Process parameters design of a three-dimensional and five-directional braided composite joint based on finite element analysis

This paper presents an analytical method for designing the configuration of composite joint with three-dimensional (3D) five-directional braided composites. Based on the analysis of 3D braided structure characteristics, the elastic properties of the 3D five-directional braided composites were determined by the volume averaging method. The effects of the braiding angle and fiber volume fraction on the elastic constants of the braided composites were also discussed. Finite element analysis on the load capacity of the 3D five-directional braided composite joint was implemented using the software ANSYS Workbench 14.0. The influence of braiding angle on the stress, strain and deformation of the composite joint under tensile loading were calculated. The results show that when the fiber volume fraction of the 3D five-directional braided preform is given, the equivalent stress of the composite joint decreases monotonically as the braiding angle increases, while the normal stress, maximum principal stress and total deformation firstly decreases and then increases. Based on the finite element analysis, we found that at the fiber volume fraction of 60%, the braiding angle within the range of 30–35° are the optimum processing parameters for the 3D five-directional braided composite joint structure that used in the tensile load 320 N condition.     

Microstructural Modeling and Second-Order Two-Scale Computation for Mechanical Properties of 3D 4-Directional Braided Composites

This study is concerned with the microstructural modeling and mechanical properties computation of three-dimensional (3D) 4-directional braided composites. Microstructure of the braided composite determines its mechanical properties and a precise geometry modeling of the composite is essential to predict the material properties. On the basis of microscopic observation, a new parameterized microstructural unit cell model is established in this paper. And this model truly simulates the microstructure of the braided composites. Furthermore, the mathematical relationships among the structural parameters, including the braiding angle, fiber volume fraction and braiding bitch, are derived. By using the unit cell model, the second-order two-scale (SOTS) method is applied to predict the mechanical properties of 3D 4-directional braided composites, including stiffness parameters and strength parameters. Besides, the effects of the braiding angle and fiber volume fraction on the elastic constants are investigated in detail. Numerical results show that the predictive stiffness and strength parameters are in good agreement with the available experimental data, which demonstrate that the established unit cell model is applicable and the second-order two-scale method is valid to predict the mechanical properties of 3D 4-directional braided composites.     

Computational Analysis of Torsional Bulking Behavior of 3D 4-Directional Braided Composites Shafts

The torsional bulking behavior of 3D 4-directional braided composites shafts was analyzed in this work. First, the unit cell models of 3D 4-directional braided composites shafts with different braiding angles and fiber volume fraction were built up. Then, the elastic parameters of 3D 4-directional braided composites shafts were predicted using the unit cells under different boundary conditions. Finally, the torsional bulking eigenvalues and bulking modes of the composites shafts were obtained by numerical simulation, and the effects of braiding angle and fiber volume fraction on the torsional bulking behavior of 3D 4-directional braided composites shafts were analyzed. The simulation results show that the bulking eigenvalues increase with the increase of braiding angle and fiber volume fraction. This work will play an important role in the design of 3D 4-directional braided composites shafts.     

Effects of braiding angle on modal experimental analysis of three-dimensional and five-directional braided composites

In this paper, the experimental modal analysis of three dimensional (3D) and five (5)-directional braided composite cantilever beams with different braiding angle was conducted systematically with a simple testing system. Preforms were made by four-step 1 × 1 square integral braiding method. The first three order modes of composite specimens were derived, which are different with braiding angles. The experimental result and mechanism were discussed. Experimental observations and analytical predictions show that the natural frequency of specimens decreased and the damping ratio of specimens increased when the braiding angle increased. Furthermore, specimens with smaller braiding angle will be valuable for the better anti-exiting property, and have an opposite effect on dissipation of vibration energy. The comparison between the specimens with different braiding angles reveals that braiding angle is a crucial factor for the vibration performance design of 3D and 5-directional braided composites.     

