Fig. 5. Simulation of the mechanical properties of the 3DGraphene foam in a wide temperature range down to the cryogenic region.

(A) Overlays of the in situ SEM images for the full compress-release cycles of the same sample at 4 and 1273 K and enlargements for the labeled areas, showing that the structural stability and the reversible deformations of graphene sheets at microscopic scale are wide temperature independent. Green and red arrows mark the same graphene sheets at 4 and 1273 K. Scale bars, 100 μm (top row) and 25 μm (bottom row). (B and C) The theoretically simulated stress-strain curves agree well with the experimental results for the compression process of the 3DGraphene foam at 4 K (B) and 1273 K (C) and also with the well-matched simulated Young’s modulus–engineering strain curves for 4 K [inset of (B)] and 1273 K [inset of (C)]. (D and E) Theoretically simulated temperature dependence curves of stress (D) and Young’s modulus (E) fit well with the experimental data, suggesting almost negligible temperature influence on the stress-strain behavior and Young’s modulus in the compression process of the 3DGraphene foam down to cryogenic temperatures. All error bars represent SDs for the repeated measurements.