bluuebunny/crossref_metadata_2025_split huggingface dataset:
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).
FRACTURE BEHAVIOUR OF A HIGHLY ALLOYED HIGH SPEED STEEL
Authors: Gomes M. A. , Wronski A. S. , Wright C. S. 
Published: April 2007

AbstractA high speed steel, processed by two powder metallurgy routes and heat treated to give a range of microstructures, was investigated in 4‐point bending at room temperature using smooth and precracked specimens. The finer microstructures were in the material from gas atomised powder which was hot isostatically‐pressed, commercial ASP60 alloy, while the coarser microstructures derived from laboratory vacuum sintering of water‐atomised powder. The resultant hardness values Hv50 were in the rage 780 to 1050, prior autenite grain sizes, 5 to 25 pm and maximum carbide sizes, 6 to 32 μm.Only some of the uncracked samples exhibited macroscopic yielding, at stresses in the range 1.64 to 2.59 GPa; the finer microstructures being asSociated with the higher strengths. Macroscopic plastic deformation never exceeded 0.33%; fracture strengths were in the range 1.46 to 2.75 GPa. Fracture toughness, Klc, varied from 12 to 17 MPa√m in the Hy50 range 920 to 800 for the directly sintered steel and only from 10 to 12 MPa√m in ASP60. The insensitivity of K1c to macroscopic hardness in ASP60 is asSociated with the plastic zone size of 1.5 μm which approximates to the average carbide spacing.Nucleation and growth of natural, i.e. stress‐induced, microcracks in un notched specimens was studied by surface replica microscopy. Crack nucleation took place at stresses between 0.5 and 1.5 GPa, i.e. below those for yielding and for fracture, σF, and was by debonding of inclusions (alumina and calcium‐alumino silicates) or cracking of carbides. In the coarsest microstructure monotonic stepwise subcritical crack growth was observed from stress levels of ∼1.3 GPa, i.e. ∼0.8 to 0.9σF. Similarities to the behaviour of short fatigue cracks in metallic materials and the R‐curve behaviour of ceramics are referred to.
CORRELATION OF FATIGUE CRACK GROWTH BY CRACK TIP DEFORMATION BEHAVIOUR
Authors: Hammouda M. M. I. , Ahmad S. S. E. , Sallam H. E. M. 
Published: April 2007

AbstractGrowth of a long mode I crack under variable fatigue loading was experimentally investigated on mild steel specimens. A dynamic elastic‐plastic two‐dimensional finite element program, purposely developed for the simulation of cyclic crack tip deformation, was utilised to model the transient effects on crack tip advance. The model accommodated crack tip opening displacement and both crack tip and crack edge closure. Fifty one different cycle patterns were analysed to include the application of a single overload, a single underload, a single cycle having a combined overload and underload and finally loading blocks of different sequences. Correlations of experimental fatigue crack growth rates were made from knowledge of crack tip deformation behaviour, including the use of data found in the literature. Specimens of eight materials and different geometries were analysed to determine the validity of the present approach.
ANALYSIS OF FATIGUE CRACK GROWTH IN ROTARY BEND SPECIMENS AND RAILWAY AXLES
Authors: DE Freitas M. , François D. 
Published: April 2007

AbstractFatigue crack growth tests have been carried out on pre‐cracked specimens of steel AFNOR XC 38 under rotary bending conditions. The semi‐elliptical surface crack shape evolution was determined and the results were analyzed by da/dN =f(ΔK) using a stress intensity factor solution for semi‐elliptical surface cracks in round bars subjected to a bending stress modified to take into account the rotatary bending conditions. Results show a very good correlation with fatigue crack growth data obtained in standard centre cracked tension specimens of the same steel. An application to the sensitivity of design parameters to an analysis of cracked railway axles is proposed, allowing an improvement in maintenance procedures.
ELASTIC‐PLASTIC BEHAVIOUR AND UNIAXIAL LOW CYCLE FATIGUE LIFE OF NOTCHED SPECIMENS
Authors: Shatil G. , Ellison E. G. , Smith D. J. 
Published: April 2007

AbstractExperimental and numerical analyses were carried out to examine the elastic‐plastic behaviour and low cycle fatigue (LCF) life of EN15R steel notched specimens. Notch root strains were measured and compared with estimates obtained from three methods: Neuber, Glinka and hite element (FE) analyses. All methods provided fairly accurate estimates of cyclic strain up to net section yield, from which point the Neuber and Glinka predictions were greater than measured. The finite element results compared well with measured results. The estimated notch root strains were used to predict the life of the notched specimens based on LCF results from unnotched specimens. Uniaxial Coffom‐Manson and multiaxial Lohr‐Ellison approaches were used. Improved fatigue life predictions were obtained when the FE predictions of the multiaxial strains were combined with a multiaxial strain parameter. The possible influence of strain gradient is inferred by comparing LCF lives for hollow thin‐walled and solid bar specimens.
NUMERICAL PREDICTION OF FATIGUE CRACK GROWTH OF A SURFACE DEFECT
Authors: Lin X. B. , Smith R. A. 
Published: April 2007

