Tossa jute yarn as received from the supplier is denoted as “hairy yarn” and after removing hairs, yarn is denoted as “hairless yarn”. Hairs are removed manually by burning using a candle flame. Tensile properties of hairy and hairless yarn are measured. Differential scanning calorimetry, X-ray photoelectron spectroscopy and fourier transform infrared analysis are performed to understand the difference in properties between hairy and hairless yarns. Unidirectional (UD) mat of “unsized yarn” is prepared by wrapping it on a metal frame and UD mat of “sized yarn” is prepared by wrapping it on a drum and applying hydroxyethyl cellulose solution (a water based adhesive) as binder. Unidirectional composites are manufactured using hairy and hairless yarns separately. Unsaturated polyester resin is used as matrix and composites are manufactured via resin transfer moulding. Composites test results show an increase in tensile modulus (5.5%) and decrease in strain at failure (7.5%) of composites manufactured with unsized hairy yarn compared to those manufactured with unsized hairless yarn in the longitudinal direction. Composites manufactured with unsized hairy yarn shows an increase in strain at failure (86%) compared to that of composites manufactured with unsized hairless yarn in transverse direction.

A novel Regularising Ensemble Kalman filter Algorithm based on the Bayesian paradigm was applied to RTM processes to estimate local porosity and permeability of fibrous reinforcements using measured values of local resin pressure and flow front positions during resin injection. The algorithm allows to detect locations of defects in the preform. It was tested in virtual experiments with two geometries, a two-dimensional rectangular preform and a more complex 3D shape, as well as in laboratory experiments. In both the virtual and laboratory experiments, it was demonstrated that the proposed methodology is able to successfully discover defects and estimate local porosity and permeability with good accuracy. The algorithm also provides confidence intervals for the predictions and estimations of defect probabilities, which are valuable for analysis of the process.

The out-of-plane permeability of two glass fibre fabrics was measured by 26 institutions using silicone oil as a test fluid. Participants in this study were free to select the test procedure, specimen dimensions and data analysis method, provided that testing was carried out at three target fibre volume fractions, 46%, 50% and 54%. While results showed a variability of two orders of magnitude between participants, most values were within a significantly narrower band. A majority of participants used 1D saturated test method. A few selected 1D unsaturated and 3D unsaturated flow method which gave very similar results. Focusing on analysis of data and results of 1D saturated flow measurements, results are not conclusive, but they are consistent with number of layers in a specimen, fibre volume fraction, injection pressure and sealing of specimen edges all having an effect on the measured permeability. Specifying limits for these parameters is expected to result in reduced scatter in measured permeability.

This paper reports the results of an international benchmark exercise on the measurement of fibre bed compaction behaviour. The aim was to identify aspects of the test method critical to obtain reliable results and to arrive at a recommended test procedure for fibre bed compaction measurements. A glass fibre 2/2 twill weave and a biaxial (±45°) glass fibre non-crimp fabric (NCF) were tested in dry and wet conditions. All participants used the same testing procedure but were allowed to use the testing frame, the fixture and sample geometry of their choice. The results showed a large scatter in the maximum compaction stress between participants at the given target thickness, with coefficients of variation ranging from 38% to 58%. Statistical analysis of data indicated that wetting of the specimen significantly affected the scatter in results for the woven fabric, but not for the NCF. This is related to the fibre mobility in the architectures in both fabrics. As isolating the effect of other test parameters on the results was not possible, no statistically significant effect of other test parameters could be proven. The high sensitivity of the recorded compaction pressure near the minimum specimen thickness to changes in specimen thickness suggests that small uncertainties in thickness can result in large variations in the maximum value of the compaction stress. Hence, it is suspected that the thickness measurement technique used may have an effect on the scatter.

3D woven composites are frequently employed due to their improved through-thickness properties and high damage tolerance compared with laminated composites. Due to the large design space for 3D weave patterns, an in-depth understanding of the relationship between the weave parameters and mechanical properties is essential for the design of these materials. This numerical study investigates the effect of fibre architecture on the mechanical performance of 3D woven composite T-joints under tensile pull-off loading. Six weave pattern variations, subjected to the same preform manufacturing constraint, are designed and numerically analysed, along with another two that have been manufactured and tested for validation previously. Results show a significant architecture dependence in the mechanical responses. Following the design of experiments on weave patterns, the complex architecture-dependant effect is decoupled by two independent variables, yarn path entanglement and yarn path crossover. The study also provides design recommendations for 3D woven T-joint reinforcements under tensile pull-off loading.

