3D cellular characterization and finite element analysis of cork compressive behavior based on high-resolution X-ray microtomography

Cork has been studied in many ways regarding its mechanical properties; however, no 3D analyses of the cellular structure have been performed at a cell-scale resolution. This paper presents the literature’s first known non-invasive 3D characterization and simulation of cork at a cellular level. A sample was scanned with a sub-micron resolution X-ray microtomography (μCT), followed by a cellular characterization and numerical analyses of the compressive behavior. A region was discretized for explicit finite element analysis (FEA), to simulate the cork cells' compression behavior along their radial (R) and non-radial (NR) directions, followed by a qualitative analysis of the Poisson effect. μCT analysis revealed the presence of cork cells with irregular morphologies scattered into the main tissue. Using the intact cork geometry from the μCT, natural cell wall corrugations were confirmed as stress concentrators and the preferred path for bending in FEA. Thanks to the combination of μCT-based FEA at a cellular level, stress–strain results showed that the R direction has superior mechanical performance than the NR, with 43% higher elastic modulus, 40% higher elastic collapse stress, and 16% higher energy absorption efficiency, approximately. As the plateau regime starts, the NR model densifies more quickly due to the lack of cell lumen for the cell walls to fold into. Finally, the Poisson effect revealed that in NR, most of the material was displaced within the NR/NR mode, due to the greater availability of cell lumen for the cell walls to fold up, and the longer lateral cork cell walls, making the NR plane less stiff when bending. On the contrary, in the R, most of the material was folded and compacted internally.