scholarly journals Progressive Damage Process and Failure Characteristics of Coal under Uniaxial Compression with Different Loading Rates

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Chuanqi Zhu ◽  
Shaobo Li ◽  
Yong Luo ◽  
Biao Guo
Keyword(s):  
Uniaxial Compression ◽  
Loading Rate ◽  
Peak Strength ◽  
P Wave ◽  
Progressive Damage ◽  
Failure Characteristics ◽  
Loading Rates ◽  
Working Face ◽  
Roof Fall ◽  
Damage Process

To study the effect of loading rate on the progressive damage and failure characteristics of coal, an ultrasonic detector and a camera were used to measure the P-wave velocity and record the failure process of cuboid coal samples in uniaxial compression tests with five loading rates. The mechanical properties, damage process, and failure characteristics of the samples were analysed, and the mechanism of the advancing velocity of the working face in coal failure was discussed. The results show that, as the loading rate increases, the peak strength of the sample generally shows an increasing trend, but the elastic modulus changes irregularly. The sample is more prone to local failure before the peak strength. An increase in the loading rate rapidly promotes damage in the sample and accelerates the transition from internal damage to macroscopic failure, with no obvious effect on the ratio of damage threshold to corresponding peak strength. At low loading rates, the samples mainly experienced static failure; the failure form was spalling, and the failure range was wide. At high loading rates, the samples were prone to dynamic failure in the local area, manifested as the ejection of slabs and debris. A greater loading rate produced smaller and thinner slabs and a greater ejection velocity. Properly increasing the advancing velocity of the working face is conducive to reducing spalling to prevent large-area roof fall, but it may increase the possibility of coal burst in local areas. The results of this study provide a reference for roof control and coal burst disaster prevention on the working face in deep coal mining.

Tests on Effects of Loading Rate on Modulus and Strength of Sandstone

2014 ◽  
Vol 1065-1069 ◽  
pp. 214-218
Author(s):  
Chun Hui Zhang ◽  
Hong Liang Yue ◽  
Lai Gui Wang
Keyword(s):  
Compressive Strength ◽  
Linear Relationship ◽  
Uniaxial Compression ◽  
Loading Rate ◽  
Strength Degradation ◽  
Peak Strength ◽  
Exponential Relationship ◽  
Loading Rates ◽  
Average Modulus ◽  
The Relationship

For studying on the effects of loading rate on modulus and strength of sandstone, uniaxial compression experiment of the samples, from Balikun mine, was performed at different loading rates. The influence of loading rate on average modulus, uniaxial compressive strength and post-peak strength degradation angle was analyzed, and the results indicate that:: The average modulus of sandstone samples increases with loading rate increasing; the both almost obey linear relationship. The peak strength of sandstone grows with the increase of loading rate; there is an approximately exponential relationship between the two. With loading rate increasing, the post-peak strength degradation angle decreases; the relationship between the both is approximately exponential.

scholarly journals Acoustic emission signatures prior to snow failure

2018 ◽  
Vol 64 (246) ◽  
pp. 543-554 ◽  
Author(s):  
ACHILLE CAPELLI ◽  
INGRID REIWEGER ◽  
JÜRG SCHWEIZER
Keyword(s):  
Loading Rate ◽  
Critical Phenomenon ◽  
Acoustic Emissions ◽  
Test Apparatus ◽  
Snow Layer ◽  
Loading Rates ◽  
Damage Process ◽  
Damage Processes ◽  
Increasing Load ◽  
Snow Samples

ABSTRACTSnow slab avalanches are caused by cracks forming and propagating in a weak snow layer below a cohesive slab. The gradual damage process leading to the formation of the initial failure within the weak layer (WL) is still not entirely understood. To this end, we designed a novel test apparatus that allows performing loading experiments with large snow samples (0.25 m2) including a WL at different loading rates and simultaneously monitoring the acoustic emissions (AE) response. By analyzing the AE generated by micro-cracking, we studied the evolution of the damage process preceding snow failure. At fast loading rates, the exponent of the AE energy distribution (b-value) gradually changed, and both the energy rate and the inverse waiting time increased exponentially with increasing load. These changes in AE signature indicate a transition from small to large events and an acceleration of the damage processes leading to brittle failure. For the experiments at slow loading rate, these changes in the AE signature were not or only partially present, even if the sample failed, indicating a different evolution of the damage process. The observed characteristics in AE response provide new insights on how to model snow failure as a critical phenomenon.

