Three-dimensional Deformation Measurement Research Articles

Three-dimensional deformation measurement techniques in space multi-physical fields based on digital image correlation

Aiming at the three-dimensional deformation measurement requirement of the high-stability structure of spacecraft in space multi-physical fields, a comprehensive instrument protection device in a vacuum high-low temperature environment is developed using ultra-low temperature anti-condensation and vacuum heat insulation technology. This ensures that the digital image correlation (DIC) measurement camera always remains in a constant temperature and pressure environment and can stably exert its original efficiency in space multi-physical field environments. Subsequently, a path-dependent DIC method based on a graphics processing unit computing parallel acceleration is proposed by combining a pre-interpolation strategy and integrated image technology, which realizes high-precision matching of digital images before and after deformation in a spatial multi-physical field environment and improves the computing efficiency. To address the problem that a common reference point may deform significantly in a space environment with a large temperature change, which leads to inaccurate system accuracy, combined with a random sampling consistency algorithm and singular value decomposition method, the optimal registration of the coordinate system and the solution of deformation were realized by setting the threshold of the reference point margin screening. Finally, a three-dimensional deformation measurement system in high- and low-temperature vacuum environments was built, and the three-dimensional deformation measurement of the satellite antenna in high- and low-temperature vacuum environments was verified, which proves the effectiveness and accuracy of the above method.

Dynamic three-dimensional deformation measurement by polarization-multiplexing of full complex amplitude.

This paper provides an extensive discussion of a complex amplitude-based dynamic three-dimensional deformation measurement method, in which the phase and amplitude of the speckle field are used for out-of-plane and in-plane deformation calculation respectively. By determining the optimal polarization states of the speckle field and reference field from the comprehensive analysis of measurement mathematical model in the principle of polarization multiplexing, the 3-step phase-shifting interferograms and one speckle gram can be directly recorded by a polarization camera in a single shot. The out-of-plane deformation would be recovered from the subtraction of speckle phases that are demodulated by a special least square algorithm; speckle gram with improved quality is offered for correlation computation to obtain in-plane deformation. The advancement and significance of the optimized strategy are intuitively demonstrated by comparing the measurement accuracy under different combinations of polarization states. Finally, the dynamic thermal deformation experiment reveals the potential in practical real-time applications.

Development of a distributed three-dimensional inclinometer based on OFDR technology and the Frenet-Serret equations

The inclinometer is a vital tool for monitoring internal displacement in slopes. However, existing fiber-optic inclinometers lack the ability to monitor three-dimensional deformation. To overcome this limitation, this study introduces a novel distributed inclinometer based on Optical Frequency Domain Reflectometer (OFDR) technology. The inclinometer uses Frenet-Serret equations to achieve three-dimensional displacement calculation. To validate the proposed method and the feasibility of the OFDR inclinometer, finite element analysis and experimental testing are conducted. A comparison is made between the proposed method and the conjugate beam and finite difference algorithm. The results demonstrate the reliability of the displacement calculation. The distributed inclinometer developed based on the Frenet-Serret equations and OFDR technology can achieve three-dimensional deformation measurement in space. The measurement results are satisfactory, with the maximum errors in the OFDR inclinometer's measurements per unit length being within 0.45%. This capability enables effective measurement of internal displacement within slopes.

Simultaneous three-dimensional deformation measurement using tri-wavelength and monochrome camera imaging with a pyramid prism.

What we believe to be a new electronic speckle pattern interferometry (ESPI) configuration is being developed for simultaneous three-dimensional deformation measurements. In this ESPI system, two pairs of symmetrical illuminating arrangement with dual-wavelength lights were used to independently sense two in-plane deformation components, one Michelson interferometer-based set illuminating with the other wavelength light was utilized to measure out-of-plane deformation. The color speckle interferogram was split into four sub-patterns by a prism, three of them were filtered by three different bandpass dichroic filters and recorded by one monochrome camera. Micro-rotation testing work firstly verifies the validation of the proposed phase-shifting device. Three-dimensional deformation information was simultaneous obtained by using temporal phase-shift method. All strain components related to the specimen surface deformation were further determined by numerical differential. The experimental results of a tested specimen were excellently consistent with those of FEM simulation, which verified the validation and feasibility of the proposed ESPI system for measuring 3D deformation.

