A crossbow system for high-strain-rate mechanical testing

Abstract

This paper describes a technique developed to measure the uniaxial compressive stress-strain properties of polymers at strain rates appropriate to ballistic and impact events over time scales of tens of microseconds using a crossbow as the projectile launch system. The instrument constructed represents a novel development of existing equipment types. The system is used for compression testing giving stress-strain measurements at strain rates of up to 104 s-1 and over a temperature range of 20-200°C. Stress is calculated directly from a measured force obtained from a calibrated pressure bar. Strain is calculated from the sample displacement measured directly from the intensity reduction of a laser-photodiode unit. The crossbow system provides a relatively inexpensive, reliable and compact alternative to a standard Hopkinson bar.