New insights into the fracture mechanism of flattened Brazilian disc specimen using digital image correlation. (July 2021)

• Record Type: Journal Article
• Authors: Yan, Zelin; Dai, Feng; Liu, Yi; Wei, Mingdong; You, Wei
• Is Part Of: Engineering fracture mechanics. Volume 252(2021)
• Publication Date: 2021-07
• Subjects: Flattened Brazilian disc -- Digital image correlation -- Rock fracture -- Tensile stress–strain curve -- Mode-I fracture toughness; Fracture mechanics -- Periodicals; Rupture, Mécanique de la -- Périodiques; Fracture mechanics; Periodicals; 620.112605
• DOI: 10.1016/j.engfracmech.2021.107810
• Languages: English
• ISSNs: 0013-7944

Abstract

Highlights: Tensile stress-strain curve of rocks is obtained in FBD tests via DIC monitoring. A modified calculation method is proposed for determining the K IC of FBD specimen. The second rise of loading curve is induced by compression-shear failure near the flattened ends. Abstract: As a simple and convenient testing method, the flattened Brazilian disc (FBD) specimen has been widely used to determine the tensile strength and mode-I fracture toughness of rocks. However, the precision of the mechanical parameters calibrated by FBD testing method needs to be further evaluated. In this paper, digital image correlation (DIC) technique is used to capture the progressive failure process of FBD specimen, and some new insights are provided for further understanding the fracture mechanism of FBD specimens. Firstly, the horizontal tensile strain history in the center region of FBD specimen is obtained via DIC technique, and combined with loading force history, the tensile stress–strain curve of rocks can be determined. Then, by analyzing the horizontal strain and displacement field near the central crack of FBD specimen, the central crack tip positions are identified. The progressive failure process of FBD specimen shows that the micro-crack and fracture process zone (FPZ) has grown at the center of FBD specimen at the moment of first peak force P max . After the P max, the central crack propagates unsteadily towards the flattened ends of FBD specimen, while is hindered after the loading force declined to the local minimal force P min . Therefore, it is not proper to determine the mode-I fracture toughness K IC using the local minimal force P min in FBD tests. In this study, a modified calculation method to determine K IC is proposed using the first peak force P max and its corresponding central effective crack length observed via DIC technique. In addition, the cracking nature of the secondary crack is identified, and the second rise of the loading force is induced by the compression-shear failure near the flattened ends of FBD specimen. These results are beneficial to better understanding the progressive fracture mechanism of FBD specimen and improving the accuracy of K IC calibrated by FBD testing method.