Composite materials are widely used in aeronautical, marine and automotive industries, because of their excellent mechanical properties, low density and ease of manufacture .However, composite laminates are susceptible to delaminations, which may not be visible externally, but can substantially affect the performance of the structure. Vibration testing, in particular delamination detection, in the composite structures is an active research area. ' D Alembert principle is used to determine the theoretical natural frequency of laminated orthotropic composite plate. The present free vibration experimental study of simply supported square laminated plates is based on the comparison between natural frequencies of healthy and delaminated composite plates. The test square plates made of hand lay up 8 layers E-glass woven fibre and epoxy resin are used here. The present paper discusses the observations made on the measured natural frequencies of vibration testing from both the healthy and the delaminated square simply supported plates. The possibility of the delamination detection by vibration testing is also introduced. The effects of delamination area on the natural frequencies of the plate are presented. The delamination in composite laminates has considerable effect on the natural frequencies of the plate.
Satellite solar array structures experience several loads during deployment and in orbit operations. Such loads cause vibrations and can lead to premature failure or improper service operation, hence, solar arrays must be designed to attenuate these vibrations. In addition, solar arrays must be as light weight as possible, which renders their design process as a fairly complicated one. An innovative approach is presented in this paper for improving the passive vibration damping of solar arrays by using adaptive boundary conditions. A case study of a solar array is investigated where experimental testing and finite element technique are efficiently integrated. In addition, a new theoretical technique is developed to predict first and second vibration modes of the solar array. The results are used to study the effects of boundary conditions on the vibration response of the solar array. They clearly show that by only changing the way the solar array is fixed, vibration damping is successfully improved.
A dynamic Analysis of thin rectangular plates made of anisotropic materials is treated. The analysis is based on the assumptions of classical plate theory in which the anisotropic characteristics of the plate material are introduced. The static lateral load on the plate is replaced by D' Alembert inertia load. The free vibration of simply supported rectangular orthotropic plates is treated as numerical examples, the obtained results are compared with the three dimensional elasticity solution. To verify the theoretical analysis, an experimental study is done using 8 layers woven cross play fiber glass/epoxy rectangular plates.
A detailed analysis for anisotropic semi-infinite medium, under the effect of concentrated forces,is given. The analysis deals with some kind of ani-: sotropy, in which the material properties are cylindrically orthotropic. The effect of a line concentrated load on a semi-infinite cylindrically orthotropic foundation is treated. The radial and tangential displacement components are chosen to satisfy the equilibrium, compatability and boundary conditions of the problem. Using the generalized Hookels law, the assumed displacement functions leads to a simple radial stress, which occurs in such kind of problems, as found in literature. The effect of anisotropic constant on radial and tangential displacement components is discussed. Variations of displacement components along the radial and tangential directions are given.
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