Search

Centre-notched tension and double-edge-notched tension tests were conducted using specimens of copy paper in order to determine the Mode I critical J -integral. The crack length was varied during the test, and the effects of the test method and crack length were examined. The critical J -integral obtained from the centre-notched tension test was significantly smaller than that obtained from the double-edge-notched tension test. In both tests, the critical stress intensity factor decreased as the initial crack length increased. When the crack length correction was performed, however, the Mode I critical J -integral could be accurately obtained while reducing the aforementioned dependencies. [ABSTRACT FROM AUTHOR]

Abstract: It is experimentally observed that the fracture process developed in an embossed paper sample having a periodic matrix organized pattern is distributed over several indentation rows in the region near a macroscopic crack. This observation suggests that the stresses at the tip of the crack is shielded by damage in neighboring rows of indentation: energy dissipation may occur not only at the tip of the main crack, but in several indentation rows parallel to the main crack. In this investigation, a model describing the in-plane fracture behavior of embossed low-basis-weight paper is developed. It is found that the model is capable of capturing the development of damage in rows parallel to the main crack and compares well with experimental results. [Copyright &y& Elsevier]

Abstract: The present paper gives comments on specimens to be considered for fracture toughness experiments. It is emphasized that the similarity between compact tension specimens, C(T), and cracks in real structures is often disregarded. [Copyright &y& Elsevier]

• The plastic influence term on crack driving force is quantitatively described by the plastic wake height. • The relation between separation displacement and the crack driving force gives an extra constraint on how to choose a proper traction-separation law. • The plastic influence term on crack driving force is found to be independent of in-plane geometry as long as the crack tip plastic zone does not reach the outer boundary or merge with the plastic zone of the outer boundary. This paper has transferred the influence of plastic dissipation on the crack driving force into the crack growth resistance curve based on a displacement quantity defined at the current crack tip. Such a displacement is the crack-tip-opening displacement of the corresponding stationary crack for an elastic–plastic growing crack and represents the plastic wake height. Then, this displacement-based resistance curve provides a quantitative description of the plastic deformation influences during crack growth. This paper has three novel points: 1) the crack-tip-opening displacement for an imaginary stationary crack is divided into the separation displacement and the plastic wake height, in which the separation displacement is related to the crack driving force and the plastic wake height is correlated with the plastic influence term. 2) A unified constraint of the traction-separation law (TSL) for the cohesive zone is provided by the relation between separation displacement and the crack driving force, which can shed further light on how to choose a proper TSL. 3) According to the relation between the plastic wake height and the plastic dissipation term, the influence of plastic deformation on the crack driving force is found to be independent of initial crack length, specimen width and geometrical type as long as the crack tip plastic zone does not reach the outer boundary or merge with the plastic zone of the outer boundary. [ABSTRACT FROM AUTHOR]

Cellulose-based materials are increasingly finding applications in technology due to their sustainability and biodegradability. The sensitivity of cellulose fiber networks to environmental conditions such as temperature and humidity is well known. Yet, there is an incomplete understanding of the dependence of the fracture toughness of cellulose networks on environmental conditions. In the current study, we assess the effect of moisture content on the out-of-plane (i.e., z-dir.) fracture toughness of a particular cellulose network, specifically Whatman cellulose filter paper. Experimental measurements are performed at 16% RH along the desorption isotherm and 23, 37, 50, 75% RH along the adsorption isotherm using out-of-plane tensile tests and double cantilever beam (DCB) tests. Cohesive zone modeling and finite element simulations are used to extract quantitative properties that describe the crack growth behavior. Overall, the fracture toughness of filter paper decreased with increasing humidity. Additionally, a novel model is developed to capture the high peak and sudden drop in the experimental force measurement caused by the existence of an initiation region. This model is found to be in good agreement with experimental data. The relative effect of each independent cohesive parameter is explored to better understand the cohesive zone-based humidity dependence model. The methods described here may be applied to study rupture of other fiber networks with weak bonds. • Fracture toughness of Whatman filter paper decreases with increasing humidity. • Cohesive zone model developed to capture crack growth. • Initiation region needed to capture force–displacement curves due to blunt crack tip. • Explored relative effect of each independent cohesive parameter. [ABSTRACT FROM AUTHOR]

• Proposing a procedure for assessment in the designing phase of an existing rivetted steel bridges. • Risk under control using the assessment procedure presented in the paper. • Structural integrity assessment of existing steel bridges by means of fracture mechanics. • The results of in-depth XFEM analysis with different crack size in the area of a riveted joint are also presented, in order to validate the algorithm. Numerous roads and railways network steel bridges exist with more than 100 years in service, often of great historical value. The in-service safety assessment of these structures is a complex problem which requires interdisciplinary approaches – from civil engineering application of Eurocodes or European recommendation for fatigue life estimation, up to an in-depth assessment by means of fracture mechanics. This article emphasizes the importance of rehabilitating the structure of existing steel bridges, considering the historical monument character of these structures, as well as the reuse of existing structures. Toward this aim, the study case for a historical riveted steel bridge build in the beginning of the twentieth century is presented, with an assessment method considering the structural integrity by means of fracture mechanics. Based on this case study, the paper is proposing an algorithm to assess historical steel bridges. The results of in-depth XFEM analysis with different crack size in the area of a riveted joint are also presented, in order to validate the algorithm. [ABSTRACT FROM AUTHOR]

• Propose symmetric line analysis method based on crack line analysis method. • Crack the difficulty of solving partial differential equations near symmetric line. • Define three symmetry problem types and obtain plastic stresses near symmetric line. • Obtain elastic–plastic solutions near symmetric line for typical symmetry problems. • Provide a new way of solving elastic–plastic symmetry problems analytically. The mathematical difficulty encountered in the elastic–plastic analysis of solids lies in solving the partial differential equations analytically in the theory of plasticity. Such a mathematical dilemma has existed for decades and analytical solutions are still waiting to be obtained. This paper extends the crack line field analysis method and puts forward a symmetric line analysis method, which uses the parity of the Taylor series expansion of the plastic stress field near the symmetric line to transform the problem of solving partial differential equations into ordinary ones, and so obtain the general Taylor series solution of the plastic stress field near the symmetric line. The symmetric line analysis method can give elastic–plastic solutions to plane and anti-plane symmetry problems that have not been analytically solved before, which achieves an essential leap forward in the analytical analysis of elastic–plastic solids in the theory of plasticity. In this paper, three types of symmetry problems are defined, and examples are given for the elastic–plastic analysis and solution of each type of symmetry problems of elastic-perfectly plastic solids with the symmetric line analysis method. [ABSTRACT FROM AUTHOR]

