Three-dimensional Braided Composites Research Articles

Investigation of the dynamic compression behavior of 3D braided composites based on a virtual fiber embedding method

The three-dimensional braided composites (3DBCs) possess a complex spatial structure, which can lead to microscopic deformation of fibers under high-speed impact. This paper proposes a quasi-fiber scale model using virtual fiber-embedded (VFE) method to simulate the impact behavior and failure of 3DBCs. The results reveal that the maximum eccentricity of the VFE model yarn cross-section is 0.318, representing a 194% improvement compared to solid yarns. According to the characteristics of damage, it can be deduced that interactions among fibers play a pivotal role in determining the failure behavior of composites, particularly concerning non-linear changes. The modulus, strength and the time of initial damage rise with an increasing braiding angle, whereas the resin stress, yarn stress, and degree of damage exhibit opposite trends. The stress distribution over the braiding path shows that the main load-bearing component at 20° braiding angles is internal yarns, whereas the surface yarns take precedence at 40°. The maximum deformation of the yarn cross-section always occurs at the center of the shear band, with a maximum eccentricity of 0.456 at 20° braiding angles. The deformation in yarn flexing and cross-section flattening cause an uneven distribution of stress and strain, leading to localized damage and ultimately catastrophic destruction.

Fatigue damage evolution and residual strength analysis of 3D5D braided composites using X-ray computed tomography, acoustic emission, and digital image correlation

The accumulation of fatigue damage leads to continuous degradation of the residual strength of three-dimensional braided composites, directly determining the fatigue life. However, the inability to continuously collect residual strength and multiple damage modes pose a challenge to study the residual strength degradation mechanisms of three-dimensional braided composites. In this work, digital image correlation and acoustic emission techniques are employed to assess the strain field and damage events of the specimens during the residual strength tests. X-ray computed tomography facilitates the visualization and quantification of the fatigue damage evolution in three-dimensional braided composites. Moreover, the “two-step” damage classification method is applied to isolate the damage mechanisms. The Pearson correlation analysis is preformed between the quantitative results of three non-destructive techniques and residual strength degradation of 3D braided composites. The integration of the outcomes provides a comprehensive depiction of the residual strength degradation mechanisms.

Towards accurate prediction of the dynamic behavior and failure mechanisms of three-dimensional braided composites: A multiscale analysis scheme

In this paper, a dynamic multiscale model is proposed for three-dimensional four-directional (3D4D) braided composites, considering the effects of strain rate and shear enhanced failure mechanism. The strain rate-dependent constitutive models are established for both resin and yarns. The accuracy of the yarn model is validated by comparing the simulated stress-strain curves with the experimental results obtained from the Split Hopkinson Pressure Bar (SHPB) tests with various strain rates. The shear enhancement coefficient of the yarn is determined from the failure envelopes with a discussion of crack propagation angles. The results show that, based on the calculated microscale properties, the mesoscale model accurately predicts both the longitudinal and transverse compressive strain-stress behavior of 3D4D braided composites at different strain rates. A comparative analysis reveals that the shear-enhanced failure model achieves a better prediction compared with other counterparts, such as Hashin-Rotem and Tsai-Wu Models. The proposed dynamic multiscale scheme for 3D braided composites is an efficient and accurate tool to characterize their multiscale features and strain rate-dependent behavior.

Experimental Analysis of the Low-Velocity Impact and CAI Properties of 3D Four-Directional Braided Composites after Hygrothermal Aging.

Three-dimensional braided composites (3D-BCs) have better specific strength and stiffness than two-dimensional planar composites (2D-PCs), so they are widely used in modern industrial fields. In this paper, two kinds of 3D four-directional braided composites (3D4d-BCs) with different braided angles (15°, denoted as H15, and 30°, denoted as H30) were subjected to hydrothermal aging treatments, low-velocity impact (LVI) tests, and compression after impact (CAI) tests under different conditions. This study systematically studied the hygroscopic behavior and the effect of hygrothermal aging on the mechanical properties of 3D4d-BC. The results show that higher temperatures and smaller weaving angles can significantly improve the moisture absorption equilibrium content. When the moisture absorption content is balanced, the energy absorption effect of 3D4d-BC is better, but the integrity and residual compression rate will be reduced. Due to the intervention of oxygen molecules, the interface properties between the matrix and the composite material will be reduced, so the compressive strength will be further reduced. In the LVI test, the peak impact load of H15 is low. In CAI tests, the failure of H15 mainly occurs on the side, and the failure form is buckling failure. The main failure direction of H30 is 45° shear failure.

