| A series of
experiments were
performed to study the
thermomechanical coupling
in steel, polyamide and
shape memory alloy. The
temperature
characteristics related
to the mechanical graphs
allows us to investigate
the phenomena that occurs
in the material during
its deformation. The
temperature measurements
were effected by
monitoring the infrared
radiation from the
surface of the specimen
during its deformation,
which requires no
physical contact with the
deforming body and
influence on the high
accuracy of obtained
results. Temperature
evolution during elasto-plastic
transformation of steel:
The effects of the
thermomechanical coupling
occurring in sheet
samples subjected to
tensile test and just
after the interruption of
this process, were
examined. The samples
made of the austenitic
steel were subjected to
elongation by means of a
testing machine with a
constant rate of loading
and unloading equal to 2´
10-3 s-1.
The gauge length was 25 5
mm. The testing were
carried out in the
following way: loading up
to 4 % of deformation (beyond
the yield point),
unloading, cooling the
specimen to its initial
temperature and straining
to 4 % again. Five such
cycles for each of steel
sample were performed in
this way. The initial
changes of temperature of
the specimen subjected to
the successive cycles of
loading and described as
a function of stresses
are shown in Figure.
Looking at
the figure it is seen,
that the initial parts of
deformation, found for
each cycle, are situated
on the same straight line:
 which
describes the elastic
deformation of the
specimen and
characterises its
material (k is the
coefficient depending on
the kind of material and
the test conditions;
Pieczyska, 1999). The
departure of the
temperature
characteristics from the
straight line indicates a
change in the character
of the process; it goes
from the elastic to the
elasto-plastic
deformation.
E.
Pieczyska, “Thermoelastic
effect in austenitic
steel referred to its
hardening”, J.
Theor. Appl. Mech., 2, 37,
1999; 281-306
Thermomechanical
effects in polymers:
The next figure shows an
example of the stress and
the temperature changes
as a function of time,
obtained during cycling
of a polyamide sample.
The thermoelastic
effects, e.g. the
decrease in temperature
during loading and the
increase in temperature
during unloading,
similarly to that
observed in steel are
registered. The
temperature changes are
higher than found for
steel - exceed 1K. It is
most observable during
the two beginning cycles,
when the viscoplastic
effect is not noticeable.
In the following cycles
thermoelastic effects are
not so noticed. The
increases in temperature
become higher and higher
because of the heat
development during the
viscoelastoplastic
deformation and small
heat dissipation.
Thermomechanical
coupling during loading
and unloading of SMA: Temperature
distribution on the
sample surface of shape
memory alloys deformed at
room temperature was
homogeneous, while
obtained at elevated
temperature was not
homogeneous; it shows a
traces of a origin and
development of martensite
phase. Especially
interesting results are
the temperature changes
obtained for various
strain rates and
described as a function
of stress. The results
obtained for the
temperature 295 K are
presented in Figure.
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