| The response of composite sandwich plates to low-velocity impact is the subject of this research. The objective of the research is to analytically model the response of composite sandwich plates to low-velocity impact. A displacement based, plane stress, finite element code is modified for this purpose. Major new algorithms include 5{dollar}rmsp{lcub}th{rcub}{dollar} order Hermitian interpolation, three-dimensional equilibrium integration for transverse stress calculations, sandwich core modeling as an elastic-plastic foundation, loading by simulated contact with a spherical indentor, adaptive mesh, damage prediction, damage progression via stiffness reduction, and local-global analysis for displacement. An experimental effort is also included in which composite sandwich plates with graphite-epoxy facesheets and Nomex honeycomb core are subjected to low velocity impact (instrumented impactor) and static indentation. Comparison of static and dynamic results indicates limitations for the quasi-static assumptions typically made. Dynamic simulation of the impact event is provided by a one-dimensional, three-degree of freedom model. Classical three-dimensional and cylindrical bending elasticity solutions attributed to Pagano are modified for Hertzian contact and sandwich structures, providing an exact solution against which the finite element analysis is benchmarked. The two-dimensional (plane stress) finite element analysis, when combined with the three-dimensional equations of stress equilibrium predicts the three-dimensional state of stress in an undamaged composite sandwich under contact-type loading. The three-dimensional stresses obtained from the equilibrium equations and the in-plane finite element stresses compare favorably with the elasticity solution. When compared to the experimental data, the finite element analysis shows the ability to model some of the important features of static indentation of composite sandwich structures. In particular, the slope of the load displacement curve (stiffness), including contact, before damage is well represented. Core failure load is predicted by the analysis within ten percent of the experimental value. Delamination patterns predicted by the analysis are similar in shape to the delaminations observed by C-scans from the experiments, but are smaller for the same load. |
