Fractional recoverable strain

An ideal shape-memory polymer for a given application has a small set of parameters that determine the usefulness, or otherwise, for a given application (1) The fractional recoverable strain the maximum fraction of the imposed strain that can be recovered when triggered. (2) The temperature of maximum recovery rate Tmax for a given rate of heating a measure of the temperature required to trigger... 

When plastics are unloaded, the creep strain is recoverable. This contrasts with metals, where creep strains are permanent. The Voigt linear viscoelastic model predicts that creep strains are 100% recoverable. The fractional recovered strain is defined as 1 — e/cmax, where e is the strain during recovery and Cmax is the strain at the end of the creep period. It exceeds 0.8 when the recovery time is equal to the creep time. Figure 7.9 shows that recovery is quicker for low Cmax and short creep times, i.e. when the creep approaches linear viscoelastic behaviour. 

The effects of changes in DR on the extent of recovery of the low-strain moduli (with time, after the brief imposition of the high strain) are illustrated by Fig. 24. The effects are similar for both G and G". The fraction recoverable was taken as G /Gq. Here, is the recovered modulus after an extrapolated... 

Huggins interaction parameter, and prp is the equilibrium pressure of the coexistent sorbate gas and liquid at the temperature of the experiment. The fractional free volume f2 of the amorphous component of a semicrystalline polymer is increased by recoverable straining and decreased by plastic deformation. As a consequence one obtains a gradual increase of sorption, diffusion, and permeability in the former and a drastic decrease in the latter case. ... 

Fig. 24 Fraction of recoverable storage modulus G /Gq of unvulcanized samples after the cessation of the brief imposition of the strain of + 50%.

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