Friction and bending in thermoplastic composites forming processes

With the demand for better fuel economy in the aerospace and automotive industries, lightweight polymer matrix composites became an attractive alternative for metal structures. Despite the inherently higher toughness and impact damage resistance of thermoplastics, thermoset matrix composites are used in the majority of applications. This is largely attributable to the higher material costs of thermoplastic coposites and the limited experience with these materials. The ability to re-melt thermplastics, however, allows automated processing methods with short cycle times, which lowers production costs to a competitive level, especially for larger series production. Thermoforming of flat laminates of continuous fiber reinforced thermoplastic laminates into 3-D parts is a complex process. Fundamental understanding of the deformation processes is needed to prevent process induced defects, such as wrinkling at critical locations, for the product or the process. The elementary deformation mechanisms need to be addressed one-by-one to develop this understanding and to translate this understanding to reliable Computer Aided Engineering tools for predictable product development processes. The major deformation mechanisms of continuous fiber reinforced composites are considered to be intra-ply shear, inter-ply slippage and ply bending. The latter two are investigated in this thesis. The objective of this thesis is to develop an understanding of the physics of the deformation mechanisms and to make it available in the form of describing constitutive equations.