A new approach for assessing the deflection and bending properties of continuous fiber reinforced thermoplastics under processing conditions. (April 2019)

• Record Type: Journal Article
• Authors: Mattner, Tobias; Drummer, Dietmar
• Is Part Of: Polymer testing. Volume 74(2019)
• Page Start: 77
• Page End: 85
• Publication Date: 2019-04
• Subjects: Organo-sheet -- Viscoelasticity -- Quasi-plastic flow -- Bending line; Polymers -- Testing -- Periodicals; Polymères -- Tests -- Périodiques; 620.1920287
• DOI: 10.1016/j.polymertesting.2018.12.024
• Languages: English
• ISSNs: 0142-9418

Abstract

Abstract: Several different measuring techniques are commonly used to quantify the bending behavior of continuous fiber reinforced thermoplastics (CFRTs) under processing conditions. However, many of these techniques are based on the characterization of dry fabrics and are not suitable for CFRTs due to their low bending stiffness at elevated temperatures. This study presents a new approach for assessing the bending behavior of continuous fiber reinforced plastics at elevated temperatures based on a variation of the single cantilever test. An acute angled piston is used to apply a deflection onto a unilaterally fixed sample while the reaction forces are measured. The bending line is evaluated by cooling and re-solidification of the deflected samples and subsequent high-resolution scans of vertically oriented samples. The results show the suitability of the presented approach to characterize and quantify the bending behavior of CFRTs under processing conditions, allowing for a differentiation of the behavior of different geometrical sections of a woven fabric. Based on a classical viscoelastic behavior, quasi-plastic flow can be identified when the applied deformation speed and relaxation speed reach an equilibrium. Shear deformation appears to increasingly dominate the deformation behavior at low bending radii and high deflections. Additional research is required to evaluate influences of different temperature levels and deformation speeds on the bending behavior and the previously described relationship of relaxation and deformation. Highlights: In actual processing, high degrees of deflection with small bending radii are generally present. The bending line evaluation reveals major differences to elastic bending behavior both at small and large deflections. Relaxation of elastic stresses into viscoelastic deformation and introduction of new elastic stresses reach an equilibrium. The newly presented method offers a new, robust way of bending line evaluation employable in several other testing setups. A variation of the sample preparation section can induce or prevent major torsion in the relaxed state.