MICRO MECHANICAL ANALYSIS OF 3-D WOVEN COMPOSITES

A micro mechanical model is carried out to predict micro stresses and macro elastic properties of 3-D woven composites. A unit cell is composed of two phases. One is fiber yarn and the other is resin or fiber yarn in transverse. The additional shearing introduced by bending of fiber yarn is considered. The method to determine the microstructure is also discussed. This model is applied to the analysis of a 3-D woven graphite/epoxy composite. Micro stresses of the cell are studied, and then macro modulus is obtained by employing the average method. The predictions agree well with experimental results.

Micro Mechanical Model of 3D Woven Composites

A combined beam model representing the periodicity of the microstructure and micro deformation of 3D woven composites is developed for predicting mechanical properties. The model considers the effects of off axial tension/compression and bending/shearing couplings as well as the mutual reactions of fiber yarns. The method determining microstructure by using woven parameters is described for a typical 3D woven composite material. An analytical cell, constructed by a minimum periodic section of yarn and interlayer matrix, is adopted. Micro stresses in the cell under in-plane tensile loading are obtained by using the proposed beam model and macro modulus is then obtained by the averaging method. Material tests and a 2D micro FEM analysis are made to evaluate this model. Analyses reveal that micro stress caused by tensile/bending coupling effect is not negligible in the stress analysis.

THREE-DIMENSIONAL EXACT MODELING OF GEOMETRIC AND MECHANICAL PROPERTIES OF WOVEN COMPOSITES

A formulation for the prediction of the influence of various parameters on the elastic moduli of three-dimensional （3D） orthogonally woven composites has been given. These parameters can be classified into different groups according to their properties, such as input design and material parameters, structural parameters etc. Some, by their nature, can be well controlled during the design and manufacture of the composite. The composite is assumed to be homogeneous and orthotropic macroscopically. With a selected representative unit cell and the stiffness model developed by author in 2000, the influence of all of these parameters can be determined. Results showing the influence of the main design geometric parameters are presented. They demonstrate that an optimal design is possible for the through-the-thickness stiffness of the composites. The methodology used can be generalized to predict the behavior of other kinds of 3D woven structures.

Hygrothermal effect on high-velocity impact resistance of woven composites

The woven glass fiber reinforced composites(GFRP)subjected to high-speed impact is investigated to identify the hygrothermal aging effect on the impact resistance.Both the hygrothermal aged and unaged glass/epoxy laminates are subjected to different impact velocities,which is confirmed as a sensitive factor for the failure modes and mechanisms.The results show the hygrothermal aging effect decreases the ballistic limit by 14.9%,but the influence on ballistic performance is limited within the impact velocity closed to the ballistic limit.The failure modes and energy dissipation mechanisms are confirmed to be slightly influenced by the hygrothermal aging effect.The hygrothermal aging effect induced localization of structural deformation and degradation of mechanical properties are the main reasons for the composite undergoing the same failure modes at smaller impact velocities.Based on the energy absorption mechanisms,analytical expressions predict the ballistic limit and energy absorption to reasonable accuracy,the underestimated total energy absorption results in a relatively poor agreement between the measured and predicted energy absorption efficiency.

Modified micro-mechanics based multiscale model for progressive failure prediction of 2D twill woven composites

To consider fiber random distribution at the microscale for the multiscale model based on the micro-mechanics failure(MMF)theory,clustering method is used for the extraction of amplification factors.As the clustering method is a kind of unsupervised machine learning method,the elements with similar mechanical behavior under external loading can be included in a cluster automatically at the microscale.With this modification,the fiber random distribution model can be used for multiscale damage analysis in the framework of MMF theory.To validate the modified multiscale analysis method,progressive damage analysis of a kind of 2D twill woven composites is conducted based on different microscale models.The stress values for microscale models with fiber hexagonal and random distribution patterns are compared first.Much higher stress concentration is generated in the fiber random distribution model due to the smaller inter-fiber distance especially under longitudinal shear loading.The obtained cluster distribution results exhibit the characters of the stress distribution in the two microscale models.Thereafter,tensile and compressive responses of the 2D twill woven composite are predicted with the modified multiscale analysis method and accuracy of the method is verified through comparison with published experimental results.From the simulation results,it can be found that the matrix damage initiation from the model based on the fiber random distribution model is premature compared with that from the model based on the fiber hexagonal distribution model.Besides,under tensile loading,the damage all initiates from the fill tows and propagates to the wrap tows.However,under compressive loading,the matrix damage initiates from the wrap tows in the model based on the fiber random distribution model.

