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Due to the existence of structural and material property discontinuities in the ring-welded joints of large-diameter, high-steel-grade pipelines, which are prone to the risk of fracture. Therefore, in this paper, computer-aided engineering techniques, based on finite element analysis and numerical calculations, have been used to establish a model of pipeline containing internal surface crack defects for simulation, and J-integral algorithms have been applied to evaluate the effect of crack parameters on fracture behavior. This research highlights the critical role of computers in pipeline engineering and provides an important theoretical and methodological basis for further optimizing pipeline design and maintenance. [ABSTRACT FROM AUTHOR]

At the tissue-scale and above, there are now well-established structure-property relationships that provide good approximations of the biomechanical performance of bone through, for example, power-law relationships that relate tissue mineral density to elastic properties. However, below the tissue-level, the individual role of the constituents becomes prominent and these simple relationships tend to break down, with more detailed theoretical and computational models are required to describe the mechanical response. In this study, a two-dimensional micromechanics damage-based representative volume element (RVE) of lamellar bone was developed, which included a novel implementation of a phase-field damage model to describe the behaviour of non-collagenous proteins at mineral-mineral and mineral-fibril interface regions. It was found that, while the stiffness of the tissue was governed by the relative proportion of extra-fibrillar mineral and mineralised collagen fibrils, the strength and toughness of the tissue in transverse direction relied on the interactions occurring at mineral-mineral and mineral-fibril interfaces, highlighting the prominence of non-collagenous proteins in determine fracture-based processes at this scale. While fractures tended to initiate in mineral rich areas of the extra-fibrillar mineral matrix, it was found that the presence of mineralised collagen fibrils at low density did not provide a substantial contribution to crack propagation behaviour under transverse loading. However, at physiological volume fraction (V f MCF = 50 %), different scenarios could arise depending on the relative strength value of the interphase around the MCFs (σ f Interphase MCF ) to the interphase between individual minerals (σ f Interphase HA ): (i) When γ = σ f Interphase MCF σ f Interphase HA < 1 , MCFs appear to facilitate crack propagation with MCF-mineral debonding being the dominant failure mode; (ii) once γ > 1 , the MCFs hinder the microcracks, leading to inhibition of crack propagation, which can be regarded as an energy dissipation mechanism. The effective fracture properties of the tissue also experience a sudden increase in fracture work density (J-integral) once the crack is arrested by MCFs or severely deflected. Collectively, the predicted behaviour of the model compared well to those reported through experimental and computational methods, highlighting its potential to provide further understanding into the mechanistic response of bone ultrastructure alterations related to the structural and compositional changes resulting from disease and aging. [ABSTRACT FROM AUTHOR]

Geometrically patterned interfaces seem to be a common motif in Nature. In particular, geometry plays an important role in increasing the strength, toughness and damage tolerance among different species. Here, we investigate the role of the shape of the opening crack behind the crack tip as the crack propagates along the interface. In particular, we studied the shape of the interface behind the crack tip for different amplitude-to-wavelength aspect ratios with two analytical models and compared with finite element simulations through the J-integral. Additionally, we explore the role of material length scale by investigating the relationship between the geometrical characteristic lengths and the emerging material length scale using a finite element-based cohesive zone model. The results suggest that geometrical toughening is influenced by a size effect, but it is bounded between two extreme conditions. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Fracture behavior of biological porous dentine is important to the success of dental restoration. The role of peritubular dentine (PTD) microstructure on the fracture properties of human dentine is investigated by analysis of its crack tip shielding effect on microcracks and macrocracks. The evolution of microcracks around the dentine tubules (DTs) and the growth of macrocracks in the dentine are experimentally observed by scanning electron microscope. Two cases of an individual PTD&DT penetrating the microcrack tip and locating ahead of the microcrack tip are discussed. The effects of multiple PTD&DTs with random distribution and various porosities on the macrocrack shielding or amplifying in dentine are also particularly investigated. The importance of modulus, thickness of PTD and porosity of DT to the shielding effect of crack growth in dentine is studied by finite element analysis, which is characterized by the dominated fracture parameter J -integral. Numerical results demonstrate that PTD can shield the growth of dentine microcracks. When the PTD is in a specific location around macrocracks, it also has a shielding effect. The thicker and harder the PTD, the greater the shielding effect on crack growth. In conclusion, the porous dentine can be used as a reference structure in the design of implant dentures to enhance the dentine toughness. Graphical abstract fx1 Highlights • Ahead of a propagating crack, microcracks initiate near the unfilled porous DTs before the main macrocrack arrived. • Individual PTD&DT has shielding effect on crack at some specific locations. Multiple PTDs always have shielding effect. • An individual or multiple PTD&DTs with appropriate modulus and thickness can impede the crack growth. [ABSTRACT FROM AUTHOR]

