bluuebunny/crossref_metadata_2025 huggingface dataset:
THE NUCLEATION AND GROWTH OF SHORT FATIGUE CRACKS BOTH AT PLAIN SURFACES AND NOTCHES
Authors: Guiu F. , Stevens R. N.
Published: April 2007

Abstract— The problem of the nucleation and growth of short fatigue cracks is addressed from an energetic point of view. It is explained that vanishingly small cracks can only nucleate and grow at the expense of the release of some locally stored energy during the fatigue deformation. This is necessary because an external loading system alone cannot provide a positive driving force for the growth of a crack whose length is below a critical value. The concept of the local driving force is used to explain the nucleation and growth of short fatigue cracks both at plain surfaces and at notches. With this approach a meaningful definition can be given of a “short fatigue crack” and a sound physical interpretation of the Kitagawa‐Takahashi plots is provided. The conditions for the existence of non‐propagating cracks are clearly established and the relationship between the stress concentration factor at the root of notches and the fatigue limit is explained. The paper sets up a physical framework for the sound understanding and treatment of short fatigue cracks and the microstructural parameters which control their growth.
RETARDATION IN FATIGUE CRACK GROWTH IN Al‐2024 AFTER BLOCKS OF UNDERLOADING
Authors: Zuidema Jan , Shen Wu Yi , Janssen Michael
Published: April 2007

In contrast with overloads, small numbers of underloads lead to acceleration in crack growth rate after application of the underloads. Larger numbers of underloads, however, give rise to retardation effects comparable with the effects of overloads. The retardation effects are attributed to the development of shear lips. Irregular shear lips show a greater effect than regular (smooth) shear lips. Increasing numbers of underloads give rise to greater retardation. For high numbers of underloads at high ΔKeff there is even an increase in the total life of the fatigue specimen with respect to the situation without underloads. High numbers of underload at high ΔKeff cause crack arrest at one side of the centre‐cracked tension specimen. The non‐growing side is often in single shear, the growing side always in double shear.
CREEP‐FATIGUE CRACK GROWTH AND FRACTOGRAPHY OF A TYPE 304 STAINLESS STEEL AT ELEVATED TEMPERATURE
Authors: Koterazawa Ryoichi , Nosho Takayoshi
Published: April 2007

Abstract— Creep‐fatigue crack growth behaviour of a Type 304 stainless steel under four types of reversed loading patterns (P‐P, P‐C, C‐P and C‐C) was investigated and the results are discussed in the light of fracture mechanics and fractography. The crack growth rate for all of the four types of loading was successfully correlated in terms of the cyclic integral range λJ. It was unnecessary, for practical purpose, to divide Ay into a fatigue component, λJf, and a creep component, λJc, as has been done elsewhere. The transition of the correlating fracture mechanics parameter from fatigue to creep was not necessarily associated with the fracture morphology. This was related to the longer transition hold time in morphology in C‐C type loading compared to C‐P type loading, and was attributed to recovery of grain boundary sliding during the compression hold in the C‐C type loading.
THE PROPAGATION OF NON‐COPLANAR SEMI‐ELLIPTICAL FATIGUE CRACKS
Authors: Soboyejo W. O. , Knott J. F.
Published: April 2007

Abstract— The results of fatigue tests on specimens containing parallel offset and parallel collinear configurations of multiple non‐coplanar cracks are presented. The fatigue growth of parallel collinear cracks is shown to be significantly affected by crack‐tip shielding and parallel offset cracks are shown to grow almost independently before their adjacent tips overlap. Subsequent growth in the region of overlap results in coalescence which begins when the deviating crack tips come into contact below the surfaces of the specimens. Simplified predictions of the propagation of offset non‐coplanar semi‐elliptical cracks are also presented and their implications for the prediction of fatigue lives in structures containing offset coplanar cracks are assessed.
THE FATIGUE LIFE OF THICK‐WALLED AUTOFRETTAGED CYLINDERS WITH CLOSED ENDS
Authors: Rees D. W. A.
Published: April 2007

Abstract— It is well known that the fatigue strength of a thick‐walled cylinder is enhanced by autofrettage. However, this does not appear to have been explained from fracture mechanics. The present paper shows that two uncertainties arise when this is attempted. Firstly, the distribution of residual stress resulting from the autofrettage pressure must be estimated and secondly a realistic stress intensity factors for subsequent fatigue cracking must be defined. A number of available stress intensity solutions are modified with the author's predictions to the residual stress following an elastic‐plastic autofrettage pressure in a closed cylinder of hardening material. A comparison with experiment has enabled the various approaches to be appraised. It is shown that a modified stress intensity factor of Bowie and Freese is most consistent with the propagation fatigue life observed in autofrettaged cylinders provided their solution is adapted to account for the propagation of a semi‐elliptical crack front in the presence of residual stress. Other K1 estimates appear to lead to dangerously optimistic predictions particularly within the range of fluctuating pressure where failure occurs between 105 and 106 cycles. The contribution to fatigue failure from initiation cycles is expressed as a power function of the observed life for cyclic pressures in the region of the fatigue limit.
THE FATIGUE CRACK GROWTH BEHAVIOR OF THE Al—Cu—Li ALLOY WELDALITE 049
Authors: Blankenship C. P. , Starke E. A.
Published: April 2007

