The use of vibration measurements for the detection of diffuse creep damage

Abstract

Abstract

The feasibility of using measurements of structural natural frequencies for the non-destructive assessment of diffuse creep damage has been investigated for a 1 per cent chromium—½ per cent molybderum—¼ per cent vanadium steel crept at stresses above and below the ductile brittle transition stress. The frequency changes observed during creep were similar to those predicted for constant volume straining of the specimen. Uncertainties arose due to the formation of an oxide layer on the specimen surface but no evidence has been found to suggest that, in either range, significant independent changes of modulus or density occur during creep. It has also been shown that the speed of sound in a material is unaffected by the presence of small voids since the apparent modulus and density are changed in the same proportions. Ultrasonic velocity measurements cannot therefore, be used to detect voiding in its early stages. The results also suggest that natural frequency measurements are unlikely to detect this type of damage.