Tensile Splitting Failure Research Articles

Dynamic properties and failure mechanism of granite with non-persistent joints subjected to impact load

A Split-Hopkinson pressure bar was used to carry out a series of impact tests on prefabricated granite specimens containing joints with different inclination angles and at different joint persistency values. The results were used to determine the degradation effect of the non-persistent joints on the specimens and investigate the failure mechanism of the granite subjected to impact load. The effect of varying the length and inclination angle of the joint on the dynamic characteristics of the granite was systematically analyzed based on a consideration of the specimens’ dynamic mechanical properties. A continuum-discrete coupled model was subsequently established based on the results of the laboratory tests and used to investigate the failure mechanism and crack propagation behavior occurring on a microscopic scale. The results show that the geometric parameters of the joints and the loading rate have a significant effect on the dynamic response of the granite. Moreover, there is a good power function relationship between the dynamic increase factor and loading rate of the prefabricated jointed rock specimen when the loading rate is low to medium. As the inclination angle of the joint increases, the failure mode of the specimen transitions from tensile splitting failure → mixed tensile–shear failure → main shear failure → micro-damage failure. As the penetration of the joint increases, the failure mode of the specimen evolves from micro-damage failure → tensile splitting failure → mixed tensile–shear failure. When subjected to uniaxial impact loading, the main cracks in the jointed rock specimen are usually wing cracks and coplanar cracks. Anti-wing cracks are not generated by themselves but appear alongside other cracks as a supplementary means of achieving stress release. The present results offer a sound basis for evaluating the stability of jointed rock mass under the dynamical loading.

Damage characteristics of weak rocks with different dip angles during creep

To investigate the influence of the weak layer dip angle on the creep rupture of the composite rock mass, this paper conducts a graded loading creep experiment on the composite rock mass with different dip angles using the acoustic emission method to examine the fracture evolution process. With increasing load grade, the cumulative total ring count of the rock mass shows a “U”-shaped trend, and the acoustic emission spatial positioning results show that acoustic emission events in the rock mass fracture process are primarily concentrated in the vicinity of the weak layer, while events in other areas are few and dispersed. For rock masses with weak layer dip angles of 0° and 15°, cracks occur in both soft and hard rocks, where shear cracks are dominant in soft rocks, tensile cracks are dominant in hard rocks, and finally, the rock mass mainly exhibits tensile splitting failure. For rock masses with weak layer dip angles of 30° and 45°, most of the cracks exist in the interior of the soft rock, which is dominated by shear cracks. With increasing graded loads, the shear cracks continue to develop along the direction of the weak layer, the upper rock mass keeps slipping and dislocating, and the final failure mode is mainly shear-slip failure. The damage evolution varies with the inclination angle of the weak layer, which can be divided into three stages: initial damage accumulation, damage acceleration, and damage destruction. This demonstrates the ability to predict, prevent, and control the occurrence of creep disasters in rock masses with weak layers.

Fracturing evolution and strain characteristics of layered rock-like materials with rough interfaces

Layered rock-like samples containing saw-tooth interfaces of various joint roughness coefficients (JRC) and included angles were conducted uniaxial compression with the loading rate of 0.005 mm/s. The peak stress declines from 38.36–39.90 MPa to 17.35–30.67 MPa for included angle = 15°–60°, and then increases to 24.30–33.83 MPa for 60°–75°, but the peak strain decreases by 22.39%–41.30%. For JRC = 0–19.55, mechanical properties of samples are enhanced, while the anisotropy weakens. When the included angle is small (15°, 30°), the layered samples show a typical tensile splitting failure crossing the weak interlayers. For a large included angle of 45°–75°, failure modes are featured by shear sliding along weak interlayers combined with tensile splitting. As JRC increases, fracturing mechanism transition from shear sliding to mixed tension shear failure then to tensile splitting can be identified. With an increase in JRC or included angles, the global lateral strain of samples in plastic deformation stages changes from “sudden increase” to “progressive increase” to “jump increase”. For included angle = 15°, the layered sample produces dramatic lateral local strain at the weak interlayers due to tensile splitting failure. For included angle = 45°, both axial and lateral local strains at the weak interlayers show an obvious increase at the main shear failure surface. For a large included angle of 75°, the lateral local strain remarkably increases at the weak interlayers along with tensile failure of samples.

