Dynamic Brazilian Tests Research Articles

Insight into the dynamic tensile behavior of deep anisotropic shale reservoir after water-based working fluid cooling

During deep shale gas production, flowing water-based working fluid inevitably cools shale reservoirs around boreholes and some fractures, and possible extraction methods induce dynamic stresses. To understand the dynamic tensile behavior of deep anisotropic shale reservoir after water-based working fluid cooling, a split Hopkinson pressure bar was used for performing the dynamic Brazilian tests on shale samples with bedding angles of 0°, 30°, 45°, 60° and 90° after reservoir temperature realization (25–200 °C) and water cooling. The results illustrate that dynamic tensile strength of shale samples decreases gradually as reservoir temperature increases under the loading rates 100–1000 GPa/s. From room temperature to 200 °C the most strength deterioration appears on samples with the bedding angle of 90°. A dynamic tensile strength deterioration model for deep shale reservoirs after water-based working fluid cooling is proposed considering the influence of loading rate and bedding angle. Geometrical trajectories of the main failure cracks are separated into three types, i.e., fully central tensile failure, tensile-shear failure and fully shear failure (sliding of bedding planes). For samples with bedding angles of 30°, 45° and 60°, increasing reservoir temperature encourages tensile failure to change into shear failure. The roles that bedding planes play in interacting with failure crack growth are summarized as IP mode (intersecting propagation), TP mode (turning propagation) and PP mode (promoting propagation). Anisotropic dynamic tensile strength responses are systematically discussed by using thermal stress simulation in ABAQUS, microstructure analyses, crack interaction conditions and the one-dimensional stress wave propagation theory. Based on experimental observations, field implications in borehole stability and fracturing of deep shale reservoirs are proposed under medium and high loading rates. This work is instrumental in providing valuable information and technology assistance for real deep shale gas production projects.

Dynamic Brazilian tests of yellow sandstone under coupled static and dynamic loads

Through a series of static mechanical tests and (SHPB) dynamic impact tests, the static and dynamic mechanical parameters of rock as represented by yellow sandstone are determined, and the Holmquist-Johnson-Cook model parameters of the rock are calibrated using the test data and theoretical calculations. The feasibility of a numerical model is verified, and numerical analysis of the SHPB impact process under different radial pressure pre-loading is carried out on the basis of good verification. The results show that with increasing impact load, the degree of rock breakage increases, as does the dynamic tensile strength. With the application of increasing pre-static pressure, the dynamic tensile strength of the rock decreases gradually, and the maximum radial cumulative strain increases continuously under a given impact pressure, indicating that micro-cracks in the rock develop initially and then expand under the influence of pre-static pressure; the rock is more easily broken, and its weakening degree increases. Under coupled dynamic and static loading, the energy utilization rate of rock in the Brazilian splitting process is jointly affected by axial compression ratio and impact load. Too large a pressure ratio will reduce the strain-rate sensitivity of rock, resulting in low energy utilization rate, while too low an axial compression ratio will make the dynamic tensile strength of rock relatively high, which is not conducive to tensile failure. Therefore, on the premise of clear fracture form requirements, a suitable combination of axial compression ratio and impact velocity can improve the rock crushing effect and energy utilization rate.

Mechanical properties and fracture surface roughness of thermally damaged granite under dynamic splitting

AbstractIn order to understand the mechanical properties and the fracture surface roughness characteristics of thermally damaged granite under dynamic splitting, dynamic Brazilian splitting tests were conducted on granite samples after thermal treatment at 25, 200, 400, and 600°C. Results show that the dynamic peak splitting strength of thermally damaged granite samples increases with increasing strain rate, showing obvious strain‐rate sensitivity. With increasing temperature, thermally induced cracks in granite transform from intergranular cracks to intragranular cracks, and to a transgranular crack network. Thermally induced damages reduce the dynamic peak splitting strength and the maximum absorbed energy while increasing the peak radial strain. The fracture mode of the thermally damaged granite under dynamic loads is mode II splitting failure. By using the axial roughness index , the distribution ranges of the wedge‐shaped failure zones and the tensile failure zones in the fracture surfaces under dynamic Brazilian splitting can be effectively identified. The radial roughness index is sensitive to the strain rate and temperature. It shows a linear correlation with the peak splitting strength and the maximum absorbed energy and a linear negative correlation with the peak radial strain. can be used to quantitatively estimate the dynamic parameters based on the models proposed.

