bluuebunny/crossref_metadata_2025 huggingface dataset:
A MODEL FOR THE FATIGUE LIMIT AND SHORT CRACK BEHAVIOUR RELATED TO SURFACE STRAIN REDISTRIBUTION
Authors: Abdel‐Raouf H. , Topper T. H. , Plumtree A.
Published: April 2007

A model based on surface strain redistribution and the reduced closure stress of short cracks is shown to successfully predict the fatigue limit and short crack growth behaviour for aluminium alloy 2024‐T351. Using this approach, the length of non‐propagating cracks can be anticipated. The local stress intensity range may be resolved into two components (first the linear elastic fracture mechanics component and the second is due to surface strain concentration). Consequently, the local stress intensity range of aluminium alloy 2024‐T351 is a maximum at a depth of approximately half a grain diameter and a minimum at a depth slightly in excess of three grain diameters. The reduced closure stress for short cracks coupled with the increased applied stress intensity caused by surface strain redistribution accounts for the variation of the effective stress intensity parameter as a function of crack depth. This parameter is a maximum for the smallest possible crack (3 μm) and decreases as crack length increases.
AN INVESTIGATION OF THE WARM PRESTRESSING (WPS) EFFECT IN A533B WELD METAL
Authors: Reed P. A. S. , Knott J. F.
Published: April 2007

Abstract— The WPS effect has been shown to be beneficial in increasing the lower shelf fracture toughness of A533B weld metal for both the load‐unload‐cool‐fracture (LUCF) and the load‐cool‐fracture (LCF) cycles. The LCF cycle gives a greater apparent increase in fracture toughness than the LUCF cycle but only a small increment of load in the lower shelf region is needed to propagate failure compared with a much increased fracture load which is required in the LUCF case. Models predicting the increase in apparent fracture toughness by superposition of the stress and strain distributions from each step in the prestress cycle are shown to be non‐conservative for failures occurring in the lower shelf brittle regime. There is evidence for the operation of a “microcrack blunting” mechanism, but the extent to which it contributes to the WPS effect is small. Stress‐relief heat‐treatments after prestressing remove nearly all the beneficial effects of WPS. Residual stresses clearly play an important role in the WPS phenomenon, and the models successfully predict experimentally observed trends. Prestressing “deactivates” failure initiation from the larger inclusions in the weld metal. This however does not affect the intrinsic fracture toughness of the material. Fracture in this weld metal, where initiation sites (inclusions) abound, appears to be a co‐operative process, and fracture is controlled by inclusions of the mean (and hence most plentiful) diameter rather than the maximum diameter.
THE EFFECT OF GEOMETRY ON THE DEVELOPMENT OF CREEP SINGULAR FIELDS FOR DEFECTS UNDER STEP‐LOAD CONTROLLED LOADING
Authors: Joch J. , Ainsworth R. A.
Published: April 2007

Abstract— The development of singular fields for defects in steadily loaded creeping structures is examined as a function of geometry and crack size using finite‐element analyses and results from the literature. Approximations for estimating the time‐development of the amplitude of the fields are examined and it is shown that simple approximations are expected to apply for a wide range of geometries. It is shown both theoretically and numerically that plasticity on initial loading produces crack tip fields closer to the steady state condition than those produced elastically.
EFFECTS OF COLD EXPANSION OF A HOLE ON FATIGUE CRACK INITIATION LOCATION AND LIFE OF AN LY12CZ ALLOY
Authors: Chao Ling , Xiulin Zheng
Published: April 2007

Abstract— In the present study the effects of cold expansion of a hole on the location of fatigue crack initiation and life of LY12CZ alloy sheets are experimentally investigated and a quantitative expression of fatigue crack initiation life presented. Test results and analysis show that there may exist an optimum amount of cold expansion, for which both the coefficient of the resistance to fatigue crack initiation and the threshold are increased, and that the direction of cold expansion has no appreciable effect on fatigue crack initiation life. Observations show that, after cold expansion the fatigue crack nearly always initiates on the final entry face from which the mandrel is introduced into the hole during the final cold expansion process. Therefore it may be thought that the entry face is less resistant to fatigue crack initiation. In addition, the assumption of equivalence of residual stresses and also the strain hardening conditions on both the entry and exit faces may be questionable.
CRACK‐LINE AND EDGE GREEN'S FUNCTIONS FOR STRESS INTENSITY FACTORS OF INCLINED EDGE CRACKS
Authors: Rooke D. P. , Rayaprolu D. B. , Aliabadi M. H.
Published: April 2007

Abstract—Fretting loads on the surfaces of structural components can cause accelerated growth of short cracks. The rate of growth will depend on the combined stress intensity factor resulting from both remote and local loading. Many stress intensity factor solutions are available for remote loading, but solutions for arbitrary fretting loads are not readily accessible. In this paper accurate crack‐line Green's functions are obtained from a boundary element analysis and then used to develop the Green's functions for loads on the edge of a half‐plane containing a slant crack at various angles to the edge. These latter Green's functions can be used to obtain stress intensity factors for arbitrary stresses (normal or shear) on the edge of the half‐plane without further stress analysis; simple integration procedures are all that is required.
ACCELERATION OF CRACK GROWTH UNDER INTERMITTENT OVERLOADING AT ELEVATED TEMPERATURE
Authors: Koterazawa Ryoichi , Nosho Takayoshi
Published: April 2007

