scholarly journals Fracture Mechanical Behavior of Cracked Cantilever Roof with Large Cutting Height Mining

2020 ◽  
Vol 2020 ◽  
pp. 1-10 ◽  
Author(s):  
Zenghui Zhao ◽  
Wei Sun ◽  
Mingzhong Zhang ◽  
Xiaojie Gao ◽  
Shaojie Chen
Keyword(s):  
Fracture Mechanics ◽  
Cantilever Beam ◽  
Crack Size ◽  
Affected Area ◽  
Mechanics Model ◽  
Large Mining Height ◽  
Mining Disturbance ◽  
Seam Mining ◽  
Cutting Height ◽  
Mining Height

Accurately predicting the roof collapse span is crucial in ensuring the safe production of thick seam mining with large mining height, which is easy in forming a “cantilever beam” structure. Considering roof damage caused by roadway excavation and coal seam mining disturbance, the fracture mechanics model of large mining height roof cantilever beam with nonpenetrating cracks was established. The roof was divided into two parts: the crack-affected area and the crack-unaffected area. The analytical expression of the boundary between the two areas was established by fracture mechanics methods. Based on the boundary equation, the influences of crack size, crack inclination, roof lithology, and roof thickness on the roof crack-affected area were analyzed in detail. Finally, the accuracy of the theoretical model was verified by numerical experiments using the extended finite element method. The results demonstrate that the size of the area affected by the vertical crack increases with the increase of the crack size and the thickness of the roof. The influence of the crack decreases with the increase of roof lithology. The probability of early periodic collapse of a thin roof with the crack is increased. When the crack is completely located in the interior of the roof, the crack-affected area shrinks greatly with the decrease of the crack inclination. When the crack inclination is small, the crack will not cause the early collapse of the roof. Overall, the conclusions obtained are of great significance for predicting the collapse span of a cantilever roof with initial damage in large mining height.

Effect of Uncertainties on the Reliability of Fatigue Damaged Systems

2004 ◽  
Author(s):  
Francisco L. Silva-Gonza´lez ◽  
Ernesto Heredia-Zavoni
Keyword(s):  
Fracture Mechanics ◽  
Failure Modes ◽  
Crack Size ◽  
Initial Crack ◽  
Wave Forces ◽  
Scale Parameters ◽  
Uncertain Variables ◽  
Mechanics Model ◽  
Distribution Of Stress

Fluctuating stresses and strains due to wave forces cause accumulated fatigue damage in tubular joints of marine platforms. Considering the uncertainties in the loads, material properties, initial crack sizes, and stress intensity factors, etc., may affect significantly the reliability assessment of marine jacket platforms. In this paper, we assessed the effect of uncertainties about such fatigue variables on the time evolution of the reliability of series and parallel systems considering correlation between failure modes. The fracture mechanics Paris-Erdogan model is used to model crack growth and a FORM method is used for computing the safety index. The uncertain variables analyzed are: initial crack size, material parameters C and m in the fracture mechanics model and the shape and scale parameters of the Weibull density function used for the long-term distribution of stress range.

scholarly journals Cutting-Caving Ratio Optimization of Fully Mechanized Caving Mining with Large Mining Height of Extremely Thick Coal Seam

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Kai Wang ◽  
Tong Zhao ◽  
Kaan Yetilmezsoy ◽  
Xiaoqiang Zhang
Keyword(s):  
Coal Seam ◽  
Influencing Factors ◽  
Recovery Rate ◽  
Engineering Application ◽  
Thick Coal Seam ◽  
Coal Wall ◽  
Large Mining Height ◽  
Cutting Height ◽  
The Relationship ◽  
Mining Height

Serious rib spalling and low recovery rate problems caused by the poor top-coal caving property (TCCP) were investigated in fully mechanized caving mining with large mining height (FMCMLMH) of extremely thick coal seam. For this aim, theoretical calculation, numerical simulation, and engineering application were applied to study the reasonable cutting-caving ratio under the influence of different factors. The calculation formula of reasonable cutting height in FMCMLMH was obtained, and effective factors were determined. Moreover, Ft (the top-coal yield failure coefficient) and Fw (the coal wall yield failure coefficient) were defined, and each factor was fitted by using a linear regression equation. The minimum Ft of fully fractured top coal was 0.6, and the main influencing factors were buried depth and Protodyakonov coefficient. The maximum Fw of the stable coal wall was 1.5, and the main influencing factors were buried depth and cutting height. According to the relationship between coal wall stability and recovery rate, the relationship between coal seam strength and top-coal thickness at different cutting heights was obtained, and the mining zone was divided into four subzones. Engineering application showed that the optimal cutting height of Xiegou Coal Mine was 4 m, the cutting-caving ratio was 1 : 2.75, and the recovery rate could reach more than 85%, which was the most reasonable.

