Abstract:
In a four-point bending (FPB) test, the beam segment near the mid-span cracking section is under pure bending. Therefore, the mode Ι fracture model can be better applied in theory. Based on this, FPB tests on notched beams were carried out. The calculation formulae of double-
K fracture parameters were established by assuming that the pure bending segment of a FPB specimen under external load is equivalent to a pure bending specimen and by using the linear superposition principle. Moreover, the effect of different initial crack-depth ratios (0.2, 0.3, 0.4, 0.5 and 0.6) on the fracture parameters was evaluated. The results indicate that with the increase of the initial crack-depth ratio, the initial fracture load,
Pini, the maximum fracture load,
Pmax and the critical relative effective crack propagation length, (
ac-
a0)/
H, decrease gradually while the initial fracture toughness,
KICini and the unstable fracture toughness,
KICun keep almost constant. Consequently, FPB tests can be applied to determine the double-
K fracture parameters of concrete.