Mathematical Fitting of Modulus-Strain Curves of Poly(ethylene Terephthalate) Industrial Yarns

Abstract

A mathematical model was developed for fitting the modulus-strain curves of poly(ethylene terephthalate) industrial yams. To develop the model, several asym metric, bell-shaped lines in different combinations were tried out on the modulus- strain curves of no fewer than 90 yarns with widely varying mechanical properties. The model that gave the best fit consists of the sum of three modified Pearson VII lines. The fitting procedure yields a set of 13 parameters by which the modulus-strain curve is fully determined. To illustrate the practical usefulness, some examples are given of relations between process conditions and the calculated modulus-strain pa rameters.