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 friction model for thermostamping commingled glass–polypropylene woven fabrics
Abstract 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 were investigated. The investigation focused on the effects of fabric velocity, normal force and resin viscosity under conditions similar to those in thermostamping processes. The effect of resin viscosity on the resulting friction coefficient was evaluated through changes in tool temperature and initial fabric temperature. The results from these experiments could be related to trends predicted by Stribeck-curve theory. Based on the effects of those parameters and the Stribeck-curve theory, an empirical friction model was developed and incorporated into ABAQUS as a user-defined friction subroutine. This paper describes the development of that friction model for use in finite element models of the thermostamping process. It also discusses the results of a parametric study conducted using the friction model with a finite element model of the thermostamping process. These results show the importance of properly accounting for changes in friction at the metal–fabric interface in numerical simulations of the thermostamping process.
Do Arab public opinion support policies of regional powers in MENA? View from Tunisia
ABSTRACT The Arab Uprisings and subsequent events continue to transform policies of regional and major powers toward the Middle East and North Africa. These powers have shown different approaches toward the Uprisings, ranging from support for the status quo to endorsing regime changes. Their policies have also exerted a significant impact on the course of events. Despite this growing importance and implications of policies of regional powers on the Uprisings and the Syrian conflict, we still do not know much about how the public assesses these policies and to what extent domestic cleavages shape these assessments. Using a nationally representative original survey conducted in 2014 in Tunisia, this study examines the perceptions of the policies of France, Turkey, and Saudi Arabia towards the Uprisings and the Syrian conflict. It finds that French and Turkish policies about the Uprisings have garnered substantial support among citizens, whereas most citizens negatively assess the Saudi policies. On the other hand, the majority of Tunisians negatively assess all these countries’ policies toward the Syrian conflict. Another major finding suggests that political identity reflecting secular/religious cleavages shapes how citizens view the policies of these three countries toward both issues, but its effect is higher in assessing the Uprisings.