1.0 Introduction - University of Minnesota（1.0介绍明尼苏达大学）.pdf
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Long term performance of polymers
1.0 Introduction
Polymer materials exhibit time dependent behavior. The stress and strain induced
when a load is applied are a function of time. In the most general form can be thought of
as a 3 dimensional surface. The stress-strain-time relationship, or constitutive law, can be
determined by loading a polymer specimen with constant stress (creep) or constant strain
(stress relaxation or isometric). We can also construct isochronous curve by cross section
of the surface with constant time levels as shown in Figure 1.
constant time section
isochronous section
constant strain section
isometric section
constant stress section
creep curve
e
m
i
S T
t Strain g
r
e o
s L
s
Figure 1. Constant stress-strain-time coordinates [1]
1.1 Creep, constant load
When a plastic material is subjected to a constant load, it deforms continuously
(Figure
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