Department of Physics/NIS, University of Torino and INFN Torino, Italy. Nicola Pugno

Transcription

1 Bio-inspired inspired strategies for the optimization of nano-material mechanical properties Federico Bosia Department of Physics/NIS, University of Torino and INFN Torino, Italy Nicola Pugno Department of Mechanical and Structural Engineering, University of Trento, Italy 1

2 Outline Motivation Optimization of Adhesion: Gecko paws Optimization of Anti-Adhesion: Adhesion Lotus leaveses Optimization of Strength and Toughness: from Spider Silk to Graphene and Carbon Nanotubes Modelling of defects, hierarchy, heterogeneity and Self-Healing Outlook 2

3 Optimization of Adhesion The most adhesive: the Tokay Gecko Ernesto: the mascotte of fthe Pugno Lab. Adhesion due to van der Waals and capillary forces; Adhesion strength of about 1 MPa, i.e. 10 times its body weight 3 requirements: - Strong adhesion - Easy detachment - Self-cleaning mechanisms 3

4 Optimization of Adhesion HIERARCHICAL NANO-ARCHITECTURES HIERARCHICAL NANO-ARCHITECTURES E.Lepore, F.Pugno, N.M. Pugno (2011): The Journal of Adhesion, 88:10,

5 Optimization of Adhesion M.Varenberg, N.M.Pugno, S.N.Gorb Soft Matter, 2010,6, SPATULAE: TERMINAL CONTACT UNITS Similar tape-like geometries (thus the detachment is due to peeling ), but of different sizes (3 billions of contacts in geckos) 5

6 Optimization of Adhesion E.Lepore, F.Pugno, N.M. Pugno (2011): The Journal of Adhesion, 88:10,

7 Optimization of Adhesion Principle of contact splitting 3 ingredients : F b 1) Super-adhesion by nanocontacts: (b total peeling line) 2) Easy detachment by controlling the peeling angle: F 1 1 cos 3) Self-cleaning Lotus effect (Hierarchical architectures) 7

8 Optimization of Adhesion THEORY OF MULTIPLE PEELING, TO DESIGN GECKO-INSPIRED ADHESIVES Experimental results Optimal angle for maximal adhesion (key parameter: surface energy divided by thickness and Young s modulus) N.M.Pugno, International Journal of Fracture (2011), 171(2), HIERARCHICAL ANCHORAGES? 8

9 Optimization of Adhesion xi Load transfer F z i X i k i i N.M.Pugno, Materials Today (2010), 13,

10 Optimization of Adhesion Design of Spiderman suit : Nano-fibres Hierarchical design Tapered spatulae 10

11 Optimization of Anti-AdhesionAdhesion Lotus leaf Contact angle 150 More than 200 plants are super-hydrophobic; Fundamental role of hierarchy yet to be clearly understood LOTUS-EFFECT Hierarchy activates rolling and self-cleaning, instead of simple sliding 11

12 Optimization of Anti-AdhesionAdhesion CLASSICAL MODELS Hierarchical surfaces Wenzel model Cassie-Baxter model N.M.Pugno, Journal of Physics: Condensed Matter 19, (2007) 12

13 Optimization of Anti-AdhesionAdhesion E.Lepore, N.M.Pugno, Bionanoscience, 8 (1), (2011) 13

14 Optimization of Strength and Toughness SPIDER SILK 14

15 Optimization of Strength and Toughness STRENGTH 1 GPa, STRAIN UP TO 750% Hierarchical heterogeneous material E.Lepore, A.Marchiore, M.Isaia, M.Buehler, N.M.Pugno, PlOS One (2012) A.Nova, S.Keten, N.M.Pugno, A.Redaelli and M.J. Buehler, Nanoletters 10, (2010) Strength and toughness are competing properties in artificial materials 15

16 Optimization of Strength and Toughness LOCALIZED LOAD MD simulations by M.J.Buehler s group, MIT S.W.Cranford, A.Tarakanova, N.M.Pugno, and M.J. Buehler, Nature 482, (2012) 16

17 Optimization of Strength and Toughness SPIDER WEB DISTRIBUTED LOAD DISTRIBUTED LOAD, E.G. WIND LOAD: THE WEAKEST LINK IS THE ANCHORAGE RATHER THAN THE WEB ITSELF. S.W.Cranford, A.Tarakanova, N.M.Pugno, and M.J. Buehler, Nature 482, (2012) 17

18 Optimization of Strength and Toughness NECESSARY INGREDIENTS : Appropriate p properties p (starting at nanoscale) Hierarchy Material heterogeneity Interaction between structure and constitutive behaviour Tailor-made topology, tapering etc... (i) Tough, soft matrix (ii) Strong hard inclusions (iii) Hierarchy + SELF-HEALING e.g. Skin, bone... 1 t h l n 18

19 Carbon Nanotubes CARBON NANOTUBES (CNT) Theoretical predicted strength 100 GPa NANOTENSILE TEST OF CNT Measured strength 60 GPa Role of defects Yu, M. Lourie, O. Dyer, M. J. Moloni, K. Kelly, T. F. Ruoff, R. S. Science 287 (5453): , (2000). 19

20 Graphene STRONGEST MATERIAL EVER MEASURED paper [Chen et al. Adv. Mat 20, 3557 (2008)] nanoribbons [Kosynkin et al. Nature 458, 872 (2009)] fibres [Xu et al. Nat. Comm. 2, 571 (2011)] large area growth increasingly possible graphene-based composites [Li et al. Science 324, 1312 (2009), Bae et al, Nature Nano 5, 574(2010) ] [Stankovich et al. Nature 442, 282 (2006)] 20

