Page 68 - Plastics Engineering
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Mechanical Behaviour of Plastics 51
A
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10000
-
lo00
-
100
-
10
1-
-
0.1
0.01 '
Log (time) b
Fig. 2.9 Typical variation of creep or relaxation moduli with time
18
14
20
16 C.C
? \
d l2
03
OL
Fig. 2.10 Construction of isometric and isochronous graphs
The creep modulus will vary with time, i.e. decrease as time increases, in a
manner similar to that shown for the relaxation modulus. The classical variation
of these moduli is illustrated in Fig. 2.9. On log-log scales it is observed that
there is a high value of creep or relaxation modulus at short times. This is
referred to as the Unrelaxed Modulus and is independent of time. Similarly at
long times there is a low value Relaxed Modulus which is also independent
of time.
