSIBLE ERROR IN FATIGUE DAMAGE FOR A DISCRETE STRAIN HISTORY
Authors: Pompetzki M. A. , Topper T. H. , Dabell B. J.
Published: April 2007

Abstract— The Markov matrix, which is a statistical representation of a service load history, is generally derived using 32 or more strain levels, since this is considered an optimum level between computational effort and accuracy of fatigue life prediction. A recently developed model which predicts the distribution of closed loops and fatigue life from the Markov matrix, is limited in the number of levels which can be analysed because of computational restrictions. This investigation was undertaken to determine the change in the accuracy of fatigue life predictions as the number of strain levels used to represent the strain history is reduced. Since each discretized level is used to represent a range of strain values, a given discretized history will represent a family of histories. A technique is developed which gives the distribution of damage for the family of histories given the discretized history and the distribution of peaks and valleys within each strain interval. By comparing the predicted damage caused by the measured history to a conservative estimate of the distribution of damage for the family of histories, the range of possible error is calculated and used to determine the relationship between the number of strain levels used in the discrete history and the possible error in predicted fatigue damage.
A STUDY OF SHEAR FATIGUE CRACK MECHANISMS
Authors: Zhizhong Hu , Lihua Ma , Shuzhen Cao
Published: April 2007

Abstract— Studies have been made of the micro‐and macroscopic features of a transverse shear fracture and a longitudinal shear fracture. The fatigue crack propagation mechanisms of mode‐II and mode‐III are described, which can be used to explain both fracture features and the crack shape. Finally a series of comparisons are made of mode‐I, ‐II and‐III fatigue crack propagation mechanisms.
CREEP FRACTURE OF Cr‐Mo STEEL
Authors: Radhakrishnan V. M.
Published: April 2007

Abstract— In this note a relationship is established which shows that the product, εmintr, is dependent on the creep rupture strain, εr and the creep strain at the onset of the tertiary state, ε23. This relation has been found to give a good description of the experimental data of ICr‐0.5Mo steel.
CORROSION FATIGUE OF AN HSLA STEEL
Authors: Ahn Seung‐Ho , Lawrence Frederick V. , Metzger Marvin M.
Published: April 2007

Abstract— Single‐pitted specimens of an HSLA steel, were tested in laboratory air and in 1 M NaCl solution to study the influence of a corrosive environment on its fatigue life.

The growth of fatigue cracks and the partitioning of the fatigue life into fatigue crack initiation and fatigue crack propagation were studied by photographing the pit and the cracks developing on it periodically during testing. Non‐propagating or dormant surface cracks were not observed in this study. Fractography using SEM showed the locations of fatigue crack initiation. The mechanisms of corrosion fatigue were studied by performing tests in 1 M NaCl at different test frequencies. Corrosion pits proved to be crack initiation sites. Hydrogen embrittlement was found to be unimportant in the corrosion fatigue of HSLA steel in this study. The 1 M NaCl corrosive environment appeared to reduce the fatigue life of this material by a dissolution mechanism. The effect of pit depth was studied by testing specimens having various pit depths. An effect of pit size was apparent. Fatigue life decreased with increasing pit depth. Pit depth, rather than the ratio of pit depth to pit diameter, influenced fatigue behaviour. A non‐damaging pit depth was found.
STRESS STATE‐RELATED FATIGUE CRACK GROWTH UNDER SPECTRUM LOADING
Authors: Wang G. S. , Palmberg B. , Blom A. F.
Published: April 2007

Abstract— The fatigue crack growth behaviour in aluminium alloy sheets of 2024‐T3 and 7475‐T761, subjected to standardized spectra (TWIST and FALSTAFF), was investigated using centre‐cracked specimens. A strip crack closure model was used to interpret experimental data, and to make predictions for the crack growth.

The strip model is based on the Dugdale concept, but modified to keep plastically‐stretched materials on the crack surface so that the crack opening load can be determined, and the fatigue crack growth can be analysed according to Elber's crack growth assumption. Differing from other models of the same kind, a variable constraint factor was introduced to account for the gradual transition of stress state at the crack tip resulting from the crack growth. It has been shown that the transition of stress state at the crack tip causes the unusual behaviour of the fatigue crack growth in sheets. Both experiments and predictions show that a crack may grow faster at a low load than at a higher one in a certain applied load range due to the crack tip stress state transition. The crack tip stress state also contributes to the thickness effect observed for the crack growth in sheets. In agreement with experimental results, it has been shown that a plane stress state will prevail at the crack tip in a thin sheet compared to that in a thick sheet. The plane stress state results in a higher crack opening level which leads to a longer fatigue life for thin sheets.
THE LINEAR NORMALIZATION TECHNIQUE—AN ALTERNATIVE PROCEDURE FOR DETERMINING J‐R CURVES FROM A SINGLE SPECIMEN TEST RECORD BASED ON LANDES' NORMALIZATION METHOD
Authors: Reese E. D. , Schwalbe K.‐H.
Published: April 2007