Mechanical behavior and failure mechanism of composite layered rocks under dynamic tensile loading

To bolster the safety and efficacy of blasting and impact drilling for underground works in composite rock strata, the dynamic tension of composite rocks requires thorough examination. Given the challenges of composite rock sampling, cement mortars with varying mix ratios are utilized to create composite rock-like test blocks. These blocks are composed of two different strength materials, further processed into differently sized experimental samples as required. Using a split Hopkinson pressure bar (SHPB) test device, we conducted dynamic Brazilian splitting tests at varying incident angles α (the angle between the incident wave direction and the bedding plane) and strain rates on these composite rock-like samples. The modes of crack propagation in some samples were recorded with a high-speed camera. Laboratory tests and PFC2D simulation were used to analyze the dynamic tensile mechanical properties and failure mechanisms of composite rock samples. Findings indicate the dynamic tensile strength of a composite rock sample is governed by the bedding plane inclination angle. As the incident angle rises from 0° to 90°, the dynamic tensile strength of the composite rock sample first decreases, then increases, consistently reaching a minimum value at α = 30°. The damage model of composite rock samples is also influenced by the dip angle of the bedding planes. At α = 0°, the composite rock sample exhibits through-cracks along the incident wave direction and splitting tensile damage is observed. As α increases, the failure mode gradually transitions from splitting tensile damage to a combination of tensile and shear slip damage along the bedding. Tensile damage always manifests in materials of lower strength. When α surpasses 45°, the failure mode reverts from combined damage to splitting tensile damage. Cross-sectional tensile stress clouds generated by PFC software demonstrate that the tensile stress contours at the specimen's center are elliptically distributed, with the ellipse's long axis nearly parallel to the bedding plane.

Tensile mechanical properties and fracture evolution characteristics of sandstone containing parallel pre-cracks under dynamic loading

Parallel cracks have a significant influence on the dynamic tensile failure behavior of rock. The systematic investigation of dynamic tensile mechanical properties and fracture evolution characteristics of fractured rocks are significant for guiding the safe excavation and stability sustaining of rock engineering. Two groups of dynamic Brazilian splitting tests were conducted for the sandstone specimens containing parallel pre-cracks. The influences of crack inclination angle (Group A) and rock bridge length (Group B) on the tensile mechanical properties and fracture evolution characteristics were analyzed. Results showed: the dynamic peak load of pre-cracked specimens is significantly lower than that of intact specimens. The peak load presents a V-shaped evolution trend with the growth of crack inclination angle. Differently, the dynamic peak load increased monotonically with the increasing of rock bridge length. In addition, the crack initiation points move from crack tips to crack walls when the crack inclination angle is increasing. When rock bridge length is large enough, the crack propagation paths are observed near the central axis of specimens. By utilizing the DIC method, six different failure modes are identified to explain the crack initiation and propagation mechanisms under dynamic loading. The tensile-shear fracture modes are mainly presented for specimens with different crack inclinations. Differently, the ultimate failure modes change from tensile-shear mode to tensile mode when the rock bridge length is increasing. In addition, numerical results (ANSYS/LS-DYNA) are in good agreement with the experimental results as a whole, which can verify and explain the experimental results. This study is expected to provide guidance for controlling fractured rock masses.

Quasi-static and dynamic Brazilian testing and failure analysis of a deer antler in the transverse to the osteon growth direction

The transverse tensile strength of a naturally fallen red deer antler (Cervus Elaphus) was determined through indirect Brazilian tests using dry disc-shape specimens at quasi-static and high strain rates. Dynamic Brazilian tests were performed in a compression Split-Hopkinson Pressure Bar. Quasi-static tensile and indirect Brazilian tests were also performed along the osteon growth direction for comparison. The quasi-static transverse tensile strength ranged 31.5–44.5 MPa. The strength increased to 83 MPa on the average in the dynamic Brazilian tests, proving a rate sensitive transverse strength. The quasi-static tensile strength in the osteon growth direction was however found comparably higher, 192 MPa. A Weibull analysis indicated a higher tensile ductility in the osteon growth direction than in the transverse to the osteon growth direction. The microscopic analysis of the quasi-static Brazilian test specimens (tensile strain along the osteon growth direction) revealed a micro-cracking mechanism operating by the crack deflection/twisting at the lacunae in the concentric lamellae region and at the interface between concentric lamellae and interstitial lamellae. On the other side, the specimens in the transverse direction fractured in a more brittle manner by the separation/delamination of the concentric lamellae and pulling of the interstitial lamellae. The detected increase in the transverse strength in the high strain rate tests was further ascribed to the pull and fracture of the visco-plastic collagen fibers in the interstitial lamellae. This was also confirmed microscopically; the dynamically tested specimens exhibited flatter fracture surfaces.

