bluuebunny/crossref_metadata_2025 huggingface dataset:
A MODEL FOR SMALL FATIGUE CRACK GROWTH
Authors: Zhu C.
Published: April 2007

Abstract— Based on the assumption that normalized Kitagawa‐Takahashi diagrams for different materials are the same, a unified model for microstructurally small fatigue crack and physically small fatigue crack growth rates was developed to describe their behaviour under different fatigue stress ranges. The stress‐sensitive blocking effect of microstructural barriers to small fatigue crack growth is satisfactorily simulated by the model. Incorporated with the materials fatigue limit and microstructural barrier spacing, this model can be easily used in the prediction of small fatigue crack lifetime. Small fatigue crack growth rates of previous experimental studies in 7075‐T6 Aluminium alloy and HT60 steel under different stress ranges are in an envelope between two boundary prediction curves corresponding to the largest and smallest stress ranges applied in the experiments. Problems concerning model accuracy and model application are also discussed in the present paper.
FATIGUE BEHAVIOUR OF A RAIL STEEL UNDER LOW AND HIGH LOADING RATES
Authors: Cheng Y. , Chen D. , Nogata F.
Published: April 2007

Abstract— In this study, both sinusoidal wave loading and rectangular pulse (impact) loading are applied to a sample of rail steel in order to compare the growth rates for a surface fatigue crack. The results show that the rectangular pulse (impact) loading gives a crack growth rate on average 5 times that of the sinusoidal wave loading but can be almost 100 times in some instances. There are distinct differences between the fractograph patterns under the two modes of loading. The fractograph under sinusoidal wave loading clearly exhibits the pearlite structure of the material but under impact loading this microstructure is not revealed; only a quasicleavage pattern is observed. Analysis of the experimental fatigue crack growth data indicated that the surface fatigue crack growth rate behaviour could be described by the Paris‐type relationship.
THE MEASUREMENT OF SURFACE BREAKING CRACKS BY THE ELECTRICAL SYSTEMS ACPD/ACFM
Authors: Dover W. D. , Monahan C. C.
Published: April 2007

Abstract— The successful implementation of a fracture mechanics approach to the in‐service structural integrity assessment of welded and machined components requires an accurate and reliable NDT method for detecting and sizing surface breaking cracks. This paper discusses and compares the crack depth sizing abilities of two theoretically‐based NDT techniques: alternating current potential difference (ACPD) and alternating current field measurement (ACFM). Surface fatigue cracks of high and low aspect ratio are used in the investigation. It is demonstrated that ACPD is capable of accurately sizing long shallow cracks and that ACFM provides accurate crack depth predictions for small deep cracks.
HIGH STRAIN BIAXIAL FATIGUE OF A STRUCTURAL STEEL
Authors: Shatil G. , Smith D. J. , Ellison E. G.
Published: April 2007

Abstract— The biaxial fatigue behaviour of two batches of a structural steel, termed isotropic and anisotropic batches, is examined. Tests were carried out using thin‐walled hollow specimens subjected to axial load and internal and external pressure. The fatigue life of the isotropic batch is found to be about two to three times greater than the fatigue life of the anisotropic material. The ratio however is found to be dependent on the degree of biaxiality. Three equivalent strain parameters were used to correlate the fatigue lives, octahedral strain, Brown‐Miller and Lohr‐Ellison parameters. The difference between the theories are compared and the relation between the shear strain orientation and failure is discussed.
MICROSTRUCTURAL AND ENVIRONMENTAL EFFECTS ON FATIGUE CRACK PROPAGATION IN DUPLEX STAINLESS STEELS
Authors: MARROW T. J. , KING J. E.
Published: April 2007

Abstract—Fatigue crack initiation and propagation in duplex stainless steels are strongly affected by microstructure in both inert and aggressive environments. Fatigue crack growth rates in wrought Zeron 100 duplex stainless steel in air were found to vary with orientation depending on the frequency of crack tip retardation at ferrite/austenite grain boundaries. Fatigue crack propagation rates in 3.5% NaCl solution and high purity water are increased by hydrogen assisted transgranular cyclic cleavage of the ferrite. The corrosion fatigue results are interpreted using a model for the cyclic cleavage mechanism.
STRESS INTENSITY FACTORS FOR CRACKS AT FASTENER HOLES
Authors: NURSE A. D. , O'BRmN E. w. , PATTERSON E. A.
Published: April 2007

Abstract— Transmission and reflection photoelasticity has been used to determine the stress intensity factors for artificial cracks emanating from a hole in two‐dimensional tensile plates. Three geometries were investigated, namely a free hole, a pin‐loaded hole and a hole with an interference‐fit pin. All these cases relate to situations commonly found in aircraft structures. The results have been compared where possible with analytical data and a good correlation was found for these cases.
UNSTABLE FATIGUE CRACK PROPAGATION AND FATIGUE FRACTURE TOUGHNESS OF STEELS
Authors: TROSHCHENKO V. T. , POKROVSKY V. V. , YASNIY P. V.
Published: April 2007

This paper presents the results of fatigue crack growth and fatigue fracture toughness studies of a high‐pressure vessel steel with particular emphasis on the influence of heat treatment, low temperatures, plastic prestraining, the stress ratio and specimen dimensions.

It has been shown that steels in an embrittled state, caused primarily by thermal treatment and low‐temperatures, exhibit unstable fatigue crack growth which is characterized by alternate crack jumps (cleavage zones) and zones of fatigue crack growth. The fatigue fracture toughness, which corresponds to the first crack jump, and final fracture can be appreciably lower (i.e. up to 50%) than the static fracture toughness under plane strain conditions at the corresponding temperature.

