The effect of temperature and pressure on necking behaviour of polycar
bonate was studied in tension. Following the concepts elucidated by Co
ates and Ward, neck geometry and neck propagation were related to the
materials parameters: strain rate sensitivity and strain hardening par
ameter. The relationship between neck profile and the true stress-true
strain curve was established by combining an analytical expression fo
r the macroscale mechanics of the flow process with a constitutive equ
ation describing the true stress, true strain and true strain rate dep
endence of the material. Having assumed a constitutive equation, the m
aterials parameters were obtained from the stable neck geometry. The s
train hardening parameter was found to be insensitive to changes in pr
essure and temperature in the range studied and had a value of approxi
mately 3.3. Since the strain hardening parameter affected primarily th
e draw ratio, the latter was essentially independent of temperature an
d pressure. The increase in strain rate sensitivity parameter with pre
ssure and decreasing temperature from 0.028 to 0.035 was manifest as a
gradual broadening of the neck. The molecular significance of the mat
erials parameters is discussed in terms of the contributions of two se
parate processes to plastic deformation: thermally activated yielding
and the temperature and pressure independent stretching of a molecular
network.