Sampling moiré method and its application to determine modulus of thermal barrier coatings under scanning electron microscope

The sampling moiré method has been widely utilized to determine the displacement and strain distributions of materials and structures at macroscales. The method exhibits a simple operation and low requirements regarding the specimen grating. Further, a single image is required for the phase analysis. The method is a promising method in the field of experimental mechanics. In this study, the mechanisms of moiré pattern generation are systematically studied using simulations. Two essential conditions for their generation are presented and the applicability of the control equation to moiré-spacing determination is discussed. To promote the application of the sampling moiré method in microdeformation measurements, three-point bending tests using thermal-barrier coating (TBC) specimens (bilayer beam structure) are performed under a scanning electron microscope (SEM). Using the soft-imprint technique, a high-frequency grating is fabricated on the side surface of the TBC specimen to generate sampling moiré patterns under the SEM. The microdisplacement and strain components are calculated using the sampling moiré method and their values are used to determine the TBC Young's modulus. To examine the reliability of the sampling moiré method, the measured strains are compared with those obtained with the geometric phase analysis (GPA). The results are in good agreement. Consequently, the sampling moiré method encourages further applications in microdeformation measurements and mechanical-property characterizations of other materials.