AbstractFatigue crack growth is modelled by an improved step‐by‐step finite element technique for a shallow and long surface crack in a finite thickness plate under different combinations of tension and bending loads. The predicted crack shape development is presented for growth through the plate thickness and the shape compared with the widely assumed semi‐elliptical profile. The predictions of the present simulation technique for the aspect ratio and the number of crack growth cycles are compared with those obtained both by Newman and Raju's method, and experimental results for aspect ratio changes taken from the literature.
FRACTURE MODELLING OF BRITTLE‐MATRIX COMPOSITES WITH SPATIALLY DEPENDENT CRACK BRIDGING
Authors: ÖStlund S. 
Published: April 2007

Abstract In brittle‐matrix composites cracking of the matrix is often accompanied by bridging of the crack surfaces. The bridging will reduce the net stress intensity factor at the crack tip and consequently increase the toughness of the composite material. The bridging mechanism is due to for example unbroken whiskers, fibres, ductile particles or interlocking grains.Analysis of the bridging mechanism in cracked structures is conveniently carried out using the concept of cohesive zone modelling. In this case the action of the bridging elements is replaced by a distribution of forces, so called cohesive forces trying to close the crack. The commonly used approach in such modelling has been to replace the action from individual bridging elements by a continuous spatially independent distribution of closing tractions whose magnitude is a function of the crack opening displacement only.In this paper the influence of the spatial distribution of bridging elements is considered for plane crack problems. The cross section of the bridging elements is assumed to be circular and the distance between the different bridging elements is determined by the volume fraction, the radius and the geometrical distribution of the bridging elements.Damage resistance curves have been calculated for typical whiskers‐reinforced ceramic composites, and the results from the present spatially dependent models are compared with results from calculations with spatially independent models. The influence of the radius of the bridging element, the volume fraction of whiskers and the material properties are illustrated and the use of spatially independent models is discussed.
APPLICATION OF THE VILLARI EFFECT IN A FATIGUE EXAMINATION OF NICKEL
Authors: Kaleta J. , ŽEbracki J. 
Published: April 2007

AbstractThis paper presents the possibility of using the reverse magnetostriction (Villari) effect in fatigue testing of ferromagnetic materials. The tests were conducted on cyclically loaded nickel with no auxiliary external magnetic field. The following properties were determined: magnetic induction B, magnetic field strength H, energy of the magnetic hysteresis loop ΔM (in the B–H coordinate system), plus such mechanical quantities as stress σ, strain ɛ, plastic strain ɛp and energy of the mechanical hysteresis loop ΔW (in the σ–ɛ coordinate system). A variety of magneto‐mechanical characteristics are presented and their susceptibility to loading parameters of the fatigue process are discussed. A relationship between ΔW and ΔM is demonstrated. The Villari effect is shown to be especially useful in determining the cyclic yield limit.
FATIGUE PROPAGATION OF SURFACE FLAWS IN ROUND BARS: A THREE‐PARAMETER THEORETICAL MODEL
Authors: Carpinteri Andrea , Brighenti Roberto 
Published: April 2007

AbstractA three‐parameter fracture mechanics model is proposed to theoretically analyse the propagation of an elliptical‐arc part‐through flaw in a round bar subjected to constant cyclic amplitude axial or bending loads. The edge flaw presents an aspect ratio α=ael/bel (ael, bel= ellipse semi‐axes) and a relative crack depth ζ=a/D, where a and D are the depth of the deepest point on the crack front and the bar diameter, respectively. Additionally a parameter s=ael/a (ellipse shifting) defines the distance of the ellipse centre from the bar circumference. The surface flaw growth occurs according to preferred patterns which tend to converge to an inclined asymptotic plane in the diagram of α against s and ζ.
EVALUATION OF LOW CYCLE FATIGUE UNDER NON‐PROPORTIONAL LOADING
Authors: Chen X. , Gao Q. , Abel A. , Wu S. 
Published: April 2007

