Search

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]

• For blunt crack tips, as the radius increases, the specimens' compliance also increases. • For sharp crack tips, as the element size of the crack tip increases, the specimens' compliance decreases. • Similar compliance results are obtained for both meshes when the radius or element size of the crack tip are low enough. • Two models were created that show the crack tip radius or the element size impact on the elastic unloading compliance. • A parameter that normalizes the crack tip radius or the element size with the specimens' width is proposed. Elastic unloading compliance is a common technique to determine instantaneous crack size in fracture mechanics properties such as resistance curves (R-curves) and fatigue crack growth. This technique uses a polynomial, developed using finite elements models, to correlate compliance with crack depth. In these models, crack tip is usually modeled with a blunt mesh (with a crack tip radius ρ) or a sharp mesh (with element size in the width direction l) , and neither are standardized in the literature. This paper shows that both affect compliance, therefore potentially impacting results of fracture mechanics properties acquired from simulations. This paper focuses on how those parameters affects compliance in SE(B) models. Finally, a parameter φ that normalizes ρ or l with the width was developed and recommended values based on compliance convergence are suggested. Controlling φ may help to ensure reliable results in fracture mechanics models where compliance needs to be determined. [ABSTRACT FROM AUTHOR]

This paper introduces a novel method for assessing fracture mechanics parameters such as Stress Intensity Factor (SIF), Energy Release Rate (J) and Crack Tip Opening Displacement (CTOD). An electromagnetic–mechanical coupling (EMC) approach is employed to evaluate and to measure these fracture parameters by monitoring the variation of impedance using eddy currents. This approach relies on the eddy current signal obtained from a sensor, which calculates and verifies SIF parameters along with the J-integral and CTOD through changing the sensor impedance. To ensure theoretical consistency, the magnetic field is theoretically used, formulated and verified. Additionally, a numerical simulation method employing the finite element method is used to analyze and identify cracks in structures and assess their propagation. The quantification of SIF and J-integral parameters is demonstrated using two sensors based on a differential probe. This research paper demonstrates that the proposed method is the most efficient approach for exploring and detecting cracks in materials, as well as understanding their propagation behavior. [ABSTRACT FROM AUTHOR]

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]

External circumferential surface crack is one of the most common defects in offshore pipes and risers. The stress intensity factors (SIFs) for specific crack shapes are essential parameters for assessing the fatigue life of surface-cracked pipes when the linear elastic fracture mechanics approach is adopted. In this paper, a general point load weight function of SIFs for external circumferential surface cracks in pipes is derived. Three-dimensional finite element (FE) analysis is utilized to calculate the SIF solutions for determining the unknown weight function coefficients. The geometric configurations of surface-cracked pipes cover wide ranges of crack aspect ratios, crack depth-to-thickness ratios and thickness-to-inner radius ratios. The obtained weight function is validated against the normalized SIF solutions available in the literature and those obtained from FE analysis for various one-dimensional and two-dimensional stress distributions, showing good accuracy. Moreover, an analytical approach for predicting the surface crack growth in pipes is established based on the developed weight function and validated against the available experimental data from literature. The results demonstrate that the present weight function can be used for SIF calculation and fatigue crack growth prediction for offshore pipes and risers under complicated loading conditions. • A general point load weight function is developed for external circumferential surface cracks in pipes. • Empirical formulas of weight function coefficients are obtained from parametric finite element analysis. • The application range of weight function covers wide ranges of geometric parameters. [ABSTRACT FROM AUTHOR]

