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Abstract: Continuum damage mechanics (CDM) is used to describe the post-elastic behavior of low-basis-weight paper. The relevance of undertaking studies of the mechanical behavior of low-basis-weight paper is that it enables characterization, optimization and quality control. In accordance with a CDM theory, an internal variable is introduced that represent the degree to which the material has degraded in a continuum sense and details inherent in a damage evolution law contain information about the rupture mechanism. To account for long ranging micro-structural effects, because of the fiber structure in the paper material, a non-local formulation of the constitutive law is considered. Of particular interest is the fracture toughness of the material, i.e. the ability to resist further crack propagation, as it is often a good measure of flaw tolerance and durability in the context of paper. The constitutive model discussed is verified against tensile tests on rectangular paper specimens containing pre-fabricated cracks. Acoustic emission was used to study the damage evolution in paper specimens during tensile loading. An orthotropic material description has been utilized. The model is contrasted with a purely isotropic formulation. It seems that for the type of problem analyzed in this work, an orthotropic material description does not significantly improve the predictive capability as compared to an isotropic formulation. It is concluded that the model can be used to evaluate the influence of arbitrary defect geometries, defect size and loading conditions and can easily be incorporated into a finite element code. [Copyright &y& Elsevier]

Understanding the formation of impact craters on planetary surfaces has fundamental importance in geology, impact dynamics, and planetary sciences. The finite element-smoothed particle hydrodynamics (FE-SPH) adaptive method combines the advantages of smoothed particle hydrodynamics (SPH) and finite element method (FEM) in solving hypervelocity impact (HVI) problems. Employing FE-SPH adaptive method is a new idea for the analysis of planetary impact cratering which is different from impact-simplified arbitrary Lagrangian Eulerian (iSALE). In this paper, we establish a complete numerical model of planetary impact cratering through the FE-SPH method, including material failure criterion, thermodynamic analysis, gravity preloading, etc. We reproduce the numerical results by Collins et al. (2012) and highly consistent results are obtained through comparative analysis. This study simulates the formation process of simple and complex impact craters, and the temperature, pressure, density, and geometric shape of the impact zone can be quantitatively obtained. We further analyze the distribution of polymorphs and rock fragmentations in the impact zone based on the theories of shock metamorphism. The proposed analysis method may assist geologists in conducting geological studies. • We establish a complete numerical model of planetary impact cratering different from iSALE. • We analyze the distribution of high-pressure polymorphs based on shock metamorphism. • The FE-SPH model has higher numerical precision for planetary cratering impacts. [ABSTRACT FROM AUTHOR]

Bending-active elastica beam is a structural configuration that is based on the elastic deformation of an initially straight beam. This deformation occurs when horizontal displacements are applied to a sliding support, causing the beam to bend into an arched shape. Previous research has focused on the stability of small-scale bending-active structures, thus not considering material strength, which is crucial in real-scale applications and structural design. This paper investigates the short-term structural behavior of bending-active elastica beams using pultruded glass fiber-polymer composite profiles, as used in real-scale structures. A series of short-term bending and service load application experiments were performed considering different bending degrees and loading scenarios. These results were used to validate finite element modeling. They demonstrated that steeper bent beams experience material failure, while shallower ones exhibit snap-through buckling. Material failure initiates on the tensile side of the beams, with cracks initiating at locations of maximum curvature. Higher bending degrees and symmetric loading result in higher maximum loads than lower bending degrees and asymmetric loading. A strain-based failure criterion, which can serve for structural design, is derived. [ABSTRACT FROM AUTHOR]

In this paper, crack growth in orthotropic materials subjected to dynamic loading is numerically studied using an adaptive phase-field method. The study starts with a coarse structured mesh and the adaptive refinement strategy based on a user-defined threshold on the phase-field variable is proposed for computational efficiency, and variable-node elements are employed to treat the hanging nodes as a result of local adaptive refinement. The Hughes-Hilbert-Taylor (HHT) time integration scheme is adopted for temporal discretization. The directionality of orthotropic materials is represented by a penalized second-order structural matrix, which is incorporated in the crack face energy density. Through numerical examples, the influence of the material orientation on the dynamic crack growth in orthotropic materials is studied and the reliability of the proposed framework is validated. • An adaptive PFM is proposed to simulate dynamic crack growth in orthotropic materials. • Time integration method HHT is combined with a staggered solving scheme. • A robust local adaptive refinement strategy is used based on a phase-field threshold. • Variable-node elements are used to overcome incompatibility in the refined mesh. • Performance of the proposed framework is demonstrated by numerical examples. [ABSTRACT FROM AUTHOR]

This work presents a novel numerical methodology to model the degradation and failure of composite materials like GFRP submitted to monotonic and high cycle fatigue loads. This is done by using the Serial–Parallel Rule of Mixtures homogenisation technique together with a proper mechanical characterisation of the constituent materials of the composite. This paper also proposes an efficient way of estimating the fatigue properties of each of the material constituents (fibre or matrix) to comply with the experimental results obtained at composite level; this enables to estimate the fatigue strength of any stacking/orientation of fibres with only one mechanical characterisation of the material properties. A comparison of the results obtained analytically and experimentally for GFRP is presented. The results show the applicability and accuracy of the proposed methodology in this field. [ABSTRACT FROM AUTHOR]

