Fracture Toughness Evaluation by Using Chevron-Notched Graphite Bend Bar Specimen

Abstract

The fracture toughness (K_IC) of the isotropic graphite was determined for four-point bend bar specimens with chevron notches. Compliance calibration in terms of chevron-notch configurations was determined to obtain the crack resistance curve (K_γ) required for obtaining the correct value of K_IC. Acoustic emission signals were measured for detecting precracking and successive crack growth. Loads and back face strains instead of load point deflection were measured for the calibration. Calculations of the stress intensity for the chevron-notched specimen were carried out based on the assumption of Bluhm's slice model. The results of the interlaminar shear correction (k) were investigated in comparison with the data of other researchers. It was concluded that the k value lay between those of other researchers, and the curve of the K_γ vs crack length was constant in the vicinity of the minimum value of the stress intensity.