Based on the ABAQUS platform for finite element analysis, the extended finite element method (XFEM) considering elastoplastic constitutive relationship is developed, by which the displacement discontinuity across the crack surface and the strong nonlinearity near the crack tip can be described more accurately. The strip specimens with unilateral cracks and central cracks under uniaxial tension are simulated using the XFEM and the FEM, respectively. The J-integral across the crack on each increment is calculated using the equivalent domain integral method (EDIM), the interaction integral method and the FEM, respectively. The effects of mesh size and mesh shape near the crack tip, element type and different calculation methods on the accuracy of J-integral are analyzed. The simulation results show that the XFEM is more accurate than the FEM with the same element size and type. The fracture tests of cast iron specimens with unilateral cracks under uniaxial tension are performed, and the J-integral criterion is valid to predict the fracture initiation in numerical simulation. The critical value of J-integral is calculated using the EDIM of the XFEM. The comparisons demonstrate that the simulated elastoplastic load–displacement curves with the XFEM are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Abstract The effect of clamping force, F c , and coefficient of friction, μ, on the elastic-plastic behavior of cracked bolted joint has been studied numerically using 3-D elastic-plastic extended finite element method. Two different failure modes of a single steel plate which contain a fastener hole are considered, i.e. net tension and bearing mode of failures. It was found that, F c and μ have a significant effect on the development of the monotonic plastic zone around the tip of the crack emanating from fastener hole. The effect of F c and μ on mode I stress intensity factor, K I , of such a crack is more pronounced when the crack tip still beneath the washer. In this region, K I is almost constant regardless the length of the crack. When the crack grows outside the washer, second region, K I increased with increasing the crack length. In both regions, K I decreased with increasing F c and μ. [ABSTRACT FROM AUTHOR]

Objective Apply high-resolution benchtop micro-computed tomography (micro-CT) to gain greater understanding and knowledge of the formation of the micro-damage process zone formed during traverse fracture of cortical bone. Methods Bovine cortical bone was cut into single edge notch (bending) fracture testing specimens with the crack on the transverse plane and oriented to grow in the circumferential direction. We used a multi-specimen technique and deformed the specimens to various individual secant modulus loss levels (P-values) up to and including maximum load (Pmax). Next, the specimens were infiltrated with a BaSO 4 precipitation stain and scanned at 3.57-μm isotropic voxel size using a benchtop high resolution-micro-CT. Measurements of the micro-damage process zone volume, width and height were made. These were compared with the simple Irwin's process zone model and with finite element models. Electron and confocal microscopy confirmed the formation of BaSO 4 precipitate in micro-cracks and other porosity, and an interesting novel mechanism similar to tunneling. Results Measurable micro-damage was detected at low P values and the volume of the process zone increased according to a second order polynomial trend. Both width and height grew linearly up to Pmax, at which point the process zone cross-section (perpendicular to the plane of the crack) was almost circular on average with a radius of approximately 550 µm (approximately one quarter of the unbroken ligament thickness) and corresponding to the shape expected for a biological composite under plane stress conditions. Conclusion This study reports details of the micro-damage fracture process zone previously unreported for cortical bone. High-resolution micro-CT enables 3D visualization and measurement of the process zone and confirmation that the crack front edge and process zone are affected by microstructure. It is clear that the process zone for the specimens studied grows to be meaningfully large, confirming the need for the J-integral approach and it does not achieve steady state at Pmax in most specimens. With further development, this approach may become valuable towards better understanding the role of the process zone in cortical bone fracture and the effects of relevant modifications towards changes in fracture toughness in a cost effective way. [ABSTRACT FROM AUTHOR]

In the present work, nonlinear fatigue crack growth analysis of an inclined edge crack is performed by extended finite element method (XFEM) [1] . The material behavior is assumed to be nonlinear, which is modelled by Ramberg-Osgood model and von-Mises yield criterion. Due to inherent material nonlinearity, the interaction integral approach cannot be used for evaluating the individual stress intensity factors (SIFs). Hence, the mixed mode crack growth problem is solved by decomposing the mixed mode J -integral into mode-I and mode-II. The decomposition of stress, strain and displacement fields is done by considering the symmetric and anti-symmetric parts of the corresponding field [2] . The symmetric part of these fields is related with the symmetric part of J -integral and provides mode-I SIF ( K I ) whereas the anti-symmetric part of these fields provides the mode-II SIF ( K II ). The equivalent K I and K II are used to find the direction of crack growth and the equivalent effective K Ieq for the obtained direction of the crack growth. The range of K Ieq (Δ K Ieq ) is used with the Paris law to evaluate the rate of crack growth. For highly nonlinear materials, J -integral decomposition method is more suitable then interaction integral approach. [ABSTRACT FROM AUTHOR]

Ceramic and composite resin blocks for CAD/CAM machining of dental restorations are becoming more common. The sample sizes affordable by these blocks are smaller than ideal for stress intensity factor (SIF) based tests. The J-integral measurement calls for full field strain measurement, making it challenging to conduct. Accordingly, the J-integral values of dental restoration materials used in CAD/CAM restorations have not been reported to date. Digital image correlation (DIC) provides full field strain maps, making it possible to calculate the J-integral value. The aim of this study was to measure the J-integral value for CAD/CAM restorative materials. Four types of materials (sintered IPS E-MAX CAD, non-sintered IPS E-MAX CAD, Vita Mark II and Paradigm MZ100) were used to prepare beam samples for three-point bending tests. J-integrals were calculated for different integral path size and locations with respect to the crack tip. J-integral at path 1 for each material was 1.26 ± 0.31 × 10 −4 MPa m for MZ 100, 0.59 ± 0.28 × 10 −4 MPa m for sintered E-MAX, 0.19 ± 0.07 × 10 −4 MPa m for VM II, and 0.21 ± 0.05 × 10 −4 MPa m for non-sintered E-MAX. There were no significant differences between different integral path size, except for the non-sintered E-MAX group. J-integral paths of non-sintered E-MAX located within 42% of the height of the sample provided consistent values whereas outside this range resulted in lower J-integral values. Moreover, no significant difference was found among different integral path locations. The critical SIF was calculated from J-integral ( K J ) along with geometry derived SIF values ( K I ). K I values were comparable with K J and geometry based SIF values obtained from literature. Therefore, DIC derived J-integral is a reliable way to assess the fracture toughness of small sized specimens for dental CAD/CAM restorative materials; however, with caution applied to the selection of J-integral path. [ABSTRACT FROM AUTHOR]

