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Maria Kashtalyan - One of the best experts on this subject based on the ideXlab platform.
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Evolution of Crack Density in Cross-Ply Laminates - Application of a Coupled Stress and Energy Criterion
Key Engineering Materials, 2016Co-Authors: Maria Kashtalyan, I.g. García, Vladislav ManticAbstract:The first damage mode to appear in continuous fibre-reinforced composite laminates subjected to in-plane loading is usually transverse cracking, i.e. matrix cracking in the off-axis plies of the laminate. Since the density of transverse cracks has a great influence on the subsequent failure steps like delaminations, it is important to be able to predict it accurately. In this paper, the evolution of crack density with increasing external load is predicted using a combination of the Coupled Criterion of Finite Fracture Mechanics and the Equivalent Constraint Model.
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predicting residual stiffness of cracked composite laminates subjected to multi axial inplane loading
Journal of Composite Materials, 2013Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:This is a contribution to the exercise that aims to benchmark and validate the current continuum damage and fracture mechanics methodologies used for predicting the mechanical behaviour of fibre-reinforced plastic composites under complex loadings. The paper describes an analytical approach to predict the effect of intra- (matrix cracking and splitting) and inter-laminar (delamination) damage on the residual stiffness properties of the laminate, which can be used in the post-initial failure analysis, taking full account of damage mode interaction. The approach is based on a two-dimensional shear lag stress analysis and the equivalent Constraint Model of the damaged laminate with multiple damaged plies. The application of the approach to predicting degraded stiffness properties of a multidirectional laminate with multilayer intra- and inter-laminar damage is demonstrated for [0/90/0] and [0/908/0] cross-ply laminates made from a specific glass/epoxy system under in-plane uniaxial and biaxial loading damage...
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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
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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.
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Mechanisms of Internal Damage and Their Effect on the Behavior and Properties of Cross-Ply Composite Laminates
International Applied Mechanics, 2002Co-Authors: Maria Kashtalyan, C SoutisAbstract:This paper is a review of experimental and theoretical studies into the damage mechanisms in glass/epoxy and carbon/epoxy cross-ply composite laminates subjected to static or cyclic loading and their influence on the behavior and stiffness properties of such laminates. How the equivalent-Constraint Model is applied to the analysis of cross-ply laminates with transverse and longitudinal matrix cracks and crack-tip delaminations is shown and discussed.
Guimin Chen - One of the best experts on this subject based on the ideXlab platform.
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determining the range of allowable axial force for the third order beam Constraint Model
Mechanical Sciences, 2018Co-Authors: Guimin Chen, Guangbo HaoAbstract:Abstract. The Beam Constraint Model (BCM) was developed for the purpose of accurately and analytically Modeling nonlinear behaviors of a planar beam flexure over an intermediate range of transverse deflections (10 % of the beam length). The BCM is expressed in the form of Taylor's expansion associated with the axial force. It has been found that the BCM may yield large predicting errors (> 5 %) when the applied axial force goes beyond a certain boundary, even the deflection is still in the intermediate range. However, this boundary has not been clearly identified so far. In this work, we mathematically determine the non-dimensional boundary of the axial force by the condition that the strain energy expression of the BCM is a positive definite quadratic form, and by the buckling condition relate to compressing axial force. Several examples are analyzed to demonstrate the effects of the axial force on the Modeling errors of the BCM. When using the BCM for Modeling, it is always suggested to check if the axial force is within this boundary to avoid large Modeling errors. If the axial force is beyond the boundary, the Chained Beam Constraint Model (CBCM) can be used instead.
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a novel fully compliant tensural compresural bistable mechanism
Sensors and Actuators A-physical, 2017Co-Authors: Qi Han, Guimin Chen, Kaifang Jin, Xiaodong ShaoAbstract:Abstract Bistable mechanisms, which can maintain two distinct positions without power input, have been widely used for harvesting vibration energy, constructing metamaterials, sensing threshold acceleration, and achieving adaptable damping. In this work, we propose a novel configuration of fully compliant bistable mechanisms called tensural-compresural bistable mechanisms (TCBMs), in which both tensural segments (compliant segments that are subject to combined tensile and bending loads) and compresural segments (compliant segments that are subject to combined compressive and bending loads) are employed. The combination use of tensural and compresural segments makes TCBMs much easier to be tailored for different design requirements. Although compresural segments are incorporated, potential problems associated with buckling can always be avoided by using compresural segments with smaller slenderness as compared to the tensural segments. To facilitate the design of TCBMs, two kinetostatic Models are developed by using the beam Constraint Model and the chained beam Constraint Model, respectively. Several TCBM designs accompanied with a prototype test are presented to demonstrate the feasibility of the new bistable configuration and the use of the two kinetostatic Models.
