Flutter of Perforated Metallic Plates Repaired with Cross-Ply Composite Patches

2009 ◽  
Vol 417-418 ◽  
pp. 709-712
Author(s):  
Ali Amin Yazdi ◽  
Jalil Rezaeepazhand
Keyword(s):  
Laminated Composite ◽  
Material Anisotropy ◽  
Perforated Plates ◽  
Closed Form Solutions ◽  
Finite Element Software ◽  
Composite Patch ◽  
Numerical Studies ◽  
Flutter Analysis ◽  
Flutter Boundary ◽  
Metallic Plates

This study investigates the application of laminated composite patches for enhancement of flutter behavior of perforated metallic plates repaired with an external composite patch. Due to material anisotropy and discontinuity in geometry involved in flutter analysis of repaired plates, closed form solutions are practically unobtainable. Numerical studies using commercial finite element software were conducted to investigate the effects of variation in lamination parameters on the flutter boundary of perforated plates repaired with cross-ply composite patches. Both ply-level and sub-laminate level configurations are investigated. Presented results illustrate that flutter boundaries of perforated plates can be changed by choosing proper stacking sequence for composite patches.

Buckling of Perforated Plates Repaired with Composite Patches

2008 ◽  
Vol 385-387 ◽  
pp. 377-380 ◽  
Author(s):  
Jalil Rezaeepazhand ◽  
H. Sabori
Keyword(s):  
Laminated Composite ◽  
Quantitative Measure ◽  
Structural Elements ◽  
Structural Element ◽  
Perforated Plates ◽  
Advanced Composite ◽  
Numerical Studies ◽  
Load Carrying ◽  
Circular Cutout ◽  
Relative Change

Performance level and life span of existing structural elements can be increased by repair and strengthening of these structural elements using advanced composite materials.The performance of damaged metallic plates reinforced with fiber-reinforced polymer composite materials (composite patch) are presented in this study. A square aluminum plate with a central circular cutout is considered as a damaged structural element. Numerical studies using commercial finite element code were conducted to investigate the effects of variation in patch geometries and lamination parameters on buckling responses of repaired plates. The varying laminate parameters such as, fiber angles and stacking sequences are considered in this study. A quantitative measure for the effectiveness of the composite patches is taken to be the relative change in buckling loads of the reinforced plates compare to those of the perfect one. The results presented herein indicated that, for buckling response of a repaired metallic plate with central cutout, a set of laminated composite patches with different shape and stacking sequences can be found which improve load carrying capacity of damaged plates.

Effect of Partial Debonding on Response of Perforated Plates Repaired with Square Composite Patches

2009 ◽  
Vol 417-418 ◽  
pp. 701-704
Author(s):  
Jalil Rezaeepazhand ◽  
H. Sabori
Keyword(s):  
Laminated Composite ◽  
Quantitative Measure ◽  
Base Plate ◽  
Structural Element ◽  
Perforated Plates ◽  
Numerical Studies ◽  
Vibration Responses ◽  
Perfect Bonding ◽  
Circular Cutout ◽  
Relative Change

The performance of perforated metallic plates repaired with laminated composite patches is presented in this study. A square aluminum plate with a central circular cutout is considered as a damaged structural element. Numerical studies using commercial finite element code were conducted to investigate the effects of variation in laminate parameters such as number of plies, fiber orientation, and stacking sequences on free vibration responses of the repaired plates. Particular emphasis is placed on the effect of imperfect bonding (patch debonding). A quantitative measure for the effectiveness of the composite patches parameters is taken to be the relative change in natural frequencies of the deboned patches compare to the patches with perfect bonding. The results presented herein indicated that, vibration response of a repaired perforated metallic plate is affected by the number of plies, stacking sequences of the patch and the quality of bonding between the patch and the base plate.

scholarly journals Experimental and Numerical Buckling Analysis of Delaminated Hybrid Composite Beam Structures

