"The study of the physical properties of the manganese-copper alloys is an intriguing one. These alloys show promise of usefulness in instances in which high internal friction is needed to reduce the noise and vibrational stresses at resonant frequencies of a part of a machine. The purpose of this study has been to learn more about the internal friction of manganese-copper alloys as a function of temperature, stress amplitude, frequency, time, and past history of the specimen. From this information the mechanism for absorption of vibrational energy is proposed, or at least some progress has been made toward its determination.
The capacity of a vibrating solid to convert mechanical energy into heat, even when isolated from surroundings, is commonly manifested by a loss of amplitude of a freely vibrating body. The processes in the material which absorb vibrational energy are caused by internal friction. A perfectly elastic material would sustain a mode of vibration forever.
There are several ways in which a metal may differ from an elastic material: it may undergo plastic flow or creep, behave non-elastically, or behave anelastically. These are types of deformation without fracture. Creep is a deformation which continues to increase as long as the stress is applied. Strain is proportional to stress in a non-elastic material and there is a partial recovery after the stress is removed. Zener defines anelasticity as "that property of solids in virtue of which stress and strain are not single valued functions of one another in that low stress range in which no permanent set occurs and in which the relation of stress to strain is still linear." This means that a step force produces an immediate displacement but that there is a time delay in reaching the steady state or maximum displacement.
Common methods of measuring internal friction include the measurement of the decay rate or logarithmic decrement of a free mode of vibration which may be torsional, transverse, or longitudinal, although the decay of a torsional mode is probably the most often applied. The angle between stress and strain in a driven torsional mode of vibration is a measure of the internal friction.
The apparatus used in this study was a modified Ke torsion pendulum. The logarithmic decrements of free modes of vibration were measured over a range of temperatures for each specimen"--Introduction, pages 1-2.
Fuller, Harold Q., 1907-1996
M.S. in Physics
Missouri School of Mines and Metallurgy
v, 45 pages
© 1957 William Paul Dixon, All rights reserved.
Thesis - Open Access
Strains and stresses
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Dixon, William Paul, "Internal friction in manganese copper alloys" (1957). Masters Theses. 2559.