bluuebunny/crossref_metadata_2025_split huggingface dataset:
SMALL CRACK GROWTH IN THE ALUMINIUM–LITHIUM ALLOYS 8090 AND 8091
Authors: Nicholls D. J. , Martin J. W. 
Published: April 2007

AbstractThe relationship between microstructure and the fatigue behaviour of small cracks has been examined for the aluminium–lithium alloys 8090 and 8091 after peak ageing at 170°C. Duplex ageing and pre‐stretching were used to vary the distribution of S'precipitates and thus the distribution of slip. No effect of S'distribution an small crack growth was observed in either alloy. This is thought to be due to a combination of the lack of closure and lower overall slip reversibility in small cracks. Small cracks in 8091 were found to grow slower than in 8090 due to differences in grain shape rather than texture. Small cracks in both alloys were observed to grow much faster than long cracks for equivalent ΔKs. This difference was reduced when small crack data were compared with long crack data generated at R= 0.7 due to the reduced closure. The use of ΔJ made long and small crack growth rates still more comparable.
GEL ELECTRODE IMAGING OF FATIGUE CRACKS IN MAGNESIUM ALLOYS
Authors: Baxter W. J. , Gorkiewicz D. W. 
Published: April 2007

AbstractThe gel electrode technique has been modified for the detection of fatigue cracks in magnesium alloys. Prior to fatigue loading, the surface is coated with a thin (70nm) insulating anodic film of magnesium fluoride. This film is ruptured wherever a fatigue crack subsequently forms in the magnesium alloy so that current from the gel electrode flows preferentially to the crack. This current forms an image of the crack on the gel electrode probe with a resolution of 0.05 mm. The image is repeatable, permitting the early stages of growth of small cracks to be monitored.
COMPATIBLE COMPLIANCE AND STRESS INTENSITY EXPRESSIONS FOR THE STANDARD THREE‐POINT BEND SPECIMEN
Authors: Bakker A. 
Published: April 2007

AbstractAvailable expressions for load‐line compliance and crack‐mouth opening compliance expressions for standard three‐point bend specimens (span over width ratio =4) are assessed. It is concluded that none of the available expressions are able to reproduce the source data (boundary collocation results and theoretical limits for relative crack depths equal to 0 and 1) for the entire range of relative crack depth. New expressions for example are proposed and the accuracy of each is indicated. A by‐product of the new expression for load‐line compliance is a new, fully compatible stress intensity expression that is, consistent with the load line compliance expression as known from theoretical considerations. Also inverse expressions are presented which predicting the crack length from compliance. To improve the accuracy of such inverse expressions, a correction that results in a considerable error reduction is presented.
MARKOV APPROXIMATION TO FATIGUE CRACK SIZE DISTRIBUTION
Authors: Solomos G. P. , Lucia A. C. 
Published: April 2007

AbstractThe distribution of the crack size during the fatigue crack propagation phenomenon is investigated. A Markovian modeling of the crack is introduced through the fatigue crack growth law, and the associated Fokker‐Planck equation is written while special care is devoted to specifying its boundary conditions. This equation is solved by the method of separation of variables and the sought distribution function is obtained in the form of a convergent infinite series. An illustrative example, demonstrating the applicability of the approach, shows satisfactory agreement between theoretical results and experimental data.
FATIGUE CRACK GROWTH THROUGH ARALL‐4 AT AMBIENT TEMPERATURE
Authors: Davidson D. L. , Austin L. K. 
Published: April 2007

