Papers by Keyword: Brazilian Test

Abstract: In this research, we have prepared epoxy/graphene nanocomposites (graphene content: 1, 3, 5, 7, and 9 wt%) to investigate some mechanical (impact strength, hardness, and Brazilian tests) and thermal properties (thermal conductivity and thermogravimetric analysis). Our results show that the impact strength, hardness, and compression strength values increased to 5.04 kJ/m², 79.8, and 27.85 MPa, respectively, as increasing graphene content up to 5 wt% and then decreased for further increasing of the graphene content. The observed reduction in the hardness could be attributed to the samples brittleness. On the other hand, the thermal conductivity increased with increasing the graphene content because of the high thermal conductivity of graphene and thus the efficiency increase with increasing of graphene content. In addition, the thermal stability of epoxy/graphene composite increase compared with pure epoxy resin, while the activation energy for samples consists of 9 wt% graphene greater than those containing 1 wt% graphene.

Abstract: Geotechnical engineering in tension damage is one of the major failure modes. For a long time, Brazil test has practical significance and wide application value that has been used to determine the tensile strength of rock. When the specimen center destroyed tensile stress play a major role that is the theoretical basis of Brazil test. This is uniaxial tensile stress state, but the reality is complex stress state. Theoretical analysis shows that the Brazilian test does not truly reflect the tensile strength of rock, its test results to error. In this paper, two-parameter parabolic Mohr strength criterion for this error analysis, and propose amendments to the formula.

Abstract: Laboratory results from sandstone Brazilian splitting tests and uniaxial compression tests based on acoustic emission (AE) monitoring indicated that the acoustic emission parameters analysis method can be applied to analyse the characteristics of acoustic emission and to classify the crack modes in rock materials. It concluded that more than 99 per cent of the whole cracking signals in Brazilian tests were classified as tensile mode, and no shear cracks occurred. And more than 65 per cent of the AE signals in uniaxial tests were tensile-shear crack mode, along with about 30 percent of tensile mode and 5 percent of shear mode, and shear cracks only occurred in the unstable crack extension stages; tensile-shear cracks are the main crack modes in the crack stable extension stage.

Abstract: To reduce stress concentration near the loading point, Brazilian test, normally used for the indirect determination of tensile strength for rock or concrete quasi-brittle materials, is usually subjected to uniformly distributed pressure over finite width (or arc) of the Brazilian disc. As an extension, the same geometry, in which a central notch is introduced in the symmetrical plane of applied forces, can be used to determine fracture toughness of the materials. For this purpose, accurate expression for stress intensity factor (SIF) for central cracked Brazilian disc should be provided first. To this end, weight function method is used in this paper where weight function for central cracked disc is available in general SIF handbooks. Meanwhile, the exact stress solution in the intact Brazilian disc subjected to uniformly distributed pressure is derived by use of numerical method. In the end, some finite element analysis is carried out using the program package ABAQUS on the Brazilian disc, and the comparison results regarding the SIF between the weight function method and numerical method prove the validity of the proposed method.

Abstract: Kaiser effect was noticed while submitting marble samples to Brazilian tests. An automatic data acquisition system was applied by means of analog to digital conversion, upon recording analog signals of stress, strain and acoustic emission (AE) emitted from Portuguese marble specimens under diametrical loadings in different loading cycles. Results confirm that the Kaiser effect was pronounced and was easy to be detected under Brazilian tests with a felicity ratio varied from 0.92 to 1.09. This means it is possible to measure the pre-existing stresses in rocks under complex states of stress by means of other tests besides uniaxial compression. Results also show that cumulative AE events vs. stress curve is more suitable for Kaiser effect recognition than cumulative AE energy vs. stress curve as every event has different scales of energy.

Abstract: The Brazilian splitting tests have been commonly and widely used as a standardized test method on disc or cylinder specimens to measure the indirect tensile strength of rocks in mining engineering and other rock engineering. In this paper, a novel numerical code, 3D Rock Failure Process Analysis code, was applied to implement the splitting tensile failure tests on rock discs. The influences of the heterogeneity on stress distribution in rock are also discussed and the splitting failure patterns of specimens subjected to Brazilian tests are simulated. The simulated splitting results of rock discs were found quite realistic, which indicate that the rock failure analysis method is applicable and practical for the study of rock disc splitting failure.

Abstract: Channelled hollow ceramic cylinders have been sliced into discs of equal thickness and submitted to an adapted diametral compression, or brazilian, test such as to evaluate their reliability. The mean Weibull modulus, of m » 18, is representative of a rather good homogeneity of the ceramic material. The shapes of the distributions reveal a probable multimodality. This is analyzed in superimposing possible unimodal distributions of given characteristic value, Weibull modulus and number of items, and comparing to the experimental plot. Iterative modifications are made until a convincing superposition is attained. Complementary numerical simulations on “thermomechanically equivalent microstructures” have been created on the computer observing actual stereological data. The micro-mechanical model accounts for cracking of grain interfaces until specimen separation. Weibull plots for model structures under pore pressure suggest multimodal distributions with moduli ranging as in the measurements. The larger scatter at higher rupture pressures may indicate a varying degree of quasi-brittleness.

Abstract: Brazilian test is a standardized test for measuring indirect tensile strength of rock and concrete disc (or cylinder). Similar test called indirect tensile test has also been used for other geomaterials. Although splitting of the disc into two halves is the expected failure mode, other rupture modes had also been observed. More importantly, the splitting tensile strength of rock can vary significantly with the specimen geometry and loading condition. In this study, a numerical code called RFPA2D (abbreviated from Rock Failure Process Analysis) is used to simulate the failure process of disc and ring specimens subject to Brazilian test. The failure patterns and splitting tensile strengths of specimens with different size and loading-strip-width are simulated and compared with existing experimental results. In addition, two distinct failure patterns observed in ring tests have been simulated using RFPA2D and thus this verifies the applicability of RFPA2D in simulating rock failure process under static loads.