Investigating the Potential of Using Off-Axis 3D Woven Composites in Composite Joints’ Applications

The effect of circular notch has been evaluated for three different architectures of three-dimensional (3D) carbon fibre woven composites (orthogonal, ORT; layer-to-layer, LTL; angle interlock, AI) through open-hole quasi-static tension and double-lap bearing strength tests in the off-axis (45°) direction. Damage characterisation is monitored using Digital Image correlation (DIC) for open-hole testing and X-ray Computed Tomography (CT) for double-lap bearing strength test. The off-axis notched 3D woven composites exhibits minor reduction (less than 10 %) of the notched strength compared to the un-notched strength. DIC strain contour clearly show stress/strain localisation regions around the hole periphery and stress/strain redistribution away from the whole due to the z-binder existence, especially for ORT architecture. Up to 50 % bearing strain, no significant difference in the bearing stress/bearing strain response is observed. However when ORT architecture was loaded up to failure, it demonstrates higher strain to failure (~140 %) followed by AI (~105 %) and lastly LTL (~85 %). X-ray CT scans reveal the effect of the z-binder architecture on damage evolution and delamination resistance. The study suggests that off-axis loaded 3D woven composites, especially ORT architecture, has a great potential of overcoming the current challenges facing composite laminates when used in composite joints’ applications.     

Experimental determination of the mode I delamination fracture and fatigue properties of thin 3D woven composites

The mode I delamination fracture toughness and fatigue strength of thin-section three-dimensional (3D) woven composite materials is experimentally determined. The non-crimp 3D orthogonally woven carbon–epoxy composites were thin (2 mm) and consequently their through-thickness z-binder yarns were inclined at a very steep angle (about 70°) from the orthogonal direction. The steep z-binder angle has a marked effect on the delamination toughening and fatigue strengthening mechanisms. Experimental testing revealed that the fracture toughness and fatigue resistance increased progressively with the volume content of z-binders. However, the steep angle caused the z-binder yarns bridging the delamination crack to deform and fail in shear and through-thickness tension, rather than in-plane tension which usually occurs in thick 3D woven composites. Mode I pull-off tests on a single woven z-binder yarn embedded within the composite revealed that the crack bridging traction load, strain energy absorption and failure mechanism were strongly affected by the steep angle.     

Influence of fibre architecture on the tensile,compressive and flexural behaviour of 3D woven composites

This paper presents a comprehensive study on the tensile, compressive, and flexural performance of six types of 3D woven carbon-fibre/epoxy composites which were manufactured using a traditional narrow fabric weaving loom and resin transfer moulding. Four orthogonal and two angle-interlock weaves were tested with the primary loading direction parallel to the warp direction. The mechanical performance was found to be affected by the distribution of resin rich regions and the waviness of the load-carrying fibres, which were determined by the fibre architectures. The binding points within the resin rich regions were found to be the damage initiation sites in all weave types under all loading conditions, which were confirmed with both visual observation and digital image correlation strain maps. Among all weave types, the angle interlock weave W-3 exhibited the highest properties under all loading conditions.     

Experimental investigation of three-dimensional woven composites

This paper summarizes an extensive experimental study of composites reinforced with three-dimensional woven preforms subjected to tensile, compressive and in-plane shear loading. Three innovative three-dimensional woven architectures were examined that utilize large 12 K and 24 K IM7 carbon tows, including two ply to ply angle interlock architectures and one orthogonal architecture. Additionally, a two-dimensional quasi-isotropic woven material was evaluated for comparison. Loads were applied in both the warp and the weft directions for tensile and compressive loading. Digital image correlation was used to investigate full field strains leading up to quasi-static failure. Experimental results including ultimate strengths and moduli are analyzed alongside representative failure modes. The orthogonal woven material was found to have both greater strength and modulus in tension and compression, though a ply to ply woven architecture was found to outperform the remaining three-dimensional architectures. Recommendations are made for improving the manufacturing processes of certain three-dimensional woven architectures.     

Compressive damage mechanism of GFRP composites under off-axis loading: Experimental and numerical investigations

Experimental and computational studies of the microscale mechanisms of damage formation and evolution in unidirectional glass fiber reinforced polymer composites (GFRP) under axial and off-axis compressive loading are carried out. A series of compressive testing of the composites with different angles between the loading vector and fiber direction were carried out under scanning electron microscopy (SEM) in situ observation. The damage mechanisms as well as stress strain curves were obtained in the experiments. It was shown that the compressive strength of composites drastically reduces when the angle between the fiber direction and the loading vector goes from 0° to 45° (by 2.3–2.6 times), and then slightly increases (when the angle approaches 80–90°). At the low angles between the fiber and the loading vector, fiber buckling and kinking are the main mechanisms of fiber failure. With increasing the angle between the fiber and applied loading, failure of glass fibers is mainly controlled by shear cracking. For the computational analysis of the damage mechanisms, 3D multifiber unit cell models of GFRP composites and X-FEM approach to the fracture modeling were used. The computational results correspond well to the experimental observations.     

