三维机织C/C-SiC复合材料弹性性能预测

试验研究了三维机织C/C-SiC复合材料的弹性性能, 基于复合材料的扫描电镜(SEM)照片, 分析了材料的细观结构的特点, 并提出了一系列的假设, 建立了三维机织C/C-SiC复合材料的细观力学模型, 利用均匀化方法预测了复合材料的弹性常数, 分析了材料的弹性性能随经纱倾斜角的变化规律。结果表明: 预测结果与试验结果吻合较好, 表明该预测模型和方法的正确性; 随着经纱倾斜角的增加, 经纱方向的弹性模量降低, 其它方向的弹性模量均增大, 但面内剪切模量和厚度方向的弹性模量增幅很小。      

A three dimensional calculation of elastic equilibrium for composite materials

A compact scheme is applied to three dimensional elasticity problems for composite materials, involving simple geometries. The mathematical aspects of this approach are discussed, in particular its solution by iteration methods. A vector processor code implementing the compact scheme is presented, and several numerical experiments are summarized.     

航空发动机复合材料叶片用3D机织预制体研究进展

三维机织复合材料（3DWCs）因其高比强度、低密度、低热膨胀系数和良好的成型性等优点受到越来越多的青睐,已经成功运用到飞机和汽车工程等领域。随着航空发动机研发力度的加大,3DWCs也在飞机发动机零部件上有所应用。综述了航空发动机复合材料叶片用三维机织预制体（3DWPs）的研究进展及现状;对比了异形高厚度3DWPs的几种织造方法;基于试验测试和仿真模拟,介绍了国内外3DWPs变形性能的研究进展;分析了3DWPs结构对其复合材料性能的影响;最后,展望了3DWPs的发展方向,为航空发动机复合材料叶片的发展提供了参考依据。     

Evaluation of three in-plane shear test methods for advanced composite materials

This paper is concerned with the evaluation of three in-plane shear test methods for advanced carbon fibre composites for aerospace applications. To accomplish this goal, the losipescu, ± 45° tensile and 10° off-axis tensile shear test methods were evaluated for three advanced epoxy matrix materials (Narmco 5245C, Hexcel F584 and American Cyanamid Cycom 1806) reinforced with Hercules IM6 carbon fibres. The values of in-plane shear moduli obtained from the three test methods and three materials were then used with other previously determined elastic constants to predict the tensile moduli of (+45°/0°/−45°/90°)_6s laminates. Comparison of the predicted and experimental laminate tensile moduli showed that any one of the three shear test methods was appropriate for determining the in-plane shear modulus to predict tensile moduli of symmetric laminates which consist of equal numbers of 0°, +45°, −45° and 90° oriented laminae.     

预定型机织物剪切变形实验研究

在改进像框实验的基础上,对斜纹和缎纹预定型碳纤维织物的剪切性能进行了实验观察。研究发现,预定型机织物的剪切机制与织物剪切相似。根据实验结果,从定型剂的浓度和织物结构分析了预定型织物的剪切性能。随着定型剂浓度提高,织物的折皱角越大,织物剪切性能越差;与预定型斜纹织物相比,预定型缎纹织物相对较容易成型,剪切载荷较小。利用立式显微镜观察剪切过程中纱线宽度的变化,拟合得到了宽度变化方程,建立预定型机织物的折皱角模型,预测结果与实验结果误差在2°内,证明了该模型的有效性。     

三维机织复合材料力学性能的各向异性

通过一系列的实验、分析, 客观地评价了4 种不同结构碳/ 环氧3D 层-层正交角联锁机织复合材料沿0°、30°、45°、60°、90°方向的拉伸、压缩、弯曲强度和模量。实验结果表明: 三维机织角联锁复合材料属正交各向异性材料, 各个方向的拉伸、压缩、弯曲强度和模量曲线呈枫叶形, 具有明显的双主轴特性; 4 种不同结构复合材料的各向异性力学性能有差异, 经向力学性能以带衬经的角联锁结构为最佳, 而纬向力学性能以纬密大的角联锁结构为最佳; 三维机织角联锁复合材料具有很强的性能可设计性, 正确选择纤维原料、纤维细度、三维预制件的组织结构和各个纱线组分的排列密度, 即可达到预期的性能指标要求。      

Computer modelling of woven composite materials

In this paper the reasons for choosing woven fabric reinforcements for composite components are given and the alternatives to woven structures are examined. The philosophy behind the development of the computer-generated model of a woven composite fabric reinforcement is discussed. The model described here is a general one, capable of producing a 3-D representation of any single layer fabric, and has been designed to facilitate manufacture of the weave and also finite element analysis of the finished composite component, as well as providing a very useful visualization of the weave. The model has the potential to be developed along a number of fronts, including improved visualization and extension to 3-D weaves.     

