Axial Yarns Research Articles

The tensile damage behavior of SiCf/SiC–B4C after oxidation in wet atmosphere based on acoustic emission pattern recognition

AbstractIn this research, SiCf/SiC–B4C composites were prepared through slurry impregnation and reaction melting infiltration (RMI). To explore the damage evolution of this composites after oxidation in wet atmosphere, the changes of damage behavior of composites before and after oxidation were studied using acoustic emission (AE) pattern recognition (PR) technology. Results show that since the damage behavior of the composites changes after oxidation, the optimal number of clusters transforms from 3 to 5. In addition, as the oxidation time increases, the area of concentration of damage events is gradually broadened towards lower stress direction due to the decrease of damage threshold of composites. Meanwhile, because the BN interface is gradually oxidized, the density of C3‐cracks (axial yarns cracks) near the fracture and the proportion of Cluster‐4 (the signals of transverse yarns cracks) will increase, for which the rising of interfacial shear stress should be responsible. Through this research, not only can the damage evolution of SiCf/SiC–B4C composites after oxidation be understood, but also the method employed in this research can be as guide for studying other similar materials.

Parameterized meso-scale modeling and experimental study on the tensile damage evolution and strength of 3D five-directional braided composites

A parametric finite element model (FEM) of three-dimensional five-directional (3D5d) braided composites was established considering the yarn space contact relationship. By adopting reasonable damage criteria and boundary conditions, the damage behavior and mechanical properties of FEM under tensile loading were investigated. The finite element prediction results are consistent with the experiments, indicating that the FEM can effectively predict the progressive damage and strength of 3D5d braided composites. Damage evolution shows that the main failure modes with small braiding angles include tensile failure of braiding yarn and axial yarn, while the large braiding angles are tensile shear failure of braiding yarn. As the fiber volume fraction increases, the initial damage location of the FEM changes from the intersection of braiding yarn/axial yarn to the junction among the braiding yarns. The stress-strain curves results show that the 3D5d braided composites exhibit brittle fracture characteristics under longitudinal tensile loading, and the mechanical properties are significantly correlated with the braiding angle and fiber volume fraction. In addition, the tensile properties of 3D5d braided composites are also compared with those of three-dimensional four-directional (3D4d) braided composites.

Microstructure modeling multiple transverse impact damages of 3-D braided composite based on thermo-mechanical coupling approach

A microstructure model based on fully thermo-mechanical coupling behavior of 3-D braided composites has been proposed for characterizing multiple transverse impact damage. The interfacial contact and cohesive debonding, as well as ductile and shear damage, incorporate with thermo-mechanical coupling constitutive equations have been employed in the model. It was shown that the adiabatic temperature rise and interfacial damage are concentrated on the impact surface with local plastic deformation. The heat energy generated in impact interaction caused local temperature rise, which further leads to thermal expansion of epoxy resin. The thermal expansion produced from the increased compression between the epoxy resin and braided preform will cause the extra internal stress and local deformation. A coupled thermal-stress closed loop will be formed during transverse impact. Compared with braided preforms with and without axial yarns, we found that the axial yarns improve heat energy absorption and impact damage tolerances, while impede impact damage growth.

On-axis fatigue behaviors and failure characterization of 3D5D braided composites with yarn-reduction using X-ray computed tomography

This paper mainly provides a thorough experimental investigation of tension-tension fatigue (R = 0.1) failure mechanisms in 3D5D braided carbon/epoxy composites without/with yarn-reduction (No-YR/In-YR) subjected to different stress levels of ultimate tensile stress (40%-75%UTS). X-ray computed tomography (Micro-CT) was conducted to visualize and quantify the damage generated in the fatigued samples. More significantly, a novel two-steps segmentation approach was proposed to classify and locate the cracks. The results indicated that the two types of specimens showed similar fatigue behavior, i.e. the extensive debonding of the braided yarns might give rise to the premature significant stiffness degradation of the fatigued samples. However, the tensile strength and the fatigue limit of In-YR 3D5D braided composites were reduced by 28.3% and 22.8% relative to No-YR 3D5D braided composites, respectively, which might be attributed to the variation of failure modes. Particularly, the failure modes of the axial yarns surround the yarn-reduction point evolved from mode I to mode II due to the deformation generated during the fabrication. It is noteworthy that the cracks presented a typical wedge distribution near the yarn reduction point due to the in-plane stress migration.

