Dmitry Ivanov

Modeling three-dimensional fabrics and three-dimensional reinforced composites: challenges and solutions:

The vast research area of modeling of three-dimensional (3D) woven fabrics can be subdivided into several domains, each of them having its own challenges and difficulties — some are already solved and implemented in software, while some still wait for their solution. This paper discusses the following problems and reviews the available solutions: coding of the structure of 3D weaves; building a geometrical model of 3D fabric; calculation of deformation resistance of a 3D fabric; transformation of the geometrical model into finite element mesh; prediction of elastic mechanical properties of 3D reinforced composites. A case study for warp interlock 3D fabrics concludes the paper.

Meso-level textile composites simulations: open data exchange and scripting

The article presents a user interface for modelling of textile composites, which combines open XML input and output formats with scripting for definitions of the reinforcement models under (local) shear, tension and compression deformations. The open input format (parameters of the textile reinforcement) allows easy integration of a meso-level (unit cell) textile processor upstream – with, for example, textile process modelling software or forming models, which define local parameters of the textile reinforcement. The scripting command format makes possible automated processing of the information on local reinforcement deformation conditions, and offers itself to be integrated in user software without accessing or knowing internal computational procedures or native data formats of meso-level textile processor. The open output format allows transferring the results of the meso-level textile processor downstream to meso-level models of the micromechanics or the permeability of a textile composite unit cell. These results can be further streamed to allow macro-level structural, forming or impregnation analysis. The integration approach is illustrated for meso-level textile processor – WiseTex software, integrated with processing of digital images and calculations of the fabric permeability tensor, micromechanics models and meso-level finite element ABAQUS model.

Homogenisation of a sheared unit cell of textile composites: FEA and approximate inclusion model

Meso-mechanical modelling of textile composites on the “meso” (unit cell) level provides information necessary to produce homogenised properties of the composite material (with the reinforcement deformed during draping), to be used in structural analysis on the “macro” (composite part) level. The input data for the meso-calculations include geometrical model of the sheared textile and properties of the fibres and matrix. Inclusion model proceeds then to an approximate description of the reinforcement as a set of stiff inclusions, representing local orientations of the fibers, and employs the Eshelby solution and Mori- Tanaka or self-consistent homogenisation scheme to calculate the effective stiffness matrix of the composite. Finite element modelling goes through stages of (1) converting the geometrical model into a solid model; (2) meshing; (3) applying periodic boundary conditions and (4) solving a set of models necessary to calculate the homogenised stiffness matrix. All these stages present specific challenges for the case of non-orthogonal translational symmetry of the problem, which are dealt with in the paper for two types of textile reinforcements: woven and non-crimp 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.

Modelling the structure and behaviour of 2D and 3D woven composites used in aerospace applications

Abstract The chapter starts from description of geometrical models of 2D and 3D woven fabrics, with an aim of creation of meso-level (textile unit cell) finite element (FE) models, and proceeds to micromechanics of woven composites, based on the method of inclusions/Mori-Tanaka homogenisation and FE analysis of the stress–strain state of the unit cell. Special attention is paid to geometrical consistency of the FE models. CDM-type damage model is presented and an example of FE modelling of a woven composite is given.

An experimental investigation of the consolidation behaviour of uncured prepregs under processing conditions

This paper presents a methodology and research study that characterises toughened materials, as is needed for optimisation of composite manufacturing processes. The specific challenge is to cover all of the stages of advanced composite manufacturing: fibre deposition by automatic fibre placement machines, hot or room temperature debulking, and consolidation in an autoclave. In these processes the material experiences a wide range of processing parameters: pressure, load rate, temperatures, and boundary constraints. In these conditions, toughened prepregs exhibit complex rheological behaviour, with diverse flow and deformation mechanisms at various structural scales. Here a series of experimental results are presented in order to describe the temperature, viscosity, flow mechanisms, and scale-effects of simple uncured prepreg stacks. The driver for this study is to obtain a further understanding of flow mechanisms throughout the consolidation phase of composites manufacture since fibre path defects are most likely to occur during compaction, prior to vitrification.

Stabilizing textile preforms by means of liquid resin print: a feasibility study

Abstract This study demonstrates the feasibility of creating stable, preconsolidated, yet permeable preforms for liquid resin infusion (RIFT) manufacture of composite materials. While being one of the cheapest and simplest methods of composites manufacture, RIFT with flexible tooling is known for high risk of dimensional and internal defects due to insufficient consolidation of textile preforms. Achieving the quality of a rigid mold solution, at the cost and simplicity of a flexible mold process, is the principal challenge of the RIFT. The approach presented suggests stabilizing a compliant preform through pointwise and highly controlled integration of a binder, and its consolidation prior to liquid molding. The printed resin creates a stiff skeleton, securing material for resin infusion and curing. This study explores the feasibility and efficiency of novel binding techniques, and the effects it may have on preform properties. Successful implementation of the concept for a multiply woven preform is demonstrated and the concept potential is discussed.

