The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Maria Kashtalyan - One of the best experts on this subject based on the ideXlab platform.
-
Analysis of delamination in laminates with angle-ply matrix cracks: Onset of damage and residual stiffness properties
Structural Integrity and Durability of Advanced Composites, 2015Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:Abstract The failure process of composite laminate under quasi-static or fatigue loading involves sequential accumulation of intra- and interlaminar cracking. Matrix cracking parallel to the fibres in the off-axis plies is the first damage mode observed. It triggers development of other harmful resin-dominated modes such as Delaminations. In this chapter, analytical modelling of crack-induced Delaminations in composite laminates subjected to general in-plane loading is presented and discussed. A two-dimensional 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 and mode II and the total strain energy release rate associated with uniform local Delaminations. These expressions could be used with appropriate fracture criteria to estimate the onset of local delamination in an already cracked off-axis laminate. Dependence of strain energy release rate on crack density, delamination area and ply orientation angle in unbalanced symmetric laminates is examined and discussed, and the effect of crack-induced delamination on the laminate stiffness is predicted.
-
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
-
Strain Energy Release Rate for Crack Tip Delaminations in Angle-Ply Continuous Fibre Reinforced Composite Laminates
European Structural Integrity Society, 2003Co-Authors: Constantinos Soutis, Maria KashtalyanAbstract:ABSTRACT The expressions for the strain energy release rate associated with local Delaminations growing from the tips of angle ply matrix cracks in orthotropic laminates loaded in tension are presented. Strain energy release rate and the laminate residual stiffness properties are predicted as functions of matrix crack density and delamination length.
-
Analysis of local Delaminations in composite laminates with angle-ply matrix cracks
International Journal of Solids and Structures, 2002Co-Authors: Maria KashtalyanAbstract:Abstract In this paper, local Delaminations growing uniformly from the tips of angle-ply matrix cracks in composite laminates loaded in tension are modelled theoretically. A 2-D shear lag method is used to determine stresses in a laminate representative segment containing one crack and two crack tip Delaminations. For the calculation of the strain-energy release rate (SERR) associated with Delaminations, the damaged layer is replaced with an equivalent homogeneous one with effective elastic properties. Closed-form expressions for the total SERR and its mode I and mode II components as a linear function of the first partial derivatives of the effective elastic properties of the damaged layer with respect to delamination area are derived. Dependence of SERRs and the laminate stiffness properties on delamination area, crack density and ply orientation angle is examined for balanced [0 2 /θ 2 /− θ 2 ] s and unbalanced [0 2 /θ 2 ] s carbon/epoxy laminates. The total SERR obtained in this study is compared to a simple closed-form expression for a uniform local delamination derived in earlier work by O'Brien (Local delamination in laminates with angle-ply matrix cracks: Part II Delamination Fracture Analysis and Fatigue Characterization. NASA Technical Memorandum 104076/AVSCOM Technical Report 91-B-011). It appears that matrix crack density and delamination size influence the SERR value significantly.
-
The effect of Delaminations induced by transverse cracks and splits on stiffness properties of composite laminates
Composites Part A: Applied Science and Manufacturing, 2000Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:Abstract In an effort to evaluate stiffness degradation due to Delaminations growing at the 0°/90° interface from the tips of transverse cracks in the 90° plies and splits in the 0° plies of cross-ply [0m/90n]s laminates, a new theoretical approach was developed. It employs the Equivalent Constraint Model of the damaged lamina [Fan J, Zhang J. In-situ damage evolution and micro/macro transition for laminated composites. Composites Science and Technology 1993;47:107–118], which allows one to avoid cumbersome consideration of the repeated laminate element defined by the intersecting pairs of transverse cracks and splits. It also uses an improved 2D shear-lag analysis [Zhang J, Soutis C, Fan J. Strain energy release rate associated with local delamination in cracked composite laminates. Composites 1994;25(9):851–862] to determine the stress fields in the explicitly damaged lamina and the In situ Damage Effective Functions to describe its reduced stiffness properties. Reduced stiffness properties of the damaged lamina are found to depend explicitly upon the crack density and relative delamination area associated with that lamina and implicitly upon two damage parameters associated with the neighbouring lamina. Theoretical predictions reveal that transverse crack tip Delaminations cause significant reduction in the shear modulus and Poisson's ratio of cross-ply and symmetric balanced [±θm/90n]s laminates. Dependence of the laminate reduced elastic properties on the orientation angle of the constraining ply is examined. Contribution of each damage mode (transverse cracking, transverse crack tip Delaminations, splitting and split tip Delaminations) into stiffness loss is established.
