The processes of tensile fracture, or extension fracture in rock have a fundamental importance for understanding and predicting failure (Gudmundsson
2011). A critical aspect of its characterization is associated with the inelastic region surrounding the crack tip called the fracture process zone (FPZ) (Zietlow and Labuz
1998; Rinehart et al.
2015). The FPZ is simply defined as the region of inelastic deformation surrounding the crack tip. Due to its fundamental influences, a variety of experimental techniques have been used to study the FPZ, including acoustic emission (AE) (Zietlow and Labuz
1998; Otsuka and Date
2000), morié interferometry (He et al.
1997), holographic interferometry (Maji and Wang
1992), speckle interferometry (Lin et al.
2009,
2012), and digital image correlation (DIC) (Zhang and Zhao
2013; Lin and Labuz
2013). Although a substantial knowledge of the FPZ has been obtained by those studies, the FPZ characterization (e.g., the size and other properties) still poses essential challenges. First, there is no standard procedure to define the FPZ using an experimental technique. The different sizes of FPZ can be obtained for the same material using different techniques (Otsuka and Date
2000). It is simply because every technique has its own advantages and limitations, so that experimental determination of the FPZ size can be influenced by the observation techniques. For example, although AE is a powerful and relatively simple approach, the selection of different position errors may demonstrate a different size of the FPZ, due to detection of noise events with different levels (Ince et al.
2009). More importantly, accurate characterizations of the local material behavior or damage inside the FPZ are difficult in the laboratory. Thus, modeling crack propagation mostly relies on global response (Rinehart et al.
2015). Here AE also presents an excellent example, i.e., the detected AE events are discrete locations, which results in a challenge to provide information about local material behavior. As a consequence, an appropriate physical quantity from AE measurements will help to evaluate the local behavior. …