An analysis has been performed of unstable and stable fatigue crack growth and a model of unstable crack propagation is proposed which accounts for the observed experimental behaviour.
ACCELERATION OF FATIGUE CRACK GROWTH UNDER INTERMITTENT OVERSTRESSING WITH DIFFERENT MEAN STRESS LEVELS
Authors: KOTERAZAWA R. , MUDJIJANA  , QINSHENG Y. , TIAN‐JIAN W. , NOSH T.
Published: April 2007

Abstract—

Fatigue crack growth behaviour under intermittent overstressing was investigated in dry air with a low carbon steel under tension‐compression and tension‐tension loading with different mean stress levels. A very small number of cycles of overstress applied intermittently during a very large number of cycles of understress below threshold caused, in all cases, a significant acceleration in crack growth rate as compared to the case of steady cyclic stress. The acceleration for the case with tensile mean stresses was a little smaller than in the case without mean stress and it was related to a little higher crack closure level in the former case. Stress history in the precracking process had some effect on crack closure and, consequently, on the acceleration. A fairly good correlation was obtained between the acceleration and the effective stress intensity range. The acceleration under multi‐level intermittent overstresses with different mean stresses could be predicted by linear summation from two‐level intermittent overstress test data. No difference was recognized in the fracture surface morphology between the cases with different mean stress level including the cases of multi‐level stresses, indicating that the micromechanism of crack growth acceleration would be the same in all cases.
EVALUATION OF FATIGUE DAMAGE ACCUMULATION BY ACOUSTIC EMISSION
Authors: FANG D. , BERKOVITS A.
Published: April 2007

Abstract—

Improvements in acoustic emission (AE) test techniques have lead to developments whereby reliable acoustic emission measurements as a fatigue damage indicator were made at room temperature on Incoloy 901 smooth specimens, over a stress‐ratio range of −1.0≤R≤0.2. Fatigue damage accumulation was evaluated in terms of an AE damage definition and a damage function was developed. Thus, various damage phases in the cumulative damage process were identified by their AE signature, and then formulated and analyzed in terms of cumulative AE ringdown counts.
APPLICATION OF ENERGY DISSIPATION RATE ARGUMENTS TO DUCTILE INSTABILITY
Authors: Kolednik O. , Turner C. E.
Published: April 2007

Abstract— Equations are established for the final macro‐unstable behaviour of a fully plastic cracked component in terms of the energy dissipation rate. Control by this first differential of energy occurs when the second differential of the energy absorbed is negative, a condition easily met for crack growth in certain fully plastic cases. The driving force for the instability is a term, I that becomes greater than the lefm term, G, as plasticity occurs. The additional component is an exchange of elastic to plastic energy, a term that is system dependent and is thus the main driving force for a fully plastic ductile instability. A possible relevance to brittle fracture and to a system dependence of both initiation toughness and the whole crack growth resistance curve is discussed.
THE RELATION BETWEEN STRESS INTENSITY FACTOR AND ENERGY RELEASE RATE IN THE PRESENCE OF R‐CURVE BEHAVIOUR
Authors: Fett T. , Munz D.
Published: April 2007

Abstract— Failure of ceramic materials occurs when the stress intensity factor of the most serious crack in a component reaches a critical value KI,C, the fracture toughness of the material. In case of ideal brittle materials the fracture toughness is independent of the crack extension and, consequently, identical with the stress intensity factor KI,Onecessary for the onset of stable crack growth. It is a well‐known fact that failure of several ceramics is influenced by an increasing crack‐growth resistance curve. The effect of increasing crack resistance has consequences on many properties of ceramic materials. In this report the authors discuss some aspects of R‐curve behaviour as represented by stress intensity factors or energies.
ANALYSIS OF CRACK TIP HYDROGEN DISTRIBUTION UNDER I/II MIXED MODE LOADS
Authors: Gao H. , Cao W. , Fang C. , de los Rios E. R.
Published: April 2007

Abstract— The distribution of hydrogen in the vicinity of a crack tip was studied using SIMS (Secondary Ion Mass Spectrometry) under different ratios of I/II mixed mode loads. Modified WOL specimens with kinked slits were employed in the course of the experimental work. Spectrographic measurements show that under I/II mixed mode loading, both in the HIC and in the rmaxp directions, there are two hydrogen accumulation peaks ahead of the crack tip, corresponding to the location of the maximum hydrostatic stress and maximum equivalent plastic strain, respectively. Based on results obtained over a range of loading conditions from mode I to a high KII/ KI, ratio, it is shown that the mode II component has a clear influence on both peaks. The conditions for hydrogen redistribution are discussed in terms of crack tip stress‐strain fields.
FINITE ELEMENT ANALYSIS OF CLOSURE BEHAVIOUR OF FATIGUE CRACKS IN RESIDUAL STRESS FIELDS
Authors: CHOI H.‐C. , SONG J.‐H.
Published: April 2007

An elastic‐plastic finite element analysis with high order elements is performed to examine closure behaviour of fatigue. cracks in residua1 stress fieids and the numerical results are then compared with experimental results. The finite element analysis, performed under plane stress using 8‐node isoparametric elements, can predict fatigue crack closure behaviour through residual stress fields very well. The crack opening and closing behaviour through a compressive residual stress field is found to be complicated and influenced by the applied load magnitude and the location of the crack tip. Three different types of crack opening behaviour, namely, normal, unsymmetric partial and symmetric partial crack opening behaviour are observed through a compressive residual stress field. The partial crack opening stress intensity factor including the partial crack opening effect is recommended for the prediction of fatigue crack growth through a compressive residual stress field.
THE EFFECT OF SAMPLE SIZE ON THE CONFIDENCE OF ENDURANCE FATIGUE TESTS
Authors: Beretta S. , Clerici P. , Matteazzi S.
Published: April 2007

