The Experts below are selected from a list of 15084 Experts worldwide ranked by ideXlab platform
Maria Kashtalyan - One of the best experts on this subject based on the ideXlab platform.
-
coupled stress and energy criterion for multiple Matrix Cracking in cross ply composite laminates
International Journal of Solids and Structures, 2018Co-Authors: Maria Kashtalyan, I G Garcia, Vladislav ManticAbstract:Abstract Transverse Cracking, i.e. Matrix Cracking in the off-axis plies of the laminate, is widely recognized as the first damage mode to appear in continuous fibre-reinforced composite laminates subjected to in-plane loading. Since transverse Cracking has a great influence on the subsequent damage steps such as delaminations or oblique cracks, it is important to be able to predict its onset and growth accurately. In this paper, it is proposed to use a combination of the Coupled Criterion of Finite Fracture Mechanics (FFM) and the Equivalent Constraint Model (ECM) to predict the evolution of crack density with increasing applied load. Two formulations – a discrete formulation and a continuous formulation – are developed for the energy criterion within the Coupled Criterion. Some dependences between the two formulations are proved, which justifies the good agreement found by the models based on continuous formulations presented by other authors despite the inherent discrete nature of the phenomenon. Dependence of the failure load predicted by the Coupled Criterion on the layer thickness ratio and brittleness number (a structural parameter that characterizes a combination of the stiffness, strength, fracture toughness and the thickness of the cracked ply of the laminate) is examined and discussed for carbon/epoxy and glass/epoxy laminates. Finally, a comparison against experimental results shows a good agreement.
-
damage mechanisms in cross ply fiber reinforced composite laminates
Wiley Encyclopedia of Composites, 2012Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:The fracture process of composite laminates subjected to static or fatigue in-plane loading involves a sequential accumulation of intra- and interlaminar damage, in the form of Matrix Cracking and crack-induced delamination, before catastrophic failure. Matrix Cracking parallel to the fibers in the off-axis plies is the first damage mode observed. It triggers development of other harmful resin-dominated modes such as delaminations. The present article reviews experimental and theoretical studies into the damage mechanisms in cross-ply composite laminates within the framework of damage micromechanics and discusses the effect of intra- and interlaminar damage on the behavior and mechanical properties of laminates, including the work of the authors on modeling Matrix Cracking and crack-induced delaminations. Keywords: Matrix Cracking; delamination; composite laminate; fiber-reinforced composite; stiffness; shear-lag models; equivalent constraint model
-
Matrix Cracking in polymeric composites laminates modelling and experiments
Composites Science and Technology, 2008Co-Authors: Dionisios Katerelos, Maria Kashtalyan, Constantinos Soutis, C GaliotisAbstract:Composites ability to retain functionality in the presence of damage is a crucial safety and economic issue. Generally the first damage mode in composite laminates is Matrix Cracking, which affects the mechanical properties of the structure long before its load-bearing capacity is exhausted. In this paper, a detailed analysis of the effect of Matrix Cracking on the behaviour of cross-ply [0/90]s and unbalanced symmetric [0/45]s glass/epoxy laminates loaded statically in tension is performed. Theoretical predictions of stiffness reduction due to damage are based on the Equivalent Constraint Model (ECM), which takes into account concurrent Matrix Cracking in all plies of the laminate, although Matrix Cracking under consideration is developing only within the off-axis ply of the laminates. The longitudinal Young’s modulus predictions are compared to experimentally derived data obtained using laser Raman spectroscopy (LRS). The good agreement between predicted and measured values of the reduced longitudinal Young’s modulus validates the ECM model and proves that its basic assumptions are accurate. Thus, the predictions for all the mechanical properties by the ECM model are within a realistic range, while experimental evidence is required for further validation.