Fatigue Behavior of 3D Braided Composites Containing an Open-Hole.

The static and dynamic mechanical performances of notched and un-notched 3D braided composites were studied. The effect of longitudinal laid-in yarn was investigated in comparison with low braiding angle composites. The specimens were fatigue tested for up to millions of cycles, and the residual strength of the samples that survived millions of cycles was tested. The cross-section of the 3D braided specimens was observed after fatigue loading. It was found that the static and fatigue properties of low angle 3D braided behaved better than longitudinally reinforced 3D braided composites. For failure behavior, pure braids contain damage better and show less damage area than the braids with longitudinal yarns under fatigue loading. More cracks occurred in the 3D braided specimen with axial yarn cross-section along the longitudinal and transverse direction.

Short Beam Shear Behavior and Failure Characterization of Hybrid 3D Braided Composites Structure with X-ray Micro-Computed Tomography.

Three-dimensional braided composite has a unique spatial network structure that exhibits the characteristics of high delamination resistance, damage tolerance, and shear strength. Considering the characteristics of braided structures, two types of high-performance materials, namely, aramid and carbon fibers, were used as reinforcements to prepare braided composites with different hybrid structures. In this study, the longitudinal and transverse shear properties of 3D braided hybrid composites were tested to investigate the influences of hybrid and structural effects. The damage characteristics of 3D braided hybrid composites under short beam shear loading underwent comprehensive morphological analysis via optical microscopy, water-logging ultrasonic scanning, and X-ray micro-computed tomography methods. It is shown that the shear toughness of hybrid braided composite has been improved at certain degrees compared with the pure carbon fiber composite under both transverse and longitudinal directions. The hybrid braided composites with aramid fiber as axial yarn and carbon fiber as braiding yarn exhibited the best shear toughness under transverse shear loading. Meanwhile, the composites with carbon fiber as axial yarn and aramid fiber as braiding yarn demonstrated the best shear toughness in the longitudinal direction. Due to the different distribution of axial and braiding yarns, the transverse shear property of hybrid braided structure excels over the longitudinal shear property. The failure modes of the hybrid braided composite under the two loading directions are considerably different. Under transverse loading, the primary failure mode of the composites is yarn fracture. Under longitudinal loading, the primary failure modes are resin fracture and fiber slip. The extensive interfacial effects and the good deformation capability of the hybrid braided composites can effectively prevent the longitudinal development of internal cracks in the pattern, improving the shear properties of braided composites.

Statistical analysis of acoustic emission signals and tensile deformation measurement for three dimensional carbon fiber braided composites

Accurate assessment for mechanical and damage behaviors of three dimensional carbon fiber braided composites by acoustic emission technique is difficult in practical application. In this study, a statistical analysis approach with calculated amplitude spectrum, probability distribution and entropy is proposed to process acoustic emission signals. Moreover, the tensile behaviors and damage characteristics of three dimensional four directional and five directional braided composites are investigated systematically by combining digital image correlation and acoustic emission methods. The results indicate that three dimensional five directional braided composites possess excellent load-bearing and deformation resistibility capacity, owing to more compact preform structure with additional axial yarns. The acoustic emission statistical analysis method can be used as criteria to distinguish and quantify various irreversible damage and failure mechanisms in three dimensional braided composites. Furthermore, the deformation, damage and failure criterion for two types of composites are fully described based on deformation fields and acoustic emission signals.

Shape adaptable and highly resilient 3D braided triboelectric nanogenerators as e-textiles for power and sensing

Combining traditional textiles with triboelectric nanogenerators (TENGs) gives birth to self-powered electronic textiles (e-textiles). However, there are two bottlenecks in their widespread application, low power output and poor sensing capability. Herein, by means of the three-dimensional five-directional braided (3DB) structure, a TENG-based e-textile with the features of high flexibility, shape adaptability, structural integrity, cyclic washability, and superior mechanical stability, is designed for power and sensing. Due to the spatial frame-column structure formed between the outer braided yarn and inner axial yarn, the 3DB-TENG is also endowed with high compression resilience, enhanced power output, improved pressure sensitivity, and vibrational energy harvesting ability, which can power miniature wearable electronics and respond to tiny weight variations. Furthermore, an intelligent shoe and an identity recognition carpet are demonstrated to verify its performance. This study hopes to provide a new design concept for high-performance textile-based TENGs and expand their application scope in human-machine interfacing.

