The Experts below are selected from a list of 1005 Experts worldwide ranked by ideXlab platform
A.w. Pryce - One of the best experts on this subject based on the ideXlab platform.
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Matrix cracking and stress/strain behaviour of continuous fibre ceramic composite laminates
1991Co-Authors: A.w. PryceAbstract:Matrix damage and its effects on mechanical properties have been examined for SiC (Nicalon1) fibre reinforced glass and glass ceramic matrix composites under quasi-static and fatigue loading conditions. Nicalon/Pyrex laminates of different lay-ups have been tested under quasi-static tension. The elastic moduli have been measured and matrix damage monitored as a function of applied strain. The mechanical properties are strongly influenced by the presence of crystalline regions in the matrix which promote microcracking. Laminated plate theory is used to provide bounds to the moduli of the laminates. For unidirectional and simple crossPly Nicalon/CAS2 laminates the quasi-static stress/strain behaviour and associated matrix damage accumulation have been examined in detail. The damage development with applied stress was quantified by counts of crack density (in both Longitudinal and transverse plies), stiffness loss and cumulative residual strain. The quasi static stress/strain behaviour during continuous tests (accumulating damage) and discontinuous tests (constant damage) have been modelled using a stress analysis based on Aveston, Cooper and Kelly (ACK) theory. The continuous stress/strain behaviour of (0/90) crossPly laminates has been modelled using a shear-lag analysis developed previously to describe the transverse Ply cracking behaviour of polymer matrix composites. The analysis is modified to account for Longitudinal Ply cracking. Matrix damage development in unidirectional and (0/90) crossPly laminates under quasistatic cycling and high frequency fatigue loading have been studied. For unidirectional laminates stable stress/strain hysteresis loops were obtained during quasi-static cycling, corresponding to stable matrix damage states. These and similar loops obtained after high frequency fatigue are modelled using, the discontinuous stress/strain analysis. It is suggested that the effect of high frequency fatigue is to decrease the interfacial shear strength.
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Matrix cracking and stress strain behaviour of continuous fibre ceramic composite laminates.
1991Co-Authors: A.w. PryceAbstract:Matrix damage and its effects on mechanical properties have been examined for SiC (Nicalon1) fibre reinforced glass and glass ceramic matrix composites under quasi-static and fatigue loading conditions. Nicalon/Pyrex laminates of different lay-ups have been tested under quasi-static tension. The elastic moduli have been measured and matrix damage monitored as a function of applied strain. The mechanical properties are strongly influenced by the presence of crystalline regions in the matrix which promote microcracking. Laminated plate theory is used to provide bounds to the moduli of the laminates. For unidirectional and simple crossPly Nicalon/CAS2 laminates the quasi-static stress/strain behaviour and associated matrix damage accumulation have been examined in detail. The damage development with applied stress was quantified by counts of crack density (in both Longitudinal and transverse plies), stiffness loss and cumulative residual strain. The quasi static stress/strain behaviour during continuous tests (accumulating damage) and discontinuous tests (constant damage) have been modelled using a stress analysis based on Aveston, Cooper and Kelly (ACK) theory. The continuous stress/strain behaviour of (0/90) crossPly laminates has been modelled using a shear-lag analysis developed previously to describe the transverse Ply cracking behaviour of polymer matrix composites. The analysis is modified to account for Longitudinal Ply cracking. Matrix damage development in unidirectional and (0/90) crossPly laminates under quasistatic cycling and high frequency fatigue loading have been studied. For unidirectional laminates stable stress/strain hysteresis loops were obtained during quasi-static cycling, corresponding to stable matrix damage states. These and similar loops obtained after high frequency fatigue are modelled using, the discontinuous stress/strain analysis. It is suggested that the effect of high frequency fatigue is to decrease the interfacial shear strength.
Christos C. Chamis - One of the best experts on this subject based on the ideXlab platform.
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Probabilistic Assessment of Composite and Smart Composite Structures
Probabilistic Structural Mechanics: Advances in Structural Reliability Methods, 1994Co-Authors: Christos C. Chamis, Michael ShiaoAbstract:A general purpose methodology for integrated probabilistic assessment of composite structures and smart composite structures is discussed and demonstrated using aircraft fuselage and wing type structures with rectangular cutouts. The computational simulation was performed for the probabilistic assessment of the structural behavior including global displacements and local stresses. The scatter in the structural response is simulated based on the inherent uncertainties in the primitive (independent random) variables at the fiber/matrix constituent, Ply, laminate and structural scales that describe the composite structures. The effect of uncertainties due to fabrication process variables such as fiber volume ratio, void volume ratio, Ply misalignment, and Ply thickness as well as those for sensors and controls is also included. Results show that in a composite structure with rectangular cutouts the uncertainties in the Longitudinal Ply stress is mainly due to the uncertainty in the laminate thickness. Results also show that a smart composite wing can be controlled to minimize distortions and to have specified stress levels in the presence of cutouts.
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Probabilistic assessment of composite structures
34th Structures Structural Dynamics and Materials Conference, 1993Co-Authors: Michael Shiao, Galib H. Abumeri, Christos C. ChamisAbstract:A general computational simulation methodology for an integrated probabilistic assessment of composite structures is discussed and demonstrated using aircraft fuselage (stiffened composite cylindrical shell) structures with rectangular cutouts. The computational simulation was performed for the probabilistic assessment of the structural behavior including buckling loads, vibration frequencies, global displacements, and local stresses. The scatter in the structural response is simulated based on the inherent uncertainties in the primitive (independent random) variables at the fiber matrix constituent, Ply, laminate, and structural scales that describe the composite structures. The effect of uncertainties due to fabrication process variables such as fiber volume ratio, void volume ratio, Ply orientation, and Ply thickness is also included. The methodology has been embedded in the computer code IPACS (Integrated Probabilistic Assessment of Composite Structures). In addition to the simulated scatter, the IPACS code also calculates the sensitivity of the composite structural behavior to all the primitive variables that influence the structural behavior. This information is useful for assessing reliability and providing guidance for improvement. The results from the probabilistic assessment for the composite structure with rectangular cutouts indicate that the uncertainty in the Longitudinal Ply stress is mainly caused by the uncertainty in the laminate thickness, and the large overlap of the scatter in the first four buckling loads implies that the buckling mode shape for a specific buckling load can be either of the four modes.