• A new computational framework of 3D peridynamic impact modeling is presented. • Impact fracture behaviors of PMMA, tempered and float glass panels are investigated. • Parametric study is conducted to examine the effects of different impact parameters. • Penetration and impact fracture phenomena in brittle materials are explained. Accurate prediction of the impact fracture behavior of brittle materials is crucial in various industries. The paper employs the peridynamic method to model the penetration and damage in brittle materials during impact. The proposed three-dimensional peridynamic impact fracture model (3D-PDIFM) overpasses other numerical models by adopting a new computational technique to couple the impact collisions of different types of projectiles with the peridynamic method. Moreover, the 3D-PDIFM is highly efficient in impact fracture simulations by focusing on the effects of the projectile without simulating its particles, thereby saving more computational efforts. Validation through comparison with experimental measurements and observations ensures that the 3D-PDIFM accurately represents the real-world impact fracture behavior of brittle materials. The paper also highlights the efficiency of the 3D-PDIFM in comparison to traditional mesh-based numerical simulations. Therefore, the 3D-PDIFM can be significant for practical engineering applications as efficient simulations can save time and computational resources. Using the validated model, the impact fracture behavior of PMMA under various conditions, such as changes in panel thickness, impact area, and projectile velocity, is investigated. This analysis gains more insights into how these factors affect the brittle material's response to impact. Moreover, the impact fracture behaviors of tempered glass and float glass panels are examined under different conditions of impact loadings. This study also explains the penetration and impact fracture phenomena in brittle materials. Overall, using the 3D-PDIFM as a modeling and simulation tool can help engineers and researchers analyze the behavior of glass panels under various impact scenarios, thus allowing for optimization of design parameters to improve impact resistance. [ABSTRACT FROM AUTHOR]

• Construct a fatigue life prediction model for flexible spoke non-pneumatic tire based on fatigue failure evaluation indexes. • The fatigue life prediction of flexible spoke non-pneumatic tire was carried out based on the J-integral method. • The Mises stress-based fatigue life prediction model having the highest fitting accuracy and prediction accuracy. To solve the complex problems of fatigue life of non-pneumatic tires, this paper constructs a fatigue life prediction fitting model for flexible spoke non-pneumatic tire based on fatigue failure evaluation indicators. The fatigue life prediction of flexible spoke non-pneumatic tire was carried out based on the J-integral method, and the effectiveness of the prediction method was verified by fatigue durability tests. The relationship between Mises stress σ r , maximum principal strain ε L , strain energy density W , strain energy density gradient G SED and fatigue life was obtained by numerical analysis methods. A fatigue life prediction fitting model for each evaluation indicator was established based on power function relationships, and a comparative analysis of the fitting accuracy and prediction accuracy of different fitting models was performed. The results show that the fatigue life prediction models based on Mises stress σ r , maximum principal strain ε L , strain energy density W , strain energy density gradient G SED all had high fitting accuracy and prediction accuracy, with the Mises stress-based fatigue life prediction model having the highest fitting accuracy and prediction accuracy. The development of the content of this paper has important theoretical significance and application value for the development of tire safety technology. [ABSTRACT FROM AUTHOR]

Commercial copy paper is a thin sheet material that has orthotropic constitutive behavior reminiscent of Al foils. Similar to Al foils, mode I crack tips in paper developed quasistatic, fully plastic, steady-state conditions even though plastic deformation in paper is not isochoric. The characteristic steady-state stress for crack growth depended on specimen orientation and contained a positive offset stress due to fiber bridging ( σ c = 37.3 MPa, σ offset = 6.0 MPa and σ c = 20.1 MPa, σ offset = 2.9 MPa for the machine and cross direction orientations, respectively). Orientation-dependent, reversed plastic zones were observed in the crack wake and transverse necking fracture processes were not present. • Steady-state, mode I crack growth was observed in single-edge notched specimens. • Steady-state process zone sizes were directly measured from full-field strain maps. • The crack growth was controlled by a characteristic steady-state stress. • The characteristic steady-state stress was offset because of fiber bridging. [ABSTRACT FROM AUTHOR]

• MLP, CNN, and DCNN models are proposed to inversely extract bilinear CZM parameters of sintered nano-silver ENF joints. • The DCNN model shows better accuracy in predicting CZM parameters compared with MLP and CNN models. • The DCNN prediction is not sensitive to the sample size of input data. • The time cost in the training process for the MLP model is the lowest, and highest for the DCNN model. The inverse identification of cohesive zone parameters is an important topic in the field of fracture mechanics. In this paper, three data-driven models, including multilayer perceptron (MLP), convolutional neural network (CNN), and dynamic convolutional neural network (DCNN), were presented to predict the cohesive zone parameters of sintered nano-silver end notched flexure (ENF) joints. Based on the construction of experimental and numerical datasets of load versus displacement curves, bilinear cohesive zone model (CZM) parameters of sintered silver joints are adopted as the prediction target. The investigation shows that MLP, CNN, and DCNN are all valid for predicting CZM parameters through load versus displacement curves with reasonable accuracy. However, DCNN has better prediction accuracy and performance than those of CNN and MLP models based on loss analysis, statistical indicator comparison, and K-fold cross-validation. DCNN can be adopted as the suitable surrogate model for CZM parameters inverse identification with high prediction accuracy. Otherwise, DCNN is also not sensitive to the load versus displacement curves data length. However, the computation efficiency of DCNN during the training process is not as high as that of MLP. Those three methods presented in this paper are very hopeful to be adopted for other inverse identifications of CZM parameters for various kinds of adhesive joints. [ABSTRACT FROM AUTHOR]

In this paper, the thermo-elastic fracture problems of functionally graded materials (FGMs) are thoroughly investigated based on a modified phase field model. In this model, the material constants and fracture toughness vary along a specified direction, the thermal conductivity and stiffness constants in the damaged regions are degraded by the phase-field variable, and the crack evolution is driven by the variation of elastic energy induced by the thermo-mechanical loading. Therefore, the temperature, mechanical and damage fields are coupled with each other. The validation of the present approach has been checked by comparing the present results with the analytical, numerical, and experimental results in literature. The examples of thermo-elastic tensile fracture and thermal shock cracking of FGMs are performed to investigate the influence of material heterogeneity and external thermal loading. Furthermore, the experimental phenomenon of crack deflection in FGMs has been captured by the present simulations. The present study provides a guidance for understanding the fracture mechanism, material design and safety assessment of FGM structures in engineering practice. • The thermo-elastic fracture of FGMs is studied based on a phase-field model. • Both the tensile fracture and thermal shock cracking of FGMs can be simulated. • Effects of material heterogeneity and heat load on fracture behavior are studied. • The present study guides the structural design of FGMs in engineering practice. [ABSTRACT FROM AUTHOR]

