The dependence of the internal friction of boron fibers on amplitude

Abstract

The dependence of the internal friction of boron on amplitude was studied in vacua at temperatures of 20,150, 300, 400 and 600 °C and for amplitudes of the relative deformations ranging from 1 × 10 −5 to 5 × 10 −3. The filament structure was finely dispersed and showed residual internal stress distributed in the bulk of the sample. A step-wise change in the internal friction was established at room temperature. Two regions of noticeable amplitude dependences of damping were observed. They were characterized by different angles of the curve slopes, i.e. by different activation energies of the processes responsible for the effects observed. The critical deformation amplitudes were found to be 5 × 10 −4 and 3 × 10 −3 respectively. It was established that repeated cyclic deformations at an amplitude of 5 × 10 −3 caused the appearance of an internal friction background in the amplitude-dependent regions. Simultaneously the critical amplitude of the deformation decreased. At 300, 400 and 600 °C the internal friction became amplitude independent. At 150 °C the steps flowed together and the critical amplitude of deformation, at which the amplitude dependence of damping began, decreased. The results obtained were analysed taking into consideration the possible effects of residual internal stresses on the energy and on the crystal geometry characteristics and the nature of interaction of the admixtures with the dislocations in finely crystalline aggregates of boron filaments.