Cortical bone fracture mechanics which quantifies the tissue's resistance to fracture is widely regarded as important to finding key determinants of bone fragility and fracture. Currently, the most widely used fracture mechanics approach is the J-integral resistance (J-R) curve as defined in ASTM E1820 standard. This standard employs an unloading compliance (UC) method to estimate crack extension, necessary for fracture toughness and resistance curve (R-curve) quantification. Further, this UC method requires a series of unload-reload cycles to be conducted during the fracture test. However, cortical bone violates some assumptions on which the UC method is based, which are: no energy loss during the unload-reload cycles and any change in unloading compliance is only due to crack extension. Consequently, the aim of this study was to examine the impact of the UC method on the accuracy of fracture toughness measurement for bovine cortical bone. Ten pairs of single edged notched bend specimens were prepared from the posterior diaphysis of bovine tibiae and underwent three-point bending fracture tests. The paired specimens were divided into two groups: a cyclic loaded group and a monotonic loaded group. Further, crack extension was determined by the UC method for the cyclic group and by an optical method for both the cyclic and monotonic groups. From these, three different approaches were used to generate J-R curves from which three fracture toughness parameters were computed and compared between the three approaches. This comparison allowed the impact of crack extension estimation by the UC method as well as the unload-reload cycles on the accuracy of the fracture toughness measures to be assessed. Results show that the UC method underestimates crack extension by an average error of 73%. In addition, the combined effects from crack extension estimation using the UC method and the unload-reload cycles lead to a significant overestimation of the specimen's fracture toughness measures. This highlights the need for more studies to establish a standardized approach to cortical bone fracture testing. • Cortical bone fracture mechanics is vital to our understanding of its fracture process. • Cortical bone behaviour violates assumptions of the most widely used fracture testing method. • The impact of this method on the accuracy of fracture toughness is examined. • This method significantly overestimates fracture toughness measures of cortical bone. • This highlights the need for better standardized cortical bone fracture testing methods. [ABSTRACT FROM AUTHOR]

Fracture assessment of axial crack in steel pipe subjected to internal pressure is reviewed. Assessment results were obtained using different methods FC, GS and FAD in order to compare between their results and facilitate their use in any maintenance program. Material type and crack geometry are considered as the main two parameters controlling the failure of the pipe. The constitutive equation of the material is represented by the Ramberg – Osgood model. Six different half crack lengths (40, 60, 80, 100, 120,and 140 mm) and four values of the ratio between the crack depth and the pipe thickness are considered (0.2, 0.4, 0.6 and 0.8). The relationship between the fracture parameters (i.e., stress intensity factor K and the J -integral) and the crack length for each assessment method is used. The material properties, plane strain fracture toughness K Ic as well as the critical value of J -integral J cr , are used to determine the critical crack size under specified internal pressure. The assessment method that gives smaller critical crack size is the one which is more conservative than the others. The results obtained by using GS and FAD assessment methods show this type of conservation. [ABSTRACT FROM AUTHOR]

Among the approaches available for structural analysis, the J-integral has received an excellent feedback as a fracture parameter under elastic-plastic conditions. In the literature and dealing with the crack case, it is proposed to evaluate the J-integral as a sum of elastic and plastic contributions. However, some uncertainties arise when applying this method to a Ramberg-Osgood law, especially under large scale yielding conditions. The aim of the present paper is to discuss how the J-integral evaluation can be performed for elastic-plastic cracked components. Two different non-linear behaviours have been considered for the material: the Ramberg-Osgood law and power law. Numerical and finite element results from different approaches have been accurately compared, proving that the most appropriate way to evaluate the J-integral for a material obeying Ramberg-Osgood law is to perform two finite element analyses evaluating separately the elastic contribution (through a linear elastic analysis) and the plastic contribution (through a nonlinear analysis considering power law behaviour). [ABSTRACT FROM AUTHOR]

This paper presents three-dimensional (3D) finite element analyses of plane-sided single-edge bend specimens to investigate the effect of the crack front curvature on the accuracy of the average J-integral (J) evaluated over the crack front using the plastic eta-factor-based approach specified in ASTM E1820-11. Specimens with average crack lengths of 0.3, 0.5, and 0.7 and thickness-to-width ratios of 1, 0.5, and 0.25 were analyzed. The analysis was based on the J2 deformation theory of plasticity and assumed stationary cracks with sharp crack tips. The curved crack front was characterized by a power-law expression proposed by Nikishikov et al. that was validated using crack front data collected in this study. The plastic eta factors specified in ASTM E1820-11 and proposed by Zhu et al. were employed. The analysis results indicate that the errors in the plastic eta-factor-based J were generally between - 7 % (i.e., underestimation) and 6 % (i.e., overestimation) for the specimens that had curved crack fronts with crack front curvature equal to the maximum allowable value specified in ASTM E1820-11. Based on the analysis results, crack front straightness criteria that are in most cases less stringent than those specified in ASTM E1820-11 are recommended. The suggested criteria could potentially lead to reduced specimen rejection rates and cost savings. [ABSTRACT FROM AUTHOR]

