Flattened Brazilian Disc Research Articles

Experimental and numerical study on the dynamic mode III fracture behaviors of rock using an axially notched flattened Brazilian disc in SHPB tests

The dynamic mode I and mode II fracture of rock have been widely investigated over the past decades. However, the lack of dynamic mode III fracture testing method and the rare understanding of mode III fracture mechanism of rock remain a significant knowledge gap in the realm of rock mechanics. In this work, an innovative axially notched flattened Brazilian disc (ANFBD) sample is proposed for the mode III fracture tests of rocks using the split Hopkinson pressure bar (SHPB). Firstly, the optimal geometrical dimension of the ANFBD sample for achieving true mode III fracture of rocks is comprehensively discussed using finite element method (FEM) analysis. Then, the reliability of ANFBD-SHPB method is experimentally verified through dynamic mode III fracture experiments on the Fangshan marble (FM). Laboratory experimental results show that the mode III fracture toughness (KIIId) values of FM are approximately 2.8 times of the mode I fracture toughness (KId) values at similar dynamic loading rates. Post-mortem examinations on the fracture surfaces show that the famous facet coarsening mechanism in mode III fracture is suppressed under high loading rates. Furthermore, insightful assessments regarding the inner progressive fracturing behaviors of the ANFBD sample are given by virtue of three-dimensional discrete element method (DEM) simulation. Moment tensor (MT) analysis indicates that the shear fracture mechanism mainly dominates the whole failure process of the ANFBD sample, while the tensile fracture mechanism slightly increases during the facet coarsening process. These results are of significant importance for revealing the failure mechanism of rock under dynamic mode III loading and give some beneficial implications for natural strike-slip fault structures.

Dynamic mode II fracture mechanism of rocks using a novel double-edge notched flattened Brazilian disc specimen in the split Hopkinson pressure bar tests

The dynamic mode I fracture behaviors of rocks have been extensively investigated during recent decades, while the dynamic mode II fracture mechanism of rocks and its comparison with dynamic mode I fracture are poorly understood. In this study, a novel double-edge notched flattened Brazilian disc (DNFBD) specimen is introduced for dynamic mode II fracture toughness tests of rocks in the split Hopkinson pressure bar (SHPB) tests. First, using the finite element method (FEM), the stress distribution of the DNFBD specimen is analyzed and the stress intensity factors (SIFs) and the T-stress at the crack tips are determined. Then, dynamic mode II fracture tests are conducted on sandstone using the DNFBD specimen with proper specimen geometry configuration. High-speed photography and digital image correlation (DIC) results show that the shear crack initiates from the notch tips and propagates along the shear ligament of the DNFBD specimen, which demonstrates the reliability of the DNFBD-SHPB method for dynamic mode II fracture tests of rocks. Experimental results show that the dynamic mode II fracture toughness KIIC of rocks generally increases with increasing loading rate, exhibiting significant loading-rate dependence. For comparative investigation, dynamic mode I fracture tests using the notched semi-circular bend (NSCB) specimen are conducted on the same rocks. The results indicate that the mode II fracture toughness KIIC values are always higher than the mode I fracture toughness KIC values of rocks over a wide range of loading rates. The microscopic fracture mechanism of sandstone is interpreted based on the thin section observations. Under quasi-static loading, trans-granular (TG) fractures are more popular in the mode II fracture tests, while inter-granular (IG) fractures dominate the failure of mode I fracture. However, with the increase of loading rate, TG fracture becomes increasingly prevalent in both the dynamic mode II fracture and the dynamic mode I fracture of rocks. The results of this study are of great significance for understanding the dynamic mode II fracture mechanism of rocks.

The incurved Brazilian disc as an alternative to the standardized Brazilian disc test

A modified configuration of the standardized Brazilian disc is proposed here, namely the incurved Brazilian disc, aiming to address the main drawback of the traditional indirect tensile test introduced by Carneiro and Akazawa (broadly known as the Brazilian disc test), namely the onset of fracture from the disc-jaw contact region rather than from the center of the disc. In this context, the disc is circularly truncated in the vicinity of the disc-jaw contact area, leading, in fact, to a wide, and as it is seen predefined contact length. The wide extent of the contact arc ensures small stress concentrations, while its predefined length ensures independence of the outcomes of the tests from material and geometry. The incurved Brazilian disc is compressed between the flat loading platens with the aid of two semicircular indenters, which will completely fit into the cavities of the disc under load. The analytical solution of the described configuration is obtained using Muskhelishvili’s complex potentials method. Comparison of the results of the present analysis concerning the stress and displacement fields with the respective ones due to existing solutions for the traditional Brazilian disc as well as with those of the flattened Brazilian disc, reveals interesting aspects of the modified configuration proposed, enlightening some advantages, concerning mainly the intensity of the stress field in the disc-jaw contact area.