-
Stiffness and fracture analysis of laminated composites with off-axis ply Matrix Cracking
Composites Part A-applied Science and Manufacturing, 2007Co-Authors: Maria KashtalyanAbstract:Matrix cracks parallel to the fibres in the off-axis plies is the first intralaminar damage mode observed in laminated composites subjected to static or fatigue in-plane tensile loading. They reduce laminate stiffness and strength and trigger development of other damage modes, such as delaminations. This paper is concerned with theoretical modelling of unbalanced symmetric laminates with off-axis ply cracks. Closed-form analytical expressions are derived for Mode I, Mode II and the total strain energy release rates associated with off-axis ply Cracking in [0/θ] s laminates. Stiffness reduction due to Matrix Cracking is also predicted analytically using the Equivalent Constraint Model (ECM) of the damaged laminate. Dependence of the degraded stiffness properties and strain energy release rates on the crack density and ply orientation angle is examined for glass/epoxy and carbon/epoxy laminates. Suitability of a mixed mode fracture criterion to predict the Cracking onset strain is also discussed.
-
Modelling off-axis ply Matrix Cracking in continuous fibre-reinforced polymer Matrix composite laminates
Journal of Materials Science, 2006Co-Authors: Maria Kashtalyan, Costas SoutisAbstract:The fracture process of composite laminates subjected to static or fatigue tensile loading involves sequential accumulation of intra- and interlaminar damage, in the form of transverse Cracking, splitting and delamination, prior to catastrophic failure. Matrix Cracking parallel to the fibres in the off-axis plies is the first damage mode observed. Since a damaged lamina within the laminate retains certain amount of its load-carrying capacity, it is important to predict accurately the stiffness properties of the laminate as a function of damage as well as progression of damage with the strain state. In this paper, theoretical modelling of Matrix Cracking in the off-axis plies of unbalanced symmetric composite laminates subjected to in-plane tensile loading is presented and discussed. A 2-D shear-lag analysis is used to determine ply stresses in a representative segment and the equivalent laminate concept is applied to derive expressions for Mode I, Mode II and the total strain energy release rate associated with off-axis ply Cracking. Dependence of the degraded stiffness properties and strain energy release rates on the crack density and ply orientation angle is examined for glass/epoxy laminates. Suitability of a mixed mode fracture criterion to predict the Cracking onset strain is also discussed.
Gregory N Morscher - One of the best experts on this subject based on the ideXlab platform.
-
stress dependent Matrix Cracking in 2d woven sic fiber reinforced melt infiltrated sic Matrix composites
2013Co-Authors: Gregory N MorscherAbstract:Abstract The Matrix Cracking of a variety of SiC/SiC composites has been characterized for a wide range of constituent variation. These composites were fabricated by the two-dimensional lay-up of 0/90 five-harness satin fabric consisting of Sylramic fiber tows that were then chemical vapor infiltrated (CVI) with BN, CVI with SiC, slurry infiltrated with SiC particles followed by molten infiltration of Si. The composites varied in number of plies, the number of tows per length, thickness, and the effective-size of the tows. This resulted in composites with a fiber volume fraction in the load-bearing direction that ranged from 0.12 to 0.20. Matrix Cracking was monitored with modal acoustic emission in order to estimate the stress-dependent distribution of Matrix cracks. It was found that the general Matrix crack properties of this system could be fairly well characterized by assuming that no Matrix cracks originated in the load-bearing fiber, interphase, chemical vapor infiltrated SiC tow-minicomposites, i.e., all Matrix cracks originate in the 90° tow regions or the large unreinforced SiC–Si Matrix regions. Also, it was determined that the higher fiber-count tow composites had a much narrower stress range for Matrix Cracking compared to the standard tow size composites.