Fracture toughness is an important parameter for measuring material properties in industry. In order to obtain data on the fracture toughness of a material it is often necessary to carry out a large number of fracture toughness experiments. The cost of the experiments is high and the experimental process is cumbersome. Moreover, in practice, there are often not a large number of materials that meet the requirements for the experiment. The relationship between different experimental ambient temperatures and fracture toughness can be determined by determining the reference temperature T 0 in the master curve method. In this paper the load-displacement curves of the specimens are obtained using finite element analysis. Determine the J integrals corresponding to the initiating load P int and the maximum load P c on the load-displacement curve using the Load Slope Compliance Changing Rate method. Determine the reference temperature T 0 in conjunction with the single temperature method. On the one hand, in order to validate the method, finite element analyses were performed on specimens of different thicknesses, temperatures, materials and types. This method was also applied to obtain fracture toughness data and to determine the reference temperature T 0. On the other hand, combining the master curve method and combining the experimental data of 16MnDR, 16MnR and 20MnMoNi55 ferritic steels were verified. The experimental results show that the results predicted by this method are in good agreement with the actual results. However, it has a certain conservative type. It provides a good solution for practical engineering. The accuracy of fracture toughness and reference temperature of ferritic steels of different thicknesses can be verified by few experiments. • The study found a Load Slope Compliance Changing Rate method for determining the specimen initiation load P int and critical load P c. • It is shown that φ in P int = P 0 + φ × (P c − P int) (0< φ <1) is not a fixed value. • The master curve for the predicted reference temperature works well and is able to include almost all experimental data for values less than K Jc(limit). • P int and Pc determined by CCR method have a quadratic relationship as the thickness changes. [ABSTRACT FROM AUTHOR]

The failure assessment diagram (FAD) is a widely used tool for evaluating the fracture acceptance of structural components. In addition to linear elastic fracture mechanics, elastic-plastic fracture mechanics, and limit load analysis, the ASME Code incorporated FAD as an alternative safety evaluation method for flaws in nuclear pipes starting from 2004 edition. This paper conducts a series of finite element elastic-plastic fracture mechanics analyses to establish the specific J –based FAD curves considering various loading and geometry conditions for ferritic pipes containing various circumferential flaws. By comparing with the suggested FAD of ASME Code Section XI - Appendix H, it is found that the radius-to-thickness ratio of pipes and the flaw depth influence the applicability of FAD, but with minor effects of crack length. In addition, the effects of material properties between base metal and weld materials on FAD are also discussed. The result of this work could be a reference when applying the FAD to evaluate the flawed piping for nuclear power plants. • The applicability of ASME FAD for ferritic piping has been investigated. • Specific FAD curves for various flawed piping conditions are calculated by conducting a series of elastic and elastic-plastic finite element analyses. • The ASME FAD is applicable for various loading combinations, pipe geometries and flaw sizes, but affected significantly by material properties. [ABSTRACT FROM AUTHOR]

Despite substantial advancements in optimizing structural designs for stiffness, the field of design against fracture is still in its early stages. This paper introduces a fundamental and standardized paradigm for structural design against brittle fracture, achieved through the minimization of the energy release rate G within the framework of linear elastic fracture mechanics (LEFM). By leveraging the Griffith criterion expression and the total potential energy in LEFM, we propose an efficient approach for structural optimization that enhances the toughness of architected materials. The energy release rate G is evaluated a synergistic application of finite element analysis and finite difference methods, yielding a precision of 0.6% compared to benchmarks in published handbooks. We demonstrate significantly reduced G values compared to standard stiffness and stress-oriented topology optimization, which directly contributes to increased toughness. To comprehensively analyze the fracture process encompassing damage, crack initiation, propagation, and failure, we employ post-processing phase field fracture modeling on the optimally designed architected materials. By performing multi-objective optimization of the stiffness and energy release rate G , the toughness and extreme load-bearing capacity can be simultaneously improved. The resulting perforated architecture effectively outperforms homogeneous structures in both toughness and peak load. Additionally, we extend our analysis to various configurations, such as non-center cracks, pure shear loading, and adherence to the standard 3D compact tension ASTM E-399-72. The designed structures are additively manufactured and experimentally validated, demonstrating a toughness increase of over 10 times compared to stress-based design. These contributions offer promising prospects for advancing the design of future engineering structures and materials with a favorable balance of critical fracture resistance characteristics. [ABSTRACT FROM AUTHOR]

• Shear bands' morphology in amorphous polymer under four-point bending is concerned. • Physical mechanisms of detour and strength decay of bands at intersections are analyzed. • Constitutive model can predict the morphology of shear bands under four-point bending. As a significant means of plastic deformation in polymers, shear bands play a crucial role in material failure and performance optimization. In this paper, the finite element method is utilized to numerically investigate the morphology of shear bands in an amorphous polymer plate under plane strain four-point bending. Amorphous polymers are characterized by the elastic-viscoplastic constitutive relationship that takes into account the effect of pressure on yielding, including intrinsic softening and subsequent orientation hardening. The impact of material parameters including intrinsic softening, orientation hardening, and initial imperfections on the evolution of shear bands and the undulations of the specimen's surface are explored in detail. In addition, the physical mechanisms responsible for the detour and strength decay of shear bands after passing the intersections are described. It appears that intrinsic softening is the driving force promoting the detour of shear bands at intersections, while orientation hardening is the driving force inhibiting the detour. By comparing the simulations with experimental observations, it is demonstrated that the model can qualitatively depict the morphology of the shear band during the four-point bending of amorphous glassy polymers. [Display omitted] [ABSTRACT FROM AUTHOR]

