Influence of Penetration Rate and Indenter Diameter in Strength Measurement by Indentation Testing on Small Rock Specimens (original) (raw)
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Estimation of Specific Energy in Rock Indentation Test
Static indentation tests were carried out in six types of rocks namely pink marble, limestone, basalt, steel gray granite, moon white granite and black galaxy granite using commercial drill bits (Cross bits) of 35, 38, 45, 48mm diametersat a loading rate of 0.1 kN/sec on Microcontroller compression testing machine (with fabrication work to hold the indenter).The tests were conducted on rocks at index angles of 100,200,300,400. The objective is to estimate the specific energy (energy necessary to excavate a unit volume of rock) during indentation and to study the influence of index angle on specific energy. From the experimental data, Force-Penetration (F-P) curves were plotted and specific energy values were calculated from F-P curves for each bit rock combinations. The optimum specific energy is at 30° index angle for the soft rocks (pink marble, limestone) whereas; the optimum specific energy is at 20° index angle for the rocks (basalt, steel gray granite, moon white granite and black galaxy granite). Keywords: Indentation, Specific energy, Index angle, Micro controller compressive testing machine
Correlation study between indentation indices and physical-mechanical properties of rocks
CRC Press eBooks, 2023
Indentation test is one of the laboratory approaches that is used to predict the performance of Raise Boring Machines (RBMs) and Tunnel Boring Machines (TBMs). This test is a nonstandard laboratory experiment that was originally developed to provide a method to predict the normal force acting on the cutters used on mechanical miners. However, in some cases due to difficulties in obtaining rock samples as well as insufficient laboratory equipment it is not possible to perform indentation test. In this study, based on the indentation tests on different rock samples obtained from raise-boring projects in Turkey, three indentation indices (brittleness indices and force index) are obtained; then, the multi-variable correlations between these indices and physical-mechanical properties of rocks are investigated. The study indicates that all three indentation indices can be estimated by using the velocity of P-wave, static elasticity modulus, Cerchar abrasivity index, and Schmidt hammer hardness of rocks.
Estimation of uniaxial compressive strength of shale using indentation testing
Journal of Petroleum Science and Engineering, 2017
A number of methods have been proposed to indirectly assess the uniaxial compressive strength (UCS) of intact rock in the drilling of oil wells and underground drilling. Indentation testing is a method in which an indentor of a specific diameter penetrates a particle of rock and the force-displacement curve is plotted to determine the critical transition force (CTF). In the present study, 10 shale block samples were collected from a cretaceous shale formation in Iran from which standard cores were prepared and subjected to UCS testing. Cubic particles 4, 5 and 7 mm 3 in size were cut and entrenched in disks containing resin and a total of 300 indentation tests were conducted on them. Empirical relations for the relation between UCS and CTF were developed for each size. The highest correlation coefficient was recorded for the 7 mm 3 particles and the lowest for the 4 mm 3 particles. A simple method is proposed to determine the empirical relationship independent of particle dimensions between UCS and CTF that has a correlation coefficient of 0.78. Verification of the proposed equations show that they predicted UCS with 85% accuracy. A comparison of the proposed relationships and those from previous studies indicates that the empirical relationship between these two variables is influenced by variation in the uniaxial compressive strength and lithology of the different samples.
Microstructure Effect on Hard Rock Damage and Fracture During Indentation Process
Geotechnical and Geological Engineering, 2015
This paper presents the results of simple and double indentation tests conducted on three hard rocks: granite, limestone and sandstone. The main objective is to analyze the rock behavior under indentation test in relation with the physical and microstructural properties. First, the experimental setup used during the tests is described as well as the sample preparation. Then, an image analysis based technique is applied on thick sections made from the tested samples in order to evaluate the size of indentation-induced cracked zone and to assess the crack types (vertical or sub-horizontal) below the indenter. The interpretation of the results was made on two levels. First, several physical parameters (energies and displacements) have been derived from the so obtained experimental indentation curves. Very high correlations were found between the loading, indentation and specific energies versus the plastic displacement. Second, cracked zone radius was estimated showing a very high correlation to the specific energy and governed by the physical and mineralogical properties of the tested rocks. Finally, the analysis of double indentation tests proved that changing the distance between two adjacent inserts allows the determination of the optimal spacing producing overlay of cracked zones and causing rock damage and large chip departure. Keywords Rock indentation Á Indentation energy Á Crack pattern Á Image analysis technique Á Cracked zone Á Brittleness Á Rock texture Á Mineralogical components Á Specific energy
Estimating elasticity modulus and uniaxial compressive strength of sandstone using indentation test
Journal of Petroleum Science and Engineering, 2018
Elastic modulus (E) and uniaxial compressive strength (UCS) are very important engineering parameters that is required for many engineering projects. In some projects such as well drilling for oil production, deep underground tunnels in crushed zone, due to the depth of the well and fractures of rocks, there are some problems for obtained standard core samples. In this situations various methods have been developed for determining UCS and E using drilling cutting. Indentation test is one of these methods, in this method, an indenter penetrates into the stabilized samples in the surrounding material and then Critical Transition Force (CTF) and Indentation modulus (IM) determine. In the present study in order to developing the application of indentation testing for sandstone, and investigate the effect of particles size, shape and thickness, 14 sandstone blocks were collected from different formations in Iran and their physical characteristics, UCS and, E were measured using standard methods. After crushing the blocks and preparing 600 particles with dimensions of 3×3×3 mm 3 , 5×5×3 mm 3 , 5×5×5 mm 3 , 5×5×8 mm 3 , and 8×8×8 mm 3 and irregular shape particles with a thickness of 5 mm, indentation tests were performed on each particle and CTF and IM were calculated for each particle separately. According to the tests carried out some empirical relationships were proposed between UCS-CTF (with R 2 ≥ 0.86) and E-IM (with R 2 ≥ 0.73) for different shapes and dimensions. Due to the differences in the dimensions of the produced particles, investigating the effect of surface and thickness of particle on the CTF and the IM revealed that the particle's surface had a considerable effect on the CTF and IM; however, the effect of thickness was negligible. Using the dimensionless surface parameter (S and S i), some empirical relationships between UCS
Journal of the American Ceramic Society, 1981
The application of indentation techniques to the evaluation of fracture toughness is examined critically, in two parts. In this flrst part, attention is focused on an approach which involves direct measurement of Vickers-produced radial cracks as a function of indentation load. A theoretical basis for the method is first established, in terms of elasticlplastic indentation fracture mechanics. It is thereby asserted that the key to the radial crack response lies In the residual component of the contact fkld. This residual term has important implications concerning the crack evolution, including the possibility of postindentation slow growth under environment-sensitive conditions. Fractographic observations of cracks in selected "reference" mater-Ys are used to determine the magnitude of this effect and to investigate other potential complications associated with departures from ideal indentation fracture behavior. The data from these observations provide a convenient calibration of the indentation toughness equations for general application to other well-behaved ceramics. The technique is uniquely h p i e in procedure and economic in its use of material.
An Analytical Model for the Indentation of Rocks by Blunt Tools
Rock Mechanics and Rock Engineering, 2000
A methodology based on the cavity expansion model is developed to analyze the indentation of rocks by a class of blunt indenters. The analysis covers the particular self-similar case of indentation by blunt wedges or cones. As an example, the main results for the indentation of rocks by a spherical tool are presented and the analytical solution is compared with experimental results obtained by indenting a sphere in Harcourt granite.