Mechanical dissipation factor

A linear relationship exists between the toughness (integrated stress-strain curve) and the dynamic mechanical dissipation factor. The types of materials that fit this relationship include glassy polymers, elastomers, and an impregnated fabric. The existence of this relationship indicates that toughness arises from the molecular motions which give rise to the dynamic mechanical properties. 

As both referees pointed out, other reasons have been offered for energy dissipation during impact. In each case however some energy dissipating mechanism must be provided. The present work indicates that, at least for the samples used, this mechanism is provided by the dynamic mechanical dissipation factor. This in turn is attributed to the fact that at the high strain rates of impact the linear viscoelastic region is the largest, if not the only, contributor to the dissipation process. 

The storage modulus, E, represents the ability of the material to elastically store the absorbed mechanical energy as potential energy. The loss modulus, E", represents the ability to dissipate the absorbed energy as heat The ratio between the dissipated and stored mechanical energy is referred to as the mechanical dissipation factor. 

Figure 12.15 Polystyrene data mechanical dissipation factor versus temperature for fractions. Fractions 1, 4, 9, 29, and 34 were tested. (Reprinted with permission from Merz, E. H., L. E. Nielsen, and R. Buchdahl Influence of Molecular Weight on the Properties of Polystyrene, Ind. Eng. Chem., vol. 43, pp. 1396-1401, 1951. Cop3night 1951 American Chemical Society.)...

The dichroic dissipation factor may also be defined in a way analogous to the mechanical dissipation factor tan S (eqn [29]). 

Dielectric strength, kV mm Electrical Volume (dc) resistivity, ohm-cm Dielectric constant (60 Hz) Dielectric constant (10 Hz) Dissipation (power) factor (60 Hz) Dissipation factor (10 Hz) Mechanical Compressive modulus, 10Mb in-2 9.8-12 24-31 16-24 1014-1016 4.5-6.0 19 335-600 14 ... 

Polytetrafluoroethylene transitions occur at specific combinations of temperature and mechanical or electrical vibrations. Transitions, sometimes called dielectric relaxations, can cause wide fluctuations in the dissipation factor. 

BiaxiaHy orieated PPS film is transpareat and nearly colorless. It has low permeability to water vapor, carbon dioxide, and oxygen. PPS film has a low coefficient of hygroscopic expansion and a low dissipation factor, making it a candidate material for information storage devices and for thin-film capacitors. Chemical and thermal stability of PPS film derives from inherent resia properties. PPS films exposed to tolueae or chloroform for 8 weeks retaia 75% of theh original streagth. The UL temperature iadex rating of PPS film is 160°C for mechanical appHcatioas and 180°C for electrical appHcations. Table 9 summarizes the properties of PPS film. 

Electrical and Mechanical Properties. Electrical properties include dielectric strength, dielectric constant, dissipation factor, and volume resistivity these properties can change with temperature and absorbed water. 

The dissipation factor of a polymer (which we also refer to as tan 5) is the ratio of energy lost to the energy stored when it is placed in an alternating field. The dissipation factor is analogous to a mechanical tan 8 describing rheological behavior. The dissipation factor at a specific frequency is defined according to Eq. 8.14. 

Insulation Integrity. Insulation integrity is a function of an interlayer dielectric/passivant defined by specific electrical, mechanical and passivation properties. The D.C. electrical property of interest is the I-V characteristic which is used to deduce conductivity and breakdown field strength. The corresponding A.C. electrical property is dissipation factor. The pertinent mechanical and passivation properties are, respectively, pinhole density and performance rating as a diffusion barrier to Na" " and H2O. 

With conventional heating, energy transfer occurs mainly through conduction and convection. With microwaves, the primary mechanism is dielectric loss4,52. The dielectric loss factor (loss factor, s") and the dielectric constant ( ) of a material are two determinants of the efficiency of heat transfer to the sample. Their quotient ( "/ ) is the dissipation factor (tan 8), high values of which indicate ready susceptibility to microwave energy. 

Dielectric constant (60 Hz) Dielectric constant (106Hz) Dissipation (power) factor (60 Hz) Dissipation factor (106Hz) Mechanical Compressive modulus, 103lb in-2 ... 

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