Page 55 - Zmist-n2-2015

Fig. 1. The scheme of the test stand:
1 – testing machine MTS 858 Mini Bionix;
2 – computer software; 3 – digital control
FlexTest SE; 4 – dynamic extensometer
Instron 2620-601.

Monotonic tensile and appropriate
tests were carried out on the fatigue testing
machine MTS 858 Mini Bionix with
digital control FlexTest SE (Fig. 1). For
the displacement measurement, and in
order to control the dynamic load the

extensometer Instron 2620-601 with the
measurement base of 20 mm and a range of ±2.5 mm was used. The samples were
mounted in the testing machine by the specially designed handles.

Table 1. The parameter values of the porous sintered material 316L
with three degrees of porosity compared to the solid material values

Porosity p, % 41 33 26 Solid 316L [10]
3
Density r, g/cm 4.5 5.2 5.8 8
Yield R 0,2 , MPa 47.0 74.2 106.0 220
Tensile strength R m , MPa 58.2 101.6 175.9 530…680
Young Modulus E, GPa 32.9 53.2 72.2 200
Elongation A 5 , % 1.78 3.23 6.31 40

Prior to strength testing, a monotonic
tensile test was performed on specimens
prepared from sintered 316L steel, with
different degrees of porosity. The nominal
stress-strain curves were obtained (Fig. 2).
To calculate the stress only the original
cross-sectional area of the sample was
taken into account. Because of the sample
shape there was no technical possibility to
measure their displacement during the
loading process. The basic mechanical
properties of this material were evaluated
(Table 1).

The uniaxial cyclic oscillating (sym-
Fig. 2. Monotonic tensile curves of sintered metrical) loading was applied. This is
316L stainless steel of different porosity: because the sintered porous 316L stainless
1 – p = 41%; 2 – 33; 3 – 26%.
steel for joint endoprosthesis components
are exposed to compressive and bending stresses with dangerous tensile zones. The
following parameters as: sample loading force, elongation of the extensometer base and
the number of cycles to crack initiation were recorded during the study. The averaged
deformation of the measurement base was the control variable. The frequency of load
change was f = 0.5 Hz. The study included various ranges of the control variable (strain
amplitude e a): 0.01, 0.008, 0.007, 0.005, 0.004, 0.0035, 0.002 [11]. Each trial was
repeated three times.

54