scholarly journals Experimental Investigation of the Dynamic Tensile Properties of Naturally Saturated Rocks Using the Coupled Static–Dynamic Flattened Brazilian Disc Method

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4784
Author(s):  
Xinying Liu ◽  
Feng Dai ◽  
Yi Liu ◽  
Pengda Pei ◽  
Zelin Yan
Keyword(s):  
Tensile Properties ◽  
High Speed ◽  
Loading Rate ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Strength ◽  
Image Correlation ◽  
Dynamic Loads ◽  
Hopkinson Pressure Bar ◽  
Dynamic Tensile Strength ◽  
Brazilian Disc

In a naturally saturated state, rocks are likely to be in a stress field simultaneously containing static and dynamic loads. Since rocks are more vulnerable to tensile loads, it is significant to characterize the tensile properties of naturally saturated rocks under coupled static–dynamic loads. In this study, dynamic flattened Brazilian disc (FBD) tensile tests were conducted on naturally saturated sandstone under static pre-tension using a modified split-Hopkinson pressure bar (SHPB) device. Combining high-speed photographs with digital image correlation (DIC) technology, we can observe the variation of strain applied to specimens’ surfaces, including the central crack initiation. The experimental results indicate that the dynamic tensile strength of naturally saturated specimens increases with an increase in loading rate, but with the pre-tension increases, the dynamic strength at a certain loading rate decreases accordingly. Moreover, the dynamic strength of naturally saturated sandstone is found to be lower than that of natural sandstone. The fracture behavior of naturally saturated and natural specimens is similar, and both exhibit obvious tensile cracks. The comprehensive micromechanism of water effects concerning the dynamic tensile behavior of rocks with static preload can be explained by the weakening effects of water on mechanical properties, the water wedging effect, and the Stefan effect.

scholarly journals Experimental Study of the Rock Mechanism under Coupled High Temperatures and Dynamic Loads

2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Huaming An ◽  
Tongshuai Zeng ◽  
Zhihua Zhang ◽  
Lei Liu
Keyword(s):  
High Temperature ◽  
Rock Strength ◽  
Loading Rate ◽  
Split Hopkinson Pressure Bar ◽  
Strength Test ◽  
Dynamic Loads ◽  
Hopkinson Pressure Bar ◽  
Split Hopkinson ◽  
Rock Mechanism ◽  
Pressure Bar

With the development of modern society, geomaterials are widely used for infrastructure. These materials often experience dynamic loading and high temperature, which significantly influences the mechanical behaviour of the materials. This research focuses on the effects of the loading rate and high temperature on rock mass in terms of rock mechanism. A state-of-the-art review of rock mechanism under coupled dynamic loads and high temperatures is conducted first. The rock mechanism under static and dynamic loads is introduced. The marble is taken as the rock material for the test, while the split-Hopkinson pressure bar system is used to take the dynamic tests. In addition, the principles of the split-Hopkinson pressure bar are introduced to obtain the dynamic parameters. The fracture patterns of the uniaxial compressive strength test and the Brazilian tensile strength test are obtained and compared with those well documented in the literature. Some curves for the relationships among the loading rate, strain, temperature, compressive or tensile strengths are explained. It is conduced that with the increase of the loading rate, the rock strength increases, while with the increase of the temperature, the rock strength decreases.

scholarly journals Dynamic Fracture Evolution and Mechanical Behavior of Sandstone Containing Noncoplanar Elliptical Flaws under Impact Loading

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Zhenyu Han ◽  
Diyuan Li ◽  
Quanqi Zhu ◽  
Meng Liu ◽  
Zhi Sun
Keyword(s):  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Shear Crack ◽  
Dynamic Strength ◽  
Crack Coalescence ◽  
High Speed Camera ◽  
Hopkinson Pressure Bar ◽  
Fracture Evolution ◽  
Deformation Properties ◽  
Pressure Bar

To investigate the effects of preexisting flaws with different geometries, including flaw inclination angle and ligament angle on dynamic strength, deformation properties, and fracture evolution of rock materials, a series of dynamic impact tests were conducted on green sandstone specimens containing double elliptical flaws using a 75 mm diameter split Hopkinson pressure bar (SHPB) testing device with a high-speed camera recording in real time. The experimental results show that dynamic strength of specimens with different flaw angles is reduced between 5.91% and 39.92% but from 18.50% to 28.44% for specimens with different ligament angles, indicating that the effect of the flaw angle on the dynamic strength is more significant than that of the ligament angle. However, the dynamic deformation properties are influenced greatly by the ligament angle. Macroscale cracks mostly initiate at or near the flaw tips and then propagate in different paths with varying flaw geometries, leading to the ultimate failure in five typical modes based on the crack coalescence. Shear crack coalescence and tensile crack coalescence are identified through both macroscopic fracturing photos taken by the high-speed camera and microscopic surface morphology obtained by the scanning electron microscope (SEM).