Fatigue life prediction model of 2.5D woven composites at various temperatures

As one of the new structural layout in the family of woven composites, 2.5D Woven Composites（2.5D-WC） have recently attracted an increasing interest owing to its excellent properties, i.e. high specific strength and fatigue resistance, in the aerospace and automobile industry. Indepth understanding of the fatigue behavior of this material at un-ambient temperatures is critical for the engineering applications, especially in aero-engine field. Here, fatigue behavior of 2.5D-WC at different temperatures was numerically investigated based on the unit cell approach. Firstly, the unit cell model of 2.5D-WC was established using ANSYS software. Subsequently, the temperature-dependent fatigue life prediction model was built up. Finally, the fatigue lives alongside the damage evolution processes of 2.5D-WC at ambient temperature（20 ℃） and unambient temperature（180 ℃） were analyzed. The results show that numerical results are in good agreement with the relevant experimental results at 20 and 180 ℃. Fatigue behavior of 2.5D-WC is also sensitive to temperature, which is partially attributed to the mechanical properties of resin and the change of inclination angle of warp yarns. We hope that the proposed fatigue life prediction model and the findings could further promote the engineering application of 2.5D-WC, especially in aero-engine field.

Geometry effect on mechanical properties of woven fabric composites

The effects of geometry on mechanical properties in woven fabric composites were explored. Two types of composites, including one-layered and two-layered composites, were designed and studied. For one-layered composites, inter-strand gap effects on the mechanical properties were studied, while three cases of geometries with inter-strand gaps in two-layered composites were evaluated. A woven fiber micromechanics analytical model called MESOTEX was employed for theoretical simulation. The predicted results show that the inter-strand gap and simple variation of the strand positions in a repeating unit cell significantly affect the mechanical properties of woven fabric composites.

Voids' System in the Woven Composite Structure

Ccanposites are common material constructions for high-tech use now. Mechanical properties of woven reinforced composites are influenced by voids inside the structure. Voids could be classified to the two sections. Long and thin cracks are more dangerous than pores. It is important to find relations between preparation and place of occurrence of voids. This paper classifies defects according to rise mechanism, point of occurrence, orientation, size and affect to the properties. Image analysis was used for observing samples. Future work would be oriented not only to observing real samples, bet also to calculate mechanical properties frwn real and ideal structures in 3D woven reinforced composites.

An investigation on anti-impact and penetration performance of basalt fiber composites with different weave and lay-up modes

The woven basalt fiber composites(WBFC) and the unidirectional [0°/90°/45°/-45°]s basalt fiber composites(UBFC) were prepared by hot-pressing.Three-point bending test,low velocity impact test,and ballistic test were performed to the prepared composites.After the tests,the specimens were recovered and analyzed for micromorphology.Three-point bending tests show that both the bending strength and stiffness of the WBFC surpass those of the UBFC.Low velocity impact test results show that the low velocity impact resistance to hemispherical impactor of the UBFC is higher than that of the WBFC,but the low velocity impact resistance to sharp impactor of the UBFC is lower than that of the WBFC.For the ballistic test,it can be found that the ballistic property of the UBFC is higher than that of the WBFC. After the tests,microscopic analysis of the specimens was applied,and their failure mechanism was discussed.The main failure modes of the UBFC are delamination and fibers breakage under the above loading conditions while the main failure mode of the WBFC is fibers breakage.Although delamination damage can be found in the WBFC under the above loading conditions,the degree of delamination is far less than that of the UBFC.

On a Standard Parametric Modeling Method of Micro-Structure of Plain Woven Composite

A new standard parametric modeling method of the micro-structure of plain woven composite is proposed. It is based on good analysis of the mechanical property of the yarn, weaving law of plain woven, and other factors. The method implements a woven fabric composite visual engineering modeling process standardization, and it gives five steps to calculate the key micro-structural parameters of the yarn including the cross-section and the trajectory of the central Line. On the basis, the digital model of a plain woven composite has been constructed. The experimental result shows that the forecast for the mechanical property of the model using finite-element simulation analysis is consistent with the actual value. The shape and the structure of the model are also consistent with the solid.