The draping of woven fabric preforms and prepregs for production of polymer composite components

Drape trials were conducted on a simple shape and a number of aircraft parts. Predictions from computer drape simulation using the pin-jointed net model were compared with draping test results. The pin-jointed net model was evaluated. Yarn slippage, and how it is affected by the material properties and part geometry, were investigated. The criteria for optimal draping, and the means of manipulation of the drape simulation are discussed. The different methods of draping constraint are compared and their most useful applications are indicated. Some useful guidance for the application of drape simulation is given.     

Effect of inter-ply sliding on the quality of multilayer interlock dry fabric preforms

Forming thick, complex shapes with several layers is needed in high technology fields. During forming, defects can occur and have to be taken into account because they can significantly affect the mechanical performance of the part. This experimental study shows that, when working with dry fabric forming, the type and number of defects is a function of the punch geometry, the process parameters, the orientation of the fabric with respect to the punch and the inter-ply friction. Inter-ply friction has a huge effect on the quality of the preform when inter-ply sliding occurs. This inter-ply friction leads to several overhanging yarn shocks that generate high tangential forces, which inhibit the relative sliding of plies. In addition, to reduce the number and amplitude of defects, the layers subjected to severe defects can be placed in the inner position where they are subjected to the compression applied by the upper layers.     

Hyperelastic model for large deformation analyses of 3D interlock composite preforms

A hyperelastic constitutive law is proposed to describe the mechanical behaviour of 3D layer to layer angle interlock composite reinforcements. The objective of this model is to simulate shaping of thick textile preforms for RTM processes. After the identification of the independent deformation modes of initially orthotropic reinforcements, a strain energy potential is built up based on strain invariants representative to those modes assuming an additive composition of them. The parameters of the proposed constitutive model are identified using standard and specific mechanical tests performed on a 3D interlock material. Then, the model is validated on forming simulations on a single curve and double curve shapes. Three point bending tests on thick interlock reinforcements have been analysed experimentally and numerically. The specific transformation of cross sections is depicted by the proposed hyperelastic model.     

A three-constituent multicontinuum theory for woven fabric composite materials

Multicontinuum theory (MCT) refers to the use of phase averaged constituent stress/strain fields for predicting failure in composite structural analysis. Given the composite material mechanical properties as well as those of the constituents, well known closed form algebraic expressions exist to decompose the composite stress/strain fields down to the constituent level. Recent research indicates constituent based failure algorithms show a great deal of promise in predicting material failure when coupled to nonlinear finite element codes. A limitation of MCT is that the traditional constituent decomposition is only valid for materials composed of two constituents. In this paper, the MCT decomposition is generalized to handle composite materials composed of three constituents. The application of interest is a woven fabric composite material. The three constituents consist of the warp bundles, fill bundles, and pure matrix pockets. Numerical results are presented for the proposed three-constituent decomposition and are shown to be in good agreement with phase averaged stresses obtained from direct volume averaging of finite element micromechanics models.     

Interlaminar fracture properties of weft-knitted/woven fabric interply hybrid composite materials

An experimental study has been undertaken to characterize the delamination behavior and tensile properties of interply hybrid laminated composites reinforced by interlock weft-knitted and woven glass fiber preform fabrics. The hybrid composites, comprising the alternate layers of interlock and uniweave fabrics, were compared to interlock knitted (only) and uniweave (only) composites with respect to delamination and tensile performances. Mode-I double cantilever beam and mode-II end-notched flexure tests were carried out to assess the interlaminar fracture toughness using aluminum-strip stiffened specimens. The mode-I and mode-II interlaminar fracture toughness values, G _IC and G _IIC, for the hybrid composite were about three and two times higher than that for the uniweave composite, respectively. The tensile strength and modulus of the hybrid composite were 315 MPa and 12.8 GPa in the wale direction, respectively, demonstrating that the strength and modulus were found to be slightly lower than those of the uniweave composite, and significantly improved in comparison with the interlock knitted composites.     

