Transient deformation behavior

From Eqn. (5) we see that the important intrinsic variables controlling creep are the boundary thickness, w, the grain size, d, and the viscosity of the boundary fluid, tj. If these parameters change in the course of the deformation process, a corresponding change in the creep rate will occur, leading to transient creep behavior. 

Itaya, Y, Taniguchi, S., and Hasatani, M., 1997, A numerical study of transient deformation and stress behavior of a clay slab during drying. Drying Technology, 15(1), 1-21. 

Relaxation and cyclic deformation behavior of the hard-elastic polypropylene is of particular interest [2]. If the fiber is allowed to relax, the stress needed to continue the deformation is different from the initial stress. The stress increment can be divided into a permanent and transient part. As the recovery properties of the fibers begin to deteriorate, the permanent increment changes from a negative to a positive value and the transient component decreases to zero. Stress relaxation of... 

Elasticity is another manifestation of non-Newtonian behavior. Elastic Hquids resist stress and deform reversibly provided that the strain is not too large. The elastic modulus is the ratio of the stress to the strain. Elasticity can be characterized usiag transient measurements such as recoil when a spinning bob stops rotating, or by steady-state measurements such as normal stress ia rotating plates. 

The defect question delineates solid behavior from liquid behavior. In liquid deformation, there is no fundamental need for an unusual deformation mechanism to explain the observed shock deformation. There may be superficial, macroscopic similarities between the shock deformation of solids and fluids, but the fundamental deformation questions differ in the two cases. Fluids may, in fact, be subjected to intense transient viscous shear stresses that can cause mechanically induced defects, but first-order behaviors do not require defects to provide a fundamental basis for interpretation of mechanical response data. 

The response of complex materials, e.g., block copolymers, may not even be periodic, as the oscillatory deformation can lead to transient changes in the properties of the material. Eventually, of course, the response should become strictly periodic as the material transforms to its new structure, although some have reported chaotic behavior. 

The fundamental assumption of the classical rheological theories is that the liquid stmcture is either stable (Newtonian behavior) or its changes are well dehned (non-Newtonian behavior). This is rarely the case for flow of multiphase systems. For example, orientation of sheared layers may be responsible for either dilatant or pseudoplastic behavior, while strong interparticle interactions may lead to yield stress or transient behaviors. Liquids with yield stress show a plug flow. As a result, these liquids have drastically reduced extrudate swell, B = d/d (d is diameter of the extrudate, d that of the die) [Utracki et al, 1984]. Since there is no deformation within the plug volume, the molecular theories of elasticity and the relations they provide to correlate, for example either the entrance pressure drop or the extmdate swell, are not applicable. 

A microemulsion is thus anomalous, because it is relatively fluid and much less viscous than expected. This has been linked with the flexibility of the structure and its transient behavior, as early mentioned byWinsor and Shinoda for the surfactant phase, as they called it (they did not use the word microemulsion). This is particularly true in the case in which extremely low interfacial tension allows easy deformation and low interfacial curvature, a feature that can be attained by adjusting the physicochemical formulation. 

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