Experiment and numerical simulation study of dynamic mechanical behavior of granite specimen after high temperature treatment

The dynamic compression experiments were conducted on granite specimens after high-temperature treatments by using split Hopkinson pressure bar test system. Subsequently, we collected the granite fragments after impacting, and the fragmentation characteristics were evaluated by the fractal dimension and average fragment size. Finally, combined with the numerical simulation results, we investigate the law of crack propagation during dynamic compression. The results show that the change in physical properties such as bulk density and mass of granite are closely related to the temperature. Microcracking occurred on the surface of granite when the temperature is 900℃. Dynamic peak strain and strain rate increased with the increase of temperature, while the peak strength and elastic modulus decreased. Additionally, the fractal dimension and average fragmentation size are closely related, and the relationship is negatively linear. The fractal dimension and average fragmentation size increase and decrease with the temperature, respectively. By combining the experimental and numerical results, we observed that the crack initially appears on the surface of the rock and then gradually propagates to the interior under impact loading. The rupture surface of granite fragmentation is approximately parallel to the axial direction and the ultimate failure mode mainly comprises the axial tensile splitting failure.

MODELING PULL-OUT BEHAVIOR OF THE DEFORMED REBAR EMBEDDED INSIDE THE REINFORCED CONCRETE

This study presents the modeling of the pull-out behavior of deformed bars embedded inside the reinforced concrete element. The simulation uses an in-house finite element package called 3D-NLFEA. Sufficiently small solid elements that consider the frictional resistance and mechanical interlocking between the bar thread and the concrete matrix were used in the simulation. The effect of concrete compressive strength, cover thickness, and stirrup configuration on the pull-out capacity of the modeled specimens are investigated thoroughly. The modeling found out that the 3D-NLFEA package can capture the bond-fracture process at the interface between the bars and concrete. The fracture that occurs in the concrete was dominated by tensile splitting failure. The presence of stirrups that confined the concrete and restrained the crack propagation significantly influences the pull-out capacity, cracking pattern, and failure behavior at the bar interface with the concrete. The analysis results from 3D-NLFEA are also compared with the 3D-RBSM analysis results available in the literature. From the comparison between the two packages, it can be concluded that the analysis result from 3D-NLFEA is somewhat more conservative compared to the 3D-RBSM.

Experimental investigation on mechanical properties and failure mechanism of rock-like specimens containing an arc-shaped ice-filled flaw under uniaxial compression

The study of rock mass properties under low-temperature conditions is an important basis to ensure the stability of engineering in alpine regions and the safety of engineering construction using low-temperature technology. In order to investigate mechanical properties and failure mechanism of water-saturated fractured rocks at low temperature, indoor tests of rock-like specimens with an arc-shaped ice-filled flaw (Type-I) under uniaxial compression were performed in this paper, and the results were compared with those of flawed specimens Type-II (at 25 ℃ and without filled ice in the flaw). The results indicated that low temperature, flaw morphology and the presence of ice-filled flaw have significant effects on the mechanical properties. The overall peak stresses of Type-I specimens were larger than those of Type-II specimens, and the plasticity of the former one was significantly higher compared with that of the latter one. Meanwhile, the existence of filled ice resulted in significant differences in the failure characteristics between two types of specimens. The failure forms of Type-I specimens were dominated by tensile-splitting failure, while the failure forms of Type-II exhibited a tendency of varying with the flaw morphology. Combined with the macroscopic test phenomena, a water migration mechanism of water-saturated Type-I specimens was proposed, and the failure mechanism with the effect of frost heaving force under uniaxial compression was further analyzed in this paper.

