Acoustic emission for polycrystalline graphite under compressive loading

Continuous-type acoustic emission (AE) from nuclear-grade isotropic graphite under compressive loading was examined to investigate the deformation behavior of the graphite. The AE increased gradually with increasing strain in the initial stage of loading followed by a decrease for further loading to the failure point. A model was proposed to explain the phenomenon qualitatively. It was based on dislocation pile up at grain boundaries. To clarify the back stress effect at grain boundaries oxidized specimens were prepared. AE in the oxidized specimens increased monotonically up to the failure point. The model proposed was supported by the experimental results. Moreover, the qualitative relationships of total plastic strain rate and plastic strain rates due to slip deformation and microcracking as a function of total strain were determined from the AE behavior. (author)