In this article we present mechanical measurements of three representative elastomers used in soft robotic systems: Sylgard 184, Smooth-Sil 950, and EcoFlex 00-30. Our aim is to demonstrate the effects of the nonlinear, time-dependent properties of these materials to facilitate improved dynamic modeling of soft robotic components. We employ uniaxial pull-to-failure tests, cyclic loading tests, and stress relaxation tests to provide a qualitative assessment of nonlinear behavior, batch-to-batch repeatability, and effects of prestraining, cyclic loading, and viscoelastic stress relaxation. Strain gauges composed of the elastomers embedded with a microchannel of conductive liquid (eutectic gallium–indium) are also tested to quantify the interaction between material behaviors and measured strain output. It is found that all of the materials tested exhibit the Mullins effect, where the material properties in the first loading cycle differ from the properties in all subsequent cycles, as well as response sensitivity to loading rate and production variations. Although the materials tested show stress relaxation effects, the measured output from embedded resistive strain gauges is found to be uncoupled from the changes to the material properties and is only a function of strain.
Get full access to this article
View all access options for this article.
References
1.
ParkY-L, ChenB-R, WoodRJ. Design and fabrication of soft artificial skin using embedded microchannels and liquid conductors. IEEE Sens J, 2012; 12:2711–2718.
2.
ChossatJB, ParkY-L, WoodRJ. A soft strain sensor based on ionic and metal liquids. IEEE Sens J, 2013; 13:3405–3414.
3.
MengucY, ParkY-L, Martinez-VillapandoE, et al.Soft wearable motion sensing suit for lower limb biomechanics measurements. 2013 IEEE International Conference on Robotics and Automation (ICRA), 2013, pp. 5309–5316.
4.
KramerRK, MajidiC, WoodRJ. Wearable tactile keypad with stretchable artificial skin. 2011 IEEE International Conference on Robotics and Automation (ICRA), 2011, pp. 1103–1107.
5.
LeeH-K, ChangS-I, YoonE. Dual-mode capacitive proximity sensor for robot application: implementation of tactile and proximity sensing capability on a single polymer platform using shared electrodes. IEEE Sens J, 2009; 9:1748–1755.
6.
CottonDPJ, GrazIM, LacourSP. A multifunctional capacitive sensor for stretchable electronic skins. IEEE Sens J, 2009; 9:2008–2009.
7.
FasslerA, MajidiC. Soft-matter capacitors and inductors for hyperelastic strain sensing and stretchable electronics. Smart Mater Struct, 2013; 22:055023.
8.
WeiW, GuoS. A novel PDMS diaphragm micropump based on ICPF actuator. 2010 IEEE International Conference on Robotics and Biomimetics (ROBIO), 2010, pp. 1577–1583.
9.
ChoMS, SeoHJ, NamJD, et al.An electroactive conducting polymer actuator based on NBR/RTIL solid polymer electrolyte. Smart Mater Struct, 2007; 16:S237.
10.
BahramzadehY, ShahinpoorM. A review of ionic polymeric soft actuators and sensors. Soft Robotics, 2014; 1:38–52.
11.
ShepherdRF, IlievskiF, ChoiW, et al.Multigait soft robot. PNAS, 2011; 108:20400–20403.
12.
SuzumoriK, EndoS, KandaT, et al.A bending pneumatic rubber actuator realizing soft-bodied manta swimming robot. 2007 IEEE International Conference on Robotics and Automation, 2007, pp. 4975–4980.
13.
PolygerinosP, WangZ, GallowayKC, et al.Soft robotic glove for combined assistance and at-home rehabilitation. Robotics Auton Syst, 2014; in press.
14.
MartinezRV, BranchJL, FishCR, et al.Robotic tentacles with three-dimensional mobility based on flexible elastomers. Adv Mater, 2013; 25:205–212.
15.
CianchettiM, MattoliV, MazzolaiB, et al.A new design methodology of electrostrictive actuators for bio-inspired robotics. Sens Actuat B Chem, 2009; 142:288–297.
16.
PelrineR, KornbluhRD, PeiQ, et al.Dielectric elastomer artificial muscle actuators: toward biomimetic motion. SPIE's 9th Annual International Symposium on Smart Structures and Materials, 2002, pp. 126–137.
17.
MaddenJD, VandesteegNA, AnquetilPA, et al.Artificial muscle technology: physical principles and naval prospects. IEEE J Ocean Eng, 2004; 29:706–728.
18.
BoleyJW, WhiteEL, ChiuGTC, KramerRK. Direct writing of gallium indium alloy for stretchable electronics. Adv Funct Mater, 2014; 24:3501–3507.
19.
MajidiC, KramerR, WoodRJ. A non-differential elastomer curvature sensor for softer-than-skin electronics, Smart Mater Struct, 2011; 20:105017.
20.
KramerRK, MajidiC, SahaiR, WoodRJ. Soft curvature sensors for joint angle proprioception. 2011 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2011, pp. 1919–1926.
21.
HammondFL, KramerRK, WanQ, et al.Soft tactile sensor arrays for micromanipulation. 2012 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2012, pp. 25–32.
OgdenRW. Nonlinear Elasticity with Application to Material Modelling. In: AMAS Lecture Notes, Vol. 6, Warsaw, Poland, 2003.
27.
DorfmannA, OgdenRW. A pseudo-elastic model for loading, partial unloading and reloading of particle-reinforced rubber. Int J Solids Struct, 2003; 40:2699–2714.
28.
OgdenRW, HolzapfelGA. Mechanics of Biological Tissue. Springer, 2006.
29.
OverveldeJT, MengucY, PolygerinosP, et al.Numerical mechanical and electrical analysis of soft liquid-embedded deformation sensors. Extreme Mech Lett, 2014; 1:42–46.
30.
SchneiderF, FellnerT, WildeJ, WallrabeU. Mechanical properties of silicones for MEMS. J Micromech Microeng, 2008; 18:065008.
31.
KimTK, KimJK, JeongOC. Measurement of nonlinear mechanical properties of PDMS elastomer. Microelectron Eng, 2011; 88:1982–1985.
32.
MullinsL. Effect of stretching on the properties of rubber. Rubber Chem Technol, 1948; 21:281–300.
33.
DianiJ, FayolleB, GilorminiP. A review on the Mullins effect. Eur Polym J, 2009; 45:601–612.
34.
FindleyWN. Creep and Relaxation of Nonlinear Viscoelastic Materials: With an Introduction to Linear Viscoelasticity. New York: Dover, 1989.
35.
McCrumNG, BuckleyCP, BucknallCB. Principles of Polymer Engineering. New York: Oxford University Press, 1997.
36.
MengE, ZhangX, BenardW. Additive Processes for Polymeric Materials. In: MEMS Materials and Processes Handbook. New York: Springer, 2011, pp. 198–271.
37.
Hyun-JoongK, SonC, ZiaieB. A multiaxial stretchable interconnect using liquid-alloy-filled elastomeric microchannels. Appl Phys Lett, 2008; 92.
