Hypervelocity Impact Detection: An Investigation into Piezoelectric Response of PVDF Films

It is proposed in this thesis that an experimental method may be successfully employed with the purpose of discerning the differences in the resultant strain of thin aluminium plates due to impacts of projectiles with varying composition and speed. It also proposes a method for discerning the relative energy imparted to a plate initially hit by a projectile, compared with a plate positioned behind the initial plate, for the purpose of speculating why a relatively energetic projectile may yield less strain of the initial plate when compared with the results of the use of lower energy projectiles of a different composition. Poly(vinylidene fluoride) films are used to measure the strain of the plates, by observing the induced voltage given by the films as they are strained along with the plate. The voltage induced by the sensors, for any impact in question within the project, is recorded over a specific time period, and from this data a peak voltage amplitude is ascertained and is associated with the energy transferred to the plate by the relevant projectile. This thesis finds that differences in the response of PVDF sensors are observed as projectiles with different characteristics are used, and that further study should be undertaken to allow for a proper understanding of the relation between projectile properties, and the amount of strain detected by impact sensors. The decay time of the acoustic signal trace given by impact sensors is shown to increase exponentially as projectile density is increased. It has been shown that for a range of projectiles used to produce penetrative impacts with thin aluminium plates, most of the kinetic energy of the projectile is retained by the projectile after penetration, and that relatively higher density projectiles retain more than those with a lower density.