Investigation into the effects of inter-ply sliding during double diaphragm forming for multi-layered biaxial non-crimp fabrics

F Yu,S Chen,L.T Harper,N.A Warrior

doi:10.1016/j.compositesa.2021.106611

Abstract

The effect of inter-ply sliding was investigated for multi-ply Non-Crimp Fabric (NCF) preforms during the Double Diaphragm Forming (DDF) process. A Finite Element (FE) model was employed to investigate the influence of the ply layup sequence and the coefficient of friction between fabric-fabric and fabric-diaphragm interfaces. Simulation results indicate that in-plane fibre compression, caused by dissimilar shear deformation between adjacent plies, can lead to out-of-plane wrinkles, where the wrinkle length is a function of the relative fibre angle at the ply-ply contact interface. The most severe wrinkles occurred when the inter-ply angle was 45° for a multi-ply biaxial NCF preform with a pillar stitch at 45° to the primary yarns. A second parametric study was conducted by incrementally reducing the coefficient of friction at the ply-ply interface. Experiments confirmed that out-of-plane wrinkles are sensitive to the friction resistance between NCF plies and therefore lubricating the fibres can minimise wrinkling defects caused by dissimilar inter-ply deformation.

Highlights

Fibre preforms for structural composite components are typically composed of multiple fabric plies, which are laid up following a specific ply orientation sequence to meet stiffness and strength requirements
This paper investigates the forming behaviour of multiple bi-axial Non-Crimp Fabric (NCF) plies during the double diaphragm forming process
Double Diaphragm Forming (DDF) simulations were performed for a series of multi-ply layups comprising two NCF plies to investigate the influence of ply orientation on the severity of wrinkling defects

Summary

Introduction

Fibre preforms for structural composite components are typically composed of multiple fabric plies, which are laid up following a specific ply orientation sequence to meet stiffness and strength requirements. Forming multiple plies with different ply orientations over complex 3D shapes significantly increases the likelihood of defects compared to sequentially forming single plies, or forming multiple plies stacked at the same fibre orientation [1,2,3] These forming induced de fects, such as wrinkles and in-plane fibre buckling, can significantly reduce the mechanical performance of the final component [4,5,6], with the presence of fabric wrinkles reported to reduce the in-plane compressive strength in the loading direction by up to 40% [7]. The asymmetric shear resistance related to the stitch pattern [9] affects the inter-ply movement and influences the formation of defects

Methods

Results

Conclusion