The Shock Induced Mechanical Response of the Fluorinated Tri-polymer, Viton B

The response of Viton B, a fluorinated tripolymer, to one dimensional shock loading has been investigated using manganin stress gauges as the diagnostic. These have been mounted such that they are sensitive to both the longitudinal and lateral components of stress. In the case of the longitudinal gauges, mounting at multiple locations within the target assembly also allows measurement of shock and release velocities as well. Results show that in terms of shock velocity and stress and shear strength, results from Viton B lie a little higher than the corresponding results for polytetrafluoroethylene (PTFE), but more similar to those of polyvinylidene difluoride (PVDF). However, in terms of the release velocity, the behaviour of Viton B is more akin to PTFE. We believe that there are two competing mechanisms at play; an electrostatic repulsion between chains due to the presence of electronegative fluorine atoms that acts against interchain interactions (hence the low shock and high release velocities) and interchain entanglement (tacticity) due to the presence of trifluoromethyl side groups on one of the monomer sub units. This will result in a greater shock velocity and increase in shear strength behind the shock front (when compared to PTFE) as adjacent polymer chains physically interact via entanglement. This should reduce the release velocity for similar reasons; however the release behaviour of Viton B and PTFE is similar. We thus suggest that the electrostatic repulsion between chains may be acting over a longer length scale than interchain entanglement.