An alternative approach for determining J‐R curves from a single specimen test based on the normalization technique is proposed. The procedure requires only the load versus load‐line displacement record and the final crack length in order to derive the J‐R curve. The method has been applied to metal and polymers of various geometries and was verified by comparison with J‐R curves obtained from potential drop and multiple specimen techniques.
ON THE BEST FIT CURVE THROUGH CRACK GROWTH FRACTURE RESISTANCE DATA
Authors: Neale B. K.
Published: April 2007

The ESIS recommendations for determining the fracture resistance of ductile materials make use of an offset power law to evaluate the best fit curve to crack growth fracture resistance data. Evaluation of the offset power law requires the use of non‐linear regression analysis, although an iterative linear regression analysis can be used if the data are transformed by taking logarithms. The two analyses are compared with a proposed alternative formulation for the offset power law which can be evaluated using an iterative linear regression analysis without the need to transform the data. Confidence limits are evaluated for the J‐Δa data of two steels and are shown to depend on the analysis procedures.
ELEVATED TEMPERATURE FATIGUE CRACK GROWTH IN ALLOY 718—PART II: EFFECTS OF ENVIRONMENTAL AND MATERIAL VARIABLES
Authors: Ghonem H. , Nicholas T. , Pineau A.
Published: April 2007

Observations concerning the effects of the environment and material variables on the crack growth process in alloy 718 are reviewed and analyzed on the basis of deformation characteristics in the crack tip region. The review of the role of material variables has focused on the effects of chemical composition and microstructure parameters including precipitate size and morphology as well as grain size and morphology. These analyses have suggested that the governing mechanism at the crack tip is the degree of homogeneity of plastic deformation and associated slip density. For conditions promoting homogeneous plastic deformation, with a high degree of slip density, the environmental damage contribution is shown to be limited, thus permitting the dominance of cyclic damage effects which are characterized by a transgranular crack growth mode and a lower crack growth rate. Under conditions leading to inhomogeneous plastic deformation and lower slip density the crack tip damage is described in terms of grain boundary oxidation and related intergranular fracture mode. Considering that the crack growth damage mechanism in alloy 718 ranges from fully cycle dependent to fully environment dependent, conflicting experimental observations under different operating conditions are examined and a sensitizing approach is suggested to increase the alloy resistance to environmental effects.
EXAMINATION OF SHORT‐CRACK MEASUREMENT AND MODELLING UNDER CYCLIC INELASTIC CONDITIONS
Authors: Vormwald M. , Heuler P.
Published: April 2007

The opening and closure behaviour of short fatigue cracks is seen as one of the important phenomena which control fatigue life of components where a major part of life consists of the growth of short cracks. Therefore attempts are undertaken to experimentally assess and to model the behaviour of short cracks with respect to opening and closure. In this paper crack opening results obtained by Sunder et al. through SEM evaluation of striation patterns of 2000 series aluminium alloys are examined and compared to predictions using a model recently developed for fatigue life prediction based on fracture mechanics of short cracks. Sunder's technique for crack opening measurements involves particular load sequences with increasing and decreasing load ranges applied to notched specimens with naturally nucleated surface cracks where crack opening levels are identified by steady‐state striation widths for increasing load ranges. A detailed review of Sunder's results, however, indicates a number of inconsistencies and contradictions which are discussed.