A Bayesian Model for the Probability Distribution of Fatigue Damage in Tubular Joints

2004 ◽  
Vol 126 (3) ◽  
pp. 243-249 ◽  
Author(s):  
Ernesto Heredia-Zavoni ◽  
Roberto Montes-Iturrizaga
Keyword(s):  
Fracture Mechanics ◽  
Probability Distributions ◽  
Error Variance ◽  
Crack Size ◽  
Offshore Structures ◽  
Density Functions ◽  
Time Varying ◽  
Tubular Joints ◽  
Mechanics Model ◽  
Distribution Of Stress

A Bayesian framework is used for updating the probability distributions of the parameters of a fracture mechanics model and of crack size in tubular joints using information from inspection reports of fixed offshore structures. An error model, defined as the logarithmic difference between measured crack size during inspection and crack size predicted by the fracture mechanics model, is assumed to have a normal distribution with known mean and uncertain variance. The distribution of the error variance is modeled by a conjugate distribution for samples of normal variables with known mean and uncertain variance. Based on these assumptions, an analytical model is obtained using a Bayesian approach for the updated distributions of the parameters of the fracture mechanics model and of crack size based. The capabilities of the model are illustrated by means of examples using the Paris-Erdogan formulation for crack growth. The examples illustrate the effects of inspection times, measured crack size, and the distribution of stress ranges on the updated density functions of crack size, time varying reliability and expected cost of failure.

scholarly journals Random Outcome and Stochastic Analysis of Some Fatigue Crack Growth Data

2001 ◽  
Vol 17 (2) ◽  
pp. 61-68
Author(s):  
W. F. Wu ◽  
C. C. Ni ◽  
H. Y. Liou
Keyword(s):  
Fatigue Crack ◽  
Fracture Mechanics ◽  
Crack Size ◽  
Experimental Result ◽  
Exceedance Probability ◽  
Growth Data ◽  
Probabilistic Fracture Mechanics ◽  
Mechanics Model ◽  
Proposed Model ◽  
Analytical Result

ABSTRACTFatigue crack propagation data of a batch of AISI 4340 steel specimens are released in the present paper. The statistical nature of the data is specially emphasized, and a probabilistic fracture mechanics model is introduced to analyze the data. The stochastic differential equation associated with the model is then solved. The solution gives us the crack exceedance probability as well as the probability distribution of the random time to reach a specified crack size. These quantities are useful in the reliability assessment of structures made of the tested material. Comparing the analytical result with the experimental result, it is found that the proposed probabilistic fracture mechanics model can reasonably explain the experimental data. For those data that cannot be fitted well by the proposed model, methods of improvement are proposed in the present paper as well.

scholarly journals Analysis of Fracture Mechanics Theory of the First Fracture Mechanism of Main Roof and Support Resistance with Large Mining Height in a Shallow Coal Seam

2021 ◽  
Vol 13 (4) ◽  
pp. 1678
Author(s):  
Dengfeng Yang
Keyword(s):  
Stress Intensity ◽  
Fracture Mechanics ◽  
Coal Seam ◽  
Main Roof ◽  
In Situ Monitoring ◽  
Control Analysis ◽  
Large Mining Height ◽  
Support Resistance ◽  
Shallow Coal Seam ◽  
Mining Height

