Relaxation relationship with creep function

In a further development of the continuous chain model it has been shown that the viscoelastic and plastic behaviour, as manifested by the yielding phenomenon, creep and stress relaxation, can be satisfactorily described by the Eyring reduced time (ERT) model [10]. Creep in polymer fibres is brought about by the time-dependent shear deformation, resulting in a mutual displacement of adjacent chains [7-10]. As will be shown in Sect. 4, this process can be described by activated shear transitions with a distribution of activation energies. The ERT model will be used to derive the relationship that describes the strength of a polymer fibre as a function of the time and the temperature. 

Clearly some simple method must he devised to characterize the mecheuiical response as a function of time (and of course temperature). Creep tests were a possibility hut the continued strain with time wo ild cause changes in structure and thereby make the structure-property relationship difficult to interpret. Stress relaxation was also a possibility but at that point there were instrumentation difficulties in obtaining short time measurements. What was needed was some simple method that wo ild cover a wide range of time scale of loading in which the applied strain magnitude was a controlled variable. This line of thought led to the development of the rotating beam dynamic tester ... 

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