Longitudinal and transverse damage taxonomy in woven composite components

This work addresses the issue of micro-structural damage in the longitudinal direction of the woven during a deformation process, primarily in the tensile mode. This paper extends the insight into self-inflicted damage in dimensional multilayer woven composites subjected to uniaxial tensile and shear loading. Two composites made of multilayer woven architectures, hereby named: orthogonal and normal layer interlock forms the basis of this study. It identifies the physical characteristics which initiate the various damage modes, what these modes are and when they occur. This work complements the work already reported on the transverse direction in woven composites.     

Pull-through performance of carbon fibre epoxy composites

An investigation of the through-thickness properties of carbon fibre prepreg laminates, Non-Crimp Fabric laminates and non-crimp 3D orthogonal woven composites by pull-through testing was performed. Influence of matrix system and curing temperature on the performance of the 3D woven composites was investigated.     

In-situ damage sensing of woven composites using carbon nanotube conductive networks

We report an in situ analysis of the microstructure of woven composites using carbon nanotube (CNT)-based conductive networks. Two types of specimens with stacking sequences of (0/90)_s (on-axis) and (22/85/−85/−22) (off-axis) were manufactured using ultra-high-molecular-weight polyethylene fibers and a CNT-dispersed epoxy matrix via vacuum-assisted resin transfer molding. The changes in the electrical resistance of the woven composites in response to uniaxial loading corresponded to the changes in the gradient of the stress–strain curves, which is indicative of the initiation and accumulation of microscopic cracking and delamination. The electrical resistance of the woven composites increased due to both elongation and microscopic damage; interestingly, however, it decreased beyond a certain strain level. In situ X-ray computed tomography and biaxial loading tests reveal that this transition is due to yarn compaction and Poisson’s contraction, which are manifest in textile composites.     

Fatigue of a 3D Orthogonal Non-crimp Woven Polymer Matrix Composite at Elevated Temperature

Tension-tension fatigue behavior of two polymer matrix composites (PMCs) was studied at elevated temperature. The two PMCs consist of the NRPE polyimide matrix reinforced with carbon fibers, but have different fiber architectures: the 3D PMC is a singly-ply non-crimp 3D orthogonal weave composite and the 2D PMC, a laminated composite reinforced with 15 plies of an eight harness satin weave (8HSW) fabric. In order to assess the performance and suitability of the two composites for use in aerospace components designed to contain high-temperature environments, mechanical tests were performed under temperature conditions simulating the actual operating conditions. In all elevated temperature tests performed in this work, one side of the test specimen was at 329 °C while the other side was open to ambient laboratory air. The tensile stress-strain behavior of the two composites was investigated and the tensile properties measured for both on-axis (0/90) and off-axis (±45) fiber orientations. Elevated temperature had little effect on the on-axis tensile properties of the two composites. The off-axis tensile strength of both PMCs decreased slightly at elevated temperature. Tension-tension fatigue tests were conducted at elevated temperature at a frequency of 1.0 Hz with a ratio of minimum stress to maximum stress of R = 0.05. Fatigue run-out was defined as 2 × 10⁵ cycles. Both strain accumulation and modulus evolution during cycling were analyzed for each fatigue test. The laminated 2D PMC exhibited better fatigue resistance than the 3D composite. Specimens that achieved fatigue run-out were subjected to tensile tests to failure to characterize the retained tensile properties. Post-test examination under optical microscope revealed severe delamination in the laminated 2D PMC. The non-crimp 3D orthogonal weave composite offered improved delamination resistance.     

Tensile fatigue behaviour of glass plain-weave fabric composites in on- and off-axis directions

The tension–tension fatigue behaviour of woven fabric composites was investigated in the on-axis and off-axis directions. Similar to the static tensile properties of woven fabric composites, the tension–tension fatigue behaviour of woven fabric composites was also observed to be anisotropic. The fatigue damage development in both the directions was studied using scanning electron microscopy and acoustic emission techniques. The influence of the applied fatigue frequency and the fatigue stress ratio in both the directions was investigated. At a fatigue frequency of 5 Hz, the hysteresis heating will occur more severely in the off-axis direction than in the on-axis direction. Increasing fatigue stress ratio will lead to a lower hysteresis heating.     