Mechanical properties and rockburst proneness of phyllite under uniaxial compression

To investigate the influence of the bedding angle, β,on the mechanical properties and rockburst proneness, uniaxial compression tests were conducted using cylindrical phyllite specimens with different bedding angles. According to the results, the peak stress, peak strain, cumulative acoustic emission counts, and potential energy of the elastic strain exhibited a U-shaped change trend. With an increase in β from 0° to 90°, the failure mode transformed from tensile splitting failure along the bedding plane to shear slip failure along the weak bedding plane. Finally, the failure mode evolved into a tensile splitting failure across the bedding plane. When β=15°, 30°, and 45°, the phyllite specimens exhibited strong, slight, and moderate rockburst proneness, with strong, slight, and moderate shear slip rockbursts, respectively. When β=0°, 60°, 75°, and 90°, the phyllite specimens had extremely strong rockburst proneness, and an extremely strong strain rockburst occurred.

Experimental Study on the Mechanical Behavior and Failure Characteristics of Layered Coal at Medium Strain Rates

The study of the mechanical properties and failure behaviors for coal with different bedding structures at various medium strain rates is of great importance for revealing the mechanism of rock burst. In our study, we systematically analyze the uniaxial compressive strength (UCS), acoustic emission (AE) characteristics, failure pattern, and risk of rock burst on coal specimens with two bedding orientations under ranged in strain rates from 10−4 s−1 to 10−2 s−1. The results reflect that and the bedding direction and the strain rates significantly affect the UCS and failure modes of coal specimens. The UCS of coal specimens with loading directions perpendicular to bedding planes (horizontal bedding) increases logarithmically with increasing strain rate while the UCS increases first and then decreases of coal specimens with loading directions parallel to bedding planes (vertical bedding). The AE cumulative energy of the specimens with horizontal bedding is an order of magnitude higher than that of specimens with vertical bedding. However, it is independent of the strain rates. The energy release rates of these two types of bedded coal specimens increase in a power function as the strain rate increases. The coal specimens with horizontal bedding show violent failure followed by the ejection of fragments, indicating a high risk of rock burst. On the other hand, the coal specimens with vertical bedding exhibit a tensile splitting failure with a low risk of rock burst. Strain localization is a precursor of coal failure, and the concentration area of local principal strain is highly consistent with the initial damage area, and the area where the principal strain gradient is significantly increased corresponds to the fracture initiation area.

Determination and numerical simulation for HJC constitutive model parameters of Jinping marble

Holmquist-Johnson-Cook (HJC) constitutive model has been widely used in dynamic response analysis of concrete-like materials under impact and explosion. Based on the available data from uniaxial compression tests, triaxial compression tests, Brazilian splitting tests as well as SHPB experiments of 2400 m deep Jinping marble, a set of HJC model parameters suitable for high strength brittle marble were determined. Then, on the basis of one-dimensional static dynamic combined SHPB experiments, the numerical simulation of one-dimensional static dynamic combined SHPB experiments of Jinping marble were carried out by LS-DYNA software. Comparing the experimental and numerical simulation results, the rationality of the model parameters was verified. The numerical simulation results show that: from the perspective of stress-strain curve, the numerical simulation curve is consistent with the experimental curve, and the deviation of peak strength is less than 5%; from the perspective of damage evolution, the marble in the one-dimensional static and dynamic combined SHPB experiments are mainly tensile splitting failure. With the increase of prestress, the more serious the crack expansion and internal damage, the more broken the rock interior. Finally, the sensitivity of each parameter in the model is quantitatively calculated, and the high-sensitivity parameters are G, B, f c, S max, μ c and K 1, which should be accurately obtained based on experiments.

Mechanical Characteristics of Frozen Sandstone under Lateral Unloading: An Experimental Study

The lateral unloading strength and deformation of surrounding frozen rock are the key parameters for safety evaluation of frozen shaft construction. A low-temperature and high-pressure rock triaxial test system was used to simulate freezing construction, and a constant axial pressure unloading confining pressure test was carried out on frozen sandstone. The effects of freezing temperature, initial confining pressure, and unloading rate on the strength, deformation, and failure modes of frozen sandstone are studied. The main results of the study are as follows: (1) under the initial confining pressure of 20 MPa, the temperature of the sandstone decreases from 20°C to –5°C, and the peak stress and elastic modulus of triaxial compression increase by approximately 3 times. Under lateral unloading conditions, the peak stress of frozen sandstone is about 2∼3 times that of 20°C sandstone, and the peak strain of 20°C sandstone is smaller than that of frozen sandstone. The temperature of frozen sandstone decreases and the rate of increase in the peak stress of triaxial compression is slightly less than the rate of increase in the peak stress of lateral unloading. (2) The initial confining pressure of frozen sandstone increases, the growth rate of axial and radial strain increases, the radial strain dominates the failure process, and the lateral unloading strength decreases significantly. (3) The lateral unloading rate of frozen sandstone increases, the peak strength increases, and the axial and radial strain decrease. At a low unloading rate, partial creep deformation occurs. (4) The frozen rock sample undergoes tensile splitting failure under lateral unloading. According to the stress-strain curve of the frozen rock sample, the relationship between changes in the deformation modulus and changes in the confining pressure unloading amount during the unloading process of the rock sample is obtained.

