Subjecting a Graphene Monolayer to Tension and Compression

Abstract

The mechanical behaviour of graphene flakes under both tension and compression is examined using a cantilever-beam arrangement. Two different sets of samples were employed involving flakes just supported on a plastic bar but also embedded within the plastic substrate. By monitoring the shift of the 2D Raman line with strain, information on the stress transfer efficiency as a function of stress sign and monolayer support were obtained. In tension, the embedded flake seems to sustain strains up to 1.3%, whereas in compression there is an indication of flake buckling at about 0.7% strain. The retainment of such a high critical buckling strain confirms the relative high flexural rigidity of the embedded monolayer. 1The mechanical strength and stiffness of crystalline materials are normally governed by the strength and stiffness of their interatomic bonds. In brittle materials, defects present at the microscale are responsible for the severe reduction of tensile strengths from those predicted theoretically. However, as the loaded volume of a given brittle material is reduced and the number of microscopic defects diminishes, the material strength approaches the intrinsicmolecular-strength. This effect was first described by Griffith in 1921 [1] and the best manifestation of its validity is the manufacture and use of thin glass and carbon fibres that nowadays reinforce a whole variety of commercial plastic products such as sports goods, boats, aircrafts, etc.With reference to material stiffness, the presence of defects plays a minor role and is rather the degree of order and molecular orientation that provide the amount of stiffness along a given axis. In other words, in order to exploit the high stiffness in crystals, the stress direction should coincide with the eigenvector of a given bond. [2] Pure stretching of covalent or ionic bonds is normally responsible for high material stiffness whereas bending or twisting provides high compliance. This is why commercial-amorphous-polymers are compliant materials since an external stress is mainly consumed in the unfolding of entropic macromolecular chains rather than stretching of individual bonds. [2] Graphene is a two-dimensional crystal, consisting of hexagonally-arranged covalently bonded carbon atoms and is the template for one dimensional CNTs, three dimensional graphite, and also of important commercial products, such as polycrystalline carbon fibres (CF). As a single, virtually defect-free crystal, graphene is predicted to have an intrinsic tensile strength higher than any other known materials [3] and tensile stiffness similar to graphite. [4] Recent experiments [4] , have confirmed the extreme tensile strength of graphene of 130 GPa and the similar in-plane Young's modulus of graphene and graphite, of about 1TPa. [4] One way to assess how effective a material is in the uptake of applied stress or strain 2 along a given axis is to probe the variation of phonon frequencies upon loading. Raman spectroscopy has proven very successful in monitoring phonons of a whole ...

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Contact interaction of two rectangular plates made from different materials with an account of physical nonlinearity

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“…Note that in mathematical models (1), (4), (9), (10) and (1), (5), (9), (10), the contact pressure is proportional to the transversal crushing w 1 − h 1 − w 2 in a zone of contact between plates, i.e. we have…”

“…The value of the threshold load decreases on amount of 2.1% with a decrease in σ s on amount of 5%. Now we consider the SSS of the contact two-layer construction simply supported along the contour (9). Here the upper plate is made from a material of different moduli and physically nonlinear (solid curves), whereas the lower plate is made from one-modulus material (dashed curves).…”