Three-Dimensional Shape and Deformation Measurements Based on Fringe Projection Profilometry and Fluorescent Digital Image Correlation via a 3 Charge Coupled Device Camera.

We propose a novel hybrid FPP-DIC technique to measure an object's shape and deformation in 3D simultaneously by using a single 3CCD color camera, which captures the blue fringe patterns and red fluorescent speckles within the same image. Firstly, red fluorescent speckles were painted on the surface of the specimen. Subsequently, 12 computer-generated blue fringe patterns with a black background were projected onto the surface of the specimen using a DLP projector. Finally, both the reference and deformed images with three different frequencies and four shifted phases were captured using a 3CCD camera. This technique employed a three-chip configuration in which red-green-blue chips were discretely integrated in the 3CCD color camera sensor, rendering independent capture of RGB information possible. Measurement of out-of-plane displacement was carried out through the implementation of Fringe Projection Profilometry (FPP), whereas the in-plane displacement was evaluated using a 2D Digital Image Correlation (DIC) method by leveraging a telecentric-lens-based optical system. In comparison to the traditional FPP-DIC hybrid methodology, the present approach showed a lower incidence of crosstalk between the fringe patterns and speckle patterns while also offering a corrective for the coupling of the in-plane displacement and out-of-plane displacement. Experimental results for the in-plane cantilever beam and out-of-plane disk comparisons with the traditional 3D-DIC method indicated that the maximum discrepancy obtained between FPP-DIC and 3D-DIC was 0.7 μm and 0.034 mm with different magnifications, respectively, validating the effectiveness and precision of the novel proposed FPP-DIC method.

Calibration of stereo-digital image correlation for large field of view measurement based on photogrammetry

Calibration of a stereo-digital image correlation (stereo-DIC) system is essential for three-dimensional (3D) shape and deformation measurement. Although the traditional planar calibration method is flexible in most application scenarios, it still has difficulties in large field of view (FOV) calibration due to the limited size of calibration board. In this paper, a stereo-vision calibration method is proposed for large FOV measurement based on the close-range photogrammetry. Specifically, a certain number of coded targets are first arranged in the area to be measured. Then, the left and right cameras are used to capture images at the calibration and measurement positions. With these images, accurate camera intrinsic parameters can be obtained by close-range photogrammetry methods through encoded targets. The extrinsic parameters can be obtained by the 3D coordinates of these corresponding points and further optimized using corresponding points obtained from both coded targets and speckle patterns. Laboratory experiments with field-of-view ranges of 25 cm by 25 cm and 2.8 m by 2.8 m demonstrate that this method can obtain precise calibration parameters and has good deformation measurement accuracy. Compared to traditional planar calibration methods, this method does not require high-quality or large-sized calibration objects, and all parameters can be calibrated on-site. A large shaking table experiment demonstrated the potential of this method in the field of engineering measurements.

Measurement of three-dimensional shrinkage deformations and volumes of stabilised soft clay during drying with Structure from Motion photogrammetry

The paper applies the Structure from Motion photogrammetry technique to measure three-dimensional shrinkage deformations of a cylindrical specimen during drying. A clay–binder mixture was statically compacted, and its shrinkage behaviour was observed for four weeks with a newly established photogrammetric system. The complete surface information including XYZ coordinates and RGB values was then reconstructed and formed into dense point cloud data, with which the volume change and shrinkage deformations are computed. In volume change determination, the reconstructed dense point cloud achieves a fine reproduction of the specimen surface, leading to satisfactory accuracy. The computed volume deviation was within 495.3 mm3 (0.24%) and 4170 mm3 (1.83%) for the dummy cylinder and clay specimen, respectively. Both values are significantly smaller than the volume deviations computed with a classical approach that involves artificially creating markers on the specimen surface. In the computation of shrinkage deformations, the paper proposes a novel method that detects the fast point feature histogram of the point clouds and then matches the detected descriptors, leading to an improvement in three-dimensional deformation determination. The compacted sample shrinks, and the computed axial deformations increase quasi-linearly with height. However, due to the noticeable tilt that occurred during drying, the calculated radial deformations are scattered at the same height and appear misleading. Circumferential deformations and strains are therefore adopted to represent the true material behaviour.

High-Accuracy Three-Dimensional Deformation Measurement System Based on Fringe Projection and Speckle Correlation.

