Researchers reveal toughening mechanism of crack front in bioinspired materials

Recently, a research team uncovered the propagation and toughening mechanism of tortuous crack front in bioinspired anisotropic heterogeneities, and developed an optimization design for toughness amplification by manipulating microstructural orientation. Their work was published in Nature Communications.

Crack-fronts in heterogeneous materials interact with the non-uniform structure, resulting in 3D tortuous crack-tip configuration that significantly increases fracture resistance. However, due to the complex nonlinear coupling between the 3D crack-front geometry and the heterogeneous structures, the quantitative relationships of heterogeneity, crack-tip geometry, and toughness remain unclear.

In recent years, bioinspired heterogeneity has gained significant attention for improving material toughness. But most studies on bioinspired heterogeneity assumed straight crack-front propagation, overlooking the 3D tortuous crack-front geometry and the additional toughening effects it induces.

To address the above problems, the team used 3D-printed bioinspired heterostructures as a model system. Through fracture tests on the 3D-printed samples, they found that the straight crack front was distorted to a 3D helical crack-front configuration when interacted with heterostructures, deviating from the original pathway. Compared to linear toughening mechanisms, the 3D twisted crack geometry provides additional toughening effects.

Simulations and theoretical analysis revealed that heterogeneous structures influence the driving forces along the crack front, inducing an orientation-dependent mixed fracture mode of crack twisting and crack bridging. This interplay leads to the formation of helical crack-tip geometries, with nonlinear relationships between crack-tip geometry, fracture toughness, and fiber orientation. Based on the findings, the researchers designed a heterogeneous plywood system with enhanced toughness by adjusting the structural parameters.

This research reveals the physical mechanism behind the toughening effect of crack front in heterogeneous material, offering innovative ideas for future design of bioinspired heterogeneous materials.

The research team was led by Prof. Ni Yong and Prof. He Linghui from the University of Science and Technology of China (USTC).