Page 215 - Handbook of Plastics Technologies
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ELASTOMERS
ELASTOMERS 4.7
FIGURE 4.5 Dynamic shear deformation.
FIGURE 4.6 Dynamic stress and strain as a function of time.
The two moduli are functions of temperature and frequency. The parameters G′ and
tan δ, for a typical uncross-linked (unvulcanized) rubber or elastomer, are shown in
Fig. 4.8 as a function of temperature (with frequency on the order of 1 Hz). The parame-
ters are plotted against frequency, at a constant temperature, in Fig. 4.9. Thus, one ob-
serves that an increase in frequency (equivalent to an increase in strain rate) is similar to a
decreased temperature.
With increasing temperature (from below T ), tan δ increases and then decreases, with
g
a maximum (peak) value at a temperature where the storage modulus G′ decreases, with
respect to temperature, at about the maximum rate. This temperature also corresponds to
the glass transition. In this transition region of temperature, the material is relatively soft
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