Material properties An experimental investigation of the effect of strain on the electrical conductivity of a shape memory polymer Fazeel Khan * , Kumar Singh Department of Mechanical and Manufacturing Engineering, Miami University, EGB 56R, 650 E. High St., Oxford, OH 45056, USA article info Article history: Received 8 October 2015 Accepted 14 November 2015 Available online 1 December 2015 Keywords: Shape-memory Polymer Electrically triggered Material characterization abstract A thermally triggered shape memory polymer (SMP) was prepared by blending electrically conductive carbon black (CB) into the resin prior to curing. The CB filled composite can then be activated through resistive heating. With the aim of using such SMPs in reconfigurable structures and/or actuators, the effect of strain on the conductive nature of the SMP composite was investigated. The study has specif- ically focused on changes to conductivity in, i) the transverse direction during tensile elongation to assess the impact of the Poisson effect, and ii) in samples deformed in compression. The dynamic response characteristics of the electrically activated SMP were also tested to assess the feasibility of using the composite in tunable vibration damping applications. Findings have shown that the pattern of changes in the transverse conductivity, which is marked by an increase-decrease-increase sequence, resembles that seen in the axial direction. SEM imaging of the samples was performed along the axial and transverse axes of deformation and shows no anisotropy in the CB filler distribution. To demonstrate potential uses of a conductive SMP in the sub- T g temperature range, a discussion of a vibration damping application has been included. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction In the past decade, shape memory polymers have been the subject of active research from the perspective of polymer syn- thesis, physical property characterization, processing and product innovation. The shape memory label is derived from the ability of this family of polymers to repeatedly recover from large levels of deformation following the application of a suitable stimulus or trigger, which permits large scale segmental motion in the chains. The trigger often takes the form of heat, but may also include light of a specific frequency or an environment with a specific acidity/ alkalinity value. SMPs are often thermoset type resins and derive their strain recovery attribute from chain crosslinking which con- tributes to the retention of high levels of elastic strain energy in the deformed matrix by restricting relative chain motion. It is pertinent to add that the shape memory effect is also exhibited by some thermoplastic polymers, such as polycarbonate, when deformed at room temperature and with strain recovery initiated by exceeding the glass transition temperature. However, a low crazing threshold strain often renders such polymers unsuitable for repeated defor- mation and recovery cycles. A long standing challenge in the consideration of SMPs in actuator type applications or reconfigurable structures has centered on response time. Being polymers, SMPs, naturally, exhibit low thermal conductivity, and thus heating methods that rely on external or surface type heating require certain soak times to achieve a uniform through-thickness temperature. Therefore, the objective of reducing heating times and temperature gradients within a material has focused on intrinsic heating approaches using either light or electrical or magnetic energy transfer. The use of an infrared (IR) laser or a more diffuse infrared light source for thermal activation has been demonstrated in Refs. [1,2]. In the former, the researchers used embedded optical fibers to achieve thermal activation, while in Ref. [2] external illumination with carbon nanotube and boron nitride fillers in the SMP com- posite to facilitate absorption and through-volume heat dissipation was used. The use of inductive heating, in which a high frequency magnetic field is used to heat metal or metallic compound fillers within the SMP, has been discussed in a review paper [3]. While the technique benefits from exploiting eddy current and/or magnetic hysteresis heating mechanisms in the filler particles, the require- ment of enveloping the part in the magnetic field and ensuing need * Corresponding author. E-mail address: khanfj@miamioh.edu (F. Khan). Contents lists available at ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest http://dx.doi.org/10.1016/j.polymertesting.2015.11.008 0142-9418/© 2015 Elsevier Ltd. All rights reserved. Polymer Testing 49 (2016) 82e87