Opening and closure behaviour of short fatigue cracks, in particular for inelastic conditions, is compared to predictions obtained with the above‐mentioned model which incorporates a constant strain opening and closure assumption. For inelastic conditions that may develop at notches this assumption means that cracks would close at considerably lower stress levels as compared to the opening stress which becomes important when effective (local) stress‐strain ranges are to be determined for fatigue life prediction under spectrum loading. The constant strain assumption is supported by a number of experimental observations from the literature as discussed in the paper. The approximative nature of this assumption and further details of the model are pointed out which show a need for further developments.
FATIGUE LIFE UNDER RANDOM LOAD HISTORY DERIVED FROM EXCEEDANCE CURVES USING DIFFERENT ALGORITHMS
Authors: Prakash Raghu V. , Sunder R.
Published: April 2007

Low cycle fatigue life and crack growth rates were analytically estimated for random load sequences, generated from three combat aircraft load exceedance curves using different algorithms, including simulated rainflow cycle count, extreme‐to‐extreme excursions, upper to lower bound excursions and unrestricted peak‐trough excursions. Also, the response of a fatigue meter to a random load sequence was simulated. Fatigue damage for the different load histories was computed using material constants for an Al‐Cu alloy. Computed fatigue damage was relatively insensitive to the algorithm used for load sequence generation from combat aircraft load exceedance curves. Fatigue meter data based damage estimates were, however, sometimes unconservative.
THE TWO THRESHOLDS OF FATIGUE BEHAVIOUR
Authors: Miller K. J.
Published: April 2007

Two limiting thresholds to fatigue crack propagation are discussed. The first threshold is related to the microstructural texture and this threshold may therefore be deemed a material‐based threshold. The second threshold is mechanically‐based, and is related only to the stress state at the tip of a substantial defect.

The material‐based threshold is characterized in terms of Microstructural Fracture Mechanics (MFM) and the mechanically‐based threshold is characterized in terms of Linear Elastic Fracture Mechanics (LEFM). The former condition is important when considering the fatigue limit of materials and components, while the latter is more applicable to the fatigue limit of structures.

The different factors which affect the two threshold conditions are briefly presented. Finally, this paper discusses aspects of MFM relevant to the fatigue resistance of metals and components.
POST WELD HEAT TREATMENT EFFECTS ON FATIGUE CRACK PROPAGATION IN AN ELECTRON BEAM WELDMENT
Authors: Hwang Jiun‐Ren , Jeng Ming‐Chang , Wang Chien‐Chun
Published: April 2007

This paper studies the effect of two post‐weld heat treatment processes on the fatigue behaviour of an electron beam weldment in 9 mm AISI 4130 steel. Electron beam tempering, in a vacuum chamber, immediately after welding and a traditional furnace tempering treatment were compared. Fatigue crack propagation resistance was assessed by a linear elastic fracture mechanics analysis. The resistance to fatigue crack growth was improved with post weld heat treatment due to residual stress relief and the existence of a toughened tempered microstructure. The specimens with an electron beam post‐weld heat treatment showed better fatigue properties than those of furnace‐treated specimens. An electron beam post‐weld heat treatment causes the fatigue crack growth rate to decrease with increasing energy input and decreasing micro‐dot‐pattern width. For a furnace post‐weld heat treatment, the fatigue crack growth rate decreases with increasing tempering temperature.
A TWO CRITERIA STATISTICAL MODEL FOR TRANSITION FRACTURE TOUGHNESS
Authors: Landes John D.
Published: April 2007

Abstract— A two criteria model is proposed to explain the nature of the fracture toughness scatter in the transition regime for ferritic steels. In the early part of the transition the model describes the data by a normal statistical distribution. Here the mean of the distribution is constant with specimen size and the variance of the distribution varies inversely with test specimen size. At a higher temperature, in the middle of the transition, the model results in a Weibull distribution in which both the mean and variance of the distribution vary inversely with change in specimen size. For both of these cases the fracture toughness scatterband from one specimen size can be used to predict the scatterband for another specimen size provided that the thickness constraint is not changed. Between these two regions the model results in a mix of normal and Weibull distributions for which the distribution from one size cannot presently be used to relate to another specimen size. The model is based upon the distribution of the transition fracture toughness data not on the observed microstructural behaviour; however, it is consistent with microstruc‐ tural observations. The model does not completely describe all observed data trends; however, it appears to describe observed behaviour better than single criterion models.
STATISTICAL EVALUATION OF FRACTURE TOUGHNESS TEST DATA
Authors: Hauge Mons , Thaulow Christian
Published: April 2007

Abstract— Application of fracture mechanics for verification of the fracture resistance of structural components and pipelines is well established in the offshore industry, and development of reliability analysis methods and calibration of assessment procedures is now in progress. One important parameter in fracture mechanics evaluations is the fracture toughness—a parameter characterized by large scatter, sensitivity to fabrication conditions and large costs related to testing. This has raised the need for efficient methods for characterization of the fracture toughness test data in terms of characteristic values and parametric distribution functions.

Two relevant data sets are investigated with respect to their statistical properties and the ability of different distribution functions to fit the data.

