Sample preparation Tooling for near net-shape compression moulding of polymer specimens Davide S.A. De Focatiis * Division of Materials, Mechanics and Structures, University of Nottingham, Nottingham NG7 2RD, UK article info Article history: Received 6 January 2012 Accepted 14 February 2012 Keywords: Compression moulding Flash moulds Tooling Polymer specimens abstract This study presents several designs for flash moulds intended to aid the damage-free production of polymeric specimens for mechanical and structural characterisation. The designs consist of interlocking metal parts that produce appropriately shaped cavities in which polymer specimens are moulded, and that are easily dismantled after moulding to allow removal of the specimens from the moulds. Very limited sample preparation is required after removal of the specimens. Several of the proposed designs have been manufactured and successfully employed in the production of rectangular specimens for characterisation of a range of polymers. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The experimental material scientist has an intrinsic need to be able to produce and reproduce test specimens with well defined geometries in order to measure the structural and mechanical response of materials. The reason for this is that a large number of material properties are typically obtained from functions of both measured experimental quantities such as forces and displacements and specimen dimensions such as lengths, widths and thicknesses. Therefore, the accuracy of the determination of such material properties is often dependent on precise measurements of the geometry of the test specimen. The experimentalist is responsible for the generation of the experimental test data necessary to aid the development of new theories and for the validation of numerical models. He or she is also responsible for providing the practicing engineer with the precise material parameters required by such models so that virtual testing of parts in service can be carried out in shorter times and at a lower cost than the equivalent additional experimental tests. In short, the experimentalist plays several important roles within engineering and materials design, and producing high quality test specimens for characterisation forms a critical part of realising the reproducible and high-quality experi- mental data desired by all concerned. One important and widely used laboratory technique for the manufacture of solid polymeric specimens is compres- sion moulding. This is the process of heating a given poly- meric material to above its glass transition (for amorphous polymers) or above the crystal melting point (for semi- crystalline polymers), under moderate pressure for a prescribed time, in a shaped cavity and, subsequently, cooling the material to induce solidification in the new shape. The polymer fills the shaped cavity, known as a mould, whilst in the molten state, and must be removed from the mould after it has solidified, often for further shaping prior to testing. The process of removal of the moulded polymer specimen from the typical metallic mould is not always straightforward because of adhesion between polymer and metal, and because of the constraints imposed by the shape of the metal mould parts. Adhesion between polymer and metal mould is a more significant issue with oxygen-containing polymers [1]. If significant stress has to be applied to the moulded polymer during the removal, it is possible that this will induce viscoelastic or even plastic deformation, and in extreme cases even crazing and cracking, invalidating subsequent mechanical testing. If separate post-moulding machining is required for the production of polymeric test specimens from moulded sheets or blocks, one needs to contend with the friction * Tel.: þ44 115 9514097; fax: þ 44 115 9514115. E-mail address: davide.defocatiis@nottingham.ac.uk. Contents lists available at SciVerse ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest 0142-9418/$ – see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2012.02.008 Polymer Testing 31 (2012) 550–556