The Experts below are selected from a list of 567 Experts worldwide ranked by ideXlab platform
Janis Varna - One of the best experts on this subject based on the ideXlab platform.
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Measurement of Crack Opening Displacement in Damaged Composite Aerospace Laminates Using ESPI
2020Co-Authors: Mohamed Sahbi Loukil, Janis Varna, Zoubir AyadiAbstract:During the service life composite Laminates undergo complex combinations of thermal and mechanical loading leading to microdamage accumulation in the plies. The most common damage mode is intralaminar cracking in layers. The crack opening displacement (COD) and the crack sliding displacement (CSD) during loading reduce the average stress in the damaged layer, thus reducing the Laminate Stiffness. In other words, the elastic modulus in the loading direction and the corresponding Poisson’s ratio decrease. Previously these parameters have been calculated using finite element method (FEM) assuming linear elastic material with idealized geometry of cracks [1]. The only correct way to validate these assumptions is through experiments. In this paper these parameters are measured experimentally providing Laminate Stiffness reduction models with valuable information for validation of used assumptions and for defining limits of their application. In particular, the displacement field on the edges of a [0/ +704/ -704]s glass fiber/epoxy Laminate specimens with multiple intralaminar cracks is studied and the COD and CSD dependence on the applied mechanical load is measured. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry) [2]. By studying the displacement discontinuities, the crack face displacements were measured. A comparison between the COD and the CSD (for the same crack) is performed.
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effective shear modulus of a damaged ply in Laminate Stiffness analysis determination and validation
Journal of Composite Materials, 2020Co-Authors: Mohamed Sahbi Loukil, Janis VarnaAbstract:The concept of the “effective Stiffness” for plies in Laminates containing intralaminar cracks is revisited presenting rather accurate fitting expressions for the effective Stiffness dependence on ...
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Crack face sliding displacement (CSD) as an input in exact GLOB-LOC expressions for in-plane elastic constants of symmetric damaged Laminates:
International Journal of Damage Mechanics, 2019Co-Authors: Mohamed Sahbi Loukil, Janis VarnaAbstract:The crack opening and crack sliding displacements of both faces of an intralaminar crack are the main parameters defining the significance of each crack in Laminate Stiffness degradation, according...
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effective transverse modulus of a damaged layer potential for predicting symmetric Laminate Stiffness degradation
Journal of Composite Materials, 2017Co-Authors: Janis Varna, Mohamed Sahbi LoukilAbstract:The old concept of the effective Stiffness of a 90-layer with intralaminar cracks is revisited performing 3-D FEM parametric analysis of symmetric and balanced Laminates. It is shown, focusing on t ...
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CHARACTERIZATION OF DAMAGED COMPOSITE LaminateS BY AN OPTICAL MEASUREMENT OF THE DISPLACEMENT FIELD
IOP Conference Series: Materials Science and Engineering, 2012Co-Authors: Mohamed Sahbi Loukil, Janis Varna, Zoubir AyadiAbstract:The degradation of the elastic properties of composite Laminates with intralaminar cracks is caused by reduced stress in the damaged layer which is mainly due to two parameters: the crack opening displacement (COD) and the crack sliding displacement (CSD). In this paper these parameters are measured experimentally providing Laminate Stiffness reduction models with valuable information for validation of used assumptions and for defining limits of their application. In particular, the displacement field on the edges of a [0/ +704/ −704]s glass fiber/epoxy Laminate specimens with multiple intralaminar cracks is studied and the COD and CSD dependence on the applied mechanical load is measured. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry). By studying the displacement discontinuities, the crack face displacements were measured. A comparison between the COD and the CSD (for the same crack) is performed.
Ramesh Talreja - One of the best experts on this subject based on the ideXlab platform.
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a synergistic damage mechanics analysis of transverse cracking in θ 904 s Laminates
Composites Science and Technology, 2001Co-Authors: Janis Varna, Roberts Joffe, Ramesh TalrejaAbstract:Abstract The deformational response of [± θ /90 4 ] s Laminates under longitudinal tensile loading is treated by a synergistic approach that combines continuum damage mechanics (CDM) and micromechanics. The constraint of θ ° plies on transverse cracks in 90° plies is represented by a crack-opening displacement (COD) parameter in the CDM model and is expressed in terms of the ply properties and ply thickness ratios on the basis of a finite-element calculation. A methodology is proposed for predicting the Laminate Stiffness variations with crack density and applied strain (or stress) for various values of ply orientation θ and is found to give good results.