-
stress dependent Matrix Cracking in 2d woven sic fiber reinforced melt infiltrated sic Matrix composites
2013Co-Authors: Gregory N MorscherAbstract:The Matrix Cracking of a variety of SiC/SiC composites has been characterized for a wide range of constituent variation. These composites were fabricated by the 2-dimensional lay-up of 0/90 five-harness satin fabric consisting of Sylramic fiber tows that were then chemical vapor infiltrated (CVI) with BN, CVI with SiC, slurry infiltrated with SiC particles followed by molten infiltration of Si. The composites varied in number of plies, the number of tows per length, thickness, and the size of the tows. This resulted in composites with a fiber volume fraction in the loading direction that ranged from 0.12 to 0.20. Matrix Cracking was monitored with modal acoustic emission in order to estimate the stress-dependent distribution of Matrix cracks. It was found that the general Matrix crack properties of this system could be fairly well characterized by assuming that no Matrix cracks originated in the load-bearing fiber, interphase, chemical vapor infiltrated Sic tow-minicomposites, i.e., all Matrix cracks originate in the 90 degree tow-minicomposites or the large unreinforced Sic-Si Matrix regions. Also, it was determined that the larger tow size composites had a much narrower stress range for Matrix Cracking compared to the standard tow size composites.
-
Matrix Cracking in 3d orthogonal melt infiltrated sic sic composites with various z fiber types
2013Co-Authors: Gregory N Morscher, Hee Mann Yun, James A DicarloAbstract:The occurrence of Matrix cracks in melt-infiltrated SiC/SiC composites with a three-dimensional (3D) orthogonal architecture was determined at room temperature for specimens tested in tension parallel to the Y-direction (perpendicular to Z-bundle weave direction). The fiber types were Sylramic and Sylramic-iBN in the X- and Y-directions and lower modulus ZMI, T300, and rayon in the Z-direction. Acoustic emission (AE) was used to monitor the Matrix-Cracking activity. For Y-direction composites, the AE data were used to determine the location (±0.25 mm) where Matrix cracks occurred in the 3D orthogonal architecture. This enabled the determination of the stress-dependent Matrix crack distributions for small but repeatable Matrix-rich “unidirectional” and the Matrix-poor “cross-ply” regions within the architecture. Matrix Cracking initiated at very low stresses (∼40 MPa) in the “unidirectional” regions for the largest Z-direction fiber tow composites. Decreasing the size of the Z-fiber bundle increased the stress for Matrix Cracking in the “unidirectional” regions. Matrix Cracking was analyzed on the basis that the source for through-thickness Matrix cracks (TTMC) originated in the 90° or Z-fiber tows. It was found that Matrix Cracking in the “cross-ply” regions was very similar to two-dimensional cross-woven composites. However, in the “unidirectional” regions, Matrix Cracking followed a Griffith-type relationship, where the stress-distribution for TTMC was inversely proportional to the square root of the height of the Z-fiber tows.
-
effects of fiber architecture on Matrix Cracking for melt infiltrated sic sic composites
International Journal of Applied Ceramic Technology, 2009Co-Authors: Gregory N Morscher, James A Dicarlo, James D Kiser, Hee Mann YunAbstract:The Matrix Cracking behavior of slurry cast melt-infiltrated SiC Matrix composites consisting of Sylramic-iBN fibers with a wide variety of fiber architectures were compared. The fiber architectures included 2D woven, braided, 3D orthogonal, and angle interlock architectures. Acoustic emission was used to monitor in-plane Matrix Cracking during unload–reload tensile tests. Two key parameters were found to control Matrix-Cracking behavior: the fiber volume fraction in the loading direction and the area of the weakest portion of the structure, that is, the largest tow in the architecture perpendicular to the loading direction. Empirical models that support these results are presented and discussed.