This paper describes the attempt to define a correlation criterion between fracture toughness, expressed in terms of J-integral, J , and crack tip opening displacement, CTOD, and referred to the thickness (B) of a specimen. From a thick component (e.g. B ≥ 150 mm) it is often difficult to take full-size specimens, because of their dimensions, and weight make handling and hence CTOD-testing difficult too; moreover, taking a full size specimens could be not possible because of the shape of the component. Therefore the need to find a correlation criterion between fracture toughness and thickness becomes relevant. A number of CTOD-tests were performed in accordance with BS 7448 part 1 on carbon steel single edge notch bend (SENB) specimens of different size. Through the experimental data a correlation was found that allows to evaluate J and CTOD for specimens with different thickness (higher or lower) than the one characterising tested specimens. The toughness-thickness correlation was verified applying the Weibull statistical weakest link theory adopted by the ASTM standard E1921-13. Furthermore, with the aim to use toughness temperature dependence for adapting testing conditions in reduced thickness specimens, data for specimens tested at different temperatures were compared. [ABSTRACT FROM AUTHOR]

In the paper the possibility to evaluate the fatigue strength of stiffener to cross beam joints in orthotropic steel decks is discussed. The proposed methodology, based on Paris-Erdogan law, allows to derive a sound estimate of the stress intensity factor K combining the indirect approach, based on the Rice J -integral, with the direct one, based on the extrapolation of experimental or numerical data. The practical implementation of the proposed methodology allowed to predict correctly the actual fatigue life of a previously tested real scale specimen, so validating its potentialities. [ABSTRACT FROM AUTHOR]

A set of standard data sets from typical fracture toughness tests was used in an analytical round-robin to determine whether the proposed data sets were suitable for use as adjuncts to ASTM E1820-09, "Standard Test Method for the Measurement of Fracture Toughness." Four laboratories participated in the round-robin and submitted analyses of all of the data sets. The results showed good agreement among the laboratories on the individual J-integral calculations and crack size estimates. However, small differences in the estimated crack extension during the tests led to large uncertainty in the calculated fracture toughness of up to 20 % of the mean value of the fracture toughness from all of the laboratories for the data set. A synthesized test record that eliminated the nonlinear behavior commonly observed in unloading compliance test records was developed and distributed to the participants. There was excellent agreement among the results from all participants for the synthesized data set. The standard data sets were determined to be suitable for validating analysis programs for calculating fracture toughness in accordance with ASTM E1820. The uncertainty in the calculated fracture toughness could be reduced by prescribing in the test method exactly which data points in an unload are to be used for estimating the crack length, rather than letting the user decide which data points to include. [ABSTRACT FROM AUTHOR]

The assessment of the structural integrity of Steam Generator Tubes (SGTs) in nuclear power plants has been receiving increasing attention in the literature in the last years due to the negative impact related to their failures. Diverse failure prediction methodologies were proposed in the past to ensure tube integrity by fulfilling regulatory authorities’ requirements. They have lead however to overly conservative plugging or repairing criteria like the so-called “40% criterion”. In the present work, in line with modern approaches, an alternative more realistic methodology based on the Failure Assessment Diagram (FAD) is proposed. With that purpose, different studies available in the literature dealing with the experimental determination of fracture toughness of SGT materials were firstly reviewed. Using the results reported in these researches, the FAD was used for predicting the failure modes (i.e., ductile fracture or plastic collapse) of defective SGTs for varied crack geometries and loading conditions. The present analysis indicates the potentiality of the FAD as a comprehensive methodology for predicting the failure loads and failure modes of flawed SGTs. [ABSTRACT FROM AUTHOR]

Abstract: Fatigue crack growth (FCG) could be encountered in many mechanical components, which can be made from either thin or thick steel plates (or shells) and, therefore, be subjected to a plane-stress or a plane-strain condition, respectively. The loads applied in a solid body containing a narrow notch or a sharp crack will induce a yield zone near its tip with a dimension that will depend on the mechanical properties of the material, as well as on the thickness of the body, the crack length and the magnitude of the loads applied. Crack propagation can then occur under mode I, II, III or mixed-mode for general loading. The paper presents JI, JII and JIII integral functions, which were correlated with the elastic stress intensity factors KI, KII and KIII, for thin and thick CT specimens. The evaluation of J-Integral values was carried out for different crack lengths, along the crack front, and using the Finite Element Method (FEM), with collapsed nodes and midside nodes dislocated to ¼ of the edge's length, in order to simulate the crack tip singularity. Interaction between in-plane, in-plane sliding and out-of-plane modes are also discussed in the paper. In addition, FCG rates under mode I, mode III and a mixed-mode (mode I+III) were experimentally determined, at room temperature, for a high-strength Cr-Mn austenitic stainless steel. [Copyright &y& Elsevier]