Daeyong Park - One of the best experts on this subject based on the ideXlab platform.
-
buckling analysis of laminated composite plates containing Delaminations using the enhanced assumed strain solid element
International Journal of Solids and Structures, 2007Co-Authors: Daeyong ParkAbstract:This study investigates buckling behaviors of laminated composite structures with a delamination using the enhanced assumed strain (EAS) solid element. The EAS three-dimensional finite element (FE) formulation described in this paper, in comparison with the conventional approaches, is more attractive not only because it shows better accuracy but also it converges faster, especially for distorted element shapes. The developed FE model is used for studying cross-ply or angle-ply laminates containing an embedded delamination as well as through-the-width delamination. The numerical results obtained are in good agreement with those reported by other investigators. In particular, new results reported in this paper are focused on the significant effects of the local buckling for various parameters, such as size of delamination, aspect ratio, width-to-thickness ratio, stacking sequences, and location of delamination and multiple Delaminations.
-
buckling analysis of laminated composite plates containing Delaminations using the enhanced assumed strain solid element
International Journal of Solids and Structures, 2007Co-Authors: Daeyong ParkAbstract:This study investigates buckling behaviors of laminated composite structures with a delamination using the enhanced assumed strain (EAS) solid element. The EAS three-dimensional finite element (FE) formulation described in this paper, in comparison with the conventional approaches, is more attractive not only because it shows better accuracy but also it converges faster, especially for distorted element shapes. The developed FE model is used for studying cross-ply or angle-ply laminates containing an embedded delamination as well as through-the-width delamination. The numerical results obtained are in good agreement with those reported by other investigators. In particular, new results reported in this paper are focused on the significant effects of the local buckling for various parameters, such as size of delamination, aspect ratio, width-to-thickness ratio, stacking sequences, and location of delamination and multiple Delaminations.
Kim Branner - One of the best experts on this subject based on the ideXlab platform.
-
the effect of Delaminations on local buckling in wind turbine blades
Renewable Energy, 2016Co-Authors: Philipp Ulrich Haselbach, Robert Bitsche, Kim BrannerAbstract:In this article the effect of Delaminations on the load carrying capacity of a large wind turbine blade is studied numerically. For this purpose an 8.65 m long blade section with different initial Delaminations in the main spar was subjected to a flapwise dominated bending moment. The model was setup in Abaqus and cohesive elements were chosen for modelling delamination growth.
-
the effect of Delaminations on local buckling in wind turbine blades
Renewable Energy, 2016Co-Authors: Philipp Ulrich Haselbach, Robert Bitsche, Kim BrannerAbstract:Abstract In this article the effect of Delaminations on the load carrying capacity of a large wind turbine blade is studied numerically. For this purpose an 8.65 m long blade section with different initial Delaminations in the main spar was subjected to a flapwise dominated bending moment. The model was setup in Abaqus and cohesive elements were chosen for modelling delamination growth. For initial Delaminations with a width of 30–50% of the cap width the study showed that delamination close to the surface started to grow in load ranges of normal operation conditions and led to local buckling modes. The local buckling caused high strains and stresses in the surrounding of the delamination, which exceeded the material design properties and therefore should be considered as dangerous. Delaminations placed near the mid-surface of the cap did not have a significant effect on the blade response under normal operation conditions. In the simulations the static load exceeded the design load by more than 40% before delamination growth or cap buckling occurred. It could be concluded that delamination induced near-surface buckling modes have to be considered critical due to an onset of local sublaminate buckling below the design load level.