Meso-scale unit cell models are often used to simulate mechanical behaviour of textile composites. Apart from reliable ways to create meso-scale geometries, such simulations require reliable meshing algorithms. While the former is made possible via dedicated textile pre-processors or high-fidelity weaving simulations, the meshing remains quite problematic for complex textiles and geometries. Even though, with a lot of user input, it is possible to create very complex meshes using meshing pre-processors, this approach remains infeasible for cases when a large number of models need to be analysed. This paper presents a meshing approach based on the combination of local octree-refinement with surface smoothing. This allows nearly conformal meshes to be generated for geometries of any complexity which achieve accuracy comparable to that of conformal meshes. A range of unit cells was analysed using the new approach and it was shown that the error in local stresses is within 10% of the reference solution and the average error is below 7%. It was found that the computational cost of the analysis using the new meshing technique is not considerably higher than for an analysis which uses a conventional conformal mesh yet the new approach allows analysis of any geometry.

This paper presents a comprehensive review of the scientific and engineering contributions of Prof. Stepan V. Lomov in a career spanning over 3 decades. Starting from his early work on the modelling of dry textiles, different aspects of composite materials have benefited from his inspiring contribution. His wide scientific curiosity drove the research on several topics, covering permeability, forming, damage, fatigue, nano-engineered composites, as well as development of analytical and numerical models at different scales. The paper presents a full spectrum of his scientific career aiming to link his achievements and the future research on composite materials.

In numerical simulations of reinforcement preforming, fabrics are often modelled using continuum approaches with homogenised material properties in order to reduce the computational costs. To predict the occurrence of meso-scale defects, in particular when membrane finite elements are used for modelling, a novel wrinkling criterion is proposed here. This criterion relates the onset of reinforcement buckling to material and process parameters. It is demonstrated that the criterion correctly predicts the occurrence of meso-scale defects and is more accurate than criteria based on a constant shear locking angle or critical strain for the defect onset, which do not to take into account local processing conditions such as friction or normal pressure.

Although good progress was made by two international benchmark exercises on in-plane permeability, existing methods have not yet been standardized. This paper presents the results of a third benchmark exercise using in-plane permeability measurement, based on systems applying the radial unsaturated injection method. 19 participants using 20 systems characterized a non-crimp and a woven fabric at three different fiber volume contents, using a commercially available silicone oil as impregnating fluid. They followed a detailed characterization procedure and also completed a questionnaire on their set-up and analysis methods. Excluding outliers (2 of 20), the average coefficient of variation (cv) between the participant’s results was 32% and 44% (non-crimp and woven fabric), while the average cv for individual participants was 8% and 12%, respectively. This indicates statistically significant variations between the measurement systems. Cavity deformation was identified as a major influence, besides fluid pressure/viscosity measurement, textile variations, and data analysis.

Various 3D woven composites have been studied and used in last several decades. It was demonstrated that these composites can have better delamination and impact resistance than conventional laminates. However, most of the 3D woven reinforcements have fibres only in two directions, warp and weft, because of weaving manufacturing constraints. This makes properties of 3D woven composites sub-optimal for most of the practical load cases. Relaxing manufacturing constraints and optimising 3D fibre architectures for more complex load cases requires new numerical meso-scale optimisation framework as well as novel manufacturing techniques to implement optimised fibre architectures. This paper presents a numerical optimisation framework which employs TexGen modelling schema and links the meso-scale unit cell properties with the macro-scale response of a composite part. The framework is applied to a vehicle floor panel for demonstration purposes. It is shown that multi-axial 3D preforms can give up to 30% weight-saving compared to aluminium parts and outperform parts made from non-crimp fabric by about 10%. Initial development of manufacturing techniques for mutli-axial 3D preforms is presented as well.

A meso-scale modelling framework is proposed to simulate the 3D woven fibre architectures and the mechanical performance of the composite T-joints, subjected to quasi-static tensile pull-off loading. The proposed method starts with building the realistic reinforcement geometries of the 3D woven T-joints at the mesoscale, of which the modelling strategy is applicable for other types of geometries with weave variations at the T-joint junction. Damage modelling incorporates both interface and constituent material damage, in conjunction with a continuum damage mechanics approach to account for the progressive failure behaviour. With a voxel based cohesive zone model, the proposed method is able to model mode I delamination based on the voxel mesh technique, which has advantages in meshing. Predicted results are in good agreement with experimental data beyond initial failure, in terms of load-displacement responses, failure events, damage initiation and propagation. The significant effect of fibre architecture variations on mechanical behaviour is successfully predicted through this modelling method without any further correlation of input parameters in damage model. This predictive method will facilitate the design and optimisation of 3D woven T-joint preforms.

To understand the influence of the fibre architecture of 3D woven composite T-joints on mechanical performance, as well as the benefits that 3D woven T-joints can offer over the equivalent 2D laminates, experimental testing is performed on two types of 3D woven T-joint with only weave variation at the junction, and one type of 2D woven laminate T-joint. A quasi-static tensile pull-off loading is selected in this work as this out-of-plane load case is one of the typical loading conditions for such T-joint structures. The significant advantages of 3D woven composite T-joints in terms of ultimate strength and damage tolerance over the 2D alternative were identified in the testing. More importantly, this work showed that variation in the fibre architecture can considerably enhance properties such as delamination resistance and total energy absorption to failure, as well as increasing slightly the stiffness and initial failure load. This experimental assessment has demonstrated that using 3D woven reinforcements is an effective way to improve the load-bearing capability of composite T-joints over laminates, and also that this improvement could be optimised with regard to fibre architecture.

