Energy release rate

The majority of hydrocarbon reservoirs worldwide are fractured reservoirs, mostly hosted by sedimentary rocks. Fracture development in reservoirs is still poorly understood, and so is the associated permeability. Here we present new results on fracture networks in limestone and shale layers, part of the Lias Group of Early Jurassic (about 200 Ma), from Kilve, Southwest England. The fractures are mostly joints (extension or mode I fractures). The apertures of 300 measured fractures range from 0.1 to 16 mm, the great majority being in the range 0.1-2 mm, and follow a crude power-law size distribution. The fracture frequency is significantly higher in the limestone layers than in the shale layers, many of the limestone fractures becoming arrested (stopping their propagation) at the contacts with shale layers. More specifically, of the fractures that meet contacts there is similar number of arrested and penetrating fractures, whereas many fractures that penetrate change their attitude o...

The three-dimensional problem of a transversely isotropic piezoelectric material with an embedded elliptic crack parallel to the material plane of isotropy is solved using an integral equation method developed earlier to solve similar problems in isotropic homogeneous elastic materials. The field equations of such medium reduce to four simultaneous partial differential equations of second order with the three displacement components and an electric potential as the basic unknowns. These partial differential equations reduce to four quasi-harmonic equations in terms of newly introduced potential functions. For the elliptic crack loaded normally with mechanical and electric loads, the mixed boundary conditions reduce the four quasi-harmonic equations to a pair of coupled integral equations – the coupling being between the normal displacement component and the electric potential function. A series of transformations together with Fourier expansions of the known and unknown fields reduc...

Flexible electronics have attracted rapidly growing interest owing to their great potential utility in numerous fundamental and emerging fields. However, there are urgent issues that remain as pending challenges in the interfacial stress and resulting failures of flexible electronics, especially for heterogeneous laminates of hard films adhered to soft polymer substrates under thermal and mechanical loads. This study focuses on the interfacial stress of a representative laminated structure, that is, the Si film is adhesively bonded to soft polydimethylsiloxane with a plastic polyethylene terephthalate substrate. An novel thermal-mechanical coupling model for this flexible structure is established in this paper, which presents the essential characteristics of interfacial shear stress. In addition, under thermal and mechanical loads, a typical case is investigated by combining an analytical solution with numerical results using the differential quadrature method. Furthermore, thermal and mechanical loads, material and geometry parameters are quantitatively explored for their influences on the interfacial shear stress. Targeted strategies for decreasing stress are also suggested. In conclusion, the thermal-mechanical model and application case analyses contribute to enhancing the design of interfacial reliability for flexible laminated structures.

In this paper, we present a general method for the calculation of the various stress intensity factors in a material whose constitutive law is elastic, linear and varies continuously in space. The approach used to predict the stress intensity factors is an extension of the interaction integral method. For this type of material, we also develop a systematic method to derive the asymptotic displacement fields and use it to achieve better-quality results. A new analytical asymptotic field is given for two special cases of graded materials. Numerical examples focus on materials with spacedependent Young modulus.

We aim to derive a damage model for materials damaged by microcracks. The evolution of the cracks shall be governed by the maximum energy release rate, which was recently shown to be a direct consequence of the variational principle of a body with a crack (Arch. Appl. Mech. 69 (5) (1999) 337). From this, we get the path of the growing crack by introducing a series of thermodynamically equivalent straight cracks. The equivalence of the energy dissipated by microcrack growth and the damage dissipation leads to our damage evolution law. This evolution law will be embedded in a ÿnite deformation framework based on a multiplicative decomposition into elastic and damage parts. As a consequence of this, we can present the anisotropic damaged elasticity tensor with the help of push and pull operations. The connection of this approach to other well known damage theories will be shown and the advantages of a ÿnite element framework will be worked out. Numerical examples show the possibilities of the proposed model.

