Crack growth and acoustic emission in graphite

Abstract

The effects of the crack plane orientation and the guiding groove in graphite were studied together with Acoustic Emission during fracture toughness testing by Double torsion technique. In the guiding grooved specimen, the fracture energy G shifted toward the lower G region in the G-V diagram due to the stress concentration on the surface of the groove. When the load was applied to the grooved specimen, the ring down count rate and low peak amplitude events were found to be greater than in the ungrooved specimen because of the open pore on the surface of the guiding groove. When the crack propagates through the grain of the graphite, the value of the fracture energy,G, and the crack growth parameter,n, and the number of high peak amplitude events were much larger than in other cases. When the crack propagates in the manner of a interlamellar crack, the fracture energy is the lowest. In the present work, the ring down count rate, N was related to the crack velocity, V as $N \times V^{1.6}$. The total ring down counts increased with the increase of the cross had speed.