Topological Interlocking: A Promising Materials Design Principle

We present a novel approach to designing materials using the topological interlocking principle. Segmentation of monolithic materials into identical interlocked building blocks provides the structure with enhanced resistance to crack propagation, high tolerance to local failures, increased sound insulation capacity and other beneficial properties [1]. In addition, different materials can be blended within such a structure in any pattern and proportion, which may provide it with multifunctionality. A further advantageous property of topologically interlocked ensembles of blocks is the possibility to control the stiffness of the assembly. By including in the structure active elements that possess shape memory, actuation becomes possible in that a precipitous change of stiffness can be produced. This will be illustrated by an assembly of osteomorphic ceramic blocks armoured with tensioning wires from a shape memory alloy (Nitinol). The constraining force imposed on the assembly through the wires governs its bending stiffness and load bearing capacity. Such a segmented plate can act as a smart structure, which changes its flexural stiffness and load bearing capacity “on demand”, in response to external stimuli, such as heat generated by the switching an electric current on and off [2]. In another example, platelets of ultra-high molecular weight polyethylene (UHMWPE) embedded in an assembly of ceramic osteomorphic blocks were used for actuation. This polymer possesses a large shape memory effect [3]. Heating of the platelets by passing an electric current was shown to produce a response of the structure by stiffening and load increment. The use of biomimetic principles in the design of topological interlocking structures will also be discussed.