Effect of Curvature on the Impact Damage Characteristics and Residual Strength of Composite Plates
The results of a study of the response and failure characteristics of thin, cylindrically cusrved, composite plates subjected to low-speed impact damage are presented. The results indicate that the plate radius and the plate thickness are important structural parameters that influence the nonlinear response of a plate for a given amount of impact energy. Analytical and experimental contact-force results are compared for several plates and the results correlate well. The impact-energy levels required to cause damage initiation and barely visible impact damage are a function of the plate radius for a given plate thickness. The impact-energy levels required to initiate impact damage for plates with a certain range of radii are greater than plates with other radii. The contact-force results corresponding to these impact-energy levels follow a similar trend. Residual strength results for plates with barely visible impact damage suggest that the compression-after-impact residual strength is also a function of plate radiu. The residual strength of impact-damaged flat plates appears to be lower than the residual strength of the corresponding cylindrically curved plates.
Nonlinear analysis of composite laminated plates subjected to impact
Nonlinear transient global response of shear deformable composite laminated plates subjected to impact loading was investigated analytically and compared with linear transient global response, which was also reviewed in this study, and with existing experimental data. Based on energy equations derived by applying geometrical nonlinearity in straindisplacement relations, the impacted plate response model was developed employing the Lagrangian equations of motion and the Rayleigh-Ritz method in conjunction with assumed mode shapes. The resulting system of second-order nonlinear differential equations with respect to time was solved using the fourth-order Runge-Kutta numerical time integration scheme to produce a transient response in terms of forceand displacement-time histories at the point of impact where a nonlinear local contact law was assumed. Comparison between linear and nonlinear analysis clearly showed the importance of considering the geometrical nonlinear effect of membrane stiffening. Comparison of the analytical results with existing experimental data indicated that the nonlinear plate impact response model with partial geometrical nonlinearity accounting for the flexible boundary was able to predict the impact response well especially for the primary frequency response. However, the secondary frequency response predicted by the model showed relatively poor correlations with the existing experimental data. Further refinement needs to be done to bring this nonlinear impact response analysis into better agreement with the experimental data. Thesis Supervisor: Michael J. Graves Title: Assistant Professor, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology
Use of reduced basis technique in the inverse dynamics of large space cranes
Abstract The inverse dynamics of adaptive structures used as space cranes can prove computationally expensive in the case of large structures, due to the large number of degrees of freedom involved. Consequently, reduced basis techniques (reduction techniques) are frequently used to reduce the problem size to a time manageable level (for possible use in real time control). A reduced basis technique is proposed which is different from, but related to, the path-derivatives reduction technique. A linearly independent set of deflection n -tuples is used, chosen at the beginning of the time range in which it is wished to reduce the equations, in whose subspace it is assumed that the deflection vectors of the unreduced problem will lie (approximately). Some theory, the implications of using this sort of a reduced basis technique as compared to the path-derivatives technique, and some results, are given.