scholarly journals Mechanical Properties and Failure Modes of CRCB Specimen Under Impact Loading

2022 ◽  
Author(s):  
Wenjie Liu ◽  
Ke Yang ◽  
Litong Dou ◽  
Zhen Wei ◽  
Xiaolou Chi ◽  
...  
Keyword(s):  
Impact Velocity ◽  
Stress Wave ◽  
Failure Modes ◽  
Rock Strength ◽  
Peak Strength ◽  
Stress Wave Propagation ◽  
Peak Strain ◽  
Impact Tests ◽  
Coal Particles ◽  
The Impact

Abstract To explore the dynamic mechanical characteristics of coal-rock combined body (CRCB) load-bearing structures, impact tests were performed on CRCB specimens by using a separated Hopkinson pressure bar test device (SHPB) combined with an ultra-high-speed camera system. The propagation characteristics of stress wave , dynamic stress-strain relationship, energy evolution law, and distribution characteristics of CRCB crushed particles in the impact tests were analyzed. The obtained results showed that: with the increasing of impact velocity, the effect of the wave impedance difference between the CRCB specimens and incident bar on stress wave propagation is gradually weakened. The peak strength (sII) and peak strain of the CRCB had obvious strain-rate effects, the ratio of reflected energy decreases linearly. In addition, with increased impact velocity, the growth rate of the peak strength and ratio of absorbed energy gradually dropped, changing approximately as a power function. Macro-fractures of the CRCB mainly occurred at the coal or rock ends which is far away from the interface. When the stress at the crack tip is greater than the "weakened" coal or rock strength, the crack will continue to develop across the coal and rock interface. With the increasing of impact velocity and rock strength, the crushed coal particles gradually transform from massive to powdering, and the average size of crushed coal blocks decreases, which leads to a gradual increase in the fractal dimension of the CRCB specimens. Therefore, the monitoring and prevention of dynamic loads should be strengthened in the coal mines with thick and hard roofs.

Investigation of Stress Wave Propagation in Brain Tissues Through the Use of Finite Element Method

2010 ◽  
Author(s):  
Biaobiao Zhang ◽  
W. Steve Shepard ◽  
Candace L. Floyd
Keyword(s):  
Finite Element ◽  
Wave Propagation ◽  
Brain Injury ◽  
Stress Wave ◽  
Brain Research ◽  
Complex Structure ◽  
Stress Wave Propagation ◽  
Wave Loads ◽  
The Impact ◽  
The Brain

Because axons serve as the conduit for signal transmission within the brain, research related to axon damage during brain injury has received much attention in recent years. Although myelinated axons appear as a uniform white matter, the complex structure of axons has not been thoroughly considered in the study of fundamental structural injury mechanisms. Most axons are surrounded by an insulating sheath of myelin. Furthermore, hollow tube-like microtubules provide a form of structural support as well as a means for transport within the axon. In this work, the effects of microtubule and its surrounding protein mediums inside the axon structure are considered in order to obtain a better understanding of wave propagation within the axon in an attempt to make progress in this area of brain injury modeling. By examining axial wave propagation using a simplified finite element model to represent microtubule and its surrounding proteins assembly, the impact caused by stress wave loads within the brain axon structure can be better understood. Through conducting a transient analysis as the wave propagates, some important characteristics relative to brain tissue injuries are studied.

Wave Propagation in an Elastic Rod Exhibiting Internal Coulomb Friction, Considered as a Model for a Ring Spring

1956 ◽  
Vol 23 (3) ◽  
pp. 367-372
Author(s):  
E. H. Lee ◽  
A. J. Wang
Keyword(s):  
Wave Propagation ◽  
Stress Wave ◽  
Coulomb Friction ◽  
Stress Wave Propagation ◽  
Infinite Length ◽  
Input Energy ◽  
Elastic Rod ◽  
Total Input ◽  
Conical Bearing ◽  
The Impact

Abstract The problem of stress-wave propagation in a ring spring is considered. A ring spring consists of rings placed normal to the spring axis with alternate internal and external conical bearing surfaces. The friction between these surfaces causes a loading-unloading relation which is strongly irreversible, leading to marked energy absorption for oscillatory stressing. The attenuation of a pulse of stress is analyzed in detail as it is propagated down a spring of infinite length. The influence of certain spring characteristics is evaluated. Concentration of the absorption of the total input energy is found in the region of the impact end of the spring, and particular examples are presented.

