Kaiser Effect Under Indirect Tensile Loading: Effect of Rotation of Principal Loading Axis and Application of Full-field Strain Measurements

Abstract Non-destructive techniques (NDTs) for stress measurement rely on rock stress memory, which necessitates precise strain and acoustic emission (AE) measurements during uniaxial cyclic loading of rock specimens. This study examined the Kaiser effect under indirect tensile loading, investigated the influence of principal axis rotation, and assessed the potential of full-field strain measurements for accurately determining applied stresses. The tests were performed on Brazilian disc specimens of Adelaide Black Granite and Hawkesbury sandstone, and the deformation was monitored using 2D digital image correlation (DIC) and an AE monitoring system. The effect of rotation of the principal axis was established by rotating the specimens in 15° increments from 0° to 90°. Although the results indicate that the rotation of the principal axis affects the Felicity Ratio (FR) in the first cycle AE analysis, the Kaiser effect can be precisely measured from the second cycle AE analysis. Moreover, the results demonstrate that the preloads can be precisely measured using the Secant Modulus Method (SMM), however, inflection points in the characteristic SMM curves are influenced by the distribution in the specimens. Precise and well-pronounced inflection points are observed from strain measurement in the localisation band even after the rotation of the principal loading axis.