Abstract— The microstructure, deformation behavior, and crack growth relationships have been examined for an Al‐5Cu‐1.3Li‐0.4Mg‐0.4Ag‐0.1Zr alloy. TEM of deformed samples revealed that the T3 temper deformed via highly localized planar slip due to the presence of small, coherent precipitates (GP zones and δ') while the T8 temper deformed homogeneously with T1 as the strengthening phase. Both constant Kmax and constant R (0.1) fatigue curves were generated for the T3 and T8 tempers in both the T‐L and L‐T orientations. The T3 temper exhibited high closure levels and an apparent intrinsic threshold of 2 MPa m1/2. The T8 temper did not exhibit high closure levels, and the intrinsic threshold was determined to be 1.3 MPa m1/2. Weldalite‐T3 has a strength comparable to 2024‐T3 but has a higher resistance to fatigue crack growth, whereas Weldalite‐T8 has a much higher strength and a comparable fatigue crack growth resistance to 2024‐T8.
THERMAL‐MECHANICAL FATIGUE OF MAR‐M 509 SUPERALLOY. COMPARISON WITH LOW‐CYCLE FATIGUE BEHAVIOUR
Authors: Franclois M. , Rémy L.
Published: April 2007

Abstract— The thermal‐mechanical fatigue behaviour of a cast cobalt based superalloy, MAR‐M 509 was investigated. Hollow smooth specimens were submitted to temperature cycling between 600 and 1050°C. The mechanical strain vs temperature cycle shows a diamond shape with peak strains at intermediate temperatures. The stress‐strain behaviour as well as fatigue life curves are reported. A significant part of total life is spent in crack initiation. Comparison with isothermal low cycle fatigue was made at the temperature where peak strains occurred. Isothermal low cycle fatigue life to crack initiation was shown to give a conservative estimate of thermal mechanical fatigue life provided extra strains due to differences in thermal expansion coefficients of the oxide scale and base alloy were taken into account.
SHORT CRACKS AT BIAXIALLY STRESSED NOTCHES: A FINE‐MESH ELASTIC‐PLASTIC FINITE ELEMENT ANALYSIS
Authors: Seed G. M. , Miller K. J.
Published: April 2007

An elastic‐plastic fracture mechanics study on the effects of biaxial stress fields is presented relating to various centre and edge notches containing short cracks under plane strain. The elastic stress intensity factor and the non‐singular elastic T‐stress term are determined by finite element analyses. Comparisons of these results with small scale yielding plastic zone size predictions are given for a wide range of applied stress intensity factors, revealing an improved correlation when considering the T‐stress effect. The influence of positive biaxial stress‐induced crack closure on the stress intensity factor is also discussed.
MODELLING SMALL FATIGUE CRACKS INTERACTING WITH GRAIN BOUNDARIES
Authors: Sun Zuyu , de, los Rios E. R. , Miller K. J.
Published: April 2007

A theoretical model which describes the microstructural aspects of short fatigue cracks is further developed to quantify the strength of microstructural barriers. The effectiveness of a barrier to decelerate or arrest short fatigue cracks in single phase materials depends on the relative orientation of the grains ahead of the barrier. A method of calculating the progression of orientation factors of the grains traversed by a fatigue crack is presented. Introducing the orientation factor into the crack growth equation allows the model to be used in the prediction of crack growth rate and of fatigue life. Comparison with experimental results, obtained with an A1‐Li alloy, establishes the accuracy of the predictions. The sequence of grain orientation factors ahead of the crack is also used to predict the stress boundary conditions for short fatigue crack propagation in the form of a Kitagawa‐Takahashi diagram which is compared with the experimental results due to Lukas.
A FULLY AUTOMATED SYSTEM FOR MONITORING SHORT CRACK GROWTH
Authors: Hussey I. W. , Roche J. , Grabowski L.
Published: April 2007

This paper describes a fully automatic short crack monitoring system used to study the growth of short cracks in Waspaloy at ambient temperature. Freely initiated fatigue cracks as small as 34 μ were detected using this system. Frequent monitoring enabled crack growth to be recorded over 2000 cycle increments. Several methods of data presentation were reviewed, the most appropriate being a linear plot of growth rate vs crack length.
FATIGUE CRACK GROWTH BEHAVIOUR IN MOLTEN‐METAL PROCESSED Sic PARTICLE‐REINFORCED ALUMINIUM ALLOYS
Authors: Kumai Shinji , King Julia E. , Knott John F.
Published: April 2007

Fatigue crack initiation and subsequent short crack growth behaviour of 2014‐5wt%SiC aluminium alloy composites has been examined in 4‐point bend loading using smooth bar specimens. The growth rates of long fatigue cracks have also been measured at different stress ratios using pre‐cracked specimens. The distributions of Sic particles and of coarse constituent particles in the matrix (which arise as a result of the molten‐metal processing and relatively slow cooling rate) have been investigated. Preferential crack initiation sites were found to be Sic‐matrix interfaces, Sic particles associated with constituent particles and the coarse constituent particles themselves. For microstructurally short cracks the dispersed SiC particles also act as temporary crack arresters. In the long crack growth tests, higher fatigue crack growth rates were obtained than for monolithic alloys. This effect is attributed to the contribution of void formation, due to the decohesion of Sic particles, to the fatigue crack growth process in the composite. Above crack depths of about 200 μm “short” crack growth rates were in good agreement with the long crack data, showing a Paris exponent, m= 4 in both cases. For the long crack and short crack growth tests little effect of specimen orientation and grain size was observed on fatigue crack growth rates, but, specimen orientation affected the toughness. No effect of stress ratio in the range R=0.2‐0.5 was seen for long crack data in the Paris region.
A BRITTLE FRACTURE KNOWLEDGE BASE AND ITS PRACTICAL APPLICATIONS
Authors: Dohnal M. , Vystrcil J. , Kvapilik M. , Vykutil J. , Dohnalova J.
Published: April 2007

