Soft is a relative term. Its scope includes the extreme of viscoelastic materials that exhibit both liquid-like and solid-like properties depending on loading conditions. Such rheologically complex materials are abundant in biological organisms, including mucin gels, blood, cellular cytoplasm, and molecules of protein or DNA. However, comparably soft, rheologically complex materials are not yet in the standard toolbox of the engineer. Engineering design generally, and robotic design specifically, stand to benefit greatly from soft and rheologically complex materials that could offer novel performance based on nonlinear material properties. In order to achieve this, several technical challenges must be overcome, including better conceptual modeling, more predictive mathematical modeling, and an overall design framework that manages the high dimensionality of rheological material properties. This article outlines the challenges, and as a first step toward overcoming them, describes a design process that manages rheological complexity in the relationship between performance, function-valued properties, and material formulation.
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References
1.
AshbyMF. Materials Selection in Mechanical Design. Boston, MA; Butterworth-Heinemann: 1999.
2.
HowellL. Compliant Mechanisms. New York; Wiley: 2001.
KimDH, SongJ, ChoiWM, et al.Materials and noncoplanar mesh designs for integrated circuits with linear elastic responses to extreme mechanical deformations. Proc Natl Acad Sci USA., 2008; 105:18675–18680.
5.
KimD-H, XiaoJ, SongJ, HuangY, RogersJA. Stretchable, curvilinear electronics based on inorganic materials. Adv Mater., 2010; 22:2108–2124.
6.
AhnBY, DuossEB, MotalaMJ, et al.Omnidirectional printing of flexible, stretchable, and spanning silver microelectrodes. Science., 2009; 323:1590–1593.
7.
KimDH, AhnJH, ChoiWM, et al.Stretchable and foldable silicon integrated circuits. Science., 2008; 320:507–511.
8.
De GennesP-G. Soft Matter. Nobel Lecture (1991).
9.
LarsonRG. The Structure and Rheology of Complex Fluids. Topics in Chemical Engineering. 238. New York; Oxford University Press: 1999.
10.
ShadwickRE. Mechanical design in arteries. J Exp Biol., 1999; 202:3305–3313.
11.
AutumnK, LiangYA, HsiehST, et al.Adhesive force of a single gecko foot-hair. Nature., 2000; 405:681–685.
12.
DennyMW. The role of gastropod pedal mucus in locomotion. Nature., 1980; 285:160–161.
13.
AksakB, MurphyMP, SittiM. Adhesion of biologically inspired vertical and angled polymer microfiber arrays. Langmuir., 2007; 23:3322–3332.
14.
KimS, SittiM. Biologically inspired polymer microfibers with spatulate tips as repeatable fibrillar adhesives. Appl Phys Lett., 2006; 89:261911.
15.
KimS, SpenkoM, TrujilloS, et al.Smooth vertical surface climbing with directional adhesion. IEEE Trans Robotics., 2008; 24:65–74.
16.
MurphyMP, SittiM. Waalbot: an agile small-scale wall-climbing robot utilizing dry elastomer adhesives. IEEE-ASME Trans Mechatronics., 2007; 12:330–338.
17.
QuL, DaiL, StoneM, XiaZ, WangZL. Carbon nanotube arrays with strong shear binding-on and easy normal lifting-off. Science., 2008; 322:238–242.
18.
SeokS, OnalCD, WoodR, RusD, KimS. Peristaltic locomotion with antagonistic actuators in soft robotics. Proceedings, IEEE International Conference on Robotics and Automation; 2010, pp. 1228–1233.
19.
LaschiC, CianchettiM, MazzolaiB, MargheriL, FolladorM, DarioP. Soft robot arm inspired by the octopus. Adv Robotics., 2012; 26:709–727.
20.
LinH-T, LeiskGG, TrimmerB. GoQBot: a caterpillar-inspired soft-bodied rolling robot. Bioinspir Biomim., 2011; 6:026007.
21.
KimS, LaschiC, TrimmerB. Soft robotics: a bioinspired evolution in robotics. Trends Biotechnol., 2013; 31:287–294.
22.
KimD-H, LuN, MaR, et al.Epidermal electronics. Science., 2011; 333:838–843.
CheneyN, MaccurdyR, CluneJ, LipsonH. Unshackling evolution: evolving soft robots with multiple materials and a powerful generative encoding. Proceedings of the Genetic and Evolutionary Compuation Conference (GECCO-2013); 2013.
25.
EwoldtRH, ClasenC, HosoiAE, McKinleyGH. Rheological fingerprinting of gastropod pedal mucus and synthetic complex fluids for biomimicking adhesive locomotion. Soft Matter., 2007; 3:634–643.
FischerC, BraunSA, BourbanP-E, et al.Dynamic properties of sandwich structures with integrated shear-thickening fluids. Smart Mater Struct., 2006; 15:1467–1475.
