Structure vibration damping properties

Structural adhesives, which have found applications in the aircraft, automobile, construction, and electronics industries, can alleviate the problems caused by stress concentration and provide additional advantages to the bonded system (see the introductory chapter of this book). Many adhesive applications involve the joining of high-modulus substrates such as metals, wood, composites, and plastics where the adhesive provides a medium for stress transfer between the substrates. The adhesive layer improves the vibrational damping capabilities of the system. Although the bonded system is susceptible to property degradation by environmental exposure, the adhesive layer increases the corrosion resistance when dissimilar metals are bonded. 

Table 5.3 lists the principal experimental methods used in dynamic mechanical testing. Of the experiments considered below, the thermal scan mode (method 1) is the technique most commonly used by thermal analysts. Here typical applications in quality control or processing look for differences in material batches, thermal history, different grades, reactivity, and other characteristics. The stepped isotherm (or step isothermal) experiment (method 2) is used mainly in studies involving detailed mechanical property determination for structural analysis, vibration damping applications, and for determining time-temperature superposition master curves. Method 3 (fast scan or single isotherm) is application specific. 

The molecular structure of the polyisobutylene ehain provides less flexibility and greater delayed elastie response to deformation than most elastomers. This imparts vibration damping and shoek-absorption properties to butyl rubber products. 

Solvent can affect the electronic structure of the solute and, hence, its magnetic properties either directly (e.g. favouring more polar resonance forms) or indirectly through geometry changes. Furthermore, it can influence the dynamical behaviour of the molecule for example, viscous and/or oriented solvents (such as liquid crystals) can strongly damp the rotational and vibrational motions of the radical. Static aspects will be treated in the following, whereas the last aspect will be tackled in the section devoted to all the dynamical effects. 

The following chapter covers several important steps in the design of a damping system. Designer must 1) verify that there is a problem which is indeed the result of resonant vibration, 2) define the dynamic characteristics of the structure under consideration and 3) define the environmental conditions in which the structure operates. These parameters are required because damping material properties are dependent on both the frequency and the temperature at which the problem occurs. 

We now present temperature measurements of the vibrational properties of the T) phase. Type II diamonds were used for mid-IR measurements to avoid interference with the characteristic absorption of the sample. The representative absorption spectra at different temperatures (see Fig. 14) clearly show the presence of a broad 1700 cm IR band (compare with Fig. 12). Its presence was also observed in the sample heated to 495 K at 117 GPa (see below). The position of the band and its damping (if fitted as one band) does not depend on pressure and temperature within the error bars. The Raman spectrum of the Tj phase obtained on heating (see below) does not show any trace of the molecular phase (see Fig. 12(b)). Careful examination of the spectrum in this case showed a weak broad band at 640 cm and a shoulder near 1750 cm (both indicated by arrows in Fig. 12(b)). For an amorphous state, the vibrational spectrum would closely resemble a density of phonon states [63] with the maxima corresponding roughly to the zone boundary acoustic and optic vibrations of an underlying structure [3-5, 55], which is consistent with our observations. The only lattice dynamics... 

Damping Characteristics. Damping causes vibrations to decay in an elastic structure and depends on the vibration frequency, the material of the elastic structure, the geometry, and the physical properties of the surrounding fluid (in the case of a shell-and-tube heat exchanger, the surrounding fluid is the shell fluid). 

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