Conventional experimental/knowledge records (usually tables, graphs and/or equations) are not suitable for an efficient uncertainty‐reasoning because of the poor knowledge‐acquisition methods used to develop them. A fuzzy knowledge base is a suitable framework for acquisition of vague, sparse and inconsistent knowledge. A revitalization of valuable records and re‐used literature knowledge items is a retrospective application of knowledge engineering algorithms. This is an ad hoc process and a general theoretical background does not exist. Therefore this paper presents a detailed description of a case study (49 variables, 4000 statements).A query as an element of a man‐machine dialogue is presented. No a priori knowledge of fuzzy mathematics is needed.
FRACTURE BEHAVIOUR OF AXISYMMETRIC BARS UNDER HIGH TRIAXIAL STRESS AND LARGE STRAIN CYCLIC LOADING
Authors: Du M. L. , Li G. C. , Zhang Y. Z. , Fang W. D.
Published: April 2007

Axisymmetric notched bars with notch roots of large and small radius were tested under large strain cyclic loading. The main attention is focused on the fracture behaviour of steels having cycles to failure within the range 1‐100. Our study shows that a gradual transition from a static ductile nature to one of fatigue cleavage can be observed and characterized by the Coffin‐Manson formula in a generalized form. Both the triaxial tensile stress within the central region of specimens and static damage caused by the first increasing load have effects on the final failure event. A generalized cyclic strain range parameter δε is proposed as a measure of the numerous factors affecting behaviour. Fractographs are presented to illustrate the behaviour reported in the paper.
PREDICTION OF CREEP CRACK GROWTH INCUBATION PERIODS
Authors: Austin T. S. P. , Webster G. A.
Published: April 2007

An incubation period is often observed prior to the onset of creep crack growth. This paper presents a procedure for estimating its duration from a knowledge only of the stress rupture properties and creep ductility of a material. Comparisons are made with experimental data on type 316L stainless steel at 600°C and a 1% CrMoV low alloy steel at 550°C. It is shown that good agreement is achieved when allowance for a build up of damage in a process zone at the crack tip during the early stages of cracking is incorporated into the analysis.
EFFECTS OF SMALL PRESTRAIN ON THE FATIGUE BEHAVIOUR OF SPHEROIDAL PEARLITE STEEL
Authors: Nagase Yasuo , Kanri Toshifumi
Published: April 2007

In order to clarify the effect of a small prestrain on the fatigue strength of a carbon steel, the fatigue behaviour of plain specimens of a eutectoid steel with spheroidal pearlite, previously subjected to a tensile prestrain, is investigated and compared with that of annealed and strain‐aged specimens. It is found that a small prestrain of a few percent does not decrease the fatigue limit nor the crack initiation or propagation lives. Fatigue slip initiation, however, is accelerated by the small prestrain. It is also observed that cyclic strain ageing does not occur. From these results, it is inferred that dislocations are unpinned by the small prestrain and this causes fatigue slip to occur more readily, but the fatigue behaviour following slip initiation is not affected because the spheroidal cementite particles act as obstacles to further slip deformation and Stage I crack propagation.
FATIGUE BEHAVIOUR OF THREE VARIANTS OF THE ROLLER BEARING STEEL SAE 52100
Authors: Christ H.‐J. , Sommer C. , Mughrabi H. , Voskamp A. P. , Beswick J. M. , Hengerer F.
Published: April 2007

Stress‐controlled, low‐cycle, push‐pull fatigue tests were performed on three variants of the bearing steel SAE 52100 with slightly different compositions and heat treatments. The experiments demonstrated differences in the cyclic plastic behaviour of differently hardened steels (bainitically‐hardened and martensitically‐hardened, respectively), whereas the two martensitic variants, which differ in composition, behaved very similarly. Bainitically‐hardened SAE 52100 steel exhibited initial hardening followed by cyclic softening above a stress amplitude level of 1200 MPa. In contrast, the martensitically‐hardened variants showed a pronounced cyclic hardening. The deformation behaviour of the martensitically‐hardened bearing steel in a monotonic tensile test and during the first cycles can be well understood on the basis of the transformation of retained austenite. This process leads to an onset of plastic deformation at lower stresses compared to the bainitically‐hardened bearing steel. As a result of the subsequent cyclic hardening of the martensitic variants, the CSS curves are almost identical for the differently hardened conditions under investigation. Additional tests under pulsating compression documented that a high negative mean stress enhances the cyclic plasticity.
THE EFFECTS OF FREQUENCY AND R‐RATIO ON FATIGUE CRACK GROWTH BEHAVIOUR IN Al‐Li‐Cu‐Mg ALLOY (8090) PLATE
Authors: Kemp R. M. J. , Wilson R. N. , Gregson P. J.
Published: April 2007

Abstract— The effects of frequency and R‐ratio on the fatigue crack growth rate of the Al‐Li‐Cu‐Mg alloy 8090 have been assessed in air. Compact tension test pieces (B= 25 mm) were tested at constant Pmax using a triangular waveform (CA) and the crack length was monitored by a four‐wire pulsed potential drop technique. Crack closure measurements were made during the test by a front face compliance technique.

The crack growth rate was found to be dominated by the high level of crack closure and the fatigue fracture morphology. Two fracture types were identified; a highly deviated “shear” fracture mode which was in competition with a macroscopically flat “tensile” fracture mode. The tensile fracture mode was predominant at low test frequency, high R‐ratio and short crack lengths whereas the shear mode was predominant at high frequency, low R‐ratio and long crack lengths. The transition from tensile to shear mode was primarily controlled by the effective stress intensity factor range, ΔKeff.

