Quantitative diagnosis of the out-of-plane displacement derivative with temporal-phase-shift shearography

Abstract

Shearography, or digital speckle pattern shearing interferometry, is highly sensitive to material strain measurements. Among various shearography systems, the temporal-phase-shift Michelson shearography system is extensively researched for its high-accuracy diagnosis of the out-of-plane displacement derivative. However, the system faces difficulties achieving quantitative measurement due to the need to calibrate parameters and control random noise. Therefore, finding solutions to improve system design and performance is essential. This paper focuses on obtaining more accurate and reliable results for out-of-plane displacement derivatives. Several methods to calibrate the magnification, the equivalent pixel size, and the shear amount are discussed. A temporal-phase-shift shearography system with an online universal calibration module is designed and tested for performance. The random noise and stability are under 1µε RMS, and the repeatability is better than 2.75%. Additionally, the system’s accuracy is verified by digital speckle pattern interferometry with a 2.5% relative error.