AbstractFatigue cracks were grown in the 5 layer aluminum alloy‐Aramid fiber laminate composite ARALL‐4 over the range of cyclic stress intensity factors (ΔK) from 3.5 to 91 MPa✓m. Near the threshold, crack growth rate was about the same as for unreinforced aluminum alloys, but at high ΔK, crack growth rates were significantly lower. Crack closure was measured over this range of growth rates and found to be different than for unreinforced aluminum alloys. The magnitude of closure was also dependent on crack length. Cracks opened progressively towards the tip with increasing load in much the same way as for unreinforced aluminum alloys. Removal of the aluminum outer layer and some of the epoxy revealed that fibers were intact close to the crack tip, but heavily damaged further away. By adjusting the fatigue crack growth curve of an unreinforced aluminum alloy for the closure exhibited by the composite, it was possible to approximate the crack growth rate for the composite over the lower to mid range of ΔK, but at higher values of ΔK, this model seriously overestimated measured crack growth rates. Therefore, fiber bridging affects both closure and maximum stress intensity factor at the crack tip. Standard fracture mechanics cannot be applied to describe these effects.
RATE‐DEPENDENT DEFORMATION AND FRACTURE OF α‐TITANIUM
Authors: Smith D. J. , Jones R. L. 
Published: April 2007

AbstractAspects of combined rate‐dependent deformation and crack growth in α‐titanium at room temperature are examined. Results are presented for tests carried out on pre‐cracked three point loaded single edge notch bend and compact tension specimens subjected to constant crack opening displacement rates and constant load. Curves of the ratio of the reference stress to the yield stress as a function of the ratio of the plastic displacement to specimen width are found to be different for different rates. The stress difference between continuously loaded curves and curves obtained from load relaxation tests (“relaxed” curves) is found to be similar to uniaxial results. Earlier uniaxial tests show that the “relaxed” curve represents a boundary below which no further creep takes place. The pre‐cracked specimen constant load curves cross the “relaxed” curve, even though the contribution from crack growth to the overall deformation is found to be small. Sustained load crack growth is observed to take place under contained yielding conditions and the sustained load resistance curves are found to be different for different reference stresses.
THE CONSEQUENCES OF SHORT CRACK CLOSURE ON FATIGUE CRACK GROWTH UNDER VARIABLE AMPLITUDE LOADING
Authors: Vormwald M. , Seeger T. 
Published: April 2007

AbstractOpening and closure of short cracks has been examined experimentally using small strain gauges fixed to unnotched specimens very close to short fatigue cracks. The results of completely reversed tension‐compression constant amplitude tests are that crack opening stresses decrease with increasing stress amplitude and that crack closure occurs at nearly the same strain as crack opening. In variable amplitude loading the crack is subjected to a low crack opening level resulting from larger cycles. Based on the results of this experimental investigation some simple approximation formulas are proposed with which decrease as well as increase of crack opening levels can be described. Using these formulas it is possible to compute crack opening strains for any load sequence. The findings of the investigations have been merged to build an algorithm for the prediction of fatigue lives to initiation of cracks of technical sizes in case of variable amplitude loading. The improvement in accuracy of life predictions compared to results of an existing damage accumulation concept is demonstrated for two materials and two load sequences.
SHORT CRACK GROWTH AND COALESCENCE ALONG THE TOE OF A MANUAL FILLET WELD
Authors: Verreman Y. , Nie B. 
Published: April 2007

AbstractAn experimental study was undertaken on the early development of fatigue cracking along the wavy toe of a manual fillet weld between structural steel plates. Stress relieved and as‐welded cruciform specimens were tested under fully reversed loading at two stress amplitudes. Miniature strain gages installed along the toe were used to monitor the crack depth and crack opening level from a crack depth of 10‐20 μ. A calibration of gage response versus crack depth from a 2D finite element analysis is shown to be acceptable. The analysis of the gage responses and of the fracture surfaces including beach marks of short cracks has revealed that discontinuous straight‐fronted cracks rapidly form along the edge of the successive weld ripples. Their aspect ratio increases until some coalescence results from a progressive bridging between the adjacent crack planes. As the step of the ridge line decreases, the cracks fully coalesce into one uniform through‐crack. Faster growth rates associated with negative opening levels are recorded in as‐welded specimens. The welding residual stress distribution makes initiation and early crack propagation concentrate at the center of the specimen which results in a long semi‐elliptical crack.
BEHAVIOUR OF SHORT FATIGUE CRACKS IN A MEDIUM CARBON STEEL SUBJECTED TO BENDING
Authors: Wu X. J. 
Published: April 2007

