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The mechanical behaviour of poly(vinyl butyral) (PVB) at small (< 0.1%) and large strains (> 200%) is investigated experimentally over a range of strain rates in order to provide data for the development and validation of constitutive models. The small-strain response is investigated using dynamic mechanical analysis at frequencies from 1 Hz to 100 Hz and temperatures from −80 • C to 70 • C. It is found that a generalized Maxwell model adequately describes the material behaviour in the small-strain regime. The large-strain response is investigated using a high-speed servo hydraulic test machine at strain-rates from 0.2s −1 to 400 s −1 . It is found that the PVB response is characterised by a time-dependent steep initial rise in stress followed by a hyperelastic type response until failure. No current material model completely captures this time-dependent behaviour at large-strains.

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In-depth understanding of microstructure development is required to fabricate high quality products by additive manufacturing (for example, 3D printing). Here we report the governing role of side-branching in the microstructure development of alloys by laser powder bed fusion. We show that perturbations on the sides of cells (or dendrites) facilitate crystals to change growth direction by side-branching along orthogonal directions in response to changes in local heat flux. While the continuous epitaxial growth is responsible for slender columnar grains confined to the centreline of melt pools, side-branching frequently happening on the sides of melt pools enables crystals to follow drastic changes in thermal gradient across adjacent melt pools, resulting in substantial broadening of grains. The variation of scan pattern can interrupt the vertical columnar microstructure, but promotes both in-layer and out-of-layer side-branching, in particular resulting in the helical growth of microstructure in a chessboard strategy with 67°rotation between layers.