3D Braided Composites Research Articles

Efficient multiscale analysis method for the compressive progressive damage of 3D braided composites based on FFT

A new efficient multiscale simulation method based on fast Fourier transform (FFT) is developed to analyze the nonlinear behaviors of three-dimensional four-directional braided composites under compressive loading which is the key concern for design in the engineering application. The braid yarns within the composites are represented by the microscale unidirectional representative volume element. Both in microscale and mesoscale, FFT method combined with damage theory is used to simulate the progressive damage and failure of the composites under external loadings, in which the interface between the fiber and matrix and fiber compression instability on the microscale and the shear nonlinearity of the braid yarns under compressive loading on the mesoscale are taken into account comprehensively in the computation model. It is verified that the compressive mechanical properties of the braided composites obtained by the efficient multiscale method are in better agreement with the experimental results.

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.

Numerical investigation of mesoscopic volumetric ablation of 3D braided charring composites

Owing to the complex mesoscopic structures, 3D braided charring composites for the thermal protection system (TPS) have the multi-scale and multi-physical high-temperature responses. The mesoscopic features can significantly affect the volumetric ablative behavior of the braided composites, which will be essential for the TPS design. To take into account the effect of mesoscopic structures on the volume ablation response, the thermo-physical properties of constituents within the braided composites are predicted using asymptotic averaging method. The volumetric ablation model of the braided composites considering the mesoscopic structures is proposed, which is calculated by finite volume method with a tightly coupled solving process. The effect of braid angles on the volumetric ablation responses of the braided composites are investigated. The maximum back temperature and the peak inner pressure of the braided composites decrease with the increase of the braid angle. The isothermal and isobaric surfaces of the braided composites under volumetric ablation exhibit complex characteristics and are not perpendicular to the heating direction, which may induce the complex thermal stress field within the composites. The study on mesoscopic volume ablation may be helpful to accurately predicting the ablation responses and guiding the material design of the braided charring composites.

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.

A coupled multi-scale method for predicting the viscoelastic behavior of resin-based 3D braided composites

A new alternative multi-scale calculation procedure was presented to characterize the time-dependent viscoelastic behaviors of resin-based three dimensional (3D) braided composites. The present investigation was processed based on micro-scale fiber/resin, meso-scale yarn/resin and macro-scale homogeneous composite. Integrating with the asymptotic expansion homogenization (AEH) method, the multi-scale physical fields in the three-scales is established, and the multi-phase finite element (MFE) method is adopted to overcome the difficulty in discretization for the heterogeneous structural models. The time-dependent stress relaxation responses under three-scales were particularly investigated by the coupling MFE-AEH multi-scale method. The time-dependent effective viscoelastic properties in the micro-sclae and meso-scale were also calculated by utilizing the Prony Series fitting to simplify the inverse Laplace transform. The accuracy and reliability are validated by the corresponding experimental and numerical results, the effects of braided angle and relaxation time on the viscoelastic properties of 3D braided composites were studied, respectively.

Open-Hole 3D Braided Composites Strength Prediction and Stress Analysis

The stress concentration caused by notches is a common engineering issue for composite structure application. 3D braided composite possess excellent damage tolerance compared to common laminates. The tensile properties of 3D braided composite with open-hole and un-notched were experimentally examined. The mechanic properties of 3D braided composite in other directions are predicted using FGM (Fabric Geometry Model) and finite element analysis. The stress distributions around the hole and perpendicular to the loading direction are analyzed based on Abaqus software. The simulation results were compared with Lekhnitskii's analytical study. The open-hole strength of 3D braided composite was predicted respectively using Average stress failure criteria, Point stress failure criteria (PSC), and also the progressive failure analysis based on different failure criteria. The predicted strength results were compared to the experimental values. The results show the PSC predicted strength matched the experiment, while the progressive failure analysis can predict the failure initiation, propagation and final failure mode.