Long-distance gas pipelines are the most common means of transporting natural gas resources. However, the propagation of longitudinal ductile fractures in gas pipelines can result in catastrophic accidents, which must be avoided as much as possible. Crack arrestors can prevent or at least limit the rapid spread of longitudinal cracks by constraining the outwall of pipelines. Carbon fiber-reinforced composite material is one of the best candidates for crack arrestors because of its excellent strength and toughness. However, due to the significant variations in composite material performance, clear design criteria for determining the size of crack arrestors have not yet been developed. This paper presents a comprehensive design procedure for determining the geometrical parameters of composite material crack arrestors based on a finite element model of dynamic pipeline fractures under crack arrestor constraints. Pipeline crack propagation is accomplished using the cohesive zone model, and composite material failure is defined by Hashin criteria. A series of numerical simulations are conducted to assess the ability of crack arrestors to stop a growing crack in a gas pipeline. Ultimately, the minimum wall thickness and axial length of the effective crack arrestor are determined. The proposed design procedure enables the numerical design of composite material crack arrestors and supports safe pipeline operation. • The proposal of a numerical design procedure for composite crack arrestors. • Establishing a numerical model of pipeline fracture under arrestor's constraints. • Evaluating the performance of crack arrestors in arresting pipeline cracks. • The determination of the composite arrestors' geometrical parameters. [ABSTRACT FROM AUTHOR]

• Considering wear improved the accuracy of fretting fatigue life prediction. • Wear delays the crack initiation and propagation, leading to an increase in fatigue life. • Wear causes the crack initiation position to move away from the symmetry center. • Wear has little effect on crack propagation path. • The effect of wear is more important under low stress amplitude. Fretting fatigue is a common type of problem in the engineering fields. Due to its multiaxial characteristics, it leads to a shorter overall fatigue life compared to plain fatigue. Fretting fatigue is caused by the micro slip at the contact surface, which is always accompanied by interface wear. This paper presents a refined elastic numerical simulation method combining interfacial wear with continuum damage mechanics (CDM) and fracture mechanics to predict fatigue life. The crack initiation life is determined by damage evolution law and the initiation position is determined by the total dissipated energy. Crack propagation life and path can be predicted using stress intensity factor. The stress redistribution and geometric change of contact surface caused by wear are considered in the whole fatigue process. Results indicate that the fretting fatigue simulation method incorporating wear has higher accuracy compared with the experimental results in the literature. It is noteworthy that wear retards nucleation damage process and crack propagation. As stress amplitude decreases, fatigue life increases, and delay effect of wear becomes more obvious. Additionally, wear causes the crack initiation position to move out, but crack initiation region is still near the slipping zone and propagation path does not change. [ABSTRACT FROM AUTHOR]

[Display omitted] • A more accurate higher-order asymptotic solution of 3D V-notch and crack front tip fields is established theoretically. • The constraint effect in 3D fracture cannot be simply separated into in- and out-of-plane parts. • A new 3D fracture parameter A 2 T related to the out-of-plane stress factor T z is proposed. • The constraint levels of 3D specimens can be characterized and quantified by combining A 2 T with T z. As one of the most important topics studied in creep fracture mechanics, mechanics fields at 3D sharp V-notch front tip in creeping solids have drawn remarkable attention at present. In this paper, the higher-order asymptotic analysis is carried out for 3D sharp V-notch front tip fields in creeping solids subjected to mode Ⅰ loading, and a 3D higher-order term solution is theoretically proposed by introducing the out-of-plane stress factor T z to establish the 3D nonlinear governing equations of front tip fields. The present higher-order asymptotic solution for 3D sharp V-notch can naturally be degenerated to that for 3D crack. It is found that the stress exponents and angular distribution functions of higher-order terms for 3D notch and crack are highly related to T z. The proposed 3D higher-order term solution overall shows better agreement with the FEA results than the existing 3D leading-term solution and 2D higher-order term solutions available in the literature, especially for smaller notch angle and shorter ligament lengths. Based on the 3D higher-order asymptotic solution, a new fracture parameter A 2 T is given and combined with T z to characterize 3D constraint effect. It is noted that the effects of A 2 T and T z on 3D constraint are highly interlinked rather than simply separated into in-plane and out-of-plane parts. The present 3D higher-order asymptotic solution can promote the understanding and characterization of 3D constraint effect and is of great significance in the evaluation of 3D fracture behavior and structural failure assessment under creep conditions. [ABSTRACT FROM AUTHOR]

• An extended fracture mechanics-based model is proposed to simulate underground injection into multilayered rock strata. • Exact analytical solutions of SIFs and ground deformation for the crack problem are obtained. • Stiffness and stiffness variation pattern of the caprock layers have significant effect on the SIFs and ground deformation. Underground injection of liquid materials is a critical practice in geological engineering with various applications, such as geologic sequestration of carbon dioxide, deep geologic disposal of hazardous waste, and hydraulic fracturing for oil and gas extraction. However, these practices can induce ground heave and alter the stress field in the surrounding geo-medium. Understanding the mechanical behaviour of rock system during the injection is thus important for mitigating underground injection-induced adverse effects. In this paper, we propose a fracture mechanics-based model to simulate the underground injection process in multilayered rock strata. In this model, the injection region is idealized as a penny-shaped crack and injection process is simulated as pressurization of the crack. The crack problem is solved analytically by the General Kelvin's Solution (GKS)-based method for multilayered elasticity and Fredholm integral equation technique. Solutions are given for the key geophysical parameters including mode I/II stress intensity factors (SIFs) and ground displacements. Numerical studies are conducted to explore the role of material inhomogeneity of the multilayered rock strata on the induced ground heave and the SIFs at the crack tip. Our results demonstrate that the shear modulus and position of the hard caprock layer significantly influence ground movements SIFs, offering valuable insights for controlling injection rates and selecting appropriate injection sites. [ABSTRACT FROM AUTHOR]

