Results of an experimental investigation of fracture kinetics and crack resistance of brittle materials

Abstract

1. For use in ordinary laboratories a comparatively simple method is developed and experimental apparatus constructed for testing tubular specimens loaded separately or together by axial compression and by internal and/or external pressure which can be applied to arbitrarily located annular sections of cylindrical specimen surfaces. 2. Qualitative differences between the deviations of the central and edge cracks from their initial growth trajectory in a pipe tested under internal pressure are discovered and explained. These differences are caused by the specific effect of homogeneous stress fields oriented along the pipe axis. 3. Experiments showed that the compression of a pipe along its axis is capable to straighten wavy trajectories of dynamic growth of a central crack. Judging from the results of this investigation the vibratory nature of its deviation from the generatrix of the pipe is caused solely by the dynamic effect generated by supercritical fracture. 4. Subcritical graphs of static fracture of glass pipes were plotted showing the dependence of these graphs and, consequently, of the crack resistance characteristics of the material on the type of crack (central or edge) and on the load acting along the pipe axis. 5. It is shown that the generally accepted concept of “critical crack length in the piping” is not justified if the characteristic of internal biaxiality B and the crack growth rate at which it has been defined are not specified. 6. A quantitative disagreement was detected between crack resistance characteristics of l 3v glass determined on tubular specimens with a central crack and on flat specimens with an edge crack.