Page 8 - Shimadzu Journal vol.2 Issue3

New Material

Within the scope of the microstructural investigations, Influence of relative humidity - Investigations have been
instrumented indentation tests according to DIN EN ISO 14577-1 performed at room temperature with a deformation speed of 10
were performed with an ultramicro hardness testing system mm/min. Fig. 7 shows the strain hardening curves for 25 % and
(Shimadzu, Type DUH 211/S) as a load-unload-test. During the test 90 % relative humidity.
the applied force in mN is logged as a function of the indentation
depths in µm. The maximum force is held constant for a few
seconds before relieving the load. After the test the elastic
indentation modulus is measured by a tangent applied to the
unloading curve and it corresponds to the E-modulus. For the tests
a maximum force of 98 mN (10 P) was set according to HV 0.01.

Influence of deformation speed - For the investigations of the
influence of deformation speed on the quasistatic material values,
vulcanized fiber specimens were conditioned in 40 % relative
humidity. Fig. 5 shows the strain hardening curves for 1mm/min
and 1,000 mm/min deformation speed.
Fig. 7 Influence of the relative humidity on nominal
stress-total strain-diagram

With rising relative humidity a decrease of the E-modulus and the
tensile strength and an increase of the maximum strain can be
seen. The countervailing effect of the curves is displayed in Fig. 8.
As the abovementioned explanations show, both variables
deformation speed and relative humidity have a strong influence
on the material properties of vulcanized fiber.
Fig. 5 Influence of the traverse speed on nominal
stress-total strain-diagram
With an increase of the deformation speed from 1 to 1,000
mm/min, an increase of the E-modulus and the tensile strength and
a decrease of the maximum strain can be seen. Fig. 6 shows the
three material properties as a function of the deformation speed in
linear or logarithmic scaling. At 1,000 mm/min the E-modulus
reaches the highest value of nearly 16 GPa. In linear scaling the
course of the curve indicates a saturation behavior so that
deformation speeds > 1,000 mm/min are supposed to have only a
small influence on this material property.
Fig. 8 Influence of relative humidity on E-modulus,
tensile strength and maximum strain

Fig. 6 Influence of traverse speed on E-modulus, tensile strength and
maximum strain in linear and logarithmic illustration

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