The effect of loading variables on the transition was explained in terms of the diffusion distance of hydrogen relative to the effective cyclic plastic zone diameter. Test piece thickness had a secondary effect on the transition and this was explained in terms of gas transport considerations.
A SIMULATION OF THE FATIGUE CRACK PROCESS IN TYPE 304 STAINLESS STEEL AT 538°C
Authors: Suh C. M. , Lee J. J. , Kang Y. G. , Ahn H. J. , Woo B. C.
Published: April 2007

Abstract— Quantitative information, such as the initiation period, growth and coalescence behaviour, statistical distributions of crack length, density of cracks, distribution patterns and crack growth properties, were obtained from fatigue tests on type 304 stainless steel at 538°C in a previous study. Using this information as input data and a condition for the connection and interactions of cracks, a statistical simulation and life prediction due to the high temperature fatigue crack growth process was performed and illustrated as output on a two‐dimensional graphical display.
PREDICTION OF THE FIRST SPINNING CYLINDER TEST USING DUCTILE DAMAGE THEORY
Authors: Bilby B. A. , Howard I. C. , Li Z. H.
Published: April 2007

Using the standard Rousselier ductile damage theory, a prediction is made of crack growth in the First Spinning Cylinder Test carried out by AEA Technology, Risley. Only data from small‐scale mechanical tests and metallography have been used. The prediction has been “blind” in the sense that, although we were aware of the observed high J‐R ‐curve (hitherto defying detailed interpretation by any of the standard fracture mechanics techniques), we restrained ourselves from any attempt to use the detailed results of the test itself in making the prediction. Indeed, we were in some confusion about the reported J‐R‐curves until a final meeting when our predictions were discussed with the experimental workers. Furthermore, crack growth versus rotation speed was predicted before sight of the experimental results.

Originally, reasonable estimates of the size scale determining the averaging involved in the damage theory gave predictions of crack growth versus rotation speed which agreed very well with the cylinder test, except near initiation, where the apparent increase in initiation toughness was not predicted. These predictions involved the parameter J only through the use of the compact tension specimen results in fitting the damage theory parameters and were quite independent of any complications which might arise from the use of J when centrifugal or body forces are present. The J‐R ‐curve predictions were not quite so good, but were still well above the small specimen results. Again, there was discrepancy near initiation.

Subsequently, we have learned that metallography which we were led to believe applied to a section perpendicular to the line of the mean crack front in fact referred to a section parallel to the mean crack plane. A rough correction using limited additional data improves our “blind” prediction slightly, but other limitations of the available small‐scale data mean that, had some suggestions in the literature been adopted, a result more in accord with that expected from the small‐scale tests might well have been obtained. It is concluded that further development of the modelling and the associated large‐ and small‐scale testing is required. Some comments on this further development and the potential of the method as a predictive engineering tool for the transfer of results from specimens to structures are made.
THE EFFECT OF ARTIFICIAL FATIGUE‐CRACK CLOSURE ON FATIGUE‐CRACK GROWTH
Authors: Ur‐Rehman A. , Thomason P. F.
Published: April 2007

An investigation of the effects of artificial fatigue‐crack closure on the subsequent growth of fatigue cracks, at constant range of stress‐intensity factor, was carried out for the following closure materials: (i) electroplated nickel; (ii) electroless nickel; (iii) ethylcyanoacrylate (ECA) adhesive; (iv) low‐melting point (LMP) solder. It was observed that (a) the wedge thickness and area of crack surface covered by the artificial‐closure material and (b) the distance of the tip of the closure wedge from the crack tip (i.e. the penetration of the closure material towards the crack tip) were the main parameters controlling the reduction in the subsequent growth rate of the fatigue crack. The results suggest that if the crack thickness (opening) is completely filled with a dense wedge of artificial‐closure material, the wedge becomes effectively rigid and the precise mechanical properties of the closure material will have only a secondary influence on subsequent fatigue‐crack growth in comparison to (a) and (b) above. This follows from the fact that the closure material is effectively a very thin strip compressed between the rough (high friction) sides of a crack. A rigid‐wedge and elastic‐crack model was found to successfully predict the changes in fatigue‐crack growth rate following artificial crack‐closure and gave a lower bound to the measured growth rates.
CHARACTERIZATION OF DUCTILE TEARING RESISTANCE BY ENERGY DISSIPATION RATE
Authors: Memhard D. , Brocks W. , Fricke S.
Published: April 2007

The J integral, which is widely used in elastic‐plastic fracture mechanics, is not the true driving force any more if the crack is propagating. This leads to some inconsistencies when ductile tearing resistance is characterized in terms of J, especially for large crack extensions. Instead, Turner has proposed the energy dissipation rate as a physically more meaningful quantity. His concept is discussed and more evidence is given that will provide a better understanding of ductile tearing. It is shown how this quantity can be determined by measuring the heat production ahead of a fast running crack, or calculated in a finite element analysis, or re‐evaluated from J‐R test records of bend and tensile specimens. The energy dissipation rate is decreasing with crack extension in gross plasticity and approaches a stationary state. From these relations, the shapes of the cumulative J‐R curves can be derived for different specimen geometries.
A STUDY OF SUPERIMPOSED FRACTURE MODES I, II AND III ON PMMA
Authors: Davenport J. C. W. , Smith D. J.
Published: April 2007