During running due to frequent braking and suddenly jamming of brakes the Railway wheel skids over rails. This frequent skidding removes large amount of metal from the surface known as Wheel-flat defect. In this paper the wheel-flat and a subsurface crack in the beneath is studied using FEA. If the wheel-flat is not detected early the subsurface crack can originate in the beneath due to inclusion, may leads to fatal accidents. In this study wheel material is taken Elastic-plastic and J-Integral factor has been obtained. The wheel–rail vehicle is modelled as a mass–spring–damper system [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the J-integral of commercially pure titanium (CP Ti) for standard compact tensile (CT) specimen was obtained by four methods containing fracture experiment, two-dimensional (2-D) finite element analysis (FEA), three-dimensional (3-D) FEA, and the calculation formula in electric power research institute (EPRI). Although the J-integral obtained by EPRI solution is consistent with that by 2-D FEA, they are lower than the result of the experiment. Moreover, the J-integral obtained by 3-D FEA is more close to that of the experiment. In order to improve the prediction accuracy of J-integral by EPRI solution, the improved EPRI solution was developed based on 3-D FEA and verified by the experiment. In addition, two failure assessment curves (FACs) of CP Ti corresponding to traditional EPRI solution and the improved one were compared with the experimental results, which indicates that the improved EPRI solution not only improve the prediction accuracy of J-integral, but also increases the reliability of FAC. [Copyright &y& Elsevier]

The crack-like defects often cause the failure of welded structures. Most of the fracture assessment procedures that are used for solving this problem are based on deterministic approaches, for example Zerbst (2007). But the experimental results show that the mechanical properties and fracture toughness of welded joints are significantly changing with a random variation. Taking this into account the fracture assessment of welded structures requires improved numerical approaches. A numerical model of heterogeneous welded joint with randomly varying yield strength was proposed. The results show that the mechanical heterogeneity leads to higher J -integral values for the defects. This implies that neglecting the mechanical heterogeneity of welded joints results in underrating of the risk of failure of welded structures. The proposed numerical estimation of the fracture toughness is used for some typical welded joints and thin-walled pressure vessel. The relations between the variation of yield strength in cracked welded joints and J -integral are presented as the correction functions for calculated parameter of crack resistance. [ABSTRACT FROM AUTHOR]

A plate with an extended surface crack under combined biaxial force and in-plane bending moment is considered. The limit load solution is first derived based on the Mises yield criterion to take account of the effect of stress parallel to the crack plane. The J values are then evaluated using elastic-plastic FE analyses and compared with the predictions of the reference stress method using the developed limit load solution. The results show that the biaxial loading effect on J estimation may be taken into account in the reference stress method if the limit load value considering the biaxial loading effect is used. [ABSTRACT FROM AUTHOR]

The influence of electrolytical hydrogenation on fracture toughness, corrosion crack-growth resistance and fracture micromechanisms of operated 12Cr1MoV steel of thermal power plant superheater collector has been studied. Compact tension specimens were cut from perforated surface of thermal power plant superheater collector dismounted after 178,500 hours of operation. Corrosion crack-growth resistance under tension of previously hydrogenated compact specimens with fatigue cracks was studied. Due to the increased concentration of hydrogen in solution an additional buffer was being created that prevents hydrogen leakage from the specimen through the fracture surface during the experiment. The hydrogenation causes the significant decrease of critical stress intensity factor K c , during the experiment in 0.1 N NaOH solution as compared with critical stress intensity factor K of non-hydrogenation 12Cr1MoV steel obtained by the 5% secant line method and in comparison with critical stress intensity factor K c , determined through the J-integral. The areas of ductile crack growth in hydrogenated and non-hydrogenated specimens were found to have similar material fracture micromechanisms with dimples creation of different shape and size. But on the ductile crack growth area in hydrogenated specimens material intergranular fracture mechanisms were found caused by the hydrogen embrittlement which are similar to areas without ridges with the products corrosion traces. [ABSTRACT FROM AUTHOR]

The present paper proposes a new and more accurate fatigue life prediction model for fillet welded joints in steel subjected to constant amplitude loading. With the traditional fracture mechanics approach, the greatest difficulty when computing the fatigue life of a welded detail is to determine the initial crack size a0 . The classical way to determine the stress intensity factor K (SIF) is by using the following formula Where σ is the applied stress, a is the crack size and g( a / T ) the geometrical correction factor which has been determined by Gurney function or similar solutions. This approach is not accurate for short crack because of the singular V-notch behaviour close to the crack tip is not taken into account. In fact, the singular behaviour at this point has a great influence on the SIF calculation. The present work proposes an alternative approach based on the determination of the Energy Release Rate ( G ) in the V-notch region at the weld toe in order to calculate the stress intensity factor as follows E being the Young's modulus. Once the Δ K is determined for varying stresses, we can calculate the life fatigue based on the Paris crack propagation law. The size of the weld toe region influenced by the singular V-notch behaviour is based on experimental work concerning a cruciform steel joint subjected to an applied axial stress of 150 MPa and a weld angle of 45°. Based the same conditions as in these experimental tests, we compared the results from the classical Gurney's approach with the results from the present methodology. The experimental results in terms of fatigue life and crack length were used as reference. When the crack growth rate is plotted against Δ K we can see that, in our approach two slopes appear. The first slope that corresponds to the short crack propagation in the weld toe region and the second slope that corresponds to the stable crack propagation far from the weld toe region. Also, for short cracks, our approach is closer to the experimental results than the Gurney's approach. Moreover, with our approach, we do not need to introduce the real initial crack size at the weld toe. It is demonstrated how the time consumed for short crack propagation becomes the dominant part of the entire fatigue life at low stress levels. The short crack propagation is more accurately described by the present model than in traditionally approaches. Future extensions of the present work will deal with the introduction of the influence of the weld toe radius and the material characteristics of the HAZ on the fatigue life duration. [ABSTRACT FROM AUTHOR]

