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
The Accuracy of Reported Insurance Status in the MEPS
Estimates of the number of insured and uninsured Americans are watched by numerous policymakers and the public, yet studies find respondents do not report their insurance status perfectly. Using four sources of validation data, including surveys of employers and providers, this paper assesses the quality of respondents' reports of private insurance and uninsurance in the Medical Expenditure Panel Survey Household Component (MEPS-HC), a nationally representative household survey. Regression analysis is used to assess the extent to which factors are associated with disagreements in reported insurance status across sources.