Piezoelectric effects in boron nitride nanotubes predicted by the atomistic finite element method and molecular mechanics

We calculate the tensile and shear moduli of a series of boron nitride nanotubes and their piezoelectric response to applied loads. We compare in detail results from a simple molecular mechanics (MM) potential, the universal force field, with those from the atomistic finite element method (AFEM) using both Euler-Bernoulli and Timoshenko beam formulations. The MM energy minimisations are much more successful than those using the AFEM, and we analyse the failure of the latter approach both qualitatively and quantitatively.

Positioning and aligning CNTs by external magnetic field to assist localised epoxy cure

Abstract This work focuses on the generation of conductive networks through the localised alignment of nano fillers, such as multi-walled carbon nanotubes (MWCNTs). The feasibility of alignment and positioning of functionalised MWCNTs by external DC magnetic fields was investigated. The aim of this manipulation is to enhance resin curing through AC induction heating due to hysteresis losses from the nanotubes. Experimental analyses focused on in-depth assessment of the nanotube functionalisation, processing and characterisation of magnetic, rheological and cure kinetics properties of the MWCNT solution. The study has shown that an external magnetic field has great potential for positioning and alignment of CNTs. The study demonstrated potential for creating well-ordered architectures with an unprecedented level of control of network geometry. Magnetic characterisation indicated cobalt-plated nanotubes to be the most suitable candidate for magnetic alignment due to their high magnetic sensitivity. Epoxy/metal-plated CNT nanocomposite systems were validated by thermal analysis as induction heating mediums. The curing process could therefore be optimised by the use of dielectric resins. This study offers a first step towards the proof of concept of this technique as a novel repair technology.

Multi-scale modelling of non-uniform consolidation of uncured toughened unidirectional prepregs

Consolidation is a crucial step in manufacturing of composite parts with prepregs because its role is to eliminate inter- and intra-ply gaps and porosity. Some thermoset prepreg systems are toughened with thermoplastic particles. Depending on their size, thermoplastic particles can be either located in between plies or distributed within the inter-fibre regions. When subjected to transverse compaction, resin will bleed out of low-viscosity unidirectional prepregs along the fibre direction, whereas one would expect transverse squeeze flow to dominate for higher viscosity prepregs. Recent experimental work showed that the consolidation of uncured toughened prepregs involves complex flow and deformation mechanisms where both bleeding and squeeze flow patterns are observed [1]. Micrographs of compacted and cured samples confirm these features as shown in Fig.1. A phenomenological model was proposed [2] where bleeding flow and squeeze flow are combined. A criterion for the transition from shear flow to resin bleeding was also proposed. However, the micrographs also reveal a resin rich layer between plies which may be contributing to the complex flow mechanisms during the consolidation process. In an effort to provide additional insight into these complex mechanisms, this work focuses on the 3D numerical modelling of the compaction of uncured toughened prepregs in the cross-ply configuration described in [1]. A transversely isotropic fluid model is used to describe the flow behaviour of the plies coupled with interplay resin flow of an isotropic fluid. The multi-scale flow model used is based on [3, 4]. A numerical parametric study is carried out where the resin viscosity, permeability and inter-ply thickness are varied to identify the role of important variables. The squeezing flow and the bleeding flow are compared for a range of process parameters to investigate the coupling and competition between the two flow mechanisms. Figure 4 shows the predicted displacement of the sample edge with the multi-scale compaction model after one time step [3]. The ply distortion and resin flow observed in Fig.1 is qualitatively retrieved by the computational model.Consolidation is a crucial step in manufacturing of composite parts with prepregs because its role is to eliminate inter- and intra-ply gaps and porosity. Some thermoset prepreg systems are toughened with thermoplastic particles. Depending on their size, thermoplastic particles can be either located in between plies or distributed within the inter-fibre regions. When subjected to transverse compaction, resin will bleed out of low-viscosity unidirectional prepregs along the fibre direction, whereas one would expect transverse squeeze flow to dominate for higher viscosity prepregs. Recent experimental work showed that the consolidation of uncured toughened prepregs involves complex flow and deformation mechanisms where both bleeding and squeeze flow patterns are observed [1]. Micrographs of compacted and cured samples confirm these features as shown in Fig.1. A phenomenological model was proposed [2] where bleeding flow and squeeze flow are combined. A criterion for the transition from shear flow to resin b...