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Graphene fatigue through van der Waals interactions

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Science Advances  14 Oct 2020:
Vol. 6, no. 42, eabb1335
DOI: 10.1126/sciadv.abb1335
  • Fig. 1 Propagation of interfacial damage zone under cyclic loading.

    (A) Schematic of cyclic loading setup. The polymer substrate is loaded cyclically where the two jaws move simultaneously outward and inward to maintain the graphene in the center for in situ observation. Inset shows a schematic of the triangular cyclic strain profile. (B) Real-time optical images showing the propagation of buckling zone after different fatigue cycles under strain range ∆ε = 5% and strain ratio R = 0. (C) AFM images of buckles that appear as black lines optically. (D and E) Damage length, a, and its propagation rate,dadN, as a function of fatigue cycle, both exhibiting a power law relation. The damage length eventually approaches the total length of the sample. (F) The damage propagation rate as a function of interfacial strain intensity factor range, ΔKint, showing that the propagation of graphene-polymer interfacial fatigue damage can be described by a modified Paris’ law as in Eq. 3. Values of m were extracted by curve fitting with SEs. Scale bars, 50 (B) and 5 μm (C).

  • Fig. 2 Mixed-mode fatigue fracture and damage of graphene.

    (A) Time-lapsed images showing the multiple fracture modes of graphene. Mode I fracture (opening cleavage) was perpendicular to the loading direction and was not caused by fatigue. Mode II fracture (in-plane shear) initiated at a fold junction and propagated along the loading direction (C15 to C500). Mode III fracture (tear) occurred at both edge and internal defective sites. (B) High-magnification image of the damaged graphene after 500 fatigue cycles, showing details of folds, tears, and cracks. (C) AFM topographic image of an internal tear in (B). (D) Schematics of the three different fracture modes observed in the experiments. (E) Separation distance between the two graphene films, showing sigmoidal behavior with cycle number. (F) Evolution of normalized area and lengths in both directions with cycle number, showing similar sigmoidal behavior. (G) Normalized damage of graphene under large strain range ∆ε = 20% and R = 0.33, highlighting local oscillation of area and lengths during cyclic loading. Scale bars, 50 (A), 10 (B), and 2 μm (C).

  • Fig. 3 Fatigue fracture by in-plane shear at fold junctions.

    (A) AFM topography images of cyclically loaded graphene showing the geometrical complexity of folds and junctions. (B) Schematics showing the mechanism of junction shear. Shear fracture initiated at the cyclic loading–induced fold junctions due to severe stress concentration. The shear crack could propagate along (i) one or (ii) both sides of the fold, as shown in examples (C) and (D), respectively.

  • Fig. 4 Fatigue fracture by tearing.

    (A) Snapshots of an internal tear propagation at different stages. (B) Tear length and area as a function of time showing unstable propagation, with the four stages in (A) indicated in the timeline. (C) Outline of the final tear with midline showing the change of tear width and propagation direction. (D) Schematic of a tear with external loading. (E) Top view of the tear schematic with acting forces on the tear front. (F) Cross-sectional view of the tear schematic highlighting graphene/graphene adhesion as an advancing force and graphene/PDMS adhesion as a resistance force.

Supplementary Materials

  • Supplementary Materials

    Graphene fatigue through van der Waals interactions

    Teng Cui, Kevin Yip, Aly Hassan, Guorui Wang, Xingjian Liu, Yu Sun, Tobin Filleter

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