Abstract— Acceleration of crack growth by intermittent overloading was investigated at 650°C by using specimens of different thickness made of Type 304 stainless steel. When the hold time of overload was very short (∼20s), the crack growth rate was significantly accelerated (20–50 times) and the fracture surface morphology showed extremely ductile transgranular fracture by glide plane decohesion or microvoid coalescence, suggesting significant recovery of the material. In the thinner plate specimens, the crack growth rate under intermittent overloading was correlated well with the modified J‐integral, i.e. J (C%) and agreed with the growth rate of static creep cracks in a J versus da/dt diagram. In the thicker plate specimens, however, this is not the case and the growth rate was about 20% of that in the thinner plate specimens in the J diagram. Transgranular fatigue type crack growth appeared in the low growth rate region.
RETARDATION AND ARREST OF FATIGUE CRACK GROWTH IN AISI 4340 STEEL BY INTRODUCING REST PERIODS AND OVERLOADS
Authors: Kim Song‐Hee , Tai Weon‐Pil
Published: April 2007

Abstract— The aim of this study is to investigate the effects of an intermittent rest period at 300°C, an overload in tension, and the combination of an overload and a subsequent rest period, on fatigue crack growth in AISI 4340 steel. The intermittent rest period was found to stop fatigue crack growth completely near the threshold level of ΔK. The alleviation effect of a rest period on crack growth was more distinct at lower levels of ΔK. With overload, the higher overload ratio caused a greater effect on crack growth rate. The reduced stress intensity factor caused by crack branching and an enhanced roughness of crack surfaces probably contribute to the retardation and arrest of fatigue crack growth. The most distinct retardation of fatigue crack growth was found after the combined treatment of an overload and a subsequent rest period. Compressive residual stresses following an overload and strain‐age hardening during the rest period at 300°C are suggested as assisting the arrest or retardation of fatigue crack propagation.
FATIGUE CRACK GROWTH OF SILICON NITRIDE WITH CRACK WEDGING BY FINE FRAGMENTS
Authors: Tanaka T. , Okabe N. , Nakayama H. , Ishimaru Y.
Published: April 2007

Abstract— Fatigue crack growth tests of silicon nitride Si3N4 were carried out under four‐point bending using square bar specimens at room temperature. A pre‐crack was introduced by a bridge indentation method. Decreasing K‐type tests at stress ratios of R= 0.1 and 0.6 and also under static load were first carried out, and after observing the cessation of crack growth, K‐increasing tests were performed except for the case of a static load. Crack closure was observed on most specimens by the elastic compliance method. Furthermore, SEM observations of the crack paths were made to see what was happening during crack growth. The threshold and the region of steady crack growth were observed more clearly under cyclic loading, and an effect of load cycling certainly existed which became more evident when the maximum stress intensity factor Kmax approached the threshold. A wedge effect, caused by fine fragments on the crack surface, played an important role in crack closure behaviour of each specimen, and it is suggested that the crack growth rate is controlled by both the effective stress intensity range ΔKeff and the effective mean stress intensity factor Km,eff at least as a first approximation.
A THREE‐DIMENSIONAL FINITE ELEMENT ANALYSIS FOR A CRYSTALLOGRAPHIC CRACK NEAR THE INTERFACE OF AN INCOMPATIBLE BICRYSTAL
Authors: Li Chingshen
Published: April 2007

On the basis of modelling bicrystal deformation, using three‐dimensional, anisotropic finite elements, the problem of a crystallographic crack approaching the interface in a [111] tilt bicrystals of 90˚ misfit angle under shear loads is solved. The influence of thickness direction material heterogeneity across the interface on the distribution of the stresses, strains and crack sliding displacements along the crack front near the interface has been revealed. As the crack approaches the interface, those mechanical parameters are considerably changed by the heterogeneity across the interface. Remarkable variations in the stresses and strains along the crack front have also been identified and are referred to the different constraint across the thickness. The maximum stress may shift from the crack tip to the interface ahead of it, where, as suggested by numerical results and previous experimental observation, a new fracture process core may be activated. The interface‐induced crack shielding or antishielding under mode II and III loading is analyzed and discussed.
FATIGUE STRENGTH OF NON‐LOAD‐CARRYING FILLET WELDED JOINTS: EFFECTS OF WELD RESIDUAL STRESSES AND STRESS CONCENTRATION
Authors: Takahashi Ichihiko , Yoshii Tokuharu , Iidaka Hiroo , Fujii Eisuke , Matsuoka Kazuyoshi
Published: April 2007

The fatigue strength of non‐load‐carrying fillet welded joints of KE36(TMCP) steel was studied. Both residual stress measurements and fatigue tests were carried out, with the plate thickness, the plate width and the heat input being varied. Specimens given a Post Weld Heat Treatment (PWHT) were also prepared.

The plate width had no effect on the fatigue strength, because it hardly affected the transverse residual stresses at the weld toe. However, the heat input influenced the transverse residual stress distribution, and a significant difference in fatigue strength due to the heat input was observed, especially when N≥ 106 cycles. It was also found that PWHT removed almost all the residual stresses at the weld toe, improving the fatigue strength drastically.

