Dynamic strength of distill water and lake water ice at high strain rates

• A modified split Hopkinson bar is developed for sub-zero temperature testing.
• Dynamic strength of lake water ice and distilled water ice is measured.
• States of stress include uniaxial compression and combined compression and shear.
• Peak strength of ice is rate sensitive over the strain rate range 100–600/s.
• Fragmented/pulverized ice maintains finite strength in its post-peak-stress regime.

In the present study, a modified split Hopkinson pressure bar (SHPB) is employed to investigate dynamic response of lake water ice and distilled water ice under dynamic uniaxial compression and combined compression and shear loading (oblique impact) at strain rates in the range of 80–600 s−1 and at test temperature of −15 °C. For both ice the uniaxial dynamic compressive strengths show positive strain rate sensitivity over the range of strain rates employed. The strength of lake water ice under uniaxial compression is observed to be consistently higher when compared to distill water ice. Moreover, the peak stresses of both lake water ice and distill water ice are observed to be consistently lower under oblique impact when compared to those obtained under uniaxial compression. In addition, for oblique impact the sensitivity of the logarithmic of peak stress to the logarithm of the applied strain rate for lake water and distilled water ice is higher than that obtained under uniaxial compression. A consistent feature observed in the post-peak stress regime of both lake water ice and distill water ice is the presence of a long tail in their dynamic stress versus strain curves, indicating complex inter-particle interactions in the fragmented ice after the attainment of the peak stresses. This residual strength of pulverized/fragmented 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/or impact-induced melting, held together by ice melt and/or recrystallization in the post-peak-stress regime.