Because the first-weighting of a main roof with a large mining height has obvious sudden characteristics and is more severe, which causes large-scale support crushing and has a great impact on the ecological environment of the mining area, it is necessary to conduct an in-depth analysis. This paper studies the mechanical mechanism and asymmetric fracture conditions of a main roof with a large mining height, with the first-weighting occurring in a shallow coal seam. In combination with an asymmetric three-hinged arch structural model, the main roof was regarded as a finite plate model with a crack, and a fracture-mechanics model was established. The conditions and main controlling factors of main roof fracture asymmetry were analyzed, and the determination methods of the first-weighting interval and support resistance were further analyzed. The results show that the stress concentration and the stress-intensity factor increase at the crack tip with the advancement of the face; when the stress-intensity factors increase beyond the critical value, the crack expands until the first-weighting. The sufficient condition for modeling the instability was the length s of the branch crack reaching the protection thickness H of the main roof, and the necessary condition was the activation of the crack. The calculation equations of the first-weighting interval and the support resistance were obtained. The influence weights of each parameter on the support resistance are ordered as follows: overburden load q > rock fracture toughness KC > crack length a > main roof thickness h > weighting interval l. Finally, the theoretical analysis results were verified by an in situ monitoring case of the no. 33,206 working face in the Bulianta coal mine, China. On this basis, a reasonable value of the support resistance is further calculated. The results mentioned above can provide a new method for researching the first-weighting of the main roof and can improve the accuracy of the roof control analysis. The research on the mechanisms of first-weighting and the support resistance can effectively promote the safety production of mine, which is in line with the concept of green and sustainable development of the mine.

A novel model of Z-pin insertion in prepreg based on fracture mechanics

2021 ◽  
pp. 095440542110144
Author(s):  
Guobiao Ji ◽  
Liang Cheng ◽  
Shaohua Fei ◽  
Jiangxiong Li ◽  
Yinglin Ke
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Analytical Model ◽  
Model Parameters ◽  
Force Model ◽  
Fe Model ◽  
Cohesive Elements ◽  
Fe Method ◽  
Insertion Force ◽  
Mechanics Model

Through-thickness reinforcement is a promising solution to the problem of delamination susceptibility in laminated composites. Modeling Z-pin–prepreg interaction is essential for accurate robotics-assisted Z-pin insertion. In this paper, a novel Z-pin insertion force model combining the classical cohesive finite element (FE) method with a dynamic analytical fracture mechanics model is proposed. The velocity-dependent cohesive elements, in which the fracture toughness is provided by the analytical model, are implemented in Z-pin insertion FE model to predict the crack initiation and propagation. Then Z-pin insertion experiments are performed on prepreg sample with metallic Z-pins at different velocities to identify the analytical model parameters and validate the simulation predictions offered by the model. Dynamics of Z-pin interaction with inhomogeneous prepreg is described and the effects of insertion velocity on prepreg contact force are studied. Results show that the force model agrees well with experiments and the fracture toughness rises with the increasing Z-pin insertion velocity.

Study on rib spalling control of shortwall drilling mining technology with a large mining height

2021 ◽  
Vol 14 (3) ◽  
Author(s):  
Yong Yuan ◽  
Cheng Zhu ◽  
Hongmin Wei ◽  
Chaofeng Yuan ◽  
Zhongshun Chen
Keyword(s):  
Mining Technology ◽  
Large Mining Height ◽  
Mining Height

Effective Modeling of Fatigue Crack Growth in Pipelines

2012 ◽  
Author(s):  
Steven J. Polasik ◽  
Carl E. Jaske
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Models ◽  
Critical Parameters ◽  
Operating Pressure ◽  
Mechanics Model ◽  
Key Variables

Pipeline operators must rely on fatigue crack growth models to evaluate the effects of operating pressure acting on flaws within the longitudinal seam to set re-assessment intervals. In most cases, many of the critical parameters in these models are unknown and must be assumed. As such, estimated remaining lives can be overly conservative, potentially leading to unrealistic and short reassessment intervals. This paper describes the fatigue crack growth methodology utilized by Det Norske Veritas (USA), Inc. (DNV), which is based on established fracture mechanics principles. DNV uses the fracture mechanics model in CorLAS™ to calculate stress intensity factors using the elastic portion of the J-integral for either an elliptically or rectangularly shaped surface crack profile. Various correction factors are used to account for key variables, such as strain hardening rate and bulging. The validity of the stress intensity factor calculations utilized and the effect of modifying some key parameters are discussed and demonstrated against available data from the published literature.

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