An analytical and numerical procedure based on an independent integral path and finite element analysis for mixed-mode fracture in viscoelastic orthotropic media is developed. The separated method employs virtual mechanics fields induced by the classical singular analytical forms. The viscoelastic generalization uses a thermodynamic approach by defining an energy release rate only taking into account a perfect uncoupling between free and viscous energies. The implementation of the Mθ -integral in finite element software and its integration into the viscoelastic incremental formulation are presented. As results, the analytical and numerical solutions are compared by the way of the energy release rate in pure mode I, pure mode II and mixed modes. In shows that, the developed model lead to accurate and efficient separated fracture mode in viscoelastic materials.

The performance and the reliability of many devices are controlled by interfaces between thin films. In this study we investigated the use of patterned, nanoscale interfacial roughness as a way to increase the apparent interfacial toughness of brittle, thin-film material systems. The experimental portion of the study measured the interfacial toughness of a number of interfaces with nanoscale roughness. This included a silicon interface with a rectangular-toothed pattern of 60-nm wide by 90-nm deep channels fabricated using nanoimprint lithography techniques. Detailed finite element simulations were used to investigate the nature of interfacial crack growth when the interface is patterned. These simulations examined how geometric and material parameter choices affect the apparent toughness. Atomistic simulations were also performed with the aim of identifying possible modifications to the interfacial separation models currently used in nanoscale, finite element fracture analyses. The fundamental nature of atomistic tractionseparation for mixed mode loadings was investigated.

During the past few decades fracture mechanics has become a necessary discipline for the prevention of many structural failures. These are problems resulting primarily from structures containing part through or through cracks. Such cracks can originate in many ways. For example, they may be introduced as cracks or as incipient cracks during manufacture of structural parts; they may grow from defects in the parent metal, from incomplete welds, from shrink cracks or other imperfections in weldments; or they may nucleate and grow in structure under fatigue loading. It is the role of fracture mechanics to determine when these cracks become critical, that is, when they will reach a size at which the crack will grow catastrophically at an operational stress well below the yield strength. The following are descriptions of a few documented fatigue-related failures that had occurred during the service life of the structure and are directly extracted from Reference [1] by Parker. Extensive scientific investigation on the nature of these structural failures indicated that in almost all cases, flat (cleavage) or brittle fracture occurred in a catastrophic manner, with high velocities and little or no shear lips. Defects in the welded parts, induced residual stresses in the weld and during the structural assembly, steel composition, cyclic and corrosion environment, transition temperature effect (ductile-brittle failure) poor design, and lack of inspection can all be responsible for these failures. Of the sources of failures reported in Reference [1], seven started in riveted structures as the source of stress concentration and 14 in welded parts.

were carried out on two large (>2000 ha) experimental fires conducted in arid savanna fuels in Kruger National Park in September 1992. Prefire fuel loads, fuel consumption, spread rates, flame zone characteristics, and in-fire and perimeter wind field dynamics were measured in order to determine overall energy release rates for each fire. Convection column dynamics were also measured in support of airborne trace gas and particulate measurements. Energy release rates varied significantly between the two fires, and this was strongly reflected in convection column development. The lower-intensity fire produced a weak, poorly defined smoke plume, while a well-developed column with a capping cumulus top developed during the higher intensity fire. Further experimental burning studies, in savannas with higher fuel loads, are recommended to further explore the fire behavior-convection column dynamics relationship investigated in this study.

There is growing interest in conducting small-scale tests to gain additional insight into the fracture behaviour of components across a wide range of materials. For example, micro-scale mechanical tests inside of a microscope (in situ) enable direct, high-resolution observation of the interplay between crack growth and microstructural phenomena (e.g., dislocation behaviour or the fracture resistance of a particular interface), and sub-size samples are increasingly used when only a limited amount of material is available. However, to obtain quantitative insight and extract relevant fracture parameters, the sample must be sufficiently large for a 𝐽-(HRR) or a 𝐾-field to exist. We conduct numerical and semi-analytical studies to map the conditions (sample geometry, material) that result in a valid, quantitative fracture experiment. Specifically, for a wide range of material properties, crack lengths and sample dimensions, we establish the maximum value of the 𝐽-integral where an HRR field ceases to exist (i.e., the maximum 𝐽 value at which fracture must occur for the test to be valid, 𝐽 max). Maps are generated to establish the maximum valid 𝐽 value (𝐽 max) as a function of yield strength, strain hardening and minimum sample size. These maps are then used to discuss the existing experimental literature and provide guidance on how to conduct quantitative experiments. Finally, our study is particularised to the analysis of metals that have been embrittled due to hydrogen exposure. The response of relevant materials under hydrogen-containing environments are superimposed on the aforementioned maps, determining the conditions that will enable quantitative insight.

