scholarly journals Experimental and DEM Analysis on Secondary Crack Types of Rock-Like Material Containing Multiple Flaws Under Uniaxial Compression

2019 ◽  
Vol 9 (9) ◽  
pp. 1749 ◽  
Author(s):  
Yong Li ◽  
Weibing Cai ◽  
Xiaojing Li ◽  
Weishen Zhu ◽  
Qiangyong Zhang ◽  
...  

To better understand the evolution of crack propagation in brittle rock mass, the particle velocity field evolution on both sides of secondary crack in rock-like materials (cement mortar specimens) with pre-existing parallel double flaws under uniaxial compression is analyzed based on the discrete element theory. By bringing in strain rate tensor, a new technique is proposed for quantifying the failure mechanism of cracks to distinguish the types and mechanical behaviors of secondary cracks between pre-existing parallel flaws. The research results show that the types and mechanical behaviors of secondary cracks are distinct at different axial loading stages and can be directly identified and captured through the presented approach. The relative motion trend between particles determines the types and mechanical behaviors of secondary cracks. Based on particles movement on both sides of secondary cracks between cracks, the velocity fields of particles can be divided into four types to further analyze the causes of different types of cracks. In different axial loading stages, the velocity field types of particles on both sides of cracks are continuously evolving. According to the particle velocity field analysis and the proposed novel way, the types of macroscopic cracks are not directly determined by the types of dominated micro-cracks. Under uniaxial compression, the particles between secondary cracks and pre-existing parallel flaws form a confined compressive member. Under the confinement of lateral particles, secondary cracks appear as shear cracks between pre-existing parallel flaws at the beginning stage of crack initiation.

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2108
Author(s):  
Guanlin Liu ◽  
Youliang Chen ◽  
Xi Du ◽  
Peng Xiao ◽  
Shaoming Liao ◽  
...  

The cracking of rock mass under compression is the main factor causing structural failure. Therefore, it is very crucial to establish a rock damage evolution model to investigate the crack development process and reveal the failure and instability mechanism of rock under load. In this study, four different strength types of rock samples from hard to weak were selected, and the Voronoi method was used to perform and analyze uniaxial compression tests and the fracture process. The change characteristics of the number, angle, and length of cracks in the process of rock failure and instability were obtained. Three laws of crack development, damage evolution, and energy evolution were analyzed. The main conclusions are as follows. (1) The rock’s initial damage is mainly caused by tensile cracks, and the rapid growth of shear cracks after exceeding the damage threshold indicates that the rock is about to be a failure. The development of micro-cracks is mainly concentrated on the diagonal of the rock sample and gradually expands to the middle along the two ends of the diagonal. (2) The identification point of failure precursor information in Acoustic Emission (AE) can effectively provide a safety warning for the development of rock fracture. (3) The uniaxial compression damage constitutive equation of the rock sample with the crack length as the parameter is established, which can better reflect the damage evolution characteristics of the rock sample. (4) Tensile crack requires low energy consumption and energy dispersion is not concentrated. The damage is not apparent. Shear cracks are concentrated and consume a large amount of energy, resulting in strong damage and making it easy to form macro-cracks.


2021 ◽  
Vol 80 (6) ◽  
Author(s):  
Rong He ◽  
Tingye Tao ◽  
Fei Gao ◽  
Yongchao Zhu ◽  
Xiaochuan Qu ◽  
...  

Author(s):  
M V Srinivas ◽  
P Alva ◽  
S K Biswas

A slip line field is proposed for symmetrical single-cavity closed-die forging by rough dies. A compatible velocity field is shown to exist. Experiments were conducted using lead workpiece and rough dies. Experimentally observed flow and load were used to validate the proposed slip line field. The slip line field was used to simulate the process in the computer with the objective of studying the influence of flash geometry on cavity filling.


2002 ◽  
Vol 123 (2-3) ◽  
pp. 242-253 ◽  
Author(s):  
Giovanna Ferrari ◽  
Massimo Poletto

2016 ◽  
Vol 851 ◽  
pp. 922-927
Author(s):  
Liang Xuan ◽  
Heng Jiang ◽  
Tian Min Guan ◽  
Ling Zhe Kong

This paper is based on completed the design of the main structure of the fumigation treatment bed according to the size of the human body’s structure. And the solid modeling of each part is carried out in the CATIA environment. Then the working process of the fumigation bed is simulated by using the virtual prototype module of CATIA software. Using the FLUENT flow field analysis software to analyze the temperature field and velocity field of the fumigation tank’s inward under different conditions. With setting different variables in each condition gradually optimize the temperature field and velocity field in the fumigation tank’s inward.


2007 ◽  
Vol 353-358 ◽  
pp. 2353-2356 ◽  
Author(s):  
Y.S.H. Guo ◽  
R.H.C. Wong ◽  
K.T. Chau ◽  
Wei Shen Zhu ◽  
Shu Cai Li

A number of instability problems in rock engineering projects are caused by crack propagation. However, crack growth mechanisms from 3-dimentional flaw are not fully understood, in particular for 3-D flaw case with varied dipping angle. This study focuses on 3-D surface flaw using real rock specimens containing a flaw with varied inclination angle α from axial loading and dipping angle γ from specimen surface under uniaxial compression. Acoustic emission technique was used for tracing the initiation and growth of micro-cracks inside of specimen. It was found that crack growth process is affected by the dipping angle γ of the 3-D flaw. When dipping angle γ ≠ 90º, the thickness of rock above the flaw plane is thinner than that of below the flaw plane. As a result, compressive crack and wing crack initiated easily from the thinner flaw tips. And, the normalized stress for crack initiation σi /σc, AE events and the AE energy for crack growth decreases with the dipping angle γ. However, for γ = 90º, the thickness of rock above and below of the flaw tips is the same, it was observed that anti-wing crack (crack growth direction opposite to wing crack) initiated first at a certain place away from the flaw tips, then wing crack and compressive crack emerged at the late stage. For this case, the stress σi /σc, AE events and the AE energy for crack initiation and propagation are at a high value. Thus, for rock mass contains flaws geometry with small dipping angle, some problems of crack propagation may be induced easily during excavation.


2012 ◽  
Vol 468-471 ◽  
pp. 1749-1752
Author(s):  
Chun Yao Wang ◽  
Xue Nong Wang ◽  
Fa Chen ◽  
Yue Liu ◽  
Jiu Peng Chi ◽  
...  

This article uses the flow field numerical simulation technology, it does simulation research for the flow field of the whole pneumatic conveying cotton trunk, through studying different types of jet orifice of the conveying trunk of comb—type cotton picker, finding out the influence of jet orifice width on pressure and velocity field, further understanding flow field distribution characteristics of the internal pneumatic cotton conveyance system, and providing necessary basis for the machine.


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