• S Balakrishna

      Articles written in Proceedings – Section A

    • Sound velocities in some Indian rock specimens

      S Balakrishna

      More Details Abstract Fulltext PDF

      The paper gives the elastic moduli and other relevant features obtained from measurements on sound velocities in about a dozen specimens of Indian rocks.

      This systematic investigation of the ultrasonic sound velocities (longitudinal and torsional) in various rock sections by the wedge method, has shown that the differences in granular structure and mineralogical composition from grain to grain are reflected in the transmission patterns that are obtained. Typical cases like limestone, consisting of practically the same chemical substance all through the section, give intense ultrasonic patterns with a large number of diffraction orders. In these rocks we are enabled, by special techniques, to determine both longitudinal and torsional velocities. Cases like granite, on the other hand, consisting of a variety of materials like mica, felspar and quartz give weak ultrasonic patterns and appear to scatter the sound to a large extent. Torsions are not easy to excite in these cases.

      There is a further point of interest that in these rocks, the transmission maxima are fairly broad unlike what we get in metals and single crystal plates where they are generally sharp.

    • Anisotropic behaviour of rocks

      S Balakrishna

      More Details Abstract Fulltext PDF

      The directional variation of ultrasonic velocity has been studied in some of the Indian rocks. Quartzites and Marbles which are monomineralic show almost perfect isotropy. Granite shows a slight departure from isotropy (5 to 8%) which is attributed to the variation in mineralogical composition and in grain size from direction to direction.

    • Measurement of ultrasonic velocities in some Indian rocks

      M Krishnamurthi S Balakrishna

      More Details Abstract Fulltext PDF

      The phenomenon of total internal reflection has been employed in developing a technique for measuring the ultrasonic velocities in solids using pulsed ultrasonic beams. The ease and accuracy with which the critical angles can be measured make this method superior to other methods in some respects. Besides the longitudinal velocities, torsional velocities have also been measured in a number of Indian rocks for the first time. It is essential to use fairly large sized samples in this method. An earlier observation indicating a dependence of sound transmission on granular texture of the rocks has been confirmed qualitatively in this investigation as well.

    • Preferred orientation in rocks and its relation to their physical properties

      S Balakrishna

      More Details Fulltext PDF
    • Effect of temperature on ultrasonic velocities in some Indian rocks

      S Balakrishna

      More Details Abstract Fulltext PDF

      The variations of both longitudinal and torsional velocities in the temperature range 3° to 110° C. have been determined in a few Indian rock specimens. It is observed that the variation is linear and the velocities decrease markedly with increase of temperature. The velocities go back again to the original values as the specimens cool provided the maximum temperature at which the measurements are taken does not exceed 110° C. and the specimens are allowed to cool for a sufficiently long time. The temperature gradient of longitudinal velocities is generally higher than that of the torsional velocities. It is possible that the high frequency method employed in this investigation is such that it is insensitive to small structural changes, if any, that occur in the rock when it is heated at ordinary pressures to 110° C.

    • Transmission of ultrasonics through rocks

      S Balakrishna

      More Details Fulltext PDF
    • Ultrasonic velocities in rocks: Some special features of Indian granites

      S Balakrishna

      More Details Fulltext PDF
    • Effect of dimensional orientation on ultrasonic velocities in some rocks

      S Balakrishna

      More Details Fulltext PDF
    • Ultrasonic velocities in relation to the degree of metamorphism in limestones

      S Balakrishna

      More Details Abstract Fulltext PDF

      It can be concluded that metamorphosed limestones or marbles show higher ultrasonic velocity values in contrast to limestones. In limestones, velocity values consequential to the degree of metamorphism to which they have been subjected to are noticed and in fact the velocity increases as metamorphism increases. Certain chosen limestones, though not metamorphosed, behave like marbles and show comparable velocities because of their fine grain texture.

    • A simple method for measuring porosity in rocks

      S Balakrishna G Shankar Narayana

      More Details Abstract Fulltext PDF

      A simple porosimeter has been designed with a view to handle large volumes of samples and determine the grain volume with the help of a calibration graph. Bulk volume is determined directly from the geometric shape of the samples. The results obtained are repeatable and are found to be in good agreement with those obtained by other methods.

  •  

© 2021-2022 Indian Academy of Sciences, Bengaluru.