Effects of repeated extension and recovery on selected physical propertiesof ISO-301 stitched seams - Part II: Theoretical model

A theoretical viscoelastic model based on the four-element Burgers model is developed to predict changes in load with time of ISO-301 stitched seams u nder longitudinal loading subjected to extension/recovery cycling at a cons tant rate of extension. Parameters calculated from experimental stress rela xation curves are used to determine the theoretical relationship between lo ad and time for tensile cycling. The model gives good agreement with experi mental stress relaxation behavior of seams over the range 0-30 seconds. The oretical predictions of load versus time give the best agreement with exper imentally derived tensile cycling curves for seams cycled between the lowes t extension limits. The exact solution of the theoretical model consists of a double exponential expression, suggesting that two processes are respons ible for the change in load of seams with tensile cycling, a result consist ent with the statistical model for seam ageing and with visual observations described in Part I of this series.