Spherical Indentation Tests on Confined Ice Specimens at Small Scales

A recent series of small-scale ice indentation tests was conducted as a continuation of previous series, to cover additional strain rates and indentor sizes, and to test the effect of scaling. Tests using indentors 10, 20, 40 and 70 mm in diameter attached to a very stiff structure were carried out at indentation rates over three orders of magnitude, while scaling indentation rate with indentor diameter. Slow rates resulted in creep-like response and deep and wide damage zones. As indentation rate was increased, sawtooth loading and random failure activity were observed, together with a thin layer of microstructurally modified ice beneath the indentor. This latest test series also included indentation tests with a flexible beam apparatus, with the aim of generating locked-in vibrations. It was determined from previous tests that indenting at much faster rates was necessary to produce lock-in with such an apparatus. For this series, two new beam apparatus of differing stiffness and variable natural frequency were fabricated; the beams were designed in a manner that enabled control and testing of the outcome of varying these factors independently. Tests were conducted with either one or two indentors attached. The typical sawtooth behaviour occurred at lower indentation rates, progressing at higher rates into lock-in activity, which occurred over a range of speeds for both beams. The frequency of lock-in vibrations was found to be lower than the structure’s natural frequency, and to increase with indentation speed over the lock-in range. The ice load on the indentor during lock-in activity appears more ‘cusp’ shaped, rather than the assumed sawtooth.