Experimental determination of the fatigue endurance (S‐N) curve of either a given material or a machine element imposes the choices of sample size and of stress levels to be tested. Since referenced recommendations do not apply when the data include run‐outs or have variable scatter, this paper studies the confidence of fatigue tests, taking into account the effect of sample size and of a statistical model. In this research, a great number of rotary bending fatigue tests were carried out, using a heat treated carbon steel with relevant scatter of fatigue lives. The statistical analysis allowed one to obtain confidence limits of the S‐N diagram estimates and to propose some criteria for a better formulation of test schedules.
A THEORETICAL AND EXPERIMENTAL INVESTIGATION OF DYNAMIC DELAMINATION IN COMPOSITES
Authors: Thesken J. C.
Published: April 2007

Abstract A fundamental understanding of dynamic delamination in composites is sought through the application of theoretical and experimental approaches familiar to dynamic fracture mechanics. Analysis of steady‐state fracture in an infinite orthotropic strip yields a simple solution which can be used to evaluate numerical procedures and experimental results. The analogous specimen consists of a single edge notched composite strip bonded to stiff steel substrates to enforce the desired displacement boundary conditions. Delamination velocities of the order of 10 to 1000 m/s were measured using a graphite gauge technique. Quasi‐static and dynamic finite element methods are applied to investigate the behavior of the specimen and to determine static initiation and dynamic delamination toughness. The experimental observations cannot be explained by linear elastic fracture theory. The absence of a unique G(ȧ) relationship might be rationalized by a simple model relating matrix crack zone size to fiber bridging mechanisms.
EFFECT OF ELASTIC MISMATCH ON THE GROWTH OF A CRACK INITIALLY TERMINATED AT AN INTERFACE IN ELASTIC PLASTIC BIMATERIALS
Authors: Delfin P. , Gunnars J. , Stárhle P.
Published: April 2007

Abstract A crack perpendicular to, and initially with the tip on, a bimaterial interface is studied. An asymptotic analysis is performed and crack growth proceeds straight ahead at constant remote load. Mode I conditions and plane strain are assumed. The materials on both sides of the interface are elastic perfectly‐plastic with different elastic properties and the same yield stress. A finite element analysis is made and crack growth is simulated by an element relaxation technique. Because of the interface, the crack‐tip driving force is not constant, which is reflected in the near‐tip state. The development of the plastic zone and the crack opening displacements is presented for different elastic mismatches. Small scale yielding like results are obtained after a crack extension of about the plastic zone size from the interface, i.e. long before a square‐root singular stress field may be expected to embed the plastic zone. An important observation is that the development of the crack opening displacement at the initial stage of growth is reversed when plasticity is introduced, as compared to the prediction by an elastic model. A region of stable crack growth is identified at the initial phase of growth into a stiffer material, solely due to elastic mismatch.
ON CRACK PHASES OF PARTICULATE‐REINFORCED METAL MATRIX COMPOSITES
Authors: Li C.‐S. , Ellyin F.
Published: April 2007

Abstract Crack growth mechanisms have been investigated in 6061 aluminum alloy reinforced with alumina particles (Al2O3/6061 Al composites). This has led to the identification of six crack phases: unstable growth; long crack growth; near‐threshold long crack growth; short crack growth; pre‐cease short crack growth, and non‐growth phases. A crack phase diagram for particulate‐reinforced composites is presented here which displays the range of applied stress and crack length for each phase. Each phase boundary corresponds or relates to an overall material property. The inability of particles to resist long crack growth has been rationalized by the variation of crack tip‐cyclic plasticity and fracture energy due to the presence of particles.
THE EFFECT OF GRAIN SIZE ON FATIGUE CRACK GROWTH IN AN ALUMINIUM MAGNESIUM ALLOY
Authors: Turnbull A. , De Los Rios E. R.
Published: April 2007

Abstract Fully reversed uniaxial fatigue tests were performed on aluminium magnesium alloy Al 5754 with four different grain sizes in order that the effect of grain size on fatigue crack growth could be examined. Surface cracks were monitored by a plastic replication technique. Fatigue strength was shown to improve with a decrease in grain size. The endurance stress is a function of the inverse square root of the grain size and is described empiricdty by a Hall‐Petch type relation. The effect of grain size on fatigue crack growth is most significant when the crack length is of the order of the microstructure. Fluctuations in the growth rate of microstructurally short cracks are most marked in a fine grained microstructure and may be related to the need to transfer slip to adjacent grains. Crack path deviation is greatest in the coarsest grained microstructure and SEM fractography reveals a more pronounced crack surface roughness in the coarser grained alloy than in the finer grained alloy.
MICROSTRUCTURAL EFFECTS ON SMALL FATIGUE CRACK INITIATION AND GROWTH IN Ti6A14V ALLOYS
Authors: Demulsant X. , Mendez J.
Published: April 2007