Numerical modeling of cracking behaviors for the rock-inclusion composite under dynamic tensile loading

Rock-inclusion composites have been widely used in underground engineering, however, the impact of inclusions with varying physico-mechanical properties, such as the strength ratio and size, on cracking behaviors under dynamic tensile loading is still unclear. In this study, using a discrete element method (DEM), a series of numerical simulations are performed on the flattened Brazilian disc (FBD) specimens to simulate the split Hopkinson pressure bar (SHPB) tests. The numerical results indicate that both the inclusion size and strength ratio can influence dynamic responses of a rock-inclusion composite. In specimens with weak inclusions, the nominal tensile strength (NTS) value is proportional with the strength ratio but negatively correlated with the inclusion size. Strength ratios are primarily responsible for determining three failure modes in specimens. During the loading process, the characteristics of acoustic emission (AE) events generated from the microcracks in specimens are analyzed in terms of moment magnitude, failure mechanism, b-value, and frequency-magnitude distribution. Additionally, energy partitions evolve synchronously with cracking behaviors in specimens, and all the loading systems show a similar trend of energy conversion. This study may provide a promising DEM model for exploring dynamic tensile failures in rock-inclusion composites and explaining the complicated cracking behaviors in underground engineering.

The actual boundary conditions in the Flattened Brazilian Disc test

In the present study an attempt is made to assess a recently presented analytical approach to the problem of the contact stresses developed along the Flattened Brazilian Disc (FBD) – loading platen interface, during the implementation of the homonymous test. In this direction, a finite element model was constructed, resembling both the FBD and the platen, using the commercially available software ABAQUS. As it is seen, the predictions of the numerical analysis for the stresses induced at the interface and inside FBD are in a satisfactory agreement with the analytical ones, justifying the proposed analytic approach for the FBD configuration. In this context, it is concluded that FBD does significantly reduce the stress severity at contact region, however, the end points of the flat edges of the FBD now become points of increased stress magnitudes so that care should be taken during the preparation of the specimens regarding the cutting process at these points.

Analysis of Optimal Loading Angle in Dynamic Flattened Brazilian Disc Splitting Test for Concrete

The mechanism of crack expansion in conventional Brazilian discs is clearly obtained with the help of numerical simulations, and the direction of crack expansion is related to the loading speed. Then the relationship between the stress field and the platform angle was given quantitatively based on the theoretical analysis. To obtain the accurate tensile strength of self-compacting concrete under the premise of numerical simulation and theoretical analysis, flattened Brazilian disc (BD) splitting tests with six loading angles were carried out by using the split Hopkinson pressure bar (SHPB) loading system. The crack initiation mode and fracture propagation mode of specimens under different loading angles and loading rates were analyzed through digital image correlation (DIC) and strain gauges. When the loading angle lies between 28° and 30°, the specimens easily meet the requirement of central cracking under high loading rates. The experimental results were well explained with theoretical analysis from a view of dimensionless Griffith’s equivalent stress. The dynamic tensile strength measured from the non-central crack mode in flattened BD splitting tests underestimates the inherent dynamic tensile strength.

Fracture characteristics of sustainable crumb rubber concrete under a wide range of loading rates

The dynamic mechanical properties of concrete materials significantly influences the safety of construction under impact loads. In this study, a comprehensive experiment on the crack straight-through flattened Brazilian disc specimens of crumb rubber concrete (CRC) is undertaken. Three specific experiments were performed to obtain the wide loading-rate ranges of fracture characteristics, i.e., the quasi-static test, drop-hammer impact test, and split Hopkinson pressure bar test. The measured and calculated results are also discussed. The results reveal that the fracture toughness and energy are both positively correlated with loading rate. Moreover, a transition loading rate (around 1 GPa × m1/2/s) exists between the high and low loading rates, and the enhancing effect of high loading rate on fracture toughness cannot be neglected. The analysis of the dynamic increased factor (DIF) on the fracture toughness (DIFk) and fracture energy (DIFg) of CRC shows that DIFk and DIFg are related to the rubber content. Furthermore, the analysis demonstrates that crumb rubber particles can enhance the crack resistance of concrete under dynamic loads. Accordingly, empirical models for the DIFk and DIFg of CRC are proposed based on the experimental data. In addition, the mechanisms by which the loading-rate affects the fracture characteristics were preliminarily identified by observing the failure modes under various loading-rate loads. This study is intended to help spread the application of crumb rubber in concrete materials.

