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. 

Much earlier than these encyclopedias is a book first published in 1941 (Chalmers and Quarrell 1941, I960) and devoted to the physical examination of metals . This multiauthor book includes some recondite methods, such as the study of the damping capacity of solids (Section 5.1). In the second edition, the authors remark Not the least of the many changes that have taken place since the first edition appeared has been in the attitude of the metallurgist to pure science and to modern techniques involving scientific principles. The two editions span the period to which I have attributed the quantitative revolution , in Chapter 5. 

Damping is often expressed in terms of quantities conveniently obtained with the type of instrument used. Since there are so many kinds of instruments, there are many damping terms in common use, such as the logarithmic decrement A, the half-width of a resonance peak, the half-power width of a resonance peak, the Q factor, specific damping capacity i <, the resilience R, and decibels of damping dB. 

The temperature for the acoustic damping capacity change from Nitinol was found to be different for alloys that were prepared at different laboratories (even though both alloys have identical composition). Further, the shape memory response to temperature change, such as how fast and how much force, also varied a great deal from one alloy to another. 

A number of unique physical property changes such as memory effect and acoustic damping capacity changes etc. associated with Nitinol transition have been known [47,48]. Here are some additional observations that are not well known [49] but show once again the support for the model presented for the Nitinol transition. 

Specific bulk modulus, 792 Specific conductivity, 287 Specific damping capacity, 411 Specific entropy of fusion, 791 Specific expansivity, 791 Specific heat, 791... 

Reinforcement of epoxy, polyester, and other resins for use in aerospace, marine, automotive and sports industries. We have previously mentioned the vibration damping capacity of Kevlar aramid fiber. Layers of woven Kevlar are used in skis for damping purposes and, of course, to reduce the weight. Kevlar is used as a protective sheath in fiber optic wave guides and to reinforce optical fiber cables because of its high tensile modulus and strength, and low electrical conductivity. 

Gas Composition. An increase in the carbon dioxide content of the gas produced has also been used to indicate the onset of digester failure. However, there is considerable variation in this with respect to time not only because of the lower damping capacity of the gas phase but also because the carbon dioxide content can be influenced by both chemical and biological reactions in the liquid phase. The normal carbon dioxide content for gas produced from domestic sewage sludge is 30-35%. 

Route piping from compressors or vacuum pumps which are prone to vibrate on supports independent of other process piping and use rests or sliding supports which provide some damping capacity rather than hangers. 

Solution The area under the loss modulus-temperature curve is a measure of the damping capacity or ability to absorb energy of the material. Obviously, A has a higher damping capacity than B. 

The specific damping capacity At//t/ of a system is obtained by normalizing to the maximum strain energy of the system ((r ejl) to give... 

The reciprocal of the phase angle is called the quality factor Q and is often used in the description of electric circuits. The inverse of Q, i.e., Q, is often called the loss factor. The specific damping capacity of the SLS can, therefore, be expressed as AUIU=2tt8=2ttQ. Although these factors depend on frequency, they should be independent of the stress amplitude. In order to characterize the loss peak in Fig. 5.16, it is common practice to measure the peak width at 1/V2 of the maximum loss, which is approximately equal ioQ. ... 

Assume an SLS is being subjected to sinusoidal stress cycling with ,=75 GPa, 2=70 GPa and 17 = 14 MPa s. Plot the phase difference, storage modulus and loss modulus as a function of frequency. At what frequency does the maximum energy dissipation occur What is the specific damping capacity of the material at this frequency ... 

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