bluuebunny/crossref_metadata_2025_split huggingface dataset:
CREEP CRACK INITIATION AND GROWTH IN INCONEL 718 ALLOY AT 650°C
Authors: Diboine A. , Pineau A. 
Published: April 2007

AbstractCreep cracking tests were performed on a nickel base superalloy, Inconel 718, using CT type specimens at 650°C in an air environment. Both time to initiate creep crack propagation (T1) and creep crack growth rate (ȧ) were measured as a function of the stress‐intensity factor, K. It is shown that crack initiation behaviour and early crack growth (stage I) are strongly dependent on test procedures. Furthermore there is no unique correlation between ȧ and K, except in the regime corresponding to relatively high crack growth rates (stage II). This conclusion was reached by conducting tests both under increasing and under decreasing K. The reasons for this behaviour are briefly discussed in relation to environmental effects. A simple model (based upon a theoretical stress‐strain field for creeping cracked solids and the ductility exhaustion concept) is used in an attempt to explain the results. The limitations for the application of this model are discussed. It is shown that this approach can explain a number of experimental results provided that it is accepted that creep ductility is time‐dependent because of environmental effects.Finally, the results of these crack propagation tests are used in conjunction with the theoretical results derived from the Riedel and Rice analysis to model both crack initiation and crack growth behaviour of Inconel 718 under sustained load.
AN INTELLIGENT CAD‐METHOD BASED ON BIOLOGICAL GROWTH
Authors: Mattheck C. , Moldenhauer H. 
Published: April 2007

AbstractLocal stress peaks are the main reason for fatigue failure of structures. It is therefore of interest to understand the stress distribution in a component under service conditions. A systematic method is proposed to show how engineering components may be designed by simulation of biological growth. The method is based on “misuse” of the swelling option in the FE‐code Abaqus in order to simulate “growth” of structures into a shape more appropriate for the actual loading case considered. The method promises to be an extremely powerful “intelligent” CAD approach.
A FATIGUE CRACK GROWTH MODEL FOR FIBER‐REINFORCED METAL–MATRIX COMPOSITES
Authors: Chan K. S. 
Published: April 2007

AbstractA fracture‐mechanics based model is proposed for fatigue crack growth in fiber‐reinforced metal‐matrix composites (MMCs). The model incorporates most of the fracture micromechanisms commonly observed in fiber‐reinforced MMCs, including (1) formation of microcracks ahead of the crack tip by either fiber fracture or interface decohesion, (2) interactions of the main crack tip with fibers and microcracks, (3) linkage of the main crack with microcracks, and (4) crack deflection by fibers. Statistical variations of fiber or interface strength are also considered. The essential feature of the model is to compute the changes in the local stress intensity due to various fracture mechanisms; the local stress intensity is then utilized to predict crack growth rate in MMCs via an elastic modulus normalization procedure. Application of the model to predicting crack growth in an alumina fiber Mg‐alloy composite is presented.
COMPRESSION FATIGUE IN β‐ALUMINA
Authors: James M. N. , Tait R. B. , Mech D. G. 
Published: April 2007

AbstractIn the presence of a notch, fully compressive loading has been shown to develop fatigue cracks, typically less than 1 mm in length, from the notch root in metals, cemented carbides and ceramics. The crack length is dependent on factors like load range, stress ratio, frequency and environmental influences. This paper examines the influence of these factors on crack growth in β‐alumina under compression fatigue. Results obtained support the constitutive microcracking model advanced by Brockenborough and Suresh, but are influenced by crack tip shielding and, at low frequencies, a small stress corrosion component of growth.
A STATISTICAL ANALYSIS OF SHORT FATIGUE CRACK GROWTH
Authors: Wang S. Z. , Miller K. J. , Brown M. W. , De Los Rios E. R. 
Published: April 2007

