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Energy Release Rate (energy + release_rate)

Distribution by Scientific Domains
Polymers and Materials Science76%
Engineering23%

Kinds of Energy Release Rate

  • strain energy release rate
    		•

    Selected Abstracts

    Fracture and fatigue study of unidirectional glass/epoxy laminate under different mode of loading

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2010
    M. KENANE
    ABSTRACT Interlaminar fracture is the dominant failure mechanism in most advanced composite materials. The delaminating behaviour of materials is quantified in terms of the strain energy release rate,G. In this paper, the experimental measurements of the fatigue delaminating growth for some combinations of energy release rate mode ratio have been carried out on unidirectional glass/epoxy laminates. On this base the constants in the Paris equation have been determined for each GII/GT considered modal ratio. The fatigue threshold strain energy release rate ,,GTth, below which delaminating doesn't occur, were measured. Three type specimens were tested, namely: double cantilever beam (DCB), end-loaded split (ELS) and mixed-mode bending (MMB) under mode I, mode II and mixed-mode (I + II) loading, respectively. Scanning electron microscopy techniques were used to identify the fatigue delamination growth mechanisms and to define the differences between the various modes of fracture. [source]

    A predictor,corrector scheme for the optimization of 3D crack front shapes

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005
    K. KOLK
    ABSTRACT A predictor,corrector scheme is presented to improve the shape of 3D crack fronts within the 3D simulation of fatigue crack growth. This concept is fully functional for mode-I, and an extension for mixed-mode problems is presented. The whole procedure is embedded in an automatic incremental crack growth algorithm for arbitrary 3D problems with linear elastic material behaviour. The numerical simulation is based on the 3D dual boundary element method (Dual BEM) and on an optimized evaluation of very accurate stress intensity factors (SIFs) and T-stresses. As part of the proposed predictor,corrector scheme, 3D singularities along the crack front especially in the vicinity of the intersection of the crack front and the boundary are considered. The knowledge of these singularities allows the specification of crack front shapes with bounded energy release rate. Numerical examples with complex cross-sections are presented to show the efficiency of the proposed crack growth algorithm. The obtained results are in good agreement with recent experimental results. [source]

    Stress intensity factors for cracked triangular cross-section thin-walled tubes

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2004
    Y. J. XIE
    ABSTRACT For one kind of finite-boundary crack problems, the cracked equilateral triangular cross-section tube, an analytical and very simple method to determine the stress intensity factors has been proposed based on a new concept of crack surface widening energy release rate and the principle of virtual work. Different from the classical crack extension energy release rate, the crack surface widening energy release rate can be defined by the G*-integral theory and expressed by stress intensity factors. This energy release rate can also be defined easily by the elementary strength theory for slender structures and expressed by axial strains and loads. These two forms of crack surface widening energy release rate constitute the basis of a new analysis method for cracked tubes. From present discussions, a series of stress intensity factors are derived for cracked equilateral triangular cross-section tubes. Actually, the present method can also be applied to cracked polygonal tubes. [source]

    A simple model for the prediction of the fatigue delamination growth of impacted composite panels

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2004
    D. G. KATERELOS
    ABSTRACT The fatigue behaviour of composite panels that have been subjected to low-velocity impact was studied. Impacted specimens were tested under compression,compression fatigue. A delamination propagation model based on the derivation of the strain energy release rate was used. The stress distribution around the initially induced delamination was derived analytically. The shape of the delamination was experimentally monitored by c-scan imaging and is assumed to be an ellipse. The orientation and aspect ratio of the ellipse were used to calculate the corresponding strain energy-release rates, which were subsequently used to predict the direction of delamination propagation. [source]

