scholarly journals Dynamic Splitting Tensile Properties and Failure Mechanism of Layered Slate

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Yunsi Liu ◽  
Chushao He ◽  
Shiming Wang ◽  
Yaxiong Peng ◽  
Yong Lei
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Loading Rate ◽  
Failure Load ◽  
Split Hopkinson Pressure Bar ◽  
Failure Mechanisms ◽  
Influence Coefficient ◽  
Layered Rock ◽  
Bedding Planes

Dynamic tensile failure is one of the main failure modes of layered rock masses during the excavation of underground engineering. This study investigates the influence of loading rate and layered inclination angle on the mechanical properties and failure mechanisms of layered slate using a split-Hopkinson pressure bar system and high-speed cameras. The results show that, overall, the dynamic elastic modulus E, postpeak stress reduction rate K, and failure load of the discs with the 7 tested bedding angles increase with the increasing loading rate. A nonlinear formula is proposed to describe the relationship between loading rate and failure load for the 7 tested inclination angles. As the inclination angle of the bedding planes increases from 0° to 90°, both the static and dynamic failure loads of the slate increased. However, with increasing loading rate, the anisotropic influence coefficient N ranges from 3.25 under the static load to 1.35 under the dynamic load, and the bedding effect gradually decreases. From the dynamic Brazilian splitting tests, the failure of the discs is mainly observed along the bedding planes when the inclination angle is less than or equal to 45°. Failure of the discs mainly occurs along the centre of the disc and previously intact planes when the inclination angle is greater than 60°. This study provides significant data to evaluate the mechanical properties and failure mechanisms of layered rock and the safety and stability of layered rock under dynamic loading.

scholarly journals Cracking Behaviors and Mechanical Properties of Rock-Like Specimens with Two Unparallel Flaws under Conventional Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Chenghua Xu ◽  
Liuyang Li ◽  
Yong Liu
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Critical Value ◽  
Tensile Failure ◽  
Rock Bridge ◽  
Bridge Length

Flaws existing in rock masses are generally unparallel and under three-dimensional stress; however, the mechanical and cracking behaviors of the specimens with two unparallel flaws under triaxial compression have been rarely studied. Therefore, this study conducted comprehensive research on the cracking and coalescence behavior and mechanical properties of specimens with two unparallel flaws under triaxial compression. Triaxial compressive tests were conducted under different confining pressures on rock-like specimens with two preexisting flaws but varying flaw geometries (with respect to the inclination angle of the two unparallel flaws, rock bridge length, and rock bridge inclination angle). Six crack types and eleven coalescence types in the bridge region were observed, and three types of failure modes (tensile failure, shear failure, and tensile-shear failure) were observed in experiments. Test results show that bridge length and bridge inclination angle have an effect on the coalescence pattern, but the influence of bridge inclination angle is larger than that of the bridge length. When the confining pressure is low, coalescence patterns and failure modes of the specimens are greatly affected by flaw geometry, but when confining pressure rose to a certain level, the influence of confining pressure is larger than the effect of flaw geometry. The peak strength of the specimens is affected by flaw geometry and confining pressure. There is a critical value for the bridge length. If the bridge length is larger than the critical value, peak strengths of the samples almost keep constant as the bridge length increases. In addition, as the bridge inclination angle increases, there is an increase in the probability of tensile cracks occurring, and with an increase in the confining pressure, the probability of the occurrence of shear cracks increases.

scholarly journals Effects of Temperature and Water on Mechanical Properties, Energy Dissipation, and Microstructure of Argillaceous Sandstone under Static and Dynamic Loads

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Rongrong Zhang ◽  
Dongdong Ma ◽  
Qingqing Su ◽  
Kun Huang
Keyword(s):  
Mechanical Properties ◽  
Energy Dissipation ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Physical And Mechanical Properties ◽  
P Wave ◽  
Peak Strain ◽  
Hopkinson Pressure Bar ◽  
Stress Strain ◽  
Sandstone Specimen

