ULTIMATE TENSILE PROPERTIES OF ACRYLONITRILE-METHYLACRYLATE COPOLYMERIC FIBERS

I. TIME AND TEMPERATURE DEPENDENCE OF ULTIMATE TENSILE PROPERTIES

Abstract

The tensile strength (σ_b) and the ultimate elongation (ε_b) of an acrylonitrile-methylacrylate copolymeric fiber were measured at various temperatures under conditions of constant stress and constant strain rate. Results obtained may be summarized as follows:
(1) In the creep rupture experiment, the curves of σ_b against the time to break (t_b) at various temperatures on double logarithmic scale are superposed by shifting them along the logt_b axis without any temperature correction of σ_b, the shift distance required to effect the superposition being loga_T. On the other hand, the curves logε_b against log t_b are superposed by shifting them along the logt_b axis and by shifting them along the logε_b axis, the shift distances required there being loga_T along the logt_b axis and logb_T along the logε_b axis. In the similar manner the composite curve of compliance at break against t_b, and a composite “failure envelope” plotting against ε_b/b_T are constructed.
(2) The tensile strength, which depends on a. local structure of the fiber, may hardly be affected by secondary structural changes of the fiber with temperature, so that the composite curve of ε_b against t_b, may be obtained without any temperature correction. The ultimate elongation, which may be correlated to sum of strains of the structural elements of fiber, may be affected by secondary structural changes of the fiber with temperature, so that the shifting along the logε_b axis is required in the superposition procedure to get the composite curve of ε_b against t_b.
(3) General behaviour of the composite curve of the compliance at break is similar to the one of the creep compliance for amorphous polymers, where the creep compliance shows the transition from the glassy to the rubbery state.
(4) In the constant strain rate experiment, the composite curve of ε_b, against t_b and the composite “failure envelope” are obtained, using the same values of the shift factors, a_T and b_T.
(5) Relation between the ultimate properties and the reduced time to break depends on the test methods, but the composite “failure envelope” is independent of the test methods.