Effects of Loading Rate on the Relaxation and Recovery Ability of an Epoxy-Based Shape Memory Polymer

Amber Mcclung,Jeffery Baur,Gyaneshwar Tandon

doi:10.3390/fluids2020013

Amber Mcclung, Jeffery Baur + Show 1 more

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https://doi.org/10.3390/fluids2020013

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Abstract

The majority of aerospace structural composites use thermoset resins for their processing flexibility, temperature capability, and environmental durability. In this study, the recovery behavior of Veriflex-E, an epoxy-based, thermosetting, thermally-triggered shape memory polymer (SMP) resin, is investigated in glassy (25 °C) and rubbery (130 °C) states, as a function of shape memory cycles, and as a means to evaluate its potential as a resin for a shape memory composite. At 25 °C, Veriflex-E exhibits a promising high elastic modulus and a positive, nonlinear strain rate sensitivity in monotonic loading. At 130 °C, the strain rate sensitivity in monotonic loading decreases. Stress relaxation after storage in the deformed temporary state and subsequent shape recovery is of particular interest, a challenge to measure, and has not been widely reported for SMPs. The current experimental program measures the influence of strain rate changes in the 10−4–10−2 s−1 range on the stress relaxation response of the material, as well as on the strain recovery behavior at both 25 °C and 130 °C. As expected, the post-relaxation strain is larger with faster loading. Unexpectedly, the total strain recovered after shape memory cycling is more similar to the low temperature deformation. Overall, the results suggest that, while being influenced by both the loading rate and the test temperature, Veriflex-E is a promising candidate for a shape memory composite which could enable adaptive structures.

Highlights

IntroductionIn the manufacturing industry for collapsible/removable tooling [3]
The field of shape memory polymers (SMPs) is rapidly developing for applications in a variety of disciplines, including the recent development in the aerospace industry for use in adaptive vehicles [1,2]and in the manufacturing industry for collapsible/removable tooling [3]
The current results provide the measured influence of the strain rate on the specific stress relaxation behavior of an epoxy-based SMP; these measured differences are essential for model development and validation for structural SMPs [2]

Summary

Introduction

In the manufacturing industry for collapsible/removable tooling [3]. Before such applications can be attempted, the 3-D mechanical behavior of SMPs must be thoroughly understood. By understanding their critical mechanical performance at temperatures below, above, and through the glass transition temperature (Tg ), the “memory” capabilities of SMPs can enable reconfigurable structures such as micro air vehicles, morphing aircraft, and deployable space structures. It has been established that polymers exhibit a strain rate dependence at room temperatures [4,5,6]. Elastomers can exhibit a deformation rate dependence [9,10]

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