The moiré interferometry can be used to measure the in-plane deformation of the loaded specimen. In order to obtain the deformation data from the moiré patterns, various techniques for fringe processing have been proposed. As an application, the moiré interferometry can be utilized to identify the constitutive parameters in combination of elasticity theory at a given loading configuration. However, the fringe processing may introduce errors. In order to reduce the mentioned errors and realize automatic identification. There is urgent need to develop new approach to identify the constitutive parameters based on the fringe pattern. In this paper, a novel one-step inversion method based on fringe pattern (IMFP) is proposed, which utilizes the unique relationship between the moiré fringe pattern and the material constitutive model parameters to directly extract the constitutive parameters from the fringe pattern. In calculation of IMFP, by comparing the measured fringe pattern and a series of digital moiré fringe patterns obtained by simulation, the inversion results can be calculated by the multi-objective optimization algorithm. Besides, the adaptability and accuracy of the IMFP are discussed in detail. The successful results verify that the IMFP method has the advantages of automatic process, better robustness, and high reliability.

Micro-Raman spectroscopy was an effective tool for the investigation of experimental mechanics. Most of traditional Raman spectroscopes based on the fixed backscattering geometric configuration were scarcely applicable for the complex stress/strain analyses of advanced nanomaterials and microstructures. This work presented the angle-resolved Raman method, which detected the Raman spectra at adjustable inclination angle, rotation angle and polarization angles of the incident laser and scattered lights. A self-built backscattering angle-resolved Raman instrument was established and the theoretical model decoupling the plane stress state of C-Si was proposed. Then, this method was applied on the studies including the analysis of 2-axis stress state on the {100} c-Si, in-strain sensor by using mono-layer graphene, and the chirality identification of phosphorene.

In the field of precise 3D reconstruction, fringe pattern profilometry (FPP) is always regarded as the preferred method for it provides relatively higher accuracy. However, the phase acquisition process generally requires a sequence of images with different phase shift, which is rather time-consuming. Thus the application scenario of FPP is greatly limited and this has long been a bottleneck in practice. Although single-frame based phase retrieval algorithms like Fourier transform profilometry (FTP) has been proposed and extensively studied, they still suffer from relatively unbearable loss of accuracy. In response to this problem, we take advantage of the deep learning techniques and present a deep-learning based phase acquisition system in which the phase can be acquired by a single frame of fringe pattern image. The network is constructed according to the procedure of phase retrieval, which is trained by thousands of fringe pattern images with the phase data being known in advance. And it can predict more preciously the phase of a new fringe pattern map. As large data set is demanded for the training and testing, we also propose a method to prepare the fringe pattern dataset and phase data, which will be opened to other researchers and free them from the massive work of building new datasets. In addition, the generated dataset is even more flexible and versatile than real captured pictures in some aspects, which enables the trained network to be more adaptable and flexible. Experiments illustrate the effect of our method which will be promising for practical use.

Optical interferometric techniques are very attractive in various research and application fields for the non-contact, high accuracy and full filed measurements they offered. Fringe patterns, which are the recorded results of these techniques, are difficult to analyze when containing discontinuity. Fringe patterns discontinuity detectable technique, i.e. discontinuous fringe pattern segmentation technique, is demanded. Inspired by the recent development of convolutional neural network, in this paper, we propose an automatic and robust single fringe pattern segmentation method based fully convolutional neural network (FCN). Both simulated and experimental fringe patterns are collected for network training and testing. With the identified discontinuous regions by FCN, the discontinues boundaries are estimated and obtained. The proposed discontinuous fringe pattern segmentation method is automatic and robust to noise and resolution changes. Simulated and experimental fringe patterns are tested and successful results have been obtained, which validate the proposed method.

Two-dimensional digital image correlation (2D-DIC) is sensitive to out-of-plane motion, which leads to rather poor strain results. Recently, optical extensometers realized by dual-reflector imaging are proposed, which can selfcompensate the strain errors introduced by out-of-plane motion. In this study, we will extend strain measurement from an extensometer to full-field deformation measurement. To this end, first, two corresponding areas of interest (AOIs) are created based on the symmetrical axis of the reference image. Second, the displacement and strain fields of these AOIs are computed with common 2D-DIC algorithm, respectively. Subsequently, high-accuracy deformation results are obtained by taking the average of the deformation of the corresponding calculation points in two AOIs. Two types of uniaxial tensile tests were conducted to validate the feasibility of the proposed self-compensation method. The first experiment indicates that the strain results obtained with the proposed method are in good agreement with those with strain gauges. The results of the second experiment are basically in agreement with those of numerical simulation ANSYS, which demonstrates the feasibility of the proposed method on measurement of nonuniform strain fields. Both the above two experiments demonstrate that the rigid out-of-plane motion will lead to a global strain-field error for common 2D-DIC.

With the combination of scanning electron microscope (SEM) and digital image correlation (DIC), the mechanical properties of interfacial transition zone (ITZ) in concrete are experimentally studied. The morphology of the ITZ is captured by SEM under compressive load, and from the recorded images the deformation of the ITZ is analyzed. After that, the distribution of the nominal compressive elastic modulus of the ITZ is obtained along the distance from the aggregate to the mortar, which can be used to characterize the size of the ITZ with the strain contour. A conclusion can be draw that the area where the nominal compressive elastic modulus is obviously less than that of the aggregate and mortar can be defined as the ITZ. With increasing distance from the aggregate boundary, the nominal compressive elastic modulus of the ITZ decreases first and then increases, and at the sides close to the aggregate and mortar, the nominal compressive elastic modulus of the ITZ gradually tends to that of the two materials. Finally, the relationship between the average nominal compressive elastic modulus and the distance from the aggregate boundary can be fitted by two order polynomial function, which can be used to describe the mechanical properties of the ITZ.