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A synergistic damage-mechanics analysis of transverse cracking in [±θ/904]s Laminates
Composites Science and Technology, 2001Co-Authors: Janis Varna, Roberts Joffe, Ramesh TalrejaAbstract:Abstract The deformational response of [± θ /90 4 ] s Laminates under longitudinal tensile loading is treated by a synergistic approach that combines continuum damage mechanics (CDM) and micromechanics. The constraint of θ ° plies on transverse cracks in 90° plies is represented by a crack-opening displacement (COD) parameter in the CDM model and is expressed in terms of the ply properties and ply thickness ratios on the basis of a finite-element calculation. A methodology is proposed for predicting the Laminate Stiffness variations with crack density and applied strain (or stress) for various values of ply orientation θ and is found to give good results.
Roberts Joffe - One of the best experts on this subject based on the ideXlab platform.
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cracking master curves of cross ply Laminates and the estimation of Laminate Stiffness reduction
International Conference on Mechanics of Composite Materials : 26 06 2008 - 30 06 2008, 2008Co-Authors: Edgars Sparnins, Janis Andersons, Roberts Joffe, O. RubenisAbstract:Cracking master curves of cross-ply Laminates and the estimation of Laminate Stiffness reduction
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a synergistic damage mechanics analysis of transverse cracking in θ 904 s Laminates
Composites Science and Technology, 2001Co-Authors: Janis Varna, Roberts Joffe, Ramesh TalrejaAbstract:Abstract The deformational response of [± θ /90 4 ] s Laminates under longitudinal tensile loading is treated by a synergistic approach that combines continuum damage mechanics (CDM) and micromechanics. The constraint of θ ° plies on transverse cracks in 90° plies is represented by a crack-opening displacement (COD) parameter in the CDM model and is expressed in terms of the ply properties and ply thickness ratios on the basis of a finite-element calculation. A methodology is proposed for predicting the Laminate Stiffness variations with crack density and applied strain (or stress) for various values of ply orientation θ and is found to give good results.
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A synergistic damage-mechanics analysis of transverse cracking in [±θ/904]s Laminates
Composites Science and Technology, 2001Co-Authors: Janis Varna, Roberts Joffe, Ramesh TalrejaAbstract:Abstract The deformational response of [± θ /90 4 ] s Laminates under longitudinal tensile loading is treated by a synergistic approach that combines continuum damage mechanics (CDM) and micromechanics. The constraint of θ ° plies on transverse cracks in 90° plies is represented by a crack-opening displacement (COD) parameter in the CDM model and is expressed in terms of the ply properties and ply thickness ratios on the basis of a finite-element calculation. A methodology is proposed for predicting the Laminate Stiffness variations with crack density and applied strain (or stress) for various values of ply orientation θ and is found to give good results.
O. Rubenis - One of the best experts on this subject based on the ideXlab platform.
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Estimation of Laminate Stiffness reduction due to cracking of a transverse ply by employing crack initiation-and propagation-based master curves
Mechanics of Composite Materials, 2008Co-Authors: Janis Andersons, E. Spārniņš, O. Rubenis, Raquel JoffeAbstract:The applicability range of toughness-and strength-based criteria for progressive cracking of a transverse layer in a cross-ply composite Laminate subjected to tensile loading is considered. Using a deterministic cracking model, approximate relations for the crack density as a function of stress are derived for initiation-and propagation-controlled types of cracking. The master-curve approach is applied to progressive cracking in glass/epoxy Laminates. The accuracy of estimation of Laminate Stiffness reduction by using crack density master curves is evaluated.
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cracking master curves of cross ply Laminates and the estimation of Laminate Stiffness reduction
International Conference on Mechanics of Composite Materials : 26 06 2008 - 30 06 2008, 2008Co-Authors: Edgars Sparnins, Janis Andersons, Roberts Joffe, O. RubenisAbstract:Cracking master curves of cross-ply Laminates and the estimation of Laminate Stiffness reduction
Kaspar Lasn - One of the best experts on this subject based on the ideXlab platform.
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comparison of Laminate Stiffness as measured by three experimental methods
Polymer Testing, 2015Co-Authors: Kaspar Lasn, Andreas T Echtermeyer, Aleksander Klauson, Farid Chati, Dominique DecultotAbstract:Abstract Three independent Stiffness measurement techniques are applied to characterize virgin glass fiber Laminates. Natural frequency based measurements of Laminate Stiffness are compared to results from simple quasi-static testing and Lamb wave dispersion curves. Genetic algorithm (GA) and a modified two-stage Simplex optimization are employed to solve parameter identification inverse problems. The two-stage Simplex method is shown to converge to similar solutions as global genetic algorithms for Lamb wave optimization. The identified elastic and shear moduli show very good agreement, confirming the feasibility of these methods for material characterization. Poisson's ratios on the other hand were not reliably obtained from these two indirect methods due to low sensitivity.