The tensile strength of unidirectional (UD) carbon fiber composites was predicted considering the interfacial shear strength (IFSS). First, the effect of the IFSS on the load transfer to the surrounding fibers when a fiber was broken was analyzed using finite element method and then the stress concentration factor (SCF) of each surrounding fiber was determined. The multiple fracture number was calculated using the SCF and a statistical approach that can calculate the probability of fiber breakage propagation due to the stress concentration when the broken fibers exist in neighbor. Finally, the tensile strength of UD carbon fiber composites was predicted using the multiple fracture number and was compared with experimental results, demonstrating the validity of the current method. An optimal IFSS that can ensure the maximum tensile strength of UD carbon fiber composites is discussed based on the calculation results.

On propose un paramètre énergétique de rupture pour les matériaux anélastiques sous forme d'une intégrale de domaine, fondé sur le taux de restitution de l'énergie mécanique totale reçue par un solide entaillé, en utilisant une méthode de dérivation par rapport à un domaine. Ce paramètre est présenté pour une classe générale de chargement et de matériaux dont l'état mécanique est décrit par des variables internes. On montre, dans le cas où le matériau est soit élastique, soit élastoplastique et soumis à un chargement proportionnel, que ce paramètre se réduit à l'intégrale J de Rice-Cherepanov.

The paper deals with the fast crack growth and arrest simulated by CZM (Cohesive Zone Models) based on energy principles. After some details about our CZM developments, validations of this model are carried out on a DCB specimen involving fast growth and arrest. In particular, the effect of cohesive parameters and stress waves round trips on crack kinematics are investigated. Then, the dynamic propagation of a subclad flaw in a PWR vessel is considered. A 6mm radial crack is embedded into the ferritic steel, under the austenitic cladding. To simulate the potential crack growth, a set of CZM elements is dispatched on a straight line on both sides of the flaw (crack kinking is not considered here). The vessel is submitted to a hypothetical loading involving a high inner pressure to start up a running crack growth. Furthermore, heterogeneous fracture properties are capable of enhancing the running process or in contrary to cause the arrest crack. The main results are the following : Th...

An arbitrary Lagrangian description is proposed for the moving crack analysis. The method is based on the use of a mapping of the moving domain to the initial stationary one (boundaries, shape and conditions may be very general). In the framework of elasticity, the energy release rate is expressed as surface integrals on the fixed domain, explicitly related to the current crack growth (or crack shape in 3D) parameter. Numerical results of an energy release rate analysis are presented for a large range of 2D and 3D crack extension. The advantages of this method are: firstly, it avoids remeshing or introducing special numerical parameters such as relaxation forces to simulate the crack growth or performing parametric analysis for different crack shape; secondly, to obtain exact derivatives of the potential energy.

On propose un paramètre énergétique de rupture pour les matériaux anélastiques sous forme d'une intégrale de domaine, fondé sur le taux de restitution de l'énergie mécanique totale reçue par un solide entaillé, en utilisant une méthode de dérivation par rapport à un domaine. Ce paramètre est présenté pour une classe générale de chargement et de matériaux dont l'état mécanique est décrit par des variables internes. On montre, dans le cas où le matériau est soit élastique, soit élastoplastique et soumis à un chargement proportionnel, que ce paramètre se réduit à l'intégrale J de Rice-Cherepanov.

The aim of this paper is the analytical determination of the strain energy release rates in a delaminated laminate by means of a model of plates which provides no singular stresses. The strain energy release rates are expressed as quadratic functions of the interfacial stresses at the crack tip. These expressions and relevant delamination criteria can help predict delamination onset and growth. As an application example, data from edge delamination tests on carbon-epoxy laminates are used for determining a mode III delamination criterion involving the corresponding energy release rate. This criterion yields very accurate predictions and its analytical expression validates from an energy point of view a maximum stress criterion proposed in an earlier paper.

