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 (
tb) at various temperatures on double logarithmic scale are superposed by shifting them along the log
tb axis without any temperature correction of σ
b, the shift distance required to effect the superposition being log
aT. On the other hand, the curves logε
b against log
tb are superposed by shifting them along the log
tb axis and by shifting them along the logε
b axis, the shift distances required there being log
aT along the log
tb axis and log
bT along the logε
b axis. In the similar manner the composite curve of compliance at break against
tb, and a composite “failure envelope” plotting against ε
b/
bT 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
tb, 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
tb.
(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
tb and the composite “failure envelope” are obtained, using the same values of the shift factors,
aT and
bT.
(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.
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