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Modeling large spatial deflections of slender bisymmetric beams in compliant mechanisms using chained spatial beam Constraint Model
Journal of Mechanisms and Robotics, 2015Co-Authors: Guimin Chen, Ruiyu BaiAbstract:Modeling large spatial deflections of flexible beams has been one of the most challenging problems in the research community of compliant mechanisms. This work presents a method called chained spatial-beam-Constraint-Model (CSBCM) for Modeling large spatial deflections of flexible bisymmetric beams in compliant mechanisms. CSBCM is based on the spatial beam Constraint Model (SBCM), which was developed for the purpose of accurately predicting the nonlinear Constraint characteristics of bisymmetric spatial beams in their intermediate deflection range. CSBCM deals with large spatial deflections by dividing a spatial beam into several elements, Modeling each element with SBCM, and then assembling the deflected elements using the transformation defined by Tait-Bryan angles to form the whole deflection. It is demonstrated that CSBCM is capable of solving various large spatial deflection problems whether the tip loads are known or the tip deflections are known. The examples show that CSBCM can accurately predict the large spatial deflections of flexible beams, as compared to the available nonlinear FEA results obtained by ANSYS. The results also demonstrated the unique capabilities of CSBCM to solve large spatial deflection problems that are outside the range of ANSYS.Copyright © 2015 by ASME
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Kinetostatic Modeling of Fully Compliant Bistable Mechanisms Using Timoshenko Beam Constraint Model
Journal of Mechanical Design, 2015Co-Authors: Guimin ChenAbstract:Fully compliant bistable mechanisms (FCBMs) have numerous applications in both micro- and macroscale devices, but the nonlinearities associated with the deflections of the flexible members and the kinetostatic behaviors have made it difficult to design. Currently, the design of FCBMs relies heavily on nonlinear finite element Modeling. In this paper, an analytical kinetostatic Model is developed for FCBMs based on the beam Constraint Model (BCM) that captures the geometric nonlinearities of beam flexures that undergo relatively small deflections. An improved BCM (i.e., Timoshenko BCM (TBCM)) is derived based on the Timoshenko beam theory in order to include shear effects in the Model. The results for three FCBM designs show that the kinetostatic Model can successfully identify the bistable behaviors and make reasonable predictions for the locations of the unstable equilibrium points and the stable equilibrium positions. The inclusion of shear effects in the TBCM Model significantly improves the prediction accuracy over the BCM Model, as compared to the finite element analysis (FEA) results. [DOI: 10.1115/1.4029024]
James R Garven - One of the best experts on this subject based on the ideXlab platform.
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insurance cycles interest rates and the capacity Constraint Model
Social Science Research Network, 1998Co-Authors: Neil A Doherty, James R GarvenAbstract:Insurance profits exhibit cyclical behavior that has been attributed to capital market Constraints. We show that changes in interest rates simultaneously affect the insurer's capital structure and the equilibrium underwriting profit. Depending upon asset and liability maturity structure, capital market access, and reinsurance availability, insurers will be differently affected by changing interest rates. We find that the average market response to changing interest rates roughly tracks market clearing prices. These "cyclical" effects are enhanced for firms with mismatched assets and liabilities and more costly access to new capital and reinsurance. This evidence supports the capacity Constraint hypothesis.
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insurance cycles interest rates and the capacity Constraint Model
The Journal of Business, 1995Co-Authors: Neil A Doherty, James R GarvenAbstract:Insurance profits exhibit cyclical behavior that has been attributed to capital market Constraints. The authors show that changes in interest rates simultaneously affect the insurer's capital structure and the equilibrium underwriting profit. Depending upon asset and liability maturity structure, capital market access, and reinsurance availability, insurers will be differently affected by changing interest rates. The authors find that the average market response to changing interest rates roughly tracks market clearing prices. These 'cyclical' effects are enhanced for firms with mismatched assets and liabilities and more costly access to new capital and reinsurance. This evidence supports the capacity Constraint hypothesis. Copyright 1995 by University of Chicago Press.
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insurance cycles interest rates and the capacity Constraint Model
Risk and Insurance, 1994Co-Authors: Neil A Doherty, James R GarvenAbstract:Although financial pricing Models imply that profits of property-liability insurance firms should conform to an unpredictable time series process, cycles are widely reported. Some controversy exists as to whether the "underwriting cycle" is a mere accounting artifact or whether it has real resource effects. We show that changes in interest rates simultaneously affect the insurer's capital structure and the equilibrium level of underwriting profit. Depending on factors such as asset and liability durations, access to capital markets, and availability of capital substitutes such as reinsurance, insurers will be differently affected by changing interest rates. Over time, we find that the average market response to changing interest rates roughly tracks market clearing prices, although the response is somewhat dampened. However, firms with mismatched assets and liabilities, as well as those with more costly access to new capital and reinsurance, are more likely to respond to interest rate changes by either rationing supply or instituting abnormal price changes.
