Application of Load-Relaxation Techniques to Study Subcritical Crack Growth in Brittle Materials

The load relaxation technique was applied to double‐ cantilever‐beam specimens for the determination of diagrams of the stress intensity factor (K1) vs crack velocity (V) for soda‐lime glass. The effect of machine compliance was explicitly incorporated into the velocity equation. The data were in good agreement with published data from different techniques. It was shown that a hard machine (small compliance) is best suited for the load‐relaxation technique. The use of a soft machine (high compliance) will lead to catastrophic failure during load relaxation. A single‐edge notched‐beam specimen in bending is unsuitable for the relaxation technique since catastrophic failure will occur during relaxation regardless of machine compliance.