Error correction for Moiré based creep measurement system

Yi Liao; Kevin G. Harding; Edward J. Nieters; Robert W. Tait; Wayne C. Hasz; Nicole Piche

doi:10.1117/12.2050595

28 May 2014 Error correction for Moiré based creep measurement system

Yi Liao, Kevin G. Harding, Edward J. Nieters, Robert W. Tait, Wayne C. Hasz, Nicole Piche

Proceedings Volume 9110, Dimensional Optical Metrology and Inspection for Practical Applications III; 911007 (2014) https://doi.org/10.1117/12.2050595
Event: SPIE Sensing Technology + Applications, 2014, Baltimore, MD, United States

Abstract

Due to the high temperatures and stresses present in the high-pressure section of a gas turbine, the airfoils experience creep or radial stretching. Nowadays manufacturers are putting in place condition-based maintenance programs in which the condition of individual components is assessed to determine their remaining lives. To accurately track this creep effect and predict the impact on part life, the ability to accurately assess creep has become an important engineering challenge. One approach for measuring creep is using moiré imaging. Using pad-print technology, a grating pattern can be directly printed on a turbine bucket, and it compares against a reference pattern built in the creep measurement system to create moiré interference pattern. The authors assembled a creep measurement prototype for this application. By measuring the frequency change of the moiré fringes, it is then possible to determine the local creep distribution. However, since the sensitivity requirement for the creep measurement is very stringent (0.1 micron), the measurement result can be easily offset due to optical system aberrations, tilts and magnification. In this paper, a mechanical specimen subjected to a tensile test to induce plastic deformation up to 4% in the gage was used to evaluate the system. The results show some offset compared to the readings from a strain gage and an extensometer. By using a new grating pattern with two subset patterns, it was possible to correct these offset errors.

Citation Download Citation

Yi Liao, Kevin G. Harding, Edward J. Nieters, Robert W. Tait, Wayne C. Hasz, and Nicole Piche "Error correction for Moiré based creep measurement system", Proc. SPIE 9110, Dimensional Optical Metrology and Inspection for Practical Applications III, 911007 (28 May 2014); https://doi.org/10.1117/12.2050595

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