Abstract
An investigation was conducted to (1) see if fiber bridging could be eliminated or at least reduced and (2) evaluate an alternative approach for determination of in-situ Mode I fracture toughness values of composite matrix materials. Toward this end, double cantilever beam (DCB) specimens were made using unidirectional layups of T6C/Hx205 composite material in which the delaminating halves were placed at angles of 0°, 1.5°, and 3° to each other. The small angles between the delaminating plies were used to avoid fiber nesting without significantly affecting Mode I behavior. A starter delamination was introduced by using a thin Teflon® insert. DCB specimens were also fabricated and tested with a 0.0254-mm thick bondline of Hx205 between aluminum adherends. This study resulted in the following conclusions: the extent that fiber bridging and interlaminar toughness increase with crack length can be reduced by slight cross ply at the delamination plane to reduce fiber nesting; some fiber bridging may occur even in the absence of fiber nesting; the first values of toughness measured ahead of the thin Teflon® insert were observed to be very close to the toughness of the matrix material with no fiber bridging; and thin (0.0254-mm) adhesive bondline of matrix material appears to give toughness values equal to the interlaminar toughness of the composite matrix without fiber bridging.
