Abstract
The increased production rate targets of the aerospace industry has driven the development of dry fibre processes and biaxial Non-Crimp Fabrics (NCFs). Understanding the forming behaviour of NCFs at scale is key to achieving high quality parts at high rates. The bias extension test is commonly used to characterise the shear behaviour of dry fabrics, for example as input to drape forming models. In industry, it is still often used as a standalone material selection tool as part of initial material selection processes. It is however well known that the boundary conditions of this test are often not representative of full-scale forming trials. A direct comparison with wrinkles observed during a forming experiment is carried out to show that the bias extension test overpredicts wrinkle height. Overall, the bias extension is considered unsuitable on its own for predicting preform quality in an NCF forming process where excess length is generated due to part geometry. If the bias extension is to be used as an NCF material ranking tool, wrinkle height data should be captured alongside force shear data, as shown in this study.
Highlights
As the commercial aerospace industry moves to high-rate processes for the generation single aisle aircraft model, the need for a standardised test to select the best performing dry fabric is ever more relevant
This study presents an experimental campaign on both bias extension and forming test set ups. 2D Digital Image Correlation (DIC) cameras were used to capture the in-plane shear behaviour of six Non-Crimp Fabrics (NCFs) samples in the bias extension test
This section of the study aims to create a direct link between bias extension test results and industrial scale forming experiments, through comparison of wrinkle data
Summary
As the commercial aerospace industry moves to high-rate processes for the generation single aisle aircraft model, the need for a standardised test to select the best performing dry fabric is ever more relevant. In-plane shear is the dominant deformation mechanism in forming (Lomov, 2016), resulting in large rotations in the fibre direction and a change in the net shape of the material (Thompson et al, 2018). Bench top tests such as the bias extension or picture frame test are commonly used to determine the shearing profile of the material. In industry the bias extension test is commonly used as a standalone material pre-selection tool before subsequent forming trials. This is why direct correlation between material performance during such tests and during forming over complex 3D geometries is of industrial interest and relevance. The result is a non-homogenous deformation of the material sample with three regions: no shear, half-sheared and fully sheared (Montazerian et al, 2019) (see Figure 1)
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