Author: Puneet Jagpaul Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
ABSTRACT Free Vibration Analyses of Stationary and Rotating Tapered Composite Beams with Delamination Puneet Jagpaul The exceptional engineering properties and customizability of the laminated composites have enabled their use in the design of the stationary and rotating tapered structures in the aerospace and energy sectors. The tailoring capabilities of the composite material can be used to stiffen the structure at one location while being flexible at other location and consequently reduce the weight, as required in specific applications such as helicopter rotor blade, windmill blade and turbine blade. The vibration characteristics (natural frequencies and mode shapes) of the stationary and rotating structures differ substantially and must be well identified in the design stage. The composite structures are prone to failures such as delamination and fiber-matrix debonding caused during their fabrication or in service, especially when used as blades and beams in various stationary and rotating applications. Delamination reduces the overall stiffness and the strength of the laminates, which may lead to local or sudden structural failures. The delaminated structure has reduced natural frequencies and exhibits different mode shapes than that of the intact structure. In the present thesis, the free vibration analyses of stationary and rotating tapered composite beams with delamination are conducted. The influence of the delamination on the vibration characteristics of the stationary and rotating tapered composite beams is comprehensively studied. The Finite Element Analysis tool ANSYS® is used to develop three-dimensional models of the intact and delaminated composite beams. The natural frequencies of the stationary and rotating intact cantilever composite beams are determined for uniform, thickness-tapered and doubly tapered beam profiles using modal analysis and the results are compared with the results available in the literature. The Mode-I and Mode-II delamination tests are performed on the numerical models of the double cantilever beam and end notch flexure test samples based on cohesive zone modeling and the results of the tests are verified with the available results. The critically stressed locations prone to delamination in the stationary and rotating composite beams are determined using the first-ply failure analyses based on Tsai-Wu failure criterion. The free vibration responses of the stationary and rotating composite beams with end and mid-span delaminations of different lengths and with different stacking sequences are obtained and they are verified wherever possible. The delamination length that has minimal effect on the first three natural frequencies of the uniform and thickness-tapered composite beams is determined and is found to be 5% of the total beam length. Higher modes should be investigated for the composite structures with smaller delamination. A basis for the non-destructive evaluation is suggested for the stationary thickness-tapered simply supported composite beams with end and mid-span delaminations. The influences of the delamination length, delamination location, fiber orientation angle, thickness-tapering, double tapering, layer reduction and taper angle on the free vibration response of the stationary and rotating delaminated composite beams are investigated for uniform, thickness-tapered and doubly tapered beam profiles through various parametric studies. The influences of the rotational velocity and hub radius on the natural frequencies of the rotating doubly tapered composite beams with delamination are thoroughly examined. The present thesis contributes towards the safe design of the composite structures. The studies performed are helpful for developing delamination detection techniques based on the free vibration response of tapered composite beams and can aid designers to model optimised tapered composite structures by considering the influences of delamination on their vibrational characteristics.
Author: Saemul Seraj Publisher: ISBN: Category : Languages : en Pages : 178
Book Description
Due to the outstanding engineering properties, such as high strength/stiffness to weight ratios, capability to be stiff at one location and flexible at another location and favorable fatigue characteristics, doubly-tapered composite beam is used in the rotating structures such as helicopter rotor blades and wind turbine blades. Due to its distinct characteristics from static beam and wide range of applications, rotating beam requires a comprehensive research to understand its dynamic response. Design of mechanical components using doubly-tapered composite beams requires a better understanding of their behavior in free vibration and their dynamic instability. In the present thesis, free vibration and dynamic instability analyses of doubly-tapered rotating cantilever composite beams are conducted considering three different types of vibrations (out-of-plane bending, in-plane bending and axial). Rayleigh-Ritz approximate method based on classical lamination theory has been employed to formulate the free vibration problem and solve it. Bolotin’s method is applied to determine the instability regions. Numerical and symbolic computations have been performed using the software MATLAB. The results for natural frequencies have been validated using Finite Element Analysis (FEA) tool ANSYS. A comprehensive parametric study is conducted in order to understand the effects of various design parameters. Moreover, critical speed of doubly-tapered rotating composite beam is determined and change of critical speed due to double-tapering is investigated. Also, change in maximum deflection due to rotational velocity and double-tapering is observed in this thesis. The material chosen in this thesis for numerical calculations is NCT-301 graphite-epoxy prepreg.
