Multi-camera Digital Image Correlation System Research Articles

A new method for localized necking detection in uniaxial tensile testing based on a multi-camera DIC system

Understanding and predicting the onset and behavior of localized necking is important for the design and optimization of structures and components. Capturing the onset of localized necking more accurately has been a challenge in experimental mechanics. In this paper, a new alternative method for detecting the onset of localized necking in uniaxial tensile tests is presented. This method is inspired by the fact that different behaviors are exhibited as localized necking starts at the different regions of the cross-sectional area. When localized necking begins to occur, the cross-sectional area in the center of the necking area decreases sharply, while the cross-sectional area at the boundary of the necking area no longer decreases. A multi-camera digital image correlation system consisting of four cameras, two placed at the front and two at the back of the specimen, has been developed to measure the cross-sectional area at different positions of the sample. The effectiveness and accuracy of the proposed method are verified through a series of tensile tests and are compared with different localized necking detection methods.

Calibration of Ring Multicamera System With Transparent Target for Panoramic Measurement

The calibration of a multicamera system is a prerequisite for high-accuracy measurement. In this study, a method for calibrating a ring multicamera system with a transparent target combined with digital image correlation (DIC) technology is proposed to achieve panoramic dynamic and static measurement of the object. The transparent target is placed in the middle of the ring camera array, and the target can be driven by the turntable to calibrate multiple cameras simultaneously. A complete refraction correction model is built on the transparent side of the target, and the corrected calibration data are integrated into the multicamera DIC system. The global optimization further improves the overall calibration accuracy of the system. Special markers are attached to the target surface to automatically identify the refractive and nonrefractive surfaces of the target. This type of camera can establish a coordinate relationship with the cameras on the other side of the target although no overlapping field of view exists between adjacent cameras on the same side of the target. The calibration data are analyzed, and dynamic and static experiments are implemented to verify the measurement accuracy of the system. All experimental results show that the calibration and measurement accuracies of the proposed method are high, and the system can be fully used for high-precision panoramic dynamic and static measurements.

Application of multi-camera digital image correlation in the stability study of the long timber column with the circular cross-section under axial compression

Displacement meter synthesis (DMS), as a traditional method, is widely used to capture the local deformation of a specimen. However, for axis-symmetrical circular columns, the axial compression instability cannot be accurately evaluated using the DMS method due to the uncertain bending direction. To address this problem, a 360° full-surface digital image correlation (DIC) system composed of eight cameras is proposed to capture the full-field deformation information of the column surfaces under axial compression. The objective of this study was to experimentally validate the efficiency of the proposed novel measurement in tracking the full-filled compressive deformation of a long wooden column with the circular cross-section. The test results showed that the columns experience instable failure. The multi-camera DIC system can completely reconstruct the three-dimensional shape of the circular column and obtain the whole process deformation state at any position on the surface of the timber column. The DIC method also can capture the uncertain lateral deformation direction and obtain the data of lateral deflection at the mid-span of timber columns. The multi-camera DIC provides an intuitive and comprehensive new test method for the test and analysis of the stability of axisymmetric long timber columns.

A Cross-Dichroic-Prism-Based Multi-Perspective Digital Image Correlation System

A robust three-perspective digital image correlation (DIC) system based on a cross dichroic prism and single three charge-coupled device (3CCD) color cameras is proposed in this study. Images from three different perspectives are captured by a 3CCD camera using the cross dichroic prism and two planar mirrors. These images are then separated by different CCD channels to perform correlation calculation with an existing multi-camera DIC algorithm. The proposed system is considerably more compact than the conventional multi-camera DIC system. In addition, the proposed system has no loss of spatial resolution compared with the traditional single-camera DIC system. The principle and experimental setup of the proposed system is described in detail, and a series of tests is performed to validate the system. Experimental results show that the proposed system performs well in displacement, morphology, and strain measurement.

Multi-perspective digital image correlation method using a single color camera

A novel 3D digital image correlation (DIC) system based on a single three charge-couple device (3CCD) color camera is proposed in this paper. Images from three different perspectives are captured by a 3CCD camera using a reflective-based pseudo-vision system. These images are then separated by the different CCD channels, and the correlation algorithm for the multi-camera DIC system is adopted to evaluate the images. Compared to the conventional multi-camera DIC system, the proposed system is much more compact. In addition, the proposed system has no loss of spatial resolution, compares to the traditional single camera DIC system. The complex surface measurement ability and the measurement accuracy is significantly improved through the use of the multi-camera DIC algorithm. The principle of the proposed system is described in detail as well as the experimental setup. A series of validation tests are performed, and the results are verified with the commercial 3D-DIC system.