Experimental study and numerical simulation of uniaxial compression on artificial rock samples with Z-shaped fractures

2021 ◽  
Author(s):  
Tao Zhou ◽  
Haijun Chen ◽  
Liangxiao Xiong ◽  
Zhongyuan Xu ◽  
Jie Yang ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Crack Length ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Surface ◽  
Peak Strength ◽  
Particle Flow Code ◽  
Compression Tests ◽  
Failure Characteristics ◽  
Change Trend

Abstract To study the influence of the inclination and length of Z-shaped fissures on the mechanical properties and failure characteristics of the rock mass, this study conducts a series of uniaxial compression tests on rock-like materials with prefabricated Z-shaped fractures. In addition, two-dimensional Particle Flow Code software is used to perform uniaxial compression numerical simulations. The results show that when the specified inclination angle γ (γ = 0°, 30° or 45°) of the parallel cracks on both sides remains unchanged, the peak strength and elastic modulus of the sample show an M-shaped change trend with an increase in the inclination angle β of the middle connection crack. When γ = 60° or 90°, however, the peak strength and elastic modulus of the sample show a trend of decreasing, increasing, and then decreasing as β increases. In addition, the peak strength and elastic modulus of the sample decrease with an increase in the crack length. The influence of crack length on the elastic modulus is less than that of compressive strength. Further, the main failure mode of specimens with Z-shaped cracks is determined to be tension–shear mixed failure manifested by crack propagation from the tip of the prefabricated crack to the upper and lower boundaries of the sample. As a result, a through failure surface is formed with the prefabricated crack, which destroys the sample.

scholarly journals Energy Analysis Method for Uniaxial Compression Test of Sandstone under Static and Quasi-Dynamic Loading Rates

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zhixi Liu ◽  
Guangming Zhao ◽  
Xiangrui Meng ◽  
Ruofei Zhang ◽  
Dong Chunliang ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Uniaxial Compression ◽  
Compression Test ◽  
Elastic Energy ◽  
Loading Rate ◽  
Uniaxial Compression Test ◽  
Input Energy ◽  
Analysis Method ◽  
Compression Tests ◽  
Loading Rates

To investigate the energy evolution characteristics of sandstone under static-quasi-dynamic loading rates (1.0 × 10−3, 5.0 × 10−3, 1.0 × 10−2, 5.0 × 10−2, and 1.0 × 10−1 mm/s), the uniaxial compression tests, the uniaxial cyclic loading-unloading tests, and the uniaxial incrementally cyclic loading-unloading tests were conducted under five different loading rates. Through analysis of the elastic energy of the uniaxial cyclic loading-unloading test and the uniaxial incremental cyclic loading-unloading test, show that the impact of the loading rate and the cycle numbers on the elastic energy is less. Hence, we can deem that when the loads of the uniaxial incremental cyclic loading-unloading test and the uniaxial compression test are equal, the elastic energy of the two also equals. The energy in the uniaxial compression tests analyzed by the uniaxial incrementally cyclic loading-unloading test show that elastic energy increased linearly when the input energy increased under different loading rates. Through the linear energy storage law and the uniaxial incremental cyclic loading and unloading test, it is possible to analyze the energy in the uniaxial compression test at any loading rates. The results show that the greater the loading rate, the greater the peak elastic energy and peak input energy. But when the load is equal, the greater the loading rate, the smaller the input energy and elastic energy. Compared with traditional methods, the new energy analysis method is accurate and simple. Meanwhile, based on energy dissipation, the damage of rock during uniaxial compression tests was studied.

