Damping characteristics

Free- Vibration Methods. Free-vibration instmments subject a specimen to a displacement and allow it to vibrate freely. The oscillations are monitored for frequency and damping characteristics as they disappear. The displacement is repeated again and again as the specimen is heated or cooled. The results are used to calculate storage and loss modulus data. The torsional pendulum and torsional braid analy2er (TBA) are examples of free-vibration instmments. 

An object can acquire the following four types of damping characteristics ... 

The occurrence of thermal failures in a plastic depends not only on the cyclic frequency and applied stress level but also on the thermal and damping characteristics of the material. For example, polycarbonate has very little... 

Excellent Bonding to Metals and Fabrics Excellent Vibration Damping Characteristics Excellent Flex Life in Dynamic Applications Excellent Weatherablllty Fungus Resistant Flame Resistant... 

As the name suggests, epoxidised NR is prepared by chemically introducing epoxide groups randomly onto the NR molecule. This chemical modification leads to increased oil resistance, greater impermeability to gases, but an increase in the glass transition temperature, Tg, and damping characteristics the excellent mechanical properties of NR are retained. 

Dynamic Mechanical and Thermomechanical Analysis. A DuPont Model 981 DMA was used to determine the dynamic modulus and damping characteristics of baseline and irradiated specimens. Transverse composite samples 1.27 cm x 2.5 cm were used so that the modulus and damping data were primarily sensitive to matrix effects. Data were generally determined from -120°C through the glass transition temperature (Tg) of each material using a heating rate of 5°C/min. 

The most important characteristics of butyl rubber are its low permeability to air and its thermal stability. These properties account for its major uses in inner tubes, tire inner liners, and tire curing bladders. Because of the poor compatibility of butyl with other rubbers (with respect to both solubility and cure), the halobutyls are preferred. The brominated p-methylstyrene-containing butyl rubbers are used in a number of grafting reactions for tire applications and adhesives. Other uses for butyl rubber are automotive mechanical parts (due to the high damping characteristics of butyl), mastics, and sealants.55... 

Kevlar aramid fiber has good vibration damping characteristics. Dynamic (commonly sinusoidal) perturbations are used to study the damping behavior of a material. The material is subjected to an oscillatory strain. We can characterize the damping behavior in terms of a quantity called the logarithmic decrement, A, which is defined as the natural logarithm of the ratio of amplitudes of successive vibrations, i.e. 

Schulze, K.D. "Investigation of Damping Characteristics of Constrained Layer Plates and Small Homogenous Specimens," Thesis, September 1985, Naval Postgraduate School, Monterey, CA 9343-5100. 

The principal characteristics of polymers which control their ability to dissipate energy are their stiffness, surface mass, and their inherent damping characteristics. In this chapter we are only concerned with the last of these three. Briefly, however, if lack of stiffness is a problem with a particular polymer in a damping system, this can be enhanced, if not completely obviated, by using the material in a constrained layer (29) mode. Surface mass refers to the mass of material behind a unit surface area. Clearly, for polymers which are all inherently low density materials, this can be increased by the incorporation of dense, particulate fillers such as lead, barytes etc. 

As part of this study on IPN compatibility and damping characteristics the creep behavior of bulk and emulsion polymerized IPN s will be compared to explore the morphological differences expected. 

Surface rheology Viscoelasticity of the monolayer differentiation between fluid and solid phases. Surface elasticity and viscosity in the transversal and longitudinal mode wave damping characteristics. Relaxation processes in monolayers. Mechanical stability of the monolayer. Interpretation often complicated because several molecular processes may be involved and because viscous and elastic components may both contribute. 

---