-
modeling stress dependent Matrix Cracking and stress strain behavior in 2d woven sic fiber reinforced cvi sic composites
Composites Science and Technology, 2007Co-Authors: Gregory N Morscher, M Singh, Douglas J Kiser, Marc R Freedman, Ram BhattAbstract:Abstract 2D woven Hi-Nicalon and Sylramic-iBN SiC fiber reinforced chemical vapor-infiltrated (CVI) SiC Matrix composites were tested at room temperature with modal acoustic emission monitoring in order to determine relationships for stress-dependent Matrix Cracking. The Hi-Nicalon composites varied in the number of plies (1–36), specimen thickness, and constituent content. The Sylramic-iBN composites were fabricated with balanced and unbalanced 2D weaves in order to vary the fiber volume fraction in the orthogonal directions. Not surprisingly, Matrix Cracking stresses tended to be, but were not always, higher for composites with higher fiber volume fractions in the loading direction. It was demonstrated that simple relationships for stress-dependent Matrix Cracking could be related to the stress in the load-bearing CVI SiC Matrix. For low-density composites, the 90° minicomposites do not share significant loads and Matrix Cracking was very similar to single tow minicomposites. For higher-density composites, where significant load is carried by the 0° minicomposites, Matrix Cracking was dependent on the unbridged “flaw” size, i.e., the 90° tow size or unbridged transverse crack size.
J W Hutchinson - One of the best experts on this subject based on the ideXlab platform.
-
composite laminates in plane stress constitutive modeling and stress redistribution due to Matrix Cracking
Journal of the American Ceramic Society, 2005Co-Authors: Guy M Genin, J W HutchinsonAbstract:Plane-stress constitutive relations for laminate composites undergoing Matrix Cracking are developed that can be fit to data from uniaxial tests. The constitutive equations are specialized to brittle-Matrix composites in the form of cross-plies and quasi-isotropic laminates. The effect of nonlinear stress-strain behavior on stress redistribution around holes and notches in laminate plates is illustrated.
-
effect of Matrix Cracking on the overall thermal conductivity of fibre reinforced composites
Phil. Trans. R. Soc.#N##TAB##TAB##TAB##TAB#Lond. A, 1996Co-Authors: J W HutchinsonAbstract:The longitudinal thermal conductivity of a unidirectional fibre-reinforced composite containing an array of equally spaced transverse Matrix cracks is calculated. The cracked composite is modelled by a cylindrical cell which accounts for altered heat transfer across the Matrix cracks as well as through debonded portions of the fibre—Matrix interface. Heat transfer mechanisms across the cracks and dedonded interfaces considered are contact, gaseous conduction, and radiation, and the relative importance of these mechanisms is discussed. Approximate closed form solutions to the cell model for the overall thermal conductivity are obtained using an approach reminiscent of the shear lag analysis of stiffness loss due to Matrix Cracking and debonding. Selected numerical results from a finite-element analysis of the cell model are presented to complement the analytical solutions. Both Matrix Cracking and interfacial debonding have the potential for significantly reducing the longitudinal thermal conductivity.
-
effect of Matrix Cracking and interface sliding on the thermal expansion of fibre reinforced composites
Composites, 1995Co-Authors: J W HutchinsonAbstract:Abstract The effect of Matrix Cracking on the thermal expansion behaviour of brittle, unidirectional fibre-reinforced composites is studied. Sliding along the fibre-Matrix interface accompanying Matrix Cracking has a major effect on the change in thermal expansion. This problem is also addressed, both with and without friction. For the most common composite systems, whose fibres have a smaller coefficient of thermal expansion than that of the Matrix, Matrix Cracking and interface sliding result in a reduction of the thermal expansion of the composite. A cylindrical cell model of a composite with uniformly spaced Matrix cracks is invoked for analysis. Shear-lag approximations, enhanced by selected finite element solutions to the cell model, provide estimates of the functional dependence of thermal expansion on constituent properties, Matrix crack density and extent of sliding. Hysteresis behaviour during thermal cycling is analysed accounting for reverse frictional sliding along debonded portions of the fibre-Matrix interface. A nondimensional parameter, E m ΔαΔT/τ (where E m is the Matrix modulus, Δα the thermal expansion mismatch between fibre and Matrix, ΔT the amplitude of the temperature cycle and τ the frictional resistance to sliding), is identified which governs the extent to which sliding reduces the effective expansion coefficient of the composite.