AbstractThis paper explores short fatigue crack growth behaviour in torsion and tension at the same equivalent stress level of 880 MPa. Quantum steps (i.e. crack growth following crack arrests at grain boundaries) occurred randomly along the curve of crack length vs number of cycles applied. A statistical model for the short crack growth process is presented in the form of a non‐stationary Markov chain which can be described with a probabilistic transformation matrix. The endurance mean value is described with a prescribed confidence level. Fatigue life, with a high degree of survivability, is determined with respect to a specified crack length. This should assist engineers concerned with the damage‐tolerant design of critical components.
BEHAVIOUR OF A 1Cr‐1Mo‐0.25V STEEL AFTER LONG‐TERM EXPOSURE‐II. CREEP CRACK INITIATION AND CREEP CRACK GROWTH
Authors: Moliniéa E. , Piques R. , Pineau A. 
Published: April 2007

AbstractBoth the initiation and the propagation of creep cracks have been studied in a 1Cr‐1Mo‐0.25V steel at 550°C using CT type specimens. The material taken from a large turbine casing was investigated in two conditions: (i) unaged and (ii) after a long exposure in‐service time of about 150,000 h at 540°C. In both cases the material was found to be creep ductile, which is justified in terms of fracture mechanics applied to creeping solids. It is shown that fracture mechanics is unable to provide unique correlations with global load‐geometry parameters, either K or C* for all the stages of both crack initiation and crack growth. However there exists a unique correlation between C* and the time to initiation, ti. This correlation does not depend on the initial conditions of the material. During crack growth two stages are defined. Stage I is a transient regime in which C* is almost constant, but the correspondence between the crack growth rate and C* is not unique since largely dependent on the initial loading applied to the specimens. It is shown that the apparent correlation between the crack propagation rate in stage II which corresponds to large crack growth rate is doubtful. A simplified method based on reference length and reference stress is used to calculate C* parameter and to simulate the load‐line displacement rate. The results obtained from this method are compared to those derived from finite element calculations published in the literature.
STUDY OF THE PHYSICAL PROPERTIES OF POLYETHYLENE POLYMERS THAT AFFECT CRACK INITIATION AND PROPAGATION
Authors: Dear J. P. 
Published: April 2007

AbstractHigh‐speed photography has been used to study the behaviour of polymer specimens subjected to high velocity impacts that excite the specimen into strong, complex vibrations. These photographic data are correlated to the outputs of sensors located on the specimen, striker and supports. Optical and scanning electron‐microscope studies of the crack initiation zone and the size and texture of other features on the fracture surfaces are also correlated to other fracture data. To obtain better information about the threshold of crack initiation of these materials and other data difficult to obtain by impact testing, a new experimental method has been developed. To assist in predicting and analysing experimental data a desk‐top computer model has been devised with good visibility of the computing steps and how these relate to crack propagation in polymeric materials.
TRANSIENT RETARDATIONS IN FATIGUE CRACK GROWTH FOLLOWING A SINGLE PEAK OVERLOAD
Authors: Damri D. , Knott J. F. 
Published: April 2007

AbstractRetardation in the fatigue crack growth rate following the application of a single peak overload in a fatigue loading sequence has been studied for a low carbon structural steel. Tests have been performed at load ratios of R= 0.2 and R= 0.6 at a baseline stress intensity range, ΔKb, corresponding to fatigue crack growth rates in the Paris regime. Single peak overloads were applied at a crack‐length to specimen‐width ratio of a/W= 0.5. At the load ratio of R= 0.6 monotonic or “static” fracture modes were observed upon application of the overload, and these produced an immediate increase in growth rate. A subsequent retardation is attributed to the presence of a residual compressive stress field ahead of the crack tip. A similar retardation was observed at a load ratio of 0.2. The importance of residual stress was established by performing stress relieving experiments. In addition, removal of the surface deformation after an overload by machining “T” sidegrooves resulted in an extended transient, which could not be explained by residual machining stresses.
CYCLIC DAMAGE AND FRACTURE IN A CAST NICKEL BASED ALLOY AT HIGH TEMPERATURE
Authors: Ellison E. G. , Plumbridge W. J. 
Published: April 2007

AbstractCyclic tests, with and without dwell periods, were carried out at temperatures of 750, 850 and 1000°C on a cast nickel base super alloy MAR M002. The cracking mechanism was mainly transgranular in the continuous cycle tests. The incorporation of a tensile dwell had little effect on life compared with the continuous cycle data though there was a significant amount of additional internal intergranular cracking. However, an unbalanced compressive dwell at 750 and 850°C caused a shorter life with transgranular cracking: only at 1000°C was the life not reduced. Prediction of life was attempted by means of what were thought to be three of the more promising methods, i.e. ductility exhaustion, crack propagation and hysteresis energy. However, these did not appear to be accurate, and it is clear that more appropriate base line data are required.
MICROMECHANICAL STRESSES DURING LOW CYCLE FATIGUE OF AN OVERAGED Al‐Mg‐Si ALLOY
Authors: Jain Mukesh 
Published: April 2007

