Determination of Impact Stress-Strain Loops of Sveral Engineering Plastics in Compression
Takashi YOKOYAMA and Kenji NAKAI
Abstract:Stress-strain loops of several engineering plastics in compression at strain rates of nearly 600/s are determined using the standard split Hopkinson pressure bar. Four plastics or typical thermoplastics PA-6, PA-66, PC and POM are tested at room temperature. Cylindrical specimens with slenderness ratio (= height/diameter) of 0.5 are used in the Hopkinson bar tests, and those with slenderness ratio of 1.5 as specified in the ASTM Standards are used in the static tests. The low and intermediate strain-rate stress-strain loops in compression are measured in an Instron testing machine. The effects of strain rate on Young's (or secant) modulus, 2.5% flow stress and dissipation energy (energy loss due to damping) are examined. It is demonstrated that the area within the stress-strain loop (or dissipation energy) increases with increasing strain rate as well as strain, that is, all plastics tested exhibit intrinsic dynamic viscoelasticity and a high elastic aftereffect following complete unloading. Key Words:Compressive properties, Dynamic viscoelasticity, Elastic aftereffect, Engineering plastics, Hopkinson bar, Strain rate, Stress-strain loops