Mechanical compression tests and computational simulation
This protocol is extracted from research article:
Bioinspired polymeric woods
Sci Adv, Aug 10, 2018; DOI: 10.1126/sciadv.aat7223

Mechanical compression and bending tests were performed on an Instron 5565A universal testing machine equipped with two flat-surface compression stages and 5000-N load cells. FEM simulations were performed with the ABAQUS program. The sample size for the three-point bending test was 2 mm × 2 mm × 10 mm. The basic unit of the models was a regular hexagonal hollow column with a uniform wall thickness. The honeycomb structure could be obtained by repeating the basic unit. We used the thin- and thick-walled models to simulate the prepared materials (CMF and CPF) with low and high matrix concentrations, respectively. Although the hollow channels in the synthesized materials were irregular and inhomogeneous relatively, the honeycomb model could characterize the structural morphology from the perspective of theoretical simulation. In all simulations, the compression was realized by a rigid plane with a uniform displacement. The wall thickness of honeycomb structures and the pore area are shown in fig. S11 and table S1. Preexisting crackles at the center of the walls along the length direction were generated by cohesive elements. The parameters of cohesive interface were referred to the experiment data of bulk materials. The low-density polymeric woods were first simulated by the thin-walled honeycomb structure (fig. S22). The step length of the displacement of rigid plate was 0.001 in all simulations. The large deflection effects were included in the solution of compression processes. Then, we used the thick-walled model with preexisting crackles (fig. S23) to simulate the high-density polymeric woods. Preexisting crackles were generated by cohesive elements. Because of our understanding of the cracking mechanism in the Brazilian test (28), we modified the thick-walled model with projecting parts at two symmetric edges. The similar thin-walled model was also simulated as a comparison (fig. S24). In FEM simulations, C3D8R and COH3D8 elements were selected for the walls and cohesive interfaces, respectively. Because of the limitations of computational cost and time, the meshing grids in thick-walled models with preexisting crackles were larger than those in thin-walled models. The wall thicknesses of the two models were 2.0 and 6.6 μm, respectively, and the side length of the hexagonal opening in both two models was 21 μm.

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