scholarly journals Experimental Study on Stress Uniformity and Deformation Behavior of Coals with Different Length-to-Diameter Ratios under Dynamic Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Qiupeng Yuan ◽  
Guangxiang Xie ◽  
Lei Wang ◽  
Zhenhua Jiao ◽  
Peng Zou ◽  
...  
Keyword(s):  
Deformation Behavior ◽  
Dynamic Compression ◽  
Test System ◽  
Peak Strain ◽  
Test Protocol ◽  
Impact Compression ◽  
Stress Equilibrium ◽  
Shpb Test ◽  
Stress Uniformity ◽  
Elastic Stage

In this study, a uniaxial impact compression test was performed on coal samples with length-to-diameter L / D ratios of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 using a Φ 50 mm split Hopkinson pressure bar (SHPB) test system. This study researched the stress uniformity and deformation behavior of coal samples with different L / D ratios during dynamic compression, defined the stress equilibrium coefficient ξ , proposed a new method for determining whether a sample meets the stress uniformity hypothesis, and obtained the critical L / D ratio of 0.6 and the optimal L / D ratio of 0.3 or 0.4 for coal samples to obtain the stress equilibrium. The experimental results showed that the dynamic stress-strain curve of coal had an elastic stage, a plastic stage, and a failure stage. As the L / D ratio increased, the proportion of the elastic stage to the prepeak curve of the samples declined progressively; with an increase in the L / D ratio, the peak part of the curve also changed from “sharp” to “stagnated,” while an increase in the plasticity led to strain softening. As the L / D ratio of the samples increased, the average strain rate decreased approximately as a power function, and the decreasing trend was gradually reduced from 296.49 s−1 ( L / D =0.3) to 102.85 s−1 ( L / D =1), with a reduction of approximately 65.31%. With an increase in the L / D ratio, the peak strain gradually decreased exponentially. This study concluded that the SHPB test protocol design is of a certain reference value for low-density, low-strength, heterogeneous brittle materials, such as coal.

scholarly journals Study on Dynamic Behavior and Energy Dissipation of Rock considering Initial Damage Effect

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Aihong Lu ◽  
Jinhai Xu ◽  
Yu Xia ◽  
Lei Sun
Keyword(s):  
Rock Mass ◽  
Test System ◽  
Energy Ratio ◽  
Dissipated Energy ◽  
Peak Strain ◽  
Impact Compression ◽  
Damage Degree ◽  
Initial Damage ◽  
Transmitted Energy ◽  
Rock Specimens

To explore the influence of initial damage on the dynamic characteristics of rock mass, the Φ 50 mm split Hopkinson pressure bar (SHPB) test system was used, and the uniaxial impact compression tests on yellow sandstone specimens with different damage degrees were conducted, and then the variation law of mechanical properties of rock specimens with the initial damage was determined. The test results show that the dynamic stress-strain curve of rock specimens with initial damage can be roughly divided into compaction stage, elastic deformation stage, crack evolution stage, and strain-softening stage; the higher the initial damage degree of rock mass, the more significant the compaction stage. With the increase of the initial damage degree, the dynamic elastic modulus and peak stress of rock mass decrease gradually in a power number, while the peak strain of rock mass increases exponentially. With the increase of the initial damage degree, both the reflected energy ratio and the dissipated energy ratio decrease linearly, while the transmitted energy ratio increases linearly; the increasing rate of the transmitted energy ratio is greater than the decreasing rate of the reflected energy ratio.

scholarly journals Hot Compression Behavior of New Al-6Mg and Al-8Mg Alloy with Improved Hot Workability Fabricated by Direct Chill Casting Method

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 288
Author(s):  
Nam-Seok Kim ◽  
Kweon-Hoon Choi ◽  
Seung-Yoon Yang ◽  
Seong-Ho Ha ◽  
Young-Ok Yoon ◽  
...  
Keyword(s):  
Dynamic Recrystallization ◽  
Compression Test ◽  
Deformation Behavior ◽  
Hot Compression ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Strength Increase ◽  
Peak Strain ◽  
Hot Workability ◽  
Hot Compression Test

A hot compression test of new Al-6Mg and Al-8Mg alloys was conducted to understand the dynamic recrystallization (DRX) behavior by Mg contents. To investigate the hot workability of Al-Mg with high Mg contents, the hot deformation behavior of Al-6Mg and Al-8Mg alloys was analyzed by a hot compression test in the temperature range of 300–450 °C, and the strain rate range of 10−3–100/s. Subsequently, high-temperature deformation behavior was investigated through the processing map and microstructure observation. In this study, the results have shown that, as the Mg contents increase, the maximum and yield strength increase while rapid flow softening after the peak strain has been observed due to accelerated dynamic recrystallization (DRX). Finally, the increase of Mg contents affects an increase of heat dissipation efficiency to be an indicator of regular deformation.