Electro-Mechanical Coupling Analysis of L-Shaped Three-Dimensional Braided Piezoelectric Composites Vibration Energy Harvester.

In this article, an L-shaped three-dimensional (3D) braided piezoelectric composite energy harvester (BPCEH) is established, which consists of an elastic layer composed of a 3D braided composite, flanked by upper and lower layers of piezoelectric material and two tuning mass blocks. Glass fiber and epoxy resin are used to produce a 3D braided composite. This L-shaped 3D BPCEH is mechanically designable and can be adapted to different work requirements by varying the braided angle of the 3D braided composite layer. The material parameters of 3D braided composites are predicted for different braided angles by means of a representative volume element (RVE). Electro-mechanical coupled vibration equations for the L-shaped 3D BPCEH are established. The impact of braided angles on voltage and power output is discussed in this article. Simulations using finite element method are conducted to analyze the voltage and power output responses at various braided angles. In addition, the effects of the mass of mass block B and the length of the beam on the output performance of the L-shaped 3D BPCEH are analyzed.

Research on foldable two-matrix 3D braided composites: Manufacturing and bending progressive damage

Research on foldable two-matrix 3D braided composites: Manufacturing and bending progressive damage

A novel modeling method to study compressive behaviors of 3D braided composites considering effects of fiber breakage and waviness defects

Fiber breakage and waviness defects are two significant and inevitable defects existing in three-dimensional braided composites (3DBCs). This work proposed a new method to create the numerical model containing fiber breakage and waviness defects at the micro-scale level according to experimental characterization results. The experimental tests of 3DBCs with various braiding angles and matrix types are then designed to verify the reliability and adaptability of the model. The results indicate that the fiber breakage and waviness defects both gave rise to an apparent decrease in the axial mechanical properties of the unidirectional and braided composites. The influences of two kinds of defects on 3DBCs are also related to the braiding angles. In addition, the effect of matrix type on the 3DBC is apparent that should not be neglected. The primary reasons of the change of compressive properties of 3DBCs with different matrix types are the variations of the matrix and interfacial properties. The proposed modeling method in this work can be extended for those composites that include a large quantity of fiber breakage and waviness defects.

A new progressive fatigue damage model for the three-dimensional braided composites subjected to locally-variable-amplitude loading

The fatigue-induced stress redistribution in three-dimensional (3D) braided composites, even when subjected to externally constant-amplitude fatigue loads, results in locally-variable-amplitude fatigue loading, significantly impacting their fatigue performance degradation. This paper is aimed to propose a novel fatigue damage analysis method to predict the fatigue behavior of 3D braided composites subjected to locally-variable-amplitude loading. To this end, the continuous damage method, residual strength, residual stiffness, and fatigue life models are combined to characterize the properties degradation of 3D braided composites with cycling. Once stress redistribution occurs, the fatigue properties degrade based on the new stress level, and the equivalent cycle number is recalculated accordingly. As the material undergoes different cycle blocks, damage accumulates, ultimately leading to failure when the overall stiffness of the material degrades to 80%. Traditional fatigue models are also employed to predict the fatigue behavior of representative volume elements for comparison. The results predicted by the present model shows good agreement with experiments. Furthermore, the influence of stress levels and architectures of 3D braided composites on fatigue performance is systematically discussed.

