Experimental validation of multiscale modeling of indentation of suspended circular graphene membranes

In recent studies, the in-plane elastic properties of graphene have been computed via Density Functional Theory (DFT) and expressed in the form of a higher-order continuum elastic constitutive model. The studies predict that graphene exhibits an anisotropic and non-linear elastic response at high strains. However, one study predicts that the rupture mechanism of graphene at its intrinsic strength is due to elastic instability whereas another study predicts the rupture mechanism at its intrinsic strength is due to phonon instability. In the present paper, we use the higher-order continuum elastic constitutive model within the context of the finite element method to simulate a set of experiments of the indentation of circular freestanding monatomic graphene membranes. There is a close correspondence between the measured and predicted measured force vs. displacement responses of indented graphene, providing experimental validation for the constitutive response. Further, there is a close correspondence between the measured and predicted breaking force of graphene via the elastic instability mechanism. Thus, the results suggest that the elastic instability precipitates failure of pristine graphene at its intrinsic strength, and also provides further experimental validation of the constitutive response.