Tensile mechanical behavior and fracture characteristics of sandstone exposed to freeze-thaw treatment and dynamic loading

Rock masses in high-elevation or cold areas are vulnerable to the joint results of freeze-thaw (F-T) action and dynamic loading, it is thus significant to evaluate the tensile mechanical behavior and fracture characteristics of F-T treated rocks under dynamic loading. In this study, based on the split-Hopkinson pressure bar (SHPB) device, the dynamic flattened Brazilian disc (FBD) tests are performed on sandstone to investigate the degradation mechanism of dynamic tensile response and fracture characteristics of rock induced by F-T treatment. Recur to high-speed photography and digital image correlation (DIC) technique, 3D scanning and scanning electron microscope (SEM), the macroscopic and microscopic fracture characteristics of F-T treated sandstone are comprehensively observed and discussed. Experimental results show that the dynamic tensile strength of sandstone constantly decreases with increasing F-T cycles at a specified loading rate. The failure mode of FBD specimen gradually transforms from slash mode to ‘Y’-shaped mode and then to ‘X’-shaped mode with increasing loading rates. 3D scanning results show that the roughness of the central fracture surface of FBD specimen decreases with increasing loading rate or freeze-thaw cycles. Furthermore, both microscopic tensile and shear fracture patterns are observed by SEM, and it is found that the trans-granular (TG) fracture become more prevalent under higher loading rate or higher freeze-thaw cycles. In addition, some hidden connection between microscopic fracture mechanism and macroscopic mechanical properties of F-T treated sandstone is analyzed and discussed.

Discrete element modeling of rock-concrete bi-material discs under dynamic tensile loading

As the most fragile component in a bi-material, the performance of the rock-concrete interface can greatly affect the stability and durability of the concrete structures founded on the rock masses. In this study, a range of numerical simulations using the discrete element method (DEM) have been conducted to identify the failure mechanism and mechanical property of the rock-concrete bi-materials under the dynamic flattened Brazilian disc (FBD) tests using the modeled split Hopkinson pressure bar (SHPB) system. There are four groups of bi-material specimens that differ in the aspects of rock type (i.e. limestone and sandstone), interface inclination (i.e. 0°, 15°, 30°, 45°, 60°, 75°, and 90°), and specimen configuration (i.e. intact and hollow). The numerical results show that the nominal tensile strength depends on the rock type, and the intact specimen has a higher loading capacity than that of the hollow specimen. The failure modes are classified into three main types in intact limestone-concrete bi-materials according to the degree of the interface angle, which is in good agreement with the previous experimental results. Such transition from interface failure to tensile failure can be observed as well in the bi-material specimens with a hole inside, while the varying inclination angle has a minimal effect on the failure pattern of the sandstone-concrete bi-material specimens. The cracking process of the specimens is visualized using the evolution of acoustic emission (AE) activities. The moment tensor inversion interprets that more energy is required for cracks to propagate from concrete to limestone. The overall AE magnitude is the lowest in limestone-concrete specimens with a pre-cut opening due to the deteriorated specimen bearing capacity.

Revisiting the flattened Brazilian disc configuration - Part I: The actual boundary conditions

In a recently presented analytic solution for the Flattened Brazilian Disc (FBD), it was shown that under the usually adopted assumption of uniform pressure on the flat edges of the FBD these edges turn to appear bent after deformation. Taking into account the high rigidity and flatness of the loading platens this bent sounds somehow unnatural. In the present study an attempt is undertaken to confront this unnatural bent by considering alternative non-uniform stress distributions on the flat edges of the FBD. In this context, the present paper, which is the first part of an ongoing research project, deals with the 1st fundamental problem for a FBD when it is compressed between two rigid flat stamps of the same length with the flat edge of the FBD. The distribution of the normal compressive stresses, and that of the respective frictional ones, imposed to the flat edge of the FBD are adopted from the approach of Muskhelishvili for the contact problem of a rigid flat stamp compressed against an elastic half plane, here the FBD in question. After obtaining the complex potentials for this 1st fundamental problem for the FBD, the stresses and the displacements are calculated in closed form everywhere on the FBD’s cross section. For the assessment of the analytic solution, a numerical model is also developed, with the aid of the Finite Element Method. The agreement between the theoretical and numerical analyses is satisfactory.