A test apparatus has been developed to study the fracture behaviour of engineering materials subjected to superimposed tensile and shear (Mode I and II) loads using a single edge notch specimen. Stress intensity factors were calculated using finite element analysis. Test results for PMMA are reported. Results from circumferentially notched round bar specimens, subjected to combined tension and torsion (Mode I and III) loading are also reported. The Mode I/II results are consistent with the mixed mode fracture response of a wide range of brittle materials, although there is some evidence of non‐linear behaviour. The fracture behaviour for superimposed Modes I and III indicates the strong influence of non‐linear deformation which causes the mixed mode toughness to be dependent on the sequence and type of loading.
EFFECT OF AN ELASTIC‐PLASTIC SHOCK WAVE PART B: ON THE FATIGUE CRACK GROWTH RATE OF WELDED JOINTS
Authors: Liangshan Chen , Huaining Chen , Zhongyao Si , Shenyu Tan , Guangyuan Chui
Published: April 2007

Fatigue crack growth behavior in welded joints subjected to elastic‐plastic shock waves was investigated using three‐point‐bend specimens. The results indicate that the fatigue crack growth rate is reduced in the affected region of elastic or plastic waves. The travel of a plastic stress wave reaches 10 to 13 mm depth, but the hardness in this region is not increased although the lattice distortion is high. The crack path morphologies were observed, and reasons for a decrease in crack growth rate are presented.
COMPARISON OF FATIGUE LIFE PREDICTIONS IN WELDED JOINTS USING 2D AND 3D K SOLUTIONS
Authors: Ferreira J. M. , Branco C. M.
Published: April 2007

The paper presents the results of fatigue life predictions in non‐loaded carrying tee and cruciform joints and also longitudinal seams of tubes, obtained with 2D and 3D stress intensity factor solutions. The 2D computational method uses the standard Bueckner weight function solution to obtain the 2D values of the stress magnifying factor MK. In the 3D approach a modified 3D weight function solution was used in conjunction with the Raju and Newman base stress intensity formulation.

Comparison of results is shown between the 2D and 3D fatigue life predictions and experimental results of fatigue strength obtained by the authors. Results are also given showing the influence of crack aspect ratio, thickness and the ratio of tube radius to tube thickness.
EXPERIMENTAL DETERMINATION OF STRESS INTENSITY FACTORS FOR CRACKS IN TURBINE DISCS
Authors: Nurse A. D. , Patterson E. A.
Published: April 2007

Stage‐II fatigue crack growth paths in firtree fixtures have been predicted using a photoelastic technique. Initiation was assumed to occur at the edge of contact on the load‐bearing flanks and, subsequently, the cracks were extended in the direction of the maximum circumferential stress. After a short initial length, in which propagation was perpendicular to the contact surface, the direction of crack growth was, in a broad sense, equivalent to the hoop direction in the disc. Stress intensity factors were found for the majority of the crack path using data taken from the isochromatic fringe patterns. It was concluded that the most catastrophic failure was likely to occur from the innermost land of the firtree and that the width of the firtree had little influence on the stress intensity factors.
NOTE ON CYCLE COUNTS IN IRREGULAR LOADS
Authors: Rychlik Igor
Published: April 2007

In this paper we discuss cycle counting methods, such as rainflow‐, crest‐to‐trough‐, positive peak‐count and different damage accumulation rules, for irregular random loads, which have an infinite number of local extremes in finite intervals, e.g. the fourth spectral moment is infinite. We present conservative bounds for the expected damage for such loads from the uncrossing intensity. These results are illustrated by examples of Gaussian, χ2, and Morison‐loads.
EFFECT OF SURFACE TEXTURE ON FATIGUE LIFE IN A SQUEEZE‐CAST 6082 ALUMINIUM ALLOY
Authors: Güngör S. , Edwards L.
Published: April 2007

The effect of surface texture on fatigue life in a squeeze‐cast Al‐Mg‐Si alloy has been investigated in terms of initiation and subsequent propagation of small fatigue cracks. Small cracks nucleated from defects on both as‐cast and polished surfaces. However, the large (∼90μm in diameter) surface defects found on as‐cast surfaces caused an approximate 20% reduction in fatigue life when compared to polished surfaces where cracks initiated from smaller (∼ 12 μm in diameter) microporosity. Integration of averaged small fatigue crack growth data enables the fatigue lives of both types of specimen to be predicted at stresses above the fatigue limit, showing that the difference in fatigue behaviour is principally due to the extra period of crack growth in the polished surfaces.
THE INFLUENCE OF STRENGTH AND STRESS RATIO ON SHORT‐CRACK THRESHOLDS AND NON‐PROPAGATING FATIGUE CRACKS
Authors: Lal D. N.
Published: April 2007

Quantitative predictions of the influence of yield strength and stress ratio, R, on the physically small crack fatigue threshold stress intensity, ΔK0(s), are presented. It is shown that at R= 0 to ‐1, although the threshold stress Δs̀0 increases, the threshold stress intensity, ΔK0(s), decreases with increasing yield strength. Moreover, a lower bound value, ΔK0(s)(min) is shown to have a constant value, irrespective of the strength and stress ratio. For a given strength, ΔK0(s), decreases with increasing R in the range ‐1R0.6 and attains a constant low value for R > 0.6. Predicted values of ΔK0(s) are in good agreement with experimental data for steels. The formation and length of non‐propagating fatigue cracks, anp, are also discussed. The methods suggested for estimating ΔK0(s) and anp may be found useful in design procedures.
DEPENDENCE OF ACOUSTIC EMISSION FOR LOW STRENGTH STEELS UPON THE EMBRITTLEMENT AND THE PLASTIC ZONE REDUCTION AT THE CRACK TIP DURING CORROSION FATIGUE CRACK PROPAGATION
Authors: Wang Z. F. , Li J. , Ke W. , Zhu Z.
Published: April 2007