Following the current trend towards the lunar exploration and habitation, this study focuses on the development of efficient arch forms to be adopted for future long-span shielding structures on the lunar surface. More specifically, the static behaviour of the optimised, varying-thickness arches (VTAs), produced by a previously proposed iterative form-finding algorithm based on limit thrust-line analysis under gravitational and seismic loading is examined herein. These form-found arches are assumed to be constructed by laser-sintered additive manufactured lunar regolith. This paper starts with the visualisation of the limit thrust line using finite element analysis (FEA) on constant-thickness arches (CTAs). Subsequently, it presents the results from FEA on both VTAs and CTAs where it is observed that the original VTAs need to be geometrically enhanced, by thickening certain weak areas of their cross-section in order to minimise the local principal stresses and strain energy. The work proceeds with the quantification of the efficiency of the enhanced VTAs against their CTA counterparts, in both terrestrial and lunar gravitational environments. The most efficient enhanced VTAs are selected and recognised as the best structural forms for either terrestrial or lunar applications among all the arches examined in this research. Eventually, the real capacity of those most efficient arches against lateral loading is attested by means of pushover analysis. As expected, it is found that the geometric enhancement has significantly increased their structural capacity. • Enhanced varying-thickness arches (EVTAs) are more resilient than simple VTAs for a given lateral load. • EVTAs are structurally more efficient than their CTA counterparts in partial gravity environments. • Terrestrial EVTAs experience material failure before reaching their design load. • Lunar EVTAs can withstand up to 90% more load than their initial design load. [ABSTRACT FROM AUTHOR]

The property measurement and structure optimization of composite materials are difficult topics due to the diversity of combinations of composite constituents and complexity of their application environments. The distribution of composite constituents and heat sources can cause heat aggregation phenomenon which may lead to failure of materials. In this paper, we first propose a deep learning-based surrogate model (DLBSM) which can quickly and accurately achieve the end-to-end prediction between the layout of composite materials under multiple heat sources and its temperature field. The prediction result depicts that the coefficient of determination for the maximum and average temperature of all cases exceeds 0.996. Then, the layout optimization is transformed into a combinatorial optimization problem, and the DLBSM is combined with optimization algorithm to optimize the maximum temperature, temperature gradient, and uniformity of the temperature field. The optimized maximum temperature and temperature gradient are significantly reduced, while the temperature uniformity is improved. These enhancements effectively reduce the probability of failure in composites. This approach can significantly improve the efficiency of thermal behavior prediction of composite and its layout optimization compared with finite element method (FEM). [ABSTRACT FROM AUTHOR]

• Mode II fatigue crack growth is characterized at the steel-to-composite interface. • Displacement and load controlled ENF and 4ENF test methods are compared. • Novel method is proposed to determine crack growth by shear strains from DIC. • Friction and geometrical non-linearity is considered by finite element models. In this paper, mode II fatigue crack growth properties of the composite-to-steel interface are characterised through different test configurations, namely ENF and 4ENF tests. Different loading types including force control and displacement control methods are compared. An innovative shear strain based method is proposed for monitoring the mode II crack growth at the bi-material interface through Digital Image Correlation (DIC). A 3D finite element model with Virtual Crack Closure Technique (VCCT) is built and used for obtaining the strain energy release rate (SERR) to investigate the effect of geometrical nonlinearity, friction at the interface and steel yielding, as well as to verify the mode mixity. The results show that the standard 3-point bending ENF specimen can be unstable under force control and sweeps narrow SERR range by a single test under displacement control. The 4-point bending 4ENF test shows stable crack propagation and clear SERR developing trend. More pronounced geometrical nonlinearity and friction effect exist for 4ENF test which can be considered when interpreting the Paris curves by a nonlinear finite element model. [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]

• The CRTS Ⅲ slab track model with prefabricated cracks is established by extended finite element method. • The stress intensity factors (SIFs) at the tips of cracks on the track slab under train load are solved. • The effects of the crack length and depth on the SIFs of three types of cracks are discussed. • The variations of crack growth rate calculated by Paris' semi-empirical during service are analyzed. Microcracks may occur in Chinese Railway Track System type III (CRTS III) ballastless track slabs during service, and it is necessary to investigate their potential propagation under train load, which could lead to slab deterioration and affect the durability of the track structure. In this paper, based on the fracture mechanics theory, the stress intensity factors (SIFs) at the tips of transverse crack, longitudinal crack and vertical crack on the CRTS III track slabs under train load are solved by the extended finite element method (XFEM) in Abaqus software. The changes of SIFs at the crack tips during the passage of the train are analyzed, and the effects of the crack length and depth on the SIFs of the three types of cracks are discussed under train load. Crack growth rate is calculated using Paris' semi-empirical law to estimate slab life. The results show that the train load contributes to the propagation of transverse and vertical cracks in the vertical direction and inhibits the longitudinal cracks. When the middle of the sixth vehicle is above the crack, the SIFs at the tips of the crack reach their maximum values. The SIF of vertical cracks exceeds the fracture toughness at a certain depth. The fatigue load cycles calculated by Paris' semi-empirical law suggest that maintenance will not be required due to insufficient propagation under train load during service. [ABSTRACT FROM AUTHOR]

Structural integrity analysis for reactor pressure vessel (RPV) nozzles has been a vital issue due to the irradiation embrittlement and especially the discontinuity of geometry in RPV nozzles, which may cause a higher stress concentration and influence the structural integrity of RPV nozzles. For the linear elastic fracture mechanics (LEFM) analysis of the RPV nozzle, a postulated crack with a specific crack depth is presumed to evaluate the stress intensity factors (SIFs) whose crack depth does not grow during LEFM analysis. Thus, this paper would discuss the crack propagation for the postulated crack with a specific crack depth under the different reference temperature of nil-ductility transition (R T N D T ), and the SIFs on the specific crack depth are also calculated. In recent research, the extended finite element method (XFEM) was developed, which is based on the enrichment solution space to simplify the computational fracture mechanics with the crack propagation of various discontinuities, and can be used to evaluate the crack propagation of RPV nozzle with a specific crack depth under R T N D T of −23.89, −10.89, 0.89, 2.69, and 2.89 °C. To investigate the crack propagation and structural integrity of RPV nozzles, the finite element analysis of Taiwan domestic boiling water reactor (BWR) nozzles containing the postulated circular corner crack with depths of one-fourth and one-tenth thickness along the 45° path from the tip of the nozzle corner is engaged. The present result shows that the crack was growing when the R T N D T was 0.89 °C and. In addition, the XFEM calculation of the SIFs for the specific crack depth is similar to the LEFM results. • The RPV nozzles with postulated cracks were established to investigate crack propagation through XFEM. • The differences in RT NDT were used to evaluate the fracture toughness and discuss the crack propagation for RPV nozzles. • The stress intensity factors (SIFs) obtained by XFEM, LEFM, and the ASME BPVC were compared. • The XFEM analysis would overestimate SIFs more than the ASME BPVC and the LEFM. [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]

