It is important to point out that material constitutive models for finite-strain
behavior of amorphous polymers can only be verified in non-isothermal loading
conditions.
Concurrent heat transfer with axial stretching of PMMA requires an absolutely
fully coupled temperature-displacement analysis.
Axial force histories of H, M and L series with respect to normalized time (t n ) are
presented in Figs. 7.15, 7.16 and 7.17 Simulation and experiment results in terms of
axial force histories are reasonably in good agreement. Unified formulation of plastic
flow rule for intermolecular structure and appropriate material property definitions
ensure smooth transition of response around θ g which is bound to take place at some
stage of all non-isothermal simulations.
0
0.5
1
1.5
2
2.5
0
50
100
150
200
250
300
350
400
450
Normalized Time (t/t l +t/t d )
Axial Force (N)
(a)
TEST-H75 TEST-H90
TEST-H50
TEST-H30
0
0.5
1
1.5
2
2.5
0
20
40
60
80
100
120
140
Normalized Time (t/t l +t/t d )
Axial Force (N)
TEST-H90
TEST-H100
TEST-H140
TEST-H125
(b)
experiment
simulation
experiment
simulation
Fig. 7.15 Axial force
histories in non-isothermal
experiments and simulations
of PMMA for H series
(0.9 mm/s forming rate)
7.7 Numerical Implementation of Dual-Mechanism Viscoplastic Model
391