Intrinsic interlayer shear strength of graphite

Graphite holds significant values in the energy and electronics industries due to its unique properties. As a quintessential example of highly anisotropic materials, the shear strength measures one of its most fundamental mechanical properties. However, the lack of ideal materials and testing methods has led to a wide dispersion in the reported values. To address this issue, we utilized epitaxially grown single-crystal graphite and developed a high-throughput sample preparation method, along with a novel loading technique in this work. The intrinsic shear strength of AB-stacked graphite was determined to be τs = 62 MPa, by excluding the size effect in measurements. The results are further compared to highly oriented pyrolytic graphite specimens processed down to nanoscale thickness, highlighting the adverse impact of twisted single-crystalline interfaces between the graphitic layers. Additionally, we observed a distinctive failure mechanism with continuous and uniform cascade plastic slips across the thickness of graphite samples, which corresponds to an interlayer shear strength approaching τs. The intrinsic shear strength characterized in our work sets an upper limit for the interlayer shear resistance of graphite. The experimental procedure for measuring shear strength can be applied to other van der Waals materials.