Damping behavior

Fig. IV-10. Wave-damping behavior of polydimethylsiloxane heptadecamer on water at 25°C at (a) 60 cps and (b) 150 cps. Curve (c) gives the ir-

Undei damped behavior. Measurement devices with mechanical components often have a natural harmonic and can exhibit underdamped behavior. The displacer type of level measurement device is capable of such behavior. 

It is difficult to specify accuracy in this experiment. One reason is that there may be sampling effects, i.e., wide variability in the samples used. Consequently, the sample should be homogeneous and representative. There is a strong dependence of the modulus and damping behavior on molecular and structural parameters. Entrapped air/gas may affect the results obtained using powder or pellet samples. 

Fig. 7. Influence of composition on the damping behavior of perfectly alternating block copolymers [52]...

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. 

Damping Behavior of Silent Paint . The damping behavior of a typical "Silent Paint" composition, cross-polv(ethyl methacrylate)-inter-cross-poly(n-butyl acrylate) 25/75, constrained with epoxy resin, was then compared with several commercial materials as a function of temperature. Figure 3. The "Silent Paint" composition, curve A, damped effectively over a broad temperature range whereas the commercial materials, curves B and C [poly (vinyl acetate) ], and D, E, and F, of various compositions, damped effectively over narrower temperature ranges. 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

The damping behavior of polymers can be altered to optimize either the temperature span covered or the damping effectiveness for particular temperatures. The area under the loss modulus temperature curve tends to be constant for some polymer combination, which has been expressed by the empirical "temperature band width law" of Oberst (2) ... 

The changes which occur in thermosetting resins undergoing cure have been studied by a variety of techniques. Supported sample methods have been used to monitor the relative changes modulus and damping behavior from the initial low viscosity liquid to the fully cured rubbery or glassy state. Torsional braid analysis (TBA) employs a resin sample impregnated on a... 

Using a computerized data reduction scheme that incorporates a generalized WLF equation, dynamic mechanical data for two different polymers were correlated on master curves. The data then were related to the vibration damping behavior of each material over a broad range of frequencies and temperatures. The master curves are represented on a novel reduced temperature nomograph which presents the storage modulus and loss tangent plots simultaneously as functions of frequency and temperature. ... 

In the same work, the damping behavior of those three component LIPNs was evaluated from the integrals of the linear loss shear modulus vs. temperature (loss area, LA) and linear tan 8 vs. temperature (tan 8 area, TA) curves measured by... 

Polyacrylate (PAcr) Poly(n-butyl acrylate) (PnBA) Damping behavior Wu and Zhao 1996... 

DMA provides materials scientists, pol5mer chemists, and design engineers with detailed information on the elastic and inelastic (plastic) deformation of materials, modulus, and damping (energy dissipation) properties of materials. The damping behavior of S5mthetic and natural mbbers is important in vibration and acoustic application, for example. 

Thermoreversibility of physical aging has been demonstrated in the time-dependent rate of stress relaxation as v/ell as in the damping behavior of the p-transition. 

Torsional braid analysis (TBA) The damping behavior of the torsion of a glass liber probe impregnated with the resin is characteristic for the increase of stiffness. 169,171,378... 

Liquids, on the other hand, flow if snbjected to a stress they do not store the energy bnt dissipate it almost entirely as heat and thns possess high damping ehar-acteristics. Viseoelastie polymers exhibit both elastic and damping behavior. Hence, if a sinusoidal stress is apphed to a linear viscoelastic matmal, the resnlting strain will also be sinusoidal, but wiU be out of phase when there is energy dissipation or damping in the polymer. 

Several authors used the continuum mechanics for modeling conventional polymer composites as well as PNC. Ren and Krishnamoorti [2003] used a K-BKZ integral constitutive model to predict the steady-state shear behavior of a series of intercalated nanocomposites containing an organo-MMT and a disordered styrene-isoprene diblock copolymer. The model predicts the low-y shear stress properties calculated from the experimental linear stress relaxation and the relaxation-based damping behavior. However, as it does not take into account the effect of clay platelet orientation, it is unable to predict the shear stress behavior at intermediate y and the normal stress behavior at all y and clay contents. 

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