Friction testing of thermoplastic composites
Friction phenomena play a major role in thermoplastic composite forming processes. In order to make use of the large potential these materials have, accurate CAE tools are needed that as a consequence incorporate temperature, pressure and velocity dependent friction behavior. To obtain a sound understanding of friction behavior a large number of friction measurement set-ups have been described in literature. A benchmark to compare different testing methods was proposed during the Esaform2010 conference. 
In this paper the material (Twintex PP) and testing conditions for the benchmark are briefly revisited and first testing results employing the in-house developed friction tester are presented. It is observed that the results reproduce very well at different conditions. Based on the Hersey number the Stribeck curve for the tested material combination is derived. It is concluded that a full state of hydrodynamic lubrication was reached with friction coefficients between 0.15 and 0.5. This opens up good perspectives for numerical modeling since all parameters are readily available in process simulations. Future comparisons within the context of the benchmark will assess the quantitative level of the identified coefficients of friction.
A characterization of shear flow in continuous fibre thermoplastic laminates
Abstract The viscoelastic response of some continuous fibre thermoplastic composites has been investigated dynamically. The contribution of the number and direction of laminate ply layers and fibre type, together with the geometry, have been explored in relation to the matrix polymer. An interpretation in terms of an apparent Maxwell viscosity is in agreement with steady shear flow viscosity, and approximates to a large strain dynamic viscosity. A yield stress of the order of 1 kPa is implied by the Maxwell interpretation together with a high stress viscosity more than 10 times the viscosity of the matrix polymer. The use of model laminates leads to the prediction of both interply and intraply polymer flow in continuous fibre thermoplastic composites.
Modeling of Friction and Shear in Thermostamping of Composites - Part I
The effects of processing parameters on the friction coefficient between commingled glass-polypropylene plain-weave fabric composites (Twintex) and the steel tool during thermostamping processes are under investigation. This work focuses on the effect of fiber orientation, fabric velocity, normal force, and resin viscosity (through variations in tool and fabric temperatures) under conditions similar to those in the thermostamping processes. In comparison to the experiments conducted to date, velocity, normal force, and tool temperature have the greatest effect on the friction coefficient. The effect of tool temperature on the friction coefficient dominated the effect of initial fabric temperature on the friction coefficient. Based on the effect of these parameters, a phenomenological model has been incorporated into ABAQUS/Standard as a user-supplied friction subroutine. This model was first used in a finite element model of the friction test. A good agreement was found between the experimentally measured friction force and the numerically calculated one.