Fringe projection profilometry (FPP) and digital image correlation (DIC) are widely applied in three-dimensional (3D) measurements. The combination of DIC and FPP can effectively overcome their respective shortcomings. However, the speckle on the surface of an object seriously affects the quality and modulation of fringe images captured by cameras, which will lead to non-negligible errors in the measurement results. In this paper, we propose a fringe image extraction method based on deep learning technology, which transforms speckle-embedded fringe images into speckle-free fringe images. The principle of the proposed method, 3D coordinate calculation, and deformation measurements are introduced. Compared with the traditional 3D-DIC method, the experimental results show that this method is effective and precise.

Three-Dimensional Shape and Deformation Measurement Using Marker Point Hiding and Extraction

Three-Dimensional Shape and Deformation Measurement Using Marker Point Hiding and Extraction

Advances in High-Accuracy Three-Dimensional Dynamic Deformation Measurement and its Applications for Large Structures

Advances in High-Accuracy Three-Dimensional Dynamic Deformation Measurement and its Applications for Large Structures

Three‐dimensional deformation measurement of aero‐engine high‐speed rotating blade surface based on stroboscopic structure digital image correlation method

Under the working conditions of aero-engine, the three-dimensional composite deformation of the blade is caused by the centrifugal force generated by high-speed rotation and the load generated by gas scouring. Aiming at the problem of three-dimensional composite deformation on the surface of aero-engine blades under high-speed rotation, a three-dimensional deformation measurement method based on stroboscopic structure digital image correlation method is proposed, and a method for eliminating rigid body displacement induced by the trigger error of the stroboscope is proposed. First, the laser trigger-stroboscopic irradiation system is used to freeze the high-speed rotating blade under a specific phase. Then, the binocular vision system is used to collect the surface image of the rotating blade. Finally, the digital image correlation method is used to measure the surface deformation field of the high-speed rotating blade. In this paper, the experimental platform is built and the displacement field and main strain field of the blade surface under high-speed rotating state are measured. The experimental results show that the stroboscopic structure digital image correlation measurement system and method have realized displacement measurement accuracy of 2 μm and strain measurement accuracy of 100 μɛ and have realized the surface deformation measurement of the ducted turbine fan blade under the condition of 6000 rpm (CFM56-7 engine N1 speed). The results show that the method is effective and can provide a reliable measurement method for the deformation measurement of high-speed rotating blades in large engine manufacturing enterprises such as Aero Engine Corporation of China.

Study of Bond-Slip Behavior and Constitutive Model of a New M-Section Steel-Skeleton Concrete.

In this study, the bond–slip behavior between a new type of M-section steel skeleton (i.e., M-section steel) applied in assembled shear wall structures and concrete was investigated. First, push-out tests were conducted on 21 M-section steel–concrete (MSSC) specimens, wherein the effects of the concrete cover, concrete strength, and anchorage length on the bond strength between the M-section steel and concrete were considered. Further, the crack patterns, strain distribution of M-section steel, and bond–slip curves of the MSSC specimens were investigated using conventional strain measurement and a non-contact optical three-dimensional deformation measurement system, Digital Image Correlation-3D (DIC-3D). The experimental results demonstrated that the bond–slip curves of the MSSC specimens were divided into four stages: the linear ascending, non-linear ascending, non-linear descending, and residual stages. The initial average bond strength was mainly affected by the concrete strength and anchorage length, whereas the concrete cover and anchorage length influenced the residual average bond strength , and the ultimate average bond strength was affected by the concrete strength, concrete cover, and anchorage length. Consequently, a bond–slip constitutive model of M-section steel and concrete was proposed based on the experimental results, and consistency was observed in comparison with the test results, which verified the applicability of the proposed model. Furthermore, to verify the rationality of the bond–slip constitutive model, a numerical simulation was performed, wherein the bond–slip curves, stress clouds, and interfacial bond damage process of the MSSC specimens were investigated. The numerical simulation results indicated that the bond–slip constitutive model could accurately predict the entire failure process of the MSSC specimens.

