Mentl V.: A Comparison of Fatigue Characteristics of Structural Steels Measured by means of

The assessment of material mechanical properties degradation as a result of long-term service at cyclic loading, creep temperatures and/or their combination has been performed on the basis of various non-destructive methods. Nevertheless, their main disadvantage stems from the fact that these methods can give qualitative (and not quantitative) results and thus the remaining lifetime cannot be exactly evaluated. New methods of mechanical testing were developed recently that are based on making use of miniature test specimens (e.g. Small Punch Test). The most important advantage of these method is the nearly non-destructive withdrawal of test material and small size of test specimen what is interesting in cases of remaining lifetime assessment when a sufficient volume of the representative material cannot be withdrawn of the component in question. In opposite, the most important disadvantage of such methods stems from the necessity to correlate test results with the results of classical test procedures and to build up a database of material data in service. The correlations among the miniature test specimen data and the results of classical tensile tests, fracture toughnesss values and time to rupture characteristics at creep temperatures and, of course fatigue S – N curves are necessary for the remainig lifetime assessment of structure in long-time service. The paper describes the results of fatigue tests performed on miniature tests specimens in comparison with classical fatigue tests for several steels applied in power producing industry. Special miniature test specimens fixture was designed and manufactured for the purposes of fatigue testing at the Zwick/Roell – Amsler 10HPF5100 test machine. The miniature test specimens were produced by water-jet cutting from the large test specimens. With respect to the specimen shape (See Figure), stress concentration and multiaxial stress situation had to be taken into consideration for the purposes of comparison with the classical test specimens