shear cracks
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2022 ◽  
pp. 136943322110651
Author(s):  
Mohammad Arsalan Khan

Studies have primarily focussed on predicting mode-II debonding failure; whereas, in real-case-scenario, flexurally strengthened reinforced concrete (RC) beams observe premature failure mechanisms under mixed-mode loading conditions engaging geometrical and material variations. Peeling is a consequence of flexural crack as debonding is of interfacial shear crack. Under bending, peeling failure is considerably catastrophic over debonding due to the nature of crack formation; therefore, this needs to be distinguished in predictive analysis. In this paper, a new numerical modeling methodology is approached using eXtended finite element method (xFEM) for flexural cracks and Cohesive Zone Model (CZM) for shear cracks without predefining crack locations. The parameters of the constitutive models are identified through comparing finite element results with the experimental data. These parameters are related to key material properties. Based on proposed framework, the models provide a good estimation of plate strain distribution, cracks and failure type, in terms of mode and load of failure. Bilinear bond-slip curve is a closer match over exponential crack evolution at interface.


Minerals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 55
Author(s):  
Xianda Yang ◽  
Lihui Sun ◽  
Jiale Song ◽  
Bensheng Yang ◽  
Chengren Lan ◽  
...  

Bond strength is one of the most important parameters and can affect the macroscopic mechanical properties and the damage state of rock to some degree. Coarse-grained sandstone was studied using the controlled variable method. The influence of parallel bond strength on the peak strength and failure mode of coarse-grained sandstone was simulated, and the evolution law of peak strength and the failure mode of bond strength were comprehensively analyzed. The results show that the peak strength of the rock was positively correlated with the bond strength; the difference in quantity between the tensile and shear cracks was negatively correlated with tensile bond strength and positively correlated with shear bond strength. With a tensile-shear bond strength ratio of less than 0.5, the peak strength of the rock was usually stable at the certain extreme value under a constant tensile bond strength. The tensile cracks were negatively correlated with the tensile-shear bond strength ratio, and the shear cracks were positively correlated with the tensile-shear bond strength ratio. The main failure mode of the coarse-grained sandstone in the weakly cemented stratum of the Hongqinghe coal mine is shear failure. The research results can be used to guide the ground control of other mine stopes or roadways with weak cementation lithology.


2021 ◽  
Vol 14 (1) ◽  
pp. 241
Author(s):  
Yang Wang ◽  
Xue Li ◽  
Jiyu Li ◽  
Jipeng Xu

Herein, a finite discrete element method was used to simulate the rockburst phenomenon of elliptical caverns with different axis ratios. Two situations were employed, namely when the disturbance direction is perpendicular and parallel to the ellipse. Based on the peak stress, maximum velocity, stress nephogram, and image fractal characteristics, the influence of axis ratio and direction of the disturbance on rockburst were analyzed. The results show that the samples with different axis ratios experienced the same process of quiet period, slab cracking period, and rockburst. The rockburst pit had V shape, and the failure modes of rockburst primarily included shear cracks, horizontal tension cracks, and vertical tension cracks. With the rise in axis ratio, the peak stress and maximum speed increased. Furthermore, the pressure area on the left and right sides of the sample cavern decreased when the disturbance direction was parallel to the short axis of the ellipse, while it increased for the sample with a disturbance direction perpendicular to the short axis. The fractal dimension value of the crack was gradually amplified with disturbance. The fractal dimension value of the sample whose disturbance direction was perpendicular to the minor axis of the ellipse was lower, and it was more difficult to damage.


2021 ◽  
Author(s):  
Yi Luo ◽  
Chenhao Pei ◽  
Dengxing Qu ◽  
Xinping Li ◽  
Ruiqiu Ma ◽  
...  

Abstract To explore the distribution of cracks in anchored caverns under the blast load, cohesive elements with zero thickness were employed to simulate crack propagation through numerical analysis based on a similar model test. Furthermore, the crack propagation process in anchored caverns under top explosion was analysed and the distribution and mode of propagation of cracks in anchored caverns when a fracture with different dip angles was present in the vault were discussed. With the propagation of the explosive stress waves, cracks successively occur at the boundary of the anchored zone of the vault, arch foot, and floor of the anchored caverns. Tensile cracks are preliminarily found in rocks surrounding the caverns. In the case that a pre-fabricated fracture is present in the upper part of the vault, the number of cracks at the boundary of the anchored zone of the vault decreases, then increases with increasing dip angle of the pre-fabricated fracture. The fewest cracks at the boundary of the anchored zone occur if the dip angle of the pre-fabricated fracture is 45º. The wing cracks deflected to the vault are formed at the tip of the pre-fabricated fracture, around which tensile and shear cracks are synchronously present. Under top explosion, both the peak displacement and peak particle velocity in surrounding rocks of anchored caverns reach their maximum values at the vault, successively followed by the side wall and the floor. In addition, they show asymmetry with the difference of the dip angle of the pre-fabricated fracture; the vault displacement of anchored caverns is mainly attributed to the formation of tensile cracks at the boundary of the anchored zone generated due to tensile waves reflected from the free face of the vault. When a fracture is present in the vault, the peak displacement of the vault decreases while the residual displacement increases.


Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Juntao Chen ◽  
Yi Zhang ◽  
Kai Ma ◽  
Daozeng Tang ◽  
Hao Li ◽  
...  