Three-dimensional shape and deformation measurement on complex structure parts

Stereo digital image correlation technique (stereo-DIC or 3D-DIC) has been widely used in three-dimensional (3D) shape and deformation measurement due to its high accuracy and flexibility. But it is a tough task for it to deal with complex structure components because of the severe perspective distortion in two views. This paper seeks to resolve this issue using a single-camera system based on DIC-assisted fringe projection profilometry (FPP). A pixel-wise and complete 3D geometry of complex structures can be reconstructed using the robust and efficient Gray-coded method based on a FPP system. And then, DIC is just used to perform the temporal matching and complete full-field pixel-to-pixel tracking. The in- and out-of-plane deformation are obtained at the same time by directly comparing the accurate and complete 3D data of each corresponding pixel. Speckle pattern design and fringe denoising methods are carefully compared and chosen to simultaneously guarantee the measuring accuracy of 3D shape and deformation. Experimental results demonstrate the proposed method is an effective means to achieve full-field 3D shape and deformation measurement on complex parts, such as honeycomb structure and braided composite tube, which are challenging and even impossible for the traditional stereo-DIC method.

Experimental verification of full-field accuracy in stereo-DIC based on the ESPI method.

This paper proposes a method to merge stereo-digital image correlation (DIC) and electronic speckle pattern interferometry (ESPI) data by camera calibration. The proposed method is employed to verify the accuracy of full-field out-of-plate displacements measured by stereo-DIC in a cantilever beam test. The mean absolute error and the root mean square error (RMSE) of the full-field displacement measured by four-megapixel cameras are 0.849 µm and 1.08 µm at 60 mm field of view, respectively, and the RMSE of the central area is 0.615 µm. The errors are not uniformly distributed because of the imperfect calibration. When the lenses are changed and the field of view reaches 120 mm, the RMSE is 1.48 µm with uniform distribution. These accuracies could be traced back to the laser wavelength to confirm the stereo-DIC data. The proposed method can be used not only to verify the full-field measurement accuracy of DIC but also to determine the rigid-body displacement for ESPI with a high-precision stereo-DIC. Thus, the displacement vector can be obtained. Furthermore, it can unify the coordinate of multiple ESPI systems to achieve a large range of high-precision three-dimensional deformation measurements.

Method of Three-dimensional Deformation Measurement for Monocular Microscopic Imaging System

Method of Three-dimensional Deformation Measurement for Monocular Microscopic Imaging System

Full-field motion and deformation measurement of high speed rotation based on temporal phase-locking and 3D-DIC

The full-field and non-contact measurement of three-dimensional motion and deformation of high-speed rotating machinery is a very challenging task in the engineering field. Two issues, the cost of high-speed camera and the decorrelation between rotated images, are hard to avoid for investigators. In this paper, a systematic solution is presented, which combines high-speed rotation image acquisition using low-speed camera with 3D digital image correlation, both low-cost, flexible and accurate. Firstly, the frequency and initial phase of high-speed rotation are calculated by FFT, and temporal phase-locked signal is generated to trigger the dual-camera asynchronously to collect the circumferential images with equal phase interval. Then a layer-by-layer matching method is proposed to search uncoded targets between two rotated images, while a binocular rotation correlating strategy to correlate the speckle subsets. Finally, the corresponded uncoded targets and speckle subsets are reconstructed in three dimension via the camera calibration results, furtherly the 3D motion and deformation fields can be obtained. Five experiments, including two measurement repeatability tests, an accuracy test, a rigid motion measurement of rotating table and a dynamic deformation measurement of ventilation fan, prove the accuracy and effectiveness of the proposed method.

Characterizing dynamic deformation of marine propeller blades with stroboscopic stereo digital image correlation

Stereo digital image correlation (stereo-DIC) technique shows a powerful capacity on full-field three-dimensional (3D) deformation measurement of rotary machine structures. However, it remains a challenge for underwater applications due to difficulties in imaging, stereo calibration, light refraction, and so on. In this paper, its potential in characterizing 3D dynamic deformation of the underwater rotor blades is shown by solving these problems. A stroboscopic stereo-DIC system is established to capture clear speckle images of a blade that rotates in the windowed cavitation tunnel under different flow speeds. To calibrate the stereo camera for underwater object measurement, an improved planar pattern-based calibration method and a globally optimal relative pose estimation algorithm are proposed to calibrate the intrinsic and extrinsic parameters of the stereo-DIC system separately. In particular, a novel refractive 3D reconstruction method for underwater objects is presented to recover the true 3D shape according to flat refraction geometry, ensuring the correctness and reliability of the measured 3D displacement fields. Several experiments demonstrated that the proposed stereo-DIC system and methods are feasible and accurate. Based on this, the measured dynamic displacement fields of a propeller blade are presented and discussed. Results herald a possibility for monitoring the full-field 3D dynamic response and structural health of underwater rotating structures by the proposed technique.

