Fracture roughness evolution during mode I dynamic crack propagation in brittle materials

摘要

The evolution of roughness RMS during dynamic fracture in thin plates of epoxy (Araldite B) was studied in relation to important fracture parameters such as crack velocity (a)over dot, acceleration and deceleration (a)double over dot and mode I stress intensity factors (K-ID) Dual-focus high speed photography was carried out to evaluate values of K-ID by the caustic (K-ID(C)) and photoelastic (K-ID(P)) methods simultaneously. A specially designed jig applied successive tensile loadings to specimens which resulted in cyclic change of (a)over dot and (a)double over dot. The changes of (a)over dot, RMS and K-ID are shown to be qualitatively similar with respect to the value of a. Quantitatively, a typical result showed that the position of the first maximum value of (a)over dot came 7 mm behind the first loading axis, while that of K-ID(P), RMS and K-ID, (C) appeared on the fracture surface 7 mm, 15 mm, and 25 mm behind the axis, respectively. The agreement between K-ID (C) and K-ID (P) was acceptable except for data around the first loading axis. Discussions are given on the uniqueness problem of (a)over dot and K-ID. [References: 31]