To further explore the crack evolution of floor rock mass, the mechanism of fault activation, and water inrush, this paper analyzes the crack initiation and propagation mechanism of floor rock mass and obtains the initiation criteria of shear cracks, layered cracks, and vertical tension cracks. With the help of simulation software, the process of fault activation and crack evolution under different fault drop and dip angles was studied. The results show that the sequence of crack presented in the mining rock mass is vertical tension cracks, shear cracks, and layered cracks. The initiation and propagation of the shear cracks at the coal wall promote the fault activation, which tends to be easily caused at a specific inclination angle between 45° and 75°. The fault drop has no obvious impact on the evolution of floor rock cracks and will not induce fault activation. However, the increase of the drop will cause the roof to collapse, reducing the possibility of water inrush disaster. Research shows that measures such as adopting improved mining technology, reducing mining disturbance, increasing coal pillar size, and grouting before mining as reinforcement and artificial forced roof can effectively prevent water inrush disasters caused by deep mining due to fault activation.


2021 ◽  
Vol 11 (23) ◽  
pp. 11346
Author(s):  
Mohammad Iqbal Khan ◽  
Galal Fares ◽  
Yassir M. Abbas ◽  
Fahad K. Alqahtani

In the present work, the structural responses of 12 UHPC beams to four-point loading conditions were experimentally and analytically studied. The inclusion of a fibrous system in the UHPC material increased its compressive and flexural strengths by 31.5% and 237.8%, respectively. Improved safety could be obtained by optimizing the tensile reinforcement ratio (ρ) for a UHPC beam. The slope of the moment–curvature before and after steel yielding was almost typical for all beams due to the inclusion of a hybrid fibrous system in the UHPC. Moreover, we concluded that as ρ increases, the deflection ductility exponentially increases. The cracking response of the UHPC beams demonstrated that increasing ρ notably decreases the crack opening width of the UHPC beams at the same service loading. The cracking pattern the beams showed that increasing the bar reinforcement percentages notably enhanced their initial stiffness and deformability. Moreover, the flexural cracks were the main cause of failure for all beams; however, flexure shear cracks were observed in moderately reinforced beams. The prediction efficiency of the proposed analytical model was established by performing a comparative study on the experimental and analytical ultimate moment capacity of the UHPC beams. For all beams, the percentage of the mean calculated moment capacity to the experimentally observed capacity approached 100%.


Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7234
Author(s):  
Suran Wang ◽  
Youliang Chen ◽  
Min Xiong ◽  
Xi Du ◽  
Guanlin Liu ◽  
...  

In the study of rock mechanics, the variation of rock mechanical characteristics in high-temperature environments is always a major issue. The discrete element method and Voronoi modeling method were used to study the mechanical characteristics and crack evolution of granite specimens subjected to the high temperature and uniaxial compression test in order to study the internal crack evolution process of granite under the influence of high temperatures. Meanwhile, dependable findings were acquired when compared to experimental outcomes. A modified failure criterion was devised, and a Fish function was built to examine the evolution behavior of tensile and shear cracks during uniaxial compression, in order to better understand the evolution process of micro-cracks in granite specimens. Shear contacts occurred first, and the number of shear cracks reached its maximum value earliest, according to the findings. The number of tensile contacts then rapidly grew, whereas the number of shear cracks steadily declined. Furthermore, it was found that when temperature rises, the number of early tensile cracks grows. This study develops a fracture prediction system for rock engineering in high-temperature conditions.


2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhenhua Wang ◽  
Jun Fang ◽  
Gang Wang ◽  
Yifan Jiang ◽  
Dongwei Li

The uniaxial compression tests were conducted on granite samples with different joint dip angles to more favorably explore the influences of the nonconsecutive joint on mechanical properties and deformation characteristics of the rock mass. The stress-strain curves, deformation and strength characteristics, and energy evolution process of the samples were analyzed. Numerical simulation using particle flow code (PFC) is employed to study the crack propagation process. The mode of jointed and fractured rock was investigated. The research results showed a significant reduction in both the peak strength and elastic modulus of jointed samples compared with intact ones: the peak strength and elastic modulus drop to the minimum at the joint dip angle of about 45°, especially for the peak strength, which takes up about 55% of the intact samples. The fractured samples’ total energy, elastic strain energy, and dissipated energy during the uniaxial compression drop significantly relative to intact samples. The proportion of the fracture modes varies with different joint dip angles, in which the ratio of shear cracks grows at first and then declines, with the highest balance at the dip angle of 45°. The damage stress’s sensitivity to the dip angle change is greater than that of the peak stress, with reduction amplitude more extensive than the latter.


Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6684
Author(s):  
Sang-Woo Kim ◽  
Kil-Hee Kim

This paper proposes a method to evaluate the effect of shear on the deflection of reinforced concrete (RC) beams. The deflection of RC beams due to the effects of flexural and shear cracks shows different results from those obtained from the elastic theory. The effect of shear on deflection was compared and analyzed in this study, on the basis of experimental results and elastic theory using the virtual work method. The shear effect on the deflection of RC beams by elastic theory was extremely small. However, experimental results showed a difference of over 40% from the results predicted by elasticity theory. In this study, a new method was developed to reasonably predict the deflection of flexure-critical RC beams using the deflection incremental coefficient due to shear. The proposed method was compared with the existing experimental results obtained from the literature for verification. As a result of the comparison, the deflection obtained using ACI 318-19 underestimated the actual deflection by approximately 33%, whereas the deflection obtained by the proposed method predicted the experimental results relatively accurately.


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