Fabrication and characterization of three dimensional woven carbon fiber/silica ceramic matrix composites

Carbon fiber reinforced fused silica composites exhibit the advantages of excellent mechanical properties, high heat resistance, low thermal expansion and low density, but low impact resistance or toughness. A novel modified slurry impregnation and hot pressing (SIHP) method was adopted to fabricate a new type of three dimensional orthogonal woven structure carbon fiber reinforced silica ceramic matrix composites (3D Cf/SiO₂ CMCs) with higher density and lower porosity. Physical characterization, flexural behavior, impact performance and toughening mechanism of the composites were investigated by three-point bending tests, impact tests, and scanning electron microscopy analysis. The 3D Cf/SiO₂ CMC showed a higher flexural strength in both warp (201.6%) and weft (263.6%) directions than those of pure SiO₂ and failed at a non-brittle mode due to the fiber debonding and pullout, and a delaminated failure of the 3D preform. The maximum impact energy absorption of the 3D Cf/SiO₂ CMC was 96.9 kJ/m², almost 4 times as much as those for typical other carbon fiber reinforced CMCs.     

In situ study of short-beam shear tests for composite materials

The shear behaviour of a unidirectional E-glass/epoxy composite was studied with four-point short-beam bending tests carried out in the interior of a scanning electron microscope. The damage process of the composite was followed during the tests and the local matrix shear strain was measured. A relationship was established experimentally between the beam shear stress and the local interface shear strain. Finite element calculations gave the correct stress distribution in the beam.     

An entropy model for shear deformation of granular materials

A statistical mechanical analogy for characterization of granular materials is discussed by using such notions as the state of the material, the density of states, entropy, canonical distribution and the partition function. The transition law of states during shear deformations of the material is microscopically investigated in the case of two-dimensional model granular materials. The assumption of entropy growth is shown to characterize the dilatancy of the material. A rough proof is given by assuming the measure preserving property of the transition and showing its ergodicity.     

层间混杂复合材料板的拉伸强度预报

采用更为合理的分散度系数表达式改进了玻/碳层间混杂复合材料板断裂应变混杂效应系数公式,结合该混杂效应系数公式与复合材料强度混合定律,提出了层间混杂复合材料单向板的拉伸强度预报方法。将该混杂效应系数公式引入复合材料多向板渐近损伤有限元分析模型,修正了低延伸率纤维单层板的拉伸强度值,在此基础上提出了层间混杂复合材料多向板拉伸强度预报方法,并讨论了刚度退化方案。结果表明,模型预报值与实验均吻合较好,尤其考虑混杂效应的预报值与实验情况更加接近;基体退化系数大的刚度退化方案与实验更为吻合。     

Cylindrical conformal single-patch microstrip antennas based on three dimensional woven glass fiber/epoxy resin composites

Three dimensional integrated microstrip antenna (3DIMA) can carry the designed load while functioning as an antenna. In this study, the cylindrical conformal single-patch 3DIMAs with various curvatures were designed, simulated, fabricated and tested experimentally using a 3D orthogonal woven glass preform/epoxy resin composite system. The electromagnetic performances of the cylindrical microstrip antennas were analyzed. The simulated and tested results matched well and the return losses of the cylindrical conformal 3DIMAs with radii of curvatures of 60, 45 and 25 mm were less than −10 dB while resonant frequencies and their gain values were significantly influenced by the radius of curvature and the feeding direction. The 3DIMAs with the curvature perpendicular to the feeding directions showed more stable resonant frequencies and larger gain values than those of 3DIMAs with the curvature along their feeding directions.     

Three‐dimensional measurement and cohesive element modelling of deformation and damage in a 2.5‐dimensional woven ceramic matrix composite

A cohesive element numerical model, which reproduces the three‐dimensional microstructure of a 2.5‐dimensional silicon‐nitrogen