In this study, we focused on the high fracture toughness of nacre, which has a microscopic structure consisting of calcium carbonate lamellae and protein stacks. We performed deformation and fracture analysis on a compact tension (CT) specimen, where a brick-like structure, with lamellae modeled as bricks and proteins as a cohesive model, was placed at the tip of an artificial crack. First, a CT specimen with a single brick-like structure was printed using an FDM 3D printer and subjected to tensile loading. Next, a finite element (FE) analysis was performed on an FE model with the same shape. As a result, it was confirmed that the nonlinear deformation behavior and fracture process obtained by the FE analysis were in good agreement with the test results. Then, using the verified FE model, finite element analysis was performed on brick-like structured CT specimens with different brick aspect ratios. The results showed that the maximum load and the maximum displacement to failure increased as the brick aspect became more elongated along the tensile loading direction. This was attributed to the resistance as the brick was pulled out of the matrix. Consequently, a finite element analysis was performed on a CT specimen with a multilayered brick-like structure, where a certain area around the tip of the artificial crack was filled with a brick-cohesive model. The results confirmed that, similar to the single brick-like structure, the pull-out resistance of the brick and the zigzag crack propagation path were effective in improving the fracture resistance. However, when the brick aspect exceeded a certain value, the brick itself cracked, causing the crack to propagate linearly and reducing the maximum load.
FUJITA et al. (Thu,) studied this question.