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• The new digital shearography meets the requirements of high standards, making it suitable for dynamic tests while providing high-quality phase maps. • Both shearing direction and amount can be controlled quantitatively and accurately. • Phase maps can be evaluated with a single exposure. • High light efficiency and accurate phase demodulation lead to high-quality phase maps. Digital shearography (DS), a laser-based optical interferometric method, is widely employed for measuring the first-order derivative of an object's surface deformation. Unlike digital holography, DS integrates self-reference optics, enhancing resistance to environmental disturbance and improving detection sensitivity, making it ideal for non-destructive testing (NDT). DS finds applications in diverse fields such as material inspection, fluid property research, medical diagnostics, cultural heritage restoration, and military defense. The conventional temporal phase-shift (TPS) method encounters limitations in dynamic tests, leading to the introduction of the spatial phase-shift (SPS) method. However, SPS is restricted by aperture size, impacting the phase map quality. The spatial light modulator (SLM) introduces a novel approach to DS system development, enabling quantitative shearing adjustments through precise SLM control. Existing DS systems using traditional phase-shift technology rely on interferometers and struggle to achieve high-quality phase maps with a single exposure. The proposed high-performance DS, leveraging both SLM and a micro-polarizer camera, overcomes this limitation, facilitates single-exposure phase map evaluation with the polarization phase-shift technique, and eliminates the need for a tiny aperture, enhancing light beam utilization and phase map quality. [ABSTRACT FROM AUTHOR]

• Multi-level point cloud processing scheme that significantly improves the quality of point cloud fusion. • The solution has the ability to process static and dynamic multi-view point clouds. • Digital image correlation can easily generate enough point cloud data. Post-processing of the initial point cloud is one of the important ways to improve the measurement accuracy of digital image correlation (DIC). In this study, a multi-level point cloud optimization scheme is proposed for processing point clouds of multi-view images in DIC systems. Dense point clouds obtained after interpolation of primary point clouds from multi-view images contain noise. First, the local Random Sample Consensus (RANSAC) algorithm is proposed to retain local features while removing coarse matching points. Defects are filled in by the adaptive cavity repair technique based on information around the cavities and restores the original surface shape to the greatest extent. Finally, a multi-layer surface filtering is executed to smooth the mesh. Experiments verify the comprehensive performance of the multi-level optimization scheme, providing excellent results in point cloud fusion, cavity repair, and mesh smoothing, regardless of static 3D reconstruction or dynamic deformation measurement. [ABSTRACT FROM AUTHOR]

• A high precision roll angle measurement method based on digital holography is proposed. • This method requires only a single hologram to obtain the phase of two object beams, thus enabling dynamic measurement of the roll angle. • Relying on the rough surface of the measured object, this method does not require the installation of a target on the measured object. • Based on the numerical reconstruction principle of digital holography, there is no need to adjust the imaging system to refocus when the measurement distance changes. Among the six degrees of freedom for a moving body, measuring roll angle is the most difficult. In this study, a noncontact, no-imaging dynamic roll angle measurement system based on holography is proposed. Two beams of light are used to irradiate the measured object symmetrically, then two reflected light and the reference light interfere with each other to produce a hologram. By extracting the phase information of the two reflected light from two illumination beams using single hologram, this method achieves dynamic measurement of in-plane deformation, and then the roll angle is obtained through subsequent data processing. The effectiveness of the proposed method in-plane roll angle measurement is validated based on theoretical and experimental results. Experimental results show that the proposed method measures roll angle with high accuracy at both fixed and varied distances. [ABSTRACT FROM AUTHOR]

Highlights • We propose an error elimination method for thermal disturbance in high-temperature environment using color speckle and camera instead of traditional industrial camera. • This measurement method is simpler and easier, and the accuracy and practicability of the measurement are higher than the existing methods. • All the advantages of digital image correlation method, including simple structure, non-contact and full field measurement. • No stringent synchronization is required because what we process is the grayscale information of different channels of each picture. • Suitable for any complex high temperature environment. Abstract Digital image correlation method is a kind of displacement and strain measurement technique based on visible light illumination. It can realize non-contact and full-field measurement with lower requirements on the measurement environment, thus it's widely used in testing and research for mechanical properties of materials at high temperature. But there are many factors affecting the measurement accuracy due to the complexity of the high temperature environment, of which the influence of the thermal disturbance on digital image correlation method is the most obvious. In order to reduce the influence of it and improve the measurement accuracy, this paper proposes a measurement method for eliminating thermal disturbance error in high temperature deformation measurement based on color speckle and camera. Two kinds of grayscale field information of different colors were endued to the surface of specimen, and we collected images by color camera with channel separation for each frame of them. Then we processed the grayscale field of two channels separately combined with the digital image correlation method, analyzed the information carried by two different grayscale fields, and a simple mathematical model was performed to separate the thermal disturbance error from the measurement results. Finally, we set up the experimental system, built the mathematical model between the two channels through static measurement experiment, which was used to extract and correct the thermal disturbance error of measurement results of the rigid body motion experiment. The high consistency between corrected result and true displacement value proved the feasibility and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Highlights • The SLM can change the phase of the light and the amount of shear. • The nonlinear random error in phase shift method can be eliminated. • The efficiency of detection can be greatly improved. Abstract The paper presents a new shearography system which applies a spatial light modulator (SLM). The system can control the shearing amount and direction as well as introduce the phase shift accurately and automatically, making shearographic testing easier and more practical. Shearography has the known advantages for nondestructive test and strain measurements of being fast, full-field, and having high sensitivity. Traditionally, the shearing amount is controlled by adjusting a reflector mechanically. Mechanical adjustment of the reflector is slow, inconvenient and not well suited for in-field NDT practice. For application of phase shift techniques, a piezoelectric transducer (PZT), which is usually used for application of phase shift techniques, introduces random error due to its tendency to be nonlinear. This paper introduces a new shearographic detection system with a spatial light modulator. The spatial light modulator controls the liquid crystal by using a birefringence effect and twisted nematic effect. The spatial light modulator can change the phase of the light and shearing amount accurately and automatically, thus eliminating the nonlinear random error in the phase shift method. Furthermore, this system also improves testing efficiency. In this paper, the fundamental of SLM shearography is presented. The capability of this optical configuration is demonstrated theoretically as well as through experiments. [ABSTRACT FROM AUTHOR]