Acoustic emission signals were continuously monitored during fatigue crack propogation for two kinds of low strength steel placed in either laboratory air or 3.5% NaCl solution. The plastic deformation of the materials at the crack tips were compared by determining the changes in specimen geometry at the fracture surface in the thickness direction while the hydrogen distribution from the crack tip material was analysed by SIMS. The results showed that acoustic emission was less active in an aqueous solution than in air and that the plastic zone size was reduced in a corrosive medium. It was considered that the entrance of hydrogen into the crack tip during corrosion fatigue results in a decrease of material ductility, which lead to a low activity in acoustic emission.
A MULTIAXIAL FATIGUE DAMAGE MODEL FOR ORTHOTROPIC MATERIALS UNDER PROPORTIONAL LOADING
Authors: Lin Hong , Nayeb‐Hashemi H. , Pelloux R. M.
Published: April 2007

A new multiaxial fatigue damage model for orthotropic materials is proposed based on the strain vector. Six material constants are included in the model. These material constants represent the dependence of fatigue resistance on material orientation, and they can be obtained by conducting strain‐controlled uniaxial fatigue tests along the three principal orthotropic directions of an orthotropic material. The model can also be transformed in new coordinate systems to predict the fatigue lives of new material orientations. Biaxial low‐cycle fatigue tests are conducted to verify the model. The prediction of the model agrees with the experimental results reasonably well.
A MECHANISTIC‐BASED THERMOMECHANICAL FATIGUE LIFE PREDICTION MODEL FOR METAL MATRIX COMPOSITES
Authors: Neu R. W.
Published: April 2007

The framework for developing a mechanistic‐based life prediction model for metal matrix composites is described. For a composite consisting of unidirectional silicon carbide fibers in a titanium aluminide matrix, SCS‐6/Ti‐24A1‐1INb (at%) [0]8, three dominant damage mechanisms were identified: (1) matrix fatigue damage, (2) surface‐initiated environmental damage, and (3) fiber‐dominated damage. Damage expressions were developed for each mechanism along with a method for determining the constants. The damage is summed to obtain the total life. The model is capable of making predictions for a wide range of histories, including isothermal fatigue at different frequencies and stress‐ratios, thermomechanical fatigue (TMF) under in‐phase and out‐of‐phase cycling conditions, thermal cycling at constant stress, and stress holds at either maximum or minimum stress. Considering the wide range of cyclic conditions, the predictions compare favorably with experiments. In addition, the controlling damage mechanism for each history is predicted.
SIZE, THICKNESS AND GEOMETRY EFFECTS ON TRANSITION FRACTURE
Authors: Landes J. D. , Heerens J. , Schwalbe K.‐H. , Petrovski B.
Published: April 2007

Abstract— Transition fracture toughness was studied to look at the effect of size, thickness and geometry. Size effects were studied on six sets of data collected from the literature in which proportionally sized compact specimens of various steels were tested. Thickness effects were studied on tests of compact specimens of constant thickness and varying planar dimensions. Tests were conducted on a pressure vessel steel at a constant thickness of 20 mm where planar dimensions were increased so that thickness constraint was decreased. Geometry effects were studied on tests from a center cracked tension specimen geometry. Initially all of the data from the tests were included in the study; none were eliminated due to a size or other validity requirement. Then two validity requirements, the KIc and the Anderson‐Dodds size requirements, were imposed to study their effect on the data.

The results showed that a smaller specimen size does not necessarily result in higher toughness. Rather, the smallest size often gave the lowest values of toughness. Loss of thickness constraint tended to increase toughness but not very much; it may not increase at all at the lower temperatures. The center cracked tension geometry appeared to have a lower constraint. These specimens showed an increase in toughness which is similar to that observed on a compact specimen for a change of temperature from −90°C to −60°C. Imposing a size validity requirement eliminated much of the fracture toughness data in the transition and influenced the distribution of data. Validity size criteria should be avoided if possible, especially for a scientific study.
ESTIMATION OF LOWER BOUND FRACTURE RESISTANCE OF PRESSURE VESSEL STEEL IN THE TRANSITION REGIME
Authors: Zerbst U. , Heerens J. , Schwalbe K.‐H.
Published: April 2007

Abstract— An empirical investigation of different procedures was carried out for determining a lower bound fracture toughness on the basis of small specimen test data in the ductile‐to‐brittle transition range. The procedures have been applied to various data sets in order to study the practicability and behaviour of the different procedures.

It has been shown that these procedures produce estimates which fall into the lower tail regime of the scatter band of fracture toughness. Within the range of the data sets investigated these estimated lower bounds do not significantly depend on the specimen size, side grooving of the specimens and the magnitude of the data set used for the estimation. Nevertheless, the estimated lower bound values themselves are different depending on the method used for the estimation.
VALIDATION OF THE FRACTURE MECHANICS TEST METHOD EGF P1–87D (ESIS P1–90/ESIS P1–92): ANALYSIS OF AN EXPERIMENTAL ROUND ROBIN
Authors: Schwalbe K.‐H. , Hayes B. , Baustian K. , Cornec A. , Gordon R. , Homayun M. , Voss B.
Published: April 2007

Abstract— The elastic—plastic fracture mechanics test method EGF P1–87 D: EGF Recommendations for Determining the Fracture Resistance of Ductile Materials has been validated by an extensive round robin, covering fracture tests and their evaluation as well as scanning electron fractography. The results confirmed the suitability of the procedure, but suggested some modifications. The resulting procedure ESIS P1–90 was then further modified and its actual designation is ESIS P1–92.