Mechanical properties and damage constitutive model for uniaxial compression of salt rock at different loading rates

2021 ◽  
pp. 105678952098386
Author(s):  
Junbao Wang ◽  
Qiang Zhang ◽  
Zhanping Song ◽  
Yuwei Zhang ◽  
Xinrong Liu
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Uniaxial Compression ◽  
Loading Rate ◽  
Peak Stress ◽  
Test Results ◽  
Salt Rock ◽  
Loading Rates ◽  
Damage Constitutive Model ◽  
Rock Specimens

To study the effect of loading rate on the mechanical properties of salt rock, uniaxial compression tests and acoustic emission tests at different loading rates were carried out on salt rock specimens. The test results show that with increases in loading rate, the peak stress of salt rock increases first and then essentially remains unchanged, and the elastic modulus increases gradually, while the strain at peak stress decreases gradually. Moreover, the Poisson’s ratio is independent of loading rate. The macroscopic failure modes of the salt rock specimens at different loading rates are all ‘X’-type conjugate shear failure. However, the loading rate is closely related to the degree of fracture, such that the smaller the loading rate is, the higher is the degree of fracture of salt rock. In order to describe the stress–strain behaviour in the process of salt rock failure, a damage variable expression represented by the deformation modulus was proposed, and a rock damage constitutive model was established according to the theory of continuum damage mechanics. The rationality of the damage constitutive model was verified by using the present uniaxial compression test results of salt rock and existing test data from the literature. The results show that the model can accurately describe the stress–strain response of rock in the failure process.

Coarse filters for pond effluent polishing: comparison of loading rates and grain sizes

2007 ◽  
Vol 55 (11) ◽  
pp. 121-126 ◽  
Author(s):  
M. von Sperling ◽  
J.G.B. de Andrada ◽  
W.R. de Melo Júnior
Keyword(s):  
Loading Rate ◽  
Uasb Reactor ◽  
E Coli ◽  
Effluent Quality ◽  
Loading Rates ◽  
Hydraulic Loading ◽  
Grain Sizes ◽  
Belo Horizonte ◽  
The City ◽  
Rock Size

A system comprising a UASB reactor, shallow polishing ponds and shallow coarse filters, treating actual wastewater from the city of Belo Horizonte, Brazil, has been evaluated. The main focus of the research was to compare grain sizes and hydraulic loading rates in the coarse filters. Two filters operating in parallel were investigated, with the following grain sizes: Filter 1: 3 to 10 cm; Filter 2: 8 to 20 cm. Two hydraulic loading rates were tested: 0.5 and 1.0 m3/m3.d. The filter with the lower rock size had a better performance than the filter with the larger rock size in the removal of SS and, as a consequence, BOD and COD. A better performance was obtained with the hydraulic loading rate of 0.5 m3/m3.d, as compared to the rate of 1.0 m3/m3.d. The effluent quality during the period with the lower loading rate was very good for discharge into water bodies or for agricultural reuse (median effluent concentrations from Filter 1: BOD: 20 mg/L; COD: 106 mg/L; SS: 28 mg/L; E. coli: 528 MPN/100 mL).

scholarly journals Development of friction-induced triboluminescent sensor for load monitoring

2017 ◽  
Vol 29 (5) ◽  
pp. 883-895 ◽  
Author(s):  
Md Abu S Shohag ◽  
Zhengqian Jiang ◽  
Emily C Hammel ◽  
Lucas Braga Carani ◽  
David O Olawale ◽  
...  
Keyword(s):  
Applied Load ◽  
Loading Rate ◽  
Turbine Blades ◽  
Wind Turbine Blades ◽  
Loading Rates ◽  
Load Monitoring ◽  
The Coefficient Of Friction ◽  
Dynamic Structures ◽  
Sample Configuration

Real-time load monitoring of critical civil and mechanical structures especially dynamic structures such as wind turbine blades is imperative for longer service life. This article proposed a novel sensor system based on the proprietary in situ triboluminescent optical fiber (ITOF) sensor for dynamic load monitoring. The new ITOF sensor patch consists of an ITOF sensor network with micro-exciters integrated within a polymer matrix. The sensor patch was subjected to repeated flexural loading and produced triboluminescent emissions due to the friction between micro-exciters and ITOF sensors corresponding to each loading cycle. The friction-induced triboluminescent intensity directly depends on the loading rate, the coefficient of friction, and the applied load on patch. In general, the triboluminescent intensity increases exponentially with an increase in load. Additionally, the sensor patches comprising the coarser micro-exciters exhibited better results. Similarly, better results were achieved at higher loading rates although a threshold loading rate is required to excite the triboluminescent crystals for this sample configuration. The proposed new sensor has the ability to monitor dynamic continuous applied loads.

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