bluuebunny/crossref_metadata_2025_split huggingface dataset:
BIFURCATIONS AND INSTABILITIES IN FRACTURE OF COHESIVE‐SOFTENING STRUCTURES: A BOUNDARY ELEMENT ANALYSIS†
Authors: Cen Z. , Maier G. 
Published: April 2007

AbstractThe “cohesive‐crack model” is adopted, together with the hypotheses of small deformations and linear elasticity outside the process zone or “craze”, for the simulation of fracture processes in structures of concrete‐like materials. A “direct”, collocation, multidomain boundary element method is employed and shown to be computationally effective in the considered situations, which are characterized by non‐linearity on interfaces only. Iterative algorithms for the direction search and interface adjustment in propagation analysis and for the determination of the response to a craze‐tip advancement are developed and numerically tested. Softening as an instabilizing factor embodied in the cohesive‐crack model may give rise to path bifurcations (“equilibrium branching”), instability under load control and intrinsic (“snapback”) instability. These phenomena are analysed by the proposed boundary element procedure and discussed.
THREE‐DIMENSIONAL SHAPE OPTIMIZATION OF A BAR WITH A RECTANGULAR HOLE
Authors: Mattheck C. , Erb D. , Bethge K. , Begemann U. 
Published: April 2007

Abstract— A cylindrical bar subjected to bending has a rectangular hole for functional reasons. The initial design failed occasionally due to fatigue cracks originating at the corners of the hole under service conditions. Therefore, a shape optimization was performed using CAO (computer‐aided optimization) based on the computer‐simulation of biological growth. A significant reduction of large notch stresses was achieved.Prototypes manufactured with the shape‐optimized design endured 40 times longer in a fatigue test than the previous design. The example demonstrates that the CAO method is a very powerful and straightforward method for the designer who wants a light‐weight and fatigue‐resistant design.
CORROSION FATIGUE OF AN HSLA STEEL
Authors: Ahn Seung‐Ho , Lawrence Frederick V. , Metzger Marvin M. 
Published: April 2007

Abstract— Single‐pitted specimens of an HSLA steel, were tested in laboratory air and in 1 M NaCl solution to study the influence of a corrosive environment on its fatigue life.The growth of fatigue cracks and the partitioning of the fatigue life into fatigue crack initiation and fatigue crack propagation were studied by photographing the pit and the cracks developing on it periodically during testing. Non‐propagating or dormant surface cracks were not observed in this study. Fractography using SEM showed the locations of fatigue crack initiation. The mechanisms of corrosion fatigue were studied by performing tests in 1 M NaCl at different test frequencies. Corrosion pits proved to be crack initiation sites. Hydrogen embrittlement was found to be unimportant in the corrosion fatigue of HSLA steel in this study. The 1 M NaCl corrosive environment appeared to reduce the fatigue life of this material by a dissolution mechanism. The effect of pit depth was studied by testing specimens having various pit depths. An effect of pit size was apparent. Fatigue life decreased with increasing pit depth. Pit depth, rather than the ratio of pit depth to pit diameter, influenced fatigue behaviour. A non‐damaging pit depth was found.
STRESS STATE‐RELATED FATIGUE CRACK GROWTH UNDER SPECTRUM LOADING
Authors: Wang G. S. , Palmberg B. , Blom A. F. 
Published: April 2007