In this study, the values of stress concentration factor K2 were estimated by Machida's method and it was concluded that the thickness effect resulted from a combination of both stress concentration and residual stresses with the contribution of the latter being particularly significant for N≥ 106 cycles.
FATIGUE PROPERTIES OF C/Al METAL‐MATRIX COMPOSITES WITH DIFFERENT INTERFACIAL BONDS
Authors: Chen Rong , Wu Renjie , Zhang Guoding
Published: April 2007

The fatigue properties of four kinds of composite wires with different interface bonds, together with the effects of a notch in the surface of the composite wires, have been studied. Fatigue endurance (S‐N) curves of these materials revealed that no definitive fatigue limit was obvious. The C/Al composites with weak interfacial bonds were insensitive to the notch, but the notch was an important source of cracks which propagated rapidly when the interface bonding was strong. Although initial cracks would occur very early in the fatigue life, their propagation were arrested by the internal structure of the composite wires with suitable interface bonds.
FATIGUE BEHAVIOUR OF STEEL CASTINGS CONTAINING NEAR‐SURFACE DEFECTS
Authors: Heuler P. , Berger C. , Motz J.
Published: April 2007

Manufacturing defects in the near‐surface region of 2¼% Cr 1% Mo castings were investigated in a joint research programme. After ultrasonic testing and X‐ray inspection, large push‐pull specimens (cross section 1000 mm2) were taken from castings in regions with indications of defects and tested under fully reversed loading in the elastic and elastic plastic region up to predetermined levels of defect growth. The defects are micropores, pin holes, slag and oxide layers or inclusions, hot tears and small micro cracks in welds.

The initiation of crack growth was analysed by two methods, namely (a) the local strain concept with idealization of defects as three‐dimensional elliptical notches and (b) by the fracture mechanics concept with idealization of defects as two‐dimensional elliptical cracks. The main results can be summarized as follows:

1. The local strain concept describes the crack initiation potential of the defects more accurately than the fracture mechanics concept.

2. Interpretation of casting defects as cracks produces very conservative estimates in many cases.

3. Analytical evaluation of crack growth behaviour using the fracture mechanics approach for defects experiencing crack growth of at least 1 mm is much more accurate than when defects having a smaller extent of crack growth are included in the analysis.

Additional evaluations of crack growth behaviour of hot tears by fracture mechanics show that crack growth starting from open and partially closed hot tears must be subjected to a larger number of cycles than normal fatigue cracks of sound material. Partially closed hot tears in the vicinity of the crack front additionally delay crack propagation.
COMPARISON OF A STOCHASTIC MODEL OF FATIGUE CRACK GROWTH WITH EXPERIMENTS
Authors: Doliński K.
Published: April 2007

A stochastic model of fatigue crack growth under constant amplitude loading, derived from a global/local energy balance, is compared with experiment data. Four random variables and a Gaussian white noise random field were assumed to model, respectively the statistical scatter of the crack length versus N curves and their stochastic fluctuations reflecting the effect of stochastic material non‐homogeneity within a specimen. The statistical analysis of the so called Virkler and Ghonem‐Dore data sets is extensively used to identify the probabilistic characteristics of the random variables and random field and to verify the stochastic model. Based on the importance sampling integration technique the fatigue lifetime probability distributions are effectively calculated. The influence of the particular assumptions accounting for the random material properties is investigated and the quality of the model prediction is verified by comparison with empirical statistical characteristics of the lifetime.
LIMIT LOAD AND J‐ESTIMATES FOR IDEALISED PROBLEMS OF DEEPLY CRACKED WELDED JOINTS IN PLANE‐STRAIN BENDING AND TENSION
Authors: Joch J. , Ainsworth R. A. , Hyde T. H.
Published: April 2007

Using simple assumed deformation fields, approximate solutions have been obtained for tension and bending specimens containing welds for both limit loads and for fully plastic proportionality coefficients between the singular field amplitude J and the strain energy. The solutions allow for the degree of over or undermatch in the material tensile properties of the weld metal relative to the parent steel, and for the size of the weld region relative to the remaining ligament ahead of the crack.

Detailed finite‐element analyses have been performed for particular values of under/over‐match and size of weld region. These refine the approximate analytical solutions for the particular cases examined, and show broad agreement with the trends predicted by the analytical models.

The results have been used to provide guidance for testing weldments using standard, bend‐type geometries. For small‐specimen testing, cracks should be sufficiently deep for the remaining ligament ahead of a centrally located crack to be less than the total width of the weld. For large specimens, the weld region should be less than 20% of the size of the remaining ligament. If these guidelines are followed then standard relationships may be used to derive J from the area under the load‐displacement curve.

Common advice that the tensile properties of the weaker material in a weldment should be used in J‐estimation techniques has been shown to be appropriate in many cases. However, the advice is likely to be overconservative when plastic deformation is predominantly in the weld even for overmatched weld properties, or predominantly in base metal even for undermatched weld properties. The results in the paper enable such cases to be identified.
A FRACTURE AND SEVERITY ANALYSIS OF COMPOSITE CERAMICS
Authors: Chu M. C. , Ando K.
Published: April 2007

Ceramic composite crucibles failed when they were operated under extreme conditions of temperature and heating rate. To analyze the failure causes, fracture stress and fracture toughness values were ascertained and previously reported. Moreover, a new failure criterion for ceramics was proposed based on the existence of a crack‐tip process zone. A probabilistic failure assessment curve was proposed to evaluate quantitatively the reliability of ceramics.