Illustrating hybrid effect and damage evolution of carbon/aramid braided composite under low-velocity impact

This study illustrates the hybrid effect and damage evolution of carbon/aramid braided composites under low-velocity impact, using a finite element model (FEM) of a complete braided structure. The model was established based on a real three dimensional (3D), five directional (5d) braided structure by taking the interior, surface, corner braided and axial yarns into consideration. Constitutive material modeling and failure criteria were introduced into the model. The degree of damage was determined by comparing the volumes of units removed on failure. Three hybrid structure types were adopted to investigate the relationships between stress distribution and damage evolution. The results showed that the impact response and failure morphology were significantly dependent on hybrid effects under different low-velocity impacts. The impact response curves of hybrid structures showed obvious toughness characteristics. The addition of aramid fiber as an axial yarn could prolong the overall impact response time and reduce failures. Moreover, the hybrid effect strongly influenced the stress distribution and damage evolution in different circumstances. Hybrid structures led to a large stress distribution area and a low stress level, which could reduce the material failure caused by stress concentration. This work provides a sound method for designing hybrid structures and expanding the application potential of 3D braided composites.

Refine reconstruction and verification of meso-scale modeling of three-dimensional five-directional braided composites from X-ray computed tomography data

This paper proposes a statistical approach to generate the refine meso-scale representative volume element of three-dimensional (3D) five-directional braided composites considering the fabric compaction and the axial yarn torsion. The method firstly extracts the regions of interest to obtain the reference model (R-model) from the X-ray computed tomography (Micro-CT) data. Then, the geometric parameters of the collected yarns of R-model are statistically analyzed based on the scanning tomograms. Consequently, the meso-scale statistical model (S-model) are reconstructed after being fitted with the appropriate function. Moreover, for the validation of S-model, the traditional ideal model (I-model) and the experimental tests are considered. The results show that the proposed S-model is capable of accurately presenting the effects of the fabric compaction and yarn torsion on the mechanical behaviors of 3D braided composites, validated by the elastic constants and the damaged modes.

Open hole tension and compression behavior of 3D braided composites

AbstractThe damage tolerant behavior of 3D braided composites is evaluated in terms of the open‐hole notch strength test under tensile and compressive loading. The influence of fiber architecture is evaluated by comparing 3D braid with and without axial yarns as well as laminated composites based on ASTM quasi‐static tension and compression testing standard. The results show that the notched and un‐notched properties of the two types of 3D braided composites are similar under tension and compression loading. Comparing to laminates, both types of 3D braided composites demonstrated superior notch insensitivity than laminated composites. For the failure behavior of the 3D braided composites, under tension loading, crack of both notched specimens tends to propagate along the notch and finally render the specimen to failure. Clear cracks usually presented on the samples without axial yarns, while not for the specimens with axial yarn. Under compression loading, the two types of 3D braided composite are also macroscopically similar, showing transverse fracture. The modified Fabric Geometry Model is used to predict the tensile properties of 3D braided composite. The predicted and experimental results are shown to be in good agreement.

Impact of progressive yarn extension on angular fibre orientation

A detailed analysis has been carried out to assess the influence of progressive yarn extension on angular fibre orientation. Analysis of 3-D trajectory of the fibre using multi coloured tracer fibre technique was carried out using specially designed microcontroller based instrument and image processing-based system. The angular orientation of fibre in the ring spun yarn has been visualised in terms of migration angle, helix angle, spatial orientation angle and three other angles defined on the basis of 3-D path of fibre. Average value of migration angle, helix angle and spatial orientation angle continuously decreases with the increase in yarn extension. The angles defined on the basis of 3-D path of fibre responded differently to yarn extension. But the value of angle related to the direction cosines defined as ratio of segmental radius to fibre element length hovers around 90° at all yarn extension levels. This confirms that model of symmetric migration remains unaffected by axial yarn extension.