Abstract— The fatigue crack growth behaviour in aluminium alloy sheets of 2024‐T3 and 7475‐T761, subjected to standardized spectra (TWIST and FALSTAFF), was investigated using centre‐cracked specimens. A strip crack closure model was used to interpret experimental data, and to make predictions for the crack growth.The strip model is based on the Dugdale concept, but modified to keep plastically‐stretched materials on the crack surface so that the crack opening load can be determined, and the fatigue crack growth can be analysed according to Elber's crack growth assumption. Differing from other models of the same kind, a variable constraint factor was introduced to account for the gradual transition of stress state at the crack tip resulting from the crack growth. It has been shown that the transition of stress state at the crack tip causes the unusual behaviour of the fatigue crack growth in sheets. Both experiments and predictions show that a crack may grow faster at a low load than at a higher one in a certain applied load range due to the crack tip stress state transition. The crack tip stress state also contributes to the thickness effect observed for the crack growth in sheets. In agreement with experimental results, it has been shown that a plane stress state will prevail at the crack tip in a thin sheet compared to that in a thick sheet. The plane stress state results in a higher crack opening level which leads to a longer fatigue life for thin sheets.
THE LINEAR NORMALIZATION TECHNIQUE—AN ALTERNATIVE PROCEDURE FOR DETERMINING J‐R CURVES FROM A SINGLE SPECIMEN TEST RECORD BASED ON LANDES' NORMALIZATION METHOD
Authors: Reese E. D. , Schwalbe K.‐H. 
Published: April 2007

AbstractAn alternative approach for determining J‐R curves from a single specimen test based on the normalization technique is proposed. The procedure requires only the load versus load‐line displacement record and the final crack length in order to derive the J‐R curve. The method has been applied to metal and polymers of various geometries and was verified by comparison with J‐R curves obtained from potential drop and multiple specimen techniques.
EXAMINATION OF SHORT‐CRACK MEASUREMENT AND MODELLING UNDER CYCLIC INELASTIC CONDITIONS
Authors: Vormwald M. , Heuler P. 
Published: April 2007

AbstractThe opening and closure behaviour of short fatigue cracks is seen as one of the important phenomena which control fatigue life of components where a major part of life consists of the growth of short cracks. Therefore attempts are undertaken to experimentally assess and to model the behaviour of short cracks with respect to opening and closure. In this paper crack opening results obtained by Sunder et al. through SEM evaluation of striation patterns of 2000 series aluminium alloys are examined and compared to predictions using a model recently developed for fatigue life prediction based on fracture mechanics of short cracks. Sunder's technique for crack opening measurements involves particular load sequences with increasing and decreasing load ranges applied to notched specimens with naturally nucleated surface cracks where crack opening levels are identified by steady‐state striation widths for increasing load ranges. A detailed review of Sunder's results, however, indicates a number of inconsistencies and contradictions which are discussed.Opening and closure behaviour of short fatigue cracks, in particular for inelastic conditions, is compared to predictions obtained with the above‐mentioned model which incorporates a constant strain opening and closure assumption. For inelastic conditions that may develop at notches this assumption means that cracks would close at considerably lower stress levels as compared to the opening stress which becomes important when effective (local) stress‐strain ranges are to be determined for fatigue life prediction under spectrum loading. The constant strain assumption is supported by a number of experimental observations from the literature as discussed in the paper. The approximative nature of this assumption and further details of the model are pointed out which show a need for further developments.
FATIGUE LIFE UNDER RANDOM LOAD HISTORY DERIVED FROM EXCEEDANCE CURVES USING DIFFERENT ALGORITHMS
Authors: Prakash Raghu V. , Sunder R. 
Published: April 2007

AbstractLow cycle fatigue life and crack growth rates were analytically estimated for random load sequences, generated from three combat aircraft load exceedance curves using different algorithms, including simulated rainflow cycle count, extreme‐to‐extreme excursions, upper to lower bound excursions and unrestricted peak‐trough excursions. Also, the response of a fatigue meter to a random load sequence was simulated. Fatigue damage for the different load histories was computed using material constants for an Al‐Cu alloy. Computed fatigue damage was relatively insensitive to the algorithm used for load sequence generation from combat aircraft load exceedance curves. Fatigue meter data based damage estimates were, however, sometimes unconservative.
THE TWO THRESHOLDS OF FATIGUE BEHAVIOUR
Authors: Miller K. J. 
Published: April 2007