AbstractThe fatigue process of a 0.45% carbon steel was studied with hour‐glass shaped specimens under rotatary bending. The plastic replication technique was applied to observe surface short fatigue cracks. Fatigue cracks initiated continuously with increasing number of cycles. The failure of a specimen largely depended on the number and distribution of these short cracks. The relationship of surface fatigue crack density to both stress amplitude and number of cycles was determined.
PREDICTION OF REMAINING LIFE OF HIGH TEMPERATURE COMPONENTS USING NON‐LINEAR FRACTURE MECHANICS
Authors: Smith D. J. 
Published: April 2007

AbstractProcedures developed by Ainsworth and Smith and Webster to assess the remaining life of high temperature engineering components containing cracks are presented and applied to a practical example of a °CrMoV steel pressure vessel operating at 565°C. The general principles of the procedures are similar. Net section creep rupture is described in terms of the reference stress method and creep crack initiation and growth is predicted using the non‐linear (creep) fracture mechanics parameter C*. However, the details of each procedure are shown to differ. The main differences lie in the predicted times for net section creep rupture and creep crack initiation. Ainsworth's method predicts shorter creep rupture times than Smith and Webster's procedure. The initiation time using the Smith and Webster procedure is predicted to occur shortly after loading while Ainsworth's estimate is about 40% of the life of the vessel. Both procedures predict similar times for failure by creep crack initiation and crack growth.
FINITE ELEMENT MODELLING OF FATIGUE CRACK SHAPES
Authors: Gilchrist M. D. , Smith R. A. 
Published: April 2007

AbstractThis paper describes a versatile finite element technique which has been used to investigate the fatigue growth and stability of a wide range of structural defects of practical importance. The procedure automatically remeshes the three‐dimensional finite element model during the stages of crack growth. Problems analysed to date include the subsurface and breakout growth of internally initiated elliptical defects, the growth of semi‐elliptical surface cracks in leak‐before‐break situations, the development of quarter‐elliptical corner defects, the interaction and coalescence of two adjacent coplanar semi‐elliptical surface defects and the fatigue growth of a defect in a round bar.
NUMERICAL RESULTS FOR VOLUME, SURFACE AND CONTOUR INTEGRALS AROUND CRACK TIPS
Authors: Blackburn W. S. 
Published: April 2007

AbstractThe repair or replacement of defective structures can be avoided if it can be shown that the defects will grow a negligible amount in service. The most robust parameters for correlating the onset of crack growth between test and service conditions can be defined as contour integrals around the crack tip. For many years, integrals of this type have been available in the post processing part of the stress analysis program BERSAFE. The new release BERSAFE 90 will include the options of evaluating these parameters by replacing most or all of the contour integration by surface or volume integration. This method known as the g function method makes them equivalent to virtual crack extension methods for an elastic material. To obtain experience of the relative accuracies of the new and old options, calculations have been carried out on coarse meshes for elastic‐plastic materials with two dimensional, axisymmetric and three dimensional geometries under both mechanical and thermal loading for various tolerances and numbers of Gauss points. It is concluded that

The quantity J*w can often be calculated more accurately by using the g function than by taking a contour integral through nodes. However further experience is required before final guidelines can be issued.
Use of 27 rather than 8 Gauss points per element did not improve the accuracy in the case considered.
For uniform tensile loading of a central cracked block, both the g function method and the contour integration method give satisfactory accuracy even with only one element through the thickness. However displacement substitution produces values which are dependent on the number of Gauss points when there is only one such element.
A close tolerance is required for thermal problems in order to obtain path independent results when using either the contour integration or the g functions.
COMPARISON BETWEEN TWO ASSESSMENT METHODS FOR DEFECTS IN THE CREEP RANGE
Authors: Piques R. , Molinie E. , Pineau A. 
Published: April 2007