• An experimental investigation of the delamination growth was presented. • Critical strain energy density (SED) approach forms the hypothesis of this paper. • Strain energy release rate at the crack onset and initial crack angle were studied. • Acoustic emission was used to give more insight into physics of delamination growth. • Delamination onset occurs before critical load obtained via experiments. In order to understand the physics of the delamination onset in laminated composites, an experimental investigation of delamination growth is presented. The main objective of this paper is to demonstrate that delamination onset occurs at lower values than G c defined by the ASTM standards, and that the strain energy release rate level at which the crack growth onset occurs under any mixed mode I/II loading is governed by the critical strain energy density (SED) approach. Quasi-static delamination experiments have been performed under mode I, mode II and mixed mode I/II loadings. The value of the strain energy release rate at the observed crack onset and the angle of the initial crack growth were correlated with the SED theory to test the validity. The acoustic emission was also used to provide more insight into the physics of the delamination growth. The investigation shows that the onset of delamination growth occurs at the strain energy release rate levels predicted by the critical SED approach, and well before reaching the critical strain energy release rate determined via delamination tests following the ASTM standards. Moreover, results indicated that the predicted angle of the initial crack for delamination onset was in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Highlights: • Fine equiaxed zone (FQZ) is a typical microstructure of fusion welded Al alloys with Zr. • FQZ is generally believed to degrade the cracking resistance of the fusion joints. • The fracture usually happens along the FQZ under static and cyclic loadings. Abstract Fine eQuiaxed Zone (FQZ) close to the fusion line is a common and unique microstructural feature for fusion welded high-strength Al alloys particularly when containing Zr element. It is well believed that the presence of FQZ can degrade the fatigue cracking resistance and tensile strength of the joints. Thus, a thorough knowledge on the formation and microstructure due to FQZ and resultant softening and failure mechanisms is necessary to be well understood on the damage tolerance and structural integrity of fusion welded joints. Current paper reviews the relevant aspects mentioned above as an important reference to be capable of correlating the microstructural response with service performance. Some potential solutions to coordinate the FQZ are therefore discussed. Furthermore, few papers up to date have focused on the fatigue and fracture mechanisms related with FQZ inside high-strength Al alloy fusion welds. By combining conventional characterization and numerical modelling approach, the high-resolution synchrotron radiation X-ray computed microtomography shows great potential in revealing the competition mechanism between FQZ and welding defects on the cracking behavior. [ABSTRACT FROM AUTHOR]

Highlights • A thermo-viscoelastic model is developed for the crack problem in an FGM. • SIFs of elastic/viscoelastic FGMs are compared to show the effect of viscosity. • Parametric studies are conducted to show the effect of gradient parameters. Abstract In this paper, a thermo-viscoelastic model is developed for the crack problem in an infinite, functionally graded half plane under a thermal shock. The moduli are assumed to be separable forms of both spatial coordinates and time, and two types of relaxation function of viscoelasticity are considered in this paper. By employing the Fourier transform and Laplace transform, coupled with the singular integral equations, the governing partial differential equations under mixed thermo-mechanical boundary conditions are solved numerically. The results show that the variations of stress intensity factors (SIFs) in viscoelastic functionally graded materials (FGMs) are significantly different than those in the elastic ones, which cannot be neglected in designing FGMs. [ABSTRACT FROM AUTHOR]

• This paper presents the fracture model calibration of SS275 hot-rolled thin plates, which involved quasi-static tests and finite element analysis. • The hardening model parameters were determined using the Swift law, while the ductile fracture model parameters were calibrated using the Hosford-Coulomb model within the linear damage framework. • The accuracy of the model was validated by comparing the results with the test data, and it was found that the highest fracture strain occurred in the uniaxial tension state. • The calibrated model was then used to predict the cycle life to failure in an extreme low cycle fatigue test, which was found to be 70 cycles. • The results indicate that the ductile fracture model performed well in predicting extremely low-cycle fatigue. • The paper's findings can be useful in predicting the fracture initniaon of engineering structures and components under multiaxial stress states, which can ultimately lead to improved designs and increased safety. The complexity of the loading conditions makes it challenging to accurately predict the damage evolution and resulting ductile fracture in materials and structures. This paper presents an application method to predict fracture initiation for low cycle fatigue of 4-point bending in structural steel SS275. The swift isotropic hardening law was used in the numerical simulation to account for large strain deformation. The damage indicator framework with the Hosford-Coulomb (HC) model was adopted to characterize the damage accumulation and fracture behavior. Uniaxial tension tests on specimens with various fracture modes were conducted to determine the material properties required for calibration of the plasticity model and fracture model param1eters. Non-linear finite element analyses were performed to identify fracture model parameters based on the loading path of fracture initiation. The presented HC model was applied to an extremely low fatigue test (less than 100 cycles) and demonstrated good accuracy in predicting fracture initiation for complex loading scenarios. [ABSTRACT FROM AUTHOR]

• An improved brittle fracture modelling using Lattice Particle Method. • A coupled SPH-LPM FSI method for solid fracture and free surface. • Implementation of SPH-LPM method in DualSPHysics for large-scale simulation. • Preliminary validation on a real fracturing concrete structure due to tsunami. This paper presents an improved failure model for simulating brittle fracture using the mesh-less Lattice Particle Method (LPM). By modelling the initial crack line using the Remove Bond (RB) approach as outlined in this paper, a new formulation is then developed for predicting the mode-I Stress Intensity Factor (SIF) near the crack tip. Compared to the conventional Remove Particle (RP) approach, it is found that the accuracy of the present SIF formulation based on the RB method is superior. A series of benchmark test cases are simulated to test the numerical accuracy and numerical convergence of the method. Finally, the LPM method is coupled with the Smoothed Particle Hydrodynamics (SPH) method for studying Fluid Structure Interaction (FSI) problems involving solid fracture and free surface. The coupled SPH-LPM method is implemented in the open-source code, DualSPHysics, which has been optimized for both CPU and GPU performances. Upon integrating LPM with SPH, the proposed FSI method is suitable for modelling fracture phenomena caused by natural hazards such as tsunami and flood. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new corrosion-fatigue crack growth rate model introducing damage is proposed. • A robust and efficient crack surface update method is proposed based on XFEM. • A fatigue life algorithm based on the cycle-by-cycle concept is developed. • The mixed-mode crack path and corrosion-fatigue life are accurately predicted. • The method is well applied to a typical ship structure. A fatigue crack growth rate model introducing corrosion damage is proposed in this paper, where the fracture parameter is modified by the damage variable and the exponential influence factor. The corrosion damage mechanism is coupled to the crack growth rate model, which quantifies the influence of the environment and reflects the interaction between corrosion and fatigue. To accurately predict the corrosion-fatigue crack growth life by the extended finite element method (XFEM), a simple crack surface updating method is developed. This method does not depend on the complex level set marching algorithm which often brings serious computational convergence problem, so it has good robustness and high efficiency. Moreover, the stress intensity factors at arbitrary crack tip can be calculated by combining the interaction integral method and the piecewise interpolation method, so it is suitable for the double crack-tip problem. The corrosion-fatigue crack growth life is calculated based on the cycle-by-cycle method and the corresponding algorithm is developed. The corrosion-fatigue crack growth life can be accurately predicted by calculating the corrosion damage and crack propagation length under each load cycle. In this paper, sufficient examples are given to verify the accuracy of the proposed method in simulating crack propagation path and predicting corrosion-fatigue life. Finally, this method is well applied to a practical engineering structure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Modeling of cutting forces while applying a slicing motion to the push-cutting process. [•] Analysis of state of stress at the cutting edge. [•] Stress Intensity Factors for cutting with a symmetrical and asymmetrical cutting knife. [•] Fracture toughness of the paper sheet material is determined through DENT test. [•] The new model is verified by sideways push-slice cutting stacked thin paper material. [Copyright &y& Elsevier]

