Stress-Strain Relationships in Yarns Subjected to Rapid Impact Loading

Abstract

An impact velocity just sufficient to cause immediate breakage in a filament im pacted in tension is called a critical velocity. Theories, of von Karman and Taylor, required for calculating critical velocities are reviewed and extended to include case of shock-wave propagation. Estimates of critical velocity are then calculated for some textile yarns using stress-strain data obtained at impact speeds near 40 m sec. The velocities obtained range in value from approximately 100 m sec for cotton sewing thread and glass fiber yarn to approximately 300 m sec for some vinal, rayon-tire-cord. acrylic, and nylon yarns. Theory is developed for calculating a limiting breaking velocity from the specific breaking energy obtained by high-velocity impact tests. It is shown that the limiting breaking velocity is higher than the critical velocity if the stress-strain curve is predominantly comcave downward, lower if the stress-strain curve is predominantly concave upward, and equal to the cricital velocity if the curve is linear. Critical velocities are also estimated from stress-strain data obtained at 100% min straining rates and compared with calculations from high-velocity-impact data. Good agreement is found in many cases.