2010 ◽  
Vol 24-25 ◽  
pp. 393-400 ◽  
Author(s):  
M.M. Nasr Esfahani ◽  
H. Ghasemnejad ◽  
P.E. Barrington
Keyword(s):  
Hybrid Composite ◽  
Laminated Composite ◽  
Composite Beams ◽  
Buckling Load ◽  
Buckling Mode ◽  
Buckling Modes ◽  
Critical Buckling Load ◽  
Finite Element Software ◽  
Numerical Studies ◽  
Laminated Composite Beams

In this paper the effect of delamination position on the critical buckling load and buckling mode of hybrid composite beams is investigated. Experimental and numerical studies are carried out to determine the buckling load of delaminated composite beams. The laminated composite beams with various laminate designs of [G90]6, [C90]8, [C0/G0]4 and [C90/G90]4 were manufactured and tested to find the critical buckling load. Three different defect positions were placed through the thickness to find three main buckling modes. It was found that delamination position and lay-up can affect the buckling mode and also the critical buckling load. By approaching the delamination position to the outer surface of the specimen the buckling load decreases. The buckling process of hybrid and non-hybrid composite beams was also simulated by finite element software ANSYS and the critical buckling loads were verified with the relevant experimental results.

Robust Flutter Analysis of an Airfoil with Flap Freeplay Uncertainty

2008 ◽  
Vol 33-37 ◽  
pp. 1247-1252 ◽  
Author(s):  
Zhi Chun Yang ◽  
Ying Song Gu
Keyword(s):  
Control Surface ◽  
Two Dimensional ◽  
Advanced Technique ◽  
Worst Case ◽  
Wing Model ◽  
Freeplay Nonlinearity ◽  
Flutter Analysis ◽  
Flutter Boundary ◽  
Nominal Parameter ◽  
Flutter Margin

Modern robust flutter method is an advanced technique for flutter margin estimation. It always gives the worst-case flutter speed with respect to potential modeling errors. Most literatures are focused on linear parameter uncertainty in mass, stiffness and damping parameters, etc. But the uncertainties of some structural nonlinear parameters, the freeplay in control surface for example, have not been taken into account. A robust flutter analysis approach in μ-framework with uncertain nonlinear operator is proposed in this study. Using describing function method the equivalent stiffness formulation is derived for a two dimensional wing model with freeplay nonlinearity in its flap rotating stiffness. The robust flutter margin is calculated for the two dimensional wing with flap freeplay uncertainty and the results are compared with that obtained with nominal parameter values. It is found that by considering the perturbation of freeplay parameter more conservative flutter boundary can be obtained, and the proposed method in μ-framework can be applied in flutter analysis with other types of concentrated nonlinearities.

scholarly journals Advanced aeroelastic robust stability analysis with structural uncertainties

2020 ◽  
Author(s):  
Özge Süelözgen
Keyword(s):  
Stability Analysis ◽  
Robust Stability ◽  
Flight Test ◽  
Alternative Measure ◽  
Aeroelastic System ◽  
Worst Case ◽  
Robust Stability Analysis ◽  
Flutter Analysis ◽  
Flutter Boundary ◽  
Structural Uncertainties

Abstract Robust flutter analysis described in this paper is based on the robust control theory framework. Therefore, a time-domain linear fractional transformation representation of the perturbed aeroelastic system is modeled. Then, the robust stability is analyzed by means of the structured singular value $$\mu$$ μ , which is defined as an alternative measure of robustness. Robust flutter analysis deals with aeroelastic (or aeroservoelastic) stability analysis taking structural dynamics, aerodynamics and/or unmodeled system dynamics uncertainties into account. Flutter is a well-known dynamic aeroelastic instability phenomenon caused by an interaction between structural vibrations and unsteady aerodynamic forces, whereby the level of vibration may trigger large amplitudes, eventually leading to catastrophic failure of the structure. The primary motivation of the robust flutter analysis is that this method allows the computation of the worst-case flutter velocity which can support, for example, the flight test program by a valuable robust flutter boundary. This paper addresses the issue of an approach for aeroelastic robust stability analysis with structural uncertainties with respect to physical symmetric and asymmetric stiffness perturbations on the wing structure by means of tuning beams.

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