Three methods for estimation of characteristic values for fracture toughness are described. Their relevance and capabilities are investigated by numerical simulations with sample data sets drawn randomly from a larger population.

It is concluded that the distribution functions based on a physical model of the fracture have disadvantages such as unstable behaviour for small data sets and lack of capability in providing certain estimations. The log‐normal distribution showed a stable and predictable behaviour for sample sizes down to 3, the methods for calculation of distribution parameters and characteristic values with specified confidence levels are demonstrated to be satisfactory.
DETERMINATION OF PREDOMINANTLY MODE II STRESS INTENSITY FACTORS FROM ISOCHROMATIC DATA
Authors: Nurse A. D. , Patterson E. A.
Published: April 2007

Abstract— A new approach to the solution of stress intensity factors from isochromatic data has been developed and is based on complex Fourier analysis. Solutions are shown to be accurate when the loading of the crack tip is predominantly Mode II and also for cases that are generally mixed‐mode. The new method and its application to a four‐point‐bend test is described in this paper. Tests on angled‐edge‐cracked specimens have also been performed to show the validity of the method for a range of mixed‐mode loadings.
FATIGUE ANALYSIS OF SURFACE CRACKS AT FILLET WELDED TOES
Authors: Pang H. L. J. , Gray T. G. F.
Published: April 2007

This paper reports a study of fatigue crack growth and coalescing behaviour at semi‐elliptical cracks in the stress concentration region of steel plates with fillet shoulders or fillet welds. Fatigue tests were carried out on machined plate specimens with a fillet geometry similar to a fillet welded joint. These specimens were notched and precracked to provide single and multiple coplanar semi‐elliptical surface cracks at the fillet toe region. Finite element stress analysis results were used to obtain approximate Mk factors (i.e.: stress concentration magnification factors) for the fillet toe geometry with a semi‐elliptical surface crack. An analytical model was developed to simulate crack shape development and growth to failure in the case of multiple coplanar semi‐elliptical cracks. In this model, a simple crack coalescing procedure is applied to merge coplanar cracks when they meet by recharacterising the coplanar cracks into a single semi‐elliptical crack. Alternative crack growth laws were investigated and comparisons made between actual and predicted shape developments and lives.
COHESIVE MODELLING OF PROCESS REGIONS FOR CRACKS IN LINEAR ELASTIC STRUCTURES—FUNDAMENTAL ASPECTS
Authors: ÖStlund Sören , Nilsson Fred
Published: April 2007

The process region at the tip of a crack in a linear elastic structure has been modelled by a cohesive zone. Growth of the front end of the cohesive zone is governed by a critical stress intensity factor criterion, and advance of the original traction free crack is determined by a critical crack opening at the rear end of the cohesive zone.

Damage resistance curves relating the applied stress intensity factor to the growth of the cohesive zone have been calculated for an idealized structure containing two characteristic dimensions. Instability resulting in failure of the structure is found to occur either by unstable growth of the front end of the cohesive zone, without a fully developed cohesive zone, or by unstable growth of the original flaw, when the crack opening displacement at the rear end of the cohesive zone reaches a critical value.

The influence of the size of the structure compared to the length of the cohesive zone is investigated, and conditions for the limits of validity of the small scale yielding assumption are discussed. Comparisons are made between the maximum load and the length of the cohesive zone at instability resulting from the present analysis, and the values predicted by linear elastic fracture mechanics.
THE INFLUENCE OF LOAD MISALIGNMENT DURING UNIAXIAL LOW‐CYCLE FATIGUE TESTING—II: APPLICATIONS
Authors: Kandil F. A. , Dyson B. F.
Published: April 2007

Abstract— Models for predicting scatter bands due to bending have been applied to four alloys, namely AISI 316L, Nimonic 101, 9 Cr‐1 Mo, and IN 718. The alloys were tested extensively by 26 laboratories in an international round robin exercise sponsored by the Community Bureau of Reference (BCR) of the EC. After initially selecting data for analysis on the basis of their confirmed conformance to the ASTM bending criterion, it has been shown that in all four materials a major fraction of the data scatter could be attributed to bending. Furthermore, at the lowest strain range the predicted bending component represents the highest proportion of the experimental interlaboratory scatter. Many laboratories did not report any measure of bending and so could not be used in the initial analysis. However, a further interesting deduction from the models is that the entire BCR data‐set can be encompassed within a scatter band based upon a bending criterion that is twice the allowable ASTM limit. Differences in the extent of scatter between materials at a given total strain range can be attributed to the gradient of the logarithmic plot of total strain range as a function of lifetime.
INFLUENCE OF CREEP‐FATIGUE INTERACTION ON HIGH TEMPERATURE FATIGUE CRACK GROWTH BEHAVIOR of Ti‐1100
Authors: Rosenberger A. H. , Ghonem H.
Published: April 2007

