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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, 2015
    Co-Authors: Maria Kashtalyan, Constantinos Soutis
    Abstract:

    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.

  • Strain Energy Release Rate for Crack Tip Delaminations in Angle-Ply Continuous Fibre Reinforced Composite Laminates
    European Structural Integrity Society, 2003
    Co-Authors: Constantinos Soutis, Maria Kashtalyan
    Abstract:

    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, 2002
    Co-Authors: Maria Kashtalyan
    Abstract:

    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.

  • Delamination Growth and Residual Properties of Cracked Orthotropic Laminates Under Tensile Loading
    Journal of Thermoplastic Composite Materials, 2002
    Co-Authors: Constantinos Soutis, Maria Kashtalyan
    Abstract:

    The expressions for the strain-energy release rate associated with Local Delaminations growing from the tips of angle-ply matrix cracks in orthotropic composite laminates loaded in tension are presented. The strain energy release rate and the laminate residual stiffness properties are predicted as functions of matrix-crack density and delamination length.

T. K. Obrien - One of the best experts on this subject based on the ideXlab platform.

  • Local delamination in laminates with angle ply matrix cracks part ii delamlnation fracture analysis and fatigue characterization
    1993
    Co-Authors: T. K. Obrien
    Abstract:

    Abstract : Constant amplitude tension-tension fatigue tests were conducted on AS4/3501-6 graphite/epoxy (02/theta2/-theta2)s laminates, where theta was 15, 20, 25, or 30 degrees. Fatigue tests were conducted at a frequency of 5 Hz and an R-ratio of 0.1. Dye penetrant enhanced X-radiography was used to document the onset of matrix cracking in the central -theta degree plies, and the subsequent onset of Local Delaminations in the theta/-theta interface at the intersection of the matrix cracks and the free edge, as a function of the number of fatigue cycles. Two strain energy release rate solutions for Local delamination from matrix cracks were derived: one for a Local delamination growing from an angle ply matrix crack with a uniform delamination growing from an angle ply matrix crack with a triangular shaped delamination area that extended only partially into the laminate width from the free edge. Plots of Gmax vs. N were generated to assess the accuracy of these G solutions. ne influence of residual thermal and moisture stresses on G were also quantified. However, a detailed analysis of the G components and a mixed-mode fatigue failure criterion for this material may be needed to predict the fatigue behavior of these laminates.

  • Local delamination in laminates with angle ply matrix cracks part 1 tension tests and stress analysis
    Ndt & E International, 1992
    Co-Authors: T. K. Obrien, S.j. Hooper
    Abstract:

    Quasi-static tension tests were conducted on AS4/3501-6 graphite epoxy laminates. Dye penetrant enhanced x-radiography was used to document the onset of matrix cracking and the onset of Local Delaminations at the intersection of the matrix cracks and the free edge. Edge micrographs taken after the onset of damage were used to verify the location of the matrix cracks and Local delamination through the laminate thickness. A quasi-3D finite element analysis was conducted to calculate the stresses responsible for matrix cracking in the off-axis plies. Laminated plate theory indicated that the transverse normal stresses were compressive. However, the finite element analysis yielded tensile transverse normal stresses near the free edge. Matrix cracks formed in the off-axis plies near the free edge where in-plane transverse stresses were tensile and had their greatest magnitude. The influence of the matrix crack on interlaminar stresses is also discussed.

  • residual thermal and moisture influences on the analysis of Local Delaminations
    Journal of Composites Technology & Research, 1992
    Co-Authors: T. K. Obrien
    Abstract:

    An analysis using laminated plate theory is developed to calculate the strain energy release rate associated with Local Delaminations originating at off-axis, angle-ply, matrix cracks in laminates subjected to uniaxial loads. The analysis includes the contribution of residual thermal and moisture stresses to the strain energy released. Examples are calculated for the strain energy release rate associated with Local Delaminations originating at 90 deg and angle-ply(non 90 deg) matrix-ply cracks in glass-epoxy and graphite-epoxy laminates. The solution developed may be used to assess the relative contribution of mechanical, residual thermal, and moisture stresses on the strain energy release rate for Local delamination for a variety of lay-ups and materials.

