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This paper presents a recent investigation into the electromechanical behavior of thermally reduced graphene oxide (rGO) as a strain sensor undergoing repeated large mechanical strains up to 20.72%, with electrical signal output measurement in multiple directions relative to the applied strain. Strain is one the most basic and most common stimuli sensed. rGO can be synthesized from abundant materials, can survive exposure to large strains (up to 20.72%), can be synthesized directly on structures with relative ease, and provides high sensitivity, with gauge factors up to 200 regularly reported. In this investigation, a suspension of graphene oxide flakes was deposited onto Polydimethylsiloxane (PDMS) substrates and thermally reduced to create macroscopic rGO-strain sensors. Electrical resistance parallel to the direction of applied tension (x^) demonstrated linear behavior (similar to the piezoresistive behavior of solid materials under strain) up to strains around 7.5%, beyond which nonlinear resistive behavior (similar to percolative electrical behavior) was observed. Cyclic tensile testing results suggested that some residual micro-cracks remained in place after relaxation from the first cycle of tensile loading. A linear fit across the range of strains investigated produced a gauge factor of 91.50(Ω/Ω)/(m/m), though it was observed that the behavior at high strains was clearly nonlinear. Hysteresis testing showed high consistency in the electromechanical response of the sensor between loading and unloading within cycles as well as increased consistency in the pattern of the response between different cycles starting from cycle 2.
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Multiscale mechanics of polydimethylsiloxane: A comparison of meso- and micro-cyclic deformation behavior
Despite plenty of static and dynamic mechanical measurements and modeling for bulk polydimethylsiloxane (PDMS) specimens, a notable gap exists in comprehensively understanding the dynamic mechanics under large cycle, low strain conditions, especially for microscale samples. This study integrates tensile testing and nanoindentation techniques to compare dynamic mechanical response for bulk PDMS samples and μ-pillars. The results from cyclic tensile testing, which involved up to 10,000 cycles at a strain range of 10%–20%, indicate a stabilization of energy dissipation rate after the initial 25 cycles. This attributes to stress relaxation and strain hardening, validating by rapid dual-phase exponential decay in maximum stress, coupled with an incremental increase in elastic modulus. In comparison to tensile testing, μ-pillars exhibited a 0.82% reduction in stiffness, stabilizing ~600th cycle. Concurrently, there was an approximately twofold increase in approaching distance during the initial 120 cycles, and an approximately fourfold increase in dissipated energy over the first 80 cycles, before reaching a plateau. This lagging hysteresis effect attributes to the distribution of the resultant force, including top tension, bottom compression, and base tilt. Overall, this study illuminates temporal mechanical deformations in PDMS under two application scenarios, enhancing our understanding of PDMS mechanical behavior.
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- Award ID(s):
- 2317510
- PAR ID:
- 10501813
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Applied Polymer Science
- ISSN:
- 1097-4628
- Page Range / eLocation ID:
- e55546
- Subject(s) / Keyword(s):
- polydimethylsiloxane (PDMS) stress relaxation strain hardening dissipated energy cyclic testing nanoindentation
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/app.55546
