Properties Of 3D Braided Composites Research Articles

An effective multiscale analysis for the mechanical properties of 3D braided composites considering pore defects

An effective multiscale analysis for the mechanical properties of 3D braided composites considering pore defects

Mechanical properties of modified aramid three‐dimensional braided composites

AbstractThree‐dimensional (3D) braided composites have good integrity and high stability, but aramid fiber (AF) has an inert surface and poor interfacial bonding with resin, which affects the mechanical properties of aramid 3D braided composites and limits their development. This paper used catechol/pyrogallol polyamine (CA/PGPA) to modify the AF. The effects of different mass fraction ratios of CA/PGPA and different reaction temperatures on the surface properties of AF and the mechanical properties of 3D braided composites were investigated. The results showed that after the CA/PGPA modification, fiber surface oxygen‐containing groups increased, the roughness became more extensive, the fiber strength increased, and the interfacial shear strength increased. When AF‐CAPG‐II‐40°C, the mechanical properties of the 3D braided composites were improved most significantly. Compared with unmodified composites, the bending modulus was increased by 70%, the compression modulus by 124%, and the shear strength by 55.7%. The epoxy resin modification was carried out based on AF‐CAPG‐II‐40°C, and when the mass fraction of aramid nanofiber/graphene nanoparticle (ANF/G) was 0.7 wt%, 3D braided composites exhibited satisfactory mechanical properties. The bending modulus, compression modulus, and shear strength were increased by 15.3%, 23.3%, and 25.7%, respectively, compared with AF‐CAPG‐II‐40°C.

A New Cell Modeling Method to Calculate the Mechanical Properties of 3D Braided Composites

A New Cell Modeling Method to Calculate the Mechanical Properties of 3D Braided Composites

Hierarchical multi-scale analysis of the effect of varying fiber bundle geometric properties on the mechanical properties of 3D braided composites

A hierarchical multi-scale numerical model is developed to predict the effect of cross-sectional geometric properties on the mechanical response of three-dimensional (3D) braided composites. In this model, the effective properties are transferred from the fiber bundle scale to the mesoscale, and the finite element and analytical methods are used to predict the macroscopic mechanical properties. Damage evolution was evaluated, based on a continuous damage mechanics approach. A user-defined material subroutine (UMAT), in a nonlinear finite element analysis, has been developed to implement the proposed model and further determine the response and subsequent damage evolution in 3D braided composites subjected to quasi-static tension. The elastic properties of the composites are predicted using a hybrid multi-scale model. The agreement between the numerical simulations and the experimental results is good. It has been shown that the cross-sectional geometry of the fiber bundle properties has a significant influence on the tensile behavior of the composite, which is captured by the proposed multi-scale damage model. This research offers a theoretical analysis for selecting the optimized fiber bundle geometry for using in FE predictions of 3D braided composites.

Liquid nitrogen temperature effects on the mechanical behaviors of three-dimensional seven-directional braided composites

Three-dimensional (3D) braided composites are broadly adopted in aerospace cryogenic fuel tanks. This work designed and fabricated 3D seven-directional braided composites (3D7dBCs) with different braiding angles, and their compression properties at room and liquid nitrogen temperatures (RT and LNT) were explored and discussed, while the mechanical properties were compared with other braided structural composites. Temperatures and braiding angles considerably influenced the properties of 3D braided composites. The multi-directional compression strength of 3D7d21-LNT and 3D7d34-LNT was 392.7 MPa, 426.1 MPa, 270.3 MPa, 210.3 MPa, and 268.8 MPa, 204.1 MPa, which was 18.1% and 18.6% higher than that of 3D7d21-RT and 3D7d34-RT in the out-of-plane direction, 5.1% and 6.5% in the longitudinal direction, 74.2% and 9.7% in the transverse direction, whereas the longitudinal strength decreased as braiding angles increased, and the out-of-plane and transverse compression strength increased. Additionally, shear cracking was the main reason for the failure of 3D7dBCs at RT, while fiber loosening, pulling-out, and interfacial debonding were exhibited at LNT. Compared to 3D five-directional and 3D six-directional braided composites (3D5dBCs and 3D6dBCs), the incorporation of seventh yarns significantly improved the out-of-plane properties of 3D7dBCs.