AbstractThe evolution of micromechanical stresses; flow stress, kinematic back stress and isotropic drag stress during room temperature, uniaxial, low cycle fatigue of overaged Al‐Mg‐Si alloy is studied. Continuous real‐time measurements of yield stresses are made in cyclic tension and compression, within the hysteresis loop, at different strain amplitudes, strain rates and number of cycles. An asymmetry is observed in flow stress and kinematic back stress in tension and compression half cycles during cyclic hardening and saturation. The phenomenological results have been analyzed in terms of kinematic and isotropic type microstructural mechanisms.
ON THE RELATIONSHIP BETWEEN LOW CYCLE FATIGUE AND CRACK GROWTH RATE PROPERTIES IN WELDED STEEL COMPONENTS
Authors: Skallerudn Bjørn 
Published: April 2007

AbstractPrevious investigations have shown that for plain materials, the crack growth rate constants applied in an elastic‐plastic crack growth model may be obtained indirectly from the constants describing the low cycle fatigue capacity of the material. In the present study a simple EPFM crack growth model, based on bulk strain amplitude as the governing parameter, is assumed. The crack growth constants derived from the linear regression constants describing the LCF capacity of manually butwelded components are determined, and the validity of the resulting EPFM crack growth model is checked against measured LCF crack growth data.
ELASTIC‐PLASTIC FRACTURE MECHANICS FOR PRESSURE VESSEL DESIGN
Authors: Nilsson Fred , Faleskog Jonas , Zaremba Krzysztof , ÖBerg Hans 
Published: April 2007

AbstractThe project has been concerned with the verification of the J‐philosophy for initiation and growth of cracks on laboratory type specimens as well as on larger surface cracked plates. The analysis of the experiments involved extensive fully three‐dimensional finite element calculations. It was found that the initiation events for the six surface cracked plates occurred at approximately the same J‐value. A corresponding relation to the laboratory type specimen was less successful, mainly because of the short‐comings of current methods for JIC‐evaluations. A somewhat puzzling feature of the surface crack experiments was that unstable crack growth occurred immediately after crack growth initiation in four out of six tests, while some amount of stable crack growth was evident in the remaining two and in all of the laboratory type specimens. An evaluation of the surface experiments by a type of R6‐analysis was also performed. Using as Kcr the mean value from the surface crack experiments, it was found that the R6‐method yielded conservative predictions.
AN EXPERIMENTAL STUDY OF FRETTING BY MEANS OF X‐RAY DIFFRACTION
Authors: Farrahi G.H. , Maeder G. 
Published: April 2007

AbstractThis paper introduces a new method of investigation in the field of fretting. This method employs X‐ray diffraction for the characterization of surface layer damage through residual stresses and work‐hardening by tribologjcal action. The effect of hardness and material residual stresses upon the state of the surface have been studied. The results showed that fretting, being a surface phenomenon, created work‐hardening of soft material or work‐softening of hard material in the near‐surface layers. When the initial residual stresses were high, fretting could not modify them because they had already reached the saturation limit. A Pole figure shows that fretting modified the texture of the specimen surface.
A REVIEW OF FATIGUE CRACK GROWTH IN STEELS UNDER MIXED MODE I AND II LOADING
Authors: Bold P. E. , Brown M. W. , Allen R. J. 
Published: April 2007

AbstractThe majority of methods for predicting the direction of propagation of mixed mode cracks have assumed that they branch to grow as mode I cracks. However, under some circumstances mode II crack growth occurs. Rolling contact fatigue cracks are one example of an industrial problem where cracks appear to grow under predominantly mode II loading without branching. This paper reviews the available models and the experimental studies in the literature on mixed mode I and II loading, and discusses the parameters that affect the mode of crack growth.
STATISTICAL CHARACTERIZATION OF RANDOM CRACK PATTERNS CAUSED BY THERMAL FATIGUE
Authors: Winkler T. , Brückner‐Foit A. , Riesch‐Oppermann H. 
Published: April 2007

