https://hal.archives-ouvertes.fr/hal-00730294/document

Simulation of wrinkling during textile composite reinforcement forming. Influence of tensile, in-plane shear and bending stiffnesses

This article presents a review of the current understanding of the mechanics of random fiber networks. The discussion refers to athermal fiber networks, for which the governing functional is the system enthalpy, as well as to molecular networks, in which thermal fluctuations are important. Fiber networks are broadly encountered in everyday life as paper, insulation and damping materials, and as the essential component of some consumer products, while molecular networks form the structure of biological and non-biological materials such as the cytoskeleton, connective tissue, gels and rubber. The mechanics of these materials is defined by the structure of the network and by the mechanical behavior of individual filaments. The structure is characterized by a number of parameters, such as the density, filament orientation, fiber waviness, density and nature of cross-links, which are discussed in the first part of the article. The constitutive behavior of individual filaments is defined by their bending and axial stiffness, and by the response to thermal fluctuations. The constitutive response of the cross-links plays a central role in defining the system-scale mechanical behavior. The analysis of the network mechanics is divided into two parts addressing cross-linked and entangled (non-cross-linked) networks. Both molecular and athermal cross-linked networks are discussed, while only the literature on athermal entangled networks is included. Flexible and semi-flexible fibers are considered, with special attention given to the second category. The constitutive behavior under small and large deformations, including attempts to define continuum representations of the discrete system, is reviewed. A number of open issues are discussed in closure.

Mechanics of random fiber networks—a review

In this second international permeability benchmark, the in-plane permeability values of a carbon fabric were studied by twelve research groups worldwide. One participant also investigated the deformation of the tested carbon fabric. The aim of this work was to obtain comparable results in order to make a step toward standardization of permeability measurements. Unidirectional injections were thus conducted to determine the unsaturated in-plane permeability tensor of the fabric. Procedures used by participants were specified in the guidelines defined for this benchmark. Participants were asked to use the same values for parameters such as fiber volume fraction, injection pressure and fluid viscosity to minimize sources of scatter. The comparison of the results from each participant was encouraging. The scatter between data obtained while respecting the guidelines was below 25%. However, a higher dispersion was observed when some parameters differed from the recommendations of this exercise. (C) 2014 Elsevier Ltd. All rights reserved.

/pdf/experimental-determination-of-the-permeability-of-3hkcug26ia.pdf

Experimental determination of the permeability of engineering textiles:Benchmark II

Numerical and experimental analyses of woven composite reinforcement forming using a hypoelastic behaviour: Application to the double dome benchmark

Hencky (Uber die angenaherte Losung von Stabilitatsproblemen im Raum mittels der elastischen Gelenkkette. Ph.D. thesis, Engelmann, 1921) proposed a discrete model for elasticae by introducing rigid bars and rotational springs. Hencky (Proc R Soc Lond A Math Phys Eng Sci 472(2185), 2016) approach has been introduced to heuristically motivate the need of second gradient continua. Here, we present a novel numerical code implementing directly the discrete Hencky-type model which is robust enough to solve the problem of the determination of equilibrium configurations in the large deformation and displacement regimes. We apply this model to study some potentially applicable problems, and we compare its performances with those of the second gradient continuum model. The numerical evidence presented supports the conjecture that Hencky-type converges to second gradient model.

/pdf/hencky-type-discrete-model-for-pantographic-structures-1p0pz3utdm.pdf

Hencky-type discrete model for pantographic structures: numerical comparison with second gradient continuum models

Textile composites made of woven fabrics have demonstrated excellent mechanical properties for the production of high specific-strength products. Research efforts in the woven fabric sheet forming are currently at a point where benchmarking will lead to major advances in understanding both the strengths and the limitations of existing experimental and modeling approaches. Test results can provide valuable information for the material characterization and forming process design of woven composites if researchers know how to interpret the results obtained from varying test methods appropriately. An international group of academic and industry researchers has gathered to design and conduct benchmarking tests of interest to the composite sheet forming community. Shear deformation is the dominative deformation mode for woven fabrics in forming; therefore, trellis-frame (picture-frame) and bias-extension tests for both balanced and unbalanced fabrics have been conducted and compared through this collaborative effort. Tests were conducted by seven international research institutions on three identical woven fabrics. Both the variations in the setup of each research laboratory and the normalization methods used to compare the test results are presented and discussed. With an understanding of the effects of testing variations on the results and the normalization methods, numerical modeling efforts can commence and new testing methods can be developed to advance the field.

https://hal.archives-ouvertes.fr/hal-01658046/document

Characterization of mechanical behavior of woven fabrics: Experimental methods and benchmark results

This article describes a method of using both picture frame (PF) and bias extension (BE) tests together to characterize accurately the trellis shearing resistance of engineering fabrics under low in-plane tension conditions. Automated image analysis software has been developed to reduce the amount of laborious manual analysis required to interpret BE data accurately. Normalization methods for both PF and BE tests on rate-independent compressible fabrics are presented. Normalization of PF test results is relatively straightforward while normalization of BE test results for direct comparison with PF data is more complicated. The normalization method uses a number of simple assumptions to account for the nonuniform shear strain field induced across BE samples during testing. Normalized results from BE tests on samples of different aspect ratios are compared and provide validation of the theory.

/pdf/normalization-of-shear-test-data-for-rate-independent-4vz7q75440.pdf

Normalization of Shear Test Data for Rate-independent Compressible Fabrics

A Constitutive Model Based on Meso and Micro Kinematics for Woven and Stitched Dry Fabrics

Non-crimp fabrics (NCFs), consisting of two or more separate layers of unidirectional tows stitched together, offer high formability and improved inplane mechanical properties. However, the stitching can cause unusual fibre patterns after forming that cannot be predicted by many existing draping models [1]. It is desirable to gain a better understanding of these fabrics, to enable better modelling of manufacture and performance, and to facilitate better fabric design.

http://userweb.eng.gla.ac.uk/philip.harrison/publications/Conference/Esaform6%20%20Wiggers%20_2003_.pdf

J. Wiggers

Papers

Characterization of mechanical behavior of woven fabrics: Experimental methods and benchmark results

Normalization of Shear Test Data for Rate-independent Compressible Fabrics

A Constitutive Model Based on Meso and Micro Kinematics for Woven and Stitched Dry Fabrics

The Effects of Stitch Architecture on the Shear Complinace of Non-Crimp Fabrics

Modelling the Effects of Blank-Holder Pressure and Material Variability on Forming of Textile Preforms