In-Process Measurement of Three-Dimensional Deformations Based on Speckle Photography

In the concept of the process signature, the relationship between a material load and the modification remaining in the workpiece is used to better understand and optimize manufacturing processes. The basic prerequisite for this is to be able to measure the loads occurring during the machining process in the form of mechanical deformations. Speckle photography is suitable for this in-process measurement task and is already used in a variety of ways for in-plane deformation measurements. The shortcoming of this fast and robust measurement technique based on image correlation techniques is that out-of-plane deformations in the direction of the measurement system cannot be detected and increases the measurement error of in-plane deformations. In this paper, we investigate a method that infers local out-of-plane motions of the workpiece surface from the decorrelation of speckle patterns and is thus able to reconstruct three-dimensional deformation fields. The implementation of the evaluation method enables a fast reconstruction of 3D deformation fields, so that the in-process capability remains given. First measurements in a deep rolling process show that dynamic deformations underneath the die can be captured and demonstrate the suitability of the speckle method for manufacturing process analysis.

High-accurate camera calibration in three-dimensional visual displacement measurements based on ordinary planar pattern and analytical distortion model

Camera calibration is crucial for geometric vision-based three-dimensional (3D) deformation measurement tasks. Among existing calibration techniques, the one based on planar targets has attracted much attention in the community due to its flexibility and reliability. Our study proposes a calibration technique to obtain high-accuracy internal and external parameters based on low-cost ordinary planar patterns. The proposed method determines the optimal internal parameters for each camera by refining 3D coordinates of planar control points, where an analytic model of optics distortion is presented to enable lens distortion to be corrected directly in subsequent external calibration and underlying 3D reconstruction. External parameters are estimated by minimizing a bundle adjustment framework, which is carefully designed based on the proposed distortion correction model and depth parameterization. In contrast to the existing techniques, the proposed method is capable of obtaining a high-accuracy calibration with ordinary targets rather than the well-designed and fabricated ones. We experimented the proposed method with a calibration performance analysis and a displacement measurement; both results demonstrated the accuracy and robustness.

Search Space Reduction for Determination of Earthquake Source Parameters Using PCA andk-Means Clustering

The characteristics of an earthquake can be derived by estimating the source geometries of the earthquake using parameter inversion that minimizes the L2 norm of residuals between the measured and the synthetic displacement calculated from a dislocation model. Estimating source geometries in a dislocation model has been regarded as solving a nonlinear inverse problem. To avoid local minima and describe uncertainties, the Monte-Carlo restarts are often used to solve the problem, assuming the initial parameter search space provided by seismological studies. Since search space size significantly affects the accuracy and execution time of this procedure, faulty initial search space from seismological studies may adversely affect the accuracy of the results and the computation time. Besides, many source parameters describing physical faults lead to bad data visualization. In this paper, we propose a new machine learning-based search space reduction algorithm to overcome these challenges. This paper assumes a rectangular dislocation model, i.e., the Okada model, to calculate the surface deformation mathematically. As for the geodetic measurement of three-dimensional (3D) surface deformation, we used the stacking interferometric synthetic aperture radar (InSAR) and the multiple-aperture SAR interferometry (MAI). We define a wide initial search space and perform the Monte-Carlo restarts to collect the data points with root-mean-square error (RMSE) between measured and modeled displacement. Then, the principal component analysis (PCA) and thek-means clustering are used to project data points with low RMSE in the 2D latent space preserving the variance of original data as much as possible and extractkclusters of data with similar locations and RMSE to each other. Finally, we reduce the parameter search space using the cluster with the lowest mean RMSE. The evaluation results illustrate that our approach achieves 55.1~98.1% reductions in search space size and 60~80.5% reductions in 95% confidence interval size for all source parameters compared with the conventional method. It was also observed that the reduced search space significantly saves the computational burden of solving the nonlinear least square problem.