Deformation Measurement Method Research Articles

Noncontact measurement of tire deformation based on computer vision and Tire-Net semantic segmentation

Tire deformation is a contributor to vehicle driving safety and an important parameter reflecting the vehicle-road/bridge interaction. Existing methods for measuring tire deformation require measuring devices in contact with the tires, which has many limitations in practice. Thus, the present study proposes a noncontact measurement method of tire deformation based on computer vision and deep learning techniques. Firstly, the diverse dataset of tire images is established based on tire images collected from roadside cameras. Next, a new semantic segmentation Tire-Net is developed to segment the tire images. Then, the quantification algorithm including the subpixel-level edge detection, key point positioning, and scale factor determination is proposed to calculate the physical value of tire deformation. Finally, field tests are carried out on the tires of cars, buses, light trucks, and heavy trucks to verify the proposed method. The results show that it performs well as a means of measuring tire deformation.

Experimental investigations of fractured rock deformation: A direct measurement method using strain gauges

Measuring fractured rock deformation under changing loading conditions is important in rock engineering projects to estimate rock strength and permeability. Measurement of deformations at less than micrometer level for rock fractures is difficult. To investigate the feasibility of the resistance strain gauge method, an experimental system was built to measure the fractured rock deformation due to cycling of confining pressure. The test results of different positions were compared and relatively reasonable test locations were selected based on the test data and regression analysis. The measurement tests were conducted on cylindrical samples with diameters of 50 mm and lengths of 100 mm of shale, granite, limestone, and marble containing a single fracture or two parallel fractures. The experimental results show that the strain gauge method and the proposed test point pattern perform well for measuring fractured rock deformation under changing loading conditions. The experimental data for the loading progress for a single fracture fits the existing fractured rock deformation models well (i.e., the Goodman model, Bandis model, and Sun model). For cyclic loading, observed cycles compared with the existing models and the hysteresis loop during deformation under cycling of the confining pressure, the strain-pressure curves of the loading and unloading processes are consistent with existing models. The strain gauge method provides a deformation measurement method of two parallel fractures. Under the pressure 15 MPa for plane α the deformation is in a state of opening with strain value more than 1003 με; but plane β is in a state of closure with strain value near −115 με.

Accurate dynamic 3D deformation measurement based on the synchronous multiplexing of polarization and speckle metrology.

An accurate dynamic 3D deformation measurement method realized by the combination of phase-shifting speckle interferometry and speckle correlation is proposed. By converting the speckle field and the reference field into a circular polarized and linear polarized state, the three-step phase-shifting speckle interferograms and one specklegram were recorded directly and simultaneously within a single image by using a polarization camera. Then, the out-of-plane deformation was demodulated from the synchronous phase-shifting fringe patterns, and the in-plane deformation was measured by performing correlation calculations by using specklegrams with the effect of the reference field ignored. Thus, the full-field 3D deformation was obtained precisely. Experimental results demonstrated the accuracy and dynamic measurement ability of the proposed method, which is compact and feasible for actual dynamic scenes.

Incorporation of motion prediction and state estimation to track dots for vision-based in-crash toeboard deformation measurement

This paper presents a marker-based stereovision method to measure toeboard deformation during a crash test. The method tracks a set of colored dots marked on the surface for stereovision using recursive state estimation that consists of a prediction step and a correction step. Prediction is based on a motion model derived by feature matching and mapping in the stereo image. In the correction step, the dots are first tracked using a dot centroid tracking (DCT) algorithm that weights the color, saturation, and brightness of pixels in a search kernel predicted by the motion model. An extended Kalman filter (EKF) subsequently fuses the prediction and the DCT measurement for the most likely dot centroid. The accuracy and robustness of the proposed method for in-crash toeboard deformation measurement are presented in a vehicle crash test. The experiment shows the proposed technique tracks the deformed surface accurately and is robust in varied light conditions and conditions when the field of view (FOV) is temporarily blocked.

Bridge Deformation Measurement Using Unmanned Aerial Dual Camera and Learning-Based Tracking Method

Bridge deformation response data are the basis for calculating the dynamic parameters of the bridge, and it is of great significance to accurately measure the deformation response of the bridge during the load test and service conditions. A bridge deformation measurement method using an unmanned aerial system (UAS) with dual cameras and a deep learning-based object tracking method is proposed to measure the bridge deformation. The contributions are as follows: (1) To address the problem that the movement of the UAS brings error to the deformation measurement results, dual cameras with telephoto and wide-angle lenses are used to simultaneously capture the deformed points and stable points on the bridge, so as to simultaneously measure the deformation of the bridge and the displacement of the UAS, and then the displacement of UAS is eliminated by using the homography relationship between the two cameras. (2) To solve the problem that the traditional digital image correlation-based displacement measurement method is easily disturbed by factors such as light changes and occlusion, a displacement calculation method based on object detection network and target tracking algorithm is proposed to achieve the stable target displacement measurement. Finally, the proposed method was verified in a laboratory test and applied to the deformation measurement of an in-service bridge to verify the practicability of the proposed method.