[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]

• A simulation of multiple transverse ply cracking in laminates is presented. • Many phase-field variables are used, each one describes the crack of the layer. • Some interesting phenomenons when the cracks appear at different layers of the structure are shown out. The phase-field theory is a well-known mathematical model for solving interface problems, including crack problems in fracture mechanics. In this study, the formula is derived by variational approaches based on the Reissner-Mindlin plate kinematics and the multi-phase-field theory for simulation of the buckling phenomenon in cracked laminates. Phase-field parameters are defined independently in different plies of laminate to capture the crack behavior of each ply. Simulation is carried out to numerically investigate the stiffness reduction and buckling behavior of transverse cracked laminated composite plates. This paper focuses on the consideration of laminated composite plates, which have a crack in each layer. Therefore, this work is more complicated than the case of the plate has one crack throughout the plate thickness. The significant advancement of the phase-field approach for laminated composite plates with complex crack geometries is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract In order to prevent well leakage in high temperature and high pressure (HTHP) wells, pressure test is a very important leak prevention operation that causes artificial high-pressure environment in wellbore. However, failure of wellbore equipment due to harsh condition is a common problem that brings great economic losses. Ram blowout preventer (BOP) is an important component of wellbore integrity, which is subjected to heavy loads from the test gas and the push rod during the pressure test. Therefore, the serious stress concentration of ram BOP induced by heavy loads and complex geometry is a major reason of fracture. Hence, the focus is to find out the fracture mechanism of ram BOP with experimental method and finite elements (FE) model in this paper. A series of damage inspection and strength test of ram BOP is carried out to find out the fracture characteristics. Based on detection information, FE analysis is conducted to analysis stress distribution and fracture reason of ram BOP. The results show that the maximum stress exceeds the yield strength (705 MPa) of the material under the actual working condition. Serious stress concentration at the notch root of the ram BOP can be easily caused by test pressure (from test gas) and contact pressure (from push rod). Both experimental method and FE analysis show the characteristics of ductile fracture obviously. Stress concentration at notch root is very sensitive to the test pressure. The work presented in this paper can provide basis and reference for preventing failure of ram BOP and improve efficiency and production. Highlights • A three-dimensional finite element model of ram BOP is established. • Stress distribution of ram BOP during service is expressed in finite element model. • Stress distribution of ram BOP is investigated under different conditions. • Stress concentration phenomenon is analyzed at different test and contact pressure. [ABSTRACT FROM AUTHOR]

Abstract In this paper, compressive material tests on unconfined/confined resin and steel reinforced resin were experimentally evaluated in order to validate the numerical results. The uniaxial model which combines damage mechanics and Ramberg-Osgood relationship is proposed in this paper to describe the uniaxial compressive behaviour of resin and steel reinforced resin. Numerical homogenization is conducted to predict the tensile and shear behaviour of steel reinforced resin after validated by compressive material test results. The friction angle β , the ratio of the yield stress in triaxial tension to the yield stress in triaxial compression K, and the dilation angle ψ of the linear drucker-prager plastic model are obtained based on experiments and numerical homogenization simulation. The confinement effects on resin and steel reinforced resin could be effectively simulated by combing above parameters and uniaxial compressive model. Finite element simulations on unconfined/ confined resin and steel reinforced resin material tests were conducted to validate the material parameters proposed in this paper. A good agreement is observed, indicating the model and parameters proposed in this paper could be effectively used in the finite element simulation of injected bolts. [ABSTRACT FROM AUTHOR]

Abstract The local cross-section behaviour of stainless steel channel sections under the combined actions of axial compression and minor axis bending moment is investigated in the present paper and its companion paper, based on a comprehensive experimental and numerical study. Two channel section sizes were considered in the experimental programme, with the test specimens laser-welded at the two flange-to-web junctions from hot-rolled EN 1.4307 and EN 1.4404 austenitic stainless steel plates. The experiments involved initial local geometric imperfection measurements and 15 eccentrically loaded stub column (combined loading) tests. The loading eccentricity was varied to achieve a range of ratios of axial compression to minor axis bending moment; both orientations of bending (web in compression and web in tension) were considered. The test setup and procedures, together with the key experimental observations, including the load-carrying and deformation capacities, load-end rotation histories and failure modes, are fully reported. A finite element simulation study is then presented, in which the models were first validated against the obtained test results and then employed, in the companion paper, for parametric investigations and the assessment of design provisions. Highlights • Laser-welded stainless steel channel sections under combined compression and minor axis bending moment has been studied. • An experimental programme including 15 combined loading tests has been carried out. • Finite element models have been developed and validated against experimental results. [ABSTRACT FROM AUTHOR]