Abstract— The nucleation and growth of small naturally initiated cracks have been investigated on Ti 6 Al 4V alloys, with bimodal or globular microstructures. Tests have been performed in air at a stress amplitude near 0.75 of the yield stress. The influence of microstructure on fatigue damage is described and the differences in fatigue life of some titanium alloys are explained. The effect of microstructure on fatigue resistance is mainly related to the early stages of damage including initiation and small crack growth. Coalescence processes favoured by a high density of initiated surface microcracks in fine α grain material, or rapid initiation of large cracks in coarse α colonies, explains low fatigue resistance or lifetime scattering in globular alloys. Small crack growth retardation due to α/β barriers associated with a low surface crack density, limiting coalescence processes, explains the highest resistance of bimodal structures.
BEACH MARK FORMATION CAUSED BY CHANGES IN ENVIRONMENTAL HUMIDITY DURING FATIGUE
Authors: Dravish M. , Johansson S.
Published: April 2007

Abstract— The application of combined low and high humidity environments during the early stages of fatigue crack propagation causes the formation of markings on the fracture surface. These markings form at the initiation zone and in the threshold region. The markings show the position of the crack front on a micro level and also give information about local crack growth rates. A comparison is made between the topography of the striations and the beach marks. Etch pitting is used to determine the orientation of crystallographic planes for crack growth in both beach mark and striation regions. The tests were carried out on two A1 alloys (7075‐T651 and 8090‐T851) at two stress ratios (R= 0.1 and 0.75).
MULTIPLE‐SITE DAMAGE IN AIRCRAFT FUSELAGE STRUCTURES
Authors: Schijve J.
Published: April 2007

Abstract— Since the Aloha accident the multiple site damage (MSD) problem of riveted lap joints in aircraft fuselages has drawn much attention. The failure scenarios for a lead crack and more small MSD cracks as discussed by Broek and Swift are summarized, including recent results of a relevant test series by Broek. It shows that small MSD cracks can significantly reduce the load for unstable crack extension. Prevention of catastrophic consequences requires crack arresting capability of the structure. Related aspects of the problem are discussed with reference to failure criteria for ligament failure, the MSD problem for existing and new aircraft, and different options for crack stopper bands.
PREDICTION OF THE FATIGUE THRESHOLD FOR A CRACKED BODY USING SHAKEDOWN THEORY
Authors: Huang Y.J. , Stein E.
Published: April 2007

Abstract— In this paper, the fatigue threshold ΔKth of a cracked body is studied. Unlike other approaches given in the literature, the shakedown theory is used for predicting ΔKth. A crack is considered as a sharp notch, the radius of which, at the threshold stress level, is a material constant. The threshold of crack propagation is explained as being due to shakedown of the cracked body, and a simple but reasonable model is derived. The value of ΔKth is found to be proportional to the yield stress multiplied by the square root of the effective crack tip radius. Using this model, ΔKth is calculated for some materials. Comparison of the predicted fatigue thresholds with those obtained by experiments, or by using other approaches, indicates that our model provides satisfying results.
FRACTURE MECHANICS ANALYSIS BASED ON A LOCAL SIMULATION PRINCIPLE
Authors: Zerbst U. , Heerens J. , Schwalbe K.‐H.
Published: April 2007

Abstract— A local simulation principle is presented which allows the transfer of geometry‐dependent fracture parameters from a specimen to a component if the local constraint conditions of the crack tip in the component are simulated by the specimen. This can be achieved by adapting the specimen to the component with respect to the ligament length, the ligament width, the crack length and the loading geometry. If these requirements are met, then the relationship between the load and the driving force in the component can be estimated from the specimen by a simple scaling procedure. The application of the local simulation principle is illustrated by an example.
HIGH CYCLE FATIGUE AND A FINITE ELEMENT ANALYSIS
Authors: Ballard P. , Van K. Dang , Deperrois A. , Papadopoulos Y. V.
Published: April 2007

Abstract— We aim to develop a systematic method of designing structures, by finite element methods, for high cycle fatigue under periodic constant load systems. After having defined a precise terminology, we quickly list those multiaxial fatigue criteria which can be found in the literature. Some criteria, derived from a microscopic approach (Dang Van's, Papadopoulos' and Deperrois' criteria) are extensively presented. The criteria which can be reasonably retained for numerical analyses of structures are underlined and compared to one another. As a conclusion, we describe a high cycle fatigue CAD system which can be derived from this analysis.
THE EFFECT OF VARIOUS CONSTRAINT CONDITIONS IN THE FREQUENCY RESPONSE MODEL OF THERMAL STRIPING
Authors: Jones I. S. , Lewis M. W. J.
Published: April 2007

Abstract— Thermal fatigue damage may be caused when incompletely mixed hot and cold fluid streams pass over the surface of a component or structure. This kind of thermal fatigue, known as thermal striping, is of particular concern in various types of nuclear reactors and for rapid shut‐downs of hot plant. A computer code, known as TBL, is an engineering design tool which has been developed to assess thermal striping damage for fully constrained plates. This model is further developed to account for various plate‐constraint conditions. It is compared with two other methods of assessing thermal striping damage. Good agreement is found for the cases when the component is (a) a plate, constrained in various ways and exposed to a sinusoidally varying temperature time striping history and (b) a shroud tube found in the above‐core region of a fast reactor pressure vessel and striped with a random temperature time history.
CYCLIC STRESS‐STRAIN, STRESS‐TEMPERATURE AND STRESS‐ELECTRICAL RESISTANCE RESPONSE OF NiCuMo ALLOYED SINTERED STEEL
Authors: Biallas G. , Piotrowski A. , Eifler D.
Published: April 2007

