<title>Dynamic moire interferometry</title>

Abstract

Dynamic observation of impact phenomena is extremely important for designing automotive and armored structures. A dynamic moire interferometer has been developed at the INEL to image surface displacement fields generated by dynamic loading events. A pulsed ruby laser is used to provide sufficient intensity to allow the imaging of displacement fields in periods of 20 ns. An electro-optic Q-switching system has been designed using standard electronic and optical components to pulse the ruby laser at rates of up to 1 Mhz. In order to capture images, a Cordin high speed framing camera was integrated into the system. The dynamic moire interferometer produces fringe fields of in-plane displacement data, similar to the fringe data captured in dynamic holography or dynamic photoelasticity. Dynamic loading events generate moving fringe fields which reduce the fidelity of acquired fringe fields. A dynamic fringe analysis similar to Neuman's analysis for dynamic holography and Dally's analysis for dynamic photoelasticity has been performed to quantify this effect for a moire interferometer. It has been determined that the contrast of the fringes depends not only on the pulse duration of the laser and transience of the fringe field, but also on the frequency of the fringe field. This analysis has been used to interpret fringe data obtained from short duration stress pulses traveling through laminated carbon-fiber epoxy composites.