Relative first cycle hysteresis

We indicated all relative quantities by asterisks. Thus we defined the relative first cycle residual strain, and relative first cycle hysteresis energy dissipation by... 

To understand the relative first cycle hysteresis we need to consider the processes of both first loading and unloading. In terms of the description above, its value is expected to be sensitive to the relative importance of the two damage processes identified (I) and (H). Thus its reduction with replacement of DBDI by MDI, or with increasing phase separation (Fig. 4.29 and 4.30) could be caused by increase in contribution from process II, relative to process I, in these cases, presumably because of weaker binding of segments to the hard phase. 

Fig. 4.29 First cycle relative residual stram on load-ing/unloading to e = 3, plotted versus first cycle relative hysteresis, showing correlation and trends with respect to choice of DI and MD. Symbols as in Fig. 4.24 [135]...

Fig. 4.31 First cycle relative hysteresis on loading to e = 3, plotted versus degree of crystaUinity. Filled symbols = MDI-based polymers open symbols = DBDI-based polymers. Lines are only to guide the eye they link materials varying only in dusocyanate (full lines) or in chain extender (dashed lines) [135]...

Also shown is the initial stress 0-300%. For comparison, the table also shows the residual elongation and relative hysteresis in first and second cycles of elongation at the same rate ffjjj and [61]. 

Fig. 7.19. Experimentally determined stress versus temperature hysteresis data for a 1 jjLm. thick A1 film deposited on a relatively thick elastic substrate. The specimen was first heated from room temperature to 300 °C (the data point set marked 1 ), held at that temperature for 30 min., and then subsequently cooled to a minimum temperature before being heated again to 300 °C. This minimum temperature was chosen to be 110, 50, 20 and —10 °C for the four thermal cycles, the heating portions of which are denoted by the numbers 2, 3, 4 and 5, respectively. The specimen was held at 300 °C for 30 min. during each thermal cycle. The as a function of temperature. The solid curves in Figure 7.19 show the response for elastic and plastic deformation implied by (7.75) and (7.76). To denotes the stress-free reference temperature. Experimental data provided by Y. J. Choi, Massachusetts Institute of Technology (2002).

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