  • Residual thermal and moisture influences on the strain energy release rate analysis of Local Delaminations from matrix cracks
    1991
    Co-Authors: T. K. Obrien
    Abstract:

    An analysis utilizing laminated plate theory is developed to calculate the strain energy release rate associated with Local Delaminations originating at off-axis, single ply, matrix cracks in laminates subjected to uniaxial loads. The analysis includes the contribution of residual thermal and moisture stresses to the strain energy released. Examples are calculated for the strain energy release rate associated with Local Delaminations originating at 90 degrees and angle-ply (non-90 degrees) matrix ply cracks in glass epoxy and graphite epoxy laminates. The solution developed may be used to assess the relative contribution of mechanical, residual thermal, and moisture stresses on the strain energy release rate for Local delamination for a variety of layups and materials.

Constantinos Soutis - One of the best experts on this subject based on the ideXlab platform.

S.j. Hooper - One of the best experts on this subject based on the ideXlab platform.

  • Local delamination in laminates with angle ply matrix cracks part 1 tension tests and stress analysis
    Ndt & E International, 1992
    Co-Authors: T. K. Obrien, S.j. Hooper
    Abstract:

    Quasi-static tension tests were conducted on AS4/3501-6 graphite epoxy laminates. Dye penetrant enhanced x-radiography was used to document the onset of matrix cracking and the onset of Local Delaminations at the intersection of the matrix cracks and the free edge. Edge micrographs taken after the onset of damage were used to verify the location of the matrix cracks and Local delamination through the laminate thickness. A quasi-3D finite element analysis was conducted to calculate the stresses responsible for matrix cracking in the off-axis plies. Laminated plate theory indicated that the transverse normal stresses were compressive. However, the finite element analysis yielded tensile transverse normal stresses near the free edge. Matrix cracks formed in the off-axis plies near the free edge where in-plane transverse stresses were tensile and had their greatest magnitude. The influence of the matrix crack on interlaminar stresses is also discussed.

Michael R Wisnom - One of the best experts on this subject based on the ideXlab platform.

  • Investigation of the compression performance and failure mechanism of pseudo-ductile thin-ply hybrid composites
    2017
    Co-Authors: Gergely Czel, Meisam Jalalvand, Putu Suwarta, Michael R Wisnom
    Abstract:

    Glass/carbon hybrid specimens were designed and loaded in four point bending in order to generate stable compressive failure which allows for detailed microscopic study of the damage mechanisms. An optical measurement technique based on the displacements of five dots on the specimen edge was applied to monitor the strain of the carbon layer from the curvature of the sample. A loading frame suitable to be inserted into the vacuum chamber of a scanning electron microscope was developed. A previously tested specimen was deformed again in the loading frame and its polished edge surface was scanned while it was kept under significant deformation. This technique was successful in visualising the microscopic deformations and allowed for a deeper understanding of the damage mechanisms. Compressive fragmentation, sliding along the inclined fracture surfaces and Local Delaminations around the crack tips were confirmed by micrographs. An explanatory schematic was generated, highlighting the microscopic displacements of a fragment upon further loading.

  • Pseudo-ductility by fragmentation of central unidirectional plies in thin CFRP angle-ply laminates
    2014
    Co-Authors: Jonathan D. Fuller, Meisam Jalalvand, Michael R Wisnom
    Abstract:

    Pseudo-ductile metal-like tensile stress-strain responses with 700 MPa ”yield stress” plateau and 4.0% failure strain have been achieved experimentally using thin-ply carbon epoxy prepreg and [±26 n/0] S (n = 8 and 10) layups. Analysis of tested specimens has been conducted using microscopy and ultrasonic C-scan. These show that periodic fibre breakages in the 0 ◦ plies lead to Local Delaminations that propagate along the 0 ◦ /− 26 ◦ interfaces. This gradual failure process of fragmentation and dispersed Local delamination allows the demonstrated pseudoductile strains.