Brittle-ductile transition of polymer blends

Based on the Ludwik-Davidenkov-Orowan theory, a new criterion of BDT for polymer blends is proposed. In this approach fracture stress (_b) and shear yielding stress (_y) governing the brittle-ductile transition (BDT) of polymer blends is combined into a dimensionless group as D_a = _b ²/_y ². The theory dictates that BDT occurs at a critical condition D_ac = 1, brittle fracture occurs when D_a < 1, and ductile fracture occurs when D_a > 1. It can be shown that D_a = F_g · L_ym/L_D, where L_ym measures the length of shear band of the matrix, L_D is a parameter determined by the morphology and interfacial adhesion of dispersed phase, and F_g is related to specimen geometry and other extrinsic parameters. It is suggested that the onset of BDT depends on the competition between the L_ym and L_D. With due consideration to blend morphology, interfacial adhesion and matrix properties, existing experimental evidence supports the applicability of the proposed criterion.The project supported by FORD and NSFC No. 09415312