Abstract Gear weight optimization is mainly through thin-web and hole in gear foundation. In this paper, an analytical-finite-element model for calculating time-varying mesh stiffness of spur gear pairs with complicated foundation (thin-web and holes) and crack is developed. The pinion and gear foundations are simulated as cylinders and modeled by three-dimensional finite element. The tooth pair is equivalent to a spring and mesh stiffness of a tooth pair is obtained by potential energy method. The spring is rigidly coupled with the pinion and gear foundations. Then, three type examples are presented to verify the model. The first type example is three spur gear pairs with solid foundation. The second type example is gear pairs with thin-web and web holes. And the third example is a gear pair with the cracked foundation. The analysis results show that the model proposed in this paper is applicable and efficient for spur gears with complicated foundation and crack. Finally, the time-varying mesh stiffness is also studied to reveal the effects of web widths, web hole radii and crack lengths. Highlights • An analytical-FE model for calculating time-varying mesh stiffness of spur gear pairs is developed. • Mesh stiffness is compared with that from finite element (FE) method. • The effects of cracked foundation are considered. • Mesh stiffness under different cases are analyzed. [ABSTRACT FROM AUTHOR]

Abstract It is frequently observed that long cracks in sea-ice tend to form between parallel channels during ice management operations. The long cracks that develop play an important role in reducing the size of the managed ice floes, which is one of the main goals in an ice management operation. However, the fracture mechanism behind these long cracks remains unclear. To address this issue, a comprehensive study is reported here in two associated papers. In the current paper (i.e., Paper I), an edge-crack theoretical model is proposed to elucidate the parallel channels' fracture mechanism. The proposed theoretical model is partially based on theories regarding ship – level ice interactions and partially based on previous studies on the general ice fracturing mechanism. The edge-crack theoretical model is extensively examined using a separately developed numerical scheme based on the eXtended Finite Element Method (XFEM), which allows for the existence of a singularity field and displacement jump within conventional Finite Elements (i.e., FEM). The numerical scheme is benchmarked against known asymptotic analytical solutions and field experiments. Afterwards, with the developed numerical scheme, through fitting numerical simulation results in terms of the edge crack's Stress Intensity Factors (SIFs) and a relevant asymptotical analysis, we managed to derive a group of closed-form formulae with wide application ranges. For the current engineering problem, this set of formulae quantifies the maximum parallel channel spacing h max , beyond which the observed parallel channels' fracturing events cease to occur. Moreover, the same numerical scheme is utilised to study parallel channels' fracturing paths. Based on the XFEM-based crack path simulations, a second group of formulae and a numerical recipe were obtained to characterise a simplified crack path. This set of equations enables us to quantify the maximum floe size L MCD that can be generated between two parallel channels and its corresponding floe size ratio. In the sequel paper (i.e., Paper II), these equations are validated by a series of well-controlled field experiments undertaken during the Oden Arctic Technology Research Cruise of 2015 (OATRC2015). Highlights • Analytical formulas to calculate Stress Intensity Factors of a quarter plane with an edge crack are developed. • Maximum ice floe size and channel spacing for ice management operations are predicted by the edge crack model. [ABSTRACT FROM AUTHOR]

• The TM-FE-FEM is proposed to simulate the thermal fracture process of quasi-brittle solids. • The TM-FE-FEM is able to simulate the heat conduction, thermal deformation and thermal fracture in quasi-brittle solids. • The accuracy and correctness of the proposed method are validated by four benchmark examples. Thermal loads and temperature changes significantly impact the deformation and fracture of quasi-brittle solids, and the computational simulation of such a process is challenging. In this paper, a coupled thermo-mechanical field-enriched finite element method (TM-FE-FEM) is proposed to simulate the thermal fracture process of quasi-brittle solids. The accuracy and correctness of the proposed coupled TM-FE-FEM are validated by four benchmark examples, and the ability to simulate thermal induced crack is validated by the plate containing single edge flaw under coupled thermo-mechanical loading. Finally, the thermal fracture process of the Lac du Bonnet (LdB) granite specimen is reproduced by the proposed method. It can be concluded from the numerical results that the proposed coupled TM-FE-FEM has the ability to simulate the processes of heat conduction, thermal deformation and thermal fracture in quasi-brittle solids. [ABSTRACT FROM AUTHOR]

This work describes a method in which the digital image correlation (DIC) method and finite element analysis (FEA) were used to create a quasi-static mixed-mode fracture envelope for bonded joints consisting of 2024-T3 Al adherends and a tough structural epoxy adhesive. Symmetric and asymmetric versions of double cantilever beam, single-leg bend, and end-notched flexure tests are used to populate the mixed-mode fracture envelope with results at several mode mixities. Experiments are conducted in a universal testing machine while recording images for subsequent DIC analysis. Finite element analysis is used to implement cohesive zone models (CZMs) of the adhesive fracture and to account for plastic deformation of adherends. Mode I and mode II traction separation laws (TSLs) are determined from a property identification method with a Benzeggagh–Kenane mixed-mode coupling law used to model mixed-mode behavior. FEA results are shown to provide a good agreement to both the crosshead displacement and DIC data. The methods in this paper serve as a potential framework for future calibration of mixed-mode fracture envelopes for joints bonded with very tough adhesives that complicate assessment with traditional data analysis methods. [Display omitted] • Mixed mode fracture envelope is characterized for a very tough epoxy. • Digital image correlation utilized to measure strains and displacements around crack. • Adherend plasticity and crack propagation addressed through FEA models utilizing CZM. • Limitations and results of LEFM techniques discussed in light of results. [ABSTRACT FROM AUTHOR]

In this paper, the thermally nonlinear response of stationary and moving cracks in isotropic media subjected to a hyperbolic thermal shock in the framework of the eXtended Finite Element Method (XFEM) is examined. For this purpose, the thermally nonlinear fully coupled Lord-Shulman (LS) model is considered as governing equations. In addition, two cases of material properties, temperature-dependent (TD) and temperature-independent (TID), are assumed. The geometry, including a predefined crack, is modeled using the XFEM for spatial discretization. For modeling the dynamic crack growth within the XFEM, the Maximum Tangential Stress (MTS) criterion is modified based on the stress field near the tip of a growing crack to calculate the dynamic crack growth angle. Besides, the nonlinear form of the Newmark integration scheme is implemented for the numerical integration in the time domain. Finally, a method based on one of the Barnet-Lothe tensors for isotropic materials is employed to extract the stress intensity factors (SIFs). In the provided examples, the effects of thermal nonlinearity, the temperature-dependency of material properties, and the LS relaxation time on the crack propagation path are explored. • Dynamic crack propagation under non-classic thermal shock is studied. • The effect of the temperature-dependency of material properties on the crack trajectory is discussed. • The impact of the relaxation time on the crack propagation is studied considering thermally nonlinear Lord-Shulman model. [ABSTRACT FROM AUTHOR]