Mesoscale progressive damage and strength analysis of three-dimensional braided composites under tension

Three-dimensional (3D) braided composites have broad development prospects in various industries. This paper establishes a real parametric finite element model (FEM) to conduct progressive damage analysis and strength prediction for 3D braided composites. 3D FEM is established with consideration of the cross-section deformations and surface contact of adjacent braiding yarns. Subsequently, 3D Hashin and maximum stress failure criteria are separately implemented as initiation damage criteria for yarn and matrix. Moreover, different damage modes are employed to predict progressive failure process of yarn and matrix. Lastly, the relationship of braiding parameters to strength was thoroughly analyzed and numerical predictions generated which were validated through the experimental data. The results demonstrate that stress–strain curves and strength values are closely related to the braiding angle and the fiber volume fraction. Moreover, damage evolutions show shear bands predominately occur in the surface of yarns for small braiding angles, while for large braiding angles, it mainly occurs in the yarn/yarn interface. The yarn damage for composites of low fiber volume fraction occurs on yarn/yarn junction and then extends to entire yarns, while for high fiber volume fraction, it takes place directly on entire yarns.

Novel processing technology and mesoscopic geometric modeling of a new three-dimensional (3D) braided composite and the study on its longitudinal mechanical properties

The paper investigates the processing technology and mechanical properties of a novel type of 3D-braided composite material, named as one-carry-two full five directional braided composite (1C2 3DF5d). The material differs from the conventional 3D-braided composites by doubling the number of braiding yarns in the cross section. This unique yarn architecture is achieved by the introduction of a novel yarn carrier path planning method and side (support) gear design on a rotary braiding machine. The proposed braiding machine and the preform manufacturing process are first compared to the established approaches in textile composite industry, namely the one-carry-one (1C1) method under a new classification scheme. A parametric representative unit cell (RUC) model of the new material is then established which reveals that the cross-section area is increased more than 58% compared to 1C1 braiding materials under the same braiding angle, and the fiber volume fraction is lower by 14%–16%. Damage propagation of the material under tensile and compressive loading conditions are simulated using finite element method based on the 3-d Hashin failure criterion. The longitudinal stiffness and strength of 1C2 3DF5d are compared to 1C1 3DF5d composites and demonstrate a reduction of more than 20% for both due to the lower fiber volume fractions. However, the loading carrying capability of the material is increased by 10%–20% due to the increased cross section area. The technology may serve as a new way to manufacture 3D-braided materials with large cross section and high load-carrying capabilities.

A novel surrogate modeling strategy of the mechanical properties of 3D braided composites

In this paper, a surrogate-based modeling methodology is developed and presented to predict the elastic properties of three dimensional (3D) four-directional braided composites. Using this approach, the prediction process becomes feasible with only a limited number of training points. The surrogate models constructed using Finite Element (FE) method and Diffuse Approximation, reduce the computational time and cost for preparing experimental samples. In the FE model, multiscale method is applied to couple the computations of elastic properties at microscale and mesoscale. Subsequently, a parametric study is performed to analyze the effects of the three design parameters on the elastic properties. Satisfactory results are obtained via the surrogate-based modeling predictions, which are compared with the experimental measurements. Moreover, the predictions obtained from surrogate models concur well with the FE predictions. This study orients a new direction for predicting the mechanical properties based on surrogate models which can effectively reduce the sample preparation cost and computational efforts.

Temperature and structure effects on the impact damage distribution of 3D braided composites

Three-dimensional braided composite materials are prepared by fiber bundle braiding and composite material forming. These materials can realize the integration of material structure to manufacture complex structural parts in a near net-shape way and reduce the number of assembly connections. This material has been widely used in the aerospace industry, high-speed vehicles, and important civil facilities. Computed tomography (CT) and finite element method (FEM) were used to characterize the relationship between the internal damage distribution of 3D braided carbon fiber/epoxy resin composites under multiple transverse impact loading, ambient temperature, and microstructure. It is determined that with an increase in the temperature, the failure mode of resin changes from brittle failure to ductile failure, the interface bond strength decreases, and the failure mode changes to fiber/resin interface cracking and resin debonding. With an increase in the braiding angle, the failure mode changes from interface cracking to resin debonding cracking; interface cracking simultaneously occurs, impact tolerance increases, and local temperature increases with an increase in the absorbed energy. With an increase in the number of impacts, the accumulation of impact damage leads to the clear cumulative effect of reinforcement deformation, interface cracking, and resin debonding.