Experimental investigation of the quasi-static and impact tests on the energy absorption characteristics of coupler rubber buffers used in railway vehicles

2018 ◽  
Vol 233 (9) ◽  
pp. 937-950 ◽  
Author(s):  
Shuguang Yao ◽  
Zhixiang Li ◽  
Wen Ma ◽  
Ping Xu ◽  
Quanwei Che
Keyword(s):  
Energy Absorption ◽  
Impact Velocity ◽  
High Speed ◽  
Compression Tests ◽  
Static Compression ◽  
Static Tests ◽  
Impact Tests ◽  
High Speed Trains ◽  
The Impact ◽  
Absorption Characteristics

Coupler rubber buffers are widely used in high-speed trains, to dissipate the impact energy between vehicles. The rubber buffer consists of two groups of rubbers, which are pre-compressed and then installed into the frame body. This paper specifically focuses on the energy absorption characteristics of the rubber buffers. Firstly, quasi-static compression tests were carried out for one and three pairs of rubber sheets, and the relationship between the energy absorption responses, i.e. Eabn  =  n ×  Eab1, Edissn =  n ×  Ediss1, and Ean =  Ea1, was obtained. Next, a series of quasi-static tests were performed for one pair of rubber sheet to investigate the energy absorption performance with different compression ratios of the rubber buffers. Then, impact tests with five impact velocities were conducted, and the coupler knuckle was destroyed when the impact velocity was 10.807 km/h. The results of the impact tests showed that with the increase of the impact velocity, the Eab, Ediss, and Ea of the rear buffer increased significantly, but the three responses of the front buffer did not increase much. Finally, the results of the impact tests and quasi-static tests were contrastively analyzed, which showed that with the increase of the stroke, the values of Eab, Ediss, and Ea increased. However, the increasing rates of the impact tests were higher than that of the quasi-static tests. The maximum value of Ea was 68.76% in the impact tests, which was relatively a high value for the vehicle coupler buffer. The energy capacity of the rear buffer for dynamic loading was determined as 22.98 kJ.

scholarly journals A Coupled Gas Flow-Mechanical Damage Model and Its Numerical Simulations on High Energy Gas Fracturing

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yu Bai ◽  
Li Sun ◽  
Chenhui Wei
Keyword(s):  
Numerical Simulations ◽  
Stress Wave ◽  
Gas Flow ◽  
High Energy ◽  
Stress Wave Propagation ◽  
Crack Evolution ◽  
Element Analysis ◽  
Unconventional Gas ◽  
Radial Cracks ◽  
The Impact

High-energy gas fracturing (HEGF) and gas fracturing (GF) are considered to be efficient to enhance the permeability of unconventional gas reservoir. The existing models for HEGF mainly focus on the dynamic loading of stress wave or static loading of gas pressurization, rather than on the combined actions of them. Studies on the combination of HEGF and GF (HEGF+GF) are also few. In this paper, a damage-based stress wave propagation-static mechanical equilibrium-gas flow coupling model is established. Numerical model and determination of mesomechanical parameters in finite element analysis are described in detail. Numerical simulations on crack evolution under HEGF, GF, and HEGF+GF are carried out, and the impact of in situ stress conditions on crack evolution is discussed further. A total of 11 cracks with length of 2.3-4 m in HEGF, 4 main cracks with length of 6.5–8 m in GF, and 11 radial cracks with length of 2–11.5 m in HEGF+GF are produced. Many radial cracks around the borehole are formed in HEGF and extended further in GF. The crustal stress difference is disadvantageous for crack complexity. This study can provide a reference for the application of HEGF+GF in unconventional gas reservoirs.

Experimental investigation of stress wave propagation in standing trees

Holzforschung ◽  
2011 ◽  
Vol 65 (5) ◽  
Author(s):  
Houjiang Zhang ◽  
Xiping Wang ◽  
Juan Su
Keyword(s):  
Wave Propagation ◽  
Stress Wave ◽  
Wave Energy ◽  
Structural Defects ◽  
Stress Wave Propagation ◽  
Tree Trunk ◽  
Wave Fronts ◽  
Contour Maps ◽  
Standing Trees ◽  
The Impact

Abstract The objective of this study was to investigate how a stress wave travels in a standing tree as it is introduced into the tree trunk through a mechanical impact. A series of stress wave time-of-flight (TOF) data were obtained from three freshly-cut red pine (Pinus resinosa Ait.) logs by means of a two-probe stress wave timer. Two-dimensional (2D) and three-dimensional (3D) stress wave contour maps were constructed based on the experimental data using a commercial software. These stress wave contour maps represent the wave fronts in a time sequence, illustrating the flow of stress wave energy within a log. The analysis of TOF data and wave fronts indicates that stress wave propagation in standing trees is affected by tree diameter, travel distance, and internal wood conditions (wood properties and structural defects). When a stress wave is introduced into a tree trunk from a point source, it initially propagates in the impact direction as a 3D wave. Then the flow of the stress wave energy gradually changes towards the longitudinal directions. As the diameter-to-distance ratio reaches 0.1 or below, the wave begins to travel as a quasi 1D wave.

