Small punch impression creep testing of materials

A horizontal impression creep apparatus with a small diameter punch has been assembled to conduct the creep measurements of ABS polymers with various butadiene contents and also of a lead crystal. The punch was a 100;The steady state impression velocities on ABS polymers are exponential functions of the punching stress and temperature from 20 MPa to 100 MPa and from 333 K to 378 K. The creep resistance decreases with increasing butadiene content. The activation strain volumes do not change with temperature in the range studied but increase with increasing butadiene contents. For temperatures below glass transition, the activation enthalpy decreases with increasing stress. We believe the deformation is a stress activated slip process in this range. For temperatures above glass transition, the activation enthalpy decreases with increasing temperature and the deformation is probably a free volume activated shearing process. The activation enthalpy goes through a maximum value around glass transition.;The results obtained from constant load compression creep tests are in general agreement with those obtained from impression creep tests. The deformation rate in both creep experiments follow the same governing equations and have the same tendency regarding the butadiene contents. The activation strain volumes and activation enthalpies determined by both tests are close to each other at temperatures below 350 K but they begin to deviate from each other at temperatures higher than 350 K. The values obtained from compression tests are higher than those from impression tests. The differences of activation values at temperatures approaching glass transition may reflect that the deformation of polymer is sensitive to the different stress distributions in the two tests.;The measurements of a lead crystal were carried out over a temperature range from 296 K to 536 K at punching stress levels from 6 MPa to 70 MPa. Both temperature and stress dependences are comparable with the reported values of the constant stress tensile creep tests under the similar conditions. A master creep curve of lead covering two orders of stress levels was established in this work.