Applied, residual strain and texture investigations by means of neutron time-of-flight diffraction combined with acoustic emission detection: Application to a gneiss sample from Forsmark, Sweden

Abstract

The mechanical behaviour of a gneiss sample from the Forsmark drilling site (Sweden) consisting of quartz, plagioclase (oligoclase), microcline and biotite, is characterized by residual strain and crystallographic preferred orientation measurements. Cyclic in situ uniaxial deformation experiments were carried out on a cylindrical sample at four uniaxial stress levels (55, 84, 114 and 141 MPa) and examined using time-of-flight neutrons and simultaneous recording of acoustic emissions. At each stress level applied, a residual strain scan was performed around the sample axis and residual strains were determined. The residual compressional strain detected for quartz was −1.0 × 10−3, the maximum value of residual strain approached 1.2 × 10−3. The onset of acoustic emissions is an indicator of the previous in situ maximum stress. Comparison of acoustic emission data with applied and residual stress values at different load levels is the key to understand the freezing-in mechanism of residual stress and the Kaiser Effect in rock.