Defect Structure of Deformed Heterogeneous Materials: Acoustic Emission and X-Ray Microtomography

Laboratory investigations of deformation of heterogeneous brittle materials (rocks) by acoustic emission (AE) and X-ray computer microtomography (CT) are presented. The experiments involved loading of cylindrical samples of Westerly granite under the condition of uniaxial compression and recording of AE signals emitted during deformation of samples at different loading-unloading stages. After each unloading of the sample a tomographic survey was performed. Totally, 11 loading-unloading stages and tomographic surveys were carried out. The defect structure evolution is considered in the framework of the concept of self-organized criticality. It has been found that the type of the energy distribution function of AE signals can be used as an indicator of the deformed material state and transition to a critical fracture stage. An exponential function points to a noncritical state of a deformed material, and a power-law function indicates that the defect accumulation has passed to a critical stage. This result is confirmed by X-ray microtomographic data.