Stress growth experiment

It is difficult to predict these responses directly because they depend upon a wide range of instrumental properties in addition to the material properties of the sample. The onset of this behaviour can be explored through the use of a stress growth experiment. 

Finally, it has to be mentioned that stress growth experiments turn out to be very sensitive to the previous history (Moldenaers, 1996). 

Using the cone and plate geometry, stress growth experiments have also been performed using different temperatures and different shear rates. Correct tangential (X+(t,Y) Tj+(t,Y)) and normal stress (Ni(t,Y) Vi(t,Y)) data were... 

The aim of a stress growth experiment is to observe how the stresses change with time as they approach their steady shear flow values. This is done by assuming that the fluid sample trapped in a small gap between two parallel plates is at rest for all times previous to t = 0 implying that there are no stresses in the fluid when steady shear flow is initiated at f = 0. For t > 0 when a constant velocity gradient is imposed, the stress is monitored with respect to time tUl it reaches steady state value. 

Figure 7.16 refers to two other standard experiments. It depicts the results of stress growth experiments , conducted again on a polyethylene melt. The... 

Fig. 7.16. Results of stress growth experiments in shear, and extension,...

Next, let us consider the predictions for a shear stress growth experiment. In a stress growth experiment, a linearly increasing shear is imposed, i.e. 

Figures 7.20 and 7.21 present experimental results which may look at first view quite astonishing. Flowing polymer melts are birefringent, for obvious reasons, and the experiment compares for tensile stress growth experiments on polystyrene the evolution with time of the birefringence...

Figure 9.18 refers to two other standard experiments. It depicts the results of stress growth experiments, conducted again on a polyethylene melt. The figure includes both measurements probing shear and tensile properties, thus facilitating a direct comparison. Curves show the building-up of shear stress upon inception of a steady state shear flow at zero time and the development of tensile stress upon inception of a steady state extensional flow. Measurements were carried out for various values of the shear rate 7 or the Hencky rate of extension ch ... 

The stress growth experiment of Figure 2(c) involves the study of the time evolution of the stresses when a fluid is brought instantaneously from a state of rest at t = 0 to a state of steady-state shear flow this is an idealized experiment which presumes that in the experiment one can effectively minimize inertial effects and achieve the linear velocity profile within an acceptably short time interval. One can then define the growth functions associated with the shear stress and the two normal-stress differences for t > 0 as follows... 

The stress growth experiment (Fig. 3.3c) is also used to characterize polymeric fluids. In this experiment the fluid that is at rest is suddenly set in motion and the stresses are measured as a function of time. Yyx f) is given mathematically as... 

FIGURE 3.7 Transient shear behavior of PPS at 330 °C. The shear and primary normal stress difference are recorded at the startup of shear flow and on cessation of flow. After 10 s the stress growth experiment is repeated. 

Stress Growth. For startup of shear flow (the stress growth experiment), Yyxif) is given by... 

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