The characteristics of thermomechanical fatigue life of complex electronic device system, micro-scaled design, is highly sensitive to changes in design factors. The solder ball, which acts as a linkage between the circuit board and the package, is a vital part to examine the performance of electronic device system. Repeated thermal loading causes the solder crack growth in models, eventually leads to the breakdown of devices. There have been lots of studies on investigating the fatigue life of solder joints employing well-established finite element procedure. However, generating a finite element model reflecting the whole device often requires unnecessarily large finite element matrices which may increase the computational cost and solder joint fatigue life can be highly dependent on the mesh resolutions. Recent studies suggest the sub-modeling method to handle the meshing process and alleviate the computational cost. In this paper, we delineate the methodology of two-step sub-modeling framework, aimed at improving the mesh fidelity of complex models while ensuring the efficiency of labor-intensive process of solder joint fatigue analysis. We employ the strain energy-based Darveaux's fatigue model to predict the fatigue life of solder joints. Through the investigation of the predicted fatigue life of solder joints across various sets of design parameters, it has been observed that the design factors of electronic devices exhibit a clear pattern in relation to the predicted fatigue life, even when only the second step of two-step sub-modeling framework is considered. Our findings suggest that it is efficient to utilize solely the second step of two-step sub-modeling framework to identify an appropriate reduced design space, where design parameters can be strategically selected for designing an optimal model. • Two-step sub-modeling enables efficient fatigue life prediction of DRAM modules compared to the conventional approach. • An efficient framework allows the geometric effect of solder ball to be quickly verified. • The proposed method aids in identifying appropriate design space guidelines to optimize subsequent model development. [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]

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 This paper presents a novel formulation of a cohesive zone model able to effectively approximate the time-and temperature-dependent fracture process along a defined interface. The formulation relies on the assumption that the relaxation behavior of the traction is the origin of the time effects, and time temperature equivalence principle can be introduced in solving the temperature effects. A series basic hypotheses are introduced according to the previous research work and will be complied in the paper. By connecting N Maxwell models in parallel and letting the time-independent traction calculated by PPR cohesive zone model as the input parameter, the time-dependent traction will be output by numerical integration. Reduced time considering the effects of temperature will replace the real time in the numerical integration. With the tool of the user subroutine element, the novel formulation is implemented in FEM code ABAQUS. Typical load cases including constant tensile test and relaxation test are analyzed to illustrate the special properties of the formulation. With three set of input parameters, the proposed model can be utilized in a wide range of applied loading rates and temperatures as validated by the remarkable agreement with the experimental data in the case of the double sandwich cantilever beam made of solid propellant/insulation adherents bonded along the liner interface. Highlights • A novel time-and temperature-dependent cohesive model is proposed in this paper. • With the numerical integration, the proposed time-and temperature-dependent cohesive model is implemented in the FEM code ABAQUS. • A typical debonding interface between solid propellant and insulation is modeled and analyzed using the inversed model parameters. • The proposed model can deal with the unsteady loading rate and changed temperature which the aforementioned models unable to cope with. [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 Temporarily plugging staged fracturing (TPSF) technique has been successfully applied in unconventional reservoirs. This paper quantificationally investigates fracture interaction between previous and subsequent fractures during TPSF through numerical experiments. Using XFEM-based CZM (the cohesive zone model based on the extended finite element method), a 2D fully fluid-solid coupling model is established to perform the investigation. Typically, the concept of "turning angle" is proposed to quantify the degree of fracture interaction under different conditions. Moreover, the opening of the previously created fracture is simulated by truss model, which indicates truss elements distributed on the fracture surfaces; the effects of formation heterogeneity are investigated by changing rock mechanical properties surrounding the subsequent fractures. Simulation results reveal that the previously created and propped fracture will generate induced stresses, which cause the subsequent fracture to propagate with curvature. Factors influencing the subsequent fracture propagation curvature during TPSF, are sorted by sensitivity (strong to weak): plugging efficiency, Young's modulus, percent of initial aperture propped, fracture spacing, horizontal stress contrast, rock tensile strength, and formation permeability. The investigations provide a deep understanding of fracture interaction between previous and subsequent fractures during TPSF. Highlights • The mechanisms of temporarily plugging staged fracturing (TPSF) technique is revealed in this paper. • A fully fluid-solid coupling model using XFEM-based CZM is established in ABAQUS to investigate fracture interaction during TPSF. • Truss model is applied to keep the previous fracture open, which can simulate the propping effects of diverting agents and fluid pressure within the fracture. • Turning angle is proposed to quantificationally investigate the subsequent fracture curvature influenced by different factors. [ABSTRACT FROM AUTHOR]