Preparation and bending properties of three dimensional braided single poly (lactic acid) composite

New three dimensional (3D) braided single poly (lactic acid) composites (PLA–SPCs) were obtained by combining 3D and five (5)-direction braiding technique and hot-compression technical process. 3D and 5-direction braided preforms with different braiding angles, thicknesses and fiber volume fractions were prepared. Preforms were preheated in the specially designed die system in order to make all of the fibers partially melted. In the next stage, the preforms were consolidated under a certain pressure (from 7.8 to 10 MPa) at temperatures ranging from 130 up to 150 °C. Under the controlled processing conditions, one part of fiber body formed matrix while the other part retained its fibrous form.At the same consolidation temperature, the maximum bending stress values resulted to be substantially dependent on the fiber volume fraction of PLA–SPCs, while the bending modulus values were largely subjected to the fiber content in the length direction. The increases of consolidation pressure gave rise to better fusion of neighboring fibers with the result that the maximum stress and modulus were increased. As the consolidation temperature increases, the fusion bonding was improved, the bending failure feature was converted from plastic to brittle, both maximum bending stress and modulus values were increased. It is expected that this study could provide a new approach for the manufacture of high-performance single polymer composites (SPCs) by using thermoplastic polymer fibers.     

Thermal and mechanical properties of waste grass broom fiber-reinforced polyester composites

The main focus of this study is to utilize waste grass broom natural fibers as reinforcement and polyester resin as matrix for making partially biodegradable green composites. Thermal conductivity, specific heat capacity and thermal diffusivity of composites were investigated as a function of fiber content and temperature. The waste grass broom fiber has a tensile strength of 297.58 MPa, modulus of 18.28 GPa, and an effective density of 864 kg/m³. The volume fraction of fibers in the composites was varied from 0.163 to 0.358. Thermal conductivity of unidirectional composites was investigated experimentally by a guarded heat flow meter method. The results show that the thermal conductivity of composite decreased with increase in fiber content and the quite opposite trend was observed with respect to temperature. Moreover, the experimental results of thermal conductivity at different volume fractions were compared with two theoretical models. The specific heat capacity of the composite as measured by differential scanning calorimeter showed similar trend as that of the thermal conductivity. The variation in thermal diffusivity with respect to volume fraction of fiber and temperature was not so significant.The tensile strength and tensile modulus of the composites showed a maximum improvement of 222% and 173%, respectively over pure matrix. The work of fracture of the composites with maximum volume fraction of fibers was found to be 296 Jm⁻¹.     

Influence of design parameters on the mechanical behavior and porosity of braided fibrous stents

In spite of all innovations in stent design, commonly used metallic stents present several problems such as corrosion, infection and restenosis, leading to health complications or even death of patients. In this context, the present paper reports a systematic investigation on designing and development of 100% fiber based stents, which can eliminate or minimize the problems with existing metallic stents. For this purpose, braided stents were produced by varying different materials, structural and process parameters such as mono-filament type and diameter, braiding angle and mandrel diameter. The influence of these design parameters on mechanical behavior as well as stent's porosity was thoroughly investigated, and suitable parameters were selected for developing a stent with mechanical characteristics and porosity matching with the commercial stents. According to the experimental results, the best performance was achieved with a polyester stent designed with 0.27 mm monofilament diameter, braiding angle of 35° and mandrel diameter of 6 mm, providing similar properties to commercial Nitinol stents.     

三维六向编织复合材料弹性性能理论预测

在三维六向编织物纱线运动规律的基础上, 建立了单胞模型, 推导了编织参数之间的数学关系。基于该模型, 采用改进的刚度平均化方法, 导出了三维六向编织复合材料的工程弹性常数, 分析了编织角和纤维体积含量对弹性性能的影响。结果表明, 三维六向编织复合材料具有良好的力学性能, 由于面内纬纱的加入, 使面内的力学性能得到了提高。      

三维五向编织复合材料纵向性能的实验研究

通过对具有不同编织结构参数的三维五向编织复合材料试件的纵向拉伸和压缩实验,分析了该类材料的纵向拉、压刚度和强度随编织工艺参数的变化规律以及材料的失效形式.三维五向编织复合材料在破坏前基本保持线弹性,纵向拉、压破坏具有脆性特征,拉伸模量和压缩模量比较接近,但拉伸强度远大于压缩强度.编织角和纤维体积含量对材料性能的影响显著,纱线粗细的影响不大.提高第五向纱线的比例,可提高材料的纵向性能.此外,研究中采用短标距薄板试件,以避免试件产生整体屈曲和端部纤维束开裂破坏.     

