Strain-Rate Dependence on Stress-Strain Characteristic of the Shock Wavefront in Two Kinds of Glassy Polymers
Yasuhisa SATO, Taku UENO, Keiou NISHIMURA, Kazunari SUZUKI and Yuhichi OGAWA
Abstract:For numerical design of safety compartments in a cabin of aircraft to maintain a survivable environment for passengers in a crash, very-high-strain-rate mechanical-properties of many kinds of aerospace materials are indispensable. On the basis of the Unsteady Wave Sensing System (UWSS), which is composed of a plate impact experiment using three in-material gauges and nanosecond Lagrangian analyses, various variables are determined at the sensing part of the central gauge. Three stress-time histories are measured by three PVDFgauges, respectively, and the time histories of the phase velocity associated with the stress:U ƒÐ, particle velocity : v, the phase velocity associated with the particle velocity : U v , and strain : ƒÃ induced by impact at velocities ca. 600 m/s are calculated by using those three stress-time curves and the conservation relations of mass and momentum. Then, the stress-strain curves at very high strain-rate of the order 106 to 107s-1 are derived under conditions of uniaxial strain. On the other hand, stress-stain curves at medium strain rate (ca . 102s-1) and at low strain rate (ca . 10-4s-1) under conditions of uniaxial stress were already determined by a drop-weight testing system and Instron testing machine, respectively. It is clearly shown that the stress-strain curves for PMMA and polycarbonate (PC) are both very sensitive to strain rate in the very wide range of strain-rate of 10-4s-1 to 107s-1 under conditions of uniaxial strain. As a result, power law relations between stress and strain-rate were observed with these glassy polymers under uniaxial strain conditions in the very wide strain-rate range. Key Words:Shock-high-pressure, Aircraft crash, Shock wavefront, Nanosecond analyses, Plate impact experiment, PVDF gauge, Glassy polymer