Membrane behavior of uni- and bidirectional non-crimp fabrics in off-axis-tension tests

The production of high-performance composite parts with non-crimp fabrics (NCFs) requires a profound understanding of the material’s behavior during draping to prevent forming defects such as wrinkling and gapping. Simulation methods can be used to model the complex material behavior of NCFs and predict their deformation during the draping process. However, NCFs do not intrinsically deform under pure shear like most woven fabrics, but often under superimposed shear, transverse tension and in-plane roving compaction. Therefore, non-standard characterization methods have to be applied besides typical picture frame tests or bias-extension tests. Off-axis-tension tests (OATs) utilize a simple setup to characterize a fabric’s membrane behavior under different ratios of superimposed shear, transverse tension and in-plane compaction. OATs at three different bias angles (30, 45 and 60) are conducted to investigate a unidirectional and a bidirectional NCF. A method is presented to measure the fiber curvatures in addition to the occurring strains. The investigations reveal a relatively symmetrical, shear-dominated behavior with limited roving slippage for the Biax-NCF. The behavior of the UD-NCF strongly depends on the stitching load during tests and is characterized by an asymmetric shear behavior as well as significant roving slippage. The off-axis-tension test results can be used as the basis for the development and validation of new simulation methods to model the complex membrane behavior of NCFs

A unit-cell mesoscale modelling of biaxial non-crimp-fabric based on a hyperelastic approach

Understanding the mechanical properties of carbon fiber reinforcements is necessary for the simulation of forming processes. A unit-cell mesoscopic model provides a tool to implement virtual material characterizations which can be served as an input for macroscopic modelling, avoiding complex experimental tests and significantly reducing calculation time. Meanwhile, the occurrence of some local defects during the forming process, such as the gapping, would be easier to be detected through a mesoscopic approach. In this research, a novel mesoscale model for biaxial non-crimp fabric is developed based on the geometry measured from the results of X-ray tomography. A hyperelastic constitutive law is applied to the fiber yarns which are considered as a continuous medium. One type of unit-cell model is chosen and validated through a comparison with experimental tests and its in-plane shear behavior is studied

Modélisation et simulation numérique de l'emboutissage d'un renfort tissé sec : Sensibilité de l'angle de cisaillement aux paramètres du procédé

Le présent travail a pour objectif de présenter une étude de sensibilité des modèles numériques réalisés avec le code ABAQUS, vis-à-vis de la variation des paramètres du procédé d'emboutissage, ainsi que l'effet d'orientation initiale du renfort, le type (coque ou membrane) et la taille du maillage. La simulation de la mise en forme est réalisée à l'échelle macroscopique en considérant le renfort comme un milieu continu. Cette approche continue s'appuie sur une loi de comportement hypoélastique qui a l'aptitude de suivre la rotation des fibres (directions d'anisotropie) au cours de la mise en forme. Cette loi de comportement est implémentée dans le code de calcul des éléments finis ABAQUS /explicit en utilisant une subroutine VUMAT

Coupled meso-macro simulation of woven fabric local deformation during draping

© 2019 Elsevier Ltd The prediction of yarn buckling and distortions require detailed modelling of the fabric and yarns deformations on the meso-level (level of the interlacing structure). In the current research, computationally viable meso-level simulation is achieved by coupling continuous macro draping simulation with a local meso-modeling in the location where the defects are expected to occur. The macro-simulation uses a membrane-shell continuous model of the fabric. A hyperelastic constitutive model for the yarns (Charmetant – Boisse) is used in the meso-modelling. The model parameters are identified and validated in independent tension, shear, compaction and bending tests of the yarn and the fabric. The simulation reproduces local yarn slippage and buckling, e.g., the yarn distortion on the 3D mould corner. The simulations are compared with the local fabric distortions observed during draping experiments for two carbon plain weave fabrics (12K carbon-fibre tows and with spread tows) on a hemispherical and on a box-shaped moulds.status: publishe

Thermal Properties of New Insulating Juncus Maritimus Fibrous Mortar Composites/Experimental Results and Analytical Laws

This study aims to study the thermal properties and the microstructure of composite materials based on mortar combined with Juncus maritimus fibers. Effective thermophysical properties of the composite materials containing Juncus maritimus fibers are experimentally and theoretically investigated. To better understand the morphology of these new composites, the corresponding microstructures were characterized in 2D by scanning electron microscope and in 3D using micro computed tomography. The local thermal conductivity of the Juncus maritimus fibers was identified using theoretical models and experimental measurement of the effective thermal conductivity of packed bed of crushed fibers. The thermal conductivity of the mortar matrix at given porosity was also determined using experimental measurement data and a theoretical model. The most appropriate analytical laws to predict effective thermal conductivity of mortar composites containing fibers are deduced from experimental thermal conductivity results

Identification and validation of a hyperelastic model for self-reinforced polypropylene draping

status: publishe