The DIC technique has been widely used in material strain measurement and crack propagation because of its simple operation, lack of contact, and high precision [18]. Li et al. [19] conducted a three-point bending test on concrete, obtained the strain field and displacement field of the surface by DIC, and summarized the morphology and crack opening displacement of the fracture process zone (FPZ) at different stages. The DIC technique is able to record the crack propagation process, but it cannot characterize the energy dissipation pattern in this process [20]. The AE technology is able to quickly and accurately detect micro-damage inside the material before macroscopic damage occurs on the surface of the material by the AE signal and is based on the stress wave propagating through the solid material when the material is subjected to strain [21]. Therefore, the combination of DIC and AE is a suitable method to monitor the energy dissipation and crack propagation during the entire damage and failure process of quasi-brittle materials such as concrete [22]. Rouchina et al. [23] used both DIC and AE to monitor the loading test of fibrous mortar specimens, and the results showed that the two techniques achieved good correlation in the progressive damage development of fibrous mortar. Liu et al. [24] obtained the displacement field on the surface of the specimen and the AE signal inside the specimen based on DIC and AE techniques, which indicated that the internal and surface characteristics of FPZ evolution were consistent during the propagation of concrete cracks. Alam et al. [25] applied these two techniques to quantitatively study the propagation of the FPZ, and the results showed that the FPZ length calculated by the crack opening (DIC) was larger than that calculated by the length of energy dissipation zone (AE). Skarżyński et al. [26] studied the fracture behavior of reinforced concrete beams under quasi-static, three-point bending through these two techniques, and analyzed the influence of aggregate particles and steel bars with different shapes, volumes, and sizes on the bending fracture of concrete. If the cracking of concrete structures is predicted in advance or monitored in real time by DIC and AE techniques, and the concrete structures are maintained and reinforced, all kinds of unnecessary accidents can be prevented.
Cs 1.6 Crack
where W is the work done by an external force on the system, U is the initial strain energy, T is the strain energy released after cracking, and D is the increased surface energy after cracking. When all of D was used to form a new crack area At, Equation (2) was satisfied: 2ff7e9595c
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