A comparative study on dynamic mechanical performance of concrete and rock

2015 ◽  
Author(s):  
Xia Zhengbing ◽  
Zhang Kefeng ◽  
Deng Yanfeng ◽  
Ge Fuwen
Keyword(s):  
Mechanical Performance ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Compression ◽  
Peak Strain ◽  
Hopkinson Pressure Bar ◽  
Dynamic Mechanical ◽  
Strain And Strain Rate ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
Relationship Of

Recently, engineering blasting is widely applied in projects such as rock mineral mining, construction of underground cavities and field-leveling excavation. Dynamic mechanical performance of rocks has been gradually attached importance both in China and abroad. Concrete and rock are two kinds of the most frequently used engineering materials and also frequently used as experimental objects currently. To compare dynamic mechanical performance of these two materials, this study performed dynamic compression test with five different strain rates on concrete and rock using Split Hopkinson Pressure Bar (SHPB) to obtain basic dynamic mechanical parameters of them and then summarized the relationship of dynamic compressive strength, peak strain and strain rate of two materials. Moreover, specific energy absorption is introduced to confirm dynamic damage mechanisms of concrete and rock materials. This work can not only help to improve working efficiency to the largest extent but also ensure the smooth development of engineering, providing rich theoretical guidance for development of related engineering in the future.

scholarly journals Blasting-Induced Permeability Enhancement of Ore Deposits Associated with Low-Permeability Weakly Weathered Granites Based on the Split Hopkinson Pressure Bar

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Lei Yan ◽  
Wenhua Yi ◽  
Liansheng Liu ◽  
Jiangchao Liu ◽  
Shenghui Zhang
Keyword(s):  
Split Hopkinson Pressure Bar ◽  
Deformation Modulus ◽  
Constant Speed ◽  
Initial Porosity ◽  
Peak Strain ◽  
Variable Speed ◽  
Hopkinson Pressure Bar ◽  
Impact Compression ◽  
Split Hopkinson ◽  
Pressure Bar

By utilizing the improved split Hopkinson pressure bar (SHPB) test device, uniaxial, constant-speed cyclic, and variable-speed cyclic impact compression tests were conducted on weakly weathered granite samples. By combining nuclear magnetic resonance (NMR) and triaxial seepage tests, this study investigated the change laws in the mechanical properties, porosity evolution, and permeability coefficients of the samples under cyclic impacts. The results showed that in constant-speed cyclic impacts with increasing impact times, deformation modulus decreased, whilst porosity firstly decreased and then increased. Furthermore, dynamic peak strength firstly increased and then decreased whereas peak strain constantly increased before failure of the samples. In the variable-speed cyclic impacts, as impact times increased, deformation modulus firstly increased and then declined with damage occurring after four impact times. The compaction process weakened and even disappeared with increasing initial porosity. Three types of pores were found in the samples that changed in multiscale under cyclic loading. In general, small pores extended to medium- and large-sized pores. After three variable-speed cyclic impacts, the porosity of the samples was larger than the initial porosity and the permeability coefficient was greater than its initial value. The results demonstrate that the purpose of enhancing permeability and keeping the ore body stable can be achieved by conducting three variable-speed cyclic impacts on the samples.

Experimental and Numerical Analysis of Qinling Mountain Engineered Rocks during Pulse-Shaped SHPB Test

2015 ◽  
Vol 16 (3-4) ◽  
pp. 165-171
Author(s):  
Shi Liu ◽  
Jinyu Xu
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Strain Rate ◽  
Energy Absorption ◽  
Absorption Rate ◽  
Failure Modes ◽  
Dynamic Compression ◽  
Peak Strain ◽  
Compression Stress ◽  
Dynamic Compressive Strength