Abstract—The influence of sintering temperature on the fatigue behaviour of a NiCuMo alloy was determined. It is common practice to characterize the cyclic deformation behaviour by means of plastic strain amplitudes. For sintered materials the quantity of the plastic strain amplitudes is influenced by microstructural changes as well as crack opening and crack growth effects and does not allow any distinction between these mechanisms. In the present work cyclic stress‐strain, cyclic stress‐temperature and cyclic stress‐electrical resistance measurements were studied simultaneously to get a more comprehensive description of the fatigue behaviour of sintered steels. The temperature is essentially sensitive to the work of plastic deformation during cyclic loading. The electrical resistance responds to microstructural changes, e.g. dislocation rearrangements and void formation as well as to crack initiation and propagation. Beyond that it is shown that continuous stress‐increase tests are a suitable short term testing method to determine cyclic stress‐strain curves which are in a very good agreement with those from single step tests.
HIGH TEMPERATURE FATIGUE‐CREEP BEHAVIOUR OF SINGLE CRYSTAL SRR90 NICKEL BASE SUPERALLOYS: PART 1—CYCLIC MECHANICAL RESPONSE
Authors: Li S. X. , Smith D. J.
Published: April 2007

Abstract—High temperature low cycle fatigue tests, with and without strain dwells, were conducted at 750°C, 950°C and 1050°C, on single crystal SRR99 nickel base superalloy, with different crystal orientations. At 750°C, SSR99 exhibited cyclic stability regardless of cycle type. The presence of strain dwells caused cyclic softening at 950°C compared with continuous cycling tests. At 1050°C, cyclic softening was observed for all the tests. The introduction of strain dwells produced significant stress relaxation at 950°C and 1050°C, but not at 750°C for the strain ranges in this study. Significant mean stress was observed at the three temperatures for tests with tensile or compressive strain dwells. The crystal orientation was found to have a dominating influence on the cyclic stress strain relationship and stress relaxation response. A simple approach is developed to correlate the effect of orientation on the cyclic mechanical response.
HIGH TEMPERATURE FATIGUE‐CREEP BEHAVIOUR OF SINGLE CRYSTAL SRR99 NICKEL BASE SUPERALLOYS: PART II—FATIGUE‐CREEP LIFE BEHAVIOUR
Authors: Li S. X. , Smith D. J.
Published: April 2007

Abstract—Experimental and theoretical investigations on the influence of temperature, strain dwells and crystal orientation on the high temperature fatigue‐creep life behaviour of single crystal SRR99 nickel base superalloy were performed. For a given temperature and loading condition, the longest fatigue life was observed for tests with [001] orientations, while the [111] orientation yielded the shortest fatigue life. A simple approach, using an orientation functionf(AhkI), was applied successfully to correlate the influence of orientation. Using this function, the shortest fatigue life was observed for tests with a compressive dwell at 750°C, but at 1050°C tests with a tensile dwell exhibited the shortest life. Compared with continuous cycling tests, tests with tensile dwells showed remarkably longer lives at 750°C, significantly shorter lives at 1050°C, and almost identical lives at 950°C; tests with compressive dwells always exhibited shorter lives than continuous cycling tests at all temperatures. The influence of strain dwells on the life of SRR99 was via the simultaneous effects of mean stress, additional inelastic strain, and time dependent damage. A mean stress modified strain range partitioning method was proposed and used to predict the fatigue‐creep life.
DYNAMIC FRACTURE TOUGHNESS MEASUREMENTS AND LOCAL APPROACH MODELLING OF TITANIUM ALLOYS
Authors: Roudier Ph. , François D.
Published: April 2007

Two titanium alloys TA6V and TD5AC were tested. Tensile tests were performed, under static and dynamic loadings, on cylindrical notched and fatigue precracked specimens. The visco‐plastic constitutive equations of the alloy were found by fitting finite element computations with the experimental results. The dynamic fracture toughness was obtained by applying the convolution method of Bui and Maigre. Results for the TA6V alloy did not display significant variations of fracture toughness with loading rate, whereas for the TD5AC alloy an increase was measured. The critical void growth was found to be independent of the strain rate. Fair predictions of the fracture toughness under static as well as under dynamic conditions could be achieved by finite element computations using these experimental critical void growth values.
A MICRO‐MECHANICS MODEL OF CORROSION‐FATIGUE CRACK GROWTH IN STEELS
Authors: de los Rios E. R. , Wu X. D. , Miller K. J.
Published: April 2007

Principles of Microstructural Fracture Mechanics (MFM) are used to develop a model for the characterization of environment‐assisted short fatigue crack growth.

Fatigue cracks are invariably initiated at corrosion pits formed at inclusions, hence the analysis includes stress concentration effects at pits that lead to the propagation of fatigue cracks the rates of which are considered to be proportional to the crack tip plastic displacement. This plasticity is constrained by microstructural barriers which are overcome in a non‐aggressive environment at critical crack lengths only when the applied stress is higher than the fatigue limit. However, the superposition of an aggressive environment assists fatigue damage via crack tip dissolution, enhancement of crack tip plastic deformation, the introduction of stress concentrations at pits and a reduction of the strength of the microstructural barrier. These environment effects are manifested in a drastic reduction of the fatigue limit and higher crack propagation rates.