AbstractThermal fatigue experiments performed with an austenitic steel give rise to an irregular pattern of cracks on the specimen surface. The investigations are aimed at characterizing the patterns in quantitative terms and at discerning trends with increasing numbers of cycles. Statistical methods based on different models of stochastic geometry are applied to take into account the random influence in pattern formation. Descriptive statistics as well as stochastic models are used to characterize the damage level. The stochastic models, such as fibre processes and random mosaics, will finally correlate the physical damage process with the random crack pattern observed. It is shown in this paper how the statistical characteristics of the random crack patterns can be related to the statistical characteristics of the stochastic models and the way the physical nature of the damage process influences these quantities.
A SIMPLE PATH‐INDEPENDENT INTEGRAL FOR CALCULATING MIXED‐MODE STRESS INTENSITY FACTORS
Authors: Zhang Z. L. , Mikkola T. P. J. 
Published: April 2007

AbstractA path‐independent integral is introduced for calculating stress intensity factors. The derivation of the integral is based on the application of the known Bueckner's fundamental field solution for a crack in an infinite body and on the reciprocal theorem. The method was applied to two‐dimensional linear elastic mixed‐mode crack problems. The key advantage of the present path‐independent integral is that the stress intensity factor components for any irregular cracked geometry under any kind of loading can be easily obtained by a contour integral around the crack tip. The method is simple to implement and only the far field displacements and tractions along the contour must be known. The required stress analysis can be made by using any analytical or numerical method, e.g. the finite element method, without special consideration of the modelling of crack tip singularity. The application of this integral is also independent of the crack type, that is, there is no difference between an edge crack and an embedded crack, provided that the crack tip asymptotic behaviour exists.
THREE‐DIMENSIONAL CONSTRAINT EFFECTS ON STRESS INTENSITY DISTRIBUTIONS IN PLATE GEOMETRIES WITH THROUGH‐THICKNESS CRACKS
Authors: Bakker A. 
Published: April 2007

AbstractThree‐dimensional finite element analyses of through‐thickness cracks in plate geometries are presented. It is shown that the local constraint variation towards the crack tip causes an increase in stress intensity which is neglected in analyses which assume a constant stress state throughout the geometry. This means that stress intensity factors for these types of crack geometries are a factor (1 — v2)‐0.5 higher than generally reported in stress intensity handbooks.Analyses on crack tunnelling situations show that if plane stress dominates the global behaviour, an almost constant stress intensity across the thickness is reached for a relative tunnelling depth of a 2.5% of the plate thickness. For geometries which are not predominantly in plane stress this value will be somewhat larger. Crack front tunnelling does not influence the mean stress intensity across the thickness.Shear lips are shown to reduce the mean equivalent stress intensity (the mode I stress intensity which has the same energy release rate as the actual combined mode I, II and III loading) by a factor equal to the square root of the ratio between plate thickness and projected length of the crack front. This may explain the reduction in crack growth rate caused by shear lips during fatigue crack growth experiments. The reduction of the mode I stress intensity factor is considerably larger, which may cause a further reduction of fatigue crack growth rate for crack growth mechanisms that depend primarily on the mode I crack tip loading.Analyses on CNT and SENB specimens show that the conclusions reached on infinite plate models also hold for real structures. However for an SENB specimen with an uncracked ligament equal to the plate thickness, the overall constraint is larger than that of a pure plane stress situation, and the effect of stress intensity increases due to the constraint transition is less pronounced.
SIMPLE Jc, ESTIMATION FORMULAE FOR THREE‐POINT BEND SPECIMENS
Authors: Sumpter J. D. G. 
Published: April 2007

AbstractThis report reviews some simple methods for determining Jc at the onset of cleavage fracture in a three‐point bend crack tip opening displacement test. It is concluded that acceptable estimates of J, can be made from specimen mouth opening displacement without precise measurement of crack length.
ELLIPTICAL‐ARC SURFACE CRACKS IN ROUND BARS
Authors: Carpinteri Andrea 
Published: April 2007

