Simulation of the forming process for curved composite sandwich panels
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ORIGINAL RESEARCH
Simulation of the forming process for curved composite sandwich panels S. Chen 1
&
O. P. L. McGregor 1 & A. Endruweit 1 & L. T. Harper 1 & N. A. Warrior 1
Received: 4 July 2019 / Accepted: 25 October 2019 # The Author(s) 2019
Abstract For affordable high-volume manufacture of sandwich panels with complex curvature and varying thickness, fabric skins and a core structure are simultaneously press-formed using a set of matched tools. A finite-element-based process simulation was developed, which takes into account shearing of the reinforcement skins, multi-axial deformation of the core structure, and friction at the interfaces. Meso-scale sandwich models, based on measured properties of the honeycomb cell walls, indicate that panels deform primarily in bending if out-of-plane movement of the core is unconstrained, while local through-thickness crushing of the core is more important in the presence of stronger constraints. As computational costs for meso-scale models are high, a complementary macro-scale model was developed for simulation of larger components. This is based on experimentally determined homogenised properties of the honeycomb core. The macro-scale model was employed to analyse forming of a generic component. Simulations predicted the poor localised conformity of the sandwich to the tool, as observed on a physical component. It was also predicted accurately that fibre shear angles in the skins are below the critical angle for onset of fabric wrinkling. Keywords Honeycomb . Process modelling . Finite element analysis (FEA) . Forming
Introduction Composite sandwich panels offer high specific bending stiffness, delivering opportunities for lightweight design. However, sandwich components of complex shapes can be costly to manufacture, as machining operations on the core are required in addition to moulding processes for the skins. In well-established high-volume applications, such as lightweight automotive interior load floor components, a comparatively low-cost composite sandwich is manufactured by pressing the core material into shape simultaneously with the skins, in a single forming operation. While the forming process causes local buckling or crushing of the core structure, the mechanical performance of the finished component has been found sufficient for this type of application [1–7]. Typical material combinations for press-formed sandwich
* S. Chen [email protected] 1
Composites Research Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK
structures include glass fibre composite skins, usually made from chopped strand mat with fibre lengths greater than 25 mm, hexagonal paper cores and polyurethane foaming resin. The reinforcement in the skins is wet out with the resin. As the resin expands during cure, it partially fills the open cells of the core (at the interface with the skins), which allows strong bonds between the core and skins to develop. Variants of this process exist, using different types of cores and carbon fibre textile sk
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