Mechanical test on different elastomer materials based on the ASTM D412-16 standard

Aim: The main goal of conducting the mechanical tensile tests was to
produce non-linear stress-strain curves for input data in the Ansys
Workbench software. These curves played an important role in the accurate
analysis of the mechanical behavior of the Finite Element Model (FEM) of
the Hybrid III 5% Female ATD lumbar spine prototype. In addition, these
curves evaluated the suitability of elastomer materials for manufacturing
the lumbar spine prototype. Method: Fourty-five Mechanical tensile tests
were performed on five different elastomer materials (NR60, EPDM60, NEO60,
CCP60, and CCP80) based on the ASTM D412-16 standard at three different
strain rates including the standard strain rate (0.32 or =8mm/s), moderate
strain rate (0.64 or =16mm/s), and high strain rate (4 or =100mm/s).
Samples with standard and moderate strain rates were taken to failure
using the MTS Insight 2 tensile testing machine. However, samples were not
taken to failure in high strain rate testing due to the limited crosshead
displacement (100mm) of the tensile testing machine (MTS 858
Bionix).  Result: The EPDM60 material with a tensile strength of
9.6 MPa demonstrated minimal Strain Rate Sensitivity (SRS =-0.06) up to
100% strain. The NR60 and CCP80 materials had greater tensile strength
(18.5 MPa and 14.8 MPa) than EPDM60, but medium strain rate sensitivity
(SRS -0.11 and -0.15). The CCP60 and NEO60 materials had lower tensile
strength (5.3 MPa and 4.8 MPa) than EPDM60, but the medium (SRS =-0.12)
and maximal strain rate sensitivity (SRS=-0.3), respectively. Conclusion:
The EPDM60 and NR60 materials appeared to be suitable for manufacturing
the lumbar spine prototype, as EPDM60 exhibits minimal SRS, whereas NR60,
despite a slight difference with a minimal range of SRS, showed maximal
strength. Results of the FEM analysis showed that the lumbar spine
prototype by using NR60 performs better than EPDM60. Therefore, NR60 as a
suitable material was selected for manufacturing the lumbar spine
prototype.