By using the above data and theories, a fracture and severity analysis for crucibles has been completed. Some manufacturing techniques are proposed to improve reliability during service.
FLEXURAL FATIGUE CHARACTERISTICS OF FRP SANDWICH BEAMS
Authors: Shenoi R. A. , Aksu S. , Allen H. G.
Published: April 2007

The flexural fatigue characteristics of FRP sandwich beams are investigated. The skins of the beams are made from hybrid glass‐aramid fibres set in epoxy resin and the core material is made from linear PVC foam. The beams under investigation have practical applications in marine operations.

The applied load is uniformly distributed throughout the length of the beam which is simply supported.

From both static and fatigue tests, it is revealed that the failure occurred in the core due to excessive shear, in turn, resulting in large deflections. An empirical expression is derived to postulate a failure criterion.
FATIGUE GROWTH OF PHYSICALLY SMALL INCLINED CRACKS
Authors: Kujawski D. , Ellyin F.
Published: April 2007

The growth of physically small, self initiated, inclined corner and through‐the‐width cracks is investigated in a carbon steel under tension fatigue (R= 0.05). A preliminary procedure involving crack initiation under far‐field cyclic compression is used. This precracking method is adopted to minimize the effect of residual damage at the tip of the crack grown (and arrested) under cyclic compression. Thus, the subsequent tensile fatigue crack propagates through a region with no (or very small) residual stress or damage. Experiments indicate that the early growth rate of the inclined corner cracks is discontinuous with a few decelerations. During the intermittent propagation period the corner cracks only extend into the thickness (depth) of the specimen and do not propagate along the width direction. However, after reaching a certain aspect ratio, the inclined flaws grow in a steady (continuous) manner in both the thickness and width directions. Through‐the‐width cracks, both inclined and perpendicular to loading direction, do not show the discontinuous growth pattern typical of the inclined corner cracks, but exhibit only one minimum in the crack growth rate behaviour.
THE EFFECT OF SPECIMEN SIZE ON THE BEHAVIOUR OF PENETRATING FATIGUE CRACKS
Authors: Nam K. W. , Ando K. , Ogura N.
Published: April 2007

Fatigue life and penetration behaviour of cracks in HT80 steel plates were examined experimentally at room temperature for both large and small specimens containing a surface crack. Application of stress intensity factor solutions from small specimens, as proposed by the present authors, to large specimens was investigated. Crack growth behaviour, crack shape and crack opening displacement after penetration can be satisfactorily determined using the K solutions proposed by the authors.
THE DEVELOPMENT OF STRESSES AND THEIR DISTRIBUTION IN TWO‐PHASE ALLOYS DURING CYCLIC LOADING
Authors: Zhonghua Li , Yimin Li , Jinghua Luo
Published: April 2007

A finite element program calculates the cyclic behaviour of the individual component phases of a multiphase material using a master curve observed in uniaxial cyclic stress tests. The fatigue behaviour of the two‐phase alloys was characterized by visualizing the evolution of the phase stress (denoted by an average effective stress and an hydrostatic stress) during cyclic loading. The evolution procedure shows a unique fatigue behaviour of the in situ component phases, which differs from that observed in uniaxial or multiaxial fatigue tests of the single phase material. The fatigue damage on a microstructural scale was identified by the distributions of the plastic strain accumulated during cyclic loading and the stress triaxility in the component phases.
SIZE EFFECTS AND A MEAN‐STRENGTH CRITERION FOR CERAMICS
Authors: Bao Y. , Jin Z.
Published: April 2007

On the basis of a large amount of research on the fracture behaviour of ceramics, a new failure criterion is advanced. It is pointed out that the rupture of structural ceramics is governed by the mean stress in a specific zone, rather than by the peak stress value. The size of the process zone was derived as a material constant, and reflects the relation between the toughness and the strength of the material. The results show that the critical maximum stress varies with the stress gradient: the steeper the stress gradient, the higher the critical peak stress. Different experiments concerning the size effect have been carried out and the reason for size effects has been explained by a mean strength theory.
A PROBABILISTIC MODEL FOR PREDICTION OF LCF SURFACE CRACK INITIATION IN PM ALLOYS
Authors: de Bussac A. , Lautridou JC.
Published: April 2007

The Low Cycle Fatigue (LCF) life of PM Ni‐base superalloys is commonly reduced by surface crack initiation at ceramic inclusions. For this reason, a probabilistic model has been developed that predicts the size of surface crack initiation sites from the inclusion size distribution. For the experimental correlation of the model two sets of alloys were examined: a “standard” (i.e. as‐received) alloy, and a second material of identical composition to which a known distribution of ceramic inclusions was incorporated (or seeded). Model predictions were found to be in excellent agreement with the results obtained from the seeded materials in which the defect size distribution is larger and better characterized, and were satisfactory for the unseeded material in which two types of surface defects (pores and ceramic inclusions) initiate LCF cracks. The results of these experiments were employed in LCF simulations of both test specimens and full scale components. These indicated that differences exist between the site preference for LCF crack initiation in small test specimens and large scale components due to a scale effect. Such results demonstrate the utility of seeding experiments for generation of LCF test data used in component design.
STRETCH ZONE GEOMETRICAL MEASUREMENT, A PARTICULAR WAY TO MEASURE FRACTURE TOUGHNESS
Authors: Pluvinage G. , Lanvin A.
Published: April 2007

Stretch zone geometry (height and length) has been measured using five methods (Transmission Electron Microscopy, Retrodiffused Electron Microscopy, Nickel Plating, Roughness Measurement, Ondulation Method). Experimental investigations show that the major difficulty of these measurements is the great scatter of experimental results. However, it is seen that Transmission Electron Microscopy and Nickel Plating give sufficiently accurate results. By using these different methods, we have found a linear relationship between stretch zone geometry and the classical fracture toughness parameterJIC.

