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** Measurement of Internal Friction **



In the following are the summary of the technical reports on the recent internal friction data and comparisons of the methods of measurement to be sent bimonthly to the registered customers by facsimili.

How to measure the activation energy of internal friction

The practical method and procedure to obtain the activation energy of internal friction from decay constants and described in the following.
In general, when stopping the forced vibration, the vibration of a material will turn to the characteristic one and be damped freely. Origin of the damping may be, for inatance, special atomic jumps, oscillation of dislocation segments or others, and its relaxation time is given by the form

@@@tt0‚…Q/RT

where t0 is the frequency factor, Q the activation energy, R the gas constants, and ‚s the absolute temperature.
When w is employed in the measurement, the internal friction peak will be maximum at

tw‚P

where w2*3.1415*‚†.@(f is the ordinary frequency /secj


By using a frequency w‚P and measuring the temperature dependence of internal friction of a material, the resonance peak will be observed at a temperature ‚s‚P and the ralation

t‚P‚P^w‚P  exp(Q/RT1j/w 0

is obtained. By taking natural logarithm of the equation is given

lnw1 -Q/RT1+ lnw0
Making another specimen of the same material with different frequency (by changing a dimension or the method of the measurement on the same specimen), one will be able to observe a similar resonance peak at another temperature, ‚s2 with a different frequency, w2 , and a similar equation.

@lnw2 -Q/RT2+ lnw0
will be made.

In the last two equations, wi(-2*3.1415*f) and Ti can be determined experimentally, and by plottin the two sets of [w‚‰, T‚‰] in the diagram of l‚Žw vs 1/RT, as shown in the figure on the right, the inclination of the straight line connecting the two points will give us the activation energy Q.


In addition, the point on the coordinate cut by the straight line in the figures gives the value of -lnt0, and the frequency factor t0 can be found. If the correlation between the value of the frequency factor and the origins of damping, such as the atomic jumps, lattice vibration, dislocation motion, electron relaxation, etc., is known, the data of t0 will give us important information on the internal structure of the specimen.

The data pile up on the relation between the internal friction and activation energy is most advanced and plenty in the study of iron, steel and other metals and greatly helps the research and development of various advanced materials.

The aparratures to measure the high temperature elastics moduli, EG-HT and JE-HT, are not only measuring the dynamical elastic constants but also able to measure in parallel internal friction, from which the activation energy and the frequency factor are easily obtained to study physical properties of materials. Especially, in the case of EG-HT, the parallel measurements of Young's modulus and modulus of rigidity have been realized for the first time, and, in addition, damping in lateral and twisting vibrations can be measured simultanuously. The precise study of internal friction in different vibrational modes and directions is now possible by our equipments, which woud enhance largely the study of properties of materials.


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