树脂基三维编织复合材料粘弹性能的数值预报

建立了基于三细胞模型数值预报三维编织复合材料粘弹性能的方法。首先构造了三维编织复合材料的三细胞模型并施加周期性边界条件,随后利用标准线性固体模型模拟树脂基体的粘弹性能,导出基体的松弛模量,再通过有限元计算及Prony级数拟合,得到三种胞元的粘弹性参数。然后根据三种胞元的体积分数和粘弹性参数,利用三个标准线性固体模型并联,模拟得到三维编织复合材料沿编织方向的粘弹性参数和蠕变本构关系。最后,分析了编织角和纤维体积含量对粘弹性能的影响。     

三维编织复合材料悬臂梁的振动特性

基于三维四向和五向编织复合材料的细观结构和单胞模型, 对三维四步法矩形截面编织复合材料悬臂梁的振动阻尼性能进行了理论分析, 研究了编织角、 纤维体积分数等工艺参数对材料振动阻尼特性的影响, 并与实验结果进行了对比。对三细胞模型进行了改进, 采用混合律得到了材料的总体刚度, 进而得到一阶固有频率。此外, 还分别计算了一个周期内不同走向纱线和基体振动消耗的能量, 以及总振动能量, 得到了材料的损耗因子。结果表明, 对于三维四向和五向编织复合材料, 一阶固有频率随编织角的增加而减小, 随纤维体积分数的增加而增大; 而损耗因子随编织角的增加而增大, 随纤维体积分数的增加而减小, 并表现出明显的非线性变化规律。      

Effect of stitch density on tensile properties and damage mechanisms of stitched carbon/epoxy composites

Experimental investigation is performed to study tensile properties, damage initiation and development in stitched carbon/epoxy composites subjected to tensile loading. T800SC-24kf dry preforms with tow orientation of [+45/90/−45/0₂/+45/90₂/−45/0]s are stitched using 200 denier Vectran® thread. Modified-lock stitch pattern is adopted, and stitch density is varied, viz. moderate density (stitched 6 × 6: stitch density = 2.8 cm⁻²) and high density (stitched 3 × 3: stitch density = 11.1 cm⁻²). The stitched preforms are then infiltrated by epoxy XNR/H6813 using resin transfer molding process. Tensile test is conducted to obtain in-plane mechanical properties (tensile strength, failure strain, tensile modulus and Poisson’s ratio). Effect of stitch density on the mechanical properties is assessed, and it is found that stitched 3 × 3 modestly improves the tensile strength by 10.4%, while stitched 6 × 6 reduces the strength by only 1.4%. In stitched 3 × 3 cases, the strength increase is mainly due to an effective impediment of edge-delamination. Tensile stiffness and Poisson’s ratio of carbon/epoxy are slightly reduced by stitching. Fiber misalignment in in-plane and out-of-plane directions is responsible for stiffness reduction, whilst reduction of Poisson’s ratio is probably caused by the orthogonal binding effect of modified-lock stitch architecture. Damage mechanisms in stitched and unstitched composites are studied using acoustic emission testing and interrupted test coupled with X-ray radiography and optical microscopy. The detailed damage observation reveals that stitch thread promotes early formation of transverse and oblique cracks. These cracks rapidly develop, and higher density of cracks ensues in stitched composites. Although this behavior triggers early formation of delamination, stitched 3 × 3 effectively impedes the growth the delamination. In contrast, stitched 6 × 6 is ineffective in suppressing the delamination yet the cracks are vast in this specimen. One of the plausible reasons of the rapid development of cracks in stitched composites is fiber compaction effect whereby fibers are compacted and the gap among fibers is reduced. The verification of compaction effect is done experimentally by performing burn-off test to measure the local fiber volume fraction. It is confirmed that fiber compaction indeed occurs as indicated by higher local fiber volume fraction between stitch lines.     