A study has been made concerning the influence of short randomly oriented steel and polypropylene fibers on the fracture of cement mortar. With regard to the steel fibers, different fiber volume fractions were considered and the results obtained indicated an increase in the J-integral values, at the onset of mortar cracking and at maximum load, as the fiber content was increased. This improvement in the toughness level was attributed to the fiber bridging effect which enhances the capacity of the reinforced mortar to deform and hence to sustain higher load than that sustained by plain mortar. Compressive strength and modulus of elasticity also were improved due to the presence of steel fibers whose elastic modulus is much higher than that of the mortar. The use of short polypropylene fibers reinforcing elements was also associated with an appreciable improvement in the mortar's toughness as well as in its flexural strength. However, consistent with their low elastic modulus, the polypropylene fibers resulted in reducing the mortar's compressive strength. [ABSTRACT FROM AUTHOR]

The phase transformation in austenitic TRIP-steels contributes to favourable mechanical properties and may affect their fracture behavior. Therefore, the influence of the phase transformation on the crack driving force is investigated. The concept of material forces is applied to a casted CrMnNi TRIP-steel by incorporating inelastic material and transformation behavior via the material model. The resultant material force expression for the near tip crack driving force is presented and evaluated by summing up nodal material forces. The advantage of this method is the separated calculation of material forces due to dissipation by plastic deformation and phase transformation as well as the material force acting directly at the crack tip. The TRIP-effect implies a considerable contribution to the material forces, i.e. the driving force for crack propagation is reduced, which indicates a shielding effect. [ABSTRACT FROM AUTHOR]

This paper is targeted on numerical methods for accurate crack tip loading analysis and crack path prediction. Those are based on finite element calculations of the boundary value problem. Applying path-independent integrals to curved cracks in order to accurately calculate the J-integral, energy release rate (ERR) or stress intensity factors (SIF) is still not state of the art. Contours which are not confined to the crack tip require special analytical preparation and numerical treatment to supply results which are sufficiently precise for reliable crack path prediction. Methods to improve the calculation of the J-integral and the interaction inte- gral (I-integral) are presented. In particular, the latter has never been applied to strongly curved cracks. Also, efficient methods for the loading analysis and crack growth simulation of multiple interacting cracks based on path-independent integrals are presented. The anisotropy of fracture toughness is taken into account being a crucial part of the numerical model. Experiments are carried out with specimens made of aluminum alloy Al-7075, comparing subcritically grown cracks with simulations. [ABSTRACT FROM AUTHOR]

The actual state of stress in the remaining ligament of a single-edge bending (SE(B)) specimen, which is neither plane stress nor plane strain, is critical in accurately predicting the crack length in the specimen involved in the unloading compliance method. Three-dimensional finite element analyses were carried out in this study to evaluate the effective modulus of elasticity that reflects the actual state of stress corresponding to the crack mouth opening displacement (CMOD) compliance of the SE(B) specimen. Both plane-sided and side-grooved specimens with a wide range of geometric configurations and crack lengths were included in the study. A practical approach is further proposed to quickly evaluate the effective modulus from the CMOD compliance determined based on the test data. The proposed approach was verified using experimental data and numerical analysis results. The results of the verification suggest that replacing the elastic modulus corresponding to the plane stress or plane strain condition with the effective modulus in commonly used a/W-CMOD compliance equations can markedly improve the accuracy of the predicted crack length. [ABSTRACT FROM AUTHOR]

In this study, transverse crack behavior for a welded HSLA-100 plate under tension is investigated. Simple and efficient finite element method for solving the welded plate with a central crack is given. In order to simplify the approximate solution, results of a general purpose finite element code are presented. Stress intensity factor for the plate is determined by using J-integral solution. Experimental results of thickness and loading rate effects on strain fields are also presented with respect to EN ISO 15614-1 welding and ASTM E338 testing procedures. Results show that numerical solutions of the repaired plate are compatible with the experimental evaluations. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, with the development of Digital Image Processing Techniques and Computer Science, the numerical simulation analysis on asphalt mixtures’ fracture characteristics has gradually become the focus of domestic and international scholars. However, during the analysis processing, most researchers took asphalt mixtures as a kind of linear elastic materials, which is incompatible with the visco-elastic mechanism of asphalt mixtures. Thus, it will not fundamentally evaluate the fracture characteristics of asphalt mixture. Based on this, considering the visco-elastic mechanism of asphalt mixtures, the paper makes a numerical simulation analysis on asphalt mixtures via a virtual loading of the notched semi-circular bending (SCB) testing, aiming to obtain the fracture characteristics of asphalt mixtures. This study emphatically investigated the effects of the different relative factors between the loading location and the pre-cracking on the fracture characteristics of the asphalt mixtures evaluated by J-integral method. The research shows that, there existed significant region of stress concentration near the crack tip; Under the same loadings, the longer distance deviated from the midline of the SCB specimen, the less possibility to induce fracture cracking. In other words, the longer distance deviated from the midline of the SCB specimen, the greater loadings is needed to complete its total fracture cracking process. [Copyright &y& Elsevier]

