Stepan Vladimirovitch Lomov

Textile geometry preprocessor for meso-mechanical models of woven composites

A mathematical model of the internal geometry of 2D and 3D woven fabrics is used as a unit-cell geometry preprocessor for meso-mechanical models of composite materials. The model computes a spatial placement of all yarns in a fabric repeat for a given weave structure (a special coding algorithm is employed) and given warp and weft yarns geometrical and mechanical parameters. The source of these data is the manufacturers documentation for a woven fabric and yarn mechanical behaviour in bending and compression, measured on standard textile-laboratory equipment. The principle of minimum energy of a fibrous assembly leads to the prediction of the yarns crimp, the forces in the warp/weft contacts and the yarn compression within a fabric. The input data for use in meso-mechanical models of composite materials is therefore provided in addition to tools for the 3D representation of the woven structure, for the creation of the unit-cell cross-sections and for the computation of the unit cell porosity.

A predictive model for the penetration force of a woven fabric by a needle

Proposes an algorithm for the computation of maximum needle penetration force; it introduces the direct dependence of penetration force on fabric structural parameters and warp and weft geometrical and mechanical properties. Uses the approach to the simulation of local deformation of woven material which accounts for the thread resistance to crimp change and friction forces when the thread is shifted from its original position in the fabric structure as the result of its interaction with a needle. The resistance of threads to tension caused by a needle pushing them from their straight‐line paths is also accounted for. The resulting formulae give the dependence of needle penetration force for a plain‐woven fabric on the following parameters: needle diameter and surface angle; warp and weft spacing, dimensions, crimp height and bending rigidity; friction coefficients thread‐thread and thread‐needle. For a non‐plain‐woven fabric the linear dependence of penetration force on the fabric tightness is suggested. The comparison with the published and specially measured penetration force data proves the predictive ability of the model to be qualitatively accurate and quantitatively reasonable.

Two‐component multilayered woven fabrics: weaves, properties and computer simulation

Presents general properties and examples of weaves for two‐component multilayered woven fabrics. Such fabrics have a combination of properties which it is difficult to achieve in traditional fabrics (bulk combined with good tenacity, high cover level with porosity), can be used in liningless garments and can cope with ergonomical restrictions when using fibres with special protective properties. Describes a CAD system which can be used as an aid for a technologist to choose yarns for warp and weft, fabric weave and picks/ends count to meet demands specified by a particular fabric usage. It employs a new method of coding of multilayered fabric structure; mathematical methods used are based on the mechanical model of yarns interaction in a fabric. This describes the spatial disposition of yarns which allows production of any desired images of fabric geometry, i.e. surface smoothness or shape of pores. Discusses the complex nature of porosity of multilayered fabrics.

In‐Situ Measurements of Fabric Thickness Evolution During Draping

The paper presents results of experimental program aimed at measuring fabric thickening while draping. The thickness evolution is important factor in resin infusion manufacturing where the resultant composite thickness is not controlled. The measurements are conducted by means of laser distance sensors adapted to the picture frame testing. Several carbon fabrics of very different architectures have been tested. Additionally, the pretension of the carbon fabric due to the gripping has been estimated by means of digital image correlation technique and an attempt to discuss the results obtained on different set‐ups is made.

Anisotropy of fabrics and fusible interlinings

As CAD fabric modelling becomes more widespread there is a need to study the applicability of fabric property parameters which are used in predicting fabric behaviour. The anisotropical mechanical behaviour of woven fabrics, fusible interlinings and their composites were studied on order to invesigate the accuracy of equations used to predict the anisotropic linear elastic behaviour of fabric for in plane and bending deformation. Bending, shear and tensile properties were measured using KES©F equipment. Results showed that the orthotropic model of anisotropy can be applied for the qualitative modelling of woven and fusible interlining fabrics and that simple mechanical models for bending properties can be used for their composites.