Akira Todoroki - One of the best experts on this subject based on the ideXlab platform.
-
delamination monitoring of cfrp laminate using the two stage electric potential change method with equivalent electric conductivity
Engineering Fracture Mechanics, 2008Co-Authors: Masahito Ueda, Akira TodorokiAbstract:Carbon fiber reinforced plastics laminate (CFRP) has a high specific strength and stiffness compared to conventional metals, although it is very sensitive to impact. A low impact leads to a delamination and results in the deterioration of the structural reliability. The present study employs a two-stage electric potential change method (EPCM) to identify delamination. In the methods, delamination is estimated using response surfaces, which require numerous experiments. An equivalent electric conductivity method is introduced to reduce this number. Delaminations are successfully estimated using response surfaces based on the results of the finite element method with equivalent electric conductivity.
-
analysis of the effect of the configuration of the delamination crack on delamination monitoring with electric resistance change method
Journal of the Japan Society for Composite Materials, 2003Co-Authors: Akira Todoroki, Miho Tanaka, Yoshinobu Shimamura, Hideo KobayashiAbstract:Since Delaminations of composite laminates are usually invisible or difficult to be detected by visual inspections, the delamination causes low reliability of primary structures. In order to improve the low reliability, automatic systems for delamination identifications in-service are desired. The present study employs an electric resistance change method for detections of the Delaminations. Although the method is effective to monitor the delamination cracks, the method requires many experiments to solve inverse problems. Since the experiment cost is high, an analytical method for preparation of the data sets of the electric resistance changes is desired. In practical delamination, however, usually includes a matrix cracking. In the present study, therefore, the effect of the matrix cracking on the electric resistance changes between the electrodes is investigated with FEM analyses. As a result, it can be concluded that the simple calculations using a straight delamination crack model are enough for obtaining the data set of electric resistance changes to calculate the response surfaces.
-
measurement of orthotropic electric conductance of cfrp laminates and analysis of the effect on delamination monitoring with an electric resistance change method
Composites Science and Technology, 2002Co-Authors: Akira Todoroki, Miho Tanaka, Yoshinobu ShimamuraAbstract:Since Delaminations of composite laminates are usually invisible or difficult to detect by visual inspections, delamination causes low reliability for primary structures. Automatic systems for delamination identifications in-service are desired in order to improve this low reliability. The present study employs an electric resistance change method for detection of Delaminations. Since the method adopts reinforcement carbon fibre itself as sensors for delamination detections, this method does not cause reduction of static strength or fatigue strength; also, this method is applicable to existing structures. In the present study, a relationship between fibre volume fraction and orthotropic electric conductivities is confirmed by experimentation and the effect of measured orthotropic electric conductance on delamination monitoring is discussed analytically with FEM analyses. Two types of cross-ply laminates are prepared for delamination monitoring analyses: [0/90]s and [90/0]s. Electric resistance changes due to delamination creation are discussed for both specimen types with results of electric current density diagrams. As a result, it can be concluded that the fibre volume fraction has a large effect on electric conductance of the transverse and thickness directions, and electric conductance of the thickness direction has significant effects on delamination detection with the electric resistance change method.