Research of Dynamic Tensile Properties of Five Rocks under Three Loading Modes Based on SHPB Device

The validity of calculating the dynamic tensile strength of rock materials based on dynamic Brazilian tests is problematic. In order to gain a deeper understanding of the effects of three typical loading methods on the damage mechanism of rock specimens in the dynamic Brazilian tests, five different rocks were selected for the study. In the constant incident energy dynamic Brazilian test, the loading modes had a significant effect on the loading rate and dynamic tensile strength of the specimen, with the highest loading rate and tensile strength of the specimens under mode-III loading, followed by mode-I loading and mode-II loading. A high-speed camera and the digital image correlation (DIC) technique were used to successfully capture the rupture process of the Brazilian disc during impact loading. The evolution of the displacement and strain fields of the specimen was obtained by DIC technique, and four typical failure patterns and two rupture characteristics in the dynamic Brazilian test were summarized. The loading mode determined the crack initiation position of the specimen in the dynamic Brazilian test. The results showed that the mode-III loading is the most consistent with the Brazilian test theory, while the mode-II loading violates the test principle.

An experimental investigation on fatigue characteristics of granite under repeated dynamic tensions

Rock engineering is prone to fatigue failure under cyclic disturbances caused by repeated dynamic loadings such as earthquakes, blasting and impacts. These cyclic dynamic loadings could be tensile under repeated implosions , excavation induced unloading and reflection of compressive waves at free surfaces or interfaces. However, compared with cyclic dynamic compression, the rock fatigue characteristics under cyclic dynamic tension remain poorly understood. To investigate the dynamic tensile fatigue characteristics of rock, cyclic dynamic Brazilian tests and direct tension tests were conducted on granite using the split Hopkinson pressure bar and the split Hopkinson tension bar, respectively. The testing results showed that the peak stress of granite decreases, while the peak strain increases with increasing impact number under a given impact stress. The fatigue thresholds of granite in the cyclic dynamic Brazilian and direct tension tests are 0.71 and 0.49 times the critical impact stress, respectively, indicating that the rock is more prone to fatigue failure under dynamic direct tension. The total dissipated energy for fatigue failure of rock increases linearly with fatigue life. The damage accumulation features defined by energy dissipation and strain are distinct, and the damage calculated by strain can display nonlinear characteristics of damage evolution. In addition, with increasing impact stress, the failure surface roughness of the specimens in cyclic dynamic Brazilian tests increases, while that in direct tension tests decreases. The findings in this study could facilitate the understanding of rock fatigue characteristics and provide a basis for stability evaluation and disaster prevention in rock engineering.

Fracturing and AE characteristics of matrix-inclusion rock types under dynamic Brazilian testing

The fracturing properties and acoustic characteristics of heterogeneous and matrix-inclusion rocks are crucial to the safety of underground infrastructures and mining projects under extreme loading conditions. In this study, elliptically shaped matrix-inclusion specimens were fabricated with cement as the matrix and three rock materials (basalt, marble and sandstone) as inclusions which cover igneous, metamorphic and sedimentary rocks with different strength ratios to the cement. Dynamic Brazilian tests were conducted on the specimens with various inclusion orientations β (i.e. angles between impact direction and inclusion major axis) in the range of 0° and 90° using a split Hopkinson pressure bar (SHPB). By combining digital image correlation (DIC) and acoustic emission (AE) techniques, the integrated system demonstrates well-synchronised dynamic forces, DIC strain fields, and AE signals. The detailed procedures were presented to interpret dynamic mechanical properties, fracturing process and AE characteristics of specimens. Generally, for stronger inclusion materials with higher stiffness and strength, dynamic peak forces, threshold orientation angles of transgranular cracks, and AE counts and duration indicate higher characteristics. For instance, the fracture pattern of basalt inclusions transforms from interfacial crack to transgranular crack with increasing orientation angle β, and the specimens with transgranular cracks exhibit higher dynamic peak forces. It is observed that transgranular cracks are mainly induced by tensile stress with a higher AE peak frequency (200–250 kHz), whereas interfacial cracks contain additional shear cracking having a relatively lower peak frequency (100–150 kHz). Meanwhile, finite element modelling demonstrates that stress fields are affected by the elastic mismatch between inclusion and matrix, while failure modes (i.e. interfacial and transgranular cracks) are mainly governed by the tensile strength of inclusions.

