Intrinsic mechanical properties of graphene oxide films: Strain characterization and the gripping effects

Graphene oxide films are excellent structural and functional materials for their outstanding performance. Recent measurements reported widely scattered mechanical properties, which have been attributed to the difference in the chemistry and complex microstructures that rely on the fabrication process. In this work, we present an experimental study showing that the procedure of mechanical characterization is also critical for measuring intrinsic mechanical properties of graphene oxide films. We find that the specimen geometry and loading conditions could lead to significant variation in the measured stress, strain and toughness. To quantify these effects, we propose a rigid-plasticity shear-lag model to capture the effect of interfacial slippage at gripping ends, which can not only eliminate artifacts in measurements, but also be used to determine interfacial mechanical properties of gripping. Effects of grip pressure, length and loading rate are also discussed, following which suggestions for the experimental setup are provided. These understandings lay the ground for probing intrinsic mechanical properties of graphene oxide films in a reliably way.