This was a purely technical investigation at a maximum temperature of 600 deg C on flat tensile specimens of 12 percent Cr cast steel with a central hole, which was heated by resistance heating. In addition to a primary tensile load, repeated thermal shocks were applied at the hole surface by forced air cooling. The aim was to simulate loadings experienced by a turbine wheel disc (features test). The longest test lasted 16,000 h. For the same geometry, compared with a stress-rupture plot of creep only data, it was shown that the creep-fatigue interaction considerably reduced the lifetime (by a factor 2-5), although no cracking was apparent. The data were analysed by finite element methods that incorporated primary and secondary creep rates and triaxial stress states. The results were displayed on a 'Cousseran Diagram' which was an engineering method to assess interacting primary and secondary loads, with respect to creep. This approach was superior to the Lemaitre parametric method, which significantly underestimated the creep rate.
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