Flexural damage behavior of carbon fiber three-dimensional braided composites using acoustic emission and micro-CT

Some factors such as braiding architectures and braiding angles may cause differences in the damage mechanism of three dimensional braided composites. To address this issue, the damage evolution and deformation process of three dimensional (3D) four-directional (4D) and three dimensional (3D) five-directional (5D) braided composites are detected by digital image correlation (DIC) methods and acoustic emission (AE) technology under three-point bend loading conditions, respectively. Furthermore, the internal damage characteristics of the fractured composite specimens are observed by micro-computed tomography (mirco-CT). The microscopic damage morphology observed by micro-CT has a good correlation with the distribution characteristics of displacement and strain fields, while peak amplitude and peak frequency distributions of AE signals can explain the whole process of damage evolution of the composites. The AE characteristics, microscopic damage morphology and damage-related out-of-plane deformation of 3D4D and 3D5D braided composite specimens with different braiding angles are compared with each other and cross validated. The results show that 3D5D braided composites is strengthened by adding axial yarns in the braiding direction, so it has higher delamination resistance. In addition to this, due to the degree of orientation of the fibers of the specimen with small braided angle is high, the process of damage is shorter and the deformation is smaller.

Mechanical Characterization and Impact Damage Assessment of Hybrid Three-Dimensional Five-Directional Composites.

The effects of braided architecture and co-braided hybrid structure on low-velocity response of carbon-aramid hybrid three-dimensional five-directional (3D5d) braided composites were experimentally investigated in this study. Low-velocity impact was conducted on two types of hybridization and one pure carbon fiber braided reinforced composites under three velocities. Damage morphologies after low-velocity impact were detected by microscopy and ultrasonic nondestructive testing. Interior damages of composites were highly dependent on yarn type and alignment. Impact damage tolerance was introduced to evaluate the ductility of hybrid composites. Maximum impact load and toughness changed with impact velocity and constituent materials of the composites. The composite with aramid fiber as axial yarn and carbon fiber as braiding yarn showed the best impact resistance due to the synergistic effect of both materials. Wavelet transform was applied in frequency and time domain analyses to reflect the failure mode and mechanism of hybrid 3D5d braided composites. Aramid fibers were used either as axial yarns or braiding yarns, aiding in the effective decrease in the level of initial damage. In particular, when used as axial yarns, aramid fibers effectively mitigate the level of damage during damage evolution.

Tensile properties of 3D multi-layer wrapping braided composite: Progressive damage analysis

An experimental and numerical study on mechanical properties and damage behavior of 3D multi-layer wrapping braided composite under axial tensile load is presented. The braiding process of this material is introduced and its tensile properties are obtained in tensile tests. Numerical simulations employ periodical boundary conditions, with interface elements between yarns and matrix added to improve the accuracy of prediction. 3D Hashin-type criteria and Von-Mises stress criterion are employed as damage initiation criteria for yarns and matrix, respectively. The obtained numerical results show a good agreement with the experimental data. The load-bearing capacity and failure mechanisms of 3D multi-layer wrapping braided composites under axial tensile loading are also discussed. A stress distribution shows that the axial yarns are the main load-bearing component of the composite. The main failure mode of the yarns is the yarn-matrix tensile cracking in the width direction, followed by the yarn-matrix tensile cracking in the thickness direction and fibre tensile failure. When the fibres in axial yarns begin to break, the material loses its load-bearing capacity.

Progressive damage analysis of three-dimensional braided composites under flexural load by micro-CT and acoustic emission

The effect of the load-bearing direction on the progressive bending damage of three-dimensional (3D) five-directional braided composites remains to be further discussed. To address this issue, two kind of samples, longitudinal and transverse, are experimentally tested three-point bending method. Simultaneously, the damage evolution behaviors are monitored by acoustic emission (AE) technology. Furthermore, X-ray micro-computed tomography (micro-CT) techniques are employed to identify the internal damage initiation/evolution and distribution characteristics of 3D braided composites. The microscopic damage morphology observed by micro-CT can be well correlated with the variation characteristics of the collected AE parameters. Through analyzing the experimental results, the damage of the longitudinally load-bearing specimen is mainly caused by the damage of the fiber and yarn, while the damage forms of transverse load-bearing materials are mainly fiber slip, interface debonding, matrix cracking and fiber fracture. Since the axial yarns and braided fibers of the longitudinal load-bearing specimens have played a supporting role, the bearing performance and the deformation resistance are superior to the transverse load-bearing material. The proposed combination of AE and micro-CT can provide a reference for monitoring the damage process and predicting the failure.