The Effect of Loading Rate on Fracture Toughness of Concrete using Type I Fracture Toughness Test Flattened Brazilian Disc (FBD) Mode

Mining activities in open pit and underground mines will always be associated with rock breaking or stripping activities (both mechanical and blasting), so that this can affect the structure and strength of rocks. The strength of the rock is strongly influenced by the presence of initial cracks (pre-existing cracks) and rock anisotropy conditions associated with discontinuous plane conditions. Fracture mechanics is a science that illustrates how a fracture can occur and propagate during applied stress on material. The main parameter in fracture mechanics is called fracture toughness which shows the resistance of the material to propagate the crack. There are several mode in determining type I fracture toughness, one of which is type I fracture toughness Flattened Brazilian Disc (FBD) mode. Type I fracture toughness test is carried out using a compression machine in a laboratory and is conducted on concrete samples consisting of 3 (three) various samples, with a ratio of cement and sand composition of 1:1, 1:2, and 2:1. This test also uses different loading rate values, namely 2.50 mm/min, 2.70 mm/min, and 2.83 mm/min. The results of the type I fracture toughness value from each loading rate will be compared to determine the effect of the loading rate on the value of type I fracture toughness. The obtained fracture toughness value is also related to the physical and mechanical properties of the samples. Based on the results of tests, it can be seen that the loading rate affects the value of fracture toughness, the increase in fracture toughness value is followed by the higher loading rate. In addition, it can be seen that the fracture toughness value is directly proportional to the uniaxial compressive strength value and the indirect tensile strength value. The average correlation value obtained is R2 = 0.9884 (indicating a strong relationship).

The Structuring and Empowerment Policy of Losari Beach Street Vendors Based on The Concept of Smart City

Mining activities in open pit and underground mines will always be associated with rock breaking or stripping activities (both mechanical and blasting), so that this can affect the structure and strength of rocks. The strength of the rock is strongly influenced by the presence of initial cracks (pre-existing cracks) and rock anisotropy conditions associated with discontinuous plane conditions. Fracture mechanics is a science that illustrates how a fracture can occur and propagate during applied stress on material. The main parameter in fracture mechanics is called fracture toughness which shows the resistance of the material to propagate the crack. There are several mode in determining type I fracture toughness, one of which is type I fracture toughness Flattened Brazilian Disc (FBD) mode. Type I fracture toughness test is carried out using a compression machine in a laboratory and is conducted on concrete samples consisting of 3 (three) various samples, with a ratio of cement and sand composition of 1:1, 1:2, and 2:1. This test also uses different loading rate values, namely 2.50 mm/min, 2.70 mm/min, and 2.83 mm/min. The results of the type I fracture toughness value from each loading rate will be compared to determine the effect of the loading rate on the value of type I fracture toughness. The obtained fracture toughness value is also related to the physical and mechanical properties of the samples. Based on the results of tests, it can be seen that the loading rate affects the value of fracture toughness, the increase in fracture toughness value is followed by the higher loading rate. In addition, it can be seen that the fracture toughness value is directly proportional to the uniaxial compressive strength value and the indirect tensile strength value. The average correlation value obtained is R2 = 0.9884 (indicating a strong relationship).

Design of Groundwater Sustain Irrigation Network System in Panca Lautang Area, Sidrap Regency, South Sulawesi