AbstractTwo limiting thresholds to fatigue crack propagation are discussed. The first threshold is related to the microstructural texture and this threshold may therefore be deemed a material‐based threshold. The second threshold is mechanically‐based, and is related only to the stress state at the tip of a substantial defect.The material‐based threshold is characterized in terms of Microstructural Fracture Mechanics (MFM) and the mechanically‐based threshold is characterized in terms of Linear Elastic Fracture Mechanics (LEFM). The former condition is important when considering the fatigue limit of materials and components, while the latter is more applicable to the fatigue limit of structures.The different factors which affect the two threshold conditions are briefly presented. Finally, this paper discusses aspects of MFM relevant to the fatigue resistance of metals and components.
POST WELD HEAT TREATMENT EFFECTS ON FATIGUE CRACK PROPAGATION IN AN ELECTRON BEAM WELDMENT
Authors: Hwang Jiun‐Ren , Jeng Ming‐Chang , Wang Chien‐Chun 
Published: April 2007

AbstractThis paper studies the effect of two post‐weld heat treatment processes on the fatigue behaviour of an electron beam weldment in 9 mm AISI 4130 steel. Electron beam tempering, in a vacuum chamber, immediately after welding and a traditional furnace tempering treatment were compared. Fatigue crack propagation resistance was assessed by a linear elastic fracture mechanics analysis. The resistance to fatigue crack growth was improved with post weld heat treatment due to residual stress relief and the existence of a toughened tempered microstructure. The specimens with an electron beam post‐weld heat treatment showed better fatigue properties than those of furnace‐treated specimens. An electron beam post‐weld heat treatment causes the fatigue crack growth rate to decrease with increasing energy input and decreasing micro‐dot‐pattern width. For a furnace post‐weld heat treatment, the fatigue crack growth rate decreases with increasing tempering temperature.
STATISTICAL EVALUATION OF FRACTURE TOUGHNESS TEST DATA
Authors: Hauge Mons , Thaulow Christian 
Published: April 2007

Abstract— Application of fracture mechanics for verification of the fracture resistance of structural components and pipelines is well established in the offshore industry, and development of reliability analysis methods and calibration of assessment procedures is now in progress. One important parameter in fracture mechanics evaluations is the fracture toughness—a parameter characterized by large scatter, sensitivity to fabrication conditions and large costs related to testing. This has raised the need for efficient methods for characterization of the fracture toughness test data in terms of characteristic values and parametric distribution functions.Two relevant data sets are investigated with respect to their statistical properties and the ability of different distribution functions to fit the data.Three methods for estimation of characteristic values for fracture toughness are described. Their relevance and capabilities are investigated by numerical simulations with sample data sets drawn randomly from a larger population.It is concluded that the distribution functions based on a physical model of the fracture have disadvantages such as unstable behaviour for small data sets and lack of capability in providing certain estimations. The log‐normal distribution showed a stable and predictable behaviour for sample sizes down to 3, the methods for calculation of distribution parameters and characteristic values with specified confidence levels are demonstrated to be satisfactory.
FATIGUE ANALYSIS OF SURFACE CRACKS AT FILLET WELDED TOES
Authors: Pang H. L. J. , Gray T. G. F. 
Published: April 2007

AbstractThis paper reports a study of fatigue crack growth and coalescing behaviour at semi‐elliptical cracks in the stress concentration region of steel plates with fillet shoulders or fillet welds. Fatigue tests were carried out on machined plate specimens with a fillet geometry similar to a fillet welded joint. These specimens were notched and precracked to provide single and multiple coplanar semi‐elliptical surface cracks at the fillet toe region. Finite element stress analysis results were used to obtain approximate Mk factors (i.e.: stress concentration magnification factors) for the fillet toe geometry with a semi‐elliptical surface crack. An analytical model was developed to simulate crack shape development and growth to failure in the case of multiple coplanar semi‐elliptical cracks. In this model, a simple crack coalescing procedure is applied to merge coplanar cracks when they meet by recharacterising the coplanar cracks into a single semi‐elliptical crack. Alternative crack growth laws were investigated and comparisons made between actual and predicted shape developments and lives.
COHESIVE MODELLING OF PROCESS REGIONS FOR CRACKS IN LINEAR ELASTIC STRUCTURES—FUNDAMENTAL ASPECTS
Authors: ÖStlund Sören , Nilsson Fred 
Published: April 2007