Impact compression behaviors of high-capacity long piles

2010 ◽  
Vol 47 (12) ◽  
pp. 1335-1350 ◽  
Author(s):  
Arthur K.O. So ◽  
Charles W.W. Ng
Keyword(s):  
Energy Transfer ◽  
Impact Velocity ◽  
Stress Wave ◽  
Impact Energy ◽  
High Capacity ◽  
Measured Data ◽  
Impact Compression ◽  
Impact Forces ◽  
The Impact ◽  
Pile Length

The Hiley formula underestimates driving resistance of long piles. Methods using affected pile length have been suggested, but have been found to be inapplicable for high-capacity piles. The impact compression behaviors of about 4700 high-capacity H-piles that were 14–80 m long at final set were studied. Measured data revealed that maximum impact forces are very scattered, but their means are independent of the hammer type, ram weight, ram drop, impact velocity, and pile length. Maximum impact compression of pile and affected pile length exist in both long and short piles. The affected pile length in turn is significant to the blow efficiency, hammer constant, and energy transfer ratio. This length is governed by the impact momentum and impact energy, and can be estimated by an energy-based equation. If the affected pile length determined by this equation is substituted into the Hiley formula to back-analyze the driving resistance, predictability of the driving formula can be improved by about 8%. This improvement is significant enough to reduce the number of hammer blows required at very hard driving conditions and reduce pile damage. Furthermore, this proposed equation is simple to use in the field and is more economical compared with stress-wave monitoring techniques.

scholarly journals Experimental Study on Mechanical Properties, Failure Behavior and Energy Evolution of Different Coal-Rock Combined Specimens

2019 ◽  
Vol 9 (20) ◽  
pp. 4427 ◽  
Author(s):  
Shang Yang ◽  
Jun Wang ◽  
Jianguo Ning ◽  
Pengqi Qiu
Keyword(s):  
Kinetic Energy ◽  
Failure Modes ◽  
Rock Strength ◽  
Compressive Loading ◽  
Dissipated Energy ◽  
Failure Behavior ◽  
Peak Strain ◽  
Energy Evolution ◽  
Coal Rock ◽  
Axial Splitting

To investigate the effect of the pure coal/rock strength on the mechanical behavior, failure behavior, and energy evolution of coal-rock combined (CRC) specimens, an AG-X250 Shimadzu Precision Universal Test was used to conduct uniaxial compressive loading, uniaxial cyclic loading, and unloading compression experiments on pure coal, pure rock, and different CRC specimens. The results show that the uniaxial compressive strength, Young’s modulus, and peak strain of the CRC specimen mainly depend on the coal specimen instead of the rock strength. The major failure modes of CRC were the shearing fracture and axial splitting failure, and for the CRC specimen with the same hard rock, the CRC specimen severely failed due to axial splitting cracks. In addition, the released elastic energy Ue, dissipated energy Ud, and kinetic energy Ur increase with increasing rock mass/coal strength, and for CRC specimen with the same coal, the greater the difference in strength between the rock and coal is, the greater the kinetic energy is.

The Buckling Mechanism of Square Tube Subjected to the Impact of a Mass

2014 ◽  
Vol 624 ◽  
pp. 267-271
Author(s):  
Zhu Hua Tan ◽  
Bo Zhang ◽  
Peng Cheng Zhai
Keyword(s):  
Numerical Simulation ◽  
Wave Propagation ◽  
Numerical Methods ◽  
Stress Wave ◽  
Significant Influence ◽  
Strain Localization ◽  
Stress Wave Propagation ◽  
Low Velocity ◽  
Buckling Modes ◽  
The Impact

The dynamic response of the square tube subjected to the impact of a mass was investigated by using experimental and numerical methods. The square tube was impacted by a mass at the velocity ranging from 5.09 m/s to 12.78 m/s, and different progressive buckling modes were obtained. The numerical simulation was also carried out to analyze the buckling mechanism of the square tube. The results show that there is obvious stress wave propagation and strain localization in the tube, which has a significant influence on the buckling mechanism of the tube. The stress wave and inertia of the mass play different roles at various impact velocities. And buckling mechanism at low velocity is mainly caused by stress wave, whereas the buckling mechanism at high velocity is resulted from the inertial of the mass.

Safe Impact Speed for Hollow Circular Cylinders

1970 ◽  
Vol 37 (2) ◽  
pp. 305-309
Author(s):  
J. C. Wambold ◽  
F. D. Ju
Keyword(s):  
Wave Propagation ◽  
Impact Velocity ◽  
Stress Wave ◽  
Experimental Tests ◽  
Circular Cylinders ◽  
Stress Wave Propagation ◽  
Analog Simulation ◽  
Impact Speed ◽  
End Caps

An analog simulation of stress wave propagation in hollow circular cylinders with, and without, end caps for the purpose of determining safe impact velocity. The results were checked with experimental tests run by Sandia Corporation.

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