Prediction of the Enhanced Out-of-Plane Thermal Conductivity of Carbon Fiber Composites Produced by VARTM

The thermal conductivity of epoxy resin can be increased by a factor of eight to ten by loading with highly conductive particles. However, higher loadings increase the viscosity of the resin and hamper its use for liquid composite molding processes. Thus, the enhancement of the out-of-plane thermal conductivity of carbon composites manufactured by VARTM and accomplished by matrix filling is limited to about 250%. In order to derive higher increases in out-of-plane thermal conductivity, additional measures have to be taken. These consist of introducing thermally conductive fibers in out-of-plane direction of the preform using a 3D-weaving process. Measured out-of-plane thermal conductivities of 3D-woven fabric composites are significantly increased compared to a typical laminated composite. It has been shown that if introducing highly conductive z-fibers, the use of a particle filled resin is not necessary and furthermore should be avoided due to the manufacturing problems mentioned above. An existing analytical model was altered to predict the effective thermal conductivity as a function of the composite material properties such as the thermal conductivities and volume contents of fibers in in-plane and out-of-plane directions, the thermal conductivity of the loaded resin, the grid-density of the out- of-plane fibers, and material properties of the contacting material. The predicted results are compared with measured data of manufactured samples.

Micromechanics of Thermal Conductive Composites:Review,Developments and Applications

Micromechanics investigations of composites with fiber-shaped reinforcement are extensively applied in the engineering design and theoretical analysis of thermal composites in the aerospace engineering and high-tech industry.In this paper,a critical review of various classical micromechanics approaches is provided based on the classification framework and the development of micromechanics tools.Several numerical micromechanics tools have been developed to overcome limitations through exactly/approximately solving the internal governing equations of microstructures.The connections and limitations of those models are also investigated and discussed,based on which three recently developed numerical or semi-analytical models are explained,including finite-element micromechanics,finite-volume direct averaging micromechanics,and locally exact homogenization theory,as well as machine learning tools.Since it is almost inevitable to mention the interfacial effects on thermal behavior of fibrous composites,we review the new mathematical relations that interrupt the original continuity conditions due to the existence of interphase/interface within unit cells.Generally speaking,the interphase/interface is demonstrated to play a significant role in influencing the effective coefficients and localized thermal fields.The present work also briefly reviews the application of micromechanics tools in emerging engineered woven composites,natural fibrous composites,and ablative thermal protection composites.It is demonstrated that sophisticated micromechanics tools are always demanded for investigating the effective and localized responses of thermal fibrous composites.

Experimental and numerical investigation of mechanical behavior of plain woven CFRP composites subjected to three-point bending

The mechanical behavior of plain woven Carbon Fiber-Reinforced Polymer(CFRP)composites under Three-Point Bending(TPB)is investigated via experimental and numerical approaches.Multiscale models,including microscale,mesoscale and macroscale models,have been developed to characterize the TPB strength and damages.Thereinto,Representative Volume Elements(RVEs)of the microscale and mesoscale structures are established to determine the effective properties of carbon-fiber yarn and CFRP composites,respectively.Aimed at accurately and efficiently predicting the TPB behavior,an Equivalent Cross-Ply Laminate(ECPL)cell is proposed to simplify the inherent woven architecture,and the effective properties of the subcell are computed using a local homogenization approach.The macroscale model of the TPB specimen is constructed by a topology structure of ECPL cells to predict the mechanical behavior.The TPB experiments have been performed to validate the multiscale models.Both the experimental and numerical results reveal that delamination mainly appears in the top and bottom interfaces of the CFRP laminates.And matrix cracking and delamination are identified as the significant damage modes during the TPB process.Finally,the quasi-static and dynamic behaviors of plain woven composites are discussed by comparing the results of Low-Velocity Impact(LVI)and TPB simulations.

Semisolid-rolling and annealing process of woven carbon fibers reinforced Al-matrix composites

Semisolid-rolling method was successfully developed to prepare the Ni-coated woven carbon fibers reinforced Al-matrix composite. Due to the appropriate matrix flowability and rolling pressure, the Al-matrix could infiltrate into the woven fibers sufficiently and attach to the reinforcements closely forming a smooth interface. The rolling speed of 4 rad/min offered a subtle equilibrium between the heat transfer and the material deformation. The covering matrix should be controlled at semisolid state to provide a better infiltration behavior and a protective effect on the carbon fibers. With the addition of fibers, an improvement for more than 25% was obtained in the bending strength of the materials. Furthermore, the woven carbon fibers could strengthen the composite in multiple directions, rather than only along the fiber longitudinal directions. The annealing process promoted the Ni coating to react with and to diffuse into the matrix, resulted in an obvious increase of the bending strength.