Fatigue Behaviour of Triaxial Braided Composites under Tension-Tension and Compression-Compression Loading

The fatigue behaviour of [0°/±45°] triaxial braided composites is investigated. Tension-tension and compression-compression loading is chosen to study main damage mechanisms and their effect on the stiffness degradation. In both cyclic loading cases a high stiffness degradation can be observed shortly after the start of cyclic loading. Inter-fibre fractures in the braid yarns with subsequent delaminations are responsible for this behaviour during tension-tension loading. Compression-compression loading leads to kink band formation in the axial yarns favoured by yarn undulations. In consequence of the observed material degradation, S-N curves based on a defined level of stiffness degradation are proposed for fatigue dimensioning instead of load cycles to fracture.

Effect of carrier configuration on the 3D four-directional and full five-directional rotary braided fabric structures

3D rotary braiding process has high flexibility to fabricate various fabric structures which lead to different mechanical properties of composites, but the carrier configuration, a key variable, has not been elucidated. This paper reveals its effect on the braided fabric structures. Potential carrier configurations are discussed and topological models are established based on representative braiding patterns. Yarn geometries are derived according to the mechanism of yarn squeezing, then unit cells are identified. Interior unit cells show total different yarn topologies, which demonstrates that either four-step or surface-core braids can be produced by rotary method. The dimension, yarn orientation and fiber volume fraction have close correlations to carrier configurations, which is attributed to the interlacing density in braiding process. However, the addition of axial yarns in full five-directional fabrics leads to same yarn topology as to eliminate the difference.

Multi-scale ageing mechanisms of 3D four directional and five directional braided composites’ impact fracture behaviors under thermo-oxidative environment

Fracture behaviors of thermo-oxidative aged 3D braided composites are significantly affected by interfacial weakening and matrix degradation. Here we report the impact fracture behaviors of three-dimensional four direction (3D4d) and five directional (3D5d) braided composites under thermo-oxidative conditions. Specimens were exposed at hot air (180°C) for 2, 4, 8 and 16 days, respectively. The oxidation-induced crack widths in aged specimen surface were observed and analyzed. The impact fracture behaviors and damage evolutions of braided specimens were recorded with high-speed camera. Based on the test results, we established a multi-scale finite element analyses (FEA) model to reveal interface failure, stress distribution and energy absorption of virgin and aged specimens at microstructure level. The impact fracture behaviors of both different braided composites continuously decreased with increasing ageing time. The matrix degradation and interfacial weakening are main degradation mechanisms. In addition, the FEA results show that the impact fracture properties significantly depend on the braided structures. The braided preform is the main energy absorption component and the axial yarns contribute the highest energy absorption capacity. With the insertion of axial yarns, the 3D5d braided composites exhibit a better fracture resistance after thermo-oxidative ageing.

Unit cell modeling on torsion damage behavior of a novel three-dimensional integrated multilayer fabric-reinforced composite tubular structure

Torsion damage behaviors of composite tubes are key factors in the design of tube structures, such as transmission shafts. During service, torsion in the transmission shaft induces delamination damage. A novel three-dimensional fully integrated multilayer tubular fabric aimed to eliminate delamination was invented by authors. This fabric is in tubular form with several layers of crimp-free in-layer yarns oriented at prescribed orientations and fully interlocked by a set of through-layer yarns, which are often made of the same type of fibers as the in-layer yarns. We investigated torsion damage behaviors of the integrated fabric-reinforced composite tubes. The torque–torsion angle curves were obtained and the torsion damages were phenomenologically analyzed. A unit cell model of the integrated fabric composite circular tube was established to numerically reveal the torsion damage mechanisms. For optimizing the torsion behaviors, the axial yarns should have high stiffness and the binder yarn should have high strength. More specifically, the axial yarn should use carbon fiber tows, and high-strength polymer fiber tows could be used for the binder yarns.