Notch effect in failure of fiberglass non-woven materials

This study is concerned with the failure characteristics of notched and unnotched specimens of a highly porous, multilayered non-woven fiber network material subjected to uniaxial tension. The network consists of glass fibers locally bonded by a polymer resin. The multilayer character of the material emerges from the manufacturing process in which the material is produced in plate form. Experiments indicate the presence of a size effect on fracture such that the net section strength of deep-notched specimens appear as higher than that of unnotched and shallow-notched specimens. For unnotched and shallow-notched specimens, failure emerges as a through-thickness delamination triggered by the failure of the interlayer bonds. The presence of notches, however, leads to a transition in deformation mechanism. For deep notches an unusual in-plane failure mode is observed where the failure plane is inclined to the notch plane. This failure mode is attributed to the fiber orientation distribution and the nonaffine characteristics of the mechanical response of the material. A computational model for the in-plane failure analysis demonstrates that failure is not defined by a fracture but rather a strength model, and this effect results from the nonaffine deformation state in the network material. The transition to the higher strength failure mode with increased notch depth results from the constraints on internal load transmission processes imposed by the notches.