Highlights • We study the accuracy of the timing measurement provided by blade tip timing method. • A detailed quasi-static finite element model of the electromagnetic field is studied. • A simulation of the application is provided by COMSOL Multiphysics® software. • A test rig was designed and manufactured to validate the models described. • We study the effects of tip clearance and blade velocity on the measurement. Abstract To monitor the vibration of blades in rotating machinery, the contactless method called Blade Tip Timing (BTT) is widely used. blade vibration and clearance are important diagnostic features for condition monitoring, including the detection of blade cracks. To perform the BTT technique, optical sensors were widely used by industry due to their high accuracy, but the main drawback of these systems is their low tolerance to the presence of contaminants. To overcome this downside, eddy current sensors are a good alternative for health monitoring applications in gas turbines due to their insensitivity to contaminants and debris. This type of sensor has been used by many researchers, predominantly on the experimental side to investigate BTT systems and there is a lack of modelling to support the measurement system design. This paper fills the gap between experiments and modelling for the particular case of a blade rotating past eddy current sensors. Hence the novelty of this paper is the simulation of the BTT application using detailed quasi-static finite element models of the electro-magnetic field to estimate the outputs from active and passive eddy current sensors. A test rig composed of a bladed disk with 12 blades clamped to a rotating shaft was designed and manufactured in order to validate the proposed models with experimental measurements. Finally, a parametric study is presented to show the effect of the blade tip clearance and the rotational speed on the accuracy of the BTT measurement. This leads to better understanding of the sources of error in the time of arrival of the blades passing the sensor and hence insight into the blade vibration measurement accuracy. [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]

• 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]

• Fretting fatigue behavior of galvanized wires was studied using strain-based fracture mechanics. • Point load weight functions for wires were developed to determine stress gradient factors. • Shape functions for strain intensity factors were determined using a 3D model. • Fatigue tests calibrated a key strain-based fracture mechanics parameter (initial crack length). The galvanized wires used in cable bridges can fail due to fretting fatigue. Experimental results have shown that defects resulting from the galvanization process are a possible source of initiation for fatigue cracks and make the life shorter than that of a wire without a galvanized layer. The investigation presented in this paper uses strain-based fracture mechanics to analyze the influence of these defects on the fatigue life of galvanized wire. The presented analysis considers nonlinear material behaviour. A 3D finite element model is used to compute the required stress field. Stress intensity factors are obtained by a proposed numerical point load weight function, and shape factors are found for the surface and deepest points of the semielliptical crack. Plain fatigue tests of galvanized wires are performed to calibrate key model parameters. The calibrated model is then shown to provide reasonably accurate but systematically conservative estimates of the fatigue life under fretting conditions typical of bridge stay cable saddle supports. [ABSTRACT FROM AUTHOR]

• Weak, brittle, low impedance material characterized with metallic Split Hopkinson Bar. • Transmitter sensitivity increasable by local taper; can cause unwanted pulse-shaping. • Mismeasurements may become acute at higher bar velocities only. • Clamp-mass, -liner and extent of local taper contribute to mismeasurements. • Digital twin is key to pre-validate bar-setup for a given specimen and strain-rate range. The Split Hopkinson or Kolsky bar is one of the most popular devices when it comes to the mechanical characterization of material samples under high strain-rates. While testing of high impedance materials, such as metal alloys, is relatively straight forward, samples with low impedance pose certain challenges. The present work focuses on the detailed implementation of a high strain-rate tensile testing method for thin, low impedance, sheet-like materials by using the Split Hopkinson test principle. In order to find a suitable Split Hopkinson setup a digital twin was created using explicit finite element methods. With the help of the digital twin, the design of the transmission bar and the sample holders including the friction liners were explored. The numerical model indicated, that a hollow transmission bar with a moderate tapering (hollow bar 1.0) is suited for the characterization of low impedance materials over a wide strain-rate range. Furthermore, this setup has to be combined with an asymmetrical sample holder configuration (heavier on the incident side and lighter on the transmission side) and aluminum friction liners to return accurate results. This numerically derived setup was validated against experimental tests on paper, representative of low impedance, sheet-like materials. [ABSTRACT FROM AUTHOR]