-
delamination identification of cross ply graphite epoxy composite beams using electric resistance change method
Composites Science and Technology, 2002Co-Authors: Akira Todoroki, Yuuki TanakaAbstract:Detection of Delaminations is a difficult task for visual inspections. Difficulty of detection underlines the importance of development of smart structures for monitoring Delaminations of graphite/epoxy laminated composites. This study employs an electric resistance change method for identification of delamination location and size; applicability of the method is investigated experimentally using beam-type specimens fabricated from cross-ply laminates. On the specimen surface, multiple electrodes are mounted by co-curing copper foil to measure electric resistance changes. Interlamina shear tests are conducted to create a practical delamination crack in a beam-type specimen. Five beam specimen types were made and tested. A large number of tests were conducted to obtain a data set for solving inverse problems to estimate delamination location and size from measured electric resistance changes. Response surfaces are employed for a solver of inverse problems instead of well-known artificial neural networks. As a result, the method successfully identifies delamination location and size for these beam type specimens. To obtain practically efficient estimation performance, at least five electrodes are indispensable for these beam type specimens.
-
application of electric potential method to smart composite structures for detecting delamination
JSME international journal. Series A mechanics and material engineering, 1995Co-Authors: Akira Todoroki, Hideo Kobayashi, Katsuya MatuuraAbstract:CF/epoxy composites have been applied to many kinds of aircraft structures. The composite laminated plate compression properties, however, are easily degraded by Delaminations. Thus an approach for detecting the Delaminations is widely desired. In this study, an electric potential method was discussed for realtime nondestructive evaluation of Delaminations because this method has several advantages in comparison with the embedded optical fiber. In order to obtain the basic properties of the CF/epoxy composites, mode I and II delamination tests were carried out and the relations between the electric resistance change and the delamination crack length were measured. As a result, the electric resistance bridge circuit approach was proven to be excellent for detecting Delaminations from the inside surfaces of aircraft structures.
E. A. Patterson - One of the best experts on this subject based on the ideXlab platform.
-
buckling and delamination growth behaviour of delaminated composite panels subject to four point bending
Composite Structures, 2016Co-Authors: Wenran Gong, Jinlong Chen, E. A. PattersonAbstract:Abstract Buckling behaviour and delamination growth have been investigated in Carbon Fibre-Reinforced Plastic (CFRP) laminates with artificial and impact-induced Delaminations when subject to four-point bending. The energy of the impact was such that the induced damage, observed using ultrasound, did not extend across the entire width of the laminates and was barely visible on the impacted face. Stereoscopic digital image correlation was used to measure the evolution of the deformation of the laminate during bending to structural failure; and the resulting full-field displacement maps and observations of failure modes from Scanning Electron Microscopy (SEM) were used to conclude that appropriately shaped and located artificial Delaminations could be employed to represent damage-induced Delaminations. This enabled the development of a non-linear Finite Element Analysis (FEA) incorporating a fibre/matrix constitutive model, a modified fibre/matrix failure criterion and a delamination growth criterion to examine the interaction between the buckling behaviour and delamination growth. The predictions of the surface displacements in bending were validated, with the aid of image decomposition, using the measured data fields for a crossply laminate. The model reliably predicted the load–displacement curve and the propagation of damage in laminates with a low level impact damage, which did not extend across the width of laminates, unlike in prior reported models.
-
an experimental study of the behaviour of Delaminations in composite panels subjected to bending
Composite Structures, 2015Co-Authors: Wenran Gong, Jinlong Chen, E. A. PattersonAbstract:Abstract Delamination is one of the most common forms of damage suffered by laminated composites and often occurs as a consequence of manufacturing defects or an impact. This paper reports an investigation of the buckling behaviour and resultant damage modes in delaminated composites subjected to four-point bending. The stereoscopic Digital Image Correlation (DIC) method was used to measure full-field deformations and to evaluate maps of surface principal strains in Carbon Fibre-Reinforced Plastic (CFRP) laminates with artificial Delaminations. The effect of delamination size and shape on buckling behaviour was investigated using circular and elliptical Delaminations in thin beams under four-point bending. For circular Delaminations, initially the delamination grew along the transverse direction and then changed to the longitudinal direction. For elliptical Delaminations, the delamination grew only along the longitudinal direction. Furthermore, the orientation of the delamination had a small influence (10–15%) on the critical delamination-buckling load, which decreased with increasing ratio of minor to major axis length of the delamination.