A stochastic multi-scale framework for textile composites to evaluate the stiffness tensor

This paper discusses the application of a multi-scale modeling technique in a stochastic framework with the aim of deriving the stiffness statistics of a composite structure. First, optical images are taken from cross sections of a laminate that consists of several layers of fabric. The characterization of these images allows constructing a dataset for each geometrical parameter of which statistical information can be extracted. Next, the model characteristics at meso- and macro-scale are calibrated, for each deterministic realization in a Monte Carlo simulation, with a sampled set from this statistical data. Several virtual composite panels are obtained and statistics of the macroscopic stiffness tensor can be derived. The procedure also permits performing a sensitivity analysis of each geometrical parameter on the stiffness values. Results are presented for the case of the laminate Young’s modulus.

Meso-macro simulation of the woven fabric local deformation in draping

The paper reports results of such combined meso-macro modelling for a plain weave carbon fabric with spread yarns. The boundary conditions for a local meso-model are taken from the macro draping simulation. The fabric geometry is modelled with WiseTex and transferred to the finite element package. 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, for example, the yarn distortion on the 3D mould corner (see the figure). The simulations are compared with the local fabric distortions observed during draping experiments.The paper reports results of such combined meso-macro modelling for a plain weave carbon fabric with spread yarns. The boundary conditions for a local meso-model are taken from the macro draping simulation. The fabric geometry is modelled with WiseTex and transferred to the finite element package. 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, for example, the yarn distortion on the 3D mould corner (see the figure). The simulations are compared with the local fabric distortions observed during draping experiments.

Machine compliance in compression tests

The compression behavior of a material cannot be accurately determined if the machine compliance is not accounted prior to the measurements. This work discusses the machine compliance during a comp...

Intra-Laminar Damage in Carbon Fiber-Reinforced Composites: Experimental Observations and Model Validation

The intra-laminar damage during quasi-static loading of Carbon Fiber-Reinforced Plastics (CFRPs) leads to degradation of ply mechanical properties. The possible intralaminar damage mechanisms are fiber failure, matrix cracking, and fiber/matrix debonding. In addition to experimental investigation of these mechanisms, modeling methodologies have been developed to predict the degradation of ply properties, accounting for (some of) these mechanisms. One of these methodologies is proposed by Ladeveze and LeDantec [1]. This model requires a set of input parameters, which are obtained through mechanical tests on laminates with prescribed lay-ups. In the current study, we extract these input parameters for an aerospace-grade CFRP, with detailed explanations. Beside the conventional parameter identification procedure, the parameters are linked to the physical progression of damage (in terms of crack densities), which is measured in the in situ images taken during the tests.

Quantification of micro-CT images of textile reinforcements

VoxTex software (KU Leuven) employs 3D image processing, which use the local directionality information, retrieved using analysis of local structure tensor. The processing results in a voxel 3D array, with each voxel carrying information on (1) material type (matrix; yarn/ply, with identification of the yarn/ply in the reinforcement architecture; void) and (2) fibre direction for fibrous yarns/plies. The knowledge of the material phase volume and known characterisation of the textile structure allows assigning to the voxels (3) fibre volume fraction. This basic voxel model can be further used for different type of the material analysis: Internal geometry and characterisation of defects; permeability; micromechanics; mesoFE voxel models.Apart from the voxel based analysis, approaches to reconstruction of the yarn paths are presented.VoxTex software (KU Leuven) employs 3D image processing, which use the local directionality information, retrieved using analysis of local structure tensor. The processing results in a voxel 3D array, with each voxel carrying information on (1) material type (matrix; yarn/ply, with identification of the yarn/ply in the reinforcement architecture; void) and (2) fibre direction for fibrous yarns/plies. The knowledge of the material phase volume and known characterisation of the textile structure allows assigning to the voxels (3) fibre volume fraction. This basic voxel model can be further used for different type of the material analysis: Internal geometry and characterisation of defects; permeability; micromechanics; mesoFE voxel models.Apart from the voxel based analysis, approaches to reconstruction of the yarn paths are presented.