Vapor grown carbon fiber composites with epoxy and poly(phenylene sulfide) matrices

Vapor grown carbon fibers (VGCF, Pyrograf III™ from Applied Sciences, Inc.), with 100–300 nm diameters and ∽10–100 μm lengths, were formulated in various fiber volume fractions into epoxy (thermoset) and into poly(phenylene sulfide) (thermoplastic) composites. Increases in stiffness were observed as with previous VGCF/organic matrix composites. Large increases in flexural strengths were achieved in both systems demonstrating for the first time that discontinuous randomly oriented Pyrograf III™ can give strength increases and has substantial potential as a reinforcement in composites. Here-to-fore, addition of VGCF caused strength decreases. Voids, residual thermal strains (as the fiber surface area is ∽35 times greater than 7 μm-diameter PAN fiber), or uncertainties about fiber strength, fiber–matrix bonding and the degree of fiber dispersion, could cause losses of strength. Thermal conductivity properties of VGCF/ABS (acrylonitrile–butadiene–styrene from GE Plastics) and VGCF/epoxy composites with various fiber volume fractions were measured. Thermal conductivity increased with an increase in fiber volume fraction. However, these increases were not significant enough to make these VGCF fiber/organic matrix composites candidates for thermally conductive materials.     

Influence of fiber content on the mechanical and dynamic mechanical properties of glass/ramie polymer composites

The combination of glass and ramie fibers with a polyester matrix can produce a hybrid material that is competitive to all glass composites (e.g. those used in the automobile industry). In this work, glass and ramie fibers cut to 45 mm in length were used to produce hybrid polymer composites by resin transfer molding (RTM), aiming to evaluate their physical, mechanical and dynamic mechanical properties as a function of the relative glass–ramie volume fractions and the overall fiber content (10, 21 and 31 vol.%). Higher fiber content and higher ramie fiber fraction in the hybrid composites yielded lower weight composites, but higher water absorption in the composite. The mechanical properties (impact and interlaminar shear strength) of the composites were improved by using higher fiber content, and the composite with 31 vol.% of reinforcement yielded the lowest value for the reinforcement effectiveness coefficient C, as expected. Although the mechanical properties were improved for higher fiber content, the glass transition temperature did not vary significantly. Additionally, as found by analyzing the adhesion factor A, improved adhesion tended to occur for the composites with lower fiber content (10%) and higher ramie fiber fraction (0:100) and the results for the adhesion factor A did not correspond to those found by the analysis of the tan delta peak height.     

Integrated Design For Manufacturing of Braided Preforms For Advanced Composites Part II: 3D Braiding

This paper presents the integrated design of manufacturing of braided preforms by two types of novel 3D braiding technology: 3D Cartesian braiding and novel hexagonal braiding. The principles for design are first introduced and the ensuing software package development is subsequently discussed. The relationships between fiber volume fraction and braiding angle which are key parameters for fiber reinforcement composites were analyzed and compared. Meanwhile, several samples are carried out to verify the software. The result shows it is consistent between theoretical and experimental results. Combined with the Part I: 2D braiding section, many complex shape performs can be made, which will be usefully for design of advanced composites.     