The present report provides comprehensive information on the determination of crack growth resistance curves and initiation values. Particular emphasis is on single specimen techniques and on determining the stretch zone width. Beyond the validation of the ESIS procedure the information given is pertinent to elastic‐plastic fracture testing in general.
THE EFFECT OF MEAN STRESS ON MIXED MODE (I + III) FATIGUE THRESHOLDS
Authors: Yates J. R. , Mohammed R. A.
Published: April 2007

Abstract— Mode I, mode III and mixed mode (I + III) fatigue crack growth threshold tests have been performed on a 3.5% NiCrMoV steel at a range of mean stresses corresponding to load ratios R = 0.06 to 0.5. Angled slit three point bend specimens were used for mixed mode (I + III) tests, circumferentially slit round bars for mode III tests and conventional three point bend specimens for mode I tests.

Test results were divided into those specimens which had failed and those in which no extension of the initial slit had occurred. The results were compared with the response predicted by two existing mixed‐mode threshold models. It was found that a model based on the magnitude and direction of mode I crack opening gave results which were in better agreement with the experimental results than a model based on branch crack formation.
SHORT FATIGUE CRACK GROWTH UNDER MEAN STRESS, UNIAXIAL LOADING
Authors: Wang C. H. , Miller K. J.
Published: April 2007

An investigation of the effects of mean and alternating stresses on short fatigue crack growth under uniaxial loading is reported. Tests under stress‐controlled conditions with different combinations of mean and alternating stresses were conducted at room temperature using a 1.99% NiCrMo steel. The fatigue process was divided into three phases: Plasticity Localization, Microstructural Short Crack (MSC) growth, and Physically Short Crack (PSC) growth. The effect of mean stress on the above three phases is studied and a set of equations is obtained which can predict the early stage and growth behaviour of short cracks under various mean and alternating stresses. Satisfactory predictions of fatigue endurance curves at different mean stresses have been achieved. This approach provides an alternative method, based on the physics of the fatigue process, for use by designers who currently rely on conventional Goodman‐type diagrams.
NUMERICAL AND EXPERIMENTAL VERIFICATION OF A NEW MODEL FOR FATIGUE LIFE
Authors: Svensson T. , Holmgren M.
Published: April 2007

Abstract— A new model for fatigue life prediction has been presented[1]. The model is based on Palmgren‐Miner's rule in combination with a level crossing analysis. Here an effort is made to verify the model, numerically and experimentally. Data from the literature and experimental data generated by us have been compared with fatigue life predictions made with the new model. The data have also been compared with traditional fatigue life estimations based on the rain flow count method. The fatigue lives predicted by the new model often agree better with actual lives than predictions made with the RFC‐method. This is especially pronounced when the loading sequence is very irregular, i.e. when the sequence contains many small cycles superimposed on large cycles. The new method is both fast and simple to use.
IMPROVEMENT OF THE FRACTURE TOUGHNESS OF AN ALUMINIUM ALLOY
Authors: Lam Y. C. , Ibrahim R. N.
Published: April 2007

Abstract— The improvement of a material's toughness has significant industrial applications. An example is the manufacture and maintenance of commercial gas containers made in the form of aluminium cylinders; a challenging design problem since they are susceptible to crack growth under a static load (internal pressure). In this investigation a new thermo‐mechanical technique was used to improve the apparent fracture toughness. This could increase significantly the safety margin and life of the cylinders. The determination of fracture toughness was carried out using a newly developed small cylindrical specimen which has a considerable cost advantage over the standard compact tension specimen. Experiments on aluminium 6351‐T6 cylindrical specimens confirmed the possibility of improving the toughness of this alloy.
FATIGUE CRACK GROWTH IN NICKEL‐BASED SUPERALLOYS AT 500‐700°C. I: WASPALOY
Authors: Lynch S. P. , Radtke T. C. , Wicks B. J. , Byrnes R. T.
Published: April 2007

Abstract— The effects of cyclic frequency, hold time, and stress‐intensity‐factor range (δK) on rates of fatigue crack growth in air at 500‐700°C have been studied for Waspaloy—a nickel‐based superalloy used for gas‐turbine engine discs. The main effects observed were: (i) higher rates of crack growth for lower cyclic frequencies at high δK at 600 and 700°C. and (ii) lower rates of crack growth at low δK (and higher δK thresholds) for longer hold times at 700°C, compared with those at a baseline frequency of 2 Hz. Metallographic and fractographic observations suggested that the effects of cyclic frequency and hold time could be rationalised in terms of the competing effects of enhancement of cracking due to creep and inhibition of cracking caused by oxide‐induced crack closure, fracture‐surface‐roughness induced crack closure, and crack‐branching/deflection. Possible mechanisms for promoting intergranular and transgranular cracking at low cyclic frequencies or long hold times are discussed.
FATIGUE PREDICTIONS AND SCATTER*
Authors: Schijve J.
Published: April 2007

Abstract— Different aspects of fatigue design problems are indicated and uncertainties are listed. Scatter as observed in many laboratory studies is analyzed. It is argued that scatter of crack initiation and crack growth are different issues. Various sources of scatter are discussed and illustrative examples are presented. Comments are given on statistical distribution functions, scatter under Variable‐Amplitude loading, and scatter in service. The discussion touches upon the experience and meaning of scatter of laboratory test series related to practical problems.
THE RELATION BETWEEN CRACK BLUNTING AND FATIGUE CRACK GROWTH RATES
Authors: Nicholls D. J.
Published: April 2007