Non-pneumatic tires (NPTs) fundamentally avoid the risk of tire blowout of traditional pneumatic tires, but the overall and key component performance inevitably degrades due to factors such as high temperature, variable load, variable working conditions and impact in its service process. Once this leads to failure, it will significantly impact on vehicle safety. To this end, this paper studied the influence of local structural damage on the dynamic response of NPTs, which lays the foundation for realizing health monitoring of intelligent non-pneumatic tires (INPTs). Firstly, a three-dimensional nonlinear finite element model of NPTs was established, and the failure locations of NPTs were determined by fracture mechanics and maximum strain energy density; Secondly, the influence of structural damage on the static and dynamic performance of NPTs was analyzed; Finally, the sensitivity of the acceleration signal and sensor position of the tire inner liner to the local structural damage was studied. The research results show that structural damage will cause the stress of the spokes and shear layer to increase, and as the number of broken spokes increases, the shear layer will bear a larger load. Compared with the circumferential and lateral acceleration, the radial acceleration has the highest sensitivity to the damage of NPTs. The sensor closest to the damage location is the most sensitive to the damage. The research results provide a reference for the structural optimization design and health monitoring of INPTs. • A three-dimensional nonlinear finite element model of non-pneumatic tyre is established by using finite element method. • The failure locations of NPTs were determined by fracture mechanics and maximum strain energy density. • When the NPT suffers spoke damaged, the stress of shear layer will increase with the aggravation of spoke damage. • The radial acceleration is more sensitive to the damage characteristics than the circumferential andlateral acceleration. • The sensor closest to the damage position is the most sensitive to the damage. [ABSTRACT FROM AUTHOR]

This discussion is based on the paper by Saviano and Pisanò (2017) (hereafter identified as “the original authors” or “the original paper”). The original authors employed a three-dimensional finite element analysis to investigate the effects of misalignment on the undrained capacity of suction anchors subjected to horizontal (H) and vertical loadings (V). In the original paper, various parametric studies including the misalignment angle, the anchor aspect ratio, the soil strength profile, and the interface adhesion factor on the HV failure envelope of suction anchors were comprehensively carried out. The discussion addresses the issues of the three-dimensional modelling approach for suction anchors using the model of the single anchor/plug rigid body employed in the original paper and questions the validity of the model if it corresponds to the most accurate representation of the numerical model for this type of offshore foundation. [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]

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]

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]

A new approach is proposed to account for the impact of sprain variables for computational simulation of fracture in quasi-brittle materials. For an isotropic solid, these variables are equal to the Laplacians of the components of the displacement field, and they were introduced in a recent study by Zhang and Bazant to resolve spurious mesh effects for cases involving softening material response. This is possible by establishing localization-resisting forces which are conjugate to the displacements with respect to a sprain energy functional, defined as a function of the sprain variables. To enable the evaluation of the sprain variables in a conventional, C 0 continuum finite element approximation, this paper introduces a set of scalar fields, each being weakly equal to the Laplacian of one of the components of the displacement vector field. This leads to a straightforward implementation with standard continuum (solid) elements, eliminating the need for approximations satisfying higher continuity requirements or for ad-hoc, finite-difference algorithms which were adopted in the original pertinent work for the calculation of the sprain variables. • Use of localization-resisting forces in continuum simulations of strain softening, to eliminate spurious mesh-size effects. • These forces are governed by a set of scalar fields, weakly equivalent to the Laplacians of the displacement components. • Weak equivalence allows to obtain the Laplacians of the displacement field with conventional, C0 finite element approximations. • The method is found to eliminate spurious effects of mesh size and of mesh orientation with respect to crack propagation path. [ABSTRACT FROM AUTHOR]

The main cause of failure in bonded ceramic restorations is material fracture due to excessive stress concentration at the base of the prosthesis. The design of restorative functionally graded materials (FGM) could represent a major advance in dissipating mechanical stresses during occlusal contacts. The aim of this paper is to carry out a complete factorial design of finite element analyses to optimize a multilayer FGM introduced at the bottom of an overlay prosthesis. The number and thickness of layers vary within a spectrum compatible with ceramic shaping processes whereas Young's moduli variations are set in the range of dental tissues. For a 1.5-mm thick prosthesis, the optimal FGM configuration appears to be a 5 layers of 0.2 mm thickness with a linear distribution of Young's modulus from 30 to 70 GPa. This configuration was implemented in a 3D model of a restored tooth with realistic geometry to validate the proof-of-concept. [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]