Implementation of Johnson-Holmquist-Beissel model in four-dimensional lattice spring model and its application in projectile penetration

• The 4D-LSM is further developed by implementing JHB constitutive model. • The JHB-4D-LSM was verified by modelling Brazilian tests and dynamic spalling tests. • JHB-4D-LSM is applied to study penetration in both thin plate targets and thick B 4 C under various impact velocities. • Good agreement among numerical simulation and numerical/ analytic results demonstrates the capability of JHB-4D-LSM. The imbedded linear constitutive model in four-dimensional lattice spring model (4D-LSM) is not sufficient or accurate enough to solve the dynamic problems with high-speed impacts. In order to produce a more realistic prediction of dynamic fracture process in brittle materials, the capability of four-dimensional lattice spring model (4D-LSM) has been further extended by implementing Johnson-Holmquist-Beissel (JHB) model. This is achieved by defining the micromechanical constitutive model parameters of 4D-LSM through the macro-scale strength parameters in JHB model, with an incremental form of 4D-LSM being developed. The incremental JHB-4D-LSM model is verified by modelling dynamic Brazilian tests and dynamic spalling tests, with good agreement between modelling results by JHB-4D-LSM and theoretical/numerical solutions in literature being obtained. For the demonstration of model application, the proposed JHB-4D-LSM model is applied to simulate and analyse the problems of projectile penetration with various initial impact speeds. Reasonable numerical modelling results indicate that, the proposed JHB-4D-LSM model can be served a promising tool to predict projectile penetration behaviour of brittle materials.

On the use of peridynamics in fracture of ultra-high performance concrete

Experimental and numerical investigations of brittle fracture are of great relevance for many engineering materials. However, numerical methods derived from classical continuum mechanics often encounter difficulties for discontinuities and cracks for unknown paths. Therefore, we employ the theory of peridynamics to study brittle fracture in ultra-high performance concrete. Specifically, we describe the capabilities of peridynamics for the numerical simulation of a dynamic Brazilian test. As a result, a simple bond-based peridynamic formulation implemented in an in-house code compares well to our experimental investigations.

Experimental investigation on the effect of open fire on the tensile properties and damage evolution behavior of granite

The stability of rock mass after fire is a concern of many engineering projects. In this paper, the effects of open fire and different cooling methods on granites were investigated. The static Brazilian test, dynamic Brazilian test, and P-wave velocity test were carried out to evaluate the mechanical properties and damage evolution behavior. A high-speed camera is employed to monitor the failure process of rock. The microstructures of the treated granites were observed by scanning electron microscope (SEM). The results showed that the fire duration and cooling treatment have a significant effect on the P-wave velocity, static nominal tensile strength, and dynamic nominal tensile strength of granite. These characteristics decrease rapidly during 0 to 10 min, and slowly decrease after 20 min. Compared to the air-cooling treatment, the water-cooling treatment has greater damage to the heated granite. To better understand the results, the rapid heating process of open fire heating was simulated using Abaqus software. The results reveal that there is a thinner compressive stress zone at the bottom of the specimen, and there is a large zone in the middle of the sample with higher tensile stress. The crack extension would be expanded due to high tensile stress, leading to the reduction of the tensile strength of the rock. This paper aims to better predict the degree of damage of rock materials after actual fire, as well as preliminarily explore the effect of the fire exposure duration and fire extinguishing method on the tensile properties of rock.

Fracturing behaviours and AE signatures of anisotropic coal in dynamic Brazilian tests

Anisotropy caused by bedding structures has a great effect on tensile properties and fracture behaviours of coal. Acoustic emission (AE) monitoring is a powerful tool in understanding the anisotropy of inherent failure mechanisms. Brazilian disc tests in a split Hopkinson pressure bar (SHPB) system were conducted on coal specimens with bedding orientations β (0°, 30°, 45°, 60°, and 90°) to investigate the damage evolution and AE characteristics. Lead Zirconate Titanate (PZT) sensors were attached on the specimens to monitor AE activities during dynamic fracturing. To obtain complete AE signals, an attenuator formed by a linear resistor was innovatively used in the circuit, which can reduce the power of a signal without distorting its waveform. Meanwhile, two high-speed cameras and the digital image correlation (DIC) technique are synchronously used with AE monitoring to record real-time coal fracturing processes and verify AE results. Results show that the jump of AE energy can be observed when the dynamic load approaches its peak, which indicates the onset of crack growth. The time to fracture tf determined by AE energy against β shows an inverted “V” shape, with the lowest and highest values at β = 0° and 60°, respectively. AE parameters like amplitude, counts and duration are heavily affected by anisotropy, among which AE count-duration relationship can be used to classify different failure modes. Moreover, the influence of anisotropic bedding planes on the evolutions of AE energy with crack growth is quantitatively presented.

