Estimation Method for Mixed Mode (I+II) Interlaminar Fracture Toughness of Composite Laminates under Low-Velocity Impact Loading

摘要

A simple experimental method was developed in order to evaluate the mixed mode (I+II) interlaminar fracture toughness of polymer matrix composite laminates under low-velocity impact loading. The MMF (Mixed Mode Flexure) specimen was employed for determining the critical energy release rate at the onset of macroscopic crack growth. The SHPB (Split Hopkinson Pressure Bar) system was used for measuring the dynamic load and displacement. The dynamic response of the specimen was studied on the basis of computational results using finite element method. The dynamic stress field in the vicinity of the crack tip was similar to the static stress field when a slow-gradient ramped incident stress wave applied to the specimen. However, the dynamic stress field was largely oscillated with time when a stepped incident stress wave was applied. In the previous case, a simple formula based on static beam theory and compliance method could be applied for calculating the dynamic energy release rate. The experimental results agreed well with the above computational results.