Non-destructive testing of industrial structures with the use of multi-camera Digital Image Correlation method

Abstract Although Digital Image Correlation (DIC) provides capabilities of scaling a field-of-view (FOV), dimensions of some industrial installations in many cases are too big to be measured with DIC based on a single camera pair. In this paper we present two strategies of spatial stitching of data obtained with multi-camera DIC systems that can be used for engineering failure analysis, namely strategy for the case when there are overlapping FOVs of 3D DIC setups and strategy for the case when 3D DIC setups are distributed and not necessarily have overlapping FOVs. Data obtained with the presented methodologies can be used to verify or update FEM models of the investigated objects. Two practical applications of the multi-camera DIC system are described in order to show its feasibility in engineering failure analysis.

Application of Multi-camera DIC System for Measurements of Industrial Structures

A multi-camera Digital Image Correlation (DIC) systems have been developed to match the specific requirements for measurements posed by building and petrochemical industries. The two most important issues are connected with considerable dimensions of objects and a time line of the measurements. Although DIC provides capabilities of scaling a field-of-view (FOV), dimensions of industrial installations in many cases are too big to be measured with DIC based on a single camera pair. In this paper we present two strategies that can be used for spatial stitching of the data obtained with multi-camera DIC systems, namely a strategy for the case when there are overlapping FOVs of 3D DIC setups and a strategy for the case when 3D DIC setups are distributed and not necessarily have overlapping FOVs. Two practical applications of the multi-camera DIC system are described in order to show its feasibility in industry.

Multi-camera DIC system with spatial data stitching procedure for measurements of engineering objects

In this paper we present the multi-camera 3D Digital Image Correlation (DIC) system with the procedure of spatial data stitching. The system diversify a single DIC setup capabilities to displacement and strain measurements of big and complex in shape industrial installations The example application of DIC system that concerns measurements of graded metal plate segments is described and an error analysis is performed in order to prove practical feasibility of the developed system Full Text: PDF References M. Sutton, J. J. Orteu, H. Schreier, Image Correlation for shape, motion and deformation measurements, (Springer, 2009). J.-J. Orteu, F. Bugarin, J. Harvent, L. Robert, V. Velay, "Multiple-Camera Instrumentation of a Single Point Incremental Forming Process Pilot for Shape and 3D Displacement Measurements: Methodology and Results", Experimental Mechanics 51, 625-639. (2011) CrossRef Y. Wang, P. Lava, S. Coppieters, P. V. Houtte, D. Debruyne, "Application of a Multi-Camera Stereo DIC Set-up to Assess Strain Fields in an Erichsen Test: Methodology and Validation", Strain 49, 190-198 (2013). CrossRef X. Chen, L. Yang, N. Xua, X. Xie, B. Sia, R. Xu, "Cluster approach based multi-camera digital image correlation: Methodology and its application in large area high temperature measurement", Optics and Lasers Technology 57, 318-326 (2014). CrossRef C.-H. Hwang, W.-C. Wang, Y.-H. Chen, "Camera calibration and 3D surface reconstruction for multi-camera semi-circular DIC system", Proc. of SPIE, vol. 8769, 876913-1 (2014). CrossRef R. Hartley, A. Zisserman, Multiple View Geometry in Computer Vision, (Cambridge University Press, 2003). M. Malesa, M. Kujawińska, "Deformation measurements by digital image correlation with automatic merging of data distributed in time", Applied Optics 52 (19), 4681-4692, (2013). CrossRef

Heterogeneity of discontinuous carbon fibre composites: Damage initiation captured by Digital Image Correlation

This paper aims to identify architectural features which lead to damage initiation and failure in discontinuous carbon fibre composites formed from randomly orientated bundles. A novel multi-camera Digital Image Correlation system was used to simultaneously view strain fields from opposing surfaces of coupons, in order to map progression of failure.The highest strain concentrations were found to occur when the ends of fibre bundles aligned in the direction of loading coincided with underlying transverse bundles. The failure plane was observed to grow between a number of strain concentrations at critical features, coalescing sites of damage to create the final fracture surface. Although potential failure sites can be detected at low global strains in the form of strain concentrations, the strain field observed at low applied loads cannot be extrapolated to reliably predict final failure.

Full-field 3D measurement using multi-camera digital image correlation system

A novel non-contact, full-field, three dimensional, multi-camera (N cameras N=2, 3 ,…) Digital Image Correlation (DIC) measurement system is proposed in this work. In the proposed system, multiple cameras are calibrated as a single system. In this system, any two arbitrary cameras can be grouped into pairs, and each pair of cameras measures a part of a 3D object based on the fundamentals of triangulation. The measured data from different pairs of cameras can be mapped into a universal coordinate system based on the calibration data. A 3D contour of the object can be extracted. Further data, such as deformation, can be obtained based on the contour of the object at a different time. The methodology of the proposed system is introduced. Four synchronized Charged Couple Device (CCD) cameras are employed in the experimental setup, and the performance of the setup is tested in both static and dynamic cases to show the potential of the system.