The model is compared with fatigue crack propagation data of a BS251A58 steel tested in reversed torsion when submerged in a 0.6M NaCl solution.
DEVELOPMENT OF A CONSTITUTIVE MODEL FOR BIAXIAL LOW‐CYCLE FATIGUE
Authors: Borodh M. V. , Kucher N. K. , Strizhalo V. A.
Published: April 2007

Abstract— A version of the endochronic theory of plasticity for the modelling of nonproportional cyclic loading has been developed. To describe an additional hardening of a material a new engineering method for defining a nonproportionality parameter is proposed for a wide class of cyclic strain paths with a prescribed maximum range of plastic or total strains. This parameter makes it possible to establish an unambiguous linear dependence between the cyclic strain path shape and the stress level in a stabilized state. Conjugation conditions have been formulated to describe complex histories of nonproportional cyclic loading. The results of the modelling are shown to be in fair agreement with the experimental data.
USEFUL SCALAR PARAMETERS FOR MULTIAXIAL FATIGUE DEFORMATION STUDIES
Authors: Tourabi A. , Guelin P. , Wack B. , Pegon P. , Favier D. , Nowacki W. K.
Published: April 2007

Abstract— Two scalar parameters relating to stored energies are defined along an arbitrary cyclic loading path for an isotropic elastic‐plastic continuum. The definitions of the parameters are introduced in the one‐dimensional case. The tensorial generalization is developed firstly under the mechanical point of view and secondly focusing attention on the thermodynamical rates. The case of the usual cyclic traction test is studied in order to suggest an interest in the proposed parameters in the quasi‐reversible range and in the subsequent transition range between reversibility and quasi‐perfect plasticity.
FATIGUE CRACK GROWTH UNDER MIXED‐MODE I AND II LOADING
Authors: Qian J. , Fatemi A.
Published: April 2007

Abstract— Mixed‐mode fatigue crack growth has been studied using four point bend specimens under asymmetric loads. A detailed finite element analysis provides the stress intensity factors for curved cracks under different mixed‐mode load conditions. Both fatigue crack growth direction and crack growth rate are studied. The maximum tangential stress and the minimum strain energy density criteria were found to provide satisfactory predictions of the crack growth directions. An effective stress intensity factor was used to correlate the fatigue crack growth rates successfully. It is found that the use of mode I fatigue crack growth rate properties results in a conservative crack growth rate prediction for mixed‐mode load conditions.
VARIABLE AMPLITUDE LOADING IN En8 (080M40) STEEL: A DETAILED EXPERIMENTAL STUDY OF CRACK GROWTH
Authors: Ng'ang'a S. P. , James M. N.
Published: April 2007

Abstract —The load interaction effects that occur under variable amplitude loading conditions following single peak overloads, low‐high blocks and high‐low blocks have been investigated on a commonly used structural steel. A detailed investigation has been carried out on long cracks which aims at developing and assessing the efficacy of a simple predictive model based on closure and plastic zone effects.

The material was tested in a quenched and tempered condition. All the tests were carried out in the four point bending mode, in both the Paris regime and near the threshold, with overloads ranging from 10% to 100%.

An attempt to relate crack closure to crack growth rates in the transient growth rate region (which follows a load change) was made.

The trends observed for a wide range of loading parameters are presented.
CRACK EXTENSION UNDER VARIABLE LOADING IN THE SHORT AND THE LONG CRACK REGIME, USING A GENERAL FATIGUE DIAGRAM
Authors: Weiss M. P. , Hirshberg Z.
Published: April 2007

Abstract— A new fatigue domain diagram, recently introduced by one of the authors, makes it possible to demonstrate the fatigue behavior of specimens under varying stress amplitude loading both qualitatively and quantitatively. The diagram is briefly reviewed and crack propagation and damage summation of steel specimens under two level and multi level tension‐compression loading are simulated and discussed. Typical patterns of low‐high and high‐low sequence levels are explained, predicted and, with careful classification, shown to follow certain cumulative damage trends. Correlation with experimental results is shown and discussed. The main conclusion is that one can show repeatable trends in H‐L and L‐H two‐step and multi‐step loading sequences, only for cases where the local material properties are not drastically changed, and the failure pattern is similar (critical crack propagation or gross yielding) in all stages of the tests. Damage accumulation, expressed as additional crack length, is clearly shown on the general fatigue diagram.
CYCLIC STRESS‐STRAIN RESPONSE AND MICROSTRUCTURE UNDER VARIABLE AMPLITUDE LOADING
Authors: Christ H.‐J. , Mughrabi H.
Published: April 2007

Abstract— In order to study the cyclic stress‐strain behaviour under variable amplitude loading in terms of dislocation glide character and microstructure, various metals and alloys were cyclically loaded in single‐step tests and in an incremental step test (IST). The cyclic stress‐strain curves (CSS curves) which correspond to the different loading conditions were compared and the shapes of the hysteresis loops were analysed with respect to Masing or non‐Masing behaviour.

As expected, cyclic loading with constant amplitude leads to the formation of a characteristic dislocation arrangement that depends on the amplitude applied. The amplitude‐related microstructure corresponds to the observation that Masing behaviour was not found in single‐step tests. However, in the IST a state of saturation, or at least approximate saturation, is attained after some or many loading blocks. In the case of single‐phase polycrystalline materials, wavy slip behaviour was found to be a prerequisite for the fulfilment of Masing behaviour. Then, the CSS curve, obtained by means of IST, intersects that of the single‐step tests at an intermediate amplitude. Planar‐slip materials show very similar CSS curves in spite of considerable differences in the dislocation arrangements for different testing modes. The behaviour of particle‐hardened alloys depends very strongly on the relative effectiveness of the precipitates as obstacles for dislocation motion and can be understood analogously to single‐phase materials on the basis of the resulting dislocation glide character.
CREEP‐FATIGUE CRACK GROWTH BEHAVIOR IN 1Cr‐1Mo‐0.25V STEEL. PART II: CRACK GROWTH BEHAVIOR AND MODELS
Authors: Adefris N. , Saxena A. , McDowell D. L.
Published: April 2007

