Behavior under More Complicated Time Patterns

VISCOELASTIC BEHAVIOR UNDER MORE COMPLICATED TIME PATTERNS 

Mechanical testing procedures in common use involve other patterns of stress history than the simple creep and relaxation experiments on which the definitions of the transient viscoelastic functions are based, and the sinusoidally varying stress which is inherent in the definitions of the so-called dynamic properties. Certain relations between the behavior under coniplicated conditions and the basic viscoelastic functions are presented here together with some related problems. They are limited to linear viscoelastic systems and hence small strains, but in some cases could be extended to describe larger deformations, especially for simple extension. 

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An additional nonlinear effect which appears in extension under high stresses, attributable to the volume expansion associated with the fact that Poisson s ratio is less than i, will be discussed in Chapter 18 it is manifested by a decrease in all the relaxation and retardation times. This effect is especially prominent in more complicated stress patterns such as combined tension and torsion, as studied by Sternstein. ° Nonllnear creep behavior under combined tension and torsion with the additional complication of changing temperature during the experiment has been studied by Mark and Findley. ... 

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