Intra/inter-ply shear behaviors of continuous fiber reinforced thermoplastic composites in thermoforming processes Qianqian Chen a , Philippe Boisse b , Chung Hae Park a,⇑ , Abdelghani Saouab a , Joël Bréard a a Laboratoire d’Ondes et Milieux Complexes, FRE 3102 CNRS, University of Le Havre, 53 rue Prony, F76600 Le Havre, France b Laboratoire de Mécanique des Contacts et des Structures, UMR 5159 CNRS, INSA Lyon, 18-20 rue des Sciences, F69621 Villeurbanne, France article info Article history: Available online 14 January 2011 Keywords: Continuous fiber reinforced thermoplastic composites Thermoforming process In-plane shear Inter-ply slip Cohesive element abstract The thermoforming of continuous fiber reinforced thermoplastic (CFRTP) composite panels generally involves significant in-plane shear deformation. In the present work, the in-plane shear behavior of woven thermoplastic composites (Carbon/Polyphenylene Sulfide) over a range of processing tempera- tures is studied by bias-test experiments at different velocities. The experimental data of force versus displacement and force versus shear strain are presented for different extension velocities and tempera- tures. A thermo-visco-elastic model for numerical simulations of woven thermoplastic composite form- ing is proposed considering the influences of temperature and of strain rate. We applied a large displacement three-dimensional cohesive element with eight nodes which has been used for crack anal- ysis in fracture mechanics by other authors, to investigate the inter-ply shear mechanism of woven ther- moplastic composites. Applying three-dimensional cohesive elements, multi-plies forming simulations are performed to show inter-ply slip behaviors at different temperatures. The proposed models can be useful to predict from the properties of reinforcement and resin the intra/inter-ply shear behaviors of woven thermoplastic composites at high temperatures if experimental characterization of composite laminate behaviors is difficult to conduct. Ó 2011 Elsevier Ltd All rights reserved. 1. Introduction Continuous fiber reinforced thermoplastic (CFRTP) composites are becoming popular in industrial applications owing to their advantages such as high performances, short processing cycle, ease in stocking, possibility of repairing and welding. Accordingly, the development of numerical method for forming process simulations becomes more and more important [1–4]. A CFRTP forming process is normally conducted at a processing temperature which is over the melting temperature of thermoplastic resin. In this case, the re- sin can be considered as liquid, of which the influence to the tensile stiffness seems to be very weak. Thus, the resin behavior can be ig- nored when the tensile mechanism is considered during the form- ing process. The in-plane shear stiffness of CFRTP, however, has been recognized as a dominant factor of wrinkle formation in zones where the three-dimensional deformation of CFRTP is re- quired, such as at corners or over spherical regions. It is not only affected by the relative movement of weft and warp of textile rein- forcement during deformation but also by the resin behavior [5–8]. Hence, the resin behavior should be taken into account if the in-plane shear mechanism of CFRTP is considered. Rogers proposed firstly theoretical models for the forming of composite materials with one or two fiber orientations [9]. The fibers were supposed to be inextensible. With an assumption of material incompressibil- ity, a suitable anisotropic constitutive relationship was proposed. Rogers noted that the existing theoretical work on linear elastic materials could be applied to linear visco-elastic and viscous mate- rials by invoking the visco-elastic correspondence principle. Based on those studies, McGuiness et al. proposed a model integrating a power law considering the non-linearity of viscosity at the forming temperature [10]. Those models can easily be integrated in stan- dard finite element (FE) computation with shell or membrane ele- ments. As the textile material is composed of warp and weft yarns, however, the representative elementary volume cannot be consid- ered to be continuous. Thus, the stress obtained by those models is not well defined. The accuracy of numerical simulations depends strongly on the measurements of material properties [11–15]. Among the charac- terization methods of the in-plane shear behavior of woven CFRTP, the bias extension test and the picture frame test are commonly used. Since the picture frame test lacks of reproducibility due to an inherent difficulty to properly align the fibers with the frame [16–18], we use the bias extension test method for the shear behavior characterization in this work. Laminate specimens are tested at high temperature above the melting temperature of the thermoplastic resin where material forming is done. 0263-8223/$ - see front matter Ó 2011 Elsevier Ltd All rights reserved. doi:10.1016/j.compstruct.2011.01.002 ⇑ Corresponding author. E-mail address: chung-hae.park@univ-lehavre.fr (C.H. Park). Composite Structures 93 (2011) 1692–1703 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct