Recoil constrained

Constrained Recoil after Cessation of Steady Shearing Flow [Bird, Evans, and Warner (3)]... 

A relationship quite similar to Eq. (19.15) is given in Eq. (12.18) in the section on constrained recoil after the cessation of steady shearing flow. 

Constrained recoil after steady shear flow... 

In constrained recoil after steady shear flow, the elastic dumbbells give a value of yw/K which is independent of k, whereas the rigid dumbbell model contains a dependence on k. ... 

Unsteady simple shear flow would occur when the stresses involved are time-dependent. Small-amplitude oscillatory flow, stress growth, stress relaxation, creep and constrained recoil are some examples of such types of flows [4]. In the following, small-amplitude oscillatory flow is treated in sufficient detail while others are briefly described... 

The aim of a constrained recoil experiment is to observe the shear displacement in a fluid sample trapped in a small gap between two parallel plates when driving shear stress is suddenly removed after steady-state and then held at zero. The shear rate would then only be a function of time in the recoiling fluid. The ultimate recoil of the fluid at infinite time can be determined in this manner. 

The breadth of the scope of nonlinear phenomena can be grasped in part by considering the various time-dependent probes of linear viscoelasticity cited in Table 3.3.2 sinusoidal oscillation, creep, constrained recoil, stress relaxation after step strain, stress relaxation after steady shearing, and stress growth after start-up of steady shearing. In the linear regime— that is, at small strains or small strain rates—the experimental results of any one of these probes (in simple shear, for example) can be used to predict results for any of the other probes, not only for simple shearing defor-... 

Factorization of the function concentrated polystyrene solution, time-strain factorability is not valid at short times after the imposition of the step shear. An accurate K-BKZ constitutive equation for shearing flows of this material will be much more complex than that for melt I. Furthermore, in strain histories in which a strain reversal takes place, such as constrained recoil (Wagner and Laun, 1978) or double-step strains with the second strain of sign opposite the first (Doi, 1980 Larson and Valesano, 1986), good agreement... 

An experiment closely related to creep is creep recovery or constrained recoil. After a creep experiment has proceeded for a time fg, the shear stress is suddenly removed, and the recoil or recovered strain is measured as a function of time. It is often found that more precise measurements can be made in this test than in a creep test. The recovered strain, y, is equal to the strain at time tg minus the strain at times greater than tg, as shown below. 

Figure 4.8 Sketch of shear strain versus time for a creep and recovery experiment. At time fo into a creep test, the shear stress is released, and there is a time-dependent, constrained recoil.

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