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

Abstract

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 5th percentile Female ATD lumbar spine prototype. In addition, these curves evaluated the suitability of elastomer materials for manufacturing the lumbar spine prototype. Forty-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). 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. 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 was selected as a suitable material for manufacturing the lumbar spine prototype.