AbstractIn order to study the dynamic compression mechanical properties of engineering rock under high strain rate （100~102 S−1）loads, dynamic compression tests of three common engineering rocks (marble, sandstone and granite) taken from the Qinling Mountain are studied subjected to five different kinds of shock air pressure using Φ 100 mm split Hopkinson pressure bar test system improved with purple copper waveform shaper. The dynamic compression stress-strain curves, dynamic compressive strength, peak strain, energy absorption rate and elastic modulus of three rocks variation with strain rate are researched. The dynamic compression failure modes under different strain rates are analyzed. Then the three-dimensional numerical simulations of waveform shaper shaping effects and stress wave propagation in the SHPB tests are carried out to reproduce the test results. The research results show that the dynamic compression stress-strain curves show certain discreteness, and there is an obvious rebound phenomenon after the peak. With the increase in strain rate, the dynamic compressive strength, peak strain and energy absorption rate are all in a certain degree of increase, but the elastic modulus have no obvious change trend. Under the same strain rate, the dynamic compressive strength of granite is greatest while of sandstone is least. With the increase in strain rate, the margin of increase in peak strain and energy absorption rate of granite is greatest while of sandstone is least. The failure modes of the sample experience a developing process from outside to inside with the increase of strain rate.

Characterization and Constitutive Modeling of a Plasticized Poly(vinyl Chloride) for a Broad Range of Strain Rates

2001 ◽  
Vol 74 (4) ◽  
pp. 560-573 ◽  
Author(s):  
Yan Wang ◽  
Ellen M. Arruda ◽  
Phillip A. Przybylo
Keyword(s):  
Vinyl Chloride ◽  
Constitutive Modeling ◽  
Split Hopkinson Pressure Bar ◽  
Test System ◽  
Strain Rates ◽  
Impact Compression ◽  
Plasticized Pvc ◽  
Rate Dependent ◽  
Poly Vinyl Chloride ◽  
Compression Data

Abstract The mechanical behavior, morphological characterization and constitutive modeling of plasticized poly(vinyl chloride) (or PVC) are studied in this paper. The plasticized PVC is tested to large strains over a broad range of strain rates. Uniaxial and plane strain compression data at various constant strain rates ranging from −0.001 to −10 s−1 are collected on a conventional servohydraulic test system. Additional uniaxial impact compression data at approximately constant strain rates ranging from −1160 to −5560 s−1 are obtained using an aluminum split Hopkinson pressure bar apparatus. The large strain load/unload response of the plasticized PVC is nonlinear, it contains hysteresis and plastic deformation, and the initial response is highly rate dependent when the strain rate spans the transition zone between quasi-static and impact strain rates at room temperature. The morphology of plasticized PVC is analyzed via differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and described as a physically entangled network. A three-dimensional rate dependent constitutive model for plasticized PVC is developed and shown to successfully predict its stress—strain behavior over a broad range of strain rates.

Design of an Experimental Test System to Investigate Parameters Affecting Distal Tip Loads of Pacemaker and Defibrillator Leads

2015 ◽  
Vol 9 (1) ◽  
Author(s):  
Elizabeth A. Stephen ◽  
Donna L. Walsh ◽  
Nandini Duraiswamy ◽  
Oleg Vesnovsky ◽  
L. D. Timmie Topoleski
Keyword(s):  
Cardiac Tissue ◽  
Test System ◽  
Load Cell ◽  
Test Protocol ◽  
Minimal Impact ◽  
Test Configuration ◽  
Cell Placement ◽  
Ventricular Dysrhythmias

The purpose of this study was to design and evaluate a system to test the mechanical behavior of pacemaker and defibrillator leads. Over 300,000 pacemaker and implantable cardioverter defibrillator (ICD) procedures are performed every year in the U.S. for the treatment of cardiac arrhythmias, ventricular dysrhythmias, and congestive heart failure. These procedures require implanting transvenous leads into the interior wall of the heart. A serious and sometimes fatal complication that may occur during or after lead implantation is perforation of the lead tip through the heart wall. The factors that lead to perforation are not fully understood. This illustrates that the mechanical interactions between the lead tip and the cardiac tissue need to be further investigated to improve the outcome for pacemaker and ICD patients. To improve the performance of lead tips, the testing protocols must reproduce physiological and clinically relevant tip-tissue interactions. As a first step toward this goal, testing parameters that influence those interactions must be identified. We investigated the effect of test system parameters, which reproduce potentially critical physiological constraints, on the load experienced at the distal tip of thirteen pacemaker and defibrillator active-fixation leads. We evaluated the use of a constraint to simulate the effect of the right ventricle (RV constraint) in vivo, how and where the lead was fixed in the test configuration, location of the load cell in the test system, rotation and frequency of the test protocol, and the effect of stylets. Results showed the RV constraint and load cell placement had the largest impact on lead tip load, while rotation of the test setup and test frequency had a minimal impact. Recommendations are made for a test system and protocol for in vitro testing of leads that take into consideration in vivo conditions. Better approximations of the in vivo environment may lead to improved product development. The potential of this system to more effectively evaluate new pacemaker and defibrillator lead designs will require further study.

