High-strain-rate tensile mechanical response of a polyurethane elastomeric material

The dynamic tensile mechanical response of a soft polymer material (Clear Flex 75) is investigated using a split Hopkinson tension bar (SHTB). Stress-strain relations are derived to reveal the mechanical properties at moderate and high strain rates. These relations appear to be rate dependent. Under static loading, the polymer exhibits an elastomeric behaviour, while under dynamic loading, the response is elasto-plastic with a hardening branch. The critical strain rate for transition from a rubbery-like behaviour at low strain rates to a glassy-like behaviour at high strain rates at room temperature is determined. The axial and lateral deformation of the specimen in the SHTB test is recorded by a high-speed camera. The final fracture surface is examined by SEM to explore the physical origins of deformation and fracture behaviour: void formation, craze nucleation, craze extension, crack initiation and propagation. Meanwhile, a shielding mechanism is revealed by the observation of crazing and micro cracking in the crack tip zone, which contributes to the dynamic tensile toughness of CF 75 polymer material.