Rolling direction, grain size, loading rate, yield stress and the material texture are the influential parameters determining the stretch zone geometry.
THE EFFECT OF MICROSTRUCTURE AND FRACTURE SURFACE ROUGHNESS ON FATIGUE CRACK PROPAGATION IN A Ti‐6A1‐4V ALLOY
Authors: Ogawa Takeshi , Tokaji Keiro , Ohya Kohji
Published: April 2007

Characteristics of fatigue crack propagation (FCP) have been studied on materials with three different microstructures of a Ti‐6A1‐4V alloy, prepared with different heat treatments. The effect of microstructure on the FCP behaviour was attributed to the development of crack tip shielding, primarily resulting from the role of crack path morphology in inducing crack closure and crack deflection. Roughness‐induced crack closure played an important role on the near‐threshold FCP behaviour at a stress ratio of 0.05, but the FCP data plotted in terms of the effective stress intensity factor range, δKeff (allowing for crack closure), still exhibited the effect of microstructure. Fractographic examinations were performed, using a scanning electron microscope (SEM) with the aid of image processing, which enabled a three‐dimensional reconstruction of the fracture surface using a stereo pair of SEM micrographs. Fracture surface roughness was evaluated quantitatively by the ratio of the real area of the reconstructed fracture surface to its projected area. As fracture surface roughness was taken into account in evaluating the FCP data in addition to crack closure, the effect of microstructure disappeared, indicating that the intrinsic FCP resistance was the same in all the materials. Thus, it was concluded that fracture surface roughness was a dominating parameter in controlling the FCP of the Ti‐6A1‐4V alloy.
FATIGUE LIFE ENHANCEMENT OF BUTT WELDS USING A THERMO‐MECHANICAL TECHNIQUE
Authors: Lam Y. C. , Cole G. K.
Published: April 2007

Previous investigations have shown that the introduction of a compressive residual stress at critical locations enhances the fatigue life of welds. In the present study a combination of heat and applied stress is used to induce a compressive residual stress at critical locations such as the weld toe. The theory of the technique is discussed and an experimental study is carried out to investigate the effect of the technique on the fatigue behaviour of transverse butt welded specimens made from C‐Mn steel.
“EFFECT OF LOADING MODE ON THE CYCLIC RESPONSE AND THE ASSOCIATED SUBSTRUCTURE OF POLYCRYSTALLINE COPPER IN THE HIGH‐CYCLE REGIME”
Authors: Llanes L. , Laird C.
Published: April 2007

Studies on the influence of loading mode on the cyclic response of small‐grained polycrystalline copper and the associated dislocation structures have been carried out in the high‐cycle regime. It is found that the saturation behaviour under constant load control, for two sets of specimens, with and without initial ramp‐loading, exhibits strong differences in the “intermediate” range of stress amplitudes, i.e., between 70 and 98 MPa. Within this range the ramp‐loading mode promotes a gradual substructure evolution which leads to localization of slip in primary systems and formation of persistent slip bands (PSBs), whereas conventional loading leads to the formation of elongated cells and multiple sets of wall structures (e.g., labyrinth structure), both intimately associated with multiple slip conditions. At low stress amplitudes observed differences in the plastic strain amplitudes obtained at saturation, as an effect of different loading modes, are relatively small and related to equally small differences in the uniformity and homogeneity, from grain to grain, of the dislocation structures associated with that stage. At high stress amplitudes equiaxed cell structures are promoted under both loading modes, the deformation is homogenized, and the cyclic response as a function of loading mode shows no differences.
GEOMETRY FACTORS IN CORROSION FATIGUE CRACK PROPAGATION
Authors: Jakubowski Marek
Published: April 2007

Abstract— Fatigue crack growth rates for a steel in saltwater at different but constant stress intensity factor ranges have been evaluated as a function of the crack length (as measured from the notch root) for cracks longer than so‐called “short” cracks. Equations describing the crack growth rate as a function of both the crack length and the stress intensity factor range have been obtained, and the effect of simulated infinite thickness of the specimens is discussed. The equations satisfactorily describe the numerous literature data for different steels, different specimens and different test conditions.
R‐CURVE MODEL OF CERTAIN CERAMIC COMPOSITES
Authors: Olsson Marten , Giannakopoulos Antonios E.
Published: April 2007

Abstract— The influence of crack‐bridging on the R‐curve for certain types of ceramic composites is modeled. Small scale bridging conditions are assumed. A recurrence procedure is used to solve the governing coupled integral equations, resulting in R ‐curves (stress intensity factor versus crack growth) that depend on well defined microstructural parameters. In addition, the bridging stresses and the crack opening diplacements were computed for all stages of the R ‐curve development. The numerical scheme is quite general and can be used for a variety of bridging laws. The convergence of the solution method is uniform, and the accuracy is a priori controlled. The results are normalized so that they can be applied for a large variety of composites with different micromechanical parameters. R ‐curves were computed for different bridiging laws, and were found to be sensitive to the specific bridging law used each time. Some strength‐toughness relations are also discussed. The results are particularly suitable for slow crack growth analysis.
THE FATIGUE RESISTANCE OF PEENED 7050‐T7451 ALUMINIUM ALLOY—REPAIR AND RE‐TREATMENT OF A COMPONENT SURFACE
Authors: Sharp P. K. , Clayton J. Q. , Clark G.
Published: April 2007