-
inelastic strains due to Matrix Cracking in unidirectional fiber reinforced composites
Mechanics of Materials, 1994Co-Authors: A.g. Evans, J W HutchinsonAbstract:Abstract Simulations of the inelastic strains caused by Matrix Cracking in unidirectional CMCs are performed. They are based on a cell model, which has previously been analyzed by a shear lag approximation. Here, finite element solutions are used to arrive at more accurate formulae, differing from the shear lag results mainly in the range of small debonds. The model relates the inelastic strain to the constitutive properties, particularly the interface sliding and debonding resistances. Comparisons with experimental results indicate good correspondence for a SiC/SiC composite but divergences for a SiC/CAS composite. The divergences are attributed to the contribution of inelastic strain from fiber failure.
-
transverse Cracking in fiber reinforced brittle Matrix cross ply laminates
Acta Metallurgica Et Materialia, 1993Co-Authors: R R Carr, J W HutchinsonAbstract:Abstract The topic addressed in this paper is transverse Cracking in the Matrix of the 90° layers of a cross-ply laminate loaded in tension. Several aspects of the problem are considered, including conditions for the onset of Matrix Cracking, the evolution of crack spacing, the compliance of the cracked laminate, and the overall strain contributed by residual stress when Matrix Cracking occurs. The heart of the analysis is the plane strain problem for a doubly periodic array of cracks in the 90° layers. A fairly complete solution to this problem is presented based on finite element calculations. In addition, a useful, accurate closed form representation is also included. This solution permits the estimation of compliance change and strain due to release of residual stress. It can also be used to predict the energy release rate of cracks tunneling through the Matrix. In turn, this energy release rate can be used to predict both the onset of Matrix Cracking and the evolution of crack spacing in the 90° layers as a function of applied stress. All these results are used to construct overall stress-strain behavior of a laminate undergoing Matrix Cracking in the presence of initial residual stress.
D. Gamby - One of the best experts on this subject based on the ideXlab platform.
-
Matrix Cracking induced by cyclic ply stresses in composite laminates
Composites Science and Technology, 2001Co-Authors: Marie Christine Lafarie-frenot, C. Henaff-gardin, D. GambyAbstract:The objective of this paper is to review the wealth of experimental results obtained in our laboratory during the last 10 years and the related analyses. The relevant studies essentially involve a brittle-Matrix composite (carbon/epoxy T300/914), intended as a model material for characterization under various experimental conditions. The physical and geometrical parameters governing the initiation, accumulation, growth and saturation of Matrix cracks under cyclic mechanical loading have been identified. A shear-lag analysis, associated with an energy release rate criterion, is used to predict Cracking development in each cross-ply laminate subjected to any fatigue loading. More recently, an experimental program has been achieved to characterize the damage development due to thermal cyclic loading. This investigation brought out the limitations of a purely mechanical approach for the prediction of Matrix Cracking due to cyclic thermal exposure.
-
doubly periodic Matrix Cracking in composite laminates part 1 general in plane loading
Composite Structures, 1996Co-Authors: C Henaffgardin, M C Lafariefrenot, D. GambyAbstract:Abstract In cross-ply long fibre composite laminates submitted to general in-plane mechanical loading, Matrix Cracking appears in both 0 ° and 90 ° layers. The number of such cracks increases throughout both quasistatic and fatigue tests. A two-dimensional shear-lag analysis for progressive damage in composite laminates is then developed to model this crack geometry. A general governing equation set is derived for [0 m , 90 n ] s laminates that involves only in-plane stresses in both layers, based on equilibrium, continuity and boundary conditions. Stress distributions, elastic constants and strain energy release rate are obtained as functions of the crack densities in 0 ° and 90 ° layers of the laminate.