Mode I fracture mechanisms and crack evolution behavior of three-dimensional braided composites

Three-dimensional braided composites possess higher inter-laminar fracture toughness than two-dimensional laminates, while the mode I fracture toughness behavior of three-dimensional braided composites is still unknown. Here we report mode I fracture behavior of three-dimensional braided carbon fiber/epoxy composites tested with the double-cantilever beam method. The samples with a pre-crack were tested using the MTS device, and the fracture process was recorded to calculate the fracture toughness. The effects of different loading rates on fracture behavior were compared. The strain field at the crack tip was obtained by the digital image correlation technique. The damage morphologies were scanned by X-ray microcomputer tomography. It was found that the bridging effect of braiding yarns prevents cracks from initiation and propagation, while the intertwining points of the braiding structure cause crack bifurcation. The braided architecture provides an effective way to hinder crack propagation. The stiffness of composites tends to decrease as the loading rate rises. The higher loading rate results in a lower critical load level for crack propagation and reduces fracture toughness. The results show that the three-dimensional braided structure is an effective method for increasing the fracture toughness. We hope the results can be used for the design of higher fracture toughness composite structures.

Improved unit cells to predict anisotropic thermal conductivity of three-dimensional four-directional braided composites by Monte-Carlo method

The analysis of 3D4d braided composites is challenging due to its complicated mesostructure. A parameterized modified three-dimensional four-directional (3D4d) braided composites unit cell model is developed in this work, along with a high-precision computation approach for it. A parametric representative volume element (RVE) method for three-dimensional braided composites is established, which is based on the coupling braiding parameters and discrete anisotropic characteristics. Additionally, a Monte-Carlo cycle framework for performing random effect verification of defects is established. To accomplish high-precision computation of effective thermal conductivity (ETC), the methodologies described in this paper include RVE unit modeling, yarns' anisotropy treatment and probability statistics on porosity can be applied to any multidirectional braided and heterogeneous materials. The ETCs of 3D4d braided composites with various fiber volume fractions, braiding angles and porosities are evaluated by the methodologies. The results demonstrate that the relative errors between the simulation results and the available experimental data are all limited within 2.8%, the thermophysical properties of 3D4d braided composites are obviously anisotropic and that the variation of ETCs with parameters exhibit quasi linear and divergent distribution characteristics. This work proposes and verifies two influence mechanisms of porosity on composites, which also provide a possibility to realize composites properties' interval estimate.

A novel bottom-up methodology for design and fabrication of three-dimensional braided hybrid composites based on the law of yarn routing and grouping

A hybrid is an effective means to improve the comprehensive properties of composites. In the current article, by investigating the yarn routing and grouping law in three-dimensional braiding, a novel bottom-up methodology for the design and fabrication of three-dimensional braided hybrid composites is proposed based on the [ m, m] hybrid unit. Three-dimensional braided hybrid composites with different sizes of hybrid unit were prepared and drop-hammer based impact tests were conducted to study the composites' dynamic mechanical performances. It was found that the three-dimensional braided hybrid composites based on the bottom-up methodology present much better structural integrity and toughness than conventional ply-stacked hybrid counterparts and significant dependence of mechanical performances on the size of hybrid unit. We found that the smaller the size of hybrid unit, the better the mechanical performance. The results demonstrated the feasibility and effectiveness of the proposed bottom-up methodology and could enable the design and fabrication of three-dimensional braided preforms and composites with certain well designed structures and functions.

Visualization and quantification of low-velocity impact damage of three-dimensional braided CFRP composites by micro-computed tomography

In this paper, the low-velocity impact response and damage of three-dimensional five-directional (3D5d) braided carbon/epoxy composites under different energies (30 J, 65 J, 100 J) are studied. Importantly, the damage is segmented from the axial and radial directions of the yarn to visualize and quantify the damage distributions in different regions based on micro-CT. The results show that as compared with the samples under 30 J and 100 J, the samples under 65 J energy perform higher impact properties. Moreover, as the impact energy increases from 30 J to 100 J, the corresponding damage volume increases from 6.886 mm3 to 477.133 mm3. Furthermore, the damage distributions are almost symmetrical in space.