A new cohesive zone model is developed in order to study the mechanisms of adhesive and cohesive failures of soft rubbery materials. The fracture energy is estimated here using a strategy similar to that of Lake and Thomas (LT) by considering the dissipation of stored elastic energy followed by the extension and relaxation of polymer chains. The current model, however, departs from that of LT in that the force needed to break an interfacial bond does not have a fixed value; instead, it depends on the thermal state of the system and the rate at which the force is transmitted to the bond. While the force required to rupture a chain is set by the rules of thermomechanically activated bond dissociation kinetics, extension of a polymer chain is modeled within both the linear and nonlinear models of chain elasticity. Closed form asymptotic solutions are obtained for the dependence of crack propagation speed on the energy release rate, which are valid in two regimes: (I) slow crack velocity or short relaxation time for bond dissociation; (II) fast crack velocity or long relaxation time for bond dissociation. The rate independent and the zero temperature limit of this theory correctly reduces to the fracture model of LT. Detailed comparisons are made with a previous work by Chaudhury et al. which carried out an approximate analysis of the same problem.

The Boeing sol-gel conversion coating (Boegel-EPII), derived from an acidcatalyzed aqueous solution of organofunctional silane and zirconium alkoxide precursors, is being used as an adhesion promoter for adhesive bonding and painting applications in the aerospace industry. A unique advantage of the sol-gel process is that strong and durable bonds are produced without the hazardous chemical usage and rinse-water requirements of conventional anodizing or etching processes. In this study, a fracture mechanics method was used to investigate the adhesion properties of sol-gel-reinforced epoxy=aluminum joints. The Hugh Brown asymmetric double cantilever beam (ADCB) wedge test was employed, which allowed the measurements of the critical energy-release rate, subcritical crack-growth kinetics, and threshold energy-release rate on a single sample in a reasonably short period of time. These experiments were carried out with aluminum substrates on which the surface morphology was systematically varied by polishing, sanding, grit-blasting, and chemical etching. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to identify the locus of failure. The surface morphology of the substrates was characterized with SEM, optical profilometry, and spreading kinetics. The macrorough structures drive the crack to within a thin epoxy layer close to the polymer=metal interface, which enhances the initial strength of the sol-gel-reinforced interface. The microroughness of the substrate is, however, more effective than the

When two thin soft elastomeric films are separated from each other, an elastic instability develops at the interface. Although similar instability develops for the case of a soft film separating from a rigid adherent, there are important differences in the two cases. For the single-film case, the wavelength of instability is independent of any material properties of the system, and it scales only with thickness of the film. For the two-film case, a co-operative instability mode develops, which is a non-linear function of the thicknesses and the elastic moduli of both films. We investigate the development of such instability by energy minimization procedures. Understanding the nature of this instability is important, as it affects the adhesive compliance of the system and thus the energy release rate in the debonding of soft interfaces.

Sensors and actuators can now achieve high levels of stretchability and functionality owning to the recent development of stretchable electronics. One main factor in creating high-performance stretchable electronics that can be adequately transferred to curved surfaces, such as human skin, is the conformal design of the island-bridge model. In island-bridge models, interconnect conductors (bridges) are the most vulnerable. Thus, it is necessary to preserve the durability and functionality of interconnect conductors under high strains. In this study, by transferring dots to the main substrate, the interconnect conductors can be protected. This causes the strain to become localized in the region between the two neighboring islands. This region is known as safe region. In the safe region, the strains bypass the other side of the stretchable electronic from the upper and lower parts. This objective was achieved using the experimental tensile test and finite element analysis. These results displayed a 4% - 9% reduction in the average strain of safe region while applying 10% - 30% strain. The design parameters were optimized with energy release rate measurement. Additionally, the interconnect conductors’ path in the safe region was optimized improving this value to at least 50% below its applied strain. This design made the stretchable electronic significantly durable while maintaining its functionality.

