During a cyclic tension test, many elastomeric materials exhibit an appreciable softening in their mechanical properties resulting from the previous stretch, known as the Mullins effect. This paper explores
the influence of the stretch induced softening effect to the free recovery behavior of an acrylate shape
memory polymer (SMP) composite by incorporating carbon black (CB) as filler materials. The observed
softening effect in this SMP composite is considered to be a consequence of stretch induced alternation of
fillerepolymer interactions inside the composite. Further experiments find that a larger prior stretch
gives a larger increase in material softening, which in turn decreases the shape recovery speed. To
capture the experimental observations, a multi-branch one dimensional (1D) model is applied, where the
modulus in the equilibrium branch is modeled to decrease with stretching deformation following a
damage-like softening function. It is found that the loss in modulus due to softening consequently reduces the driving force for recovery and thus results in a slow recovery. Parametric studies further
demonstrate that the discounted shape recovery speed will finally reach a saturated level when gradually
increasing the programmed strain level in a shape memory cycle.
3. Strain controlled cyclic tension tests for CB0 and CB9. (a) Test on CB0 at 50
C. (b) Test on CB0 at 62.7
C (T
g
þ 20
C). (c) Test on CB9 at 50
C. (d) Test on CB9 at 67.6
C
(T
g
þ 20
C). Note: in (a)e(d), the strain amplitude is fixed amplitude at 10%, and N indicates cycle number. (e) Test on CB9 at 50
C. The strain amplitude is varied as 10%, 15% and
20% respectively. The dash line denotes reference virgin stressestrain curve without previous strain history
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