Internal friction and microplasticity of iceI h

Abstract

This study is concerned with internal-friction measurements made at low frequency (torsion pendulum) on specimens of iceIh. In the case of a single crystal, the spectrum of internal frictionvs. temperature exhibits the classical relaxation peak. This peak is followed by an increase of damping above 260 K. Furthermore, in this temperature range, the internal friction δ is shown to be amplitude dependent: δ increases with shear strain γ as long as the temperatureT is high. These features are strongly modified by plastic deformation of ice; in particular i) high-temperature internal friction is increased as long as the plastic deformation ratio is important, ii) high-temperature internal friction becomes more amplitude dependent. In the high-temperature range the mobility of dislocations in ice increases quickly. During the internal-friction measurements the cyclic stress causes movement of linear defects and, hence, damping phenomena. Then, the theoretical analysis of the dynamic behaviour of dislocations in ice has been used to interpret the preceding results. This interpretation allows us to connect our damping data with the microplastic behaviour of ice.