[Display omitted] • New ring tensile specimen for pipeline material fracture testing is examined. • Specimens (ring and plane) produced by selective laser sintering from polymer PA12. • Determined dependence on specimen geometry and stress concentrator length. • PRNT specimen enables good assessment of pipeline material fracture properties. • Simple fabrication from pipe; Pressure simulated by contact with the testing tool. In order to develop a non-standard method for determining the resistance to fracture and damage of pipeline materials, a new geometry of ring-shaped specimens with sharp notches or cracks has been defined. The need to develop a new method for testing of the specimens cut from the pipes arises due to the difficulties in determination of fracture mechanics parameters on thin-walled pressure pipelines, especially those with a smaller cross-section, by application of the standard procedures/specimens. Previous studies dealing with the topic of pipeline testing by non-standard methods are presented in the introductory part of the paper. In the experimental part of the research, tests on PRNT (Pipe Ring Notched Tension) and SENT (Single Edge Notched Tension) specimens are performed. Samples of these specimens were produced by SLS (Selective Laser Sintering) technique of additive production from PA12 (polyamide PA 2200) material. For the purpose of this study, a tool that is protected at the national level (in Serbia) as intellectual property is used for testing of the ring-shaped PRNT specimens. Tensile testing of both types of specimens is monitored by Aramis GOM 2M system; its operation is based on the method of digital image correlation, DIC. Additionally, finite element analyses are conducted on the PRNT and SENT geometries, enabling the calculation of the fracture mechanics parameter – Stress intensity factor K. It is concluded that the presented procedure based on the PRNT specimen has a good potential for use as a non-standard method for fracture resistance examination of pipeline materials. It can be performed on the specimens cut directly from the pipes (new or from exploitation). The dependence of the fracture resistance on the stress concentrator size is not pronounced, which means that the results depend dominantly on the material properties, rather than on geometry. [ABSTRACT FROM AUTHOR]

This paper provides several simple but significant formulas that shed light on the connection between the derived transverse stress and some special phenomena, including the premature fracture and largely slant fracture line, occurring during the uniaxial tensile test of sheet metals. Studying two kinds of nearly isotropic materials, theory and simulation analysis found that a non-null transverse stress ( σ 2 ) was derived on the tensile specimen after the onset of necking, which grew from 0 and was always less than half of the corresponding longitudinal principal stress. The derived transverse stress was believed to be a primary factor for hindering the development of the neck, promoting the reduction of the thickness, and determining the orientation of the fracture angle. Furthermore, a special necking phenomenon, i.e., crossed necking, was observed during the transition period of the instability in the test and was studied 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]

For the analysis of low-velocity impact damage, many analytical and numerical models were developed by various authors. These models range from simple approaches with a single degree of freedom up to finite element models on micro-scale. The prediction of delamination, fiber failure, and inter-fiber damage, as well as a physically sound kinematic behavior, are usually the objectives of these simulations. However, achieving satisfactory results requires massive computation and modeling efforts. In the present paper, we review the capability to capture impact damage on the coupon and the structural level. For this purpose, a large compendium of analytical and numerical analysis methods from various authors is considered. Based on existing works, six representative modeling approaches of different abstraction scales are derived and considered on a qualitative and quantitative benchmark study. We analyze all models regarding their advantages and deficiencies. With two experimental coupon impacts, all approaches are tested on their predictive capabilities on the coupon level. The applicability of these methods on the structural level is evaluated according to the benchmark results. Modeling approaches included in the benchmark range from high-fidelity models on meso-scale, macro-scale shell models, and analytical estimations. The focus is put on stacked layer models with solid or shell elements and various cohesive zone approaches. With this paper, we also present guidelines for impact analysis strategies on the structural level. These guidelines aim for a good balance between accuracy and computation effort and involve various simplifications of impact scenarios. In this regard, the range of low-velocity has to be monitored. The energy distribution over the eigenmodes of the impact system suitably indicates the limit of low-velocity impact. [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]

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]

Nonlinearities effects at the crack tip, due to the elastic-plastic material behavior, impact the crack growth rate and path. This paper is devoted to the study of the plastic zone evolution in the crack tip region. The methodology relies on coupling an elastic-plastic Finite Elements Method (FEM) model and experimental displacements measured by Digital Image Correlation (DIC). These latter are introduced as Dirichlet boundary conditions in the finite elements analysis. The considered FEM domain is constant, i.e. the same mesh with a centered crack is moved to each new crack tip position deduced from DIC. The new boundary conditions are updated and the residual stresses and plastic strains of the former computation are interpolated and actualized on the mesh shifted to the new crack tip position in order to incorporate them in the numerical model. The coupling method allowed applying experimental boundary conditions in order to be as close as possible to real experimental conditions and to observe the plasticity evolution from small to large scale yielding conditions. A fatigue test was conducted to validate the proposed approach. The identification residues are proved to be lower than those obtained with an experimental displacements projection onto Williams' series basis, which is a method commonly used with DIC. The coupling results present an attractive similarity with Irwin's model regardless of the crack length. Thus, the definition of the mask needed for the displacements fields projection on Williams' model can be deduced with a reliable estimate of Irwin's plastic radius. [ABSTRACT FROM AUTHOR]

