Failure Processes in Embedded Monolayer Graphene under Axial Compression

Abstract

Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of –0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1–2 nm. These results were compared with DFT computations performed on analogue coronene/PMMA oligomers and a reasonable agreement was obtained.

Graphene resting on substrate: Closed form solutions for the perfect bonding and the delamination case

“…k; l are the Lame constants of the substrate. We disregard viscous effects, since we have in mind experiments with slow rate such as the one's performed in Androulidakis et al (2014). e 0 b denotes the internal strain field the substrate has.…”

“…For the substrate we make three different assumptions corresponding to three common materials used as substrate: Polyethylene terephthalate (PET), Polymethyl methacrylate (PMMA) and Polydimethylsiloxane (PDMS). In the mathematical model these are introduced through their Lame constants, k; l. Being aware that these polymeric substrate's behave in a viscoelastic manner, we assume the viscous response to be negligible, since we have in mind experiments with slow rate such as those in Androulidakis et al (2014).…”

“…Then the technique of Raman spectroscopy can be applied to measure the mechanical properties of graphene by measuring the G and 2D peak of the Raman spectra. In Androulidakis et al (2014) we embed a graphene flake on a substrate and apply a tensional loading to the system graphene/substrate using either the technique of cantilever beam or the four point bending technique.…”

Nanoscale Mechanics of Graphene and Graphene Oxide in Composites: A Scientific and Technological Perspective

“…l c is larger in case of poor stress transfer (i.e., low interaction) between the sheet and the matrix. [15,16] The strain within single graphene sheets [17][18][19] or even in composites [20] can be measured and mapped using Raman microscopy; for multilayer graphene ≈10 times larger than the one of macroscopic steel sheets (Figure 1c). [13] The mechanical behavior of graphene and graphene oxide (GO) at the nanoscale has been also intensively studied using atomistic modeling [10] (Figure 1d,e), or correlating mechanical properties with structure and geometry of chemical bonds at atomic scale (Figure 1f,g), [7,14] as described in more detail in following sections.…”

“…[5,19,48] 3) Chemistry -a fine control of the surface chemistry of the nanosheets will be required to tune the density and nature of chemical defects, to maximize the interaction between the sheets and the polymer matrix and hence ensure uniform dispersion in the composite and efficient stress transfer between the different phases of the composite material with moderate intrinsic flake strength reduction.…”