Experimental Investigation of Tow Deformation During Draping of Woven Fabrics - abstract
SB Sharma1, MPF Sutcliff1, M Clifford2, A Long2
1 Department of Engineering, Cambridge University, Cambridge CB2 1PZ, UK.
1 School of Mechanical Engineering, University of Nottingham, Nottingham NG7 2RD, UK.
A detailed understanding of the drape behaviour of woven fabrics is important to enable accurate predictions
of the mechanical properties of complex-shaped structures made from woven fabric and to optimise their
manufacture. It has been established that pure shear is the main mechanism allowing a woven fabric to conform
to double-curvature shapes. Accordingly most previous researchers have focused on studying the shearing of
fabrics, and on developing kinematic models for fabric draping. Several questions however still need to be
- Are other mechanisms apart from 'pure shear' significant?
- How do the local restraints such as tool friction affect the fabric drape?
- Do membrane forces developed in the fabric affect draping?
The work presented in this paper is part of a larger project which aims to extend kinematic models of draping
and investigate their accuracy as applied to complex-shaped structures. The degree to which additional
mechanisms need to be included in a 'next generation' model will depend in part on answers to the above
questions. This paper describes a set of experiments which examine the details of fabric deformation in a
range of non-standard tests, to help address these questions.
The details of the deformation are examined using Surface Displacement Analysis (SDA), software supplied by
Instron. SDA measures the strain in a specimen as it undergoes deformation by comparing the speckle pattern
on undeformed and deformed images. This technique, when applied to the above two loading cases of shear or
bias extension, results in 2D plots of displacement and strains in the principal displacement directions.
These strains are resolved along the fabric tow directions to obtain the rotation and slippages. SDA on the
picture frame test showed uniform shear across the specimen surface while the bias extension test results in
varying shear. It was found that reducing the axial length of the fabric specimen in the bias extension test
leads to more uniform shear, as might be expected. To help understand the effect of the tool constraint and
friction on shearing, a test thought to be closer to draping over a mould was conducted. The fabric was
curved around a cylindrical tool during a bias extension test. The results show the effects of different
loading and restraint conditions on shear.
The paper also reports on the measurements of through-thickness tow deformations over sheared