ABSTRACT Delayed fracture, a behavior observed in colloidal and polymeric gels, when materials suddenly fracture under elastic loading, has not previously been reported in crosslinked shape memory polymers (SMPs). As SMPs can generally undergo large reversible strains, delayed fracture during the shape setting process could limit their utility in a range of applications by reducing the strains they can endure during packaging. In this work, delayed fracture behavior in SMPs is reported for the first time in both acrylate and thiolene‐acrylate systems. Parameters such as temperature, strain, strain rate and cross‐linker density were investigated relative to delayed time to fracture. Packaging strain normalized to strain‐to‐failure has the greatest impact on time to fracture. Additionally, by applying an oscillation during stress relaxation, moduli were tracked during packaged relaxation up to the point of delayed fracture, which surprisingly reveal no significant changes. While several mechanisms in delayed fracture have been proposed for colloidal/polymer gels in the past, the mechanisms do not seem appropriate for the behavior described herein for crosslinked SMPs and given the similarity in the underlying chain structures of the materials, the prevailing proposed mechanism in literature for other systems as well is likely wrong or at best incomplete.
Prima et al. (Thu,) studied this question.
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