    Conserving Galerkin weak formulations for computational fracture mechanics

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2002
    Shaofan Li
    Abstract In this paper, a notion of invariant Galerkin-variational weak forms is proposed. Two specific invariant variational weak forms, the J-invariant and the L-invariant, are constructed based on the corresponding conservation laws in elasticity, one of which is the conservation of Eshelby's energy-momentum (Eshelby. Philos. Trans. Roy. Soc. 1951; 87: 12; In Solid State Physics, Setitz F, Turnbull D (eds). Academic Press: New York, 1956; 331; Rice, J. Appl. Mech. 1968; 35: 379). It is shown that the finite element solution obtained from the invariant Galerkin weak formulations proposed here can conserve the value of J-integral, or L-integral exactly. In other words, the J and L integrals of the Galerkin finite element solutions are path independent in the discrete sense. It is argued that by using the J-invariant Galerkin weak form to compute near crack-tip field in an elastic solid, one may accurately calculate the crack extension energy release rate and subsequently the stress intensity factors in numerical computations, because the flux of the energy-momentum is conserved in discrete computations. This may provide an alternative means to accurately simulate crack growth and propagation. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Criterion for the Avoidance of Edge Cracking in Layered Systems

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004
    M. Y. He
    When fabricating multilayers with brittle constituents, a prevalent design strategy is to choose fabrication conditions and thermal expansion coefficients that impose in-plane compression on the brittle layers. In such designs, a small zone of out-of-plane tension is induced at the edges that can cause cracks to form and extend, especially along the midplane. The associated stresses and energy release rates have been analyzed, revealing a fail-safe criterion, attributed to the existence of a maximum possible energy release rate, Gmax. Equating this maximum to the toughness defines a fail-safe parameter expressing the influence of the layer thickness, the misfit stress, and the toughness. When fail-safe designs cannot be realized, thin interlayers can be interposed in a manner that diminishes Gmax, broadening accessibility. The roles of misfit stress and interlayer thickness in attaining this condition are derived. [source]

    Effect of cooling rate and crack propagation direction on the mode 1 interlaminar fracture toughness of biaxial noncrimp warp-knitted fabric composites made of glass/PP commingled yarn

    POLYMER COMPOSITES, Issue 3 2008
    Yantao Wang
    The mode 1 interlaminar fracture toughness of biaxial (±45°) noncrimp warp-knitted fabric composites made of glass/PP commingled yarn was investigated. The crack propagation along the warp and weft directions, respectively, was considered for the composites cooled at two different rates during laminate molding. The interlaminar fracture toughness was characterized by determining the critical strain energy release rate (GIC) of initiation and propagation measured from the double cantilever beam tests. In the case of a slow cooling rate (1°C/min), most specimens possess pure interlaminar crack propagation and direction-independence characteristics. Nevertheless, the high-cooled (10°C/min) specimens fractured in both directions suffer extensive intraply damage (crack branching, debonding, and bridging of 45°-oriented interfacial yarns) and knit thread breakage, leading to GIC of propagation two times higher than that of the slow-cooled specimens, and the clear difference in the GIC values of initiation between the two directions may be due to the contribution of the knit thread breakage to the fracture energy. POLYM. COMPOS., 2008 © 2007 Society of Plastics Engineers [source]

    Impact behavior of a short glass fiber reinforced thermoplastic polyurethane

    POLYMER COMPOSITES, Issue 3 2000
    J. Jancar
    The temperature dependence of critical strain energy release rate (Gc,) and standardized Charpy notched impact strength (CNIS) were measured for a thermoplastic polyurethane (TPUR) reinforced with 30 wt% of short glass fibers (SGF) over a temperature interval ranging from ,150°C 23°C (RT) at two strain rates, 70 and 150 s,1, respectively. Fractographic observation of fracture planes was used to qualitatively assess the fracture modes and mechanisms. Adhesion between the reinforcement and the matrix was excellent and the integrity of the fiber-matrix interfacial contact was relatively insensitive to exposure to hydrolysis during the immersion in boiling water for 100 hours. At temperatures above ,30°C, there was a large extent of plastic deformation in the vicinity of crack planes while at temperatures below ,50°C, the extent of plastic deformation was substantially reduced. This resulted in a change in the major energy dissipation mechanism and led to a decrease of both CNIS and Gc, values for SGF/TPUR composites. It was suggested that the plastic deformation of TPUR matrix in the immediate vicinity of glass fibers was the primary source of energy dissipation at temperatures above ,30°C, while the friction and fiber pull-out was the main dissipative process below ,50°C. Over the whole temperature interval investigated, greater Gc, values were obtained at higher strain rate of 150 s,1, without any significant change in the fractographic patterns observed on the fracture planes. The CNIS/Gc, ratio, used to assess suitability of CNIS for comparison of materials, changed with temperature substantially suggesting that the functional dependences of CNIS and Gc, on temperature differ substantially. Hence, CNIS data do not provide a reliable base for material selection and for design purposes in this case. [source]