三维四向编织碳纤维/环氧树脂复合材料在热环境中的拉压力学性能实验

针对不同编织角度的三维四向编织碳纤维/环氧树脂复合材料,进行了热环境下的轴向拉伸和压缩力学性能实验研究,讨论了温度对三维四向编织复合材料的轴向拉伸和压缩力学性能的影响,并根据宏观断裂形貌和SEM图像分析了材料的破坏和断裂机制。结果表明,随着测试温度的升高,三维四向编织碳纤维/环氧树脂复合材料的纵向拉伸强度有小幅提高,而纵向压缩强度显著降低。在室温条件下,编织角对材料的纵向拉伸破坏特征没有影响,而对材料的纵向压缩破坏特征有较大影响。随着测试温度的升高,不同编织角度复合材料的纵向拉伸和压缩的损伤破坏形态均与室温条件下明显不同。      

Effects of volume fraction on the microstructure and tensile properties of in situ TiBw/Ti6Al4V composites with novel network microstructure

In order to better understand the relationship of structure–mechanical properties of TiBw/Ti6Al4V (TiBw/Ti64) composites with a network microstructure and deduce the upper limit of TiBw volume fraction, the effects of volume fraction on the microstructure and tensile properties were further investigated. The equation calculating the optimal and maximum volume fractions of reinforcement for the composites with a network microstructure was deduced. For the present system, the optimal and maximum volume fractions were verified to be 5.1 vol.% and 10.2 vol.%, respectively, by calculation, microstructure observation, tensile properties. When the volume fraction was equal and lower than 5.1 vol.%, the coarse TiBw formed, or else, the fine TiBw, the cluster TiBw and the block TiBw, even unhealed pores formed. The tensile strength of TiBw/Ti64 composites increases and then hastily decreases, while the ductility keeps on decreasing with increasing volume fractions of TiBw reinforcement.     

三维五向炭纤维/酚醛编织复合材料的压缩性能及破坏机制

针对不同编织角、 不同纤维体积分数的三维五向炭纤维/酚醛编织复合材料在不同温度下进行了纵向(编织方向)压缩和横向压缩试验 , 获得了其主要压缩力学性能 , 分析了编织参数、 温度对材料压缩力学性能的影响。对试件断口进行了宏观及扫描电镜观察 , 从宏、 细观角度研究了材料的变形及其破坏机制。结果表明 , 三维五向炭纤维/酚醛编织复合材料的压缩应力2应变曲线呈现明显的非线性特征 , 且温度效应明显; 编织角和纤维体积分数是影响材料压缩性能的主要参数。三维五向炭纤维/酚醛编织复合材料的纵向压缩与横向压缩具有完全不同的破坏机制。      

Finite Element Analysis of Thermo-Mechanical Properties of 3D Braided Composites

This paper presents a modified finite element model (FEM) to investigate the thermo-mechanical properties of three-dimensional (3D) braided composite. The effective coefficients of thermal expansion (CTE) and the meso-scale mechanical response of 3D braided composites are predicted. The effects of the braiding angle and fiber volume fraction on the effective CTE are evaluated. The results are compared to the experimental data available in the literature to demonstrate the accuracy and reliability of the present method. The tensile stress distributions of the representative volume element (RVE) are also outlined. It is found that the stress of the braiding yarn has a significant increase with temperature rise; on the other hand, the temperature change has an insignificant effect on the stress of the matrix. In addition, a rapid decrease in the tensile strength of 3D braided composites is observed with the increase in temperature. It is revealed that the thermal conditions have a significant effect on the strength of 3D braided composites. The present method provides an effective tool to predict the stresses of 3D braided composites under thermo-mechanical loading.     

Effect of submicron size SiC particles on microstructure and mechanical properties of AZ31B magnesium matrix composites

The magnesium matrix composites reinforced with three volume fractions (3, 5 and 10 vol.%) of submicron-SiC particles (∼0.5 μm) were fabricated by semisolid stirring assisted ultrasonic vibration method. With increasing the volume fraction of the submicron SiC particles (SiCp), the grain size of matrix in the SiCp/AZ31B composites was gradually decreased. Most of the submicron SiC particles exhibited homogeneous distribution in the SiCp/AZ31B composites. The ultimate tensile strength and yield strength of the 10 vol.% SiCp/AZ31B composites were simultaneously improved. The study of interface between the submicron SiCp and the matrix in the SiCp/AZ31B composite suggested that submicron SiCp bonded well with the matrix without interfacial activity.