21 Graphene monolayer graphene: experimental stiffness and strength determination E D E = (1.0 ± 0.1) TPa D = (-2 2.0± 04)TPa 0.4) 2 intrinsic i i strength: th = (130 ± 10) GPa [Lee et al. Science 321, 385 (2008)] 21

22 Nanoscrolls NANOSCROLL FORMATION NANO-CHANNELS NANO-OSCILLATORS Self rolling of graphene nanoribbons due to the competition between surface (VdW) and elastic (bending) energies Collaboration with with H. Gao s group, Brown University it NANOMOTORS X. Shi, N. M. Pugno and H. Gao, 2011, International Journal of Fracture, Vol. 171(2), pp Y. Cheng, X. Shi, N.M. Pugno and H. Gao, 2012, Physica E, Vol. 44(6), pp

23 Theory/Numerical simulations Important tools in evaluating the effect of the adopted optimization strategies In nano-materials (e.g. Graphene/CNT ): Effect of defects, grain boundaries, etc Effect of upscaling In nano-composites: Need to optimize mechanical performance (stiffness, strength, toughness, adhesion...) as a function of material properties, volume fractions, structure, topology, hierarchy, etc. Need for theoretical modeling and simulations using a relatively simple model which is capable of spanning various orders of magnitude 23

24 Quantized fracture mechanics Discretization of Linear Elastic Fracture Mechanics, introducing a fracture quantum W A 0 G * W A G C Comparison with atomistic simulations: Strength [GPa] n=2 n=4 n=6 n=8 (n=2) MM - (80,0) QFM [N.M.Pugno. Philosophical magazine 84, 2829 (2004)] 1 vacancy: strength reduction 20% 24

25 Hierarchical Fibre Bundle Model (HFBM) Based on a Fibre Bundle Model, applied recursively in a hierarchical scheme Weibull distributed fibre strengths and stiffnesses at level 0 linear/nonlinear elastic behaviour assigned to fibres multiple fibre types possible brittle/ductile fracture behaviour possible Equal Load Sharing (ELS) : after each fibre break, load is redistributed equally among surviving fibres stiffness/strength/toughness for fibre bundle derived from repeated simulations (~10 3 ) fibrecharacteristics at level (i+1) derived fromlevel i bundle results different hierarchical structures evaluated (load redistribution) Full-scale properties derived from level 0 characteristics (no additional parameters) Ideal for evaluating the mechanical behaviour of multiscale defective or heterogeneous materials under tensile loading 25

26 Scaling/defects: strength reduction NANOTUBE-BASED SPACE ELEVATOR CABLE Evaluation of the role of defects on strength [N.M.Pugno and F.Bosia. Small 4, 1044 (2008)] 26

27 CNT composites CNT-PVA composites RECORD TOUGHNESS: 870 J/g Ductile matrix / brittle reinforcing fibres [F.Bosia, N.M.Pugno, M.J. Buehler Phys.Rev.E 82, (2010)] 27

28 Hierarchy Tendon Twisted cable yarns (Bombyx mori silkworm yarns ) Evaluation of the role of pure hierarchy N = 8 Increasing hierarchy [N.M.Pugno, F.Bosia, T.Abdalrahman, Phys.Rev.E 85, (2012)] Hierarchy alone does not provide improved strength... 28

29 Hierarchy/heterogeneity...but hierarchy and fibre mixing together can Hierarchical composites N = 480 Fibre 1: σ 01 =10 GPa, m 01 =2 Fibre 2: σ 02 =0.01 GPa, m 02 = Mixing ratio: = 50% Which h configurations? [F.Bosia, N.M.Pugno, T.Abdalrahman. Nanoscale 4, 1200 (2012)] 29

30 Hierarchy/heterogeneity Systematic study of all possible configurations (hierarchy levels h=1,2,3) 3 rd level hierarchical structure with N=3600 and mixing ratio = 20% h = 3 ( = 20%), ~ 5000 configurations strength variability of >40% mean strength improvement of up to 22% ( = 50%) higher hierarchical levels more promising In future, numerical optimization procedure to determine best configurations as a function of input parameters [F.Bosia, F.Della Croce, N.M.Pugno. J. Mech. Behavior Biomed. Mat. In press (2012)] 30

31 Self-healing IN ARTIFICIAL MATERIALS (a) Damage event causes crack formation in the matrix; (b) crack ruptures the microcapsules, releasing liquid healing agent into crack plane; (c) healing agent polymerizes upon contact with embedded catalyst, bonding crack closed [White et al. Nature 409:794 7 (2001)] Numerical model: 1. Random healing : replace random fibre at a healing rate 2. Local healing : replace last fractured fibre at healing rate 31

32 Self-healing NUMERICAL MODELLING RESULTS Considerable improvement in Strength and especially Toughness, as well as lifetime where material heals is critical Strength vs. Dissipated energy vs. [F.Bosia, T,Abdalrahman, N.M.Pugno. Nanotoday In preparation (2012)] 32

33 Tesi di Laurea Tesi disponibili: Simulazioni numeriche agli elementi finiti (FEM) su multiple peeling e ancoraggi a geometria gerarchica Sviluppo modelli numerici di adesione per superfici nanostrutturate gerarchiche Simulazioni numeriche sull ottimizzazione della resistenza/tenacità di strutture gerarchiche self-healing Contatti: Federico Bosia Dipartimento di Fisica fbosia@to.infn.it tel.: ufficio: T50 (piano terra ala vecchia) 33