Thesis-1993-Dawson.pdf (4.78 MB)
The mechanical and thermal behaviour of polymers under high strain rate compression
thesis
posted on 2013-01-29, 11:01 authored by Patricia C. DawsonRelatively few studies have been carried out on polymers at high rates of
deformation compared to more traditional materials such as metals, and it
is therefore important to develop constitutive models to help predict how
materials will behave under specified conditions. The stress-strain
behaviour of polymers shows a very marked dependence on time (or rate)
and temperature. Polymers (including polyethylene, polypropylene, nylon
66, polyetherketone, polyetheretherketone, a liquid crystal polymer,
polyethersulphone and polycarbonate) have been compressed at strain
rates of -10-3 to 1O-1s-1 (using an "Instron" which measures deformation
versus time at constant rates of compression) and _103s-1 (using a novel
drop-weight impact machine) to strains of up to -100%. This drop-weight
system is different from commercially available machines in that it
operates in compression rather than fracturing specimens and provides
stress-strain data directly. The initial crystallinity and orientation of
specimens were examined using x-ray diffraction, and kinetic
decomposition parameters were obtained using differential scanning
calorimetry. Also thermocouples were inserted into some specimens
compressed at high strain rates in order to measure any rises in
temperature.
Several important results have emerged so far: I) sufficiently high bulk
temperature rises occ;ur during high rate deformation to considerably alter
the stress-strain curve from isothermal conditions; 2) localised deformation
in the form of cracking or shear banding in tough polymers appears to
lead to temperature rises sufficiently high for significant thermal
decomposition to occur; 3) data obtained at lower rates could be
approximately fitted to the Eyring Theory unlike that obtained at the
highest rate; 4) initial investigations suggest that Poisson's ratio varies
with strain and strain rate and is not a constant of 0.5 as generally
assumed.
History
School
- Science
Department
- Physics
Publisher
© Patricia Carol DawsonPublication date
1993Notes
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough UniversityEThOS Persistent ID
uk.bl.ethos.357995Language
- en