Friction in Forming of UD composites

Inter‐ply and tool/ply friction play a dominant role in hot stamp forming of UD fiber‐reinforced thermoplastic laminates. This research treats friction measurements of a PEEK‐AS4 composite system. To this end, an in‐house developed friction tester is utilized to pull a laminate through two heat controlled clamping platens. The friction coefficient is determined by relating the clamp force to the pull force. The geometry of the gap between the clamping platens is monitored with micrometer accuracy. A first approach to describe the relation between the geometry and frictional behavior is undertaken by applying a standard thin‐film theory for hydrodynamic lubrication. Experimental measurements showed that the thin‐film theory does not entirely cover the underlying physics. Thus a second model is utilized, which employs a Leonov‐model to describe the shear deformation of the matrix material, while its viscosity is described with a multi‐mode Maxwell model. The combination of both models shows the potential to capture the complete frictional behavior.