Page 8 - Shimadzu Journal vol.2 Issue3
P. 8

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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