Strain-induced hardening

The referential formulation is translated into an equivalent current spatial description in terms of the Cauchy stress tensor and Almansi strain tensor, which have components relative to the current spatial configuration. The spatial constitutive equations take a form similar to the referential equations, but the moduli and elastic limit functions depend on the deformation, showing effects that have misleadingly been called strain-induced hardening and anisotropy. Since the components of spatial tensors change with relative rigid rotation between the coordinate frame and the material, it is relatively difficult to construct specific constitutive functions to represent particular materials. 

The deformation may be viewed as composed of a pure stretch followed by a rigid rotation. Stress and strain tensors may be defined whose components are referred to an intermediate stretched but unrotated spatial configuration. The referential formulation may be translated into an unrotated spatial description by using the equations relating the unrotated stress and strain tensors to their referential counterparts. Again, the unrotated spatial constitutive equations take a form similar to their referential and current spatial counterparts. The unrotated moduli and elastic limit functions depend on the stretch and exhibit so-called strain-induced hardening and anisotropy, but without the effects of rotation. 

Fig. 1.29 Strain-induced hardening of austenitic stainless steel subjected to 30 cycles of 0.0126 total strain at -143 °C [34]...

First direct evidence of flow-induced orientation of clay tactoids. Strain-induced hardening and rheopexy originate from the perpendicular alignment of clay layers to the stretching direction. 

Sinha Ray S, Okamoto K, Okamoto M (2006), Melt rheology and strain induced hardening behaviour of biodegradable poly(butylene succinate)/synthetic fluorine mica nanocomposites , Langmuir, submitted. 

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