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Mechanical Behaviour of Plastics 91

0 tl 12 Time

Fig. 2.39 Response of combined Maxwell and Kelvin models

0
0 100 200 300 400 500
Time (hours)

Fig. 2.40 Creep curve for acrylic at 20°C
Solution The spring element constant, 61, for the Maxwell model may be
obtained from the instantaneous strain, ~1. Thus
,--=-- 14 - 2800 MN/m2
oo
' - e1 0.005
The dashpot constant, VI, for the Maxwell element is obtained from the slope
of the creep curve in the steady state region (see equation (2.32)).
a0 14
?)I=-= = 1.2 x io7 MN.iu/m2
E 1.167 x
= 4.32 x 10" MN.s/m2