Experimental assessment of the mechanical behaviour of 3D woven composite T-joints

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

Meso-scale modelling of 3D woven composite T-joints with weave variations

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

Dynamic response of orthogonal 3D woven carbon composites under soft impact

This paper presents an experimental and numerical investigation into the dynamic response of 3D orthogonal woven carbon composites undergoing soft impact. Composite beams of two different fibre architectures, varying only by the density of through-thickness reinforcement, were centrally impacted by metallic foam projectiles. Using high speed photography, the centre-point back-face deflection was measured as a function of projectile impulse. Qualitative comparisons are made with a similar uni-directional laminate material. No visible delamination occurred in orthogonal 3D woven samples, and beam failure was caused by tensile fibre fracture at the gripped ends. This contrasts with uni-direction carbon fibre laminates, which exhibit a combination of wide-spread delamination and tensile fracture. Post-impact clamped-clamped beam bending tests were undertaken across the range of impact velocities tested in order to investigate any internal damage within the material. Increasing impact velocity caused a reduction of beam stiffness: this phenomenon was more pronounced in composites with a higher density of through-thickness reinforcement. A three-dimensional finite element modelling strategy is presented and validated, showing excellent agreement with the experiment in terms of back-face deflection and damage mechanisms. The numerical analyses confirm negligible influence from though-thickness reinforcement in regards to back-face deflection, but significant reductions in delamination damage propagation. Finite element modelling was used to demonstrate the significant structural enhancements provided by the through-the-thickness weave. The contributions to the field made by this research include the characterisation of 3D woven composite materials under high-speed soft impact, and the demonstration of how established finite element modelling methodologies can be applied to the simulation of orthogonal woven textile composite materials undergoing soft impact loading

Effect of fibre architecture on tensile pull-off behaviour of 3D woven composite T-joints

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

Effect of specimen history on structure and in-plane permeability of woven fabrics

Before being processed into composites, reinforcement fabrics may undergo repeated involuntary deformation, the complete sequence of which is here referred to as specimen history. To mimic its effect, fabric specimens were subjected to sequences of defined shear operations. For single fabric layers with unconstrained thickness, quantitative evaluation of photographic image data indicated that repeated shear deformation results in a residual increase in inter-yarn gap width. This translates into an increase in measured fabric permeabilities in multi-layer lay-ups at given compaction levels. The extent of both interrelated effects increases with increasing yarn density in the fabric and with increasing maximum angle in the shear history. Additional numerical permeability predictions indicated that the increase in permeability may be partially reversed by through-thickness fabric compression. The observations suggest that the effect of involuntary deformation of the fabric structure can result in variations in the principal permeability values by factors of up to 2

The Application of Carbon Fiber Composites in Cryotank

To meet the design goal for lightweighting the next-generation launch vehicles, carbon fiber reinforced polymeric-based composites are being explored for cryogenic fuel tank applications. The applications of carbon fiber composites in liquid hydrogen (LH2) and liquid oxygen (LOX) fuel tanks were introduced in this chapter. The materials, processing, and design of DC-XA LH2 tank, X-33 LH2 tank, SLI LH2 tank, and CCTD Program tank were discussed. Lockheed Martin LOX tank and Space X LOX tank were introduced. Technology development, materials development, and development trend of cryogenic fuel tanks were discussed. Thin-ply hybrid laminates and out-of-autoclave tanks are projected for future space missions

Fibre architecture design of 3D woven composite with genetic algorithms: a unit cell based optimisation framework and performance assessment