Abstract— Metal and glass‐bead peening treatments, widely used throughout the aircraft industry to enhance the fatigue performance of many steels and titanium alloys, are now being routinely applied to high‐strength aluminium‐alloy components. This paper describes the effects of peening on the fatigue life of 7050 aluminium alloy material, which is representative of alloys used for many components in modern military aircraft. Using simulated service loading, two proposed peening/re‐peening procedures were evaluated and compared with both the original peened surface and a simple hand‐polished surface. The results show that optimisation of peening parameters to reduce surface damage can provide a substantial improvement in fatigue life over both the original peening treatment and the polished surface treatment, however, poor control of peening procedures, or unnecessary “overpeening” can lead to a relatively poor fatigue life. For re‐peened surfaces, a procedure incorporating a polishing step, designed to repair any damage from the severe peening applied initially, gave the best fatigue performance. Results are discussed in relation to the stability of the residual surface stresses under fatigue loading, the surface roughness, and the number and types of defects introduced by the peening treatments.
FRACTURE TOUGHNESS MEASUREMENTS AND FAILURE MECHANISMS OF METAL MATRIX COMPOSITES
Authors: Hadianfard M. J. , Heness G. , Healy J. C. , Mai Y.‐W.
Published: April 2007

Abstract— This paper compares the fracture toughness values obtained from two different specimen geometries, i.e. pre‐cracked compact tension and chevron‐notched short rod. The former is in widespread use, however, the latter has significant advantages in that no pre‐cracking is required resulting in more economical use of material and reduced machining. Four 6061‐aluminium‐matrix composites reinforced with discontinuous alumina particles were investigated. Good agreement in fracture toughness values from the two specimen geometries was obtained for all the materials and all the heat treatments examined. Detailed analyses of the fracture surfaces were used to identify the fracture mechanisms. The effects of specimen geometry, volume fraction of reinforcement and ageing treatment on fracture toughness are discussed.
FATIGUE CRACK GROWTH IN NICKEL‐BASED SUPERALLOYS AT 500‐700°C. II: DIRECT‐AGED ALLOY 718
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°C and 700°C have been studied for the direct‐aged version of the nickel‐based superalloy 718. The main effects were similar to those observed for Waspaloy (Part I), namely: (i) small effects of cyclic frequency and hold time at 500°C, (ii) higher rates of crack growth at lower cyclic frequencies at high ΔK at 700°C, and (iii) lower rates of crack growth at low ΔK (and higher ΔK thresholds) for longer hold times at 700°C. For DA 718, there was no increase in crack growth rates with increasing hold times (0–60 s) at high ΔK at 700°C (unlike the large increases reported for standard processed Alloy 718). Metallographic and fractographic observations showed that crack growth was predominantly transgranular at 500°C, and predominantly intergranular at 700°C except at 2 Hz at high ΔK. The precise intergranular crack path, extent of branching, and fracture‐surface appearance depended on ΔK, wave‐form and cycle‐period. The mechanisms responsible for the observed effects, and possible explanations for the different behaviour of DA 718 and standard processed Alloy 718, are discussed.
ON THE EQUIVALENCE OF STRESS INTENSITY AND ENERGY APPROACHES IN BRIDGING ANALYSIS
Authors: Jain L. K. , Mai Y.‐W.
Published: April 2007

Abstract— Through‐thickness reinforcement is effective in suppressing delamination in composite laminates. It provides bridging in the crack wake during delamination crack growth. The closure traction behind the crack tip due to this bridging increases the delamination toughness significantly. The effect of bridging may be analysed using the stress intensity approach or the Griffith energetic approach. In this paper, delamination crack growth resistance KR,(Δa) of a double‐cantilever‐beam specimen, with through‐thickness reinforcement, under Mode I delamination is determined using these two approaches. Additionally, the J‐integral analysis is also employed. A comparison between the theoretical results predicted by these three methods is provided using the example of stitched CFRP.
EFFECT OF TEMPERATURE ON FATIGUE CRACK GROWTH IN THE POLYMER ABS
Authors: Kim H. S. , Wang X. M. , Abdullah N. A. H. Nik
Published: April 2007

Abstract— Fatigue crack growth in a commercial grade ABS over the temperature range ‐ 50°C to 80°C has been studied. An Arrhenius type relationship between fatigue crack growth rate and absolute temperature was found to describe the experimental data. At ΔK= 1 MPa√m, the activation energy for crack growth in the temperature range −50°C to 19°C is 3.47 kJ/mole and in the temperature range 30°C to 80°C it is 19.63 kJ/mole. The two different activation energies were found to be associated with the roughness of the fracture surfaces. The roughness of the fracture surfaces is discussed in relation to modes of fatigue crack growth. In the low temperature range (− 50°C to 19°C) the fracture surfaces were found to be rather coarse, whereas in the high temperature range (30°C to 80°C) they were found to be somewhat smooth. These different roughnesses were deduced to be due to different modes of crack branching influenced by crazing. A “stress intensity factor”‐biased Arrhenius equation for fatigue crack growth successfully predicts growth rates at various temperatures.
STRENGTH PREDICTION AND DAMAGE MECHANISMS OF GLASS/EPOXY WOVEN LAMINATES WITH CIRCULAR HOLES
Authors: Xiao J. Y. , Bathias C.
Published: April 2007

