Crack growth in nanostructured ceramics by high resolution 3D imaging

A number of groups around the world have been trying to replicate the hierarchical structure of bone using a range of techniques from ice-templated freeze-cast metal composites to nano-micron-millimetre structured polymer-glass-titanium scaffolds. However, there is a paucity of 3D data on the efficacy of crack shielding mechanisms, thus these designs are simple copies, rather than informed engineered structures. Our challenge is to study damage accumulation during in situ testing while under 3D x-ray tomographic imaging so as to identify the efficacy of different crack shielding mechanisms and thereby optimise the latest novel bio-inspired microstructures.

Using some of the best x-ray imaging equipment anywhere in the world in Manchester and at the Diamond Synchrotron Light Source we will unlock the key mechanisms by which nature’s hierarchical structures blunt crack-tips. These insights will be used to develop entirely new types of biomaterials. The current generation of biomimetic materials are based on mimicking morphology alone; this new generation will include knowledge of interface behaviour during crack propagation. These new materials will be engineered by combining the state-of-the-art fabrication techniques of my collaborators at Berkeley and Imperial College, i.e. freeze casting (Richie/Siaz), nano-hybrids (Jones), hierarchical Ti structures (Lee) with our own extensive experience in composites. We will examine hierarchically structured composites based on novel ceramic bridged laminates or porous metallic frameworks, but with tailored micron scale sub-structures. Direct X-ray microscope observations of the crack tips will allow the morphology, strength (and interface strength), as well as size and volume fractions to be calculated a priori, rather than via hit and miss experiment. With the phase fractions, their morphologies, and their interfaces optimised to increase toughness. In some cases it will also be possible to use high resolution x-ray diffraction to map the crack tip stresses to gain further insight into the extent to which the microstructure can shield the crack from the applied crack driving force.