Suppressing scratch-induced brittle fracture in silicon by geometric design modification of the abrasive grits

The overarching goal of this research was to investigate the application of spherically shaped abrasive particles in achieving ductile-mode cutting. Scratching experiments were carried out to assess the differences between arbitrarily and spherically shaped diamond and tungsten carbide (WC) grits in inducing brittle fracture or ductile plasticity in single-crystal silicon. It was observed that the arbitrarily shaped particles produce brittle fracture in contrast to the spherically shaped grits. The sharp edges and corners of grits result in high tensile stress-concentrated regions causing cracking and spalling. Contrary to this, spherically shaped WC particles induce uniform cutting pressure, which suppresses the extent of the brittle fracture and the mode of material removal was completely dominated by ductile-cutting until a threshold load for ductile-to-brittle transition (the first cracks appearance). These observations are expected to provide a suitable pathway in making the Diamond Wire Sawing machining operations more robust by providing a control on brittle damage

Ceramic Armour for Armoured Vehicles Against Large-Calibre Bullets

Modelling the armour-piercing bullets B-32 calibre 12.7 mm penetration into the double-layer ceramic-composite armour has been performed for the armour blocks of two designs. The first one is a layer of ceramic square tiles supported by the glass or polyamide fabric. Modelling and subsequent ballistic tests have shown that the conical Hertz crack localized in the ceramic tile is formed. The tile is destroyed from the spread of radial cracks, and the entire armour unit becomes unable to sustain the repeated hit of the bullet. In the second case, the armour block consists of the discrete epoxy-filled cylindrical ceramic elements with spherical ends. The advantage of this "discrete" armour is localization of the damage zone and thus an ability to sustain the multiple bullet hits. The ballistic tests of the compared armour units have shown that both provide effective additional protection of light-armoured vehicles against the normal impact of the calibre 12.7 mm bullet