Impact response of laminated plates subjected to transverse loading.

摘要

This dissertation presents results of an analytical solution and comprehensive experimental program to investigate the impact response of laminated plates subjected to transverse loading. The objectives of the study were to develop an efficient method to predict the maximum impact force from the energy-balance model, and to assess the impact damage resistance.; In the analytical study, the dynamic governing equations based on the classical laminate theory were expanded to obtain more generality. The derived equations of motion were solved in terms of natural frequency using Laplace transform. From Lagrangian equations of motion, the effective bending-shear stiffness of composite laminates was determined by using the fundamental natural frequency. This efficient approach can be used in place of the static compliance test conventionally conducted. A modified energy-balance model utilizing this stiffness predicted the maximum impact force at various impact energies using a numerical technique.; Comprehensive experimental studies were performed utilizing the systematically designed instrumented drop weight tester to obtain the impact force vs characteristic time of the AS4/APC-2 thermoplastic and AS4/3501-6 thermoset laminates at various energies, specimen configurations, and stress states. The experimental program included the assessment of damage and the analysis of failure mechanisms by ultrasonic C-scan and scanning electron microscope (SEM), respectively.; The maximum impact force obtained from the analytical solution agreed well with the experimental data up to a certain impact energy for thermoplastic laminates due to their linear elastic characteristics. The data for thermoset composites, however, were not compatible with the solution because of the reduced bending-shear stiffness. In the analysis of experimental results, higher impact force and shorter characteristic time were correlated with smaller damage size. Thus, these parameters could be substituted for traditional absorbed energy criteria in assessing the impact damage resistance. The failure mechanisms of the increased damage resistance resulted from fiber pull-out and fiber breakage rather than wide delaminations.; The data obtained provide a basis for improved design and analysis of composite structures subjected to dynamic loading. Further, a model created for impact parameters in this research can be applied to various composite materials.