Abstract— A series of low cycle fatigue experiments have been conducted on a 42CrMo steel under tension‐torsion loading. Thin‐walled tube specimens were used. Low cycle fatigue under various loading paths, including circular and square paths, have been investigated.The plastic work criterion for low cycle fatigue failure has previously been generally accepted, but it is difficult to calculate stress and strain for complex loading paths, especially for non‐proportional loading. This present study suggests a simple method for the calculation of the stable cyclic stress and strain values based on a Modified Endochronic Constitutive Theory (MECT) that redefines an intrinsic time scale. The loading path effect under non‐proportional loading is also considered when evaluating fatigue life.The results show that the plastic work approach using the MECT method in multiaxial fatigue calculations correlates reasonably well the data and is a reflection of loading path dependence.
EFFECT OF NON‐PROPORTIONAL OVERLOADING ON FATIGUE LIFE
Authors: Hua Gao. , Fernando Upul. S. 
Published: April 2007

Abstract— The effect of non‐proportional overloading on both low cycle and high cycle fatigue life has been studied. Low cycle multiaxial fatigue tests were performed on EN 15R (a low alloy steel) using sequential loading blocks which comprised uniaxial “ordinary” cycles and torsion “overload” cycles, and vice versa. In high cycle fatigue, the behaviour of mode I crack growth in a medium carbon steel subjected to mixed (I and II) mode overloading was examined.Under tension‐torsion sequential overloading, crack growth behaviour shows an earlier transition from Stage I to Stage II with a pronounced reduction in accumulated fatigue life. Tensile overloading on torsion cycles was found to be more damaging compared to torsion overloading on repeated tensile cycles. The crack‐load interaction in sequential overloading and its influence on crack growth and fatigue life is discussed. In low strain fatigue, Stage II crack growth retardation closely relates to the overload plastic zone size, crack tip blunting and crack surface shielding. Mixed mode overloading is shown to have a significant effect only if the mode I component of overloading is large enough to keep the crack open. Under both low cycle and high cycle fatigue conditions non‐proportional overloading is shown to be more damaging than proportional overloading.
AN ANALYSIS OF MEAN STRESS IN MULTIAXIAL RANDOM FATIGUE
Authors: Brown M. W. , Surer D. K. , Wang C. H. 
Published: April 2007

Abstract— Generally engineering components are subjected to multiaxial variable amplitude loading, which may be non‐proportional. One of the best known low cycle fatigue design codes that addresses non‐proportional loading problems is the ASME Boiler and Pressure Vessel Code, but this does not include a cycle counting method and it does not allow for the presence of a mean stress. Traditional rainflow methods, incorporating a strain range and a mean stress, are applicable only where there is a single load varying with respect to time, or possibly where multiaxial loads are proportional. So a multiaxial non‐proportional cycle counting method and a fatigue damage calculation procedure are proposed here, based on plastic deformation response and a critical plane hypothesis that incorporates the effect of mean stress. A cyclic deformation model, based on the Ramberg‐Osgood equation and a multiaxial memory rule, is used to calculate the mean stress response under variable amplitude loading.The proposed procedure is assessed with combined tension/torsion tests on En15R steel under variable amplitude loading. Fatigue life predictions are compared for analysis with and without mean stress corrections, to assess the sensitivity to mean stresses of non‐proportional fatigue endurance in the low cycle regime.
THE RANDOMNESS OF FATIGUE CRACK GROWTH UNDER CONSTANT‐AMPLITUDE LOADS
Authors: Lapetra C. , Mayo J. , Dominguez J. 
Published: April 2007

Abstract—An analysis of fatigue crack growth from an statistical point of view has been carried out. Eighteen pre‐cracked specimens obtained from the same sheet of aluminium alloy were subjected to identical load and environmental conditions. Tests were conducted under constant‐amplitude loads in order to isolate the effect of material randomness. The experimental results exhibited two different types of dispersion: one showed as a change in the mean growth rate between tests and the other as nonuniform growth in the same specimen.At a subsequent stage, the statistical distribution of the experimental results was studied and a theoretical model was developed to account for the growth pattern observed. The proposed model uses a growth law comprising random parameters to account for the low‐frequency component (slow changes). The comparison of the performance of two different laws, viz. the Paris‐Erdogan law and the cubic law, is presented. Both were tested on the assumption of randomness in two of their fitting parameters. In addition to the above‐mentioned law, the model uses a stochastic log‐normal process to model the high‐frequency component (rapid changes). The parameters for this process were determined by time series analysis of fatigue crack growth rate data.
CONSTRAINT BASED EVALUATION OF CRACK GROWTH EXPERIMENTS IN THE TRANSITION REGION
Authors: Shehu S. , Nilsson F. 
Published: April 2007

