1993 年 42 巻 479 号 p. 969-975
By assuming that the fracture toughness value (crack resistance force) R is expressed by a constitutive relation as R (a, a) ∝ R1(a)·am*, (a and a; crack length and crack velocity, m*; rate sensitivity parameter), the stability condition of cracked specimens is analytically discussed for rate sensitive brittle materials such as glasses and ceramics. The stability criterion obtained is identical in its form to the one reported by Gurney and Hunt in which the rate effect is not taken into account. However, by introducing the rate effect into the analysis, it was found that an initial crack begins to extend before the load maximum appears. This fact that load gets larger, nevertheless crack extends, is named “pseudo stable phenomena (PSP)”.
Load-displacement and crack extension behaviour were simulated by numerical calculations including the rate effect. The PSP was confirmed to appear in rate sensitive brittle materials. Experiments on Pyrex glass also showed the appearance of PSP, which is prominent when EBΛ* gets larger (E and B; Youngs modulus and thickness of the specimen, Λ*; the compliance of the testing machine).