Creep Behavior Characterization of Nickel-Based Single-Crystal Superalloy DD6 Thin-Walled Specimens Based on a 3D-DIC Method.

The thickness debit effect of creep behavior has been a focal point of nickel-based single-crystal superalloy research, and there is a need for an advanced creep deformation measurement method. This study developed a novel high-temperature creep test system based on a single-camera stereo digital image correlation (DIC) method with four plane mirrors to conduct creep tests on thin-walled specimens of a nickel-based single-crystal alloy, DD6, with thicknesses of 0.6 mm and 1.2 mm under experimental conditions of 980 °C/250 MPa. The reliability of the single-camera stereo DIC method in measuring long-term deformation at a high temperature was experimentally verified. The experimental results show that the creep life of the thinner specimen was significantly shorter. It was found the lack of coordination in the creep deformation process of the edge and middle section of the thin-walled specimens may be an important factor in the thickness debit effect according to the full-field strain contour. By comparing the local strain curve at the rupture point with the average creep strain curve, it was found that the creep rate at the rupture point was less affected by the specimen thickness during the secondary creep stage, while the average creep rate in the working section significantly increased as the wall thickness decreased. The thicker specimen usually had a higher average rupture strain and higher damage tolerance, which prolonged the rupture time.

A Comparison of Surface Deformation Measurement Methods for Slopes

This study aimed to promote an efficient and reliable collection of deformation data for earthen slopes by comparing the Total Station (TS), Distributed Strain Sensing (DSS), and Uncrewed Aerial System (UAS)-based deformation measurement methods. The TS-based method was a two-person task with a longstanding “tried and true” reputation, and it provided acceptable results. However, it included a major portion of manual work in the field, potentially consuming extended time to obtain high-resolution data. The DSS-based method was a fiber optic cable-based one-person work, and it showed substantially faster and easier measurement. This method possessed the capability of collecting unattended measurements. The method also required anchor posts to measure deformation in segmented sections; some anchor posts became loose from shrinkage cracks and resulted in invalid measurements, particularly for soils of high plasticity. The UAS-based method was an aerial photogrammetric method. It provided an extremely high-resolution deformation profile but required a manual survey for an elevation check at reference points, although the surveying took a short amount of time by utilizing a Global Navigational Satellite Survey (GNSS) technique. This method required one operator and an assistant. From a comparison of the characteristics of the three different methods, it was found that each technique has its pros and cons, and the combination of different methods may greatly enhance the accuracy and convenience of the measurement.

Study on deformation measurement method based on structured light point clouds

For the requirement of structural deformation measurement, a deformation measurement method based on structured light point clouds is proposed. A structured light measurement system is built, and the calibration process based on the assumption of the projector's reverse camera and with the help of the checkerboard calibration board is completed. The pattern projected by the projector is designed by using a four-step phase-shift technique assisted by Gray code. By combining with system parameters which have been calibrated, the three-dimensional reconstruction of the object surface is completed. A structural deformation measurement method based on the statistical analysis of the distance between point clouds is proposed, and the principles of three points cloud distance calculation methods including point-to-point, point-to-surface and surface-to-surface are analyzed. The feasibility and accuracy of the deformation measurement method based on the structured light point cloud proposed in this paper are verified via experiments. Experimental results show that this method can achieve out-plane high-precision displacement measurement of structures.

Full-field deformation measurement of structural nodes based on panoramic camera and deep learning-based tracking method

Full-field deformation measurement of structures generally requires the aid of complex and expensive multi-camera measurement systems. A full-field structural deformation measurement method using a single panoramic camera and deep learning-based tracking algorithm is proposed. The contributions are as follows: (1) To address the problem that existing full-field image acquisition methods rely on multi-camera systems, a full-field image acquisition method based on a single panoramic camera is proposed, in which a distortion-free planar image covering the full-field of the structure is obtained by decomposing the projection in multiple directions based on the panoramic camera imaging model and the cubic projection method. (2) To solve the problem that the nodes of structures usually contain little texture and are difficult to track robustly with existing image processing methods, an object detection network with a modified tiny feature map layer and attention mechanism is applied to extract the region of interest (ROI) of each node automatically. (3) Finally, the ROIs of the identified nodes are clustered using a perceptual hashing method and then the node coordinates are calculated using a line segment detector (LSD) and intersection fitting. The proposed method is validated on a scaled model of a stadium, and the comparison to the deformation results of total station shows that the proposed method can calculate the displacement of all node at once, and the average error between the displacement results and those of the total station is 3.7 mm, which proves the practicality of the proposed method.