RMT-150B rock mechanics and split Hopkinson pressure bar (SHPB) devices were adopted to investigate the physical and mechanical properties, energy dissipation, and failure modes of argillaceous sandstone after different high temperatures under air-dried and saturation states. In addition, SEM and EDS tests were conducted to investigate its microstructure characteristics. Results showed that both the P-wave velocity and density of argillaceous sandstone specimen decreased with the increase of high temperature, while its porosity increased. Compared with static stress-strain curves, there was no obvious compaction stage for dynamic stress-strain curves, and the decrease rate of dynamic curves after peak strain was obviously slow compared with static curves. Both the static and dynamic strengths of argillaceous sandstone specimens decreased with increasing temperature, and the critical temperature point for the strength of argillaceous sandstone was 400°C. At the same temperature, the specific energy absorption under air-dried state was generally smaller compared with that under saturated state. Both the strain rate and temperature showed significant effect on the failure mode. After 100∼1000°C heat treatment, the granular crystals of the clastic structure gradually became larger, and both the number and average size of the original pores decreased, resulting in the deterioration of mechanical properties of argillaceous sandstone specimen.

scholarly journals Nanomechanical Properties and Failure Mechanisms of Two-Dimensional Metal-Organic Framework Nanosheets

2020 ◽  
Author(s):  
Zhixin Zeng ◽  
Irina Flyagina ◽  
Jin-Chong Tan
Keyword(s):  
Mechanical Properties ◽  
Failure Modes ◽  
Metal Organic Framework ◽  
Failure Mechanisms ◽  
Cohesive Elements ◽  
Plastic Properties ◽  
Interfacial Sliding ◽  
Porous Nanosheets ◽  
Metal Organic ◽  
Organic Framework

Nanoscale mechanical properties measurement of porous nanosheets presents many challenges. Herein we show atomic force microscope (AFM) nanoindentation to probe the nanoscale mechanical properties of a 2‑D metal‑organic framework (MOF) nanosheet material, termed CuBDC [copper 1,4‑benzenedicarboxylate]. The sample thickness was ranging from ~10 nm (tens of monolayers) up to ~400 nm (stack of multilayers). In terms of its elastic‑plastic properties, the Young’s modulus (<i>E</i> ~ 22.9 GPa) and yield strength (𝜎<sub>Y</sub> ~ 448 MPa) have been determined in the through-thickness direction. Moreover, we have characterized the failure mechanisms of the CuBDC nanosheets, where three failure mechanisms have been identified: interfacial sliding, fracture of framework, and delamination of multilayered nanosheets. Threshold forces and corresponding indentation depths corresponding to the failure modes have been determined. To gain insights into the failure mechanisms, we employ finite-element models with cohesive elements to simulate the interfacial debonding of a stack of 2‑D nanosheets during the indentation process. The nanomechanical AFM methodology elucidated here will be pertinent to the study of other 2‑D hybrid nanosheets and van der Waals solids.

scholarly journals Dynamic Fracturing Behavior of Layered Rock with Different Inclination Angles in SHPB Tests

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Jiadong Qiu ◽  
Diyuan Li ◽  
Xibing Li ◽  
Zilong Zhou
Keyword(s):  
Shear Stress ◽  
Tensile Stress ◽  
Split Hopkinson Pressure Bar ◽  
Impact Compression ◽  
Failure Patterns ◽  
Layered Rock ◽  
Bedding Planes ◽  
Loading Direction ◽  
Fracturing Process ◽  
Inclination Angles

The fracturing behavior of layered rocks is usually influenced by bedding planes. In this paper, five groups of bedded sandstones with different bedding inclination angles θ are used to carry out impact compression tests by split Hopkinson pressure bar. A high-speed camera is used to capture the fracturing process of specimens. Based on testing results, three failure patterns are identified and classified, including (A) splitting along bedding planes; (B) sliding failure along bedding planes; (C) fracturing across bedding planes. The failure pattern (C) can be further classified into three subcategories: (C1) fracturing oblique to loading direction; (C2) fracturing parallel to loading direction; (C3) mixed fracturing across bedding planes. Meanwhile, a numerical model of layered rock and SHPB system are established by particle flow code (PFC). The numerical results show that the shear stress is the main reason for inducing the damage along bedding plane at θ = 0°~75°. Both tensile stress and shear stress on bedding planes contribute to the splitting failure along bedding planes when the inclination angle is 90°. Besides, tensile stress is the main reason that leads to the damage in rock matrixes at θ = 0°~90°.

