抄録
An experiment on a tensile fracture in a glass plate with a pre-existing crack is carried out in order to elucidate the time-dependent property of anelastic deformation around a tip of extending-crack. Two types in shape of crack are prepared; one is with crack edges of circular arcs in the cross-section along the crack length by using a discgrinder and the other with non-circular edges by using a cutting machine of supersonic vibration. A crack is created by heating at a point in the direction of the major axis of the pre-existing crack, and extended toward a tip of the pre-existing crack. The time interval is measured between the time when the tip of the crack by heating is incident on a tip of the pre-existing crack and the time when a new crack is created at the other tip of the pre-existing crack. This time interval may be interpreted as the time required for the tip of the crack by heating to be propagated without loss of surface energy from a tip to the other tip of the pre-existing crack. The propagation velocity v is calculated from the time interval and the length of the pre-existing crack.
The observed time intervals are found to have a linear relation with the length of pre-existing crack in each of two types of crack shape. The values of v are estimated to be greater on an average than the terminal rupture-velocity (0.28Vp) of the tensile fracture observed in the same kind of glass plates and less than that (0.58Vp) of Rayleigh waves expected theoretically for the terminal rupture-velocity, where Vp is the P wave velocity. The values of v in the case of the pre-existing crack by disc-grinder seem to be greater than that in the case of the other.
The above time interval is alternatively interpreted as follows: If the propagation velocity of fictitious rupture-front along the pre-existing crack is considered to be equal to that of Rayleigh waves, the measured time-interval may be considered to be the sum of the time estimated from the velocity of Rayleigh waves and the time during which an anelastic deformation takes place around the tip of pre-existing crack to create a new crack. The observed time-interval suggests that the time required for the anelastic deformation increases linearly with the creek length.