AbstractThe process region at the tip of a crack in a linear elastic structure has been modelled by a cohesive zone. Growth of the front end of the cohesive zone is governed by a critical stress intensity factor criterion, and advance of the original traction free crack is determined by a critical crack opening at the rear end of the cohesive zone.Damage resistance curves relating the applied stress intensity factor to the growth of the cohesive zone have been calculated for an idealized structure containing two characteristic dimensions. Instability resulting in failure of the structure is found to occur either by unstable growth of the front end of the cohesive zone, without a fully developed cohesive zone, or by unstable growth of the original flaw, when the crack opening displacement at the rear end of the cohesive zone reaches a critical value.The influence of the size of the structure compared to the length of the cohesive zone is investigated, and conditions for the limits of validity of the small scale yielding assumption are discussed. Comparisons are made between the maximum load and the length of the cohesive zone at instability resulting from the present analysis, and the values predicted by linear elastic fracture mechanics.
INFLUENCE OF CREEP‐FATIGUE INTERACTION ON HIGH TEMPERATURE FATIGUE CRACK GROWTH BEHAVIOR of Ti‐1100
Authors: Rosenberger A. H. , Ghonem H. 
Published: April 2007

Abstract— A series of crack growth experiments has been preformed on the near alpha titanium alloy, Ti‐1100, to determine the mechanism of the creep‐fatigue interaction. Based on pure creep crack growth results, the increase in the creep‐fatigue crack growth rate is not amenable to separate contributions of creep crack growth and fatigue crack growth.A mechanism has been proposed to account for the increase in creep‐fatigue crack growth rate that is based on the planar slip of titanium alloys which results in the formation of dislocation pileups at the prior beta grain boundaries and leads to intergranular fracture. This mechanism has been validated through crack growth experiments preformed on a Ti‐1100 that has been microstructurally modified through the precipitation of internal slip barriers. These show that the intergranular fracture and increase in crack growth rate are absent.
FATIGUE LIFE PREDICTION OF NOTCHED COMPOSITE COMPONENTS
Authors: Shen G. , Glinka G. , Plumtree A. 
Published: April 2007

Abstract— The local stress/strain approach has been used to predict the fatigue lives of notched composite components. The method was based on a microstress analysis and the application of a multiaxial fatigue parameter incorporating the alternating strain components on the critical plane. This parameter was able to correlate the fatigue lives obtained under a variety of multiaxial loading and geometrical configurations, enabling a generalized fatigue life curve to be determined on the basis of limited experimental data.The ability of the multiaxial fatigue parameter to relate the fatigue behaviour of composites was illustrated by predicting the locations of crack initiation sites in a unidirectional silicon carbide fibre reinforced titanium plate containing a circular hole tested under constant amplitude cyclic loading. The same approach was also successfully employed to predict the fatigue lives of graphite reinforced epoxy composite tubes with circular holes tested under several combinations of cyclic tension and torsion.
STRAIN BASED CREEP‐FATIGUE DESIGN RULES
Authors: BESTWICK R. D. W. , BUCKTHORPE D. E. 
Published: April 2007

Abstract—Although there has been considerable success in the development of design methods for assessment of fatigue and creep fatigue damage there is need for further improvement particularly for creep damage estimation. Strain based creep‐fatigue rules have been developed for liquid metal fast breeder reactor technology (LMFBs) which give improved estimation of fatigue and creep damage compared with presently available procedures in commercially available high temperature design codes such as ASME CCN47 and RCC‐MR. Presently however their scope is confined to full in‐elastic analyses.This paper provides a summary of the approach used in the strain based rules in relation to base material and weldments of 316L(N) austenitic steel. The paper examines the application of the strain method to thermal shock tests on long cylinders in which the testing cycle includes periods of constant temperature and some of the test pieces contain circumferential welds. Comparisons are made with time fraction based estimates and those of full cyclic in‐elastic analyses. Conclusions are drawn concerning the benefits of the method compared with presently available code procedures. The experience to date shows that the strain based rules give a more realistic interpretation of thermal shock experiments.
CORRELATION BETWEEN HYDROGEN INDUCED CRACKING INITIATION SITES AND CRITICAL STRESS INTENSITY FACTORS
Authors: GAO H. , Cao W. , Fang C. , De Los Rios E. R. 
Published: April 2007

