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An induction heating procedure coupled with an advanced alternating-current potential drop (ACPD) system to study thermal fatigue crack initiation and growth is presented. This technique can be adapted for various specimen geometries and is well suited for studying isotropic as well as anisotropic alloys. Details of the experimental apparatus and ACPD system are given. To illustrate the procedure, the effect of three cyclic thermal histories on the number of cycles to crack initiation of double-edge wedge specimens of IN-100 and MA-6000 superalloys was studied in air. The thermoelasto plastic finite-element analyses (FEA) to determine the critical locations and their respective stress-strain histories are presented. For this particular geometry of specimen, the initiation of microcracks about 10 to 20 μm in length could be detected and crack growth rates lower than 1 μm/cycle were measured. The experimental results combined with the FEA showed that the peak compressive strains encountered on specimen heat-up are more critical to crack initiation and surface degradation than total stress or strain ranges.
thermal fatigue, induction heating, crack initiation, crack growth, superalloy, IN-100, finite element, A-C potential drop (ACPD)
University research fellow, Ecole Polytechnique, Montreal, PQ
Project engineer, Motoren und Turbinen Union (MTU), München,
Professor, Swiss Federal Institute of Technology, Lausanne,