The condition of interfacial debonding at a fiber/matrix interface has been defined by two criteria: the strength criterion, and the critical energy release rate criterion. The applied stresses required to initiate interfacial debonding during fiber pull-out or push-out are analyzed by using an improved shear-lag model, in which both Poisson's effect and the radial dependence of the axial stress in the matrix are included. Both the strength and the energy criteria are considered. The bonded fiber length dependences of the debond stresses are obtained for both criteria. For the energy criterion, the asymptote of the debond stress obtained in the present study and the length-independent debond stress derived elsewhere are in excellent agreement. The effects of the properties of the fiber and of the matrix on the debond stress are also shown for both criteria which provide a basis for experimental verification of these two criteria.

A Hookean material containing an increasing number of non-interacting microcracks is studied from the aspect of continuum thermodynamics. Rectilinear microcracks in a two-dimensional body are examined. The former model by Basista ( ) is enhanced to describe the response of microcracks to compression. Microcrack densities introduced here enter into the formulation of continuum thermodynamics as internal variables. The strong physical foundation of these internal variables makes them more attractive quantities for damage mechanics than variable damage, the physical background of which is sometimes unclear. The model is coded as an Abaqus VUMAT subroutine and applied to the creep of ice.

Newton's law of visocosity is a commonly used constitutive theory for deviatoric Cauchy stress tensor. In this constitutive theory originally constructed based on experimental observation, the deviatoric Cauchy stress is proportional to the symmetric part of the velocity gradient tensor. The constant of proportionality is the viscosity of the fluid. For all continuous media if the deforming matter is in thermodynamic equilibrium then all constitutive theories including those considered here must satisfy conservation and balance laws. It is well known that only the second law of thermodynamics provides possible conditions or mechanisms for deriving constitutive theories. The constitutive theory for deviatoric stress tensor used here can be shown to be a simplified form of the constitutive theory derived using conditions resulting from the entropy inequality in conjunction with the theory of generators and invariants that contains up to fifth degree terms in the components of the symmetric part of the velocity gradient tensor. In general the constitutive theory for deviatoric stress tensor is basis (covariant, contravariant, or Jaumann) dependent as it uses convected time derivatives of the Green and Almansi strain tensors of orders higher than one. However, the first convected time derivative of the Green and Almansi strain tensors are in fact symmetric part of the velocity gradient tensor which is basis independent. Thus, if the constitutive theory for deviatoric Cauchy stress tensor is only dependent on the symmetric part of the velocity gradient tensor, then it is basis independent. This is the case for the theory presented in this paper. In this paper we limit the constitutive theory for deviatoric Cauchy stress tensor to contain only up to quadratic terms in the components of the symmetric part of the velocity gradient tensor. The objective is to study the resulting flow physics due to the constitutive theory for deviatoric Cauchy stress tensor that contains up to quadratic terms in the velocity gradient tensor. Model problems consisting of fully developed flow between parallel plates, square lid-driven cavity, and asymmetric sudden expansion are used to present numerical solutions. Numerical solutions of the model problems are calculated using least squares finite element formulation based on residual functional in which the local approximations are considered in higher order scalar product spaces that permit higher order global differentiability solutions. Nonlinear system of algebraic equations are solved using Newton's linear method with line search.

The debonding of a skin/stringer specimen subjected to tension was studied using threedimensional volume element modeling and computational fracture mechanics. Mixed mode strain energy release rates were calculated from finite element results using the virtual crack closure technique. The simulations revealed an increase in total energy release rate in the immediate vicinity of the free edges of the specimen. Correlation of the computed mixed-mode strain energy release rates along the delamination front contour with a two-dimensional mixed-mode interlaminar fracture criterion suggested that in spite of peak total energy release rates at the free edge the delamination would not advance at the edges first. The qualitative prediction of the shape of the delamination front was confirmed by X-ray photographs of a specimen taken during testing. The good correlation between prediction based on analysis and experiment demonstrated the efficiency of a mixed-mode failure analysis for the investigation of skin/stiffener separation due to delamination in the adherents. The application of a shell/3D modeling technique for the simulation of skin/stringer debond in a specimen subjected to three-point bending is also demonstrated. The global structure was modeled with shell elements. A local three-dimensional model, extending to about three specimen thicknesses on either side of the delamination front was used to capture the details of the damaged section. Computed total strain energy release rates and mixedmode ratios obtained from shell/3D simulations were in good agreement with results obtained from full solid models. The good correlations of the results demonstrated the effectiveness of the shell/3D modeling technique for the investigation of skin/stiffener separation due to delamination in the adherents.

