TENSILE STRENGTH OF BRITTLE MATERIALS.

The tensile strength of an alumina body was investigated by using hydraulically expanded cylindrical test specimens, and the effect of stress rate, gauge volume, and static stress on the ultimate tensile strength was evaluated. Experimental results showed that the tensile strength of alumina is strongly dependent on stress rate but not on gauge volume. At higher stress levels the resistance of alumina to constant static stress is relatively low, but there is a stress level, approximately 18,000 psi, which can be sustained for long periods of time, and which does not lower the ultimate tensile strength of alumina. This stress level is reached at the rate of 4000 psisec and represents 60 of the average ultimate strength 29,640 psi obtained at the same stress rate. Test specimens subjected for twenty-four hours to this static stress, and loaded subsequently to failure at a constant rate, showed the same ultimate tensile strength as specimens stressed directly to failure at the same rate. Author