Beam-like topologically interlocked structures with hierarchical interlocking

TL;DR

This paper introduces a hierarchical surface morphology design for beam-like topologically interlocked structures, significantly enhancing their mechanical performance and approaching theoretical strength limits with realistic friction coefficients.

Contribution

It proposes a biologically inspired hierarchical interlocking surface design that improves the effective friction and structural capacity of topologically interlocked structures.

Findings

Surface morphology increases effective frictional strength.

Design can reach theoretical strength limits with realistic friction.

Surface curvature and gradient predict interface friction enhancement.

Abstract

Topologically interlocked materials and structures, which are assemblies of unbonded interlocking building blocks, are promising concepts for versatile structural applications. They have been shown to exhibit exceptional mechanical properties, including outstanding combinations of stiffness, strength, and toughness, beyond those achievable with common engineering materials. Recent work has established a theoretical upper limit for the strength and toughness of beam-like topologically interlocked structures. However, this theoretical limit is only achievable for structures with unrealistically high friction coefficients; therefore, it remains unknown whether it is achievable in actual structures. Here, we demonstrate that a hierarchical approach for topological interlocking, inspired by biological systems, overcomes these limitations and provides a path toward optimized mechanical performance. We consider beam-like topologically interlocked structures that present a sinusoidal surface morphology with controllable amplitude and wavelength and examine the properties of the structures using numerical simulations. The results show that the presence of surface morphologies increases the effective frictional strength of the interfaces and, if well-designed, enables us to reach the theoretical limit of the structural carrying capacity with realistic friction coefficients. Furthermore, we observe that the contribution of the surface morphology to the effective friction coefficient of the interface is well described by a criterion combining the surface curvature and surface gradient. Our study demonstrates the ability to architecture the surface morphology in beam-like topological interlocked structures to significantly enhance its structural performance.