Stress uniformity process of specimens in SHPB test under different loading conditions of rectangular and half-sine input waves

2008 ◽  
Vol 14 (6) ◽  
pp. 450-456 ◽  
Author(s):  
Liang Hong ◽  
Xibing Li ◽  
Xiling Liu ◽  
Zilong Zhou ◽  
Zhouyuan Ye ◽  
...  
Keyword(s):  
Loading Conditions ◽  
Shpb Test ◽  
Stress Uniformity

scholarly journals Study of Acoustic Emission and Mechanical Characteristics of Coal Samples under Different Loading Rates

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Huamin Li ◽  
Huigui Li ◽  
Baobin Gao ◽  
Dongjie Jiang ◽  
Junfa Feng
Keyword(s):  
Acoustic Emission ◽  
Elasticity Modulus ◽  
Loading Rate ◽  
Peak Stress ◽  
Test System ◽  
Strong Impact ◽  
Peak Strain ◽  
Compression Tests ◽  
Loading Rates ◽  
The Relationship

To study the effect of loading rate on mechanical properties and acoustic emission characteristics of coal samples, collected from Sanjiaohe Colliery, the uniaxial compression tests are carried out under various levels of loading rates, including 0.001 mm/s, 0.002 mm/s, and 0.005 mm/s, respectively, using AE-win E1.86 acoustic emission instrument and RMT-150C rock mechanics test system. The results indicate that the loading rate has a strong impact on peak stress and peak strain of coal samples, but the effect of loading rate on elasticity modulus of coal samples is relatively small. When the loading rate increases from 0.001 mm/s to 0.002 mm/s, the peak stress increases from 22.67 MPa to 24.99 MPa, the incremental percentage is 10.23%, and under the same condition the peak strain increases from 0.006191 to 0.007411 and the incremental percentage is 19.71%. Similarly, when the loading rate increases from 0.002 mm/s to 0.005 mm/s, the peak stress increases from 24.99 MPa to 28.01 MPa, the incremental percentage is 12.08%, the peak strain increases from 0.007411 to 0.008203, and the incremental percentage is 10.69%. The relationship between acoustic emission and loading rate presents a positive correlation, and the negative correlation relation has been determined between acoustic emission cumulative counts and loading rate during the rupture process of coal samples.

scholarly journals Study on Low-Frequency TEM Effect of Coal during Dynamic Rupture

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Cheng-wu Li ◽  
Chuan Wang ◽  
Bei-jing Xie ◽  
Xiao-yuan Sun ◽  
Xiao-meng Xu
Keyword(s):  
High Strain ◽  
Low Frequency ◽  
Test System ◽  
Test Results ◽  
Dynamic Rupture ◽  
Monitoring Technique ◽  
Shpb Test ◽  
Coal Rock ◽  
And Performance ◽  
Electromagnetic Monitoring

Dynamic loads provided by the SHPB test system were applied to coal specimens, and the TEM signals that emerged during coal rupture were recorded by the TMVT system. Experiments on coal-mass blasting rupture in excavating workface were also carried out, and the emerged TEM signal was analyzed. The results indicate that the low-frequency TEM signals were detected close to the coal specimens under high strain dynamic load applied by the SHPB, initially rising sharply and dropping rapidly, followed by a small tailing turbulence. And the field test results obtained during coal blasting process coincided with the results from the SHPB tests. Furthermore, its initial part shaped like a pulse cluster had a more pronounced tail and lasted even longer. And the generation mechanism of the low-frequency TEM effect was analyzed. It suggests that the low-frequency TEM effect of coal during dynamic rupture is contributed by the fractoemission mechanism and the resonance or waveguide effects. Because its wavelength is longer than the higher ones, the low-frequency TEM has a good anti-interference performance. That can expand the scope and performance of the coal-rock dynamic disaster electromagnetic monitoring technique.

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