Neil A Doherty - One of the best experts on this subject based on the ideXlab platform.
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insurance cycles interest rates and the capacity Constraint Model
Social Science Research Network, 1998Co-Authors: Neil A Doherty, James R GarvenAbstract:Insurance profits exhibit cyclical behavior that has been attributed to capital market Constraints. We show that changes in interest rates simultaneously affect the insurer's capital structure and the equilibrium underwriting profit. Depending upon asset and liability maturity structure, capital market access, and reinsurance availability, insurers will be differently affected by changing interest rates. We find that the average market response to changing interest rates roughly tracks market clearing prices. These "cyclical" effects are enhanced for firms with mismatched assets and liabilities and more costly access to new capital and reinsurance. This evidence supports the capacity Constraint hypothesis.
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insurance cycles interest rates and the capacity Constraint Model
The Journal of Business, 1995Co-Authors: Neil A Doherty, James R GarvenAbstract:Insurance profits exhibit cyclical behavior that has been attributed to capital market Constraints. The authors show that changes in interest rates simultaneously affect the insurer's capital structure and the equilibrium underwriting profit. Depending upon asset and liability maturity structure, capital market access, and reinsurance availability, insurers will be differently affected by changing interest rates. The authors find that the average market response to changing interest rates roughly tracks market clearing prices. These 'cyclical' effects are enhanced for firms with mismatched assets and liabilities and more costly access to new capital and reinsurance. This evidence supports the capacity Constraint hypothesis. Copyright 1995 by University of Chicago Press.
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insurance cycles interest rates and the capacity Constraint Model
Risk and Insurance, 1994Co-Authors: Neil A Doherty, James R GarvenAbstract:Although financial pricing Models imply that profits of property-liability insurance firms should conform to an unpredictable time series process, cycles are widely reported. Some controversy exists as to whether the "underwriting cycle" is a mere accounting artifact or whether it has real resource effects. We show that changes in interest rates simultaneously affect the insurer's capital structure and the equilibrium level of underwriting profit. Depending on factors such as asset and liability durations, access to capital markets, and availability of capital substitutes such as reinsurance, insurers will be differently affected by changing interest rates. Over time, we find that the average market response to changing interest rates roughly tracks market clearing prices, although the response is somewhat dampened. However, firms with mismatched assets and liabilities, as well as those with more costly access to new capital and reinsurance, are more likely to respond to interest rate changes by either rationing supply or instituting abnormal price changes.
Constantinos Soutis - One of the best experts on this subject based on the ideXlab platform.
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predicting residual stiffness of cracked composite laminates subjected to multi axial inplane loading
Journal of Composite Materials, 2013Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:This is a contribution to the exercise that aims to benchmark and validate the current continuum damage and fracture mechanics methodologies used for predicting the mechanical behaviour of fibre-reinforced plastic composites under complex loadings. The paper describes an analytical approach to predict the effect of intra- (matrix cracking and splitting) and inter-laminar (delamination) damage on the residual stiffness properties of the laminate, which can be used in the post-initial failure analysis, taking full account of damage mode interaction. The approach is based on a two-dimensional shear lag stress analysis and the equivalent Constraint Model of the damaged laminate with multiple damaged plies. The application of the approach to predicting degraded stiffness properties of a multidirectional laminate with multilayer intra- and inter-laminar damage is demonstrated for [0/90/0] and [0/908/0] cross-ply laminates made from a specific glass/epoxy system under in-plane uniaxial and biaxial loading damage...
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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
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Strain Energy Release Rate for Off-Axis Ply Cracking in Laminated Composites
International Journal of Fracture, 2001Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:Strain energy release rate associated with matrix cracking in the θ - layer of unbalanced symmetric [ 0 / θ ], composite laminate is predicted analytically using a 2-D shear lag stress analysis and the Equivalent Constraint Model (ECM). Its dependence 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 discussed.
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stiffness loss due to transverse cracking and splitting in cross ply laminates under biaxial loading
Proceedings of ICCM12. 1999;:5-9., 1999Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:In an effort to evaluate the stiffness degradation of composite cross-ply laminates due to matrix cracking both in the 90 and 0 plies, a new theoretical approach was developed. It employs the Equivalent Constraint Model (ECM) [1, 2] and subsequent an improved 2-D shear lag analysis to determine stress field in the damaged laminate. In-situ Damage Effective Functions (IDEFs), used to describe stiffness reduction of the cracked or split lamina, were found to depend explicitly upon the crack density in the damaged lamina and implicitly upon the crack density of the neighbouring lamina. Theoretical predictions for CFRP and GFRP laminates revealed significant reduction in the shear modulus and Poisson's ratio due to splitting. Comparison of the new approach with existing Models has shown reasonable agreement.