Abstract— A series of crack growth experiments has been preformed on the near alpha titanium alloy, Ti‐1100, to determine the mechanism of the creep‐fatigue interaction. Based on pure creep crack growth results, the increase in the creep‐fatigue crack growth rate is not amenable to separate contributions of creep crack growth and fatigue crack growth.

A mechanism has been proposed to account for the increase in creep‐fatigue crack growth rate that is based on the planar slip of titanium alloys which results in the formation of dislocation pileups at the prior beta grain boundaries and leads to intergranular fracture. This mechanism has been validated through crack growth experiments preformed on a Ti‐1100 that has been microstructurally modified through the precipitation of internal slip barriers. These show that the intergranular fracture and increase in crack growth rate are absent.
A REVIEW OF MODELLING SMALL‐CRACK BEHAVIOR AND FATIGUE‐LIFE PREDICTIONS FOR ALUMINUM ALLOYS
Authors: Newman J. C.
Published: April 2007

Abstract— The small‐crack effect, where small fatigue cracks grow faster and at lower stress‐intensity factors than large cracks, has been found to be significant for many materials and loading conditions. In this paper, plasticity effects and crack‐closure modelling of small fatigue cracks are reviewed. A crack‐closure model with a cyclic‐plastic‐zone‐corrected effective stress‐intensity factor range (related to the cyclic J ‐integral) and microstructural data on crack‐initiation sites were used to calculate small‐crack growth rates and fatigue lives for unnotched and notched specimens made of two aluminum alloys. The crack‐closure transient from the plastic wake was shown to be the dominant cause of the small‐crack effect and plasticity effects on the cyclic‐plastic‐zone‐corrected stress‐intensity factor range were negligible except at extremely high stress levels. Small‐crack growth rates and fatigue lives under both constant‐amplitude and spectrum loading from tests and analyses agreed well.
THE DETERMINATION OF HYSTERESIS LOOPS IN THERMO‐MECHANICAL FATIGUE USING ISOTHERMAL STRESS‐STRAIN DATA
Authors: Skelton R. P.
Published: April 2007

Abstract—Thermo‐mechanical fatigue stress‐strain data on ferritic/austenitic steels and superalloys from a variety of sources are analysed with regard to hysteresis loop stress asymmetry. This arises from a decoupling of the thermal and mechanical strain signals in the test technique so that many tension‐compression load combinations are possible. Data from simplified isothermal and bithermal tests are also examined. Taking a typical example of an “out‐of‐phase” thermo‐mechanical loop on a 1/2 CrMoV steel cycled between 200 and 550°C, isothermal stress‐strain data were generated at 50°C intervals on material from the same cast and, used in conjunction with the elastic characteristics of the apparatus, an attempt was made to re‐create this loop. The methods employed were (i) a graphical construction between appropriate isothermal yield contours (ii) a tangent modulus calculation (iii) a secant modulus calculation. Method (i) appeared to give the closest agreement in the present case.
EFFECT OF SCRATCHES ON THE FATIGUE BEHAVIOR OF AN Al‐Li ALLOY
Authors: Inchekel A. , Talia J. E.
Published: April 2007

Abstract— An experimental investigation of the effects of small surface scratches on the fatigue behavior of Al‐Li alloys has been carried out. Small scratches were generated onto the specimen surface which were then subjected to fatigue testing. These scratches were characterized by three different parameters, scratch angle, scratch tip radius of curvature, and scratch depth. These parameters have exhibited an important influence on the fatigue life of the scratched samples. In particular, it was found that the fatigue life decreased sharply as the scratch depth increased. In addition, the scratch surface and fracture surfaces were examined under a scanning electron microscope. The observations helped in the assessment and identification of the mechanisms responsible for failure.
DAMAGE MECHANISMS IN ALLOY 800H UNDER CREEP‐FATIGUE CONDITIONS
Authors: Mu Z. , Bothe K. , Gerold V.
Published: April 2007