LeeYS, WetzelED, WagnerNJ. The ballistic impact characteristics of Kevlar® woven fabrics impregnated with a colloidal shear thickening fluid. J Mater Sci., 2003; 38:2825–2833.
34.
DennMM. Fifty years of non-Newtonian fluid dynamics. AIChE J., 2004; 50:2335–2345.
35.
MiddlemanS. Fundamentals of Polymer Processing. New York; McGraw-Hill: 1977.
36.
TadmorZ. Principles of Polymer Processing. New York; Wiley: 1979.
37.
BirdRB, ArmstrongRC, HassagerO. Dynamics of Polymeric Liquids: Volume 1 Fluid Mechanics. New York: John Wiley and Sons, 1987.
38.
BharadwajNA, AllisonJT, EwoldtRH. Early-stage design of rheologically complex materials via material function design targets. ASME 2013 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference; 2013.
39.
DealyJM. Official nomenclature for material functions describing the response of a viscoelastic fluid to various shearing and extensional deformations. J Rheol., 1995; 39:253–265.
EwoldtRH, McKinleyGH. Creep ringing in rheometry or How to deal with oft-discarded data in step stress tests. Rheol Bull., 2007; 76:4.
42.
FerryJD. Viscoelastic Properties of Polymers. Third edition. Wiley: 1980.
43.
MøllerPCF, MewisJ, BonnD. Yield stress and thixotropy: on the difficulty of measuring yield stresses in practice. Soft Matter., 2006; 2:274–283.
44.
MøllerPCF, FallA, BonnD. Origin of apparent viscosity in yield stress fluids below yielding. EPL, 2009; 87:38004.
45.
BarnesHA. The yield stress—a review or “παντα ρɛι”—everything flows?. J Non-Newtonian Fluid Mech., 1999; 81:133–178.
46.
PiauJM. Carbopol gels: elastoviscoplastic and slippery glasses made of individual swollen sponges. J Non-Newtonian Fluid Mech., 2007; 144:1–29.
47.
PipkinAC. Lectures on Viscoelasticity Theory. Applied Mathematical Sciences. Vol. 7. New York; Springer: 1972.
48.
EwoldtRH, BharadwajNA. Low-dimensional intrinsic material functions for nonlinear viscoelasticity. Rheologica Acta., 2013; 52:201–219.
49.
EwoldtRH, GurnonAK, López-BarrónC, McKinleyGH, SwanJ, WagnerNJ. LAOS Rheology Day, Friday the 13th, Colburn Laboratory, University of Delaware. Rheol Bull., 2012; 81:12–16,25.
50.
DieterG. Engineering Design: A Materials and Processing Approach. New York; McGraw-Hill Higher Education, 2009.
51.
CusslerE. Chemical Product Design. Cambridge; Cambridge University Press: 2012.
52.
CusslerEL, MoggridgeGD. A changing chemical industry. Rev Chem Eng., 2012; 28:73–79.
53.
LinseyJS, TsengI, FuK, CaganJ, WoodKL, SchunnC. A study of design fixation, its mitigation and perception in engineering design faculty. J Mech Des., 2010; 132:041003.
54.
UlrichK, EppingerSD. Product design and development. New York; McGraw-Hill: 2012.
55.
DealyJM, WissbrunKF. Melt rheology and its role in plastics processing: theory and applications. New York; Van Nostrand Reinhold: 1990.
56.
MacoskoCW. Rheology: principles, measurements, and applications. Advances in Interfacial Engineering Series. New York; Wiley-VCH: 1994.
57.
GiacominAJ, BirdRB, JohnsonLM, MixAW. Large-amplitude oscillatory shear flow from the corotational Maxwell model. J Non-Newtonian Fluid Mech., 2011; 166:1081–1099.
58.
HiltonHH. Optimum linear and nonlinear viscoelastic designer functionally graded materials—characterizations and analysis. Composites Part A., 2005; 36:1329–1334.
59.
HiltonHH, LeeDH, El FoulyARA. Generalized viscoelastic designer functionally graded auxetic materials engineered/tailored for specific task performances. Mech Time-Depend Mater., 2008; 12:151–178.
60.
HiltonHH, YiS. Analytical formulation of optimum material properties for viscoelastic damping. Smart Mater Struct, 1992; 1:113.
61.
WeaverPM, AshbyMF. The optimal selection of material and section-shape. J Eng Des., 1996; 7:129–150.
62.
MøllerP, FallA, ChikkadiV, DerksD, BonnD. An attempt to categorize yield stress fluid behaviour. Philos Trans A Math Phys Eng Sci., 2009; 367:5139–5155.
63.
Materials Genome Initiative for Global Competitiveness, Executive Office of the President of the United States. 2011.
