جستجوی مقالات مرتبط با کلیدواژه "tensile strength" در نشریات گروه "مهندسی معدن"

The mechanical behavior of rock-rock bolt interface considering the effects of indents’ shape and their number was numerically simulated based on discrete element method using the two-dimensional particle flow code. The conventional and standard uniaxial compressive and Brazilian tensile strengths tests were used to calibrate the modelled samples with 100 cm 100 cm in dimension. The numerical models were prepared such that different indent shape and number were inserted in the cable bolts arrangements during the rock reinforcement process. The effects of confining pressure 3.7 MPa and different shear failure loads were modeled for the punch shear test of the concrete specimens. The results of this study showed that the dominant failure mode of the rock-cable bolt interface was of tensile mode and the shape and number of cable indents significantly affected the strength and mechanical behavior of the modelled samples. It has also been showed that the indent dimensions and number affected the shear strength of the interfaces.

Porosity plays a crucial role in both natural and man-made materials, serving as a fundamental microstructural characteristic that has a significant impact on their physical properties. Soils and rocks in nature are porous materials that are usually saturated with different fluids such as water, oil and gas. Therefore, it is very important to investigate the properties of porous materials and a better understanding of porous materials properties can lead to progress in oil, mining, and civil industries. In this research, porous samples with different porosity percentages were made and analyzed. The laboratory generation of actual porosity within the rock-like material samples was one of a significant aspect of this research. 5 groups of samples with different percentage of porosities were prepared including: 20%, 15%, 10%, 5%, 2% porosity and classified in 5 groups of A, B, C, D and E, respectively. Various experimental tests were performed with loading rate .5 MPa per second on the samples and the mechanical parameters of the samples were determined. These experiments show that the uniaxial compression and tensile strengths and elastic modulus of the rock-like specimens decrease with increasing their porosity. The mechanical parameters' maximum values were associated with group E samples (with 2-3% porosity). This group demonstrated a strength of approximately 34 MPa, an elastic modulus of 36 GPa, and a tensile strength of 7.3 MPa. The minimum values were observed in group A (with 20% porosity), which exhibited a strength of approximately 13 MPa, an elastic modulus of 16 GPa, and a tensile strength of 2.7 MPa. The study also investigated the Poisson’s ratio. The results indicate that Poisson's ratio increases with increasing porosity. The maximum Poisson's ratio was found in group A, which had 20% porosity and 11% Poisson's ratio, while the minimum value was found in group E, which had 2-3% porosity and 26% Poisson's ratio. the result show that Porosity has the greatest effect on the tensile strength parameter, which can change the tensile strength by 270% with a 20% change.

The tensile strength of rocks plays a noteworthy role in their failure mechanism, and its determination can be beneficial in optimizing the design of the rock structures. Schistose rocks due to their inherent anisotropy in different foliation directions show a diverse strength at each direction. The purpose of this work was to compare and assess the tensile strength of phyllite, which was obtained in direct and indirect tensile tests in different foliation directions. To this end, several phyllite specimens with different foliation angles (0º, 30º, 45º, 60º, and 90º) related to the loading axis (β) were prepared. Finally, the direct tensile test, diametrical and axial point load tests, Brazilian test, and Schmidt hammer test were conducted on 188 samples. The results of the experimental tests revealed that the maximum and minimum tensile strengths in direct tensile testing tension were directly related to the angles of 0º and 90º. Also it was observed that the Brazilian tensile strength overestimated the tensile strength. Furthermore, an exponential correlation was introduced between the direct tensile strength and the Brazilian tensile strength.

The tensile strength (σt) of a rock plays an important role in the reliable construction of several civil structures such as dam foundations and types of tunnels and excavations. Determination of σt in the laboratory can be expensive, difficult, and time-consuming for certain projects. Due to the difficulties associated with the experimental procedure, it is usually preferred that the σt is evaluated in an indirect way. For these reasons, in this work, the adaptive network-based fuzzy inference system (ANFIS) is used to build a prediction model for the indirect prediction of σt of sandstone rock samples from their physical properties. Two ANFIS models are implemented, i.e. ANFIS-subtractive clustering method (SCM) and ANFIS-fuzzy c-means clustering method (FCM). The ANFIS models are applied to the data available in the open source literature. In these models, the porosity, specific gravity, dry unit weight, and saturated unit weight are utilized as the input parameters, while the measured σt is the output parameter. The performance of the proposed predictive models is examined according to two performance indices, i.e. mean square error (MSE) and coefficient of determination (R2). The results obtained from this work indicate that ANFIS-SCM is a reliable method to predict σt with a high degree of accuracy

Temperature has a significant role in many actions performed on rocks. An example would be the effect of temperature on rocks in the burial of nuclear waste, geothermal energy extraction, deep oil well drilling, and fires in tunnels. In addition, due to diurnal/nocturnal as well as seasonal temperature variations, rocks undergo a process of heating and cooling. In the present work, the effect of temperature as well as heating and cooling cycles on the rock properties was studied. The utilized samples included tuff, andesite, and sandstone. In addition to natural samples, concrete was also studied in this research work. The aim of this work was to evaluate the effect of temperature on the tensile strength of rocks and the velocity of longitudinal waves in a single heating and cooling cycle of samples as well as evaluating the effect of the number of heating and cooling cycles on the tensile strength of rocks and the velocity of longitudinal waves. In order to investigate the effect of temperature on the tensile strength of rocks as well as the velocity of longitudinal waves in a single heating and cooling cycle, the samples were heated in a furnace. After cooling the samples, the Brazilian and the sound velocity tests were carried out on them. These tests were conducted at the three temperatures of 100, 200, and 300 °C. In order to examine the effect of the number of heating and cooling cycles on the tensile strength and the velocity of longitudinal waves, the samples were heated up to the temperature of 100 °C and then cooled down in order to reach the room temperature. In this case, the work was conducted in the three modes of 5, 10, and 15 cycles. The test results showed that the velocity of longitudinal waves and the tensile strength of samples decreased but their porosity increased. Reduction in the tensile strength varied in different rocks so that the greatest and lowest reduction in the tensile strength was observed in concrete and andesite, respectively.

Considering the fact that rocks fail faster under tensile stress, rock tensile strength is of great importance in applications such as blasting, rock fragmentation, slope stability, hydraulic fracturing, caprock integrity, and geothermal energy extraction. There are two direct and indirect methods to measure tensile strength. Since direct methods always encompass difficulties in test setup, indirect methods, specifically the Brazilian test, have often been employed for tensile strength measurement. Tensile failure is technically attributed to crack propagation in rock. Fracture mechanics has significant potential for the determination of crack behaviour as well as propagation pattern. To apply Brazilian tests, cracked disc geometry has been suggested by the International Society for Rock Mechanics ISRM. Accordingly, a comprehensive study is necessary to evaluate stress field and stress intensity factor (SIF) around the crack in the centre of the specimen. In this paper, superposition principle is employed to solve the problem of cracked straight-through Brazilian disc (CSTBD), using two methods of dislocation and complex stress function. Stress field and SIF in the vicinity of the crack tip are then calculated. With the proposed method, the magnitude of critical load for crack initiation in structures can be predicted. This method is valid for any crack of any arbitrary length and angle. In addition, numerical modelling has been carried out for the Brazilian disc. Finally, the analytical solution has been compared with numerical modelling results showing the same outcome for both methods.