Analysis of Cracking Processes of Sandstone in Rockburst Test

2012 ◽  
Vol 256-259 ◽  
pp. 1052-1059
Author(s):  
De Jian Li ◽  
Fei Zhao ◽  
Run Jie Ma ◽  
Li Qiang Han ◽  
Xiao Hu Wu
Keyword(s):  
Growth Rate ◽  
Fractal Dimension ◽  
Crack Propagation ◽  
High Speed ◽  
Fractal Dimensions ◽  
Rock Surface ◽  
Horizontal Line ◽  
High Speed Camera ◽  
Camera System ◽  
Very High

High speed camera system is used to record crack propagation on rock surface during the lab rocburst experiment. This paper presents the specific analytical method of crack propagation with high speed images. Crack propagation types and directions are briefly described, and the lengths, growth rate and fractal dimension of cracks are calculated. The results show that the crack grows mainly along the horizontal line on the unloading surface, at a low speed before rockburst and reaches a very high speed abruptly near the burst point. The fractal dimensions demonstrated that the crack turns to be rough when rockburst happens. The study on the crack propagation is benefit to the understanding on the mechanism of rockburst.

scholarly journals Dynamic characteristics and fractal representations of crack propagation of rock with different fissures under multiple impact loadings

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bing Sun ◽  
Shun Liu ◽  
Sheng Zeng ◽  
Shanyong Wang ◽  
Shaoping Wang
Keyword(s):  
Fractal Dimension ◽  
Crack Propagation ◽  
Crack Growth ◽  
Impact Test ◽  
Fractal Theory ◽  
Dynamic Change ◽  
Fractal Dimensions ◽  
Peak Stress ◽  
Dynamic Mechanical Properties ◽  
Gravitational Potential Energy

AbstractTo investigate the influence of the fissure morphology on the dynamic mechanical properties of the rock and the crack propagation, a drop hammer impact test device was used to conduct impact failure tests on sandstones with different fissure numbers and fissure dips, simultaneously recorded the crack growth after each impact. The box fractal dimension is used to quantitatively analyze the dynamic change in the sandstone cracks and a fractal model of crack growth over time is established based on fractal theory. The results demonstrate that under impact test conditions of the same mass and different heights, the energy absorbed by sandstone accounts for about 26.7% of the gravitational potential energy. But at the same height and different mass, the energy absorbed by the sandstone accounts for about 68.6% of the total energy. As the fissure dip increases and the number of fissures increases, the dynamic peak stress and dynamic elastic modulus of the fractured sandstone gradually decrease. The fractal dimensions of crack evolution tend to increase with time as a whole and assume as a parabolic. Except for one fissure, 60° and 90° specimens, with the extension of time, the increase rate of fractal dimension is decreasing correspondingly.

scholarly journals Crack Propagation Velocity Determination by High-speed Camera Image Sequence Processing

2020 ◽  
Author(s):  
Frank Liebold ◽  
Ali A. Heravi ◽  
Oliver Mosig ◽  
Manfred Curbach ◽  
Viktor Mechtcherine ◽  
...  
Keyword(s):  
Crack Propagation ◽  
High Speed ◽  
Vector Fields ◽  
Displacement Vector ◽  
Image Sequence ◽  
High Speed Camera ◽  
Sequence Processing ◽  
Image Sequence Processing ◽  
Propagation Velocities

The determination of crack propagation velocities can provide valuable information for a better understanding of damage processes of concrete. The spatio-temporal analysis of crack patterns developing at a speed of several hundred meters per second is a rather challenging task. In the paper, a photogrammetric procedure for the determination of crack propagation velocities in concrete specimens using high-speed camera image sequences is presented. A cascaded image sequence processing which starts with the computation of displacement vector fields for a dense pattern of points on the specimen’s surface between consecutive time steps of the image sequence chain has been developed. These surface points are triangulated into a mesh, and as representations of cracks, discontinuities in the displacement vector fields are found by a deformation analysis applied to all triangles of the mesh. Connected components of the deformed triangles are computed using region-growing techniques. Then, the crack tips are determined using principal component analysis. The tips are tracked in the image sequence and the velocities between the time stamps of the images are derived. A major advantage of this method as compared to established techniques is in the fact of its allowing for spatio-temporally resolved, full-field measurements rather than point-wise measurements and that information on crack width can be obtained simultaneously. To validate the experimentation, the authors processed image sequences of tests on four compact-tension specimens performed on a split-Hopkinson tension bar. The images were taken by a high-speed camera at a frame rate of 160,000 images per second. By applying to these datasets the image sequence processing procedure as developed, crack propagation velocities of about 800 m/s were determined with a precision in the order of 50 m/s.

Design of high speed camera system with area-CCD KAI-0340DM

2011 ◽  
Vol 19 (11) ◽  
pp. 2791-2799 ◽  
Author(s):  
余达 YU Da ◽  
郭永飞 GUO Yong-fei ◽  
周怀得 ZHOU Huai-de ◽  
武星星 WU Xing-xing ◽  
李广泽 LI Guang-Ze ◽  
...  
Keyword(s):  
High Speed ◽  
High Speed Camera ◽  
Camera System

scholarly journals Fractal Characteristics of Chip Morphology and Tool Wear in High-Speed Turning of Iron-Based Super Alloy

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 1020
Author(s):  
Xu Zhang ◽  
Guangming Zheng ◽  
Xiang Cheng ◽  
Rufeng Xu ◽  
Guoyong Zhao ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Tool Wear ◽  
High Speed ◽  
Cutting Speed ◽  
Fractal Dimensions ◽  
Chip Morphology ◽  
Color Changes ◽  
Fractal Characteristics ◽  
Iron Based ◽  
Super Alloy

Considering that iron-based super alloy is a kind of difficult-to-cut material, it is easy to produce work hardening and serious tool wear during machining. Therefore, this work aims to explore the chip change characteristics and tool wear mechanism during the processing of iron-based super alloy, calculate the fractal dimensions of chip morphology and tool wear morphology, and use fractals to analyze their change trend. Meanwhile, a new cutting tool with a super ZX coating is used for a high-speed dry turning experiment. The results indicate that the morphology of the chip is saw-tooth, and its color changes gradually, due to the oxidation reaction. The main wear mechanisms of the tool involve abrasive wear, adhesive wear, oxidation wear, coating spalling, microcracking and chipping. The fractal dimension of the tool wear surface and chip is increased with the improvement of cutting speed. This work investigates the fractal characteristics of chip morphology and tool wear morphology. The fractal dimension changes regularly with the change of tool wear, which plays an important role in predicting this tool wear. It is also provides some guidance for the efficient processing of an iron-based super alloy.

Testing and Analysis of High-Speed Camera for Droplet Transition

2011 ◽  
Vol 271-273 ◽  
pp. 79-83 ◽  
Author(s):  
Yuan Mei Wen ◽  
Shi Sheng Huang ◽  
Gui Xiong Liu
Keyword(s):  
Arc Welding ◽  
High Speed ◽  
High Speed Camera ◽  
Gravity Center ◽  
Camera System ◽  
Molten Droplet ◽  
Electrical Arc ◽  
Complicated Process ◽  
Welding Metal ◽  
Droplet Transition

The droplet transition of electrical arc welding is a complicated process that combines heat, mass and momentum transfer. A high-speed camera system with laser in the background is established to observe the fast changing process of molten droplet transition. A group of high-speed camera pictures which indicate the droplet gravity center is unstable in welding metal transfer process are taken and analyzed. The experimental results show that the electromagnetic force is the unstable root of the droplet gravity center.

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