CRACK GROWTH AND PREDICTION OF ENDURANCE IN THERMAL‐MECHANICAL FATIGUE OF 12Cr—Mo—V—W STEEL

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Abstract
Fractography and fracture mechanics were used to study the behaviour of a crack that emanated from a starter notch on a specimen surface subjected to thermal cycles, and which grew in the direction perpendicular to the surface, under out‐of‐phase loading conditions. A 12Cr–Mo–V–W steel was used as representative of an elevated temperature material, and one that is frequently employed for vessels or heat‐exchanger tubes. A low power travelling microscope observed crack length changes on the specimen surface. It was shown that the growth rate of a part‐through crack could be expressed in terms of a strain intensity factor range and two constants, and that the striation spacings agreed with the microscopically observed crack growth rate. The integration of the crack growth rate equation gave an approximate evaluation of thermal fatigue life of smooth specimens.