Abstract— Creep‐fatigue crack growth (CFCG) behavior of an ex‐service 1Cr‐1Mo‐0.25V steel was investigated for hold times of 100 s, 15 min, and 8 h for a trapezoidal loading waveform at a temperature of 538°C. The correlation of the crack growth rate with (Ct)avg for various hold times was significantly improved when an appropriate estimation scheme, previously proposed by the authors, was used to estimate this creep fracture mechanics parameter for this material. Crack growth data under creep‐fatigue conditions and analysis procedures used to reduce them are described in detail in this paper.
CRACK INTERACTION, COALESCENCE AND MIXED MODE FRACTURE MECHANICS
Authors: Wang Y.‐Z. , Atkinson J. D. , Akid R. , Parkins R. N.
Published: April 2007

Abstract— Multiple cracks are often observed in engineering structures; and their interaction and coalescence may significantly affect the lifetime of a component or structure. In this paper, the general features associated with crack interaction and coalescence are presented, and the conditions for coalescence in various forms are reviewed. A model has been developed based on the principles of mixed mode fracture mechanics, to provide a rational explanation for the phenomenon of crack interaction and to predict the coalescence conditions. The latter is found to agree reasonably with the experimental observations.
J‐INTEGRAL APPROACH TO MODE III FATIGUE CRACK PROPAGATION IN STEEL UNDER TORSIONAL LOADING
Authors: Tanaka K. , Akiniwa Y. , Nakamura H.
Published: April 2007

Abstract—

Mode III fatigue crack propagation tests were conducted on circumferentially cracked bars of a medium carbon steel under a constant value of the J‐integral range. The ΔJ value was evaluated from the loading part of the hysteresis loop of the applied torque and the angle of twist. The fracture surface was macroscopically flat for all cases examined in the present study. The crack propagation rate decreased with crack extension, because of the shear contact of the crack faces. The crack propagation rate, without contact shielding, obtained by extrapolating the relation between the crack propagation rate and the crack length to the pre‐crack length, was a power function of ΔJ irrespective of the initial notch depth.
A MICROCRACK GROWTH LAW FOR MULTIAXIAL FATIGUE
Authors: McDowell D. L. , Bennett V. P.
Published: April 2007

Abstract—

Within the past decade, critical plane approaches have gained increasing support based on correlation of experimentally observed fatigue lives and microcrack orientations under predominately low cycle fatigue (LCF) conditions for various stress states. In this paper, we further develop an engineering model for microcrack propagation consistent with critical plane concepts for correlation of both LCF and high cycle fatigue (HCF) behavior, including multiple regimes of small crack growth. The critical plane microcrack propagation approach of McDowell and Berard serves as a starting point to incorporate multiple regimes of crack nucleation, shear growth under the influence of microstructural barriers, and transition to linear crack length‐dependent growth related to elastic‐plastic fracture mechanics (EPFM) concepts. Microcrack iso‐length data from uniaxial and torsional fatigue tests of 1045 steel and IN 718 are examined and correlated by introducing a transition crack length which governs the shift from nonlinear to linear crack length dependence of da/dN. This transition is related to the shift from strong microstructural influence to weak influence on the propagation of microcracks. Simple forms are introduced for both the transition crack length and the crack length‐dependence of crack growth rate within the microcrack propagation framework (introduced previously by McDowell and Berard) and are employed to fit the 1045 steel and IN 718 microcrack iso‐length data, assuming preexisting sub‐grain size cracks. The nonlinear evolution of crack length with normalized cycles is then predicted over a range of stress amplitudes in uniaxial and torsional fatigue. The microcrack growth law is shown to have potential to correlate microcrack propagation behavior as well as damage accumulation for HCF‐LCF loading sequences and sequences of applied stress states.
APPROXIMATE EXPRESSIONS FOR THREE‐DIMENSIONAL NOTCH TIP STRESS FIELDS
Authors: Xu R. X. , Thompson J. C. , Topper T. H.
Published: April 2007

Abstract—

The analytical solution of Sadowsky and Sternberg for the stress field around an biaxial elliptical cavity in an infinite elastic body was carefully examined. For uniaxial tension, it was found that the stress concentration factor varies very slowly along the equator of the cavity, regardless of the shape of the cavity. As was found for two dimensional notch problems, the normalized stress fields around cavities with different shapes are virtually identical within the stress concentration region and differ only slightly beyond that region. This fact permits simple, yet very accurate approximate stress equations to be developed for three dimensional notch problems by modifying the previously obtained solutions for two dimensional notch problems.
THE FRACTURE MECHANISM IN 475°C EMBRITTLED FERRITIC STAINLESS STEELS
Authors: Marrow T. J.
Published: April 2007

Abstract—

The mechanism of “475°C embrittlement” in age‐hardened ferritic stainless steel, E‐Brite and A129‐4, is investigated. Experimental results for smooth tensile and notched bending fracture tests are interpreted using a finite element simulation of the stresses at fracture. Yield is characterised by profuse slip band formation. Transgranular fracture initiation is observed at slip band intersections with grain boundaries. Deformation twinning occurs during brittle fracture. Slip bands and deformation twins are identified using lattice rotations measured with electron back‐scatter diffraction patterns. Mechanisms for the ductile‐to‐brittle transition are discussed.
THE FRACTURE MECHANISM OF 475°C EMBRITTLEMENT IN A DUPLEX STAINLESS STEEL
Authors: Marrow T. J. , Harris C.
Published: April 2007