Abstract—Hydrogen induced cracking (HIC) initiation sites and their correlation with the critical stress intensity factors of hydrogen charged specimens were studied under combined I/II mode loading. Two series of tests, is. constant load (CL) tests and slow strain rate (SSR) tests, were carried out. Experimental results showed that in CL tests, irrespective of the ratio KIJKl, the HIC initiation sites always correspond to the point of maximum hydrostatic stress; which is located some distance ahead of the notch tip. However, for SSRT tests, when K11/K1> 1, HIC started at the notch tip which corresponds to the point of maximum equivalent plastic strain. When K11/K1<1 in SSR tests, HIC occurred initially some distance ahead of the notch tip.The relationship between the critical stress intensity factor for HIC and K11/K1 was shown to be different for the two types of test. Multiple effects of stress and strain on hydrogen redistribution and hence on HIC initiation sites, as well as critical stress intensity factors, are discussed.
A STUDY OF THE INTERNAL PARAMETERS OF DUCTILE DAMAGE THEORY
Authors: LI Z. H. , BILBY B. A. , HOWARD I. C. 
Published: April 2007

Abstract—In this paper the Rousselier ductile damage model is used to simulate the softening behaviour of notched bars and crack growth in a pre‐cracked specimen of an A508 pressure vessel steel. The effect of the internal parameters needed to represent the damage on the calculated results is studied. The interactions between these parameters and their effects on the calibration process are discussed. The effect of the cell size on the values of the damage parameters obtained during calibration and on the response of the specimens is briefly reviewed.
A MULTIAXIAL FATIGUE STRAIN ENERGY DENSITY PARAMETER RELATED TO THE CRITICAL FRACTURE PLANE
Authors: Glinka G. , Shen G. , Plumtree A. 
Published: April 2007

AbstractThe cyclic strain energy density parameter W for the critical or failure plane has been successfully applied in predicting the multiaxial fatigue life of an iron‐base and a nickel‐base alloy. This parameter has the advantage of being independent of loading condition, allowing a universal energy‐life curve to be determined for a variety of torsion, tension and bending stress and strain states. The critical strain energy density parameter has been verified using experimental data obtained from tubular and notched specimens of SAE‐1045 steel and Inconel 718.
A HIGH‐CYCLE FATIGUE CRITERION APPLIED IN BIAXIAL AND TRIAXIAL OUT‐OF‐PHASE STRESS CONDITIONS
Authors: Papadopoulos I. V. 
Published: April 2007

AbstractA high‐cycle fatigue criterion suitable for multiaxial non‐proportional stress loading is proposed in this paper. The criterion is based on some microscopic considerations related to the crystalline structure of metals. The purpose of the present paper is mainly the application of this criterion in two loading cases: (a) biaxial loads involving two normal stresses or one normal and one shear stress, and (b) triaxial load with two normal stresses and one shear stress. Stress states of these kinds are very common in piping assemblies. Application of the proposed criterion in the case of triaxial loading, where the three stress components are of the same frequency, but out‐of‐phase, leads to a simple analytical formula. This formula is the equation of a bounding surface that delimits in the space of the above three stresses the safety domain against fatigue crack initiation. A remarkable theoretical result concerns the phase difference of the shear stress, which does not appear in the derived formula. Consequently, according to our proposal the safety domain (i.e. the limiting fatigue endurance) under combined out‐of‐phase biaxial normal stress loading and torsion is independent of the phase difference of the torsion. Obviously this result holds also for the simpler case of axial load and torsion. On the contrary the phase difference between the two normal stresses has a strong detrimental effect on the fatigue endurance of a metal. As is shown these theoretical conclusions are in good agreement with fatigue limit test data found in the scientific literature.