INVESTIGATION OF FIBER BRIDGING IN DOUBLE CANTILEVER BEAM SPECIMENS.

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 in-situ Mode I fracture toughness values of composite matrix materials. A starter delamination was introduced by using a thin Teflon insert. 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 Telfon insert were observed to be very close to the toughness of the matrix materials 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.