Tensile properties and failure mechanisms of 3D woven GRP composites

Tensile tests were performed on glass reinforced polymer (GRP) composites with three-dimensional (3D) orthogonal, normal layered interlock, and offset layered interlock woven fibre architectures. The mechanical properties and failure mechanisms under tensile loading were similar for the three composites. Cracks formed at low strains within the resin-rich channels between the fibre tows and around the through-thickness binder yarns in the composites, although this damage did not alter the tensile properties. At higher applied tensile stresses the elastic modulus was reduced by 20–30% due to inelastic tow straightening and cracking around the most heavily crimped in-plane tows. Further softening occurred at higher strains by inelastic straightening of all the tows. Composite failure occurred within a localised region and the discrete tow rupture events that have caused tow lock-up and pullout mechanisms in other 3D woven composites were not observed.     

Creep of plain weave polymer matrix composites under on-axis and off-axis loading

Despite the increasing use of polymer woven composites in load-bearing structural applications, published research on their long-term durability is very limited. Hence, creep of plain weave polymer woven composites was investigated experimentally and analytically, using Hexcel Corporation’s F263/T300 2-harness (HS) composite material under on-axis (0°) and off-axis (45°) loading. Constant load creep experiments were conducted over a wide range of temperatures (80–240 °C) and stresses (1–70% of the ultimate tensile strength). Time–temperature-superposition-principle (TTSP) was used to obtain master creep curves at each stress level for a time period beyond the experimental time window. A modified equivalent laminate model (MELM) was developed to predict the creep compliance of plain weave composites for any load orientation with respect to fiber axis, using experimental creep compliance of unidirectional polymer composites. The model predictions were found to be in good agreement with the experimental results, within as well as beyond the experimental time window.     

Progressive damage analysis and strength prediction of 2D plain weave composites

A two-step, multi-scale progressive damage analysis is implemented to study the damage and failure behaviors of 2D plain weave composites under various uniaxial and biaxial loadings. In the progressive damage mode (PDM), a formal-unified 3D Hashin-type criterion is formed to facilitate analysis work and engineering application, with shear nonlinearity considered in the stiffness matrix of yarn. The periodic boundary conditions are developed for the off-axis loading simulations. The simulated stress–strain curves under on-axis uniaxial tension and compression show good agreements with experimental results. The influences of different 3D Hashin-type criteria are subsequently discussed. Moreover, the strength decrease at different off-axis angles and the failure envelopes under on-axis and 45° off-axis biaxial loadings are obtained, with the discussion of different failure characteristics under each loading condition.     

Damage characterization of two-dimensional woven and three-dimensional braided SiC-SiC composites

A comprehensive investigation of the room temperature behaviour of two-dimensional woven and three-dimensional braided SiC-SiC composites fabricated by the chemical vapour infiltration route has been conducted. A morphological study of the residual porosity in the composites revealed the existence of primarily two populations of pores: small intrayarn pores and larger interyarn pores. The sizes and the shapes of the two types of pores depended largely on the fibre architecture; the two step braided composite in which the majority of the fibre yarns were orientated along the axial direction exhibited the smallest pore size. The pore size and shapes in turn influenced the onset of damage in the composites under tensile loading. Damage was found to be initially matrix dominated, thus being essentially independent of the fibre architecture. At higher stress levels, however, fibre dominated damage prevailed. Unlike the tensile behaviour, where damage led to non-linearity in the stress-strain curve, the compressive behaviour of the composites was linear elastic almost up to failure. The off-axis tensile properties as well as compression after tension behaviour of the two-dimensional woven composites were also investigated. The information obtained from these tests provides the basis for the modelling of damage in these materials.     

A test device for damage characterisation of composites based on in situ computed tomography

For engineering design of composites, suitable damage models are required which have to predict the onset of damage, the successive failure and the subsequent reduction of the mechanical properties. To verify existing modelling approaches, the clear experimental identification of the particular damage entities is an essential condition. However, due to the complexity of the failure mechanisms of novel materials like heterogeneous textile composites, a comprehensive damage analysis is still a challenging problem. Recent progress in the field of computed tomography enables in situ measurements to detect damage phenomena in composites under loading. The article describes such a novel test device that combines an integrated testing machine with a high precision computer tomograph. The in situ method was used to study the damage evolution in carbon fibre reinforced plastics (CFRPs) made of weft knitted and woven preforms. A special focus was set to damage processes under loading in thickness direction. For this purpose, cylindrical tensile specimens according to ASTM D 7291 were manufactured and tested. Compression specimens with different aspect ratios have been used to study the compressive failure of CFRP woven composites. The experimental results are discussed with respect to the possibilities and limitations of the in situ based test method.     

