A laboratory study of the "barrel shape" effect in a viscoelastic cylindrical sample at seismic frequencies

Abstract

The "barrel shape" effect caused by axial pressure applied to a cylindrical acrylic sample was studied using a low-frequency laboratory apparatus utilizing stress-strain relationship, which was developed to measure the complex Young's moduli of elastic materials at seismic frequencies, confining or axial pressures from 0 to 70 MPa, and strain amplitudes 10^-8–10^-7. To increase the effect, the experiments were performed at axial pressures only. The elastic and anelasic parameters of the 15 cm length sample were measured with strain gauges glued in the middle of the sample and at two centimetres from one of the ends at axial pressures of 7 MPa and 15 MPa. Our experiments show that all measured parameters are independent from the location of the strain gauges on the sample. These results confirm that the barrel shape of the sample caused by applied stress does not affect reliability of low-frequency laboratory measurements.