Experimental Study on Dynamic Mechanical Properties of Amphibolites, Sericite-quartz Schist and Sandstone under Impact Loadings

2012 ◽  
Vol 13 (2) ◽  
pp. 209-217
Author(s):  
Jun-Zhong Liu ◽  
Jin-Yu Xu ◽  
Xiao-Cong Lv ◽  
De-Hui Zhao ◽  
Bing-Lin Leng
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Failure Mode ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Mechanical Properties ◽  
Tensile Failure ◽  
Strength Increase ◽  
Dynamic Mechanical ◽  
Rock Samples

Abstract In order to investigate rock dynamic mechanical properties of amphibolites, sericite-quartz schist and sandstone under the different strain rates varying from 30 s -1 to 150 s -1 , the specimens were subjected to axial impact at different projectile speeds by using the split Hopkinson pressure bar (SHPB) of 100 mm in diameter. The optimal experimental size of rock samples is verified by analyzing the stress equilibrium of cylindrical rock samples in different thicknesses. It has studied the mechanic properties of these three rocks which under impact loadings; and analysed the dynamic compressive strength, failure modes, energy dissipation variation with the strain-rate and the strain-rate hardening effect from the perspective of material microstructure. Experimental results show that the dynamic Young's modulus of rock samples increase with strain-rate slightly. The dynamic failure modes of different rock samples are always different. When at a lower strain-rate, the damage of sandstone takes a peeling off the external radial tensile failure mode, but that of amphibolites takes axial splitting mode; when at a higher strain-rate, sandstone takes granular crushing failure mode, and that of amphibolites and of sericite-quartz schist take massive crushing mode. Significant strain-rate effect can be represented by a linear relation between the specific energy absorption and the strain-rate , or between the dynamic strength increase factor η and .

scholarly journals Experimental Study of the Dynamic Tensile Mechanical Properties of a Coal Sandstone Disc with a Central Hole

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Jiehao Wu ◽  
Qi Zong ◽  
Ying Xu
Keyword(s):  
Mechanical Properties ◽  
Tensile Stress ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Impact Pressure ◽  
Critical Ratio ◽  
Outer Diameter ◽  
Splitting Test ◽  
Inner Diameter ◽  
Peak Value

Deep mine rocks are often subjected to rock burst induced by dynamic load. The existence of initial holes will reduce the mechanical properties of rocks and affect the stability and safety of the tunnel excavating. In order to study the effect of the ratios of inner and outer diameter on disc specimen dynamic mechanical properties and failure modes, we use cylindrical sandstone specimens of Φ50 × 25 mm to process center holes of different diameters, and a series of dynamic splitting test were carried out with a system of split Hopkinson pressure bar (SHPB) with the diameter of Φ50 mm when the pressure is 0.15 MPa, 0.3 MPa, and 0.5 MPa. The results show that (1) the dynamic tensile stress-time-history curve exhibited double peak phenomena, and the second peak value is less than the first peak value, (2) the dynamic tensile stress peaks decrease nonlinearly with the increasing of the ratios of inner and outer diameter, and the dependence is more obvious when the pressure is higher, and (3) there is a tensile crack running along the loading direction in the failure modes of the five samples with the ratio of inner to outer diameter under three kinds of impact pressure. Under the same impact pressure, when the ratio of inner diameter to outer diameter is greater than the critical ratio of inner diameter to outer diameter, there is an obvious empty hole effect; that is, the sample develops secondary tensile cracks that develop from the upper and lower ends of the pore disc to the center of the inner hole. With the increase of the ratio of inner diameter to outer diameter, the width of the penetration crack increases. With the increase of impact pressure, the critical ratio of inner diameter to outer diameter decreases gradually. The research results have certain significance for understanding the mechanical properties of porous rocks.

scholarly journals Study on the Effect of Precrack on Specimen Failure Characteristics under Static and Dynamic Loads by Brazilian Split Test

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Enyan Liu ◽  
Fuchun Liu ◽  
Youwei Xiong ◽  
Xianquan Lei ◽  
Shiming Wang
Keyword(s):  
Dynamic Load ◽  
Loading Rate ◽  
Failure Load ◽  
Split Hopkinson Pressure Bar ◽  
Failure Process ◽  
Crack Tip ◽  
Dynamic Loads ◽  
Failure Characteristics ◽  
Loading Direction ◽  
Secondary Cracks