Abstract—

The mechanism of “475°C embrittlement” of a duplex stainless steel was investigated using finite element modelling of the stress distribution at brittle fracture initiation. Brittle fracture initiated at a critical shear stress, which increased with ferrite hardness. The fracture stress was affected by the duplex microstructure. Fracture was nucleated by deformation twins, which were identified using electron back‐scatter diffraction. The ductile‐to‐brittle fracture transition was sensitive to age‐hardening and could be described simply by the effect of age‐hardening and test temperature on the yield stress.
A TECHNICAL NOTE. INFLUENCE OF MEAN STRESS ON FATIGUE IN SEVERAL ALUMINIUM ALLOYS UTILIZING Kcmax THRESHOLD PROCEDURES
Authors: Clark T. R. , Herman W. A. , Hertzberg R. W. , Jaccard R.
Published: April 2007

Abstract—

Recent interest in the constant Kmax (Kcmax) threshold testing procedure has resulted in a more in‐depth study of the influence of Kmax level on fatigue response and ΔKth in aluminium alloys. Under Rc= 0.1 conditions, which cause large amounts of closure, ΔKth levels were typically 2 to 4 Mpam. However, under Kcmax test procedures, associated with no measurable closure at threshold, ΔKth was typically 1 Mpam. A slight Kcmax level effect on ΔKth was observed at high Kmax values for some of the alloys, and was deemed to be a pure mean stress effect, separate from closure arguments.
NEW APPROACH FOR ESTIMATION OF ΔJ AND FOR MEASUREMENT OF CRACK GROWTH AT ELEVATED TEMPERATURE
Authors: Rie K.‐T. , Wittke H.
Published: April 2007

Abstract— The ACPD‐method was used to measure crack growth in low cycle fatigue tests at elevated temperature. The material which was investigated at T= 550°C was the ferritic steel 2.25Cr–1Mo. Characteristic values of representative hysteresis loops were determined. The crack growth data were correlated with the effective part of the fracture mechanics parameter ΔJ. A new method for the calculation of ΔJ is proposed.
CYCLIC BEHAVIOUR AND ROOM TEMPERATURE MICROMECHANISMS OF 3Y‐TZP CERAMICS AT SUBMICRON AND NANOCRYSTALLINE LEVELS
Authors: Zheng Y. , Yan D. , Gao L.
Published: April 2007

Abstract— The cyclic behaviour and micromechanisms of 3Y‐TZP ceramics were investigated at a stress ratio, R, of 0.1 and a frequency of 0.1 Hz at room temperature for both nanocrystalline (100nm) and submicron polycrystalline (0.35μm) 3Y‐TZP ceramics. The nanocrystalline material displayed cyclic softening, but the submicron polycrystalline material displayed cyclic hardening. The cyclic hardening resulted mainly from saturation of tetragonal to monoclinic phase transformation which induced a higher internal stress in the material; the cyclic softening resulted partly from the formation of microcracks along the grain boundary of the tetragonal phase.

Superplastic deformation was first found by the Scanning Electron Microscope and the Atomic Force Microscope (AFM) in some micro‐areas of the fatigue fracture surface of the nanocrystalline material. Furthermore it was observed by AFM that there were a large number of slip lines and an early stage for the formation of an extrusion on the side edge of the fracture. From this it was deduced that the micromechanism of local superplasticity resulted from the slip motion of dislocation.
EFFECT OF NON‐METALLIC INCLUSIONS ON CORROSION FATIGUE RESISTANCE OF P/M DUPLEX STAINLESS STEELS
Authors: Laitinen A. , Hänninen H.
Published: April 2007

Abstract— The effect of non‐metallic inclusions on high‐cycle fatigue resistance of powder metallurgically (P/M) fabricated and hot isostatically pressed (HIP) duplex stainless steels (DSSs) was investigated with axial fatigue test specimens in a chloride and sulphate containing aqueous solution at room temperature. The inclusion content of the studied materials was analysed with bulk oxygen content measurements as well as with optical and digital inclusion analysis methods. Fatigue crack initiation was observed to take place at material defects, i.e., on contaminated prior powder‐particle boundaries or, especially, at oxide inclusions. Localised corrosion was not noticed at the initiation sites. Material defects had an especially pronounced effect on fatigue properties, when the stress ratio was R=0, but their effect decreased, when the calculated stress intensity factor was reduced below a certain value. Moreover, the change of the stress ratio from R=0 to R=‐1 decreased the difference in high‐cycle corrosion fatigue properties between P/M‐HIP DSSs with different inclusion contents.
MODELLING THE CONDITIONS FOR FATIGUE FAILURE IN METAL MATRIX COMPOSITES
Authors: de los Rios E. R. , Rodopoulos C. A. , Yates J. R.
Published: April 2007

Abstract— An investigation on the fatigue crack growth (FCG) and fatigue failure in metal matrix composites (MMCs) has been conducted using a model based on micromechanical elasto‐plastic fracture mechanics (EPFM) principles. To evaluate the model, comparisons between experimental and predicted fatigue life have been made for two silicon carbide strengthened (SCS)‐6/Ti‐based MMCs. Conditions for crack arrest and crack instability have also been considered in order to define the fatigue damage limits. Crack arrest occurs from the added effects of fibre bridging and the constraint provided by the fibre on matrix microplasticity, while crack instability is achieved when the fibre constraint effect is minimum and the fatigue resistance of the material is reduced due to the accumulation of fatigue damage. Comparisons of the predicted fatigue damage limits with experimental results show good agreement which underlines the usefulness of a microstructural fracture mechanics model.