Stress-Strain Relationships in Yarns Subjected to Rapid Impact Loading

Abstract

If a textile yarn, marked at intervals along its length, is struck transversely by a rifle bullet, a flash photograph taken shortly after impact will reveal a shifting of the marks caused by passage of a strain wave. Analysis of these shifts provides data on the dis tribution of strain and strain velocity in the wave. Tests were performed on specimens of a high-tenacity nylon and a high-tenacity polyester yarn, to determine strain-velocity distributions at various times after impact and at various impact velocities. The observed distributions were then compared with the predictions of a theory which assumed that stress-strain behavior was independent of strain rate. From discrepancies between theo retical and observed results, it was concluded that at strain levels up to 9%, significant creep and stress relaxation occurred within 30 μ sec after impact, but in the time interval 30 μ sec to 300 μ sec, creep and stress relaxation were negligible. For strains of the order of 1%, the 30 μ sec creep and stress relaxations at the point of impact were of the order of 15% and 5%, respectively.

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