Analysis of internal defects in 3D braided composites based on ultrasonic C-scan technique

Defects can form within 3D braided composites as a result of their special production processes, which can affect the mechanical performance of the composites. Thus, it is absolutely essential to test for and analyse different types of defect. This paper reports on the detection of specific artificial defects in 3D braided composites, assessed using an ultrasonic system with typical examination techniques for non-destructive testing (NDT) and employing an ultrasonic C-scan technique to identify the artificial defects. Eight types of artificial defect are embedded and detected in these 3D braided composites. The study shows that this ultrasonic C-scan technique is an effective tool for inspecting the state of failure of 3D braided composites.

A data-driven self-consistent clustering analysis for the progressive damage behavior of 3D braided composites

A data-driven self-consistent clustering analysis (SCA) method is applied to investigate the progressive damage behavior of 3D braided composites. The SCA-based method is split into the offline stage and the online stage. In the offline stage, the high fidelity RVE is compressed into a reduced RVE composed of several clusters. In the online stage, the mechanical responses are calculated by solving the discretized Lippmann-Schwinger integral equation. To validate the accuracy of proposed model, the SCA-based simulation is compared with the corresponding experiments and finite element analysis (FEA). The results show that the SCA method can accurately capture the stress and damage distribution, and the predictive stiffness and strength agree well with experimental data. More importantly, with the same constitutive laws and geometric model, SCA only takes a few hundred seconds, which is 1771 times faster than FEA. Because of the high efficiency, the SCA has the potential to be applied in concurrent multiscale analysis for braided composites.

Prediction of mechanical properties on 3D braided composites with void defects

Void defects have appeared inevitably during the manufacturing process of braided composites, which directly affect the mechanical properties and strength of braided composites. First, the influence of internal void and porosity on the mechanical properties of resin was predicted. Second, the evolution in the mechanical properties of three dimensional (3D) braided composites was obtained using the Mori-Tanaka method. Finally, the strength prediction, failure mode, stress and strain field of 3D braided composites with void defects were investigated by means of finite element simulation based on the progressive damage theory in ABAQUS, which will compare the simulation results with the theoretical results and other scholar's experiments. The innovation of this work is to establish the constitutive model and finite element model of 3D braided composite material with voids and predict the evolution of the mechanical properties of 3D braided composite material with defects. The results will provide the theoretical and design basis for evaluating the influence of void defects on the mechanical properties of 3D braided composites.

A hierarchical multiscale model for the elastic-plastic damage behavior of 3D braided composites at high temperature

A hierarchical multiscale model is established to reveal the failure mechanism of three-dimensional (3D) braided composites at high temperature. Firstly, the tensile and bending tests of the composites were performed at three different temperatures, and the properties of microscale constituents, i.e., carbon fiber, epoxy resin and interface, were also calibrated by experiments at different temperatures. Then, the elastic-plastic damage constitutive laws were proposed to characterize the mechanical behavior of microscale and mesoscale components. These constitutive models were implemented by a user-defined subroutine UMAT in ABAQUS. Finally, based on the homogenization procedure and the multiscale analysis method, the effects of temperature on microscale, mesoscale and macroscale properties of 3D braided composites were analyzed sequentially. The results showed that the temperature has the significant effects on the performances of 3D braided composites. With the increase of temperature, the properties of 3D braided composites decreased, and the failure modes changed from fiber breakage to matrix plastic deformation. Besides, the macroscopic simulation of strain fields agreed well with the DIC measurements and the temperature-dependent failure modes agreed well with SEM observation. It is expected that the established multiscale framework can predict high-temperature behavior of 3D braided composites and reveal the different failure mechanisms at different temperatures.

