Dynamic compressive behavior of ice at cryogenic temperatures

In the present study dynamic behavior of distilled water ice (polycrystalline ice Ih) is investigated under uniaxial compression at strain rates in the range of 100 s(-1) to 1350 s(-1) and at temperatures in the range of-15 degrees C to -173 degrees C using a modified split Hopkinson pressure bar (SHPB). The peak compressive strength is found to increase from 32 MPa to 112 MPa as the test temperatures are decreased from -15 degrees C to -125 degrees C. With a further decrease in test temperature from -125 degrees C to -173 degrees C the peak strength is observed to remain nearly constant and lie in the range of 110-120 MPa. In addition, the,ice samples show positive strain rate sensitivity over the range of strain rates employed in the present tests at test temperatures in the range of -15 degrees C to -125 degrees C. However, the sensitivity of the logarithmic of peak stress (strength) to logarithmic of strain rate decreases with decreasing test temperatures, and the ice samples are observed to be nearly insensitive to strain rate at test temperatures lower than -125 degrees C. An interesting feature of the dynamic compressive behavior of ice is the presence of a shoulder/double-peak in the dynamic stress versus strain curves at test temperatures in the range of -50 degrees C to -150 degrees C. Another feature of the post-peak stress regime of distilled water ice is the presence of a long tail in the dynamic stress versus strain curves at a test temperature of -15 degrees C. At lower test temperatures (from -150 degrees C to -173 degrees C) the residual strength of ice is observed to become negligible. These artifacts in the dynamic behavior of ice can be attributed to details associated with dynamic failure of the ice samples and geometric effects emanating from the finite size of the samples and the diameter of the loading bars. The residual dynamic strength of ice can be best understood by considering the damaged/fragmented ice as an assemblage of wet highly-fragmented granular material created by adiabatic heating during grain-to-grain frictional sliding and held together by ice melt and/or recrystallization in the post peak-stress regime.