Investigation on off-axial tensile properties of 3D braided composites considering void defects

3D braided composites have been increasingly applied in the aerospace, automotive, and other high-tech industries as primary load-bearing structures due to their excellent integrated performance. Evaluation on the failure behavior of 3D braided composites subjected to off-axial loading still remains a challenging topic. We present in this paper a meso-scale finite element (FE) model containing void defects for investigating the off-axial tensile behavior of 3D braided composites. The FE model is verified and the effects of porosity are discussed in on-axial tensile conditions, and then it is executed to predict the mechanical response in general off-axial tensile cases. The strength properties of 3D braided composites, and more importantly the progressive damage behavior under typical off-axial loadings, are analyzed in detail. It is found that the off-axial tensile strength and corresponding failure mode of 3D braided composites are mainly affected by the braiding angle of specimen. The proposed FE modeling provides an appropriate reference for the numerical study of void defects and off-axis load problems in other textile composites.

A parameterized unit cell model for 3D braided composites considering transverse braiding angle variation

In this paper, a parameterized unit cell model for 3D braided composites considering transverse braiding angle variation is proposed, to assist the mechanical characterization of such materials. According to the geometric characteristics of 3D braided composites, a method for automatically generating textile geometries based on practical braiding parameters, including the main braiding angle, the transverse braiding angle, and the fiber volume fraction, is established and implemented in a CAD software package. In this model, the addition of transverse braiding angle educes a more flexible control of fiber volume fraction distribution, and with the combination of control parameters according to the actual fiber distribution needs of users, it can suggest the appropriate parameters for the unit cell. The generated unit cell models are used in finite element analysis and the results are validated against experiments for a number of 3D braided composites in terms of fiber volume fraction and elastic constants, and good agreement is observed. Based on the parameterized unit cell model, the effects of main braiding parameters on the elastic properties of 3D braided composites are discussed.

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.

A higher-order three-scale reduced homogenization approach for nonlinear mechanical properties of 3D braided composites

A more effective higher-order three-scale reduced homogenization (HTRH) approach is developed for predicting the nonlinear mechanical properties of three-dimensional (3D) 4-directional braided composite. In this work, the 3D braided composites are considered by periodic distributions of different unit cells on microscale and mesoscale configurations. First, the various high-order unit cell functions based on the microscopic and mesoscopic domain are obtained by multiscale expansion methods. Then, two kinds of homogenization coefficients are given, and relative nonlinear homogenized equations are derived on the macroscopic domains. Further, the reduced order systems for the nonlinear multiscale problem are constructed. The significant features of the reduced-order multiscale method are: (i) an asymptotic higher-order homogenized solution evaluated by post-processing that does not need high-order continuities for the homogenization solutions, (ii) an effective model reduction format for investigating the higher-order nonlinear multiscale problems with less computational cost and (iii) an novel three-scale formulas established for analyzing the 3D braided composites. Finally, the validity of the proposed approach in comparison to the direct numerical simulations and classical multiphase method is computed on some damage and elasto-plastic problems. These numerical examples show that the HTRH method is effective to study the nonlinear problems of the 3D braided composites, and provides a potential application for practical engineering calculation.

Mechanical response and failure mechanism of three-dimensional braided composites under various strain-rate loadings by experimental and simulation research: a review

The high stiffness and great strength of three-dimensional (3D) braided composites mean they are widely used in the aerospace, marine and automotive industries. Three-dimensional braided composites exhibit very different mechanical responses under various strain-rate loadings (such as tensile, compression, punch and shearing) due to their complex structural characteristics. Studies under quasi-static and low strain-rate loadings predict the elasto-plastic properties of 3D braided composites, and research under high strain-rate loading has explored the conditions of industrial composites used in special environments. The investigation of the strain-rate effect can provide a sound database reference for engineering design. Through experiments and simulation analysis methods, this work reviews the braided structural effect, mechanical response and failure mechanism of 3D braided composites under various strain rates. Mechanical properties under different theoretical and structural models are reviewed and summarized. In particular, the damage evolution and stress propagation of 3D braided composites were revealed from both macroscopic and microscopic perspectives through finite element modeling.

Micro-mesoscopic prediction of void defect in 3D braided composites

Void defects will inevitably occur in 3D braided composites during Resin Transfer Molding (RTM) process, which may reduce mechanical properties of 3D braided composites. Therefore, this paper focuses on void generation in 3D braided composites and optimizes its manufacturing technology. First, the basic governing equations considering flow, temperature changing and resin curing process are derived to describe the conservation of momentum, energy and mass of resin during RTM process. Second, the whole RTM process for 3D braided preform cell is simulated by means of finite element method (FEM), which indicates the distribution of resin flow speed, pressure and void content. Third, influences of resin injection flow volume, outlet pressure, volatile content in resin and curing temperature on void distributions and contents in 3D braided composite cell are investigated. The results will provide theoretical basis for analyzing void generation and evaluating the quality of 3D braided composites made by RTM technology.