General definition of 3D warp interlock fabric architecture

3D warp interlock fabric can be used as a fibrous reinforcement for composite material. Despite of the numerous research papers dealing with this specific woven structure, few researches were conducted to clearly define this multi-layer fabric. Moreover, in many research papers, unskilled scientists of weaving technology have some difficulty to describe the different components of the 3D warp interlock fabric and sometimes make some confusion between the different architecture. Then, with a lack of a clear definition of these 3D multi-layer fabrics, most of the research papers are conducted on a very limited number of structures such as orthogonal, angle and layer to layer interlock.Thus, based on different definitions proposed by skilled scientists, a new general definition of a 3D warp interlock fabric has been proposed to better describe the position of the several yarns located inside the 3D woven structure. Thanks to this improved definition, we hope that the scientific community will use it in order to better design new architectures and conduct finer research based on these product parameters.     

Multi-Scale Finite Element Analyses of Thermal Conductivities of Three Dimensional Woven Composites

This paper summarizes an extensive experimental and prediction study of thermal conductivities of three-dimensional woven composites (3DWCs). Three kinds of innovative 3D woven architectures are examined, including 2.5D angle-interlock, 2.5D angle-interlock (with warp reinforcement), and 3D orthogonal woven architectures. The differences of thermal behaviors of 3DWCs in plane and out of plane are assessed by using multi-scale finite element analysis. For the validation of models, the thickness direction thermal conductivity of 3DWCs are measured. It is indicated that the predicted results are in good agreement with the experimental results. The effects of weave density and fabric architecture on the distribution of heat flux and temperature have been discussed in this work, which determined the thermal conductivities of 3DWCs. From this study, it can be expected that the need of thermal performance of 3DWCs can obtained according to optimize the weave parameters based on the high designability of 3DWCs.     

Modelling and simulation of earthquake resistant 3D woven textile structural concrete composites

Concrete is a composite material composed of water, sand, coarse granular material called aggregate and cement that fills the space among the aggregate particles and glues them together. Conventional building structures are made up of steel skeleton with concrete impregnation. These are very heavy weight structures with steel vulnerable to corrosion. The conventional concrete structures tend to undergo large deformations in the event of a strong earthquake. Mechanical simulation of various textile structural concretes is carried out successfully for their ductility behaviour. 3D woven reinforced concretes display superior ductile character showing ray of hope to develop seismic resistant building. Simulation of three 3D woven fabrics and their composites was carried to predict ductility and strengths of fabric reinforced concrete structures. Maximum deformation was observed for beam reinforced with orthogonal interlock fabric under the same load and minimum deformation was observed for plain concrete. Maximum equivalent stress was observed to be highest for plain concrete followed by beam reinforced with angle interlock fabric followed by orthogonal fabric and warp interlock fabric under similar loading conditions. From the results it was clear that 3D fabric reinforced structures are more ductile than the traditional steel reinforced structures. Hence 3D fabric reinforced concrete structures are much better in strength and ductility as compared to conventional construction materials. Among the three 3D fabric, orthogonal fabric reinforced composites are most ductile and are also less stiff. They can deform more than the other two fabric composites. Hence, orthogonal fabric reinforced composites can undergo higher deformations without collapsing. These composites can be more elastic under earthquake shaking.     

Evaluation of the integrity of 3D orthogonal woven composites with embedded polymer optical fibers

Due to their high flexibility, high tensile strain and high fracture toughness, polymer optical fibers (POF) are excellent candidates to be utilized as embedded sensors for structure health monitoring of fiber reinforced composites. In 3D orthogonal woven structures yarns are laid straight and polymer optical fiber can be easily inserted during preform formation either as a replacement of constituents or between them. The results of the previous paper indicated how an optic fiber sensor can be integrated into 3D orthogonal woven preforms with no signal loss. This paper addresses whether incorporating POF into 3D orthogonal woven composites affects their structure integrity and performance characteristics. Range of 3D orthogonal woven composites with different number of layers and different weft densities was fabricated. The samples were manufactured with and without POF to determine the effect of embedding POF on composite structure integrity. Bending, tensile strength tests, and cross section analysis were conducted on the composite samples. Results revealed that integrity of 3D orthogonal woven composite was not affected by the presence of POF. Due to its high strain, embedded POF was able to withstand the stresses without failure as a result of conducting destructive tests of the composite samples. Micrograph of cross-section of composite samples showed that minimum distortion of the yarn cross-section in vicinity of POF and no presence of air pocked around the embedded POF which indicates that 3D woven preform provided a good host for embedded POF.