AbstractIn recent years considerable effort has been made to understand the behaviour of creep defects at elevated temperature. A large number of experimental studies have been devoted to creep crack growth behaviour. In Europe, both in U.K. (CEGB) and in France (EMP), attention is focussed not only on crack growth but also on creep crack initiation behaviour in the assessment of defects at high temperature. This paper describes and applies both methods, first to laboratory test results and then to a cracked component. The comparison with test data is made with three materials, a ferritic 1 Cr‐1Mo‐0.25 V steel and two austenitic stainless steels, while the application to a cracked pressure vessel deals with a ½ Cr‐Mo‐V steel. For these materials which are creep ductile, the relevant load‐geometer parameter for stationary creep cracks is the C* parameter, which relies on the concept of reference stress and reference length. The expressions used for these parameters in both procedures are compared. Then the methods used for calculating the time for incubation prior to crack extension, t1, the time for subsequent growth, tg, and the time to failure, tF=ti+tg are compared. This comparison is made not only for laboratory test data but also for a cracked pressure vessel. It is shown that, in spite of different approaches, especially in the assessment of tg, both methods provide comparable t1 ‐ C* and tF=C* diagrams. The reasons for this situation are briefly discussed.
SENSITIVITY ANALYSIS OF THE DOUBLE CLIP GAUGE METHOD
Authors: Manzione P. , Ipiñta J. E. Perez 
Published: April 2007

AbstractDuring fracture toughness testing, the stable crack growth measurement is necessary for the construction of the R‐curves of J vs Δa or CTOD vs Δa. One possible measurement technique uses the Double Clip Gauge Method, which is based on the assumption that the specimen is deformed like two rigid arms that rotate around an apparent centre of rotation located in front of the crack tip. This apparent centre moves as the crack grows in a stable way, and its position can be estimated through the measurement of two crack opening displacements located at different heights. As a consequence the crack growth can be calculated. In this paper the behaviour of the equations that govern the Double Clip Gauge Method are described, and the zones of greatest sensitivity for the location of the clip gauges are determined. A sensitivity analysis of the most influential intervening variables is also made.
FRACTURE MECHANICS ANALYSIS OF FATIGUE RESISTANCE OF SPOT WELDED COACH‐PEEL JOINTS
Authors: Wang Pei‐Chung , Ewing K. W. 
Published: April 2007

AbstractResistance spot welding is the most widely used joining method in automobile manufacture. The number, location, and quality of welds are some of the factors that influence the performance of welded subassemblies, and body panel structures. Therefore, design optimization requires knowledge of not only sheet metal behavior, but also weld behavior under service loadings. A linear elastic fracture mechanics approach was employed in this study to estimate the fatigue lives of spot welds subjected to tearing loads in a coach‐peel specimen. Using a finite element method (FEM), the initial J‐integral values for five coach‐peel joints, each with different geometries, were calculated. Fatigue tests conducted on the same weld geometries provided life data. The experimental data were used to derive a relationship between the initial elastic J‐integral values (ΔJe) and the fatigue life. It was found that the total fatigue life (Nf) of a weld at one applied stress range is related to its range of J‐integral value such that a ΔJe vs Nf log‐log plot gives a straight line relationship. This relationship can be used to evaluate the effects of geometrical variables on the fatigue life of coach‐peel joints. The results show that, within the dimension range studied here, the effects of geometrical variables on the fatigue resistance can be ranked in the following decreasing order: weld eccentricity, sheet thickness and weld nugget diameter.
ACCELERATION OF CRACK GROWTH UNDER INTERMITTENT OVERSTRESSING IN DIFFERENT ENVIRONMENTS
Authors: Koterazawa Ryoichi , Nosho Takayoshi 
Published: April 2007

AbstractFatigue crack growth behaviour under intermittent overstressing was investigated in moist air, dry air, nitrogen and vacuum with low carbon steels under tension‐compression loading with a few tests under compression‐tension loading. A very small number of cycles of overstress applied intermittently during a very large number of cycles of understress below threshold caused significant acceleration, of about one hundred times, in crack growth rate as compared to the case of steady cyclic stress in the cases of moist air, dry air and nitrogen. In the region of low understress, the acceleration in moist air was appreciably less than that in dry air and nitrogen due to oxide‐induced crack closure. The acceleration in vacuum was smaller than that in other environments over all understress levels, possibly because of rewelding. There was no effect of an overstress sequence on the acceleration.
A MODIFIED FRACTURE MECHANICS APPROACH TO METAL FATIGUE
Authors: DuQuesnay D. L. , Abdel‐Raouf H. , Topper T. H. , Plumtree A. 
Published: April 2007

