Measurement of the force occuring at the impact of a non-lethal projectile with the Flexiforce sensor

Force measurements are important to experimentally assess the effects of a non-
lethal projectile on a human body. In addition they are also necessary to
evaluate the bio-fidelity of a system regarding PMHS (post mortem human
subject) data. So far, as we can see in the literature, these measurements are
usually achieved with an accelerometer placed inside the projectile. By
assuming this projectile is perfectly rigid, the impact force can be calculated [1,
2].
However, the limitations are obvious: on the one hand the embedded
accelerometer will change the projectile properties. On the other hand the force
cannot directly be deduced for the deformable projectiles usually used
nowadays.
Therefore, a new system to measure impact force has to be developed. In this
study, we propose to use the Flexiforce sensor, which is a cheap and very thin
force sensor compatible with the expected measurement range [3].
The final objective is to realise an efficient force measurement on any kinetic
energy non-lethal weapon (KENLW) projectile, using this particular sensor. We
can find in the literature some static calibration [3,4]. As our application is
highly dynamical, we started this study with the design and application of a
dynamic calibration process. Then results from rigid projectiles (comparing to a
classic KENLW projectile) impacting rigid targets (comparing to human body
or a biofidelic surrogate) are collected and Flexiforce and accelerometer signals
are compared (“rigid-rigid impacts). Finally, force measurements of projectiles
impacting deformable surfaces (comparing to the projectile ) with the Flexiforce
sensor are achieved (“rigid-soft impacts”).