    Oriented crystallization and mechanical properties of polypropylene nucleated on fibrillated polytetrafluoroethylene scaffolds

    POLYMER ENGINEERING & SCIENCE, Issue 4 2005
    Douwe W. van der Meer
    It is known that friction deposited polytetrafluoroethylene (PTFE) layers are able to nucleate crystallization of thin films of isotactic polypropylene (iPP). In order to investigate the influence of PTFE on the crystallization behavior and morphology of iPP in bulk, PTFE-particles of two different sizes in various concentrations were melt-blended with iPP and subsequently processed by injection molding. For one size of particles, high resolution scanning electron microscopy (HR-SEM) showed the presence of a PTFE scaffold consisting of highly fibrillated PTFE particles. With X-ray diffraction (WAXD) pole-figures, it was evidenced that, after melting and recrystallization of the iPP matrix, a strongly oriented crystallization of iPP on this PTFE scaffold takes place (quiescent crystallization conditions). With WAXD it was also shown that under processing conditions, PTFE acts as a nucleating agent for iPP and that PTFE strongly enhances the formation of processing induced morphologies. Impact and tensile performance of the mixtures were measured. Both the strain energy release rate (GI) and the E-modulus were found to increase upon introducing PTFE in iPP. POLYM. ENG. SCI., 45:458,468, 2005. © 2005 Society of Plastics Engineers. [source]

    On rate independent models for crack propagation

    PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008
    Dorothee Knees
    We model the evolution of a single crack as a rate,independent process based on the Griffith criterion. Three approaches are presented, namely a model based on global energy minimization, a model based on a local description involving the energy release rate and a refined local model which is the limit problem of regularized, viscous models. Finally we present an example which sheds light on the different predictions of the models. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Development of the DYNA3D simulation code with automated fracture procedure for brick elements

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2003
    Ala Tabiei
    Abstract Numerical simulation of cracked structures is an important aspect in structural safety assessment. In recent years, there has been an increasing rate of development of numerical codes for modelling fracture procedure. The subject of this investigation is implementing automated fracture models in the DYNA3D non-linear explicit finite element code to simulate pseudo 3D crack growth procedure. The implemented models have the capabilities of simulating automatic crack propagation without user intervention. The implementation is carried on solid elements. The methodology of implementing fracture models is described. An element deletion-and-replacement remeshing procedure is proposed for updating the explicit geometric description of evolving cracks. Fracture parameters such as stress intensity factors, energy release rates and crack tip opening angle are evaluated. The maximum circumferential stress criterion is used to predict the direction of crack advancement. Seven crack problems are presented to verify the effectiveness of the methodology. Mesh sensitivity and loading rate effects are studied in the validation of the presented procedure. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Criterion for the Avoidance of Edge Cracking in Layered Systems

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004
    M. Y. He
    When fabricating multilayers with brittle constituents, a prevalent design strategy is to choose fabrication conditions and thermal expansion coefficients that impose in-plane compression on the brittle layers. In such designs, a small zone of out-of-plane tension is induced at the edges that can cause cracks to form and extend, especially along the midplane. The associated stresses and energy release rates have been analyzed, revealing a fail-safe criterion, attributed to the existence of a maximum possible energy release rate, Gmax. Equating this maximum to the toughness defines a fail-safe parameter expressing the influence of the layer thickness, the misfit stress, and the toughness. When fail-safe designs cannot be realized, thin interlayers can be interposed in a manner that diminishes Gmax, broadening accessibility. The roles of misfit stress and interlayer thickness in attaining this condition are derived. [source]