抄録
The caustic method and the optical interferometry are applied to fracture problems of glass plates with a crack. First, an improved technique for producing a natural crack in glass plate is proposed. This technique based on three-point bending is combined with the caustic method, and expecting crack length a can be controlled by monitoring the caustic pattern. The minimum value of crack width which can be detected by penetration test is evaluated as 0.3 μm by using the optical interferometry. The optical interferometric technique using various kinds of light sources is in detail examined for measuring crack opening displacement (COD). Next, stress intensity factor is determined through COD obtained from the optical interferometric fringe pattern under static and quasi-static loading conditions, and it is in good agreement with K-value evaluated by the caustics and the theoretical K-value. Moreover, it is shown that fracture toughness values of glass plate under various loading conditions can be lined up as K_<Id>, K_<IC>, K_<ID> and K_<Ia> in order of decreasing value.