AbstractThe crack aspect ratio influence on the stress‐intensity factor of elliptical‐arc edge flaws in solid round bars under tension or bending loading is discussed. The relative crack depth ξ=a/D between the depth a of the crack's deepest point and the bar diameter D ranges from 0.1 to 0.6, while the aspect ratio a/b of the flaw is made to vary from 0.0 (straight crack front) to 1.0 (circular‐arc crack front). For each value of ξ being considered, the maximum stress‐intensity factor is attained in correspondence to the deepest point on the crack front in the case of a/b= 0.0, while it is attained near the external surface in the case of a/b= 1.0. For intermediate aspect ratios, the stress‐intensity factor presents the maximum value at the crack's deepest point for ξ≤ξCR and near the free surface for ξ≥ξCR, with the critical relative crack depth ξCR getting lower and lower as the parameter a/b is increased.
PROCESS ZONE SIZE FAILURE CRITERION AND PROBABILISTIC FRACTURE ASSESSMENT CURVES FOR CERAMICS
Authors: Ando K. , Kim B. A. , Iwasa M. , Ogura N. 
Published: April 2007

AbstractData of fracture toughness and fracture stress of ceramics, generally show considerable size effects and scatter. This presents problems for the integrity of structural ceramics. Fracture mechanics test results on Si3N4 and A12O3 reveal a sensitivity to crack size and the necessity to invoke probabilistic concepts to evaluate their integrity. A new failure criterion is proposed here, based on the existence of a crack‐tip process zone. A probabilistic failure assessment curve is also proposed to quantitatively evaluate reliability.
A δJ‐BASED APPROACH TO BIAXIAL FATIGUE
Authors: McDowell David L. , Berard Jean‐Yves 
Published: April 2007

AbstractAn energy‐like approach is introduced for correlation of biaxial fatigue. The approach is motivated by the elastic‐plastic δJ‐integral which has previously been successfully applied to correlate uniaxial fatigue microcrack propagation. In addition, the most salient aspects of critical plane theories are included to reflect the driving force for microcracks in Stage I shear‐dominated fatigue growth. Comparisons are made with some recent critical plane theories on the basis of generic completely reversed fatigue life behavior and for specific Case A and Case B biaxial loadings of Inconel 718 and 1045 steel.
ELASTIC‐PLASTIC FINITE ELEMENT ANALYSES OF CRACKED NOTCHES IN PLATES UNDER MIXED‐MODE LOADING
Authors: Kfouri A. P. , Wong H. D. , Miller K. J. 
Published: April 2007

AbstractPlates containing inclined elliptical notches with and without cracks are analysed for five different major axis inclinations, namely, θ equal to 0, 11.25, 22.5, 33.75 and 45˚. Short cracks emanating from the roots of such inclined circular and elliptical notches are analysed. Under various mixed‐mode loading conditions, when cracks are present, a simple method is described for the evaluation of the Mode I and Mode II stress intensity factors, for the elastic state. Values of the J integral along three different contours are also evaluated in the elastic and elastic‐plastic states, as well as the Mode I and Mode II components of the crack tip opening displacenient (CTOD), the maximum principal stresses, the maximum average equivalent plastic strains and the location of the elements in which they occur. Comparisons of the different loading conditions are presented and the implications of the effects of mixed‐mode loading on fracture and fatigue crack propagation are discussed.
FATIGUE LIFE ESTIMATION IN RESISTANCE SPOT WELDS: INITIATION AND EARLY GROWTH PHASE
Authors: Sheppard Sheri D. , Strange Michael 
Published: April 2007

Abstract— The main objective of this research is to develop a model of fatigue crack initiation and early crack growth in resistance spot welds that is specimen independent. This objective is achieved by examining the stress state around a resistance spot weld. A general expression for the structural stress around the weld is formulated that is dependent only on the loading immediately surrounding the weld. As such, it is specimen independent.An additional objective is to explore the feasibility of applying this fatigue crack initiation model of life estimation using structural response data from finite element analysis (FEA). This numerical technique is often used for evaluating structural integrity of assemblies. Limited verification examples show that the structural stress range as calculated from FEA reaction load data is capable of describing fatigue crack initiation and early crack growth in cyclically loaded resistance spot welds.