Dynamic Tensile Test of Coal, Shale and Sandstone Using Split Hopkinson Pressure Bar

2010 ◽  
Vol 1 (2) ◽  
pp. 24-37 ◽  
Author(s):  
Kaiwen Xia ◽  
Sheng Huang ◽  
Ajay Kumar Jha
Keyword(s):  
Tensile Strength ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Strength ◽  
Static Strength ◽  
Test Method ◽  
Hopkinson Pressure Bar ◽  
Dynamic Tensile Strength ◽  
Sandstone Sample ◽  
Rock Samples ◽  
Sandstone Rock

The dynamic tensile strength plays a pivotal role in rock fragmentation affecting the overall economics under the present ‘Mine to Mill Concept’. In this paper, a modified SHPB technique and Brazilian test method is presented to test the dynamic tensile strength of coal, shale and sandstone rock samples collected from three opencast mines of Coal India Limited and is compared with the static strength value. The dynamic tensile strength of coal and rock is much higher than static strength and tensile strength of coal and rock samples increase with loading rate. The result shows that the dynamic strength of the coal sample is 1.5 times higher than static strength and the dynamic strength of the sandstone sample is 3 times higher than the static strength.

scholarly journals Rock Dynamic Fracture Characteristics Based on NSCB Impact Method

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Yanbing Wang
Keyword(s):  
Fracture Toughness ◽  
Dynamic Fracture ◽  
High Speed ◽  
Loading Rate ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Fracture Toughness ◽  
High Speed Photography ◽  
Rate Dependency ◽  
Hopkinson Pressure Bar ◽  
Rock Materials

In 2012, the International Society for Rock Mechanics (ISRM) recommended a new Notched Semicircular Bend (NSCB) method for the determination of dynamic fracture toughness of rock materials, but it did not consider the effect of some uncontrollable factors in the course of the experiment on the test result. This thesis firstly carried out dynamic fracture toughness experiments on several typical rock materials such as sandstone using the modified Split-Hopkinson Pressure Bar (SHPB) experimental system with high-speed photography, directly compared the dynamic fracture failure characteristics of several rock materials, and examined the loading rate dependency of the dynamic fracture toughness of rock materials. Based on the numerical analysis method of Discrete Lattice Spring Model (DLSM), it focused on the effect of bullet impact loading rate, loading area of incident bar, support restraints of clamping specimen, and other uncontrollable factors in the course of SHPB experiment on test results. The findings can be referenced for the improvement of NSCB method.

Dynamic Tensile Test of Coal, Shale and Sandstone Using Split Hopkinson Pressure Bar

2012 ◽  
pp. 188-202
Author(s):  
Kaiwen Xia ◽  
Sheng Huang ◽  
Ajay Kumar Jha
Keyword(s):  
Tensile Strength ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Strength ◽  
Static Strength ◽  
Test Method ◽  
Hopkinson Pressure Bar ◽  
Dynamic Tensile Strength ◽  
Rock Samples ◽  
Split Hopkinson ◽  
Pressure Bar

The dynamic tensile strength plays a pivotal role in rock fragmentation affecting the overall economics under the present ‘Mine to Mill Concept’. In this paper, a modified SHPB technique and Brazilian test method is presented to test the dynamic tensile strength of coal, shale and sandstone rock samples collected from three opencast mines of Coal India Limited and is compared with the static strength value. The dynamic tensile strength of coal and rock is much higher than static strength and tensile strength of coal and rock samples increase with loading rate. The result shows that the dynamic strength of the coal sample is 1.5 times higher than static strength and the dynamic strength of the sandstone sample is 3 times higher than the static strength.

STUDIES ON THE DYNAMIC FRACTURE PROPERTIES AND FAILURE MODES OF A PBX

2014 ◽  
Vol 06 (04) ◽  
pp. 1450039 ◽  
Author(s):  
R. CHEN ◽  
L. CHENG ◽  
Y. LIN ◽  
F. LU
Keyword(s):  
Dynamic Fracture ◽  
High Speed ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Particulate Composite ◽  
Image Correlation ◽  
Initiation Toughness ◽  
Hopkinson Pressure Bar ◽  
Fracture Properties ◽  
Fracture Velocity

Polymer-bonded explosives (PBXs) are particulate composite materials composed of crystalline explosive grains bound in a relatively soft polymeric binder. It is important to optimize the fracture properties, while still maintaining the low sensitiveness and high explosiveness of PBX. This paper describes a study on the fracture properties and failure modes of a PBX by adopting a newly proposed dynamic fracture experimentation method — notched semi-circular bend (NSCB) specimen loaded with split Hopkinson pressure bar (SHPB) which was used in this study. This method offers the advantage of simultaneously determining the fracture initiation toughness, fracture energy, fracture propagation toughness and fracture velocity. The crack propagation is monitored by using a synchronous high-speed camera, which allows the observation of strain field history via digital image correlation process. The experimental results indicate that both the initiation toughness and the propagation toughness linearly increase with loading rate. The propagation fracture toughness is found to increase with fracture velocity, and a limiting fracture velocity is obtained. The failure modes are interpreted by using various theoretical models. Results suggest that the debonding strength of the binder is much smaller than the crystal fracture strength. The tensile strength is similar to the debonding strength, while the compression strength is somewhere intermediate between them.

