Drop-weight impact tests with the use of laser-Doppler velocimetry

Abstract

The application of laser-Doppler velocimetry to the measurement of pro­jectile velocity during falling-weight, three-point bend impact tests on PMMA has allowed the determination of parameters hitherto inaccessible by conventional energy-measuring methods. At projectile velocities of 2 m/s and typical impact loading times of less than 1 ms, more than 50 velocity readings were possible. The ability of the method to provide detailed measurements of the velocity variation with respect to time allowed the computation of fracture energies that compare well with previous experiments by means of a pendulum impact tester and result in a similar impact fracture toughness, G ( ca . 1.0 kJ/m 2 ). The measured loading times are also in the same range (0.1 - 0.6 ms) as those calculated theoretically from a pendulum machine at a similar striking velocity. The stress intensity factor, K ( ca . 2.83 MN/m 3/2 ), and modulus, E ( ca . 8.2 GN/m 2 ), were also determined and correlate well with predicted behaviour but are substantially greater than values obtained from static tests.