With the development of mechanical structure in large scale, the dimension difference between whole structure and part damage-crack can be widely further. In order to get a precise analytic result of crack structure the grid of crack structure finite element model should be meshed very dense so that the calculation scale is very large and calculation efficiency is lower even the calculation cannot be completed. To solve this multi scale problem of crack structure, presently the submodel method is used, but in the method crack growth trajectory need to be supposition and the crack model also need to be built by man-made, which is not satisfied with need of mix-mode crack growth especially for continuously reconstructing of crack model. In this paper the parametric submodel will be put forward. The method describes crack coarse model and submodel data by parameter way, including meshing, load, boundary condition etc. In the method dynamic relationship of analytical results between coarse model and submodel is built, so that crack stress intensity factor and growth angle can be automatically calculated for every crack tip. According to the dynamic modification of crack coarse model and submodel, the crack growth trajectory simulation can be calculated through iterative steps instead of the traditional supposition growth trajectory and crack propagation life calculation can also be finished. The method gets the accuracy crack growth trajectory and improves analytical efficiency. At last the case of the crack growth trajectory and life analysis in gantry crane verifies the validity of this method. • The typical finite element submodel method efficiently solves the multi scale problem of crack structure. • Stress intensity factor and growth angle can be automatically calculated with results of coarse model and submodel. • With dynamic modifying of coarsemodel and submodel crack growth trajectory and propagation life can be calculated. [ABSTRACT FROM AUTHOR]

Due to the stress concentration and large strain gradient around the crack tip, strong flexoelectric effect would be produced there. Meanwhile, the flexoelectric effect could conversely affect the mechanical fields in materials, thus influence the fracture property of materials. To model the impact of flexoelectricity on crack tip fields and the electromechanical behaviors of materials, intensive mesh refinement is needed around the crack tip. Thus, an efficient numerical method is desired. In this paper, the flexoelectric effect around the tip of nano-cracks is simulated by using a collocation mixed finite element method (MFEM). Our collocation MFEM is based on C 0 continuous approximation and does not involve additional degrees of freedom (DOFs), so that it is quite efficient, which has been verified in our previous study (Tian et al., 2021). Using the collocation MFEM, we simulate the electric potential and field distributions around the crack tip in flexoelectric materials, and the influences of the direct flexoelectric effect on the crack tip opening displacement and J -integral are also studied. Numerical results indicate that the flexoelectric effect around the crack tip would be enhanced by increasing the tensile loading and crack length. Besides, the direct flexoelectric effect around the crack tip enhances the local strength of materials, and plays an important role in fracture mechanics of materials. [Display omitted] • The flexoelectric effect around the crack tip enhances the local strength. • Our collocation MFEM is based on C0 continuous approximation and efficient. • The existence of the direct flexoelectric effect decreases the J -integral. [ABSTRACT FROM AUTHOR]

• A fracture failure of an inter-shaft bearing outer ring is reported. • Failure root causes and mechanism of the fractured outer ring are investigated. • Numerical simulations are performed considering multi-physical loads. • Crack growth paths simulation is conducted using the fracture mechanics theory. The inter-shaft bearing is a critical but vulnerable component of dual rotors, because of the severe operational conditions and loads. This paper investigates the failure mechanism of a fractured inter-shaft bearing belonging to a high thrust-weight ratio turbofan engine. Fractographic and microscopic analyses of the fracture surfaces were conducted, followed by vibration signal processing. Finite element analyses of the outer ring were also performed considering the centrifugal, thermal, and roller-raceway loads. What's more, using the linear elastic fracture mechanics theory, the crack growth path simulation was obtained, whose result showed good agreement with the real fracture morphologies. The results indicated that due to the clearance between the outer ring and its housing during the operation, the anti-rotation tabs of the outer ring were subjected to non-uniform load, thus several tabs might suffer large stress concentrations at the root fillets, which could lead to the crack initiation. During the following operation of the aero-engine, the crack propagated through the outer ring and cause the fatigue fracture of tabs. The investigation provided herein suggests that the outer ring and its housing should be redesigned to eliminate the clearance during the operation, an outer ring formed integrally with the bearing housing flange is one of the failure preventions of this failure mode. [ABSTRACT FROM AUTHOR]

• Viscoplastic contact law. • Calculation of the COR. • High-velocity hail impact experiments. The dynamic response of composite structures under impact loading conditions is a complex problem which is attracting substantial attention. Specifically, the case of hailstone impact introduces additional challenges that are urging to be encountered. Hence, the main goal of this paper is to present the development and validation of a computationally efficient impact model that encompasses a novel semi-empirical viscoplastic contact law for crushable ice impactors together with a new time domain spectral shear plate finite element formulation including nonlinear effects due to large displacements and rotations. The new viscoplastic contact law, which provides the coupling between the hailstone impactor and the targeted composite plate, is derived from analytical expressions and observations based on experiments and high-fidelity finite element simulations which utilize a fully integrated ice failure material model. High-velocity spherical hailstone impact experiments on woven glass/epoxy composite plate target structures are conducted using a high pressure pre-charged gas gun Obtained results are validated against high fidelity finite element models and experimental measurements. The results demonstrate the adequacy of the proposed contact law to capture the impact loading, as well as the accuracy, computational efficiency and additional benefits of the presented computational framework compared to other well-established numerical tools. [ABSTRACT FROM AUTHOR]

This paper revisits the problem of computational modelling of a fluid-driven fracture propagating in a permeable porous medium using zero-thickness flow cohesive interface elements. Both cases of continuous and discontinuous pressure field across the fractures are implemented in a unified formulation. The paper provides computational aspects of hydraulic fracture modelling such as mesh generation, execution time, convergence and numerical integration issues. We show that Newton-Cotes quadrature must be used for quadratic flow cohesive interface elements at least for the presented problems. Our simulations exhibit the so-called intermittent crack tip advancement as recently confirmed in the literature. This paper is addressed to researchers who would like to have a quick working implementation of the zero-thickness flow cohesive interface elements for simulating hydraulic fracturing processes with finite elements. [ABSTRACT FROM AUTHOR]