Investigation of the accuracy of Digital Image Correlation (DIC) in measuring full-field strain for timber materials

As one of the most successful techniques in experimental mechanics, digital image correlation (DIC) has been widely used to measure the motion and deformation of solid materials, especially in situations where non-contact measurement is required. This study describes and provides a comprehensive overview of the application of DIC using the open-source platform Ncorr on orthotropic materials. Orthotropic materials are a subset of anisotropic materials; their properties depend on the direction in which they are measured. Deformation displacement and in-plane strain in two directions are extracted from digital image correlation using a reference image recorded during the experiment. Tests are carried out on Laminated Veneer Lumber timber specimens according to the ASTM standard to determine the mechanical properties of materials under compression. DIC has proven to be a reliable, consistent, and cost-effective non-contact deformation measurement method that can assist in the extraction of mechanical properties of orthotropic materials. This study also showed that DIC analysis with a natural timber grain can be used to measure the displacement and strain fields of the material.

Large Deformation Measurement Method of Speckle Images Based on Deep Learning

Large Deformation Measurement Method of Speckle Images Based on Deep Learning

Bi-prism-based single-bilateral-telecentric-camera stereo-DIC for accurate underwater 3D deformation measurement: Implementation of a parametric model

Full-field surface shape and deformation measurements of submerged objects using stereo-digital image correlation (stereo-DIC) remains challenging due to the light ray refraction occurred on the interface of two different transparent media (e.g., air, glass and water). In this work, we proposed an underwater full-field 3D deformation measurement method based on the bi-prism-based single-bilateral-telecentric-camera (SBTC) stereo-DIC, which adopts a parametric model to establish the mathematical relationship between the image points and their corresponding object points by taking the refraction into account in the ray-tracing process. The key parameters (e.g., bi-prism/glass orientation and position) of the parametric model were calibrated by a one-step calibration. To verify the correctness and effectiveness of the proposed method, translation tests with a rotated bi-prism and underwater translation tests were performed. Experimental results indicate that the proposed parametric model can effectively handle the imperfect system configuration and the unavoidable light ray refraction that occurred on the optical path, thus allowing high-accuracy underwater deformation measurement. Compared with the existing underwater deformation measurement approaches, the proposed method can not only deliver displacement measurement with higher accuracy, but also is free of any assumptions on the configuration of the camera system or the refractive interface.

Experimental Investigation: Vibration Measurement of a Rotating Blade with Digital Image Correlation and Blade Tip-Timing.

High cycle fatigue has been known as an important form of aeroengine blade failure. This study aims to achieve a method of investigation for a rotating blade vibration measurement, combining the two non-contact optical techniques of digital image correlation (DIC) and blade tip-timing (BTT). Dynamic parameters of a thin-blade were obtained on a stationary vibration platform with stereo-DIC system. Meanwhile, the finite element analysis (FEA) of this thin-blade was performed within different rotating speeds. Then, the set of thin-blades was mounted in a simulated compressor test rig equipped with BTT and a wireless strain gauge (SG) system. A rotor speed sweep experiment was carried out and the blade synchronous resonance parameters were extracted. Results show that the displacement mode shapes match well between DIC and FEA, and that MAC values of the first six order modes are over than 0.88. The predicting strain from the FE model and SG agreed to within 32.41% in the worst case, and the predicting strain from the DIC model corresponds to 28.53% in the worst case. This is an effective non-contact, high-precision full-field deformation measurement method that is worth exploring for structural design and dynamic strain assessment of vibrating components.