Mining activities in open pit and underground mines will always be associated with rock breaking or stripping activities (both mechanical and blasting), so that this can affect the structure and strength of rocks. The strength of the rock is strongly influenced by the presence of initial cracks (pre-existing cracks) and rock anisotropy conditions associated with discontinuous plane conditions. Fracture mechanics is a science that illustrates how a fracture can occur and propagate during applied stress on material. The main parameter in fracture mechanics is called fracture toughness which shows the resistance of the material to propagate the crack. There are several mode in determining type I fracture toughness, one of which is type I fracture toughness Flattened Brazilian Disc (FBD) mode. Type I fracture toughness test is carried out using a compression machine in a laboratory and is conducted on concrete samples consisting of 3 (three) various samples, with a ratio of cement and sand composition of 1:1, 1:2, and 2:1. This test also uses different loading rate values, namely 2.50 mm/min, 2.70 mm/min, and 2.83 mm/min. The results of the type I fracture toughness value from each loading rate will be compared to determine the effect of the loading rate on the value of type I fracture toughness. The obtained fracture toughness value is also related to the physical and mechanical properties of the samples. Based on the results of tests, it can be seen that the loading rate affects the value of fracture toughness, the increase in fracture toughness value is followed by the higher loading rate. In addition, it can be seen that the fracture toughness value is directly proportional to the uniaxial compressive strength value and the indirect tensile strength value. The average correlation value obtained is R2 = 0.9884 (indicating a strong relationship).

A wing-crack extension model for tensile response of saturated rocks under coupled static-dynamic loading

Saturated rocks, widely existing in various deep underground engineering, are likely to be encountered coupled static-dynamic loading. It is thus vital to acquire the combined effect of water saturation and static pre-tension on the dynamic tensile strength, and establish a reasonable crack extension model for describing the fracturing mechanism of saturated rocks under coupled static-dynamic tension. In this study, from the perspective of meso-mechanics, the relationship between pore water pressure and static pre-tension loading are first deduced, and then the analytic solution of stress field of elliptical crack orifice under coupled pore water pressure and far-field stress is solved using complex function. The effect of pore water pressure is considered into Griffith theory, and the most dangerous fracture azimuth angle of elliptical crack in rocks under combined far-field stress and pore water pressure are determined. Second, the length of fracture process zone of initial crack in saturated rocks under static pre-loading is estimated based on Schmidt's maximum tensile stress criterion. Finally, a wing-crack extension model is proposed to analyze the dynamic fracturing behavior of saturated rocks under pre-tension, and the theoretical calculation formula for tensile strength of saturated rocks under combined static-dynamic loading is obtained. To validate this new model, nine coupled static-dynamic tension tests with different pre-static loading ratio are performed on saturated flattened Brazilian disc (FBD) specimens, in virtue of the split Hopkinson pressure bar (SHPB) specialized with an axial confining apparatus. A rational consistency is observed between the experimental and theoretical results in terms of the dynamic tensile strength of saturated rocks.

Efficient Investigation of Rock Crack Propagation and Fracture Behaviors during Impact Fragmentation in Rockfalls Using Parallel DDA

The study of the rock crack propagation and fracture behaviors during impact fragmentation is important and necessary for disaster evaluation of rockfalls. Discontinuous Deformation Analysis (DDA) incorporating virtual joints can offer a powerful tool to solve such a problem. In the analysis process, the computational efficiency is critical because the mesh must be very dense to make crack propagation more realistic. Thus, parallel DDA using OpenMP is applied. The flattened and precrack Brazilian disc tests are first reproduced, respectively, to verify the accuracy and efficiency of the parallel DDA with virtual joints. Then, the impact fragmentation process is simulated and validated with corresponding laboratory experiments in terms of crack propagation results. Furthermore, the effects of joint-slope angle, joint connectivity rate, and impact velocity on rock fracture behaviors are investigated. It is concluded that the peak number of cracks occurs when the joint-slope angle ranges between 30° and 45°; the higher impact velocity and joint connectivity rate tend to cause more cracks and larger damages to the specimen.

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

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.

Experimental and numerical study on the dynamic fracture of flattened Brazilian discs with prefabricated cracks

A split Hopkinson pressure bar system was used to apply a high-speed dynamic load to a flattened Brazilian disc, and the dynamic characteristics of purely type-I or -II fractures or mixed type-I-II composite fractures were studied in detail. The effect of the strain rate and the inclination angle of the prefabricated cracks was analyzed and compared with theoretical results. Furthermore, a dynamic three-dimensional numerical model was developed on the basis of the mesoscopic nonuniform distribution of materials. The failure process, failure pattern and acoustic emission performance of the disc were observed step by step in the numerical simulation. The experimental and numerical results were in good agreement and showed that the strain rate and inclination angle affected the strength, failure pattern and toughness of the dynamic fracture. This study contributes to numerical simulation in which the failure process of secondary cracks was well presented by introducing mesoscopic nonuniformity into the model.