The prediction and control of crack widths in reinforced concrete structures has been the subject of research for many years. However, there is still a lack of consensus on the design of reinforcement for crack control in walls with edge restraint. The paper describes an experimental programme undertaken to investigate the influence of early-age thermal contraction and long-term shrinkage on cracking in four edge-restrained reinforced concrete walls loaded in bending about their major axis. Bending was introduced as a result of initial preload as well as restraint of deflection due to volumetric change. The walls measured 3500 mm long by 180 mm thick with heights of 500 mm and 750 mm. The paper highlights the main findings of the experimental programme and presents the results of nonlinear finite element analysis that was carried out to investigate the effects of wall geometry and reinforcement ratio on crack widths in edge-restrained walls. Results suggest that crack widths in edge-restrained walls are significantly influenced by the wall geometric properties such as wall aspect ratio and wall height which are only indirectly accounted for through the restraint factor in crack width calculations to EN 1992. [ABSTRACT FROM AUTHOR]

This paper presents numerical results from an investigation of the mechanism of coalescing patterns in a rock-type material with three flaws whose arrangements are different under uniaxial compression. The numerical experiments are conducted through the parallelized peridynamics code coupled with the finite element method, which is capable of capturing more realistic fracturing behaviors. Under the effect of various bridging angles, the process of initiation, propagation, and coalescence of new cracks is discussed. In addition, coalescing behaviors affected by the interaction of newly growing cracks are observed along with various flaw arrangements. Several types of coalescence occur due to the interaction of wing cracks, horsetail shear cracks, and anti-wing cracks and the extension of central tensile crack segment, and these results are compared with experimental results. Furthermore, by comparing coalescence types and corresponding flaw arrangements, the coalescence mechanisms are discussed in detail toward the end of the paper. [ABSTRACT FROM AUTHOR]

We in this paper present a novel adaptive finite element scheme for limit analysis of cracked structures. The key idea is to develop a general refinement algorithm based on a so-called polytree mesh structure. The method is well suited for arbitrary polygonal elements and furthermore traditional triangular and quadrilateral ones, which are considered as special cases. Also, polytree meshes are conforming and can be regarded as a generalization of quadtree meshes. For the aim of this paper, we restrict our main interest in plane-strain limit analysis to von Mises-type materials, yet its extension to a wide class of other solid mechanics problems and materials is completely possible. To avoid volumetric locking, we propose an approximate velocity field enriched with bubble functions using Wachspress coordinates on a primal-mesh and design carefully strain rates on a dual-mesh level. An adaptive mesh refinement process is guided by an L 2 -norm-based indicator of strain rates. Through numerical validations, we show that the present method reaches high accuracy with low computational cost. This allows us to perform large-scale limit analysis problems favorably. [ABSTRACT FROM AUTHOR]

This paper deals with the Fatigue Crack Growth evaluation of a crack located at a nozzle corner and submitted to thermal transients. In such situation, it is well known that it is important to consider the effect of plasticity. Thus, the background of an evaluation scheme relying on the ΔJ parameter is presented in the first part of the paper. In the second part, the Fatigue Crack Growth evaluation scheme relying on semi-circular defects is validated through a comparison to reference Finite Element modeling. It is then shown that the assumed semi-circular defect is justified and also that the complete analytical scheme based on a K I compendium and the simplified k th coefficient formulation allows to accurately evaluate the Fatigue Crack Growth Rate of this complex configuration. [ABSTRACT FROM AUTHOR]

A recent comprehensive investigation into residual stress distributions in pipe and vessel longitudinal seam welds is presented in this paper, covering component wall thickness from 1/4″ (6.35 mm) to 10″ (254 mm), component radius to wall thickness ratio from 2 to 20, and linear welding heat input from low (50 J/mm) to high (6000 J/mm). Through the use of a residual stress decomposition technique, two key parameters that govern through-thickness residual stress distributions in terms of their membrane and bending content have been identified. One is component radius to wall thickness ratio ( r / t ) and the other is a characteristic heat input density ( Q ^ ) having a unit of J/mm 3 . With these two parameters, a unified functional form for estimating through-thickness residual stress profile in seam welded components is proposed in this paper (Part I) for supporting fitness for service assessment for crack-like flaws in weld region. A curved beam bending theory based model is introduced in Part II as a means of analytically describing through-thickness residual stress profile as a function of circumferential position away from the weld region until residual stresses become zero. The effectiveness of this proposed framework for achieving residual stress profile estimation within weld region (Part I) for longitudinal seam welds in pressure vessel and piping components has been confirmed by finite element residual stress analysis results on a large number of component configurations and different welding conditions. [ABSTRACT FROM AUTHOR]

The Strong Discontinuity Approach (SDA) is a popular method to incorporate cracks as displacement discontinuities into finite elements. In the first part of the paper, different SDA formulations (denoted as SOS, KOS and SKON) are assessed numerically based upon different error norms including a norm to evaluate the variational consistency of SDA elements. Results are compared with analytical solutions as well as with results from interface elements and the element erosion technique for cohesionless cracks. In the second part of the paper, a new method to improve the computational robustness of SDA analyses is proposed. In addition to using arc-length control to solve the nonlinear equation system, a sequential un- and reloading scheme is proposed with the crack state frozen during unloading to avoid, that more than one new crack segment is activated within an increment. The performance of the algorithm is demonstrated by numerical analyses of a tension test on a dog-bone shaped specimen by means of different variants of the SDA and, for comparison, also using interface elements. [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]