Electrical-mechanical behaviors of three-dimensional braided composites under three-point bending

Electrical responses of three-dimensional braided composites under mechanical loads are important for the design of structural health monitoring in real time. Here we reported electrical properties and electrical-mechanical behaviors of three-dimensional braided composites with different braiding angles under three-point bending load, and investigated the correlation between electrical resistance and damage of the three-dimensional braided composites. We found that change of resistance reflected damage modes of the composite. In addition, we proposed an electrical-mechanical model to explain the resistance changes of three-dimensional braided composites based on the Weibull distribution function. The results of the model verify the effectiveness and rationality of the experimental results under bending load, which provides a theoretical basis for the structural health monitoring of three-dimensional braided composites through a electrical resistance change method.

Progressive damage and failure analysis of three-dimensional braided composites under multiaxial loadings

A meso-mechanical computational model based on the finite element method (FEM) is developed to predict the progressive elastic-plastic damage and failure behavior of three-dimensional four directional (3D4D) braided composites under multiaxial loadings. Firstly, the constitutive laws for mesoscale constituents (i.e. yarn, matrix and interface) of braided representative volume element (RVE) are established and implemented by the user defined material subroutine UMAT in ABAQUS. Then, how to build the braided RVE and conduct the simulation are introduced. After that, the uniaxial tensile data is used to verify the proposed model. Finally, the damage and failure behavior of the RVE under multiaxial loadings is investigated, considering the effects of loading paths and interface. The results show that loading path and interface have little effect on the strengths. The predicted failure envelopes in different stress spaces for RVE are compared with the Tsai-Wu and Hoffman theories, which are much closer to the Tsai-Wu theory.

Three-dimensional braided composites as innovative smart structural reinforcements

This study is a systematic effort focused on the development of feasible self-sensing braided composite rods (BCRs) for structural reinforcement and damage monitoring. In this route, BCRs were produced and reinforced with different carbon-based conductive fillers, including hybrid carbon nanotubes (CNTs)/graphene nanoplatelets (GNPs), chopped carbon fibres (CCFs), and directed (unidirectional) carbon fibres (DCFs) using a specific process. The mechanical and self-sensing performances of the BCRs were evaluated using various tests. Furthermore, a honeycomb 3D system of DCF/BCRs was used to reinforce a 100 mm × 100 mm × 850 mm concrete beam, and the piezoresistivity of the specimen was investigated under cyclic flexural loading with different patterns. The maximum tensile strength and elastic modulus were observed for the BCR reinforced with 1.0% (wt) CCFs. However, the maximum sensitivity was attained for the BCRs with 3.0% hybrid CNTs/GNPs. The analysis of the results and economic assessment showed that DCF-reinforced BCRs are the optimum choice for developing a feasible, reliable, and economic structural health monitoring technique.

Effect of Braiding Architectures on the Mechanical and Failure Behavior of 3D Braided Composites: Experimental Investigation.

Benefiting from the multi-directional load-bearing capability, the three-dimensional braided composites (3DBC) have found a wide application in primary structures. It is therefore of great importance to fully understand their mechanical behavior and failure modes. In the present paper, the tensile and compressive tests were carried out, according to standardized testing methods, for eight types of 3DBC, which were manufactured by resin transfer molding (RTM). It was found that the mechanical properties of the 3DBCs decreased with an increasing braiding angle. When the braiding angle was 20°, 3D 5-directional braided composite (3D5dBC) exhibited the best mechanical properties, while for the braiding angle of 40°, the mechanical properties of 3D6dBC were the most prominent. Moreover, the tensile strength of the 3DBCs is approximately two times as much as the compressive strength; however, the compressive modulus is always 10% higher than the tensile modulus. The failure modes of the 3DBCs with a braiding angle of 20°greatly depended on the braiding structures. However, they tend to be consistent when the braiding angle increases to 40°.

A label-free amperometric immunosensor with improved electrocatalytic 3D braided AuPtCu-SWCNTs@MoS2-rGO for human growth differentiation factor-15 detection.