Abstract— The interaction between fatigue damage (i.e., fatigue crack propagation) and internal grain boundary damage (i.e., cavity formation at grain boundaries) has been studied for the Alloy 800H at 750°C for constant plastic strain ranges but different experimental conditions. Most experiments were performed at constant ranges of alternating tensile/compression stresses. Symmetrical as well as asymmetrical tests (with larger compression stresses) were performed. In comparison to the former tests, asymmetrical tests led to shorter cyclic lifetimes mainly due to cavity formation which was not observed for symmetrical tests. It could be shown that a fast compressive and a slow tensile half cycle (at large compressive and low tensile stresses) are ideal conditions for the nucleation and growth of cavities. Based on quantitative measurements of the cavity density from interrupted fatigue tests, a physical model is presented which can predict the number of cycles to failure. This cycle number is determined only by fatigue crack growth which is controlled by (a) athermal plastic deformation, (b) creep deformation and (c) rate enhancement by cavitation.
CORROSION FATIGUE OF SiC WHISKER OR SiC PARTICULATE REINFORCED 6061 ALUMINUM ALLOY
Authors: Yu S.‐Y. , Ishii H. , Tohgo K.
Published: April 2007

Abstract— Fatigue strengths of Sic whisker or Sic particulate reinforced 6061‐T6 aluminum matrix composite (SiCw/Al or SiCp/Al), fabricated by a high pressure infiltration method, were obtained in laboratory air, ion exchanged water and a 3 pct NaCl aqueous solution. A comparison was made with the properties of the matrix aluminum alloy 6061‐T6. The SiCw/Al composite maintained a higher fatigue resistance than the SiCp/Al composite or the monolithic 6061 Al, even in a 3 pct NaCl solution. Good correlation was observed between a deterioration in the fatigue strength and the value of the corrosive potential and current, when changing the environment from laboratory air or ion‐exchanged water to a 3 pct NaCl aqueous solution.
TWO‐PARAMETER MODEL OF FRETTING FATIGUE CRACK GROWTH
Authors: Troshchenko V. T. , Tsybanev G. V. , Khotsyanovsky A. O.
Published: April 2007

Abstract— A fretting fatigue crack growth model is proposed accounting for the effects of tribological parameters of the contacting materials and the biaxiality of contact together with bulk stresses, upon fretting fatigue crack growth rate and direction of growth in the fretting‐zone subsurface layers. Based on this model a new technique is developed to determine fatigue life and predict the fatigue limit in an aluminium alloy, AMg6N, and a titanium alloy, VT9, under fretting conditions. For the above cases, fretting fatigue crack growth behaviour predicted by the proposed model is in good agreement with the experimental results.
FATIGUE LIFE PREDICTION OF NOTCHED COMPOSITE COMPONENTS
Authors: Shen G. , Glinka G. , Plumtree A.
Published: April 2007

Abstract— The local stress/strain approach has been used to predict the fatigue lives of notched composite components. The method was based on a microstress analysis and the application of a multiaxial fatigue parameter incorporating the alternating strain components on the critical plane. This parameter was able to correlate the fatigue lives obtained under a variety of multiaxial loading and geometrical configurations, enabling a generalized fatigue life curve to be determined on the basis of limited experimental data.

The ability of the multiaxial fatigue parameter to relate the fatigue behaviour of composites was illustrated by predicting the locations of crack initiation sites in a unidirectional silicon carbide fibre reinforced titanium plate containing a circular hole tested under constant amplitude cyclic loading. The same approach was also successfully employed to predict the fatigue lives of graphite reinforced epoxy composite tubes with circular holes tested under several combinations of cyclic tension and torsion.
ELASTOPLASTIC CONVERGENT AND DIVERGENT CRACK PATHS IN TEAR TESTING OF SHEET MATERIALS
Authors: Muscat‐Fenech C. M. , Atkins A. G.
Published: April 2007

Abstract— When an initially‐parallel‐sided tab of material, cut into an isotropic finite‐width sheet, is torn by pulling the outer tabs in one direction, and the center in the opposite, the cracks may follow a parallel path, diverge outwards, or converge inwards depending on the widths of the inner and outer “legs”. At the same time, the untorn portion of the material may rotate relative to the pulling axis. The phenomenon is observed in globally elastic tearing, elastoplastic tearing, and in rigid‐plastic tearing. A fracture mechanics model using minimum energy explains the tear paths and rotations. Experiments on NS4 aluminium alloy confirm the analysis. The relationship of leg widths and bend radii with standard trousers tear testing of ductile materials is explained.
A RE‐EVALUATION OF THE LIFE TO RUPTURE OF DUCTILE METALS BY CYCLIC PLASTIC STRAIN
Authors: Kapoor A.
Published: April 2007

