Three-point-bending test under the constant load was conducted on Sanjome-andesite to investigate the time dependency of crack extension of Mode I. Crack length was calculated from the crack mouth opening displacement using the unloading compliance method.
After the loading, the crack extension rate continuously decreases at first while the stress intensity factor increases. Thereafter, the crack extension rate takes its minimum, and then accelerates toward the final failure. In the last region where crack extension rate accelerates, it was found that the crack extension rate α can be expressed as
α=Kn/A
where K is stress intensity factor and A is a constant. This equation has the same form with that obtained by the double torsion tests.
The mathematical model of crack growth proposed by Okubo et al. is
(Δα)=Kn·(C1·(Δα)-m+C2)
where Δα is the crack extension, and C1, C2 are constants. It was found that the equation can be applicable through the tests carried out in this study including the first region where the crack extension rate decreases.
