Internal friction damping

Kerwin, E. M., Jr. In Internal Friction Damping and Cyclic Plasticity ASTM Special Technical Publication No. 378 American Society for Testing and Materials Philadelphia, 1965 pp 125-149. 

J.D. Morrow, Symposium on Internal Friction, Damping and Cyclic Plasticity ASTM STP 1964, p 378... 

Morrow, J. Cyclic plastic strain energy and fatigue of metals. Intern. Friction Damping Cyclic Plast ASTM-STP 378, 45 (1965)... 

Morrow, J.D. Internal friction, damping and cyclic plasticity. American Society for Testing and Materials, ASTM STP-378, pp. 45-87 (1965)... 

Morrow, J.D. Cyclic Plastic Strain Energy and Fatigue of Metals. International Friction, Damping and Cyclic Plasticity, pp. 45-86. ASTM, PA (1965)... 

Zho] Optical microscopy, TEM Internal friction, damping capacity... 

Modtilus Measurements Another SCC test technique is the use of changes of modulus as a measure of the damping capacity of a metal. It is known that a sample of a given test material containing cracks will have a lower effec tive modulus than does a sample of identical material free of cracks. The technique provides a rapid and reliable evaluation of the susceptibility of a sample material to SCC in a specific environment. The so-called internal friction test concept can also be used to detect and probe nucleation and progress of cracking and the mechanisms controlling it. 

Such transformations have been extensively studied in quenched steels, but they can also be found in nonferrous alloys, ceramics, minerals, and polymers. They have been studied mainly for technical reasons, since the transformed material often has useful mechanical properties (hard, stiff, high damping (internal friction), shape memory). Martensitic transformations can occur at rather low temperature ( 100 K) where diffusional jumps of atoms are definitely frozen, but also at much higher temperature. Since they occur without transport of matter, they are not of central interest to solid state kinetics. However, in view of the crystallographic as well as the elastic and even plastic implications, diffusionless transformations may inform us about the principles involved in the structural part of heterogeneous solid state reactions, and for this reason we will discuss them. 

The linear model of Equation (4) gives a representation of damping of vibrations by internal friction 2J. When a steady sinusoidal excitation is involved, the internal friction causes a phase delay in the transmission of signals through the material which can be expressed as a loss-tangent, tan 5, which is related to i6, y and the frequency w, of the signal by... 

Equations 11.8 and 11.9 are isomorphous to equations 9.9 and 9.10 which define the storage and loss components of the complex dielectric constant . Similar equations are also used to define the complex bulk modulus B, the complex shear modulus G, and the complex Poisson s ratio v, in terms of their elastic and viscous components. The physical mechanism giving rise to the viscous portion of the mechanical properties is often called "damping" or "internal friction". It has important implications for the performance of materials [8-15],... 

Most real systems, as distinct from idealized assemblies of point masses linked by two-body forces, show deviations from the simple behaviour discussed in the previous sections. One of these types of more complex behaviour is associated with the internal friction of the material which leads to the damping of free vibrations, even in the most perfectly isolated systems. We have seen that the most convenient way of determining elastic moduli is by examining the vibration frequencies of carefully shaped samples and, in the same way, internal friction or mechanical relaxation can be studied by examining the logarithmic decrement of these same vibrations when the external excitation is removed. The logarithmic decrement 8 is so defined that an oscillation of angular frequency (o is damped by a factor exp (- It is thus n times the loss... 

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