Coupled effects of static-dynamic strain rates on the mechanical and fracturing behaviors of rock-like specimens containing two unparallel fissures

Widely existing in various underground engineering structures, rock masses containing unparallel fissures are likely to be subjected to static pre-stress and dynamic loads simultaneously. Understanding the effects of coupled static-dynamic strain rates on the mechanical and fracturing behaviors of rocks with unparallel fissures is significant for assessing the stability of rock engineering structures. In this study, the mechanical properties and the coalescence behaviors of both intact and fissured specimens under different coupled static-dynamic loads are investigated in the laboratory, involving four static pre-stress and three strain rates. Under the same dynamic strain rate, the coupled strength and the elastic modulus of both intact and fissured specimens first increase as the static pre-stress increases up to 50% uniaxial compression strength, and then decrease. However, under the same static pre-stress, the rock-like specimens with higher dynamic strain rate are characterized by higher coupled strength and elastic modulus. In the view of energy principle, under the same static pre-stress, more energy dissipates in the loading process and releases at the end of loading under higher dynamic strain rate. Nevertheless, at the same dynamic strain rate, the highest released elastic energy occurs under the static pre-stress of 50% uniaxial compression strength. All the rock-like specimens feature the prominent tensile splitting failure through the entire specimen, and five coalescence modes of fissured specimens are summarized in the present study.

Mechanical and failure properties of rocks with a cavity under coupled static and dynamic loads

In this study, a series of one-dimensional coupled static and dynamic loading tests were performed by using a modified split Hopkinson pressure bar. Intact prismatic sandstone specimens and specimens with a prefabricated internal circular cavity were tested. The results show that, the dynamic strength of intact specimens and specimens with a cavity decreases with the increase of axial static pressure under 20–70% of the uniaxial compressive strength (UCS). However, the combined dynamic-static strength of intact specimens and specimens with a cavity increases slightly with the increase of the axial static pressure. Besides, the total strain of specimens under coupled axial static and dynamic loads is approximately a fixed value (about 1.16%). Under a low axial static pressure (20–40% of UCS), dynamic load plays a major role in rock failure, resulting in tensile splitting failure in intact specimen; under a medium axial static pressure (60% of UCS), both of static and dynamic loads play a major role in rock failure, resulting in a composite tensile-shear failure in intact specimen; under a high axial static pressure (70% of UCS), static load plays a major role in rock failure where shear failure occurs in intact specimens. However, for the specimen with an internal cavity, no matter how large the axial static pressure is, X-shaped shear failure occurs under the combined axial static and dynamic loads.

Mechanical behavior of intermittent jointed rocks under random cyclic compression with different loading parameters

Rock engineering structures are likely to be subjected to random cyclic loading resulting from earthquakes during their service lives. Characterizing the mechanical behavior of rocks under random cyclic compression is thus essential, especially for the intermittent jointed rocks widely existing in various engineering structures. This study experimentally investigates the fatigue mechanical response of synthetic intermittent jointed rocks subject to different random cyclic compression, regarding four loading amplitudes and four loading durations. Our results report the influence of the two loading parameters on the mechanical behavior of synthetic jointed rocks, involving the strength and deformation characteristics, the fatigue damage evolution and the progressive failure behavior. Both the fatigue strength and the deformation modulus of jointed samples decrease with increasing loading duration, while they exhibit opposite variation with increasing loading amplitude. The hysteresis loops can be observed in the stress-strain curves of jointed samples under various random cyclic loading, and the irreversible plastic strain exists in each hysteresis loop; this irreversible strain develops in a two-stage manner with increasing cycle number. Under higher loading amplitude or duration, the synthetic jointed rock is characterized by higher cumulative fatigue damage. The fatigue failure modes of jointed samples are independent of random cyclic loading, and the tensile splitting failure is dominate in all the recovered jointed samples. Five crack coalescence patterns are observed in the present study based on the interaction between two adjacent joints, and the progressive failure process of tested jointed sample is captured via a high resolution industrial camera. The surface cracks always initiate from the joint tips, and then propagate at a certain angle with the intermittent joints towards to the maximum compression direction.