Abstract: This work addresses a comparison between fully plastic solutions and the reference stress approach which are applicable to determine Jin circumferentially cracked cylinders under pure bending. The 3-D analyses provide representative functions relating the elastic-plastic crack-tip driving forces with the applied (remote) bending moment for both J estimation procedures. [Copyright &y& Elsevier]

Abstract: In this paper, two practical linear-elastic equations for the evaluation of the critical value of the J-integral in plates with U-notches under Mode I loading are presented and applied to brittle and quasi-brittle materials. It is found that these two proposed equations provide the same results with differences being negligible. By using one of these equations one can evaluate the Jcr and then predict the critical fracture load by means of the Jcr criterion. The results show that the material control radius to the notch root radius ratio (Rc/ρ), and the Poisson''s ratio affect the critical value of the J-integral (Jcr) in U-notches under Mode I loading, and other parameters may be negligible. The predicted fracture loads are compared with experimental results. Two different materials are considered in the tests: a composite material (Al-15%SiC) tested at room temperature and a steel with a ferritic-pearlitic structure tested at −40°C. [Copyright &y& Elsevier]

Abstract: This work addresses a comparison between fully plastic solutions and the reference stress approach which are applicable to determine Jin circumferentially cracked cylinders under pure bending. The 3-D analyses provide representative functions relating the elastic-plastic crack-tip driving forces with the applied (remote) bending moment for both J estimation procedures. [Copyright &y& Elsevier]

Abstract: In this paper, two practical linear-elastic equations for the evaluation of the critical value of the J-integral in plates with U-notches under Mode I loading are presented and applied to brittle and quasi-brittle materials. It is found that these two proposed equations provide the same results with differences being negligible. By using one of these equations one can evaluate the Jcr and then predict the critical fracture load by means of the Jcr criterion. The results show that the material control radius to the notch root radius ratio (Rc/ρ), and the Poisson''s ratio affect the critical value of the J-integral (Jcr) in U-notches under Mode I loading, and other parameters may be negligible. The predicted fracture loads are compared with experimental results. Two different materials are considered in the tests: a composite material (Al-15%SiC) tested at room temperature and a steel with a ferritic-pearlitic structure tested at −40°C. [Copyright &y& Elsevier]

Abstract: Model I quasi-static nonlinear fracture of aluminum foams is analyzed by considering the effect of microscopic heterogeneity. Firstly, a continuum constitutive model is adopted to account for the plastic compressibility of the metallic foams. The yield strain modeled by a two-parameter Weibull-type function is adopted in the constitutive model. Then, a modified cohesive zone model is established to characterize the fracture behavior of aluminum foams with a cohesive zone ahead of the initial crack. The tensile traction versus local crack opening displacement relation is employed to describe the softening characteristics of the material. And a Weibull statistical model for peak bridging stress within the fracture process zone is used for considering microscopic heterogeneity of aluminum foams. Lastly, the influence of stochastic parameters on the curve of stress-strain is given. Numerical examples are given to illustrate the numerical model presented in this paper and the effects of Weibull parameters and material properties on J-integral are discussed. [Copyright &y& Elsevier]

The boundary element method is a numerical method that can be advantageously used for a wide range of engineering problems, including the stress concentration problems encountered in fracture mechanics. In linear elastic fracture mechanics (LEFM), the stress intensity factor is an important parameter. Cracks, if present in the region experiencing the modes of deformation, increase the stress amplitude significantly and this high stress may lead to premature failure of the engineering components. If the value of the SIF is known, it is possible to predict whether the crack will propagate or not. As the conventional boundary integral equation (CBIE) degenerates when a mathematical crack is modelled, a previously developed dual boundary integral equation approach has been adopted in the current work. It utilizes the hypersingular boundary integral equation (HBIE) along with the CBIE. A weakly singular form of HBIE is utilized in the current work to eliminate the hypersingularity analytically. Stress intensity factors are evaluated using the crack opening displacement (COD), displacement extrapolation (DE), and the J-integral approaches. A stand-alone code has been developed for calculating the stress intensity factors of general two-dimensional domains with cracks. The code has been validated by evaluating the stress intensity factors for the standard components, for which the stress intensity factor values are available in the literature. Accurate and well-converged results are obtained proving the robustness of the code. A linear combination of the CBIE and HBIE was applied at the crack and a significant (87-97 per cent) reduction in the condition numbers for the system of equations was observed for the examples studied. Again, the results obtained are accurate and well converged. [ABSTRACT FROM AUTHOR]