-
doubly periodic Matrix Cracking in composite laminates part 2 thermal biaxial loading
Composite Structures, 1996Co-Authors: C Henaffgardin, M C Lafariefrenot, D. GambyAbstract:Abstract In a first part of this paper, an analysis of Cracking evolution in cross-ply composite laminates under general in-plane mechanical loading has been presented. This second part is concerned with this damage evolution, but this time under thermal loading. The preceding interlaminar shear stress analysis for progressive damage is applied to the present test conditions, in order to obtain stress distributions and strain energy release rate as functions of two damage parameters which are the crack densities in 0 ° and 90 ° layers of the laminate. Experimental observations of damage evolution have also been carried out in T300/914 carbon/epoxy laminates, during thermal fatigue tests. The influence of temperature amplitude on damage is investigated throughout tests. Damage consists of Matrix Cracking in both 0 ° and 90 ° layers, followed by delamination along cracks at the 0 °/90 ° ply interfaces. It appears that, depending on the temperature amplitude, the damage evolution is either non-existent, rather slow, or very fast. It also appears that the predictions of the analysis are in good agreement with the experimental observations.
A Friedman - One of the best experts on this subject based on the ideXlab platform.
-
advanced waveform based acoustic emission detection of Matrix Cracking in composites
Materials evaluation, 1995Co-Authors: W H Prosser, K E Jackson, S Kellas, B T Smith, J Mckeon, A FriedmanAbstract:An advanced, waveform based acoustic emission system was used to study the initiation of transverse Matrix Cracking in cross-ply graphite/epoxy composites. The acoustic emission signals were detected with broad band, high fidelity sensors, and digitized for analysis. Plate wave propagation analysis was used to discriminate noise signals from those generated by cracks. The noise signals were confirmed to have originated in the specimen grip region by a new, highly accurate form of location analysis which was independent f threshold setting. Six different specimen thicknesses ([0{sub n}, 90{sub n}, 0{sub n}], n = 1 to 6) were tested under stroke controlled, quasi-static tensile loading. The presence and location of the cracks were confirmed post test by microscopy. Back scatter ultrasonics, penetrant enhanced X-ray techniques, and in limited cases, destructive sectioning and microscopy were also used to determine the length of the cracks. The average absolute value of the difference between the microscopy determined crack location and the acoustic emission crack location was 3.2 mm (0.125 in.) for a nominal sensor gage length of 152 mm (6 in.). For all cracks, the location of the crack initiation site was at one of the edges of the specimen.
-
advanced waveform based acoustic emission detection of Matrix Cracking in composites
Ndt & E International, 1995Co-Authors: W H Prosser, K E Jackson, S Kellas, B T Smith, J Mckeon, A FriedmanAbstract:An advanced, waveform based acoustic emission (AE) system was used to study the initiation of transverse Matrix Cracking in cross-ply graphite/epoxy (gr/ep) composites. The AE signals were detected with broad band, high fidelity sensors, and digitized for analysis. Plate wave propagation analysis was used to discriminate noise signals from those generated by cracks. The noise signals were confirmed to have originated in the specimen grip region by a new, highly accurate form of location analysis which was independent of threshold setting. Six different specimen thicknesses ([0n, 90n, 0n], n = 1 to 6) were tested under stroke controlled, quasi-static tensile loading. The presence and location of the cracks were confirmed post test by microscopy. Back scatter ultrasonics, penetrant enhanced X-ray techniques, and in limited cases, destructive sectioning and microscopy were also used to determine the length of the cracks. For thicker specimens (n < 2), there was an exact, one to one correspondence between AE crack signals and observed cracks. The length of the cracks in these specimens extended the full specimen width. Precise linear location of the crack position was demonstrated. The average absolute value of the difference between the microscopy determined crack location and the AE crack location was 3.2 mm. for a nominal sensor gage length of 152 mm. A four sensor array was used which not only improved the linear location accuracy, but also provided the lateral position of the crack initiation site. This allowed determination of whether the cracks initiated in the interior bulk of the specimens or along the free edges. For all cracks, the location of the crack initiation site was at one of the edges of the specimen. The cracks were more difficult to detect with AE in the thin specimens (n < 2). The cracks in these specimens also initiated at the specimen edge, but did not immediately propagate across the specimen width. They generated significantly smaller amplitude AE signals. These measurements demonstrated that the same source mechanism can generate a wide range of AE signal amplitudes.
