The principle of the method specified is subjecting a standard test specimen to a bending stress equal to 1/10 of a specified or measured flexural strength, raising the temperature at a uniform rate, measuring the temperature, at which a specified deflection occurs. The test load used is not a fixed load as in part 2, but a function of the ultimate or specified load. This allows the method to be applied to materials with a wide range of strength and bending moduli.