There are vast possibilities in fibre architecture design of 3D woven reinforcement. This paper considers the application of Genetic Algorithm (GA) in 3D woven composites optimisation. A set of real and integral variables, representing 3D fibre architecture, are formulated into a mixed integer Genetic Algorithm. The objective function is evaluated through automation of the unit cell based finite element analysis, by using the open source pre-processor TexGen and the commercial solver ABAQUS. The mixed integer Genetic Algorithm is adapted to a micro-population, aiming to improve computational efficiency. The study uses statistical tests to quantify the performance of the Genetic Algorithm schemes and the choice of parameters. The proposed approach was applied to the optimisation of 3D woven composites for maximum buckling resistance for the case of a landing gear brace. This study demonstrated that the optimisation converged to the optimum design within 20 iterations, considering 300 out of 7000 permissible solutions. In terms of buckling performance, the optimum design performed twice as well as cross-ply laminated composites and at least 50% better than known orthogonal 3D woven composites

Fibre architecture design of 3D woven composite with genetic algorithms: a unit cell based optimisation framework and performance assessment

There are vast possibilities in fibre architecture design of 3D woven reinforcement. This paper considers the application of Genetic Algorithm (GA) in 3D woven composites optimisation. A set of real and integral variables, representing 3D fibre architecture, are formulated into a mixed integer Genetic Algorithm. The objective function is evaluated through automation of the unit cell based finite element analysis, by using the open source pre-processor TexGen and the commercial solver ABAQUS. The mixed integer Genetic Algorithm is adapted to a micro-population, aiming to improve computational efficiency. The study uses statistical tests to quantify the performance of the Genetic Algorithm schemes and the choice of parameters. The proposed approach was applied to the optimisation of 3D woven composites for maximum buckling resistance for the case of a landing gear brace. This study demonstrated that the optimisation converged to the optimum design within 20 iterations, considering 300 out of 7000 permissible solutions. In terms of buckling performance, the optimum design performed twice as well as cross-ply laminated composites and at least 50% better than known orthogonal 3D woven composites

Recent developments in the realistic geometric modelling of textile structures using TexGen

Realistic geometric representation of fabrics is essential for modelling of mechanical and physical properties of textiles and textile composites. It is also advantageous to be able to generate those models quickly and easily. Recent developments in TexGen which automate the creation of models for 3D orthogonal, angle interlock and layer-to-layer fabrics and sheared 2D fabrics are described. Micro-Computed Tomography data of 3D fabrics has been used to identify geometrical characteristics which have formed the basis for implementation of refinements to the idealised fabrics generated automatically in TexGen. In 3D orthogonal textiles local geometrical variations, particularly in yarn cross-section, surface crimp and binder yarn path are apparent at different levels of compaction. The “refine” option in TexGen‟s 3D wizard automatically adjusts these features to achieve compaction to a specified thickness, using yarn volume fraction as a constraint. For sheared textiles a generic 2D plain weave fabric was used to identify key geometric features. Yarn rotation has been identified as one of these and the geometric description of the sheared fabric considers yarn rotations in terms of two elliptical cylinders crossing each other at an oblique angle. The rotational angle is derived mathematically from the tangential contact between yarns. Variations in yarn height along the length of the yarn have also been identified and both of these features are incorporated into a refine function for sheared textiles. Compatible voxelised mesh and periodic boundary conditions for the sheared domain have also been implemented. The models have been used to generate manufacturing data: permeability data for the 3D fabric and coefficient of thermal expansion for the sheared 2D fabric

Advanced geometry modelling of 3D woven reinforcements in polymer composites: processing and performance analysis

Numerical methods have become increasingly effective tools for analysis and design of composite materials. This study investigates how the inclusion of geometrical variations in modelling 3D woven fabrics affects the accuracy of numerical predictions. Based on micro-Computed Tomography data of 3D orthogonal woven composites, unit cell models were generated in TexGen at different levels of geometrical detail. Two types of analysis were implemented: (a) computational fluid dynamics (CFD) simulates resin flow during fabric impregnation in composites processing to predict permeability; (b) implicit static finite element analysis predicts in-plane tensile strength of the composites. By comparison with experimental data, the numerical predictions indicate that local geometrical variations, particularly in yarn cross-section, surface crimp and binder yarn path, have significant influence on both permeability and material strength. It is important to model the precise geometry in certain locations while the overall geometry can be simplified in order to maintain the practicality of model generation