The influence of various assumptions on the modeling of cleavage fracture in the presence of residual stresses was investigated. Analyses were undertaken for modified single edge notched bend specimens, manufactured from A533B ferritic steel. The influence of residual stress fields, introduced by a method of in-plane compression, was investigated through the use of a modified J-integral, designed to retain path independence in the presence of initial stress and strain fields and nonproportional loading. Application of modified J values to predict fracture using probabilistic methods, and their use in a well-known structural integrity assessment code, showed that assumptions about levels of out-of-plane constraint, material hardening behavior and the method of crack introduction have a significant influence on the conservatism of the resulting failure predictions. It was found that more realistic modeling of crack introduction had a major effect on the accuracy of failure predictions, with the effects of material hardening being of secondary importance. [ABSTRACT FROM AUTHOR]

Element-free Galerkin (EFG) method is applied to solve the elasto-plastic fracture problems of aluminum foams under uniaxial tensile load. Firstly, a continuum constitutive model is taken into account for the plastic compressibility of aluminum foams. The Weibull statistical analysis is used to represent microscopic heterogeneity. Then, the increments of stress and strain are used to characterize the elasto-plastic constitutive relationship on the basis of EFG method with penalty function method. Considering the discontinuity of crack, Newton-Raphson iteration method is used in computation. Lastly, several examples are given to show the influence of parameter on curve of stress-strain and the relation of values of J-integral versus relative density. The numerical analysis for aluminum foams shows that the influence of the scale parameter of Weibull distribution upon macroscopic mechanical properties and fracture parameter J-integral is significant, while the shape parameter is not obvious. [ABSTRACT FROM AUTHOR]

J-resistance properties of automatic narrow gap gas tungsten arc welds (NGGTAWs) for ferritic primary loop piping were investigated. The piping diameter is 1066 mm, and its thickness is 76 mm. The tensile, microhardness, and J-R tests were. performed, and mi- crostructures of the welds were examined. Tensile and J-R tests were conducted at 316°C and 177° C for temperature effect, and at 1 mm/mm and 1000 mm/mm for strain rate effect. The results were compared with other welds, which are fabricated by the conventional shielded metal arc weld (SMAW) process. The NGGTAW welds investigated in this paper have lower i-R curves than the SMAW welds. Fracture surfaces of the NGGTAW welds showed deep ditches and holes due to inclusions and pores. It is believed that the high density of the inclusions and the pores, which exist in the NGGTAW welds, is responsible for this lower toughness and the fracture surface appearances. Therefore, to improve the NGGTAW weld toughness, it is recommended that sulfur content should be limited to a considerably low level, and the pores should be eliminated by modifying the welding procedure specification. [ABSTRACT FROM AUTHOR]

An adaptive finite element method for analyzing two-dimensional and axisymmetric nonlinear elastic fracture mechanics problems with cracks is presented. The J-integral is used as a parameter to characterize the severity of stresses and deformation near crack tips. The domain integral technique, for which all relevant quantities are integrated over any arbitrary element areas around the crack tips, is utilized as the J-integral solution scheme with 9-node degenerated crack tip elements. The solution accuracy is further improved by incorporating an error estimation procedure onto a remeshing algorithm with a solution mapping scheme to resume the analysis at a particular load level after the adaptive remeshing technique has been applied. Several benchmark problems are analyzed to evaluate the efficiency of the combined domain integral technique and the adaptive finite element method. [ABSTRACT FROM AUTHOR]

Due to the influence of material inhomogeneity in functionally graded piezoelectric materials (FGPMs), the standard J-integral loses the path independence. This paper presented a modified J-integral, which retains the path-independence in FGPMs, for calculating the energy release rate. Some numerical examples were provided to demonstrate the superiority of the modified J-integral over the standard J-integral. [ABSTRACT FROM AUTHOR]

Through this paper an alternative procedure to obtain fracture toughness parameters on blunt-notched samples rather than on standard sharp-notched samples has been applied to several materials which display different fracture behavior. An aluminum alloy, an austempered ductile iron (ADI), and two different polymeric materials, polyamide 6 and poly(methyl methacrylate) (PMMA), were tested. The use of the alternative methodology allows simplification and cost reduction in fracture toughness evaluation. For the aluminum alloy, the fracture parameter obtained by this method was 16 % lower than that determined using ASTM standard methodology with data scatter similar to that reported in literature. For the ADI. fracture toughness values from blunt-notched samples were close to those obtained using standard test samples, showing low sensitivity to the changes in the crack tip diameter. For polyamide 6, the alternative methodology led to a toughness value within the same range of the values obtained from the traditional technique. In the case of the PMMA, the KIc values obtained from both methods showed good agreement. [ABSTRACT FROM AUTHOR]

This paper provides an engineering J estimation equation for surface cracked plates under combined bending and tension. The proposed equation is based on the reference stress approach, and the most relevant normalizing loads to define the reference stress for accurate J estimations are given for surface cracked plates under combined bending and tension. Comparisons with J results from extensive three-dimensional finite element (FE) analyses, covering a wide range of crack geometry, plate geometry and loading combination, show overall good agreement not only at the deepest point but also at arbitrary points along the crack front. For pure tension, agreement between the estimated J values and the FE results is excellent, even at the surface point. On the other hand, for pure bending and combined bending and tension, the estimated J values become less accurate for locations close to the surface point. [ABSTRACT FROM AUTHOR]