Preliminary Investigation of Dual Mode Fracture Sustained by Graphite/Epoxy Laminates Impacted by High-Velocity Spherical Metallic Projectiles (Final Report, January 1, 1990-December 15, 1991).

摘要

This thesis studies the basis for delamination initiation and propagation within an impacted laminate. The work provides an explanation for fracture mode transformation along the projectile's path. Post-impact observations of graphite/epoxy (AS4/3501-6) laminates penetrated by steel spheres (0.5-inch diameter) reveal a fracture mode, similar to shear plugging, adjacent to the impacted surface. This fracture mode is contrasted with that of delamination adjacent to the rear surface. The sudden transition from shear plugging to delamination occurs when the projectile interacts with the returning impact-generated tensile wave. To demonstrate the transition, results are presented from ballistically impacted laminates containing a series of embedded carbon stress and constantan strain gages. Results are based on impact velocities of 1825 and 2380 f/s. Transverse stress waves are shown capable of creating delamination until attenuated by a localized compression front associated with the on-coming projectile. Delamination Initiation, Delamination Propagation, Fracture Mode Transformation, Stress Wave.