Assessment of speckle-pattern quality in digital image correlation based on gray intensity and speckle morphology

Fang

et al. 2020

Shock and Vibration

Most of the roadway excavation is completed by the drilling and blasting method. With the increase of buried depth, the existence of ground stress will generate a significant impact on the rock blasting, especially on the smooth blasting. In this study, self-made homogeneous similar materials and digital image correlation methods were used to determine influence of ground stress on the smooth blasting under uniform explosive charge parameters and various in situ stress conditions. The results show that the crack outline after blasting changes from zigzag to straight in shape, and multifractal calculation results of the rupture section between blastholes show that the fracture surface becomes flatter as ground stress increases, which is conducive to roadway formation. The strain and equivalent strain rate obviously decrease as the distance between the blasthole and measuring points increases. The same trend occurs as the confining pressure goes up. Meanwhile, a postexplosion acoustic wave test indicates that confining pressure inhibits damage of the retained rock, which is consistent with strain and equivalent strain rate results. Finally, we discussed the crack propagation mechanism of rock in smooth blasting.

Section: Test Principle and Equipmentmentioning

confidence: 99%

In Situ Stress Effects on Smooth Blasting: Model Test and Analysis

Fang

et al. 2020

Shock and Vibration

“…Measuring displacements and strains in real time is also possible. After the image capture of the sample deformation process, a mathematical correlation analysis is carried out, displaying bulk deformation by comparing deformed and un-deformed digital images, determining the displacements field and mapping their distribution [24][25][26][27]. Another important advantage is that this technique can be applied to 2D or 3D case studies without increasing much the difficulty of the analysis.…”

Section: Introductionmentioning

confidence: 99%

2D–3D Digital Image Correlation Comparative Analysis for Indentation Process

et al. 2019

Nowadays, localized forming operations, such as incremental forming processes, are being developed as an alternative to conventional machining or forming techniques. An indentation process is the main action that takes places in these forming activities, allowing small, localized deformations. It is essential to have the knowledge of the material behavior under the punch and the transmitted forces to achieve correct control of the entire procedure. This paper presents the work carried out with the digital image correlation (DIC) technique applied to the study of the material flow that takes place under an indentation process. The material flow analysis is performed under 2D and 3D conditions, establishing the methodology for the calibration and implementation for each alternative. Two-dimensional DIC has been proven to be a satisfactory technique compared with the 3D method, showing results in good agreement with experimental tests and models developed by the finite element method. Notwithstanding, part of the indented material flows under the punch, emerging on the front surface and generating a dead zone that can only be addressed with a 3D technique. So, the main objective is to carry out a comparison between the 2D and 3D techniques to identify if the 3D application could be mandatory for this type of process. Also, a 2D-3D mix analysis is proposed for study cases in which it is necessary to know the material flow in that specific area of the workpiece.

Measurement Science Review

“…Furthermore, speckle image systems are similar to two-axis scatterometry systems, but the amount of information obtained is less than that in three-axis scatterometry [28], [29]. Speckle pattern can evaluate the value of surface roughness but cannot display a clear surface image [30]- [36]. Information collected by twoaxis scatterometry is limited, and a three-axis scatterometry system has to be developed.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Surface Micro-Roughness by Off-Specular Measurements of Polarized Optical Scattering

Liu¹,

Chang²

2019

The characterization of surface micro-roughness is investigated by using off-specular measurements of polarized optical scattering. In the measurement system, the detection angles of optical scattering are defined by the vertical and level scattering angles. The rotating mechanism of angles is controlled by stepper motors. Waveplate and polarizer are used to adjust light polarization and detection. We conduct the optical scattering measurements by using four standard metal sheets of surface roughness. The nominal values (Ra) of standard micro-roughness are 1.6 μm, 0.8 μm, 0.4 μm, and 0.1 μm, respectively. Samples with different surface roughness are evaluated with the utilization of laser sources at three incident wavelengths. These polarized images are analyzed using a computer program to obtain the distribution of light intensity. The results show great correlation between the metal surface roughness and polarization states. This measurement system can be used to quickly and accurately distinguish between different surfaces and properties.