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.
Characterization of the tool/fabric and fabric/fabric friction for woven-fabric composites during the thermostamping process
The dynamic coefficients of friction for Twintex® commingled glass-polypropylene balanced plain-weave and unbalanced twill-weave fabrics at the tool/fabric and fabric/fabric interfaces during the composite thermostamping process are characterized. The effects of fabric velocity and pressure on the coefficients of friction under conditions similar to those during the thermostamping process are studied. A phenomenological friction model accounting for pressure and velocity dependence is developed based on the experimental results and implemented into the commercial finite element codes ABAQUS/Explicit and LS-DYNA via user-defined subroutines. The mechanical behavior of the fabric is modeled using a mesoscopic approach. The friction subroutines are validated with a finite element model of the experimental friction test. The forming of a hemispherical dome is simulated using ABAQUS and LS-DYNA. Punch forces and yarn stresses are compared between variable friction and constant friction models, and the simulation results justify the necessity for a variable friction model to accurately predict part quality.
An investigation of interply slip behaviour in AS4/PEEK at forming temperatures
Abstract A test procedure was developed to evaluate the behaviour of the deformation mechanism known as interply slip at temperatures representative of solid-phase and melt-phase forming. The interfaces resulting from plies oriented parallel to the deformation direction and from plies of differing orientation are examined. Results of these tests are presented and observations are noted. The primary influences were found to be temperature and interfacial shear rate. Power-law approximations are determined for the rate variations, and the correlation of these power-law parameters with temperature is discussed.