Abstract— Experiments have been performed on specimens subjected to strain cycles similar to those experienced by sub‐surface elements of material in rolling/sliding contact. It has been observed that if the strain cycle is closed then failure takes place by low cycle fatigue and the Coffin‐Manson relationship may be used to predict the number of cycles to failure. If however, the strain cycle is open, so that the material accumulates unidirectional plastic strain (the situation known as “ratchetting”) a different type of failure, which is termed ratchetting failure may occur. It occurs when the total accumulated plastic strain reaches a critical value which is comparable with the strain to failure in a monotonic tension test. The number of cycles to failure under these circumstances may be estimated by dividing this critical strain by the ratchetting strain per cycle. It is suggested that low cycle fatigue and ratchetting are independent and competitive mechanisms so that failure occurs by whichever of them corresponds to a shorter life. The results of both uniaxial and biaxial tests reported in the literature have been re‐evaluated and these, together with new data on biaxial tests on copper, found to be consistent with this hypothesis.
STRAIN BASED CREEP‐FATIGUE DESIGN RULES
Authors: BESTWICK R. D. W. , BUCKTHORPE D. E.
Published: April 2007

Abstract—Although there has been considerable success in the development of design methods for assessment of fatigue and creep fatigue damage there is need for further improvement particularly for creep damage estimation. Strain based creep‐fatigue rules have been developed for liquid metal fast breeder reactor technology (LMFBs) which give improved estimation of fatigue and creep damage compared with presently available procedures in commercially available high temperature design codes such as ASME CCN47 and RCC‐MR. Presently however their scope is confined to full in‐elastic analyses.

This paper provides a summary of the approach used in the strain based rules in relation to base material and weldments of 316L(N) austenitic steel. The paper examines the application of the strain method to thermal shock tests on long cylinders in which the testing cycle includes periods of constant temperature and some of the test pieces contain circumferential welds. Comparisons are made with time fraction based estimates and those of full cyclic in‐elastic analyses. Conclusions are drawn concerning the benefits of the method compared with presently available code procedures. The experience to date shows that the strain based rules give a more realistic interpretation of thermal shock experiments.
FRETTING FATIGUE OF AN AUSTENITIC STAINLESS STEEL IN SEAWATER
Authors: Takeuchi M. , Satoh T. , Mutoh Y. , Waterhouse R. B. , Kon Y.
Published: April 2007

Abstract— Fretting fatigue tests of an austenitic stainless steel used for a propeller tail shaft were carried out in seawater and in air. In seawater, fretting significantly reduced the fatigue strength, however, the fretting fatigue lives at higher levels of stress were longer than those in air. The tangential force coefficient (defined as the ratio of the frictional force amplitude and the contact load) in seawater was much lower than that in air and varied in the range from 0.3 to 0.5 during the fretting fatigue tests. The lower tangential force coefficient in seawater seems to be the main reason for the longer fretting fatigue life in seawater. The prediction of fretting fatigue life was made on the basis of elastic‐plastic fracture mechanics, where the frictional force between the specimen and the contact pad was taken into consideration. The predicted fatigue lives agreed well with the experimental results in both air and seawater.
CORRELATION BETWEEN HYDROGEN INDUCED CRACKING INITIATION SITES AND CRITICAL STRESS INTENSITY FACTORS
Authors: GAO H. , Cao W. , Fang C. , De Los Rios E. R.
Published: April 2007

Abstract—

Hydrogen induced cracking (HIC) initiation sites and their correlation with the critical stress intensity factors of hydrogen charged specimens were studied under combined I/II mode loading. Two series of tests, is. constant load (CL) tests and slow strain rate (SSR) tests, were carried out. Experimental results showed that in CL tests, irrespective of the ratio KIJKl, the HIC initiation sites always correspond to the point of maximum hydrostatic stress; which is located some distance ahead of the notch tip. However, for SSRT tests, when K11/K1> 1, HIC started at the notch tip which corresponds to the point of maximum equivalent plastic strain. When K11/K1<1 in SSR tests, HIC occurred initially some distance ahead of the notch tip.

