19. Overcoming Challenges in Material Characterization of Polymers at Intermediate Strain Rates

Simulations of dynamic loading on polymers often require rate dependent, large-strain material test data to sufficiently calibrate material laws such as nonlinear viscoelastic–viscoplastic. Physical testing at intermediate strain rates creates many challenges because the measurements are susceptible to distortion due to factors including: test specimen variations, fixtures, hydraulic actuator control, instrumentation complexity, data acquisition, electrical noise and post processing. For example, hidden time delays within the total data acquisition system (load cells, displacement sensors, amplifiers/conditioners) create confusion when specimen failure captured by a sensor does not agree in time with images from high speed video. Additionally, noise in measurements can occur due to sample misalignment, fixture and test-stand rigidity, subtleties of a slack adapter (if one is used), and distortions caused by the test environment. After care is taken to minimize structural-born distortions, noticeable levels of noise and oscillations may still exist from these mechanical sources as well as electrical sources such as channel cross-talk of a video camera shutter pulse bleeding onto other sensor channels. Ultimately, prudent use of DSP techniques may be needed to further improve data quality and interpretation. This paper demonstrates success over many such difficulties when performing tensile tests of polymer materials up to 100 s⁻¹.