Reseachers have been developing new methods to improve the accuracy of digital image correlation (DIC) for decades, and the proposed methods could be mainly divided into two classes, the software and the hardware methods. One embranchment technique among the hardware methods is increasing the spatial resolution of the imaging system, which means recording more details of target surface by increase the pixel resolution with the field of view fixed. Since more information of interested area adopted in the image correlation processing, higher displacement and strain measurement accuracy could be achieved. To increase spatial resolution of imaging system a simple super resolution methods is proposed, in which a telecentric lens and two pieces of sheet glass are employed as the imaging system. The optical field from the target surface propagates through the two glass sheets and into the telecentric lens. By tilting one glass sheet slightly the optical field would be translated by sub pixel, thus a translated image could be obtained. Assembling the translated images, a super resolution image with much higher spatial resolution could be formed. Applying the digital image correlation algorithm to the super resolution images, the improved displacement and strain accuracyt could be achieved.

Digital Image Correlation (DIC) is a superior tool that makes it possible to measure the surface deformation of objects with a high level of accuracy. Traditional view thinks that there must be random characteristic in the speckle pattern adopted in DIC, but in this paper the application of regular pattern in DIC method is developed and proved to have better performance than random pattern. Subsequently, if the used pattern in DIC is regular, it is proved that non-maximum correlation coefficient includes the information of deformation. A new Moiré processing method, based on correlation coefficient, is also proposed in this study for deformation measurement directly without any optimization iterations. Finally, by combining the two methods, a DIC/Moiré hybrid method with regular pattern is used to measure large in-plane deformation. Verification experiments are conducted to prove the less computed time demand and high accuracy in our method.

The video deflectometer based on digital image correlation is a non-contacting optical measurement method which has become a useful tool for characterization of the vertical deflections of large structures. In this study, a novel method which considers the variations of pitch angles in full field has been proposed. This method allows deflection measurement at a wide working distance with high accuracy. A monocular video deflectometer has been accordingly developed with an inclination sensor, which facilitates dynamic determination of the orientations and rotation of the optical axis of the camera. This layout has advantages over the video deflectometers based on theodolites with respect to convenience. Experiments have been presented to show the accuracy of the new imaging model and the performance of the monocular video deflectometer in outdoor applications. Finally, this equipment has been applied to the measurement of the vertical deflection of Yingwuzhou Yangtze River Bridge in real time at a distance of hundreds of meters. The results show good agreement with the embedded GPS output.

The residual stress generated during the deposition of the film may cause unpredictable deformation or damage to the component; therefore, it is vital to understand residual stress. Reliable measurement and modelling of residual stresses at the micron-scale for small-scale structures and nanostructured materials is a tremendously challenging task. The analysis of depth profiles of residual strain requires detailed knowledge of in-depth lattice strain function in order to calculate the residual stress profile in a manner that considers both the mechanical anisotropy and the texture of the materials.

Full-field measurement of the deformation behaviour of small scale structures and nanostructured materials has recently been made possible by combining Scanning Electron Microscopy (SEM) and Digital Image Correlation (DIC) techniques. The DIC techniques were first introduced by Sutton who used the calculation of a grayscale digital image through bilinear interpolation for the object translation. It was suggested that a discrete digital image be interpolated for a continuous smooth secondary function. Although a high-quality pattern can be artificially applied for a better measurement, the mechanical behaviour of sample structures may become affected by the patterning process. The high magnification of SEM-DIC leads to complex image distortions. Long image scanning times can capture high-noise sensitivity and drift from SEM parameters; therefore, the development of a proper scheme for digital correlation of SEM images with natural surface features is needed.

Prior to this present research, a study was made on the methodology and validation of DIC under SEM to minimize errors and use it for surface deformation and strain measurement of CMOS IC samples with multiple thin layers, and to validate the DIC method and its parameters using SEM images under spatial translation or time. For the present study, DIC with proper image correlation criteria postulated in the previous study was performed to obtain stability and accuracy for the specimen images. The images were acquired by incremental focused ion beam (FIB) ring-core drilling with various depth steps. The FIB-DIC was then used to calculate the residual stress. This study used a semi-destructive measurement method, which is not limited to crystalline and amorphous materials, and is suitable for analyzing uneven structures. Further, several semidestructive measurement methods were used to gauge the strain relief when the material was removed or deformed.

Reliable measurement and modeling of residual stresses at the micrometer scale for small-scale structures and nanostructured thin films is a challenging task. The analysis of the depth profiles of the residual strain requires detailed knowledge of the in-depth lattice strain function, so the residual stress profile calculated in a manner that considers the mechanical anisotropy and texture of the materials. The development of a microstructure independent procedure for depth-resolved measurement of residual stress is an issue of strategic interest. In this study, a digital correlation (DIC) of the specimen images acquired by incremental focused ion beam (FIB) ring-core drilling with various depth steps was performed. A translation test was performed first to study the applicability of DIC to FIB images, and a proper procedure was established to obtain more accurate results. Moreover, state of the film in terms of the residual stress was evaluated and compared to illustrate the feasibility of this technique.