• An analytical method to predict residual strength based on critical CTOA is proposed. • This method is validated by M (T) and C (T) specimens. • This method has successfully predicted the residual strength of stiffened panels. An analytical method to predict residual strength based on critical crack tip opening angle (CTOA) is proposed in this paper. According to a previous study, the plastic wake profile and then the stationary crack opening profile can be considered as a kind of crack growth resistance. The core idea of the proposed method is transferring critical CTOA to stationary crack opening profile based crack growth resistance curve. M(T) and C(T) specimens are taken to validate this method. All of these predicted results have an accuracy of 4%. In addition, the proposed method has successfully predicted the residual strength of rivet stiffened panels (the accuracy is 5%) by assuming that stiffeners are only geometry constraints of simple specimens that don't affect the crack growth resistance. It is worth stressing that no finite element analysis is used in this paper. [ABSTRACT FROM AUTHOR]

Continuum models of fracture should be equipped with a localization limiter to prevent pathological discretization sensitivity of finite element simulations. Moreover, stiffness recovery, called also crack closing effect, should be reproduced in the modelling of quasi-brittle materials when reversed loading is applied. In this paper the efficiency of two different established damage-plasticity models for concrete is assessed from the viewpoint of the two above-mentioned aspects. The first description is the so-called concrete damaged plasticity model, available in the ABAQUS package. In this model the plasticity theory is not only augmented with stiffness degradation and recovery, but also with the crack band approach and viscoplastic regularization. The gradient-enhanced damage description, which is the second one considered, can also be coupled to plasticity. In this model additional averaging equation prevents the pathological discretization sensitivity of fracture simulations. Two fields, displacements and averaged strain measure, are interpolated and suitable finite elements are programmed by the authors in the FEAP package. Basic concepts of the numerical analysis of the crack closing phenomenon are reviewed. Both models are capable of avoiding mesh-sensitivity, but it is achieved in a different manner and it is shown in the paper that the users of ABAQUS should employ the crack band options with particular care. Representative examples in the context of the examined issues are demonstrated: uniaxial tension of a bar and a cantilever beam. The results obtained using both the models are compared and the effects of regularization and crack closing are illustrated. [ABSTRACT FROM AUTHOR]

Upon realizing the importance of the sweat in controlling the performance of the interface crack between skin and flexible membrane, the effect of sweat on the crack opening under action of the far-field tensile stress is analysed in present paper. Application of the complex variable method and the principle of superposition gives the crack opening displacement and the stress intensity factors, which are functions of the surface tension, contact angle, location and size of the sweat. The location of sweat has important influence on the stress intensity factors, although it induces very little changes in the shape of the crack opening. Without or with the action of a small far-filed tensile stress, the sweat can induce the crack partial closure. With the increase of the far-field tensile stress, the crack opening displacement will be large enough to cause the disruption of the sweat, even induce the crack growth. So, the far-field tensile stress, which can split the sweat, is derived in present paper. [ABSTRACT FROM AUTHOR]

The three-part paper deals with energy-minimal multiple crack propagation in a linear elastic solid under quasi-static conditions. The principle of minimum total energy, i.e. the sum of the potential and fracture energies, which stems directly from the Griffith’s theory of cracks, is applied to the problem of arbitrary crack growth in 2D. The proposed formulation enables minimisation of the total energy of the mechanical system with respect to the crack extension directions and crack extension lengths to solve for the evolution of the mechanical system over time. The three parts focus, in turn, on (I) the theory of multiple crack growth including competing cracks, (II) the discrete solution by the extended finite element method using the minimum-energy formulation, and (III) the aspects of computer implementation within the Matlab programming language. The key contributions of Part-III of the three-part paper are as follows: (1) implementation of XFEM in Matlab with emphasis on the design of the code to enable fast and efficient computational times of fracture problems involving multiple cracks and arbitrary crack intersections, (2) verification of the minimum energy criterion and comparison with the maximum tension criterion via multiple benchmark studies, and (3) we propose a numerical improvement to the crack growth direction criterion that gives significant gains in accuracy and convergence rates of the fracture paths, especially on coarse meshes. Finally, the open-source Matlab code, documentation, benchmarks and other example cases are included as supplementary material . [ABSTRACT FROM AUTHOR]

This paper focuses on a new algorithm for the quasi-static simulation of unstable crack propagation in time-independent brittle material. The proposed approach is based on a combination of the standard Newton’s algorithm with a fictive path loading algorithm. First, a time step refinement process, associated to the Newton’s algorithm, enables us to efficiently detect the beginning of unstable crack extension. Then, a fictive path loading algorithm is performed to assess an estimation of the post instability solution. Finally, this estimated solution is used as initial guess in the standard Newton’s algorithm for the same time increment. The final converged solution satisfies both the mechanical equilibrium and the mechanical behaviour integration. This paper highlights several advantages of the proposed algorithm such as robustness, easy implementation on an existing Newton’s type solver, genericity for different unstable nonlinear physical problems. An application of this new method is presented for a smeared crack model, based on a local continuous damage formulation, devoted to the simulation of brittle nuclear fuel rupture. The efficiency of the proposed algorithm is demonstrated through a set of 2d and 3d simulation results. [ABSTRACT FROM AUTHOR]

This paper addresses the challenges in designing high pressure, durable, safe, and cost-effective vessels for storage of gaseous hydrogen and the role of fracture mechanics in meeting those challenges. The design life limiting material property for vessels made from tempered martensitic steel is the environment assisted fatigue crack growth rate (FCGR) that depends on ΔK, the load ratio, loading frequency, and the H 2 pressure. The effects of these variables individually and synergistically are explored in this paper. FCGR behavior at negative load ratios, R, of −1.0 and −0.5 were found to be comparable to those at load ratios of 0.1 and 0.2; the effects of load ratio appear to become stronger for R > 0.2. The effect of decreasing loading frequency, ν , on the FCGR behavior in H 2 gaseous environment is small for frequencies less than 1 Hz. FCGR behavior is shown to increase with gas pressure and the effect appeared to be highest in going from air environment to 10 MPa H 2 pressure and then it saturated at 45 MPa. The impact of these variables and others such as autofrettage, on the design life of H 2 storage vessels are explored. [ABSTRACT FROM AUTHOR]

• An extrapolation method is proposed to assess the DFT of the ideal cracks. • The K plane is used to illustrate the comprehensive sensitivity of the DFT to the two factors. • The influence of notch width on DFT is more pronounced than that of loading rate. • The propagation of cracks is governed by interactions between dynamic shear fracture and ASB. Existing work on size effects in the measurement of dynamic fracture toughness (DFT) has focused mainly on the overall geometric dimensions of the test specimens, while the effects of notch width and loading rate were not explored. In this paper, DFT experiments were conducted using Ti-6Al-4V alloy to study the effects of notch width effect and loading rate effect on its dynamic mode II fracture toughness. An extrapolation method is proposed to estimate the DFT of an ideal sharp crack, and the relationship between DFT, loading rate, and notch width is captured with a 3D spatial plane. Results revealed that the DFT decreases with a reduction of the notch width and increases with loading rate. The effects of notch width on DFT will be shown to be more sensitive compared to loading rate. The failure mode transitional behavior from ductile fracture to adiabatic shearing will be revealed through fractographic analysis of the microstructural evolution, which will elucidate the effects of loading rate on the failure mechanism of the material. [ABSTRACT FROM AUTHOR]

