Ideal Forming of Non-Crimp Fabric Preforms through Optimization of Blank Shape and Blank Holding Force

ABSTRACT: The ultimate goal of this study is to develop a method that can provide an optimized initial blank shape and blank holding force (BHF) for sheet forming of complex composite parts. For that purpose the forming process for a double dome geometry is being studied using non-crimp fabric (NCF). The forming behaviour of the NCF is dependent on the blank shape which affects the propagation mode of shear resistance, and also the blank holding force that controls in-plane tension of the fabric. To investigate the effect of these factors on the formed shapes, finite element (FE) simulations are performed using a non-orthogonal constitutive equation that utilises fabric structural parameters and the shear response of the material. Since NCFs usually feature a preferred shear response according to shear direction, asymmetric shear is reflected in the FE simulation by using an exact linearization scheme of the shear response from picture-frame experiments. Based on the formed shapes due to several blank geometries and holding forces, an inversion problem, to determine optimized blank shape and blank holding force from final product shape and material properties, is proposed. Key words: Ideal composite forming, non-crimp fabric (NCF), asymmetric shear response, finite element analysis