Thermal Shock Effects on Dynamic Deformation Mechanisms in Ti2AlC

2012 ◽  
Author(s):  
R. Bhattacharya ◽  
N. C. Goulbourne
Keyword(s):  
Thermal Shock ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Deformation ◽  
Compressive Loading ◽  
Image Correlation ◽  
Deformation Mechanisms ◽  
Hopkinson Pressure Bar ◽  
High Speed Imaging ◽  
Full Field

The present study is aimed at understanding the effects of thermal shock and associated microstructural features on the dynamic deformation mechanisms in Ti2AlC, a Mn+1AXn phase ternary ceramic. These materials crystallize in a Hexagonal Close Packed (HCP) structure with a c/a ratio greater than 1.67 which results in kink band formations when subjected to loading. In this work, we report the microstructural changes associated with thermal shocking of Mn+1AXn phases and its effects on deformation mechanisms, under dynamic compressive loading. The specimens are heated to temperatures of 220, 550 and 900°C, held at each temperature for 5–10 minutes, and subsequently quenched in water at 20°C to induce thermal shock. The thermal shock resistance and its effect on mechanical properties is investigated by subjecting heat treated specimens to compressive loading at high strain rates (∼1000–4500 s−1) using a Split Hopkinson Pressure Bar (SHPB). The microstructures of thermally shocked specimens are characterized by Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectroscopy (EDS) analysis to reveal the surface morphologies and characteristics. The displacements during the deformation events are captured using in situ high speed imaging, with full-field 2D Digital Image Correlation (DIC) technique. The key microscale mechanisms of deformation are studied using SEM analysis of deformed/fractured specimens.

scholarly journals ‘Seeing’ Strain in Soft Materials

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 542 ◽  
Author(s):  
Zhiyong Xia ◽  
Vanessa D. Alphonse ◽  
Doug B. Trigg ◽  
Tim P. Harrigan ◽  
Jeff M. Paulson ◽  
...  
Keyword(s):  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Color Change ◽  
Soft Materials ◽  
Image Correlation ◽  
High Rate ◽  
Hopkinson Pressure Bar ◽  
Dimethyl Siloxane ◽  
Split Hopkinson ◽  
Pressure Bar

Several technologies can be used for measuring strains of soft materials under high rate impact conditions. These technologies include high speed tensile test, split Hopkinson pressure bar test, digital image correlation and high speed x-ray imaging. However, none of these existing technologies can produce a continuous 3D spatial strain distribution in the test specimen. Here we report a novel passive strain sensor based on poly(dimethyl siloxane) (PDMS) elastomer with covalently incorporated spiropyran (SP) mechanophore to measure impact induced strains. We have shown that the incorporation of SP into PDMS at 0.25 wt% level can adequately measure impact strains via color change under a high strain rate of 1500 s−1 within a fraction of a millisecond. Further, the color change is fully reversible and thus can be used repeatedly. This technology has a high potential to be used for quantifying brain strain for traumatic brain injury applications.

Experimental Calibration of ISV Damage Model Constants for Pure Copper for High-Speed Impact Simulation

2016 ◽  
Author(s):  
Yangqing Dou ◽  
Yucheng Liu ◽  
Wilburn Whittington ◽  
Jonathan Miller
Keyword(s):  
High Speed ◽  
Impact Analysis ◽  
Split Hopkinson Pressure Bar ◽  
Internal State ◽  
Pure Copper ◽  
Damage Model ◽  
Hopkinson Pressure Bar ◽  
Experimental Calibration ◽  
High Speed Impact ◽  
The Impact

Coefficients and constants of a microstructure-based internal state variable (ISV) plasticity damage model for pure copper have been calibrated and used for damage modeling and simulation. Experimental stress-strain curves obtained from Cu samples at different strain rate and temperature levels provide a benchmark for the calibration work. Instron quasi-static tester and split-Hopkinson pressure bar are used to obtain low-to-high strain rates. Calibration process and techniques are described in this paper. The calibrated material model is used for high-speed impact analysis to predict the impact properties of Cu. In the numerical impact scenario, a 100 mm by 100 mm Cu plate with a thickness of 10 mm will be penetrated by a 50 mm-long Ni rod with a diameter of 10mm. The thickness of 10 mm was selected for the Cu plate so that the Ni-Cu penetration through the thickness can be well observed through the simulations and the effects of the ductility of Cu on its plasticity deformation during the penetration can be displayed. Also, that thickness had been used by some researchers when investigating penetration mechanics of other materials. Therefore the penetration resistance of Cu can be compared to that of other metallic materials based on the simulation results obtained from this study. Through this study, the efficiency of this ISV model in simulating high-speed impact process is verified. Functions and roles of each of material constant in that model are also demonstrated.

Sign in / Sign up

Export Citation Format

Share Document