• A phase field method considering the initial state of quasi-brittle structure. • The initial equilibrium iteration addresses fuzzy stress prediction data. • Capable of transforming various initial states into a unified load format. • Offers strong compatibility with diverse phase field models. • The theory is straightforward and highly applicable to engineering. To solve the simulation problem of crack propagation in solid structures with initial stress, this paper proposes a phase field approach that considers the initial state of the quasi-brittle structure. By using the initial equilibrium iteration method, the estimated initial state of the structure, including initial stress, is transformed into internal stress loads of the structure. Thus, the problem of non-convergence caused by inaccurate initial state estimation of the structure in engineering calculations was solved, and an improved subproblem staggered iteration method was adopted to simulate crack propagation of the structure under external loads. The universality and computational accuracy of this method for different phase field models were verified by using pre made notched thin plates for the expansion of mode I and II cracks in different initial states. Among them, the calculation error using the PF_CZM model is within 1%, and the calculation error of the AT2 model increases with the initial stress, but is less than 7%. At the same time, the crack growth problem of cracked structures under different uniform initial stresses is accurately simulated, which reflects the applicability of this method to actual engineering. In addition, the study also verified the universal applicability of the adaptive refinement strategy proposed based on the AT2 model for other phase field models. [ABSTRACT FROM AUTHOR]

• The finite crack growth energy release rate is extended for anisotropic plane strain problem. • A single and constant parameter can predict the crack growth behavior of the DCB at different temperatures. • The relationship between the ductility of matrix and mode I interlaminar fracture toughness of composite is determined. The interlaminar fracture toughness of unidirectional fiber reinforced polymer composite material is temperature and crack growth history dependence. The non-constant interlaminar fracture toughness challenges the wide application of the linear elastic fracture mechanics-based approach for analyzing the interlaminar crack growth in composite material and structures. In addition, a quantitative relationship between the ductility of the matrix and interlaminar fracture toughness of the fiber reinforced composite is still highly desirable. In this paper, both pure resin and composite double cantilever beam (DCB) are tested at different temperatures. A finite crack growth energy release rate is used to analyze the interlaminar crack growth behavior of composite material at different temperatures. The plasticity of the composite DCB is modeled by Hill's anisotropic plasticity, with the properties determined from multiscale analyses. It is found that a single constant finite growth energy release rate can well predict the interlaminar mode I crack growth of composite material at different temperatures. The roles of the ductility of matrix, thickness of the DCB, and crack growth history on the interlaminar mode I fracture toughness of composite material are quantitatively determined by using the present method. [ABSTRACT FROM AUTHOR]

The phase-field method is based on the energy minimization principle which is a geometric method for modeling diffusive cracks that are popularly implemented with irreversibility based on Griffith 's criterion. This method requires a length-scale parameter that smooths the sharp discontinuity, which influences the diffuse band and results in mesh-dependent fracture propagation results. Recently, a novel approach based on the optimization on Riemann ian shape spaces has been proposed, where the crack path is realized by techniques from shape optimization. This approach requires the shape derivative, which is derived in a continuous sense and used for a gradient-based algorithm to minimize the energy of the system. In this paper, the novel approach based on shape optimization is presented, followed by an assessment of the predicted crack path in both isotropic and anisotropic brittle material using numerical calculations from a phase-field model. • Novel approach in fracture mechanics based on shape optimization is introduced. • Less computationally expensive approach than phase-field method. • Validation is performed by means of the phase-field method for fracture propagation. • Predicting the crack path successful even for anisotropic brittle materials. [ABSTRACT FROM AUTHOR]

• Finite element method for calculating material entropy generation based on the viscoplastic UMAT. • An entropy-based crack driving force was proposed within defined fracture process zone (FPZ). • A crack growth criterion based on cumulative entropy generation as crack grows a length of FPZ. • An entropy-based model was proposed to predict fatigue crack growth in GH4169 at high temperature. This paper developed an entropy-based approach to estimate the fatigue crack growth (FCG) behavior of GH4169 at high temperature. Firstly, systematic FCG experiments of GH4169 at 650 °C were conducted to obtain the experimental data. Then, a finite element analysis combined with Chaboche viscoplasticity and node release technology was developed to obtain cyclic stress–strain responses and entropy generation fields. Based on thermodynamic analysis, numerous discrete material elements as sub-systems were divided along the crack growth direction in simplified representative 2D middle section. Fracture process zone (FPZ) was defined equal to the size of discrete material elements (ρ) which can be determined by distribution of normal stress perpendicular to the crack plane. Subsequently, an effective cyclic entropy generation related to ρ was defined as the crack driving force. Effective cumulative entropy generation was calculated when crack increment was ρ and the results indicated that effective cumulative entropy generation float within a certain range. The average of all effective cumulative entropy generation values was defined as crack growth entropy. Finally, an entropy-based FCG rate model was established to estimate the FCG behavior of GH4169, and a good correlation between experimental results and model predictions are achieved for all the high temperature FCG tests. [ABSTRACT FROM AUTHOR]

• Method to predict fracture resistance of pre-strained materials using multi-axial fracture strain damage model. • Quantification of the pre-strain effect on the critical damage using plastic strain energy density of tensile data. • Experimental validation using published pre-strained SUS316 and SM490A test data. • Application of the developed method to irradiation-embrittled SUS316 material. This paper proposes a numerical method to predict fracture resistance of pre-strained materials, which is further applied to predict fracture resistance of irradiation-embrittled materials. The proposed method is based on a multi-axial fracture strain damage model using the fracture strain locus and critical damage. The key point is that the pre-strain effect on the critical damage is predicted using the pre-strain effect on plastic strain energy density of tensile data. Application to published experimental data for pre-strained SUS316 and SM490A shows that the predicted fracture toughness results agree well with experimental data. Based on published experimental results that the pre-strain effect on tensile and fracture toughness properties is similar to the irradiation effect, the proposed model is further applied to predict fracture toughness of irradiation-embrittled SUS316 material. Although only numerical simulation results are available, they show that maximum loads for irradiated specimens are higher than those for un-irradiated specimens. Furthermore, the effect of irradiation gradient along the crack growth direction is not so significant. [ABSTRACT FROM AUTHOR]