Abstract— The notched strengths of four woven laminates (two orthotropic, one quasi‐isotropic and one square symmetrical) under monotonic uniaxial loading, predicted with the point and average stress criteria, the two parameter criterion, the progressive degradation model, and the initial and improved point and minimal strength models, have been respectively compared with the experimental data. The damage mechanisms for the laminates were tentatively studied. The results show that, for minimal experimental information, the notched strengths predicted by the improved minimal strength models are the most precise and the progressive degradation model can numerically illustrate the damage mechanisms in detail. The damage mechanisms of the woven laminates were found to be very different from those of non‐woven laminates.
FRETTING PATTERNS IN A CONDUCTOR–CLAMP CONTACT ZONE
Authors: Zhou Z. R. , Cardou A. , Goudreau S. , Fiset M.
Published: April 2007

Abstract— Cyclic bending fatigue tests have been performed on a typical electrical conductor held by a suspension clamp. Surface damage of the aluminium wire has been induced during short duration tests. Various degradation zones have been characterized between wire layers and the clamp. Metallographic examination has shown that two process zones are critical with respect to fretting crack nucleation. Fatigue tests at different bending amplitudes have shown that the wire breaks in these critical zones.
A MECHANISM FOR PLASTICITY‐INDUCED CRACK CLOSURE UNDER PLANE STRAIN CONDITIONS
Authors: Pippan R. , Kolednik O. , Lang M.
Published: April 2007

Abstract—Plasticity‐induced crack closure is associated with a wedge of material in the wake of a fatigue crack. A model is proposed to explain the development of this wedge under plane strain conditions. This model is based on the non‐linearity of the crack path. If the plastic zone size is an order of magnitude or larger than the characteristic length of a crack deflection, then the plastic deformation changes the shape of both crack flanks in different ways. This causes a residual displacement on the crack flanks. Different examples for the development of such plasticity induced wedges are shown.
STRESS RESPONSE UNDER THERMAL‐MECHANICAL STRAIN CYCLING FOR A 1 CrMoV FERRITIC STEEL AND TWO 316 STAINLESS STEELS
Authors: Ellison E. G. , Al‐Zamily A.
Published: April 2007

Abstract— Isothermal and thermal‐mechanical strain fatigue tests were conducted in air on representative service alloys; a 1 CrMoV steel, and two batches of 316 stainless steel. Data was obtained for thermal‐mechanical in‐phase and out‐of‐phase cycles, and also for isothermal tests at the maximum, minimum, and mid‐temperature of the thermal‐mechanical cycle. Dwell periods were also incorporated in the cycle to assess their effects.

A comparative evaluation has been made on the basis of the materials' cyclic stress response. In general, the results have shown that the thermal‐mechanical strain cycling tests cause a large increase in stress range over those tested under isothermal conditions at maximum temperature. In addition, mean stress and strain offsets were developed in continuous cycle thermal‐mechanical tests, whereas negligible offsets occurred in isothermal tests.

It appears that the response of the materials could not always simply be explained by reference to the temperature change itself.
ANALYSIS AND TESTING OF SURFACE COLD‐WORK PROCEDURES APPLIED TO NOTCHED, FLAT ELEMENTS
Authors: Banks‐Sills L. , Dagani E. , Eliasi R. , Reinberg E. , Schwartzman R.
Published: April 2007

Abstract— Several surface cold work procedures are developed to induce compressive residual stresses adjacent to a notch in a flat element. It would appear that they should all lead to fatigue life enhancement. For sharp notched specimens excellent fatigue life enhancement is observed. For moderately notched specimens only one of the procedures produces this enhancement. In order to shed light on the shortcomings of two of the procedures, the residual stress field is determined by means of finite element analyses in two and three dimensions. It is observed that the two‐dimensional analyses predict a residual stress field which should lead to fatigue life enhancement. It is the three‐dimensional analyses which help to explain why two of the cold work procedures fail.
A FRACTOGRAPHIC RECONSTITUTION OF A FATIGUE CRACK FRONT
Authors: Lauschmann H. , Blahout M.
Published: April 2007

Abstract— A hypothesis on the statistical relation between the local microscopic directions of fatigue crack growth and the macroscopic crack front shape is postulated. The method of fractographic reconstitution of the fatigue crack front shape from local microscopic directions of crack growth is proposed and tested in two different applications.
THE USE OF A LOAD SPECTRUM IN PREDICTING AIRFRAME FATIGUE DAMAGE
Authors: Adrov V. M.
Published: April 2007

Abstract— The use of a load spectrum in airframe fatigue life predictions is considered. In‐service fatigue lives are predicted using a probabilistic approach that takes into account the main aspects of deterministic methods. Expressions are derived for damage under fixed flight‐hours together with data scatter. The influence of material fatigue properties on scatter are shown. An algorithm for obtaining simple formulae for accounting for equivalent airframe fatigue conditions are demonstrated. An example is given for deriving a safe fatigue life distribution function.
FATIGUE LIFE ESTIMATION OF WELDED JOINTS OF AN ALUMINIUM ALLOY UNDER SUPERIMPOSED RANDOM LOAD WAVES: APPLICATION OF A 2‐DIMENSIONAL RAINFLOW METHOD
Authors: Takahashi I. , Maenaka H. , Miyamoto T.
Published: April 2007