This paper presents an alternative approach to constructing computer experiment designs based on stochastic process theory, specifically marked point processes with two types. The originality of this method lies in the use of Markov Chain Monte Carlo (MCMC) techniques, combined with the Metropolis-Hastings algorithm and a new dynamic called local shift dynamics. These tools enable the generation of highly flexible and adaptable experimental designs, which can be tailored to a variety of specific objectives according to experimental needs. Special attention has been given to analyzing the convergence of the Markov chain, thus ensuring the robustness and efficiency of the results obtained. Additionally, a comparative study was conducted to position our method relative to other existing computer designs. This comparison highlights the advantages and disadvantages of our approach in terms of modularity and performance.

This paper deals with the fracture problem in timber structures subject to mechanical and climatic loadings. Mechanical tests illustrate local and global fracture properties at different moisture content levels on DCB specimens of douglas fire. It is shown the dependence of moisture content in terms of compliance and energy release rate. To highlight the hygro-mechanical coupling, tests employ an electromechanical press associated with an environmental chamber in which humidity and air temperature are regulated. Two families of tests are performed, the first in dry state conditions and the second in a wet state conditions. The main objective of this paper is to fix first experimental results in order to integrate, in future works, mechano-sorptive effects on the crack growth process by taking into account moisture content variations in the crack tip vicinity associated with sorption kinetics.

In this paper, mode I interlaminar fracture in stitched reinforced composite laminates is modelled using a cohesive model. The test configuration used in this study is a stitched reinforced double cantilever beam specimen. A bilinear damage-ratedependent cohesive traction-separation law is adopted to model the woven composite fracture and discrete nonlinear spring elements to represent the stitches effect. A novel macroscopic law adopted from a 1D micromechanical-stitching model, is developed to model the stitches effect along the interface. The numerical simulations of DCB test with the present model, shows a good agreement with the experimental results.

This paper shows distinctive features and some results obtained with a new numerical methodology for Computational Fluid Dynamics (CFD), which is the result of the right combination of Bond Graph concepts with elements of Numerical Methods. This methodology was used so far to model single-phase, single-component and single-phase, multicomponent flows. The main characteristics of this new methodology, called BG-CFD, are summarized. Some results of one-dimensional, single-component problems corresponding to heat conduction, convection-diffusion and compressible flows are discussed, showing that this methodology is a foundation of a bridge between Bond Graphs and CFD.

Approved for public release; distribution unlimited. Reproduction in whole or in part is permitted for any purpose of the United States Government. stress-relaxation, fracture, crazing, polystyrene, fractograph, J-integral, energy release rate, fracture toughness, crack propagation. --Microscopic observations of precracked polystyrene samples under fixed elongation conditions reveal that crack propagates discontinuously under diminishing stress to a stable configuration. A zone of intensive crazes in the vicinity of the crack tip evolves concurrently with crack growth. Fracture occurs as the translation and expansion of the crazed zone ahead of the crack. The phenomenon has been successfully explained using a crack layer model. Contrary to conventional fracture mechanics ideas, crack propagation is found DO 1 FA'.

In this companion article, we present, within the finite element context, the numerical algorithms for the integration of the thermodynamically consistent formulation of the elastic plastic and damage model for concrete materials derived in part I of this work. The proposed unified integration scheme is based on the spectral return-mapping algorithm accounting for the use of the principal stresses along with the stress tensor invariants. An operator split structure is used, consisting of a trial stress state followed by corrector steps applied through imposing the generalized plastic and damage consistency conditions. Furthermore, a trivially incrementally objective integration scheme is established for the rate constitutive relations. The proposed elastic-predictor and uncoupled plastic and damage corrector algorithms allow for a straightforward integration scheme that can be easily implemented into the existing finite element codes. The nonlinear algebraic system of equations is solved by consistent linearization and the Newton-Raphson iteration scheme. The proposed model is implemented in the implicit finite element code ABAQUS via the user subroutine UMAT. Model capabilities are illustrated through its application to the analysis of Reinforced Concrete (RC) beams tested experimentally and available in literature. The simulated results illustrate the potential of the proposed model in dealing with the reduction of the effect of the well known mesh sensitivity problem through the application of the fracture energy concept-related parameters.