Abstract— Previous work has shown that the inclusion of the strain energy released by crack blunting leads to an energy minimum for fatigue crack growth that can be used to predict stage II fatigue crack growth. The present work assumes a polynomial relation between crack blunting and crack extension to derive an expression for the rate of fatigue crack growth that is dependent upon only the applied ΔK, E, σys, Kc, and the exponent p in the relation between crack blunting and crack extension. This expression is thought to be generally valid since it accurately predicts fatigue crack growth rates for a wide variety of titanium, nickel, aluminium and steel alloys. A unique characteristic of the model is its ability (for long crack, slow crack growth) to account for the different slope for different materials in the Paris Law region of the da/dN vs. δK curve. The model specifically shows that this slope, m, is dependent solely upon the exponent, p, in the relation between crack blunting and crack extension.
ELEVATED TEMPERATURE FATIGUE CRACK GROWTH BEHAVIOR OF Ti‐1100
Authors: Parida B. K. , Nicholas T.
Published: April 2007

Abstract— The fatigue crack growth behavior of Ti‐1100 is analyzed at elevated temperatures to evaluate the effects of mechanical and environmental variables. Experiments conducted over a wide range of frequencies from 0.01 Hz to 200 Hz indicate a strong dependence of the growth rate upon cyclic loading frequency. Superposition of hold time at maximum and minimum loads over a baseline 1.0 Hz cyclic loading frequency produces an insignificant variation in crack growth rate, which may be attributed to the combined effects of enhanced environmental degradation, crack‐tip blunting and increased asperity‐induced closure level in this material. It is deduced that a hold time at maximum load results in an interaction of the environmental effects with a retardation effect due to crack tip blunting as a consequence of creep under maximum applied load, whereas for hold at minimum loads, extensive crack‐branching and micro‐cracking appear to enhance crack closure loads resulting in lower crack growth rates. A linear superposition model is employed to account for the complex interactions due to fatigue, creep and environmental degradation.
FATIGUE RESISTANCE OF A MEDIUM CARBON STEEL WITH A WEAR RESISTANT THERMAL SPRAY COATING
Authors: Rakitsky A. A. , de los Rios E. R. , Miller K. J.
Published: April 2007

Abstract— The fatigue behaviour of a Ni‐Cr‐base powder flame‐spray coating on a 0.4% C steel is investigated. Fatigue tests were carried out using mild hour‐glass profile specimens. Cracks were detected and measured using plastic replicas and an image analysis system. Coated specimens showed a slightly lower fatigue endurance than plain specimens under torsion loading, while the opposite was observed for push‐pull loading. Microcracks in coated specimens invariably form at pores.

Contrary to the usual case of stage I shear growth for a plain 0.4% C steel in tension or torsion loading, the coated specimens show initial crack growth from pores along directions perpendicular to the maximum tensile stress. The crucial behaviour of short cracks, and their growth rates, relative to the thickness of the coating, are discussed in some detail.
THE USE OF A SECONDARY STATE TO DETERMINE THE T‐STRESS
Authors: Seed G. M.
Published: April 2007

Abstract— This paper examines the determination of the T‐stress by making use of a secondary state and the complex‐variable forms of the work reciprocal and Rice's Jx integrals in terms of the Muskhelishvili complex stress functions. A simple relationship is found which relates the stress intensity factors and T‐stresses of the two states and is applied to the problem of a crack at the root of a notch.
SHORT FATIGUE CRACK PATH DETERMINANTS IN POLYCRYSTALLINE Ni‐BASE SUPERALLOYS
Authors: Boyd‐Lee A. , King J. E.
Published: April 2007

Abstract— Fifty seven short fatigue cracks in the Ni‐base superalloy AP1 have been examined, to ascertain how the paths taken by growing fatigue cracks are determined. The observations were made on the surface of a smooth specimen, and on the exposed fracture surfaces. Three dimensional reconstructions of the vulnerable microstructures in the vicinity of the cracks were produced. Initiation occurred in mode II, with the lines of intersection of the initiation sites with the specimen top surface orientated at approximately 45° to the tensile axis. These initiation sites developed in slip bands which crossed a large grain and at least one other grain via a grain boundary with a low angle of misorientation. ‘River markings’ on one of the initiation facets, indicated that the crack first opened from the top centre of the initiation grain. Subsequent to initiation, the growth paths of these cracks are related to the misorientations of the grains and the progress of the crack front.
FRACTURE AND LIFE PREDICTION UNDER THERMAL‐MECHANICAL STRAIN CYCLING
Authors: Ellison E. G. , Al‐Zamily A.
Published: April 2007

Abstract— Thermal‐mechanical cyclic strain tests were carried out under in‐phase and out‐of‐phase conditions on a ferritic 1 CrMoV steel in the temperature range 315 to 565°C and two different batches of a 316 stainless steel in the temperature range 400 to 625°C. The results were compared with isothermal data.

In general, lives for in‐phase thermal‐mechanical tests were lower than for equivalent isothermal tests. This was substantiated by metallographic examination which indicated greater intergranular damage for the in‐phase specimens. The addition of a tensile dwell to the in‐phase condition caused even greater differences.

Three life prediction methods were used: the ductility exhaustion and a modified strain range partitioning approach gave reasonable estimates of life, whilst the linear life fraction method produced poor prediction.