Abstract— Fatigue tests were carried out on welded T‐joints of JIS A5083P‐O Al‐Mg alloy under constant amplitude and superimposed random load waves. Each random wave was generated by superimposing a secondary zero‐mean random process on a constant amplitude pulsating trapezoidal wave, which simply simulated the GAG (ground‐air‐ground) stress cycles, or on a constant d.c. (direct current) component. It is proved that the 1‐dimensional rainflow method is insufficient as the mean stress effects are not considered. From a procedure using a 2‐dimensional rainflow method and the original and a modified Goodman diagram, it was concluded that the mean stress effects on secondary waves are larger in the case of GAG than d.c. Considering this, a life estimation procedure is proposed that gives consistent and acceptable estimation results.
STRUCTURAL COLLAPSE, THE FAILURE ASSESSMENT DIAGRAM AND “OFF‐THE‐SHELF” OPERATION
Authors: Garwood S. J. , Leggatt R. H. , Ingham T.
Published: April 2007

Abstract— The criteria for determining whether ferritic material exhibits fully ductile behaviour are generally based on the fracture toughness vs temperature relationship determined from standard laboratory test pieces (e.g. Charpy V Impact tests or fracture toughness specimens). This relationship defines a ductile‐brittle transition region. When fully ductile, microvoid coalescence behaviour is experienced, and fracture toughness is described as being on the “upper shelf”. At “off the shelf” temperatures brittle, cleavage fracture is experienced. On the lower shelf the material is entirely brittle, exhibiting 100% crystallinity on the fracture face. As the temperature increases, initiation of tearing by microvoid coalescence occurs and some stable tearing can occur prior to the cleavage event. Material toughness increases with temperature until the upper shelf condition is achieved.

The characteristics of fracture toughness tests in terms of the toughness level exhibited and the extent of ductile tearing experienced have been used as a guide to whether the structural application (e.g. a pressure vessel) will behave in a brittle or a ductile manner. This paper reports on a feasibility study where various worked examples have been performed to examine the concept of using a “cut off” on the failure assessment diagram, determined from the conditions required to cause plastic collapse of a pressure vessel, as a criterion for defining effective “ductile” operation. Fracture assessment procedures (R6 revisions 2 and 3 and PD6493 levels 2 and 3) have been utilised to determine the influence on pressure vessel performance of the behaviour of fracture toughness test specimens.

The procedure of plotting a structural collapse “cut off” on a failure assessment diagram enables the assessment of whether a particular flaw geometry would result in gross deformation of the structure at failure. The use of this procedure provides an unambiguous demarcation between “fracture dominated” and “collapse controlled” conditions. This procedure facilitates judgements on the level of toughness necessary to ensure ductile operation and whether a “tearing plus toughness” requirement is necessary.

It is recommended that consideration be given to including structural collapse into fracture assessment procedures carried out using R6 revision 3 or PD 6493:1991 procedures in order to determine the conditions when enhanced toughness no longer influences structural performance (i.e. when effective “upper shelf” conditions are attained).
AN ANALYSIS FOR THREE DIMENSIONAL CRACKS
Authors: ISIDA M. , TSURU H. , NOGUCHI H.
Published: April 2007

Abstract— A new method of analysis is proposed for an infinite solid containing an embedded plane crack of arbitrary shape. The analysis is fundamentally based on the body force method, but proper expressions of the body force densities are introduced and the stress conditions of the crack surface are replaced by the resultant force conditions in order to improve the accuracy and validity of the method. Numerical results for typical crack problems, based on coarse mesh patterns, are shown to be in remarkable agreement with known solutions. The method is also applied to the bending of circular and rectangular cracks generated from compressive surface contacts for which reliable solutions have not yet been proposed by any other methods. The results are found to be very different from conventional free‐surface solutions.
EFFECT OF RELATIVE SLIP AMPLITUDE ON FRETTING FATIGUE OF HIGH STRENGTH STEEL
Authors: NAKAZAWA K. , SUMITA M. , MARUYAMA N.
Published: April 2007

Abstract— The effect of relative slip amplitude on fretting fatigue in high strength steel was studied at various contact pressures using fretting pads of various lengths. Under a given contact pressure, the fretting fatigue life showed a minimum at a certain relative slip amplitude. Under a fixed pad length, the life also showed a minimum at a certain contact pressure. A map of fretting fatigue life versus contact pressure and relative slip amplitude was obtained using the data of this study. The map indicated that both the phenomena which showed a minimum life in relation to slip dependence and contact pressure dependence were the same, as were the underlying mechanisms. The minimum life was interpreted in terms of local stress concentration at the fretted area.
OBSERVATIONS OF FATIGUE FAILURE IN SYNCHRONOUS BELTS
Authors: IIZUKA H. , WATANABE K. , MASHIMO S.
Published: April 2007

Abstract— The morphologies of failures in synchronous belts were observed following four types of fatigue test. Two modes of initiation were observed. One was due to cord failure which was observed under various conditions. Detailed observations showed that the interfaces between stranded glass filaments were separated at the centre of the cords. The extended direction of the separations was mainly vertical to the back face of the synchronous belt. The second mode of crack initiation was observed under relatively high loadings of the mating flank of the belt tooth. The cracks were initiated at the tooth roots of the synchronous belts. Finally, the deformation behaviour of a synchronous belt was measured under static loading.