AbstractThe fatigue lives, the fatigue limit stress ranges and fatigue notch factors for metallic specimens can be predicted using a modified fracture mechanics model for short cracks based on the combination of solutions for the non‐uniform strains at the surface of a metal and the development of crack closure. The resulting local stress intensity factor exceeds that indicated by linear elastic fracture mechanics at short crack lengths. The model predicts a smooth and continuous variation of the fatigue notch factor with notch size between a lower bound of unity and an upper bound equal to the theoretical notch stress concentration factor. The model is verified using experimental data for a 2024‐T351 aluminium alloy for smooth and notched specimens tested at various stress ratios.
CTOD FOR SLOW STABLE CRACK GROWTH CONDITIONS
Authors: Ipiña J. E. Perez 
Published: April 2007

AbstractA procedure for CTOD calculation under slow stable crack growth conditions is presented in this work. This procedure gives more accurate CTOD values than those obtained using existing standards, and can be used in tests in which the slow stable crack growth is measured. An analysis of the errors made, when the traditional ([I], ASTM STP 668, pp. 307‐333) or the European Group of Fracture equations are used, is also made. A weighting factor on Δa is proposed for tests without crack growth measurement.
STRESS SINGULARITIES IN BI‐MATERIAL WEDGES WITH ADHESION AND DELAMINATION
Authors: van Vroonhoven J. C. W. 
Published: April 2007

AbstractThe order of the stress singularity at corners in bi‐materials is calculated by means of a local approximation of the stresses. This is performed for interfaces with adhesion and for interfaces which show delamination. It is demonstrated that the singular behaviour is less severe in the case of adhesion, i.e. when delamination is prevented. This result provides an explanation for the phenomenon that cracking at comers of bi‐material wedges only occurs in the presence of delamination. This conclusion is confirmed by experiments on micro‐electronic devices using scanning acoustic tomography, Fracture of the plastic encapsulation and failures of the electrical circuits are only observed in areas where the plastic has delaminated from the chip surface.
CRACK TIP BEHAVIOUR AND CRACK PROPAGATION IN DUCTILE MATERIALS
Authors: Li G. C. , Liu H. Q. , Du M. L. , Hong Y. S. , Zhang X. 
Published: April 2007

AbstractDilatational plastic equations, which can include the effects of ductile damage, are derived based on the equivalency in expressions for dissipated plastic work. Void damage developed internally at the large‐strain stage is represented by an effective continuum being strain‐softened and plastically dilated. Accumulation of this local damage leads to progressive failure in materials. With regard to this microstructural background, the constitutive parameters included for characterizing material behaviour have the sense of internal variables. They are not able to be determined explicitly by macroscopic testing but rather through computer simulation of experimental curves and data. Application of this constitutive model to mode‐I cracking examples demonstrates that a huge strain concentration accompanied by a substantial drop of stress does occur near the crack tip. Eventually, crack propagation is simulated by using finite elements in computations. Two numerical examples show good accordance with experimental data. The whole procedure of study serves as a justification of the constitutive formulation proposed in the text.
CONVERSION OF SHORT FATIGUE CRACKS INTO A LONG CRACK
Authors: Hyspecký P. , Strnadel B. 
Published: April 2007

AbstractThis paper presents a method for the statistical processing of results of initiation and propagation of short fatigue cracks. The distribution of the lengths of these cracks followed a Weibull distribution function. The value of the size parameter of this distribution grows with the number of cycles, but the value of the shape parameter declines as the number of cycles increases. A study of the modal value of fatigue crack lengths as a function of the number of cycles yielded a statistical criterion defining the conversion of the short fatigue crack initiation and propagation stage into the long fatigue crack propagation stage. One condition for this conversion is a zero magnitude of the first derivative of the modal value of fatigue crack lengths by the number of cycles. When the dependence of the Weibull distribution shape parameter and size parameter upon the number of cycles was inserted in this condition, solution of the resultant expression revealed the critical number of cycles that is necessary for the formation of a long fatigue crack.