This study involves the numerical simulation of crack growth in girth welds of steel catenary risers under constant tension and cyclic bending. The modeling was carried out with the aid of a finite elements framework and a fracture mechanics program, which generates the initial crack and updates the model mesh according to the local energy release rate of the crack front nodes. The non-linear analysis comprises three-dimensional model mesh with solid elements, finite rotations, elastic-plastic behavior of the material and the linear theory of fracture mechanics. The numerical results were qualitatively compared with proposed fatigue curve of the British Standard International code.

For a monocoque hull structure, the bulkhead is used to separate the hull into many compartments. A typical joint between the hull and bulkhead used in such structure is known as a Tjoint. It consists of composite overlaminates over a shaped fillet to allow the transmission of direct and membrane shear stresses. This paper describes the numerical solutions of the analytical approach in studying of the effect of disbond for a composite ship T-Joint using two methods, the VCCT (Virtual Crack Closure Technique) and CTE (Crack Tip Element) method. The analysis was conducted for T-Joints with various disbond sizes. It was subjected to a straight pull-off load to simulate normal operational conditions. An experimental investigation was conducted to validate the FE (Finite Element) models. The results of the numerical and experimental studies are discussed to corroborate the effectiveness of using fracture mechanics for this analysing this structure. A modified CTE model for the T-joint is proposed to enable a like-for-like comparison to that evaluated by the VCCT method.

Technological advancements in real-time distributed sensing and processing for structural health monitoring systems have enabled exploration of the next frontier in structural health monitoring for in-situ condition-based prediction of remaining life of damaged or aging structures. In that context, model-based prognostics methods have shown considerable promising results. These methods require that suitable damage progression models are available or be developed. Recent works have shown that energy release rate models work effectively for predicting material stiffness degradation based on matrixcracking. However, since delamination and matrix-cracking damage modes are known to co-exist and fuel each other's progression, it is desirable to investigate extension of these models for multiple damage modes. To that end, this paper analyzes several multiple damage-mode models from composite modeling literature and assesses them against experimental data from run-to-failure aging experiments. These models aim to estimate and correlate strain energy release rate and the residual stiffness as a function of the damage extent. Model review in this work reports modeling behavior and mathematical complexity along with strengths and limitations of these models. This is expected to guide selection of suitable model for a more robust prognostic solution generalized for more realistic degradation scenarios.

The modeling of the welding is desirable to guess the deformation of the components during manufacture, the position and the magnitude of maximum residual stresses and to envisage metallurgical effects in specific zones. The welding are problems of complex modeling requiring the thermal and structural solutions. This has to lead to the development of several software packages and codes for simulation by finite elements. The welding condition, the properties of the structure and their interactions have significant influences on the thermal and structural responses (temperature history, distortion, and residual stress) in welded structures. This paper presents a finite element procedure for the prediction of welding-induced residual stresses and distortions. Comparison is made with tow numerical example. The first example is a butt welded joint of two plates, while the second is a Cruciform welded joint of two plates with four passes. Moreover, a comparison between the Cruciform weld and the butt-weld which we can obtain the parameters of the linear fracture mechanics; stress intensity factor K and energy release rate G.

Delamination in multilayered three-point bending beam configurations is analyzed assuming non-linear behaviour of the material in each layer. For this purpose, an analytical approach is developed by using the Ramberg-Osgood equation. A solution for the strain energy release rate is derived by considering the energy balance. The strain energy release rate is obtained also by analyzing the complementary strain energy for verification. The solution derived is valid for a beam made of an arbitrary number of adhesively bonded horizontal layers of different thicknesses and material properties. Besides, the delamination can be located arbitrary between layers. The solution is applied for parametric investigations of delamination behaviour. The effects of delamination position along the beam height, material non-linearity and delamination length on delamination behaviour are evaluated. The results obtained in the present study are benefit to structural design of multilayered three-point bending beams exhibiting material non-linearity.

