Mechanical Engineering Journal (Apr 2017)

Influence of substrate twisting on Young's modulus measured by four-point bending test for thermal barrier coatings

  • Masahiko KATO,
  • Yuuki MATSUO,
  • Hiroyuki WAKI,
  • Satoru TAKAHASHI,
  • Hiroyuki AKEBONO,
  • Atsushi SUGETA,
  • Yoshitaka KOJIMA,
  • Fumio ONO

DOI
https://doi.org/10.1299/mej.16-00714
Journal volume & issue
Vol. 4, no. 5
pp. 16-00714 – 16-00714

Abstract

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The influence of specimen twisting on Young's modulus of thermal barrier coatings (TBCs) was studied using four-point bending tests based on ISO 19477 and three-dimensional finite element analysis (3D FEM). Twisted substrate specimens were four-point bent using a jig with or without pin rotation to investigate the influence of pin contact conditions. The Young's modulus was calculated by strain gauge and maximum-displacement methods. The results showed that load-strain and load-maximum displacement curves of the twisted substrate specimens showed linear relationships for fixed and rotating pin conditions. The decrease in the Young's modulus with increasing twisting angle was not observed for the strain gauge method but was for the maximum-displacement method. However, the maximum decrease of around 5% for the maximum-displacement method was improved by pin rotation. 3D FEM results showed that the Young's modulus obtained by the FEM quantitatively agreed well with the experimental value. Analyzed strain distribution clarified the insensitivity to specimen twisting for the strain gauge method because of the small difference in the strain at the center of the specimen where the strain gauge was attached. The decrease in the Young's modulus of the twisted specimen for the maximum-displacement method corresponded to the inhomogeneous curvature distribution of the specimen. The influence of the specimen twisting of TBCs on Young's modulus was evaluated by 3D FEM. The same tendency as that for the substrate specimen was observed, but the amount of decrease became large. A decrease around 5 times larger than that for the substrate specimen was observed with a twisting angle of 0.058 by the maximum-displacement method under fixed pin conditions. However, the decrease was improved by pin rotation. The analysis result showed that the strain gauge method had sufficient accuracy to evaluate the Young's modulus of twisted TBC specimens up to a twisting angle of 0.058.

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