Non-linear response in oscillatory testing

In oscillatory testing, great care has to be taken to ensure that the experiment takes place in the linear region where G and G are independent of the maximum amplitude or stress of the oscillation. A number of examples of non-linear testing are shown in figures 35 - 40 where we see that the most sensitive parameters to breakdown is usually G, since it eventually falls faster, whereas when G does change it can increase before decreasing. 

The extent of the linear region can vary from a fraction of one per cent strain up to a strain of imity for certain rubbery systems. In most cases the strain at which non-linearities first become apparent are nearly independent of frequency. This means that for controlled-stress experiments, results can be difficult to compare with corresponding controlled-strain results unless both sets of results are reduced to the same basis. 

7 Using osdllatoty data to monitor curing, and rebuilding after shear 

Obviously the gelling times are crucial in, for instance, dental applications, where patients will not tolerate very long curing times for moulding materials in 

Suddenly deforming a viscoelastic liquid to a predetermined strain results in a stress that, once attained, begins to fall off rapidly with time. This decrease eventually slows down, and sometimes appears to approach a steady-state value at long times. 

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