This paper couples bulk damage modeling and cohesive zone modeling to get the benefits of both. Damage brings the directionality for the crack propagation as well as the possibility of crack branching while cohesive zone modeling allows for an explicit discrete crack modeling. The coupling is made easy through the Thick Level Set approach. The originality is that the coupling induces concurrent development of bulk and interface degradation.

Descripció: En este artículo se describe el modelaje de elementos de concreto armado sometidos a flexo-compresión biaxial dentro de una nueva teoría de pórticos llamada teoría del daño concentrado. Esta teoría puede ser considerada como una mecánica de la ...

An experimental study has been carried out using geometrically similar notched plain concrete three-point bend (TPB) specimens of different sizes and the acoustic emissions (AE) are monitored during fracture process. In the present study , measurement of the AE ener gy released during the fracture process of plain concrete beams is carried out. A monotonically increasing load applied on a series of concrete beam specimens of dif ferent sizes with different strength. While testing concrete specimens for fracture energy, AE ener gy release was monitored at the same time. An attempt has been made to relate AE ener gy and size independent specific fracture ener gy of concrete. The experimental study show that it may be possible to get an idea about the fracture ener gy from the measured AE ener gy. may be supposed that AE ener gy also should be size dependent to fracture energy. In order to obtain a size independent AEE the concept adopted earlier by previous researchers is used in the ...

In this work, an analytical solution of the thermal stresses for a fiber embedded in a matrix is presented based on the idea of the boundary layer and under some simplifying assumptions. These assumptions include: the properties of both materials, fiber and matrix, remain constant; both materials remain in the elastic range so no plastic-deformation are considered; there exists a perfect bonding between the fiber and matrix so the condition of no-opening holds over the entire interface; and the composite is subjected to an uniform change of temperature. The analytical solution to the problem is found for the case when the length of the embedded bar (fiber) is much greater than its radius, and the Young's modulus of the matrix is much less than that of the fiber. The problem is also solved numerically by means of finite element analysis using a commercial package. Both results are compared and it is shown that both approaches coincide very close qualitatively and quantitatively although significant discrepancies may appear at specific points for specific cases.

Approximation of u 2,1 (x, 0) by a finite sum of Chebyshev polynomials (400 terms) for γ = 0.05 and far-field loading σ = 0.01, 0.02, 0.04. 47 3.3 Approximation of u 2,1 (x, 0) by a finite sum of Chebyshev polynomials (400 terms) for far-field loading σ 0 = 0.02 andγ = 0.

Multilayered delaminated plates are analyzed here using an 2D plate model. Alternative to the existing three-dimensional finite element methods (3D-FEM), the proposed model, named LS1, is a layerwise stress model proving significantly less computationally expensive while accurate and efficient [see 1, 2, 3, 4, 5]. In particular this paper uses experimental data from different test specimens (DCB, ELS, ADCB, MMF) in a finite element code, which is based on LS1, in order to calculate strain energy release rates (SERR) in different modes of delamination. The focus is on two types of delaminated interfaces 0/0 and 0/45. The obtained SERR results are in very good agreement with the experimental values and, in the case of mixed-mode delamination, they are as accurate as the SERR obtained by 3D-FE models. The other interesting property of the LS1 model is the very fast calculation speed as the SERR can be analytically deduced from interfacial stresses. This relation which only depends on the stacking sequence and the position of delamination is presented.

Reinforced concrete continuous coverings are partly used as a fine revetment in river dikes. In icy regions, there is the possibility of freezing the water surface. If this condition happens, even once during the design period of a revetment, it will have severe destructive effects on it. Therefore, the strength control of revetments under the ice loads caused by frozen water surface would be essential in sub-zero conditions. The most critical condition would be when a frozen layer forms on water surface and then the water level under this frozen layer drops which may cause the frozen layer floated. In this paper, the analytical study of the revetment strength under ice loads considering the above critical situation and under the condition of existence of nonzero axial force has been carried out. This method would be applicable in rivers capable of freezing in which concretelined dikes is designed and applied.