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Effect of cell-size on the energy absorption features of closed-cell aluminium foams, Acta Astronautica, http://dx. Abstract:The effect of cell-size on the compressive response and energy absorption features of closed-cell aluminium (Al) foam were investigated by finite element method. Micromechanical models were constructed with a repeating unit-cell (RUC) which was sectioned from tetrakaidecahedra structure. Using this RUC, three Al foam models with different cell-sizes (large, medium and small) and all of same density, were built. These three different cell-size pieces of foam occupy the same volume and their domains contained 8, 27 and 64 RUCs respectively. However, the smaller cell-size foam has larger surface area to volume ratio compared to other two. Mechanical behaviour was modelled under uniaxial loading. All three aggregates (3D arrays of RUCs) of different cell-sizes showed an elastic region at the initial stage, then followed by a plateau, and finally, a densification region. The smaller cell size foam exhibited a higher peak-stress and a greater densification strain comparing other two cell-sizes investigated. It was demonstrated that energy absorption capabilities of smaller cell-size foams was higher compared to the larger cell-sizes examined.

Abstract. The process of composite metal foil manufacturing (CMFM) has reduced a number of limitations associated with commercial additive manufacturing (AM) methods. The existing metal AM machines are restricted by their build envelope and there is a growing market for the manufacture of large parts using AM. These parts are subsequently manufactured in fragments and are fastened together. This paper analyses the thermal stresses around cylindrical fasteners for three layered metal composite parts consisting of aluminium foil, brazing paste and copper foil layers. The investigation aims to examine the mechanical integrity of the metallurgically bonded aluminium/copper foils of 100 micron thickness manufactured in a disc shape. A cylindrical fastener set at an elevated temperature of 100 °C is fitted in the middle of the disc which results in a steady-state thermal distribution. Radial and shear stresses are computed using finite element method which shows that non-zero shear stresses developed by the copper layer inhibit the axial slippage of the fastener and thereby establishing the suitability of rivet joints for CMFM parts.

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The hybrid flexible risers have a multi-layered structure and use thermoplastic composite for the pressure and tensile armour. In contrast, a conventional flexible riser uses heavier carbon steel as armour which significantly contributes to its weight. For shallow-water applications, the conventional risers are widely used in offshore oil and gas industry due to their corrosion resistance properties and low transportation costs. However, the weight of conventional risers is a key limitation in ultra-deep-water applications. This shortcoming can be addressed by including a lightweight carbon fibre reinforced polymer (CFRP) composite as one of the individual layers. The use of CFRP reduces the effective tension at the hang off point which is a key limitation in extending the range of flexible risers. Here, the dynamic stability and functional load interactions of both risers (viz: a thermoplastic CFRP riser and a conventional flexible riser) at a water depth of 3000 m were studied. A global analysis was performed considering the onerous 1000-year hurricane wave with 100-year currents. The investigation considered ±150 m vessel offsets, three vessel headings (viz: 135, 180, 225°) and three vessel draughts (ballasted, empty, loaded). Additionally, a numerical model with a variable bending stiffness was used to capture the orthotropic material behaviour of a flexible riser. Results showed that the buoyancy requirement and effective tension were 2.1 times greater and 2% higher for the conventional riser compared to its composite counterpart. The most onerous case for a conventional riser was at zero offset whereas for its composite counterpart was at –150 m along the length of a riser. It was observed that the heavier masses of a conventional riser aid in aligning the weight vector with the upward direction of the buoyancy force. Contrarily, the composite risers undergo large displacements leading to misalignments and instability. Furthermore, the observed bending radius of the flexible riser was found to be within the allowable minimum bend radius at the hog bend location.