Using Artificial Neural Networks to Predict Influences of Heterogeneity on Rock Strength at Different Strain Rates.

Pre-existing cracks and associated filling materials cause the significant heterogeneity of natural rocks and rock masses. The induced heterogeneity changes the rock properties. This paper targets the gap in the existing literature regarding the adopting of artificial neural network approaches to efficiently and accurately predict the influences of heterogeneity on the strength of 3D-printed rocks at different strain rates. Herein, rock heterogeneity is reflected by different pre-existing crack and filling material configurations, quantitatively defined by the crack number, initial crack orientation with loading axis, crack tip distance, and crack offset distance. The artificial neural network model can be trained, validated, and tested by finite 42 quasi-static and 42 dynamic Brazilian disc experimental tests to establish the relationship between the rock strength and heterogeneous parameters at different strain rates. The artificial neural network architecture, including the hidden layer number and transfer functions, is optimized by the corresponding parametric study. Once trained, the proposed artificial neural network model generates an excellent prediction accuracy for influences of high dimensional heterogeneous parameters and strain rate on rock strength. The sensitivity analysis indicates that strain rate is the most important physical quantity affecting the strength of heterogeneous rock.

Microscopic Failure Mechanism Analysis of Rock Under Dynamic Brazilian Test Based on Acoustic Emission and Moment Tensor Simulation

The dynamic tensile failure of rock is a main failure mode in deep underground engineering projects. The microscopic failure mechanism analysis of this failure mode plays a key role in dynamic disaster warning. Moment tensor inversion is a very well-known method used to analyze failure mechanisms. However, an acoustic emission (AE) event cannot be accurately distinguished in rock dynamic experiments at the laboratory scale, because there are hundreds of AE events generated within a few hundred microseconds in one dynamic test. Therefore, moment tensor analysis is rarely applied in rock dynamic tests with laboratory scale. In this paper, AE and moment tensor simulations with the discrete element method (DEM) are introduced to analyze the microscopic failure mechanism of rock under a dynamic Brazilian test. Comparing the simulation results of AE and moment tensor analysis with the simulation results of micro-crack with DEM, the moment tensor discriminant method can obtain the mechanical mechanism and energy level of micro-cracks. Furthermore, R, which is the ratio of isotropic and deviatoric components of the moment tensor, is used to analyze the AE source mechanism. The implosion, shear, and tensile of the AE source mechanism can better explain the evolution process of main axial crack and the shear failure zones of the Brazilian disc specimen under dynamic tensile simulation. These findings contribute to a better understanding of the microscopic failure mechanism of rock under a dynamic tensile test than the statistical types of micro-cracks based on break bonds with DEM.

Influence of free water on dynamic tensile behavior of ultra-high toughness cementitious composites

The influence of free water on the dynamic tensile behavior of UHTCC was studied using the dynamic Brazilian test. The result showed that the moisture content of the saturated UHTCC reached up to 17%–18% due to their porous properties, which have an influence on their strain rate, splitting tensile strength and dynamic increase factor (DIF). Under the same impact pressure, the dynamic tensile strain rate of saturated UHTCC decreased by 25%–41% compared with that of dry ones. The softening effect of water on the quasi-static and dynamic tensile strength of UHTCC was observed in the study, and the softening coefficients of UHTCC were influenced by the strain rate. The immersion of free water led to the improved strain rate sensitivity of UHTCC, however, the increase in DIF after water infiltration is less significant in the UHTCC than in the steel fiber reinforced concrete and normal concrete under the similar strain rate. The mechanism underlying such phenomenon was discussed.

