Experimental investigation of progressive cracking processes in granite under uniaxial loading using digital imaging and AE techniques

• Published in: Journal of structural geology Vol. 126; pp. 129 - 145
• Main Authors: Zhou, Xiao-Ping, Zhang, Jian-Zhi, Qian, Qi-Hu, Niu, Yong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2019
• Subjects: Acoustic emission; Cracking process; Digital image correlation; Granite; Inter-event time function; Process zone nucleation; Acoustic emission; Cracking process; Inter-event time function; Process zone nucleation; Digital image correlation; Granite
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/j.jsg.2019.06.003

For a full understanding of the cracking processes in granite, uniaxial compression tests are conducted on prismatic specimens with pre-existing flaws, and digital imaging and AE techniques are applied to monitor real-time rupture behaviors. The digital image correlation (DIC) method is used to detect the process zone nucleation characteristics in granite. A novel approach for representing AE data in terms of the inter-event time (IET) function F(τ) is employed to analyze fracture-related AE event rate characteristics. Based on the coupled analyses of the acousto-optic-mechanical characteristics, the complete cracking processes of granite are classified into six levels, which are distinguishable by five characteristic stresses. Process zone nucleation, which represents the clustering of micro-cracks, is incorporated into the classification for the first time. Process zone nucleation is visualized as a white patch and is either linear or diffuse. By DIC analysis, the maximum principal strain field reliably predicts a linear white patch, and the maximum shear strain field implies a diffuse white patch. The evolutionary rules of the IET function F(τ) strongly support the new classification of cracking levels in granite. For the identification of stress thresholds and cracking levels, a combined acousto-optic-mechanical methodology is established, in which the role of the IET function F(τ) is highlighted.
•Acousto-optic-mechanical characteristics are analyzed in a coupled way to study the cracking process of granite.•Process zone nucleation is incorporated into the classification of cracking levels for the first time.•The DIC method is used to evaluate the process zone nucleation characteristics.•The inter-event time function F(τ) is first applied to identify the cracking processes of granite.•The combined acousto-optic-mechanical methodology is established to identify stress thresholds.