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]

• Crack tunneling affects the elastic unloading compliance mostly reducing it. • Within the allowed ASTM E1820 curvature limits, the compliance errors are mostly negligible. When such limits are violated, the effects on compliance are significant, and results show that a/W estimation employing the elastic unloading compliance is affected. Since fracture mechanics properties are inherently dependent on the instantaneous crack size, these should also be affected to some degree. • Even though the ASTM E1820 is focused on the determination of the nonlinear energy release rate J and resistance curves, this paper is not focused on determining errors directly on the crack driving forces - in this case, J-integral. • A new proposal for measuring the crack front is presented and measuring errors are minimized when those limits are violated. • Additional work is being done to develop a more comprehensive proposal - independent of crack size, thickness and, if possible, specimen type. This paper covers the effects of crack tunneling on SE(B) , C(T), and clamped SE(T) specimens and presents a correction methodology for this effect and is divided in two parts. Part one presents an investigation of how crack front curvature affects instantaneous crack size predictions based on the elastic unloading compliance technique. Relative crack depths (a/W) of 0.2 , 0.5, and 0.7 , were considered alongside five levels of crack curvature. Refined finite element models provided load- CMOD records in order to support compliance assessment. The crack front was modeled as a semi-ellipse, and the compliance results agreed with experimental data from the literature. It was shown that for the same equivalent physical straight crack standardized by ASTM , compliance generally decreases as tunneling increases. Since the maximum crack curvature allowed by the aforementioned standards is very restrictive, compliance did not meaningfully change within that limit, however, if violated, this paper shows that higher deviations may occur, leading to inaccurate crack depth estimations and invalid test results. These limits and deviations were clearly determined and, as a step to improve the techniques, this paper also presents – in part two – an exploration of a possible approach to mitigate this problem, which is based on the modification of how the equivalent straight crack of a curved crack front is determined. This new approach presents reduced errors in compliance-based crack size estimation as crack curvature increases when compared to current standardized protocols, and it can support further investigations in order to validate and standardize improved measuring techniques. Finally, it is important to state that even though the ASTM E1820 is used for the determination of crack driving forces, this study is based only on the study of the crack front curvature, the limit imposed by this standard and the deviations on crack size estimation when those limits are violated, while not focusing on determining errors directly on the J-integral. This paper is a further development on the studies published before by the research group. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical behavior of fibrous networks is governed by complex multiple mechanisms. This study examines the effect of microstructure on the macroscopic deformation and fracture of two-dimensional random fiber networks and its practical implications for understanding the material failure in paper materials by using finite element models. Remote load is a pure mode I opening field, applied via a boundary layer. Characteristic networks, consisting of the union of solutions of several unique networks, are interpolated on a rectangular grid covering the whole problem domain. The interpolated solutions are interpreted as network-equivalent continuums representing the mechanical behavior, on average, for a specific set of structural properties. A regularization routine is included in a variational procedure in order to minimize potential energy in the body and produce continuous strains at cell borders in the grid. It is shown that using a classical continuum linear elastic fracture mechanics (LEFM) approach to describe macroscopic singular-dominated fields in fiber networks, can lead to erroneous results especially in networks having a low degree of bonds per fiber. The classical continuum description is too simple to capture the essential mechanical behavior for this class of material since a structural effect, that alters the displacement field, becomes pronounced. It is necessary to include a nonlocal theory to describe the mechanical behavior at a continuum level. By using an appropriate characteristic length in a nonlocal continuum formulation, strain energies, in the neighborhood of a dominant macroscopic singularity, are calculated that agree well with characteristic network models and hence produce fairly good agreements between the networks and the nonlocal continuum models. A key conclusion found is that, only for networks with a high degree of bonding, can the mechanical behavior around a macroscopic singularity be captured by the classical local continuum theory. In networks with a low degree of bonds per fiber, there are regions far away from the macroscopic singularity that have relatively higher magnitudes of strain energy than predicted by the classical theory. A relation between an internal length scale parameter, used in the nonlocal continuum model, and the structural properties of the network is approximated by a simple function. [Copyright &y& Elsevier]