Direct shear behavior of concrete filled hollow steel tube shear connector for slim-floor steel beams

In this paper, a hollow steel tube (HST) shear connector is proposed for use in a slim-floor system. The HST welded to a perforated steel beam web and embedded in concrete slab. A total of 10 push-out tests were conducted under static loading to investigate the mechanical behavior of the proposed HST connector. The variables were the shapes (circular, square and rectangular) and sizes of hollow steel tubes, and the compressive strength of the concrete. The failure mode was recorded as: concrete slab compressive failure under the steel tube and concrete tensile splitting failure, where no failure occurred in the HST. Test results show that the square shape HST in filled via concrete strength 40 MPa carried the highest shear load value, showing three times more than the reference specimens. It also recorded less slip behavior, and less compressive failure mode in concrete underneath the square hollow connector in comparison with the circular and rectangular HST connectors in both concrete strengths. The rectangular HST shows a 20% higher shear resistance with a longer width in the load direction in comparison with that in the smaller dimension. The energy absorption capacity values showed 23% and 18% improvements with the square HST rather than a headed shear stud when embedded in concrete strengths of 25 MPa and 40 MPa, respectively. Moreover, an analytical method was proposed and predicts the shear resistance of the HST shear connectors with a standard deviation of 0.14 considering the shape and size of the connectors.

Numerical simulation of macro-meso mechanical behaviours of sandstone containing a single open fissure under uniaxial compression

By employing the improved rigid block spring method, the failure process of a sandstone example containing a single open fissure under uniaxial compression is modelled. In this method, the intact rock is considered as an assemblage of rigid polygonal blocks. Macro mechanical behaviours are governed by mechanical properties of interfaces between two neighbouring blocks. In the local scale on interfaces, both tensile splitting failure and shearing sliding failure are considered. Micro properties are obtained by a calibration procedure against the stress–strain curve of intact rock under uniaxial compression in the lab. Influences of fissure inclination and length on the uniaxial compression strength (UCS) and failure modes are discussed. Comparisons between numerical simulations and laboratory tests are presented. The growth process of micro-cracks is studied and the mechanism of micro-crack propagation is studied through analysis on the displacement evolution. Some conclusions are drawn: numerical results generally agree well with those from lab tests; the UCS of fissured rock is lower than the intact one; the UCS first goes down then goes up as inclination increases, but decreases gradually as fissure length increases; the micro failure modes are governed mainly by tensile splitting failures.

Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

Dynamic response and failure mechanism of Brazilian disk specimens at high strain rate

The effect of strain rate on the failure mechanism of rocks is one of the most important aspects in the field of rock dynamics and has been considered in many research works due to its extensive application. This study focuses on dynamic features and failure mechanism of Brazilian disk specimens under high-rate loading. For this purpose, particle flow code 2-dimensional (PFC2D) was used for simulation of Brazilian disk samples. The numerical models were validated by comparing with results of uniaxial compression, Brazilian and Split-Hopkinson Pressure Bar (SHPB) laboratory tests and it is demonstrated that the result of numerical modeling has a good agreement with those of the experimental measurements. The validated numerical model was used for further study of the mechanical behavior of rock specimen at high strain rate. The results of numerical models revealed that there are three different of failure modes for Brazilian disk specimens at different strain rate: (1) tensile splitting failure mode for specimen at strain rate smaller than 150 (1/s), (2) branching failure mode when strain rate varies in range of 150–600 (1/s) and (3) crushing failure mode when the strain rate increases to more than 600 (1/s).