TexGen is open source software developed at the University of Nottingham for the geometric 3D modelling of textiles and textile composites. It has a large number of users worldwide and underpins a significant number of research publications. While many users make simplifying assumptions about the structure of a textile, in reality the internal geometry of a textile or textile composite is complex. Capturing this complexity is vital for the prediction of properties such as permeability and mechanical failure. Examples will be given of the characterisation of a material and how the complex features are captured and implemented in TexGen, making use of functionality such as the ability to vary the cross-sectional shape along the length of a yarn. The effect on prediction of properties as a model is refined will be demonstrated. Recent additions to the software will also be highlighted. Laminated structures can be quickly and easily constructed from a selection of textiles and several nesting options are available. A new rotate textile option can then be used to create laminates with varying ply angles. Where the unit cell is also rotated, appropriate periodic boundary conditions have been implemented and are automatically generated in an ABAQUS input file. A new feature is described which generates a TexGen model from a weave pattern file. Future developments of this may improve accessibility of the software to the weaving community. The generation of a pattern draft output from the TexGen model is also described.

Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the geometrical parameter describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.

This study analyses the influence of the random filament arrangement in fibre bundles on the resin flow behaviour. Transverse steady-state resin flow that occurs behind a liquid resin flow front was simulated numerically through statistically equivalent micro-structures at high-fibre volume fractions, Vf > 0.6, as observed in fibre bundles. The need of applying a minimum gap distance between neighbouring filaments was overcome by automated local mesh refinement. The derived permeability values showed significant scatter. Convergence of these values was determined at a ratio of flow length to filament radius greater than 20 for all three analysed fibre volume fractions. Mean permeabilities were between 6 and 10 times lower than those predicted for a hexagonal fibre array. A statistical model is proposed, which is able to predict the scatter of observed permeabilities based on simple micro-structural descriptors.

Development of novel textile preforming concepts driven by multi-objective optimisation techniques will be reported here. One of the main goals here is to completely relax the manufacturing constraints imposed by conventional textile machinery. Several examples towards this goal are presented in this paper. Robotic/mechatronic concepts have been employed in creating optimised fibre architectures.

The effect of the stitch thread tension on fibre bundle geometry and in-plane permeability of unidirectional carbon fibre non-crimp fabrics (NCFs) was studied. Constraining the bundle mobility by increasing the stitch tension was found to result in decreasing levels of fibre bundle waviness. The stitch thread tension affects the size and geometry of fibre bundles and inter-bundle gaps in the fabric. Experimental observations suggest that this has an effect on the in-plane permeability, particularly transverse to the fibre bundles.

A common method to fabricate net-shaped three-dimensional (3D) woven preforms for composite T-joints is to weave flat 3D preforms via a standard weaving machine with variation in binder yarn path and then separate the preform in the form of a bifurcation. Folding introduces fiber architecture deformation at the 3D woven bifurcation area. In this paper, a geometric modeling approach is proposed to represent the realistic fiber architecture, as a preprocessor for finite element analyses to predict composite structural performance. Supported by X-ray micro-computed tomography (µCT), three important deformation mechanisms are observed including yarn stack shifting, cross-section bending, and cross-section flattening resulting from the folding process. Furthermore, a set of mathematical formulae for simulation of the deformations in the junction region are developed and satisfactory agreement is observed when compared with μCT scan results.

Microscopic observation and analysis are used to examine the role that contact conditions play in determining the frictional behaviour of non-crimp fabrics (NCFs). The true fibre contact length is measured over a range of normal pressures. For the NCF considered, the contact length is 67% lower than for a corresponding unidirectional tow on -tool contact at a pressure of 240 kPa. The difference in contact behaviour is associated with the fabric architecture, specifically stitching and gaps between tows. These microscopic observations are used to predict friction using a constant interface shear strength model. These predictions are found to compare well with macroscopic friction measurements taken using a sliding sled arrangement, once the roughness of the sled tool is taken into account.

Consolidation of a prepreg layup to a target thickness is critical in order to achieve the required fibre volume fraction and dimensions in a composite part. Experiments show that different processing conditions lead to different levels of compaction and variability in the thickness. This paper presents an analysis of processing conditions and their effects on consolidation of thick composite components. A model that accounts for both percolation and squeezing flow is employed to study two toughened prepreg systems – IM7/8552 and IMA/M21. This paper analyses the significance of the process parameters on the thickness of prepregs and its variability. The analysis of different layups and processing conditions suggests several strategies to control target thickness and its variability. The IMA/M21 prepreg system was found to have lower variability due to its toughening mechanism. The presented results provide a better understanding of the composite manufacturing and can be used to provide an informed choice in design for manufacture of composite structures.