Boxing Qian’s research while affiliated with Xi'an University of Technology and other places

Given the low accuracy of the traditional digital image correlation (DIC) method in complex deformation measurement, a color DIC method is proposed using a prism camera. Compared to the Bayer camera, the Prism camera can capture color images with three channels of real information. In this paper, a prism camera is used to collect color images. Relying on the rich information of three channels, the classic gray image matching algorithm is improved based on the color speckle image. Considering the change of light intensity of three channels before and after deformation, the matching algorithm merging subsets on three channels of a color image is deduced, including integer-pixel matching, sub-pixel matching, and initial value estimation of light intensity. The advantage of this method in measuring nonlinear deformation is verified by numerical simulation. Finally, it is applied to the cylinder compression experiment. This method can also be combined with stereo vision to measure complex shapes by projecting color speckle patterns.

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.

Based on digital image correlation and binocular stereo vision, a method is proposed for measuring full field deformation and strain of cantilever beam under forced vibration. First, in the actual measurement, the traditional correlation function with linear model may not be reliable to describe the deformation and light intensity change of subset. Therefore, the radial basis function is introduced into the correlation function to specify the weight of each pixel in the subset, which improves the reliability of the correlation matching. Second, the rigid motion of the excitation source is monitored by sticking a marker at the fixed end. By measuring the position of the marker in the process of vibration, the motion direction of the excitation source can be obtained and then define the new Z-axis along the motion direction. After transformation of the coordinate system, the pure deformation at any position of the beam surface is equal to the displacement at that point minus the displacement of the excitation source. Finally, the deformation and maximum principal strain field of cantilever beam under sinusoidal excitation at different frequencies is compared and analyzed. The method can provide a reference for the deformation measurement under forced vibration.

Optical devices cannot directly obtain the deformation for welding residual stress (WRS) measurement since it is difficult to get the surface characteristic with a high accuracy of measurement. This paper therefore presents a full-field fast method for WRS measurement based on heterodyne multiple frequency phase shift technology. Furthermore, in order to denoise the acquired point cloud, this paper proposes a novel compensation filter method (CFM) to extract accurate surface topography: specifically, to slice the original point cloud into several independent groups, then smooth each group of the point cloud to obtain the compensation value, and finally to fuse the filtered point cloud with the compensation value to extract surface characteristic. As a result, the simulation and the experiment results show that the CFM can reduce the noise by about 80%. It demonstrates that the novel CFM can maintain the features of the point cloud and remove noise efficiently, indicating the high accuracy of the CFM result and the potential to realize fast WRS measurement.

A crash test is a common method to evaluate passive vehicle safety, but its full-field deformation and strain is difficult to measure due to instantaneous large deformation during the intense impact process. By means of high-speed cameras, a full-field deformation and strain measurement under high-speed impact is presented based on digital image correlation and binocular stereo vision. To deal with weak correlation in image matching caused by optical noise and large deformation, a controllable Gaussian filter and adaptive light intensity coefficients are used to suppress image intensity interference introduced by optical noise. In addition, based on deformation continuity of the neighboring states, images before and after large deformation are matched by the minimization of reference datum and transfer of deformation coefficients. Finally, full-field deformation and strain data are obtained from an impact test on an engine cover made from DC04 steel. Results show that the deformation measurement accuracy of the method can achieve 0.03 mm within a 500 × 400 mm² field of view. This study solves the problems of limited measurement points and low efficiency both in the contact measurement method by displacement sensors and traditional optical measurement by the detection of artificial target points, and provides a scientific basis for quantitative analysis of vehicle impact safety, vehicle body structure and material improvement, and finite element simulation of impact theory.

An optical method based on digital image correlation (DIC) technology was proposed to measure the plastic evolution of the high-strength low alloy steel H340LAD_Z. The basic principle of DIC technology is introduced, and then, the use of a 3D deformation measurement system and electronic universal testing machine to dynamically measure plastic evolution during the tensile yield stage is described. Through the full-field full-process measurement of plastic deformation during the yield stage in the 0°，45 ° and 90 ° loading directions, the plastic evolution law was revealed. The results demonstrate that the proposed 3D DIC method can accurately reveal the starting and ending times for plastic evolution. The specimens in the three directions exhibit different plastic evolution behaviors, although they have similar yield strengths and yield times. The specimens in the 45 ° and 90 ° loading directions began to enter plastic deformation from bottom to top and the plastic area was maintained in a constant deformed state, while the evolution behavior in the 0 ° direction transited from both sides to the middle and plastic deformation was uneven. It is important to study plastic evolution of a metal sheet to determine the material properties and to provide an accurate basis for finite element modeling.