Development of a Numerical Simulator for 3-D Dynamic Fracture Process Analysis of Rocks Based on Hybrid FEM-DEM Using Extrinsic Cohesive Zone Model

The combined finite-discrete element method (FDEM) has attracted significant attention for numerical simulations of complex fracture process of rock-like materials as one of the promising hybrid methods. The mainstream of FDEM simulators developed to date is based on the intrinsic cohesive zone model (ICZM) in which cohesive elements are inserted into all the boundaries of continuum solid elements at the onset of simulations and an artificial elastic behavior must be incorporated to model the intact deformation of rock-like materials. However, the effect of introduction of the artificial elastic behavior on the precision of intact stress wave propagation has not been discussed in previous literatures and this paper discusses this issue. As an alternative for the ICZM-based FDEM, we apply the FDEM based on the extrinsic cohesive zone model (ECZM). An advantage of the ECZM-based FDEM is presented through the 3-dimentional (3-D) numerical modelling of dynamic tension test. In addition, the effect of considering the anisotropy of wave propagation in granite, which has been neglected in all the previous works using FDEM, is investigated through the ECZM-based 3-D FDEM simulation of dynamic Brazilian test with a split Hopkinson pressure bar apparatus. Through the presented numerical simulations, it can be concluded that the ECZM-based FDEM may be an alternative for numerical simulations of complex dynamic fracture process of rock-like materials instead of the ICZM-based FDEM.

Contribution of steel fiber on the dynamic tensile properties of hybrid fiber ultra high toughness cementitious composites using Brazilian test

A series of quasi-static and dynamic Brazilian tests were conducted in this study to investigate the influence of steel fiber (SF) on the dynamic tensile behavior of hybrid fiber ultra-high toughness cementitious composites (UHTCCs). Four different kinds of hybrid fiber UHTCCs were prepared with different SF content, but the polyvinyl alcohol (PVA) fiber content remained as 2%. Under quasi-static tensile loading, the composites with 0.5% SF exhibited the highest energy dissipation approximately 2.9 times that of the composites with 1.5% SF. However, the composites with 1.5% SF was recommended to resist the dynamic tensile loading with the highest dynamic tensile strength and energy dissipation among the four composites. The increase in SF content improved the dynamic tensile strength and energy dissipation of hybrid fiber UHTCC, and their contribution was influenced by the strain rate. Based on the high speed image investigation, the crack velocity in the UHTCC increased with the strain rate, which led to the strain rate effect on the various micromechanical parameters of the fiber tension and pullout. By comparing the dynamic tensile behavior of hybrid fiber UHTCC and ultra-high performance concrete (UHPC), it was found that the dynamic energy dissipation of UHTCC were similar with that of UHPC under the same impact loading, although their dynamic tensile strength was 59%–73% of UHPC.

Fracture Characteristics of Orebody Rock with Varied Grade Under Dynamic Brazilian Tests

In mining engineering, the grade of the orebody significantly influences mining activities. Typically, the grade of completed mine sequences can be used to estimate the yearly mine’s production and profit. However, the strength of orebody varies in different parts of the mine, as demonstrated by the requirement for different blast design. The degree of rock fragmentation cannot be accurately predicted after production blasts; in addition, secondary breakage of oversized rock affects the mining plan. In this study, split Hopkinson pressure bar tests were conducted to obtain the dynamic tensile strength and fracture energy of orebody rock having different grades. The fracture surfaces were obtained using a 3D scanner and surface roughness was estimated on the basis of fractal dimensions. The failure process of ore rock was reproduced through the flat-joint model (FJM) in PFC2D on the basis of microscopic and macroscopic images of the fracture surface using a special FJM structure. Physical experiments and numerical simulations indicated that the mechanical properties and fracture characteristics of the orebody rock vary with its grade. This difference should be considered during mining activities, specifically in blast and draw point designs.

Static and Dynamic Brazilian Tests on Layered Slate considering the Bedding Directivity

A layered rock usually exhibits strong anisotropy due to its layered structure. In order to study the anisotropic effect on its static and dynamic tensile properties, a medium strength anisotropy slate is chosen and tested in five groups of bedding plane dip angles. The dynamic tests were carried out by a split Hopkinson pressure bar (SHPB), and the failure process of rock samples is recorded by a high‐speed camera. The failure mode and strength characteristic of the slate are analyzed. The static test results show that layered structure significantly affects the failure mode, and the influence of the bedding plane depends on the degree of anisotropy. The static and dynamic “tensile strength” exhibit the “U” type strength anisotropy. For samples in the same dip angle group, the “tensile strength” shows clear dynamic strengthening effect, and the growth rate is most significant at θ = 45°.