Abstract
The four point bending strength of porcelain-fused-to-metal (PFM) in Ar gas at 37℃ was measured at the strain rate of 8.33×10-5sec-1, and the critical stress intensity factor was obtained by SEPB (single edge precracked beam) method. Using the strength data in distilled water at 37℃ reported previously at five strain rates, the effect of water on the crack growth of PFM was investigated. According to Weibull analysis of strength in both Ar gas and distilled water at the same strain rate, the strength coincided at the side of low fracture probability and the Weibull parameters were 15.3 in distilled water and 8.1 in Ar gas. The ratio of crack length just before rupture in distilled water to Ar gas increased with increasing fracture probability and finally became about twice. Besides, supposing that the fracture was initiated from the surface flaw and that the crack growth length in Ar gas was zero, the length of the crack growth by the start of rupture in the distilled water was estimated to be 5〜36 μm and increased with decreasing strain rates. Furthermore, as the strain rate decreased, the crack growth in each specimen became almost equal and did not depend on the initial size of the flaw.
