J. Phys. Colloques
Volume 42, Numéro C5, Octobre 1981
Seventh International Conference on Internal Friction and Ultrasonic Attenuation in Solids
Page(s) C5-157 - C5-162
Seventh International Conference on Internal Friction and Ultrasonic Attenuation in Solids

J. Phys. Colloques 42 (1981) C5-157-C5-162

DOI: 10.1051/jphyscol:1981524


H. Mizubayashi et S. Okuda

Institute of Materials Science, University of Tsukuba, Sakura-mura, Ibaraki 305, Japan

In situ observation of changes in vibrational period (P), internal friction (IF) and driving force (DF) was made for as-drawn and as-annealed copper polycrystals during the strain-controlled fatigue test at around room temperatures using resonant flexural vibration at about 200Hz. The maximum surface strain used was an order of 10-4. IF first increased, then stayed almost constant and finally increased. P increased continuously. DF was not parallel with IF, but rather decreased in the middle stage where IF stayed almost constant. Overlapped on the above general changes, almost periodic saw-toothed changes were observed in P and DF, in the initial and middle stages of the fatigue life. For a typical case, the amplitude of this sawtooth in P amounted to an order of 10-4 in a relative value of P and stayed almost constant at least in the initial and middle stages. The period or the width of tooth was about 3min which corresponded with an order of 104 cycles of deformation. This period decreased as the fatigue proceeded. No change in IF corresponding with this change in P was detected probably because IF was less accurate. It was observed that the general feature was not sensitive to the strain amplitude and the pre-treatment of specimens, but the characteristic periodic changes were strongly dependent on the strain-amplitude and condition of the specimens before the fatigue test. Comparable fatigue tests made for as-drawn vanadium polycrystals showed analogous results with those observed for as-drawn copper polycrystals. Therefore, these observed phenomena were considered to be associated with the fundamental fatigue processes. It is considered that the above saw-toothed type change in P is possively associated with dislocation avalanche or strain burst typically observed in fatigued specimens, but further study is needed to correlate them.