Author: Hasnet Eftakher Uddin Ahmed Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Tapered composite beams formed by terminating or dropping-off some of the plies from primary structure are being used in various engineering applications since the mid-1980s. Because of their structural tailoring capabilities, damage tolerance and potential for creating significant weight savings in engineering applications such as helicopter yoke, robot arms and turbine blades, tapered composite beams have received much attention from engineers and researchers. Design of mechanical components using tapered composite beams requires a better understanding of their behavior on free and forced vibrations. In the present thesis, free and forced vibration analysis including the effects of axial force and damping of tapered composite beams is conducted using conventional, and higher-order finite elements and the Rayleigh-Ritz method. Composite beam samples are manufactured and tested for the determination of mechanical properties and damping loss factor. Conventional and higher- order finite element formulations are established based on classical laminate theory. Since conventional finite element has limitation in obtaining accurate results with fewer elements, higher-order finite element formulation is developed considering four degrees of freedom per node (deflection, rotation, curvature and gradient of curvature) to overcome that problem. Rayleigh-Ritz method is used to obtain solutions for different boundary conditions to validate the results obtained by finite element methods. A detailed parametric study is conducted to investigate the effects of boundary conditions, laminate configurations, taper configurations, taper angle, the ratio of the length of the thick section to the length of thin section, axial force, and damping. The NCT-301 graphite-epoxy composite material is used in the experimental work, analysis, and in the parametric study.
Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781722248307 Category : Languages : en Pages : 28
Book Description
Free vibration of laminated composite beams is studied. The effect of interply delaminations on natural frequencies and mode shapes is evaluated both analytically and experimentally. A generalized vibrational principle is used to formulate the equation of motion and associated boundary conditions for the free vibration of a composite beam with a delamination of arbitrary size and location. The effect of coupling between longitudinal vibration and bending vibration is considered. This coupling effect is shown to significantly affect the calculated natural frequencies and mode shapes of the delaminated beam. Shen, M.-H. H. and Grady, J. E. Glenn Research Center RTOP 505-63-00...
Author: F. Daniel F. Duarte Publisher: ISBN: Category : Languages : en Pages :
Book Description
A study on the optimization of tapered composite beams for vibration is conducted. Designers of tapered rotating structural components such as wind mill, helicopter or turbine blades are increasingly considering composite materials as an option to create lighter structures without compromising structural stiffness and to significantly increase their efficiency. In the design of composite material structures, a challenge arises due to a large number of design variables, therefore numerical optimization is required for a better design. Given this, the purpose of this study is to propose an optimization methodology for the design of a tapered beam, considering the vibration constrains present in rotating components. This is achieved by coupling a numerical model which considers the bending modes of vibration, with an optimization algorithm, both coded in MATLAB. Five optimization algorithms, heuristic and deterministic, are coded and compared and the most efficient method is selected. Because the ply orientation angles can assume an infinite number of possible angles, or follow the regular 0 / ±45 / 90 degrees approach, four possible tuning approaches are defined. The beam is optimized for the following design cases of boundary conditions and design requirements: the presence or absence of a tensile axial force, the presence or absence of a taper, three taper configurations, four proposed structural tuning approaches and four boundary conditions. Two of these structural tuning approaches are compared for its influence in the dynamic behavior of the structural component and in achieving better values of in-plane and out-of-plane stresses. The results demonstrate the Genetic Algorithm is an efficient method for optimization, a design analysis is an important step in optimization, and an appropriate tuning approach can improve the overall efficiency of the optimized structure.
Author: Puneet Jagpaul
Author: Saemul Seraj
Author: Lin Chen
Author: Hasnet Eftakher Uddin Ahmed
Author: Mohammad Amin Fazili
Author: National Aeronautics and Space Administration (NASA)
Author: 
Author: Abolghassem Zabihollah
Author: F. Daniel F. Duarte
Author: Pooya Salajegheh