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Three-point bending tests are performed on notched concrete beams under various cyclic loading regimes. Meanwhile, the digital image correlation (DIC) method is used to monitor the crack propagation. The fatigue fracture life decreases with the loading level increases for constant-amplitude cyclic loading. The residual crack mouth opening displacement (CMOD) accumulates and fracture stiffness degrades with the loading process. The size of fracture process zone (FPZ) can be determined based on the full displacement field monitored by DIC method. The length of FPZ increases linearly with the increasing of effective crack length before the crack tip opening displacement (CTOD) exceeds the critical value. When CTOD exceeds the critical value, a macroscopic crack formed in front of the initial crack tip. For cyclic envelope loading, the length of FPZ increases at beginning and then decreases with the increasing of effective crack length. For constant-amplitude loading, CTOD never reaches the critical value, and the macroscopic crack does not propagate forward. Finally, it is found that both the calculated effective crack lengths of concrete under constant-amplitude loading by two-parameter model (TPM) and DIC methods present three-stage feature, but the values calculated by TPM are smaller than those by DIC method. [ABSTRACT FROM AUTHOR]

In order to study the effect of loading rate on fracture behavior of dam concrete, wedge splitting tests of various loading rates (0.1, 0.01, and 0.001 mm/s) are carried out on two kinds of full-graded dam concrete notched cubes with side lengths of 300 and 450 mm, respectively. Digital image correlation and acoustic emission technique are used to measure the deformation and acoustic emission parameters of the dam concrete. Test results show that: the peak load and fracture energy of dam concrete specimens increases with the increase of loading rate. And the higher the loading rate is, the fracture of concrete shows more obvious brittleness. Influenced by the boundary effect, the CTOD increases with the increasing of loading rate, however, the length of crack decreases as loading rate increases. With the loading rate increases, the energy mutation area is more obvious, while the accumulated acoustic emission energy is affected by both the loading rate and the maximum aggregate size. The number of acoustic emission three-dimensional locating points and the shear signal decrease with the increase of loading rate, which is attributed to that the faster the loading rate is, the less sufficient the development of micro cracks in concrete is. The test results can supply experimental data to the fracture mechanics of dam concrete. [ABSTRACT FROM AUTHOR]