Variance of adhesive strength and fracture mechanism of fibre/matrix joints

A study was made of the fracture mechanism in fibre/polymer joints tested b y the pull-out technique. The shear adhesive strength tau of joints between epoxy matrix EDT-10 (based on DGEBA) and high-strength steel wire of diame ter 150 mum was determined at room temperature and the variance D of the ta u values was analyzed. The number of specimens tested reached 1269. The are as of joints S were varied from 0.04 to 1.2 mm(2). The large number of spec imens and the wide range of areas S gave us the possibility to construct no t only the tau -S curve but also the D-S one. Whereas the tau -S function d ecreases non-linearly and significantly as the joint area S increases, the values of variance D do not markedly depend on the joint sizes when those s izes are not so small (S > 0.2 mm(2)). This independence and other obtained data support the conjecture that the fracture of fibre/polymer joints star ts near that end of joint where external force is applied. (C) 2001 Elsevie r Science Ltd. All rights reserved.