[en] Highlights: • Effective design of graphene/ceramic nanocomposites by algebraic topological methods. • Arrangement of rGO inclusions affects conductivity stronger than their mass fraction. • Localised sub-structures created by varying rGO size provide optimal conductivity. The design of new ceramic materials with specific thermo-electrical and mechanical properties is important for a range of engineering applications. Recent research has demonstrated that inclusion of soft reduced graphene oxide (rGO) in hard ceramic matrix produces nano-structured ceramic composites with improved electrical conductivity and fracture toughness. The emergent properties of such composites are strongly related to the mass fraction and spatial distribution of rGO inclusions. Their micro-structure includes sub-structures with different dimensions - 1D, 2D and 3D - which calls for entirely new approaches to characterisation and design. In this theoretical work, a new discrete (combinatorial) strategy is proposed that allows for capturing all sub-structures, employing elements of algebraic topology and modern graph theory. It is demonstrated how this strategy can be applied to the flexible design of nano-structured ceramics with a superior balance between conductivity and resistance to fracture.

[en] The stress concentration and distribution around an inhomogeneity of threefold symmetry in a polycrystalline ceramic matrix is considered. The perturbation method in the theory of plane elasticity is used to solve the problem of a nearly circular inhomogeneity of threefold symmetry under remote loading in the first-order approximation. The solution was specified to the uniaxial tension of convex and concave rounded triangular inhomogeneities. The stress concentration on the interface as well as the stress distribution in both inhomogeneity and matrix along the inhomogeneity symmetry axes are studied and discussed in detail. The numerical results, obtained analytically with the first-order approximate solution, are compared with those of finite-element calculations.

[en] Systematic experiments have been performed to characterize defect structures in deformed Gum Metal, a special titanium alloy with high strength, low Young's modulus, excellent cold workability and low resistance to shear in certain crystallographic planes. Results from high-resolution transmission electron microscopy characterization reveal nanodisturbances (planar nanoscopic areas of local shear) as typical elements of defect structures in deformed Gum Metal. A theoretical model is suggested describing nanodisturbances as nanoscale dipoles of non-conventional partial dislocations with arbitrary, non-quantized Burgers vectors. It is shown theoretically that the homogeneous generation of nanodisturbances is energetically favorable in Gum Metal, where they effectively carry plastic flow

[en] Sliced SiC boule grown by physical vapor transport is investigated using synchrotron white beam phase contrast imaging combined with Bragg diffraction. The evolution of defects is revealed. In the early growth stage, foreign polytype inclusions not only induce massive generation of full-core dislocations and dislocated micropipes but also attract them, forming slit-type pores at the boundaries of inclusions. In the intermediate stage, when inclusions stop to grow and become overgrown by the matrix, the pore density significantly reduces, which is attributed to their transformation into new micropipes. In the later stage, the micropipe density decreases, providing evidence for their partial annihilation and healing. Mechanisms for the evolution from inclusions to pores and finally to micropipes during the crystal growth are further discussed. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)