• A triple-phase-field model is proposed to capture the mixed-mode fracture behavior of bedded shale. • The method constructs the energetic driving force for compressive-shear cracks with Mohr-Coulomb criterion. • Lower-dimensional interfacial elements are applied to capture bedding fractures. • The approach is validated by comparison with published 2D numerical and 3D experimental results. Comprehending the intricate mechanics and fracture characteristics of shale holds significant importance in the realm of controlling the reconstruction of shale gas reservoirs. It is noteworthy that shale typically exhibits a distinctive bedding structure which sets it apart from other geological formations. Previously, single-mode cracks in shale have been widely studied by former researchers. However, its matrix and bedding may undergo various fracture modes under loading due to the bedded structure. To effectively capture the mixed-mode fracture behavior observed, a triple-phase-field model is proposed in this paper. Three phase-field variables are introduced herein to track pure-tension, tensile-shear, and compressive-shear cracks in the matrix and bedding, respectively. The energetic driving forces governing the propagation of pure-tension and tensile-shear cracks are formulated through the spectrum decomposition of positive strain tensor with its volumetric and deviatoric components; while the energetic driving force that propels the progression of compressive-shear cracks is derived by employing the Mohr-Coulomb criterion within the context of the negative strain tensor. For the bedding plane, lower-dimensional interfacial elements are adopted to capture the mixed-mode fracture. Based on the above triple-phase-field model, both 2D and 3D problems are modeled with good results. The heterogeneity of material is also considered. The simulations reveal that the compression strength and fracture mode of bedded shale are highly related to the orientations of the bedding plane and pre-existing fissure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fatigue crack path in porous materials predicted with a stochastic peridynamic (PD) model. • Heterogeneity is preserved without explicitly representing the detailed pore geometry. • The path independence of the PD J-integral in porous materials is verified. • Capable of capturing the influence of porosity on fatigue life and crack growth. • Simulated porosity-fatigue life dependence matches well with the experimental observation. Pores are a key type of concerns in additive manufacturing technology. They can significantly affect materials' fatigue resistance and fatigue crack growth in the structures. In this paper, an intermediately-homogenized (IH) peridynamic (PD) fatigue crack model is introduced for simulating the fatigue crack growth in porous materials. The effect of micro-scale heterogeneity on fatigue failure is preserved in the IH-PD model, where stochastically-generated pre-damage matches materials' porosity. The PD J-integral, a key parameter used to connect the fatigue simulation and the experimental measurements, is calculated under different porosities, and the independence of PD J-integral on its integration path is verified. Then, the PD fatigue crack model combined with the IH-PD material model is applied to study the dependence of the crack path and growth rate on porosity in compact tension alloy samples. The normalized fatigue life between experimental measurements and numerical results is compared. The normalized fatigue life-porosity relationship calculated from the IH-PD fatigue model matches the average trend of the experimental measurements. [ABSTRACT FROM AUTHOR]

Mixed mode fractures can be triggered by either multi-axial stresses or inclined cracks or both. Little research has been undertaken on J -integral for inclined surface cracks in plates under biaxial loading. This paper intends to determine the elastic and fully plastic J -integral for mixed mode fracture induced by inclined surface cracks in plates under biaxial loading conditions, using three-dimensional finite element method. Various geometries, biaxiality and material properties of cracked plates, including crack depth to plate thickness ratios, inclination angles, strain hardening exponents and biaxiality ratios, are considered. From numerical results, it is found that for elastic analysis, the equivalent influence coefficients increases with the increase of the relative crack depth and the magnitude of the biaxiality ratios. It is also found that for a given crack and plate geometry, the values of normalized fully plastic J -integral h 1 decrease along the whole crack front for different strain hardening exponents n with the increase of the inclination angles from 0 ° to 45 ° for uniaxial loading. It can be concluded that the method presented in the paper can determine the J -integral for inclined surface cracks in plates with reasonable accuracy. The results presented in the paper can equip practitioners for more accurate prediction of plate failures under various loads. [ABSTRACT FROM AUTHOR]

The paper is focused on fatigue crack propagation in the threshold area of the EA4T railway axle steel. Railway axles represent one of the most critical components for safety of trains. The main aim of this paper is to describe fatigue crack closure mechanisms in EA4T, which significantly influence the threshold value – a crucial parameter for determination of residual fatigue lifetime of railway axles. Investigated fatigue crack closure mechanisms are: plasticity induced crack closure, roughness-induced crack closure and oxide-induced crack closure. One part of this paper is focused on comparison of crack closure determined by NASGRO relationship (including plasticity induced crack closure mechanism only) with the experimentally obtained one. Difference between these two approaches is explained by presence of roughness and oxide induced crack closure. Based on theoretical models different sources of fatigue crack closure mechanisms was separated and evaluated. The significance of oxide-induced crack closure was confirmed based on experimental measurement of fatigue crack propagation in low humidity air. Finally, the effect of a reduced threshold value in low-humidity air on residual fatigue lifetime of railway axles is demonstrated. [ABSTRACT FROM AUTHOR]

Concrete structures are intentionally built with notches or incomplete joints in many engineering practices to deal with complex loading conditions. It is of great significance to improve the crack resistance and the installation of a channel steel plate ahead of the purpose-built notch (or joint) tip may serve such a purpose. This paper presents an investigation into the strengthening mechanism of installing a channel steel plate at the head of a notch for concrete beams against opening mode fracture failure. Both test and numerical studies have been undertaken and particular attention is given to the effects of key factors on the load carrying capacity and the failure pattern. Two types of three-point bending tests were conducted on concrete beams with or without channel steel plate reinforcement for a comparison study. The test results demonstrated the capability of channel steel plate measure for increasing the beam load capacity, and the interface debonding and matrix cracking were responsible for the eventual failure of reinforced concrete beams. Correspondingly, finite element based numerical models were established to investigate the progressive cracking in test beams and the strengthening mechanism by the installation of a steel plate. A damage-plasticity material model was used for simulating the cracking development in concrete, whilst two different approaches were adopted for the steel-concrete interface modelling: one assumed a perfect bond while the other incorporated a discrete thin layer of interface to allow for potential debonding and slippage. A comparison between the numerical and test results was given, and the effects of key factors on the performance of beams with steel plate measure were investigated through parametric numerical studies. The paper ends with some discussions on the strengthening mechanism and conclusions. [ABSTRACT FROM AUTHOR]

