Strain damping

By calculating the energy to heat it is possible to determine the vibration levels to which the structure can be exposed and still exhibit critical damping. There is one area that must be evaluated. Plastics exhibit a spectrum of response to stress and there are certain straining rates that the material will react to almost elastically. If this characteristic response corresponds to a frequency to which the structure is exposed the damping effect is minimal and the structure may be destroyed. In order to avoid the possibility of this occurring, it is desirable to have a curve of energy absorption vs. frequency for the material that will be used. 

A technique for performing dynamic mechanical measurements in which the sample is oscillated mechanically at a fixed frequency. Storage modulus and damping are calculated from the applied strain and the resultant stress and shift in phase angle. 

C. Fluctuations are partially damped by chain interferences. This leads to a result intermediate between A. and B. To be specific, a model proposed by Flory (16) is adopted here. In this model, the inhibitory influence on junction fluctuations is assumed to be affine in the strain. One finds... 

Factorizability has also been found to apply to polymer solutions and melts in that both constant rate of shear and dynamic shear results can be analyzed in terms of the linear viscoelastic response and a strain function. The latter has been called a damping function (67,68). 

The strain-stress relationship ay = Cykfiki is valid when strain is instantaneously provoked by stress, i.e., no dephasing process occurs. In fact, it was observed that the magnitude of acoustic waves decreased as a function of the travelling distance. Introducing a damping term proportional to the time course of strain variations can solve this discrepancy ... 

An important aspect of any structure is its ability to store energy when work has been done on it by imposing a strain. One result of this storage ability is that an impulse can be transmitted over significant distances, i.e. a wave can travel through the material over distances comparable to the wavelength or greater. Loss processes will inevitably occur and at low Deborah numbers the viscous processes rapidly damp out the oscillation... 

For this to happen we know that f(y) = y in the low shear limit. As the shear stress is increased we also know that we want our viscosity to fall so we need to multiply our strain by a damping function that reduces from unity at low strains to a lesser value at high strains. A good candidate for... 

Dynamic mechanical testers apply a small sinusoidal stress or strain to a small sample of the polymer to be examined and measure resonant frequency and damping versus temperature and forced frequency. Instrument software computes dynamic storage modulus (G ), dynamic loss modulus (G") and tan delta or damping factor. Measurements over a wide range of frequency and temperature provide a fingerprint of the polymer with sensitivity highly superior to DSC. 

Epoxidized natural rubber is still a strain crystallizing mbber and therefore retains the high tensile strength of natural rubber. However, as can be seen from Table 5, in other respects they have very little in common. The epoxidation renders a much higher damping mbber, a much-improved resistance to oil swelling (insofar as a 50 mol % modified natural mbber has similar oil resistance to a 34% nitrile mbber), and much-reduced air permeability. This latest form of modified natural mbber therefore widens the applications base of the natural material and enables it to seek markets hitherto the sole province of some specialty synthetic mbbers. 

Polymer liquid crystal solutions respond in an interesting way to a transient flow field. For example, a damped oscillatory response was observed upon a flow inception or flow reversal [150,156,157], and the strain was recovered to some extent after a creeping flow [158], These phenomena suggest that liquid crystal solutions have some textured structure, i.e., the spatial variation in the... 

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