Direct Measurement of Fracture Energies of Brittle Heterogeneous Materials

A noncatastrophic fracture was shown to exist in the three-point bending test with a "hard-beam" machine when an artificially cracked or notched specimen was used. In this mode of fracture the energy produced by external work was transformed completely into the effective surface energy (fracture energy) of the specimen. The energy was measured from the load-time curve for the test. The fracture energies obtained by this method for plate glass were in the range 3 to 6 × 10³ ergs cm⁻², in good agreement with results obtained by other methods. The effective fracture energies of firebrick were about one order of magnitude larger than those of glass.