Michael Shiao - One of the best experts on this subject based on the ideXlab platform.
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Probabilistic Assessment of Composite and Smart Composite Structures
Probabilistic Structural Mechanics: Advances in Structural Reliability Methods, 1994Co-Authors: Christos C. Chamis, Michael ShiaoAbstract:A general purpose methodology for integrated probabilistic assessment of composite structures and smart composite structures is discussed and demonstrated using aircraft fuselage and wing type structures with rectangular cutouts. The computational simulation was performed for the probabilistic assessment of the structural behavior including global displacements and local stresses. The scatter in the structural response is simulated based on the inherent uncertainties in the primitive (independent random) variables at the fiber/matrix constituent, Ply, laminate and structural scales that describe the composite structures. The effect of uncertainties due to fabrication process variables such as fiber volume ratio, void volume ratio, Ply misalignment, and Ply thickness as well as those for sensors and controls is also included. Results show that in a composite structure with rectangular cutouts the uncertainties in the Longitudinal Ply stress is mainly due to the uncertainty in the laminate thickness. Results also show that a smart composite wing can be controlled to minimize distortions and to have specified stress levels in the presence of cutouts.
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Probabilistic assessment of composite structures
34th Structures Structural Dynamics and Materials Conference, 1993Co-Authors: Michael Shiao, Galib H. Abumeri, Christos C. ChamisAbstract:A general computational simulation methodology for an integrated probabilistic assessment of composite structures is discussed and demonstrated using aircraft fuselage (stiffened composite cylindrical shell) structures with rectangular cutouts. The computational simulation was performed for the probabilistic assessment of the structural behavior including buckling loads, vibration frequencies, global displacements, and local stresses. The scatter in the structural response is simulated based on the inherent uncertainties in the primitive (independent random) variables at the fiber matrix constituent, Ply, laminate, and structural scales that describe the composite structures. The effect of uncertainties due to fabrication process variables such as fiber volume ratio, void volume ratio, Ply orientation, and Ply thickness is also included. The methodology has been embedded in the computer code IPACS (Integrated Probabilistic Assessment of Composite Structures). In addition to the simulated scatter, the IPACS code also calculates the sensitivity of the composite structural behavior to all the primitive variables that influence the structural behavior. This information is useful for assessing reliability and providing guidance for improvement. The results from the probabilistic assessment for the composite structure with rectangular cutouts indicate that the uncertainty in the Longitudinal Ply stress is mainly caused by the uncertainty in the laminate thickness, and the large overlap of the scatter in the first four buckling loads implies that the buckling mode shape for a specific buckling load can be either of the four modes.
E Spārniņs - One of the best experts on this subject based on the ideXlab platform.
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statistical model of the transverse Ply cracking in cross Ply laminates by strength and fracture toughness based failure criteria
Engineering Fracture Mechanics, 2008Co-Authors: Jānis Andersons, Roberts Joffe, E SpārniņsAbstract:Cross-Ply laminate subjected to tensile loading provides a relatively well understood and widely used model system for studying progressive cracking of the transverse Ply. This test allows to identify material strength and/or toughness characteristics as well as to establish relation between damage level and the composite stiffness reduction. The transverse Ply cracking is an inherently stochastic process due to the random variability of local material properties of the plies. The variability affects both crack initiation (governed by the local strength) and propagation (governed by the local fracture toughness). The primary aim of the present study is elucidation of the relative importance of these phenomena in the fragmentation process at different transverse and Longitudinal Ply thickness ratios. The effect of the random crack distribution on the mechanical properties reduction of the laminate is also considered. Transverse Ply cracking in glass fiber/epoxy cross-Ply laminates of the lay-ups [0 2 /90 2 ] s , [0/90 2 ] s , and [0/90 4 ] s is studied. Several specimens of each lay-up were subjected to uniaxial quasistatic tension to obtain crack density as a function of applied strain. Crack spacing distributions at the edge of the specimen also were determined at a predefined applied strain. Statistical model of the cracking process is derived, calibrated using crack density vs. strain data, and verified against the measured crack spacing distributions.
Takaaki Tanaka - One of the best experts on this subject based on the ideXlab platform.
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Electrical Resistance Characteristics in Wet CFRP Cross-Ply Laminates with Matrix Cracking
Journal of the Japan Society for Composite Materials, 2011Co-Authors: Keiji Ogi, Takaaki TanakaAbstract:This paper presents electrical resistance change due to moisture in a CFRP cross-Ply laminate with and without matrix cracking. First, the electrical resistance change was measured for wet unidirectional and cross-Ply laminates at room temperature and below the freezing point. Next, an equivalent circuit model was proposed for the cross-Ply laminate, taking the resistance change ascribed to matrix cracking into account. It was found that resistance characteristics of the intact cross-Ply laminate were similar to those of the Longitudinal Ply. Resistance properties of the wet cross-Ply laminate with matrix cracking were dominated by those of the Longitudinal Ply, while the resistance change of the dry cracked cross-Ply laminate was affected by the matrix crack resistance. The resistance of the dry cracked laminate decreases below the freezing point. Contrarily, the resistance of the wet cracked laminate increases below the freezing point.