Influence of material heterogeneity on failure intensity in unstable rock failure

Unstable failure of brittle rocks is a hazardous problem in deep mining and tunneling projects. Failure of brittle rocks around excavation boundaries is dominated by tensile fracturing. Homogeneous models cannot capture this rock failure mechanism while heterogeneous models are proven capable of capturing it. A question that may arise is how a change in failure mechanism influences the failure intensity. In this paper, an explicit FEM tool (Abaqus) is employed to simulate failure of homogeneous and heterogeneous rocks. Material heterogeneity is introduced into Abaqus models using Python scripts and the simulation results demonstrate that heterogeneous models can capture splitting rock failure. The effect of material heterogeneity on rock failure intensity in unconfined and confined compression tests is investigated. The simulation results from both types of models show that rock failure is more violent when the loading system is softer and the confinement is lower. However, it is observed that when two materials have the same peak strength, the heterogeneous model has more released energy than the homogeneous model due to the difference in the failure mode. The tensile splitting failure mode of the heterogeneous model releases more energy than the shear failure mode of the homogeneous model. This can be an important point to be considered for rockburst support design. Furthermore, the simulation results show that for two models with similar material composition, the strength of the more heterogeneous model is lower than the less heterogeneous model; as a result, the failure of the more heterogeneous model will be less violent if it fails in an unstable fashion, and this is in good agreement with field observation results.

Semi-analytical and Numerical Studies on the Flattened Brazilian Splitting Test Used for Measuring the Indirect Tensile Strength of Rocks

Based on the two-dimensional elasticity theory, this study established a mechanical model under chordally opposing distributed compressive loads, in order to perfect the theoretical foundation of the flattened Brazilian splitting test used for measuring the indirect tensile strength of rocks. The stress superposition method was used to obtain the approximate analytic solutions of stress components inside the flattened Brazilian disk. These analytic solutions were then verified through a comparison with the numerical results of the finite element method (FEM). Based on the theoretical derivation, this research carried out a contrastive study on the effect of the flattened loading angles on the stress value and stress concentration degree inside the disk. The results showed that the stress concentration degree near the loading point and the ratio of compressive/tensile stress inside the disk dramatically decreased as the flattened loading angle increased, avoiding the crushing failure near-loading point of Brazilian disk specimens. However, only the tensile stress value and the tensile region were slightly reduced with the increase of the flattened loading angle. Furthermore, this study found that the optimal flattened loading angle was 20°–30°; flattened load angles that were too large or too small made it difficult to guarantee the central tensile splitting failure principle of the Brazilian splitting test. According to the Griffith strength failure criterion, the calculative formula of the indirect tensile strength of rocks was derived theoretically. This study obtained a theoretical indirect tensile strength that closely coincided with existing and experimental results. Finally, this paper simulated the fracture evolution process of rocks under different loading angles through the use of the finite element numerical software ANSYS. The modeling results showed that the Flattened Brazilian Splitting Test using the optimal loading angle could guarantee the tensile splitting failure initiated by a central crack.

Experimental, numerical and analytical studies on tensile strength of rocks

The difficulties associated with performing a direct uniaxial tensile test on a rock specimen have led to a number of indirect methods for assessing the tensile strength. This study compares experimental results of direct and indirect tensile tests carried out on three rock types: Brisbane tuff, granite and sandstone. The standard Brazilian indirect tensile test caused catastrophic crushing failure of the disk specimens, due to the stress concentration produced by the line loading applied and exacerbated by the brittleness of the rock tested, rather than the expected tensile splitting failure initiated by a central crack. This finding led to an investigation of the effect of loading conditions on the failure of Brazilian disk specimens using three steel loading arcs of different angle applied to three different rock types, using numerical modeling and analytical results. Numerical modeling studies were also performed to investigate the effect of a pre-existing crack on the stress distribution within Brazilian disk specimens. It was found that there is substantially higher tensile stress concentration at the center of the disk with a pre-existing crack compared with that for a disk without a pre-existing crack. The maximum stress intensity factor (fracture toughness) values at the tip of the central pre-existing cracks were determined from numerical modeling and compared with fracture toughness values obtained experimentally for the three rock types. It was concluded that a 20° loading arc gives the best estimate of the indirect tensile strength.