Abstract
A technique is presented for measuring the local crack tip displacement fields and the global applied parameters during mode I loading of delaminations in composite laminates up to and including failure. To achieve this objective, an instrumented loading set-up has been designed to fit inside the chamber of a scanning electron microscope (SEM).
With this technique, the SEM images of loaded specimens are analyzed to obtain the crack opening displacements (COD) as a function of distance from the crack tip. For mode I tests conducted on AS4/3501-6 unidirectional material, good agreement is obtained between the Linear Elastic Fracture Mechanics (LEFM) calculations and the measurements, in terms of both general shape and magnitude. The results show that the COD increases linearly with the applied displacement up to failure.
Thus, for the case of a brittle material under mode I loading, there is good agreement between the measured and calculated crack tip displacements, and the material behaves in a linear elastic way up to failure. By extending the technique to mode II and mixed-mode loading and by testing other tougher materials in the future, we hope to increase our understanding of mixed-mode failure criteria, which play an important role in the detailed analysis of complex composite structures under realistic loading.