Model Of Internal Friction Research Articles

Inelastic Behaviour of Ice Ih Single Crystals in the Low-Frequency Range Due to Dislocations

AbstractThe inelastic behaviour of ice Ih single crystals has been investigated by an inverted torsional pendulum in the low-frequency range. Three features are distinguished:(i) a relaxation peak previously observed by several authors in the higher-frequency range,(ii) an internal friction increasing with temperature in the high-temperature range (230–273 K),(iii) within this high-temperature range, internal friction becomes amplitude dependent, and this dependence becomes greater the greater the temperature.In this case, the internal friction has been interpreted in terms of movements of dislocations. Hence, the experimental results are interpreted with a model of internal friction based on an empirical relation for the velocity of dislocations. This model of internal friction is in fair agreement with experimental data . It is possible then to get an estimate of dislocation density. Hence it is shown that internal friction experiments can be useful in the study of the plastic behaviour of ice single crystals.

Modèle pour les pics de frottement interne observés a haute température sur les monocristaux

Abstract A model for internal friction peaks observed at high temperatures in single crystals A model is presented for treating internal friction peaks observed between 0-3 T t and 0-6 T t (T t being the absolute melting temperature) in high purity copper and aluminium single crystals. The relaxation is related to the migration, by vacancy diffusion, of geometrical jogs along dislocation lines. In the case of peaks observed at about 0-3 T t, the activation energy is close to one half of the self-diffusion energy, and it is supposed that vacancies diffuse along dislocation lines. In the case of higher temperature peaks the activation energy is close to the self-diffusion energy and corresponds to bulk vacancy diffusion. From this model it may also be seen that the peaks probably correspond to isolated dislocation climb and that the high temperature background is due to dislocations belonging to polygonization cells.

The Attenuation of Love Waves and Toroidal Oscillations of the Earth

An attempt has been made to invert a large set of attenuation data for Love waves and toroidal oscillations in the earth, using a recent method by Backus and Gilbert. The difficulty in finding an acceptable model of internal friction which explains the data, under the assumption that the internal friction is independent of frequency, casts doubt on the validity of this assumption. A frequency-dependent model of internal friction is presented which is in good agreement with the seismic data and with recent experimental measurements of attenuation in rocks.

Theory and Application of a Superposition Model of Internal Friction and Creep

Energy dissipation in solids is important in both transient and steady-state measurements. The results of such measurements can be associated with a distribution of relaxation times provided the material is linear. In the present work, general relations are derived for the attenuation factor, phase factor, and specific dissipation function 1/Q pertaining to transmission of small amplitude stress waves in a material describable by a distribution of relaxation times. Next, a specific, physically realizable relaxation time distribution is used to obtain a creep function and to relate transient creep and frequency response measurements. Curves of 1/Q vs frequency are calculated with a digital computer and show a region approximately proportional to frequency at sufficiently low relative frequencies, a region of virtual frequency independence, and a final region proportional to inverse frequency at high relative frequency. The relation of the present work to other treatments of creep and internal friction is discussed, and the applicability is examined of the analytic and numeric results to creep measurements on metals and rocks, to low-frequency wave transmission in the earth, to other damping results for the earth as a whole, and to higher-frequency wave transmission and vibration results for geophysical and other solids. Good agreement between theory and experiment is found for frequency regions where adequate data are available, indicating that all the damping phenomena considered may be well described by a linear theory in the range of very small strain.

Frequency and Temperature Dependence of Internal Friction in Pure Copper

Measurements have been made at low strain amplitudes, of the internal friction, Q−1, for 99.999% pure copper for frequencies from 100 cy to 14 mc and from 4.2°K to room temperature. If one plots the Q−1 values against the log of the frequency for a given temperature, a linearly decreasing relation is obtained. At low temperatures the internal friction becomes very small. Although the loop length dependence agrees with the Koehler pinned loop model of internal friction, the present data shows that the frequency dependence does not. It is suggested that another source of dissipation is needed. The present data suggest that this is connected with the displacement occuring as the loop moves and is of a hysteresis nature. The frequency and temperature data show that the hysteresis lag in the motion cannot follow the applied stress at high frequencies or low temperatures.