Micro-CT based trans-scale damage analysis of 3D braided composites with pore defects

Pore defects that inevitably produce during the manufacturing process, have distinct effects on the mechanical properties of 3D braided composites. A trans-scale method coupled with Micro-CT is developed to investigate the strength and damage behavior of 3D braided composites with pore defects. Pore defects and yarns are measured by Micro-CT and reconstructed. Then, the trans-scale finite element models are established on the Micro-CT data. The progressive damage model and cohesive-zone model are applied to simulate the damage behavior of braided composites, and effects of interface strength are also investigated. Effective properties of yarns are predicted by the micro-scale analysis and then transferred to conduct the meso-scale analysis. The meso-scale finite element model can predict the stress-strain response well, which has been validated by experiments. The failure modes of yarn damage, matrix cracking and interface debonding are recognized and correspond well with the final failure morphology of the sample. The damage appears around the pore defects and then develops to the weak region in the matrix. The interface properties show diverse influences on yarns and braided composites under different loading conditions. As experimentally demonstrated, the present research scheme can well capture the void features, and therefore efficiently predict the tensile behavior of 3D braided composites considering pore defects.

Crack spatial distributions and dynamic thermomechanical properties of 3D braided composites during thermal oxygen ageing

Thermal oxygen ageing behaviors of polymer matrix composites depend on resin and preform architecture. This paper concerns effects of braided architectures on thermo-oxidative ageing, including inner and surface crack initiations and propagations in 3D braided carbon fiber/epoxy composites. The ageing behaviors of unidirectional (UD) was also tested for comparison. Attenuated total reflectance Fourier transform infrared spectroscopy, two-dimensional infrared correlation spectrum, and micro-computer tomography technique have been used to characterize ageing behaviors. Aromatic formation was found ether on the surface of epoxy resin appeared prior to peroxide. The resin shrinkage could appear on the surface, and the changes of shrinkage rate of the UD composites and the 3D braided composites were consistent with cracks volume fraction. In addition, the cracks in the 3D braided composites initiated later and propagated slower than those in the UD composites. The 3D braided structure was beneficial for retaining the stiffness and damping properties after ageing.

Two-scale damage failure analysis of 3D braided composites considering pore defects

Pore defects tend to form in the manufacturing process, and significantly influence the mechanical properties of 3D braided composites. To predict the failure modes and strength properties considering pore defects, a two-scale progressive damage method coupled with representative volume cell (RVC) has been developed due to the periodic feature across different scales of 3D braided composites. Different void generating methods across two scales are established, including the element-model by elements chosen and the void-model by voids explicitly constructed. The user-defined material subroutine (UMAT) is coupled in the nonlinear finite element analysis software ABAQUS to implement the damage model for micro and meso numerical models. Also, the Chamis model considering pore defects are employed and verified. It shows that results by void-model agree well with the Chamis model and the experimental data. And, the void-model is superior to the element-model when predicting the mechanical properties of braided composites. The pore defects weaken the matrix properties, and therefore largely determine the strength and damage mechanism of 3D braided composites with large braiding angle. This two-scale damage failure analysis method by void-model is effective to predict strength and damage failure mechanism of 3D braided composites considering pore defects.

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.

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.

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.

Experimental investigation on the tensile and compressive properties of 3D 4-directional braided carbon fiber/epoxy resin composites in thermal environment

The longitudinal tensile and compressive experiments on 3D 4-directional braided carbon fiber/epoxy resin composites with three different braiding angles were performed in thermal environments. The effects of temperature on the longitudinal tensile and compressive properties of 3D braided composites were discussed. Macro fracture morphology and SEM micrographs were examined to understand the damage and failure mechanism. The results show that the longitudinal tensile strength of 3D 4-directional braided carbon fiber/epoxy resin composites goes up slightly and the longitudinal compressive strength decreases obviously with the increase of testing temperature. The braiding angle has no apparent impact on the longitudinal tensile failure characteristics of composites. However, the effect of braiding angle on the longitudinal compressive failure characteristics of composites is obvious. As the temperature increases, the damage and failure patterns of 3D braided composites with three different braiding angles are obviously different than in room.

A novel finite element method for predicting the tensile properties of 3D braided composites

A novel unit-cell model which considers the structure interference of braiding yarns in the external region is proposed to describe the geometric structure of 3D braided composites. Based on the multi-scale homogenization theory, mesoscopic structure finite element analysis model is established to predict the stiffness matrix of unit-cells. Periodic boundary conditions are applied on the periodic surfaces of unit-cells to reflect the repeating feature. And the node deformation matching equations are applied on the internal connected faces of the surface unit-cell and the corner-cell, so that the displacement continuity conditions and traction continuity conditions are satisfied. In allusion to 3D braided composites with small braiding angle, principal tensile strength forecasting model is developed.