New insights into the fracture mechanism of flattened Brazilian disc specimen using digital image correlation

As a simple and convenient testing method, the flattened Brazilian disc (FBD) specimen has been widely used to determine the tensile strength and mode-I fracture toughness of rocks. However, the precision of the mechanical parameters calibrated by FBD testing method needs to be further evaluated. In this paper, digital image correlation (DIC) technique is used to capture the progressive failure process of FBD specimen, and some new insights are provided for further understanding the fracture mechanism of FBD specimens. Firstly, the horizontal tensile strain history in the center region of FBD specimen is obtained via DIC technique, and combined with loading force history, the tensile stress–strain curve of rocks can be determined. Then, by analyzing the horizontal strain and displacement field near the central crack of FBD specimen, the central crack tip positions are identified. The progressive failure process of FBD specimen shows that the micro-crack and fracture process zone (FPZ) has grown at the center of FBD specimen at the moment of first peak force Pmax. After the Pmax, the central crack propagates unsteadily towards the flattened ends of FBD specimen, while is hindered after the loading force declined to the local minimal force Pmin. Therefore, it is not proper to determine the mode-I fracture toughness KIC using the local minimal force Pmin in FBD tests. In this study, a modified calculation method to determine KIC is proposed using the first peak force Pmax and its corresponding central effective crack length observed via DIC technique. In addition, the cracking nature of the secondary crack is identified, and the second rise of the loading force is induced by the compression-shear failure near the flattened ends of FBD specimen. These results are beneficial to better understanding the progressive fracture mechanism of FBD specimen and improving the accuracy of KIC calibrated by FBD testing method.

Influence of Disc Specimen Configuration on Its Three-Dimensional Dynamic Stress Balance

In order to investigate the dynamic stress balance of different configurations of rock specimens, three-dimensional finite element models of SHPB were established. Five types of configuration disc specimens with a diameter of 75 mm and a thickness of 30 mm were impacted at a speed of 5 m/s using a special-shaped bullet. The propagation laws of stress wave on the contact surface of the specimen-bar and the inside of the specimen were analyzed, and the time history of the stress balance factors at different positions of the specimen was obtained. The results show that the amplitudes of the transmitted waves corresponding to the five types of disc specimens with different configurations have obvious differences, and the stress propagation in the specimen has three-dimensional characteristics. According to the ease of achieving stress balance, the five configuration specimens are ordered by notched semicircular bending disc, flattened Brazilian disc, cracked straight-through flattened Brazilian disc, Brazilian disc, and cracked straight-through Brazilian disc specimen. Among them, only the first three configurations of the specimen reached the stress balance. The dynamic stress balance is affected by the disc loading mode, end contact conditions, the presence of prefabricated cracks, and disc thickness. In addition, as the disc loading end is a processed platform, it is beneficial to achieve stress balance. Prefabricated cracks are not conducive to achieving stress balance. The loading method of the notched semicircular bending disc is more conducive to achieving stress balance. This research has a certain guiding significance for selecting suitable specimen configuration and research methods to carry out rock dynamic fracture experiments.

Dynamic splitting tensile behaviours of distilled-water and river-water ice using a modified SHPB setup

The tensile strength of ice subjected to dynamic loading constitutes many ice engineering applications such as ice blasting and hail-aircraft impact. In this study, the dynamic tensile behaviours of distilled-water and river-water ice were firstly investigated using the flattened Brazilian disc method with a modified split Hopkinson pressure bar system. Columnar freshwater ice samples were tested at strain rates ranging from 20 to 135 s−1 and temperatures ranging from −5 to −45 °C. The effects of impact velocity, loading rate, and ice sample thickness on the dynamic splitting tensile strength were also explored. Distilled-water ice specimens exhibited a higher indirect tensile strength than their river-water counterparts. The lower the temperature, the greater is the tensile strength, particularly in the case of distilled-water ice in the strain rate range of 89–135 s−1. The temperature had less effect on the dynamic tensile strength of distilled-water ice compared to the loading rate, and the specimen thickness had little effect on the dynamic indirect tensile strength. A large number of non-penetrating cracks were observed on the disc surface, indicating the inhomogeneous distribution of the tensile stress interpreted based on the 3D Brazilian disc theory. The closer the two end faces in the central cross section, the greater the tensile stress. The presence of single and multiple strip cracks on the splitting surface were discovered, possibly because of the instant expansion of the ice specimen and subsequent formation of mode-I cracks in the thickness direction.