Nonlinear Out-of-Plane Mechanical Behaviours of Rectangular Woven Composite Flexible Skin Under Uniform Normal Pressure

This paper seeks to investigate nonlinear out-of-plane mechanical behaviours of woven composite flexible skin(WCFS)through experimental and theoretical methods.Firstly,quasi-static experiments are carried out on rectangular WCFSs with different aspect ratios under uniform normal pressure to measure out-of-plane deformation and failure loads.Afterwards,a new three-parameter geometric model is presented to describe 3D geometry of pressurized WCFS,and thus,a nonlinear mechanical model is deduced for depicting the relationship between pressure and out-of-plane displacement.The application of the aforementioned models for experimental results shows that the new models have adequately and logically depicted deformation geometry and nonlinear mechanical characteristics.

An integrated preforming-performance model for high-fidelity performance analysis of cured woven composite part with non-orthogonal yarn angles

Preforming process would change yarn angle and yarn orientation,its influence on the material properties and material orientations needs to be considered in the performance analysis.However,most current performance models fail to account for the preforming effect.An integrated performance model accounting for the impact of preforming has been developed.In this integrated model,part geometry,yarn angle and orientation after preforming of multiple prepreg layers are predicted by Finite Element Analysis(FEA)using a non-orthogonal constitutive law.Experiments were conducted to validate the preforming simulation for a single dome composites structure made by two prepreg layers with different initial fiber orientations.Performance analysis until failure was then conducted for the single dome structure to validate the integrated performance model.Comparison between simulation and experiment shows that not only the failure mode and failure zone,but also the force-displacement curve during compression process are captured correctly by the performance model,demonstrating the effectiveness of the newly proposed model in accounting for the impact of preforming process.

Progressive damage behaviors of woven composite laminates subjected to LVI, TAI and CAI

This paper seeks to deal with progressive damage behaviors of woven composite laminates subjected to low-velocity impact(LVI),tension-after-impact(TAI)and compression-afterimpact(CAI).The LVI,TAI and CAI tests were conducted on woven carbon fibre lamina3238 A/CF3052 and woven glass fibre lamina 3238 A/EW250 F,and the time-dependent LVI contact force and deflection curves,static TAI and CAI load versus displacement curves were determined and discussed.A modified progressive damage model was presented for explicit dynamic LVI and implicit static TAI and CAI analysis by using basic material properties and geometrical dimensions,and progressive damage LVI,TAI and CAI behaviors of woven composite laminates were simulated,demonstrating a good correlation between simulations and experiments.

Structural effects of three-dimensional angle-interlock woven composite undergoing bending cyclic loading

This paper reports the structural effects of three-dimensional(3-D)angle-interlock woven composite(3DAWC)undergoing three-point bending cyclic loading from experimental and finite element analysis(FEA)approaches.In experiment,the fatigue tests were conducted to measure the bending deflection and to observe the damage morphologies.By the FEA approach,a micro-structural unit-cell model of the 3DAWC was established at the yarn level to simulate the fatigue damage.The stress degradation at the loading condition of constant deformation amplitude was calculated to show the degradation of mechanical properties.In addition,the stress distribution,fatigue damage evolution and critical damage regions were also obtained to qualitatively reveal the structural effects and damage mechanisms of the 3DAWC subjected to three-point bending cyclic loading.

Continuum damage mechanics based modeling progressive failure of woven-fabric composite laminate under low velocity impact

A continuum damage mechanics (CDM) meso-model was derived for both intraply and interply progressive failure behaviors of a 2D woven-fabric composite laminate under a transversely low velocity impact.An in-plane anisotropic damage constitutive model of a 2D woven composite ply was derived based on CDM within a thermodynamic framework,an elastic constitutive model with damage for the fibre directions and an elastic-plastic constitutive model with damage for the shear direction.The progressive failure behavior of a 2D woven composite ply is determined by the damage internal variables in different directions with appropriate damage evolution equations.The interface between two adjacent 2D woven composite plies with different ply orientations was modeled by a traction-separation law based interface element.An isotropic damage constitutive law with CDM properties was used for the interface element,and a damage surface which combines stress and fracture mechanics failure criteria was employed to derive the damage initiation and evolution for the mixed-mode delamination of the interface elements.Numerical analysis and experiments were both carried out on a 2D woven glass fibre/epoxy laminate.The simulation results are in agreement with the experimental counterparts,verifying the progressive failure model of a woven composite laminate.The proposed model will enhance the understanding of dynamic deformation and progressive failure behavior of composite laminate structures in the low velocity impact process.