Abstract. Digital shearography (DS) is a noncontact, whole-field, and laser-based optical interferometric method. It is a valuable tool in the field of nondestructive testing (NDT) and received considerable acceptance in the automotive and aerospace industries. Conventional DS only detects the flaws in one or two shearing/sensitive directions, which leads to the missed inspection and leaves quite a lot of suspected defects underdefined. A trishearing DS for NDT is proposed to solve the mentioned issue. The presented shearography is designed based on a multiplexed Mach–Zehnder interferometer embedded with the spatial phase shift technique. It measures the defects in three sensitive directions simultaneously and has balanced optical paths with high light efficiency. Moreover, the measurement sensitivity of each direction can be adjusted during the test, without affecting the carrier frequencies, so it meets various needs for NDT applications. The principle and the experimental validation of the proposed system are introduced in detail.

Simultaneous trishearing digital shearography for nondestructive testing

Digital shearography (DS) is a noncontact, whole-field, and laser-based optical interferometric method. It is a valuable tool in the field of nondestructive testing (NDT) and received considerable acceptance in the automotive and aerospace industries. Conventional DS only detects the flaws in one or two shearing/sensitive directions, which leads to the missed inspection and leaves quite a lot of suspected defects underdefined. A trishearing DS for NDT is proposed to solve the mentioned issue. The presented shearography is designed based on a multiplexed Mach–Zehnder interferometer embedded with the spatial phase shift technique. It measures the defects in three sensitive directions simultaneously and has balanced optical paths with high light efficiency. Moreover, the measurement sensitivity of each direction can be adjusted during the test, without affecting the carrier frequencies, so it meets various needs for NDT applications. The principle and the experimental validation of the proposed system are introduced in detail. 

Electronic speckle pattern shearing interferometry, also known as shearography, is a highly sensitive technique that can measure the distribution of the displacement derivatives of the object surfa...

Application of Electronic Speckle Pattern Shearing Interferometry with High-Speed Camera in Vibration Analysis of Piezoelectric Transducer

Digital shearography, also called digital speckle pattern shearing interferometry, is described as a robust measuring method due to its simple optical setup and the relative insensitivity against ambient noise. It has been applied for nondestructive testing and strain measuring. This paper explores its possibilities for vibration analysis. The measuring device performing both continuous (time-average method) and stroboscopic illuminations is described. The selection of the illumination mode is made by adjusting a controller and performed simply by a computer. The real-time observation with refreshing reference frame technique and the quantitative evaluation with the phase shift technique are presented. The results show this measuring device is well suited for both qualitative and quantitative vibration analysis.

Vibration analysis by means of digital shearography

Estimation of TiO2 thin film shift by electronic speckle interferometry

Laser shearography is a powerful optical tool that is able to directly measure the displacement derivatives using interferometric effects. Stroboscopic shearography provides a full field, reliable and repeatable inspection process that facilitates defect visualization. The aim of this paper is to investigate the effectiveness of laser shearography for inspection of a large aluminum plate with a large wall thinning. A modified Michelson interferometer is introduced in order to inspect the entire aluminum plate simultaneously. The wall thinning is visualized as the region of the anomaly in the quasi-uniform and homologous shearography fringe pattern. The boundaries of the wall thinning cannot be indicated precisely due to the nature of the formation of shearography fringes. Therefore, the small shearing method is applied to determine the dimensions of the wall thinning. This approach allows for the detection of the wall thinning in the wider range of excitation frequencies. The wall thinning is successfully detected using the small shearing method as a light rectangle in the inconspicuous background. Finally, a novel averaging approach is proposed to eliminate the effects of noise and uncertainty in the calculation of the boundaries. Using this approach, the shearography interferometric effects are significantly reduced.

Hamidreza Asemani

Papers

The Effectiveness of Laser Shearography for the Inspection of Wall Thinning in a Large Aluminum Plate

Application of Electronic Speckle Pattern Shearing Interferometry with High-Speed Camera in Vibration Analysis of Piezoelectric Transducer