Abstract—A large number of experiments has been performed over a wide temperature range in the transition region of a ferritic steel with the aim of studying its fracture behaviour and assessing the applicability of a two parameter fracture mechanics approach for such situations.The experimental results clearly show a constraint effect, reflected in a decrease of the transition temperature with a decrease in specimen size and in a narrower transition region for shallow cracks. The results also show that theJ‐Qmodel, in conjunction with a fracture criterion (like the RKR criterion for cleavage fracture) is a promising approach for predicting the cleavage fracture event even in the transition region. No constraint effect could be detected for ductile initiation. The cleavage stress has been measured directly by testing. This reduces the number of fracture tests needed for the construction of the criticalJ‐Qlocus and improves the accuracy of the predictions.
THE INFLUENCE OF THE HARDENING STATE ON TIME DEPENDENT DAMAGE AND ITS CONSIDERATION IN A UNIFIED DAMAGE MODEL
Authors: Aktaa J. , Schinke B. 
Published: April 2007

Abstract— A model is presented for the prediction of the lifetime of metals in the high‐temperature range under arbitrary variable multiaxial load. The definition of an internal variable for damage in continuum damage mechanics is adopted, which allows indirect measurement of damage via the deformation behaviour. To acquire some knowledge of damage evolution, damage is measured in two ways during uniaxial strain controlled cyclic tests: (a) a change of the modulus of elasticity and (b) a decrease of the peak stress. Surprisingly, both methods lead to results which are in good agreement. A new damage law is then developed (with reference to known models and lifetime rules) which is a modification of the creep damage law of Rabotnov that is extended by a dependence on the inelastic strain rate instead of the dependence on internal variables to take into account the hardening state. Uniaxial as well as multiaxial formulations of the new damage model (Inelastic Strain Rate Modified (ISRM) model) are presented.The parameters of the ISRM model are determined with a view to applying them to AISI 316 L(N) austenitic steel. Some of the parameters are derived from standard creep experiments. To determine further parameters, the ISRM model is applied to uniaxial cyclic tests. Both failure behaviour and damage evolution are well described.
SURFACE MICRO‐CRACKS IN BLOCK AND RANDOM FATIGUE CYCLING OF 500 MPa STRENGTH STEEL AND WELD METAL
Authors: Iida K. , Shimamoto H. , Itoh N. 
Published: April 2007

Abstract— Crack density, main crack length and the sum total length of micro‐cracks, which initiated and extended on the surface of a 500 MPa strength steel and its weld metal, were investigated by a replica technique applied during fatigue tests. The base and weld metal specimens were subjected to constant amplitude, random and block strain cycling. The base metal specimens were further tested under 4 kinds of block cycling and 2 kinds of incremental strain cycling. All the cumulative cycling patterns in random and block modes followed the so‐called p‐distribution.As a result of an analysis of micro‐cracks, it was shown that the most useful parameter to estimate the accumulated fatigue damage was the sum total length of micro‐cracks in a unit area, which increased exponentially with cycle ratio. Empirical formulae were obtained expressing the increasing tendency as a function of the cycle ratio for three groups of the equivalent strain amplitude. The formulae were applicable to all strain cycling patterns investigated in the present study.
FATIGUE DESIGN CRITERION FOR WELDED STRUCTURES
Authors: Fayard J.‐L. , Bignonnet A. , Van K. Dang 
Published: April 2007

Abstract— For continuously welded structures subjected to cyclic loading, the highly stressed zones where cracks initiate and lead to failure are usually located at weld toes. At these critical points, called hot‐spots, the very local stress states are difficult to determine so that standard fatigue criteria are very difficult to apply for fatigue life prediction.This work presents a fatigue design criterion for continuously welded thin sheet structures, based on a unique S‐N curve. The approach, which refers to the hot‐spot stress concept, defines the design stress S as the geometrical stress amplitude at the hot‐spot.In practice, the geometrical stress state is calculated by means of the finite element method (FEM) using thin shell theory. Meshing rules for the welded connection, which can be applied methodically to any welding situation, allow the hot‐spot location, and therefore the design stress of any structure, to be determined.Experimental data and FEM calculations show that a unique S‐N curve can be obtained whatever the geometry of the welded structure and the loading mode.
THE FRACTURE BEHAVIOUR OF A CENTRE CRACKED TENSILE SPECIMEN
Authors: Lei Y. , Neale B. K. 
Published: April 2007

Abstract— This paper reviews the stress intensity factor, limit load, compliance and J‐integral functions for a centre cracked tensile (CCT) specimen available in the literature. Compliance and J‐integral functions are derived from the optimum stress intensity factor and limit load solutions. The functions are compared with the results obtained from two‐dimensional finite element analyses of the specimen.The finite element results have confirmed the accuracy of the compliance and limit load functions available in the literature and suggest that the unloading compliance technique, based on crack mouth opening displacement, could be developed for a CCT specimen. Non‐linear finite element analyses have shown that J can be estimated from the measured load versus load‐point displacement behaviour providing a/W≥ 0.5