The relationship between the critical stress intensity factor for HIC and K11/K1 was shown to be different for the two types of test. Multiple effects of stress and strain on hydrogen redistribution and hence on HIC initiation sites, as well as critical stress intensity factors, are discussed.
A STUDY OF THE INTERNAL PARAMETERS OF DUCTILE DAMAGE THEORY
Authors: LI Z. H. , BILBY B. A. , HOWARD I. C.
Published: April 2007

Abstract—

In this paper the Rousselier ductile damage model is used to simulate the softening behaviour of notched bars and crack growth in a pre‐cracked specimen of an A508 pressure vessel steel. The effect of the internal parameters needed to represent the damage on the calculated results is studied. The interactions between these parameters and their effects on the calibration process are discussed. The effect of the cell size on the values of the damage parameters obtained during calibration and on the response of the specimens is briefly reviewed.
FINITE ELEMENT AND EXPERIMENTAL STUDIES OF CRACK GROWTH IN CLADDED SEN(B) SPECIMENS
Authors: Sattari‐Far I.
Published: April 2007

Abstract— The transferability of fracture results between homogeneous and cladded specimens was studied in single edge‐notched bend specimens. The test material was of A533‐B steel with a clad layer deposited by a commercial strip welding process. The fracture resistance properties were developed independently for cladding and base material using homogeneous specimens of each material. The experimental data from tests on cladded specimens were analysed with the finite element method. The 3D J‐values were compared with values evaluated using the measured crack extension in the cladded specimen and the JR‐data of the respective material provided from homogeneous specimens. A reasonably good agreement was obtained in this comparison for a limited amount of crack growth.
A FATIGUE DESIGN PARAMETER FOR SPOT WELDS
Authors: Swellam M. H. , Aś G. Ban , Lawrence F. V.
Published: April 2007

Abstract— Mode I and mode II stress intensity factors for two half‐spaces connected by a circular patch were used to develop a mixed‐mode stress intensity factor (termed the stress index Ki) which can correlate the fatigue life of all spot weld geometries, base metals, and specimen dimensions. Empirical corrections were applied to Broek's equivalent stress intensity factor (Klq) to account for the weldment geometry (sheet thickness, nugget diameter, specimen width) and the effect of mean stress. The final expression, (Ki), is a measure of the notch‐root stress field in the location where crack initiation and early crack growth occur. The stress index (ki) should be a useful tool for spot‐weld fatigue design.
A NEW APPROACH TO THE DETERMINATION OF THE CRACK VELOCITY VERSUS CRACK LENGTH RELATION
Authors: Mishnaevsky L. L.
Published: April 2007

Abstract— A mathematical model of crack propagation due to the formation of a fractal cluster of voids and microcracks is presented. The initiation of a microcrack from a pile‐up of dislocations in the vicinity of a crack tip is modelled. A method to determine the fractal dimension of a crack, based on the crack growth analysis, is developed. A crack length versus crack velocity relation, based on the physical mechanisms of crack growth and the fractal nature of a crack, is deduced. A formula for the time to fracture is obtained.
MESH INDEPENDENT CELL MODELS FOR CONTINUUM DAMAGE THEORY
Authors: Bilby B. A. , Howard I. C. , Li Z. H.
Published: April 2007

Abstract— The conventional use of continuum ductile damage mechanics in finite element analyses identifies the “cell” in which damage occurs with the finite elements in which the distribution of stress and strain is modelled. Since the cell size is a fixed, metallurgically‐defined, property of the material being analysed, this methodology forces a minimum size for the finite element mesh. Mesh refinement is thereby disallowed. This paper presents one way of avoiding the problem by developing a mesh‐independent cell model which, with a fixed cell size, allows the finite element mesh to be refined to any degree within the cells. Procedures which average some state variables within the cells are introduced to prevent the localisation of damage after a certain critical stage is reached. The method has been tested in numerical simulations of (a) the deformation of a notched tensile bar, (b) a 35 mm compact tension specimen and (c) the first of the AEA spinning cylinder tests. There is a reasonable agreement between the results of the computer simulations and those of the experiments.
A MULTIAXIAL FATIGUE STRAIN ENERGY DENSITY PARAMETER RELATED TO THE CRITICAL FRACTURE PLANE
Authors: Glinka G. , Shen G. , Plumtree A.
Published: April 2007

The cyclic strain energy density parameter W for the critical or failure plane has been successfully applied in predicting the multiaxial fatigue life of an iron‐base and a nickel‐base alloy. This parameter has the advantage of being independent of loading condition, allowing a universal energy‐life curve to be determined for a variety of torsion, tension and bending stress and strain states. The critical strain energy density parameter has been verified using experimental data obtained from tubular and notched specimens of SAE‐1045 steel and Inconel 718.