A hopper wagon is a type of railroad freight car used to transport many types of materials such as coal, ore, grain, ballast and minerals and bulk cargo. It is a complicated welded structure. When performing a safety assessment of cracks in a hopper wagon, it is necessary to consider fatigue crack propagation and fracture among the possible modes of failure. In any such analysis the stress intensity factors at crack tips are important parameters for estimating both residual life and criticality (residual strength). The purpose of this paper is to present engineering fracture analysis method for calculating the stress intensities for cracks in a hopper wagon. The advantage of the present approach is that it negates the need to explicitly model cracks. A crack of any size can be analysed using the original (un-cracked) finite element model. Furthermore, as cracks are not modelled explicitly a coarse mesh can be used to minimise the number of degrees of freedom, thereby reducing the analysis time. As such solutions for the stress-intensity factors can then be obtained quickly and easily for a variety of cracks and crack lengths using the original uncracked finite element analysis. The interaction between neighbouring cracks growing towards each other have been considered in this paper. Comparing the values of stress intensity factors computed using traditional finite element, the results obtained by new method presented in this paper suggest an agreement of within 3.5%. Therefore, this approach is sufficiently satisfactory to enable engineering estimates for residual strength (safety) and residual life. The method used in this paper is approximately ten times faster than computationally expensive methods. [ABSTRACT FROM AUTHOR]

Linear elastic fracture mechanics has been widely employed for fracture analysis of cracked pipes. For ductile metal pipes, the existence of plasticity eases the stress concentration at the crack front, which increases the fracture toughness of the pipe. Therefore, when using linear elastic fracture mechanics to predict the fracture failure of ductile pipes, the plastic portion of the fracture toughness should be excluded. This paper intends to derive an analytical model of elastic fracture toughness for ductile metal pipes with circumferential external surface cracks under combined axial tension and bending. The derived elastic fracture toughness is a function of crack geometry, material properties and loading conditions of the cracked pipe. The significance of the derived model is that the well established linear elastic fracture mechanics can be used for ductile materials in predicting the fracture failure. It is found in the paper that, the elastic fracture toughness increases with the increase of the internal pressure of the pipe and that an increase in fracture toughness and yield strength of the pipe materials will result in a more ductile and brittle pipe failure respectively. The derived analytical model enables more accurate prediction of fracture failure of ductile metal pipes with circumferential external cracks. [ABSTRACT FROM AUTHOR]

Brittle fractures caused by accidental or environmental damage of high-strength steel bars are occasionally reported in civil engineering. To analyse such ruptures, knowledge of bar plane strain fracture toughness is needed. Unfortunately, plane strain fracture toughness cannot be measured as bar diameters of commercial bars are not compatible with the thickness requirements of standardized fracture specimens according ASTM E399. The ASTM E1304 is less restrictive by using short bar specimens (SBS) but these can be ineffective with very brittle steels. This situation can be overcome, as shown in this paper, by modifying the SBS specimen. A second aim of this paper is to provide several examples of how to analyse brittle fractures of commercial high-strength steel bars considering knowledge of its plane strain fracture toughness. Direct and indirect analyses have been carried out. [ABSTRACT FROM AUTHOR]

• A numerical scheme to obtain C (t)-integral considering residual stress effect is given. • Eigenstrain and mechanical loading induced residual stress effects on C (t)-integral and transition time are computed and compared. • Tensile and compression residual stresses on C (t)-integral are studied. • Effects of nonproportional loading on C (t)-integral and transition time are confirmed and presented. Nonproportional loading and residual stresses effects on creep crack tip fields are important topics in fracture mechanics at elevated temperature. In this paper, nonproportional loading and residual stresses effects on creep crack tip fields are systematically investigated based on the novel interpretation of C (t)-integral considering residual stress. With the numerical implementation of the corrected C (t)-integral considering residual stress, the eigenstrain and mechanical induced residual stress effects on the creep crack tip fields are studied. We find that C (t)-integral level is affected remarkably in the presence of residual stress regardless of eigenstrain or mechanical induced residual stresses for creep crack tip under small scale creep. However, level of C *-integral is not significantly influenced under the effects of residual stresses in presence of large-scale creep although the transition creep time is remarkably changed. Otherwise, C (t)-integral is highly affected by loading path under small scale creep. However, C *-integral is independent of the loading path if the creep time is long enough. Nonproportional loading effect on C *-integral is very limited for creep crack tip field according to our study. The investigation given in this paper could deepen the understanding the effects of residual stress and nonproportional loading on the creep crack tip field. [ABSTRACT FROM AUTHOR]

Corrosion, manufacturing defects or complex stress state can induce inclined surface cracks on pipes that lead to failure by mixed mode fracture. Very few studies have been undertaken on stress intensity factors for inclined cracks with mixed modes. This paper presents a combined J integral and finite element method to determine the stress intensity factors for inclined external surface cracks in pressurized pipes. A meshing technique is proposed to model the complex region around the crack. To facilitate the practical use of the proposed method, formulae for the influence coefficients of stress intensity factors with mixed modes are developed. Based on numerical results, it is found that the influence coefficients of Mode I and equivalent stress intensity factors decrease with the increase of the inclination angle along the whole crack front whilst those of Mode II and Mode III reach the maximum when the inclination angle is 45°. It is also found that the influence coefficients of all three modes increase with the increase of crack relative depth along the whole crack front. The results presented in the paper can be used by practitioners to assess the fracture conditions of both brittle and ductile pipes. [ABSTRACT FROM AUTHOR]

• Quantified the effect of Hill anisotropic plasticity on J-Q characterization of semi-circular surface cracks. • Demonstrated that the isotropic and anisotropic J – Q parameters can significantly diverge, especially, when crack planes are misaligned with respect to the material coordinate system. • The results are important for providing accurate predictions of failure in pipeline steels that often show significant plastic anisoptropy. In this paper, the J - Q two-parameter characterization of Hill-anisotropic elastic–plastic crack-front fields are examined for surface cracked plates under uniaxial tensile loadings. A method for two-parameter characterization crack-front field in anisotropic plastic materials is presented. Extensive three-dimensional elastic–plastic finite element analyses were performed for semi-circular surface cracks in a finite thickness plate, under remote uniaxial tension loading conditions. Surface cracks with relative depths a / t = 0.2, 0.6 were investigated. The loading levels spanned from small-scale to large-scale yielding. Different crack orientations with respect to the material coordinate directions were also considered. In topological planes perpendicular to the crack front, the crack-front stress fields were obtained. In order to facilitate the determination of Q -factors, modified boundary layer analyses were also conducted. The modified boundary layer analyses were adapted to account for plastic anisotropy. The J - Q two-parameter approach was then used in characterizing the elastic–plastic crack-front stress fields along these 3D crack fronts. Complete distributions of the J -integral and Q -factors for a wide range of loading conditions were obtained. The results indicate that the J – Q characterization is applicable to Hill-anisotropic plastic materials and provides good estimate for the crack-front constraint loss experienced under large-scale yielding. It was also observed that the isotropic and anisotropic J – Q parameters can significantly diverge, especially, when crack planes are misaligned with respect to the material coordinate system. This highlights the importance of the consideration of plastic anisotropy when performing constraint-based fracture mechanics analyses. [ABSTRACT FROM AUTHOR]