This paper presents a Dual Directional Sheared Spatial Phase-Shift Digital Shearography (DDS-SPS-DS) system for simultaneous measurement of strains/displacement derivative in two directions. Two Michelson Interferometers are used as the shearing device to create two shearograms, one in the x -shearing direction and one in the y -shearing direction, which are recorded by a single CCD camera. Two lasers with different wavelengths are used for illumination, and corresponding band pass filters are applied in front of each Michelson Interferometer to avoid cross-interference between the two shearing direction channels. Two perpendicular shearing directions in the two measurement channels introduce two different spatial frequency carriers whose spectrums are orientated in different directions after Fourier Transform. Phase maps of the recorded two shearograms can be obtained by applying a windowed inverse Fourier transform, which enables simultaneous measurement of dual directional strains/displacement derivatives. The new system is well suited for nondestructive testing and strain measurement with a continuous or dynamic load. The capability of the dual directional spatial phase-shift digital shearography system is described by theoretical discussions as well as experiments. [ABSTRACT FROM AUTHOR]

• A compact common-path dynamic phase shifting shearography system is proposed, which only needs to insert a LCPG between an imaging lens and a polarization camera. • The spatial phase shifting method is used to realize dynamic detection. • The shear amount generated by the LCPG and the spatial carrier introduced by the polarization camera are decoupled. • The effectiveness of the proposed method is verified theoretically and experimentally. A concise and dependable dynamic phase-shifting shearography system based on common-path interferometer is proposed. Two lateral sheared images with common optical path are generated using a liquid crystal polarization grating (LCPG). The sheared images of the object under test interfere with each other, and a pixelated micropolarizer array is used to introduce pixelated carrier, enabling the measurement of dynamic deformation using dynamic phase-shifting. Compared with the ordinary imaging system, the shearography system only needs to insert LCPG between an imaging lens and a camera with pixelated micropolarizer array. The system is resilient to environmental disturbances benefitting from the compact common-path and dynamic phase-shifting method. Theoretical analysis and experiments have been completed, showing that the system can fully exploit the advantages of shearography and improve the reliability of shearography applications. [ABSTRACT FROM AUTHOR]

• Mirror-assisted DIC system is proposed to realize 360-deg panoramic dynamic and static measurement of the object. • Two plane mirrors form four images (two real images and two virtual images), which provides more effective data. • The DIC system consists of three cameras and has higher measurement accuracy • The trinocular DIC system can effectively solve the problems of field-of-view occlusion and receding correlation during the large deformation and distortion of the specimen In this paper, we propose a new technique to achieve 360° panoramic large deformation measurement with the help of trinocular digital image correlation (3DT-DIC) system assisted by two mirrors. Two reflecting mirrors can image the rear of the specimen with virtual reality (secondary reflection). The trinocular vision system simultaneously captures the deformation images of the front and rear of the specimen and completes 360° profile reconstruction and large deformation measurement. The 3DT-DIC system can effectively solve the problems of field-of-view occlusion and receding correlation during the large deformation and distortion of the specimen. A printed speckle pattern for precise positioning of the two reflecting mirrors' poses and virtual reality transformation during the mirror imaging are introduced. Static and dynamic experiments are conducted separately. Experimental results show that the proposed method has better 360° panoramic reconstruction and stress–strain measurement capability. Compared with the binocular DIC system, the proposed method can calculate more effective points and has better 3D reconstruction capability under distorted large deformation. The proposed method can effectively solve the problems of field-of-view occlusion and receding correlation under large deformation. It provides a new idea for realizing 360° panoramic large deformation measurement. [ABSTRACT FROM AUTHOR]