Abstract: Crack-path prediction for crack-turning problems in stiffened structures is an important issue in modern aircraft design processes because the ability of modeling a crack-path correctly allows the engineer to predict lifecycles and maintenance cycles more appropriate. In this paper the method of material forces as a simple method to describe crack-turning problems is introduced. At first, simple problems are examined, in order to make sure that the computed numerical results are comparable to known analytical results. Thereafter a simple academic example of a stiffened structure is shown and the crack-path is predicted by means of an implementation of the material force method in a finite element analysis formulation. The results of these computations have been compared to the results achieved by several known methods for computing the stress intensity factors, the crack-path and the energy release rate. It can be seen that computations of the material force deliver all necessary information to describe a crack by linear elastic fracture mechanics. [Copyright &y& Elsevier]

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 a comprehensive survey on the modeling of tissue cutting, including both soft tissue and bone cutting processes. In order to achieve higher accuracy in tissue cutting, as a critical process in surgical operations, the meticulous modeling of such processes is important in particular for surgical tool development and analysis. This review paper is focused on the mechanical concepts and modeling techniques utilized to simulate tissue cutting such as cutting forces and chip morphology. These models are presented in two major categories, namely soft tissue cutting and bone cutting. Fracture toughness is commonly used to describe tissue cutting while Johnson–Cook material model is often adopted for bone cutting in conjunction with finite element analysis (FEA). In each section, the most recent mathematical and computational models are summarized. The differences and similarities among these models, challenges, novel techniques, and recommendations for future work are discussed along with each section. This review is aimed to provide a broad and in-depth vision of the methods suitable for tissue and bone cutting simulations. [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]

Composites reinforced with carbon fibers are widely used in automotive, aviation, nautical, in the blades structure of the wind turbines. Composite structures shows outstanding mechanical properties at static and cyclic behavior but the impact damage represents a problem extensively studied because during and after impact local damage and interlaminar fissures occur which cannot be detected easy. As a result, the experimental and theoretical approach to impact behavior of composites is a method of diagnosis and prognosis of phenomena that develop as a result of shock stresses. The paper focuses on the finite element modeling of the composite plate made of twelve layers which are arranged at an angle of 45° to each other, thus obtaining a quasi-isotropic material. The impact of the plate with low energy was simulated, resulting the equivalent stresses von Mises, shear stresses and deformations of each layer. It was found that the variation of stresses von Mises on the thickness of plate is linear and the shape and magnitude of the delamination developed in each layer depend on the difference between stiffness of the successive layers and rigidity of the interface between layers. The FEM results were confirmed experimentally. The novelty of the paper consists of the plate modeling as a multilayers structure and the simulation of impact with low energy. It were analyzed the shapes of strains from each layer and compared with experimental results. [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]

The paper presents a review of the developments in ship collision analysis over the last 10 years and the challenges to an Accidental Limit State (ALS) design method of ships based on collisions. It aims to discuss the technical difficulties in finite element analysis, especially the mesh-dependent material failure criterion, the accuracy of the analytical and semi-analytical formulae and the acceptance criterion in ALS design. In recent literature, various material failure criteria are proposed and validated in the fine-meshed models, but their accuracy is not clear in the applications of coarse-meshed models. The analytical calculations provide a relatively accurate prediction of the purely plastic responses of ship structures under impact loads, but a universal approach has not been found for fracture predictions. A semi-analytical method is a good approach in the ALS design, but the accuracy needs further improvements. The technical challenges are summarised in ship collision analysis for accurately assessing the structural damage with numerical and theoretical methods. • The paper presents a review of the developments in ship collision analysis in the recent 10 years. • It discusses the technical difficulties in conducting FE analysis, especially the mesh-dependent material failure criterion. • It covers the accuracy of the analytical and semi-analytical formulae and the acceptance criterion in ALS design. • The technical challenges in ship collision analysis are summarised. [ABSTRACT FROM AUTHOR]