Abstract
Finite element (FE) forming simulation offers the possibility of a detailed analysis of the deformation behaviour of engineering textiles during forming processes, to predict possible manufacturing effects such as wrinkling or local changes in fibre volume content. The majority of macroscopic simulations are based on conventional two-dimensional shell elements with large aspect ratios to model the membrane and bending behaviour of thin fabrics efficiently. However, a three-dimensional element approach is necessary to account for stresses and strains in thickness direction accurately, which is required for processes with a significant influence of the fabric’s compaction behaviour, e.g. wet compression moulding. Conventional linear 3D-solid elements that would be commercially available for this purpose are rarely suitable for high aspect ratio forming simulations. They are often subjected to several locking phenomena under bending deformation, which leads to a strong dependence of the element formulation on the forming behaviour [1]. Therefore, in the present work a 3D hexahedral solid-shell element, based on the initial work of Schwarze and Reese [2,3], which has shown promising results for the forming of thin isotropic materials [1], is extended for highly anisotropic materials. The advantages of a locking-free element formulation are shown through a comparison to commercially available solid and shell elements in forming simulations of a generic geometry. Additionally, first ideas for an approach of a membrane-bending-decoupling based on a Taylor approximation of the strain are discussed, which is necessary for an accurate description of the deformation behaviour of thin fabrics.
Highlights
Lightweighting is a development strategy that aims to increase a system’s efficiency and to decrease CO2 emissions rather than just reducing the weight of a system
A relatively low stiffness of 1000 MPa in the principal material directions is chosen to reduce the explicit time increment in this comparative study, while maintaining a large anisotropy ratio and limiting the in-plane strains in fibre direction: The application to model a single-layer hemisphere forming test leads to hourglassing instabilities on the edges during the initial contact of the fabric and tool, cf
A linear solid-shell element suitable for the forming simulations of highly anisotropic materials with a membranebending decoupling based on a Tailor expansion of the strain is presented
Summary
Lightweighting is a development strategy that aims to increase a system’s efficiency and to decrease CO2 emissions rather than just reducing the weight of a system. State of the art forming simulation approaches mainly apply conventional two-dimensional shell approaches [5] to efficiently model the deformation of thin fibrous reinforcements, since they allow for high aspect ratios while still accurately describing the membrane and bending behaviour Those approaches cannot model out-of-plane compaction, which is an important forming mechanism to predict local fibre volume contents [6] and influences the permeability of the reinforcement during processes such as wet compressions moulding [7,8]. An approach for the membrane-bending decoupling within the linear 3D element formulation is proposed It is based on a Taylor approximation of the strain with respect to the out-of-plane direction and does not require to consider the displacements of neighbouring elements. The potential of this decoupling method is shown by application to numerical coupon and component forming tests
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