Growth differentiation factor-15 (GDF-15) is a member of the transforming growth factor-β family. GDF-15 is overexpressed in cardiovascular diseases and has become a novel biomarker for these diseases. In this study, we fabricated a label-free electrochemical immunosensor for sensitive detection of GDF-15. Briefly, a three-dimensional braided composite of AuPtCu-SWCNTs@MoS2-rGO (denoted A@M), which served as a label-free immunosensor platform, was obtained by wrapping single-walled carbon nanotubes (SWCNTs) with trimetallic nanoflowers (AuPtCu NFs) woven on a three-dimensional network nanostructure composed of Molybdenum disulfide (MoS2) and reduced graphene oxide (rGO) nanosheets. This optimization improved the ability of the platform to immobilize antibodies, accelerated the reduction of hydrogen peroxide, and promoted the migration rate of electrons on the electrode surface, thereby further amplifying the electrical signal and improving the sensitivity. The constructed sensor exhibited high sensitivity over a wide linear range from 1 pg mL-1 to 50 ng mL-1, with a low detection limit of 0.825 pg mL-1 for GDF-15. The fabricated label-free immunosensor exhibits satisfactory reproducibility, selectivity, and stability. The detection of actual samples was successful, enabling a broad scope of application in the early diagnosis, prognosis, and treatment of cardiovascular diseases.

Full-field strain and temperature evolution of electroactive three-dimensional braided thermoplastic shape memory composites

Three-dimensional (3D) braided shape memory polymer composites (SMPCs), combining braided structure with stimuli-responsive shape memory polymers, have broad potential for intelligent material design. We fabricated the 3D braided SMPCs with different braiding angles (15°, 25°, 35°) using a pre-impregnation method. The dynamic thermomechanical behaviors, three-point bending properties, recovery force, and shape memory behaviors were characterized. The full-field strain and temperature evolution during recovery have been recorded with 3D digital image correlation (DIC) technique and infrared camera. We found that the storage modulus, flexural modulus, and recovery force increase with the braiding angle decreased. The samples with the smaller braiding angle recover faster than that of the samples with bigger braiding angle. The shape recovery of the samples with 15° braiding angle occurred before being heated to the glass transition temperature. It is expected that the 3D braided SMPCs could be applied to smart structural design.

Strain-Sensing Characteristics of Carbon Nanotube Yarns Embedded in Three-Dimensional Braided Composites under Cyclic Loading

Carbon nanotube yarns are embedded in three-dimensional (3D) braided composites with five-axis yarns, which are used as strain sensors to monitor the damage of 3D braided composites. In the cyclic mechanical loading experiment, the strain-sensing characteristics of 3D braided composites were studied by in situ measuring the resistance change of the embedded carbon nanotube yarn. The 3D five-directional braided composite prefabricated part based on carbon nanotube yarns was developed, and the progressive damage accumulation experiments were carried out on carbon nanotube yarns and specimens embedded in carbon nanotube yarns. The research results show that there is a good correlation between the change of relative resistance of the carbon nanotube yarn and the strain of the composite specimen during cyclic loading and unloading. When the tensile degree of the specimen increases beyond a certain range, the carbon nanotube yarn sensor embedded in the specimen shows resistance hysteresis and produces residual resistance. Therefore, the fiber can better monitor the progressive damage accumulation of 3D five-direction braided composites.

Effects of structural defects on low-velocity impact damage mechanisms of three-dimensional braided composites based on X-ray micro-computed tomography

This paper presents the influence of the braiding structural defects on the low-velocity impact damage mechanisms of three-dimensional (3D) braided carbon/epoxy composites. The braiding structural defects are formed by reducing-yarn process. Also, for the samples with and without reducing-yarn defects, two kinds of braided angles, 20° and 40°, are selected, respectively. All the samples are experimentally tested via drop-weight impact method. X-ray micro-computed tomography (micro-CT) techniques are employed to identify the internal damage characteristics. The results show that the structural defects significantly influence the impact mechanical properties of 3D braided composites. Compared to non-defect samples, 3D braided composites with reducing-yarn defects exhibit lower loads and less response time. Moreover, the 40° samples exhibit lighter damage and less damage volume than that of the 20° samples.