Mesoscopic simulation on curing deformation and residual stresses of 3D braided composites

Both cure deformations and residual stresses of 3D braided composites are studied based on the representative volume element (RVE) by means of thermochemical and thermodynamic model. First, the curing analysis model of cubic braided RVE is established, and the HETVAL, UMAT, UEXPAN and USDFLD subroutines are used to define the properties of the resin and the fiber about curing reaction kinetic, thermal conductive and viscoelastic model, respectively. Second, both thermochemical and thermodynamic behaviors of the RVE in 3D braided composites are simulated and analyzed which indicates the relationship among curing process, deformation and residual stress in mesoscopic scale. Finally, the influences of temperature rising rate and curing temperature on degree of curing, curing deformation and residual stresses of 3D braided composites under different curing process are investigated. These results will play an important role for designing curing technology and evaluating the residual stress in 3D braided composites.

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.

Multi-scale elastic property prediction of 3D five-directional braided composites considering pore defects

Pore defects are unavoidable in 3D braided composites, and can highly reduce the mechanical performance. In this paper, multi-scale analyses are conducted to investigate the effects of pore defects on elastic constants for 3D five-directional braided composites. A modified Chamis model is proposed to calculate elastic properties of yarns with pore defects and validated by the finite element method (FEM). The representative volume cell (RVC) with pore defects is established to predict elastic constants of braided composites, and results are compared with those by experiments and full-scale conventional model. Also, how voids influence elastic properties of yarns and braided composites are fully discussed. Furthermore, the homogenized full-scale model is developed in order to evaluate the possibility and facility in macroscopic performance characterization of braded composites with void defects. Results show that the analytical model is efficient and accurate in elastic property calculation of yarns. It is proper to predict elastic performance of braided composites by RVC with voids. The conclusion indicates elastic properties of yarns and braided composites are significantly influenced by voids. The full-scale conventional modeling of braided composites with voids is extremely complex and time-consuming, which can be solved by the homogenization method to a great extent.

Study on Microstructures of 2D and 3D Chemical Vapor Infiltration SiC/SiC Composites

The chemical vapor infiltration (CVI) SiC/SiC composites are porous materials, and the porosity affects the molten salt infiltration and may affect the mechanical properties. Therefore, the internal microstructures of the 2D and 3D silicon carbide composites are studied by synchrotron radiation micro‐computed tomography (micro‐CT) technology. The cross‐sectional slice and 3D volume image of the composite are reconstructed, then the pores of the composites are visualized in three dimensions, and the porosity is quantitatively analyzed. The results indicate that most of small pores (micrometer) exist between filaments and larger pores (millimeter) occur between fiber bundles, and the internal pores of 2D and 3D composites are greatly influenced by the fabric structure. In contrast, the 3D braided composites have lower porosity, smaller pore distribution fluctuations, and more stable internal structure.

Modeling the coupling effects of braiding structure and thermo-oxidative aging on the high-speed impact responses of 3D braided composites

Abstract We proposed a thermo-mechanical coupled model to better understand the coupling effects of thermo-oxidative aging and braiding structure on the high-speed impact responses of 3D braided carbon fiber reinforced epoxy composite. The impact responses of the aged and unaged braided composites with different braiding structures were experimentally and numerically investigated. We found that both thermo-oxidative aging and braiding structure have a significant influence on the impact responses of braided composites, and they also affect each other. Stress, adiabatic temperature rise, thermal strain and thermal stress of composites will decrease after aging, while increase with the increase of braiding angle. Increasing the braiding angle of the braided composite can effectively reduce the effect of thermo-oxidative aging on the impact responses. When the braiding angle is 42, the mechanical properties and damage of the composites are almost unaffected by thermo-oxidative aging, but the thermal stress in the impact process decreases significantly after aging.