Deformation Measurement of a SS304 Stainless Steel Sheet Using Digital Image Correlation Method

The digital image correlation (DIC) method is widely used in deformation measurements as it has the advantages of being a non-contact, high precision method that provides full field measurements, and requires simple experimental equipment. Traditionally, the grayscale speckle patterns captured by a monochromatic camera are used in the DIC method. With the growing development of consumer color cameras, there is great potential for developing color information in the DIC method. This paper proposes a displacement- and stress–strain-invariant DIC deformation measurement method based on the integer-pixel matching approach for speckle patterns during a tension test. For the integer-pixel matching stage, the load and displacement and stress–strain-invariant histories feature is used to estimate the initial value of the deformation parameters. In addition, this paper proposes a reverse retrieve strategy, instead of a forward search, to reduce the search time. Experiments show that the proposed DIC deformation measurement approach is not only capable of displacement invariance measurement, with robustness and high efficiency, but also that the average accuracy of the stress–strain result can reach 0.1%.

Three dimensional deformation measurement method based on image guided point cloud registration

3D geometric capturing technologies based on camera and laser scanning have undergone huge advances. However, accurate 3D displacement measurement especially for in-plane movement based on point clouds remain unsolved problems. To deal with this challenge, a novel 3D deformation measurement method based on image guided point cloud registration is proposed. 2D digital image correlation method is adopted to calculate image displacement field and used to search the corresponding point from deformed point clouds. Then, accurate 3D displacement field can be obtained. Experiments have verified that the proposed method can realize accurate 3D displacement measurement at both short and far distance. The precision of 3D displacement measurement is 0.1 mm and 1 mm with structured light system and camera assisted TLS system separately.

Parallel optimization of tridimensional deformation measurement based on correlation function constraints of a multi-camera network.

This study primarily investigates the low accuracy and redundant time-consuming problem of speckle registration in the full-field deformation measurement of slender and biggish specimens. To solve these problems, a parallel optimization of the tridimensional deformation measurement method is proposed based on what we believe is a novel correlation function constraints of a multi-camera network. First, a neotype correlation function is built based on the joint constraint relationship among the multiple cameras, which is capable of accurately restricting the search for homologous points in image pairs to the epipolar line, instead of the entire image, while significantly narrowing the search space and accelerating the search. The multiple cameras are bundled as a whole, thus reducing the dimension of the Jacobian matrix and the normalized matrix to a certain extent. Subsequently, more speckle images can be calculated in one iteration. Furthermore, the decomposition of the derived correlation function and the scheme of the parallel algorithm are decomposed via the kernel function based on the GPU parallel mechanism of the compute unified device architecture source program, thus increasing the subpixel search speed of speckle matching and ensuring the calculation performance of the stereo deformation measurement method to reach a higher level. Lastly, the experimental results revealed that the proposed strategy could allow the calculation speed-up ratio of speckle sequence and stereo registration to reach 20.390 times and 17.873 times, respectively, while ensuring the out-of-plane displacement average measuring accuracy to be higher than 0.179mm within the spatial range of [2m, 2m, 3m]. As a result, the proposed approach has crucial applications in rapid and stable tridimensional deformation measurement.

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.

Research and application of deformation measurement method of hydraulic turbine head cover

Aiming at the deformation of hydraulic turbine head cover during operation, a non-contact eddy current sensor is proposed. In this method, the turbine pit wall is taken as the static reference point, a fixed support is erected on it, and the eddy current probe is fixed at the other end of the support. Measure the gap change between the eddy current sensor probe and the head cover to calculate the absolute deformation of the head cover. The effectiveness of the proposed method is verified by taking the lifting amount test of hydraulic turbine head cover in a power plant as an example. The results show that this method has the characteristics of simple test equipment, strong adaptability and high accuracy, and can be applied to the field test of hydraulic turbine head cover deformation.

Optimization of the digital image correlation method for deformation measurement of geomaterials

Optimization of the digital image correlation method for deformation measurement of geomaterials

Characterization of toughness enhancement of aligned steel fibers in cement-based composites based on DDM method and meso-scale simulation

In this study, the toughness enhancement of aligned steel fibers in cement-based composites was mainly characterized. Three-point bending fracture tests with different fiber orientations and fiber volume contents were performed; additionally, crack propagation processes of random and aligned steel fiber reinforced cement-based composites (SFRCs and ASFRCs, respectively) were investigated using the discontinuous deformation measurement (DDM) method. The evolution of the fiber stress and resultant fiber force F on the fracture surface was analyzed through a meso-scale simulation analysis. Results of the DDM method, reveal that compared with the SFRC, smaller strain concentration regions are observed for the ASFRC under the same load. A higher ultimate load and use efficiency of steel fibers are obtained for the ASFRC. Moreover, a higher maximum value of F is presented for the ASFRC; the same tendency is exhibited for F at the initial loading stage. Both these trends indicate that the aligned steel fibers improve the crack-resistance ability and result in a better toughness enhancement effect for the ASFRC than that of the SFRC.