Simulation of the forming process for curved composite sandwich panels

S Chen,O P L Mcgregor,A Endruweit,N A Warrior,L T Harper

doi:10.1007/s12289-019-01520-4

S Chen, O P L Mcgregor + Show 3 more

Open Access

https://doi.org/10.1007/s12289-019-01520-4

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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.

Highlights

Composite sandwich panels offer high specific bending stiffness, delivering opportunities for lightweight design
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 [1,2,3,4,5,6,7]

Summary

Introduction

Composite sandwich panels offer high specific bending stiffness, delivering opportunities for lightweight design. The shape of the stress-strain curves indicates that the introduction of the dummy flanges or the infill material does not significantly influence the effective compressive behaviour of the core, but is suitable to overcome the difficulty with convergence of the original meso-scale model. High in-plane tensile forces occur in the fabric plies in the region of lowest material compression These forces prevent the fabric from conforming to the tool surface and cause the core to crush locally, creating gaps along the edges of the geometry which fill with resin. This indicates that the relevant mechanisms of the forming process are reproduced in the macro-scale model, proving the suitability of this approach.

Conclusions

Findings

Compliance with ethical standards