Abstract
The size of the fracture process zone (FPZ) has significance for studying the fracture mechanism and fracture characteristics of concrete. This paper presents the method of assessing the FPZ of Mixed-Mode I-II for quasi-static four-point shearing concrete beams with pre-notched by Lagrangian strain profiles from digital image correlation (DIC). Additionally, it explores the influences of volume rates of the coarse aggregate of 0%, 28%, 48%, and 68%, and the specific surface areas of 0.12 m2/kg, 0.15 m2/kg, and 0.26 m2/kg on the size of the FPZ. It shows that the size of FPZ in four-point shearing concrete beam can be characterized by the displacement field and strain field using DIC. The size of FPZ conforms to linear positive correlation with the volume rate of coarse aggregate, and linear negative correlation with the specific surface area of coarse aggregate. It presents that the crack initiation of the four-point shearing beam with the pre notch is dominated by mode I load, and the propagation and fracture of Mixed-Mode I-II cracks are caused by the combined effect of Mode I and Mode II loading.
Highlights
The fracture of concrete and other quasi-brittle materials may exhibit a significant nonlinear region surrounding the tip of macroscopic cracks, similar to the plastic zone at the tip of cracks in metal materials
It can be seen that the compliance of the curve that is measured by digital image correlation (DIC) and sensor is very high under different mix proportions
The fracture process zone (FPZ) of mixed-mode I-II crack was studied by four-point shearing tests combining with the Lagrange strain monitoring results of DIC technology
Summary
The fracture of concrete and other quasi-brittle materials may exhibit a significant nonlinear region surrounding the tip of macroscopic cracks, similar to the plastic zone at the tip of cracks in metal materials. The micro-crack zone and the subcritical propagation zone at the crack tip are called fracture process zone (FPZ), which is often considered to be the material property [1]. The primary cause is a mutual influence between micro-cracks by heterogeneous property of the mesoscopic structure of concrete, and it constitutes the network of micro-cracks within a certain zone. This has an effect of degradation and shielding to the propagation of microscopic cracks, including micro crack initiation, detours around the crack, bridging toughening of aggregate, friction between crack surface, passivation, and bifurcation of the cracks. The size of FPZ has significance for studying the mechanism and characteristics of concrete fracture
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