To analyse the dynamic failure characteristics of the rock with a crack in rock engineering, the Brazilian split tests were conducted on the split Hopkinson pressure bar (SHPB) using precrack specimens under dynamic loads. In the study, five groups of different precrack angles are selected; they are 0°, 30°, 45°, 60°, and 90°, respectively. The results show that the static failure load of the specimen as a whole decreases to increase with the growth of the loading angle, and the DIF linear increases with the increase of the loading rate; the failure load of the specimen with an angle of 45° precrack is the most sensitive to the loading rate, followed by 0°, 60°, 30°, and 90°. The crack initiation time of specimen with 30°, 45°, and 60°precrack decreases with the loading rate, while it has no obvious change with the loading rate with 0° and 90°precrack. The failure mode of the specimen was controlled by the stress concentration at the crack tip; the main cracks all point from the crack tip to the loading end. When the precrack and the loading direction are at a certain angle, the failure process will produce secondary cracks; it would be particularly obvious under dynamic load splitting. Once the precrack and the loading direction are at a certain inclination angle, type-II secondary cracks will develop under dynamic load splitting.

scholarly journals Effect of Silica Fume in Concrete on Mechanical Properties and Dynamic Behaviors under Impact Loading

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3263 ◽  
Author(s):  
Shijun Zhao ◽  
Qing Zhang
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Silica Fume ◽  
Impact Loading ◽  
Failure Modes ◽  
Mechanical Performance ◽  
Split Hopkinson Pressure Bar ◽  
Hopkinson Pressure Bar ◽  
Dynamic Tensile Strength ◽  
Dynamic Behaviors

The effect of silica fume (SF) in concrete on mechanical properties and dynamic behaviors was experimentally studied by split Hopkinson pressure bar (SHPB) device with pulse shaping technique. Three series of concrete with 0, 12%, and 16% SF as a cement replacement by weight were produced firstly. Then the experimental procedure for dynamic tests of concrete specimens with SF under a high loading rate was presented. Considering the mechanical performance and behaviors of the concrete mixtures, those tests were conducted under five different impact velocities. The experimental results clearly show concrete with different levels of SF is a strain-rate sensitive material. The tensile strength under impact loading of the tested specimens was generally improved with the increasing content of SF levels in concrete. Additionally, the tensile strength under impact loading of the concrete enhances with the increase of the strain rates. Finally, failure modes, dynamic tensile strength, dynamic increase factor (DIF), and critical strain are discussed and analyzed. These investigations are useful to improve the understanding of the effect of SF in concrete and guide the design of concrete structures.

scholarly journals Nanomechanical Properties and Failure Mechanisms of Two-Dimensional Metal-Organic Framework Nanosheets

2020 ◽  
Author(s):  
Zhixin Zeng ◽  
Irina Flyagina ◽  
Jin-Chong Tan
Keyword(s):  
Mechanical Properties ◽  
Failure Modes ◽  
Metal Organic Framework ◽  
Failure Mechanisms ◽  
Cohesive Elements ◽  
Plastic Properties ◽  
Interfacial Sliding ◽  
Porous Nanosheets ◽  
Metal Organic ◽  
Organic Framework

Nanoscale mechanical properties measurement of porous nanosheets presents many challenges. Herein we show atomic force microscope (AFM) nanoindentation to probe the nanoscale mechanical properties of a 2‑D metal‑organic framework (MOF) nanosheet material, termed CuBDC [copper 1,4‑benzenedicarboxylate]. The sample thickness was ranging from ~10 nm (tens of monolayers) up to ~400 nm (stack of multilayers). In terms of its elastic‑plastic properties, the Young’s modulus (<i>E</i> ~ 22.9 GPa) and yield strength (𝜎<sub>Y</sub> ~ 448 MPa) have been determined in the through-thickness direction. Moreover, we have characterized the failure mechanisms of the CuBDC nanosheets, where three failure mechanisms have been identified: interfacial sliding, fracture of framework, and delamination of multilayered nanosheets. Threshold forces and corresponding indentation depths corresponding to the failure modes have been determined. To gain insights into the failure mechanisms, we employ finite-element models with cohesive elements to simulate the interfacial debonding of a stack of 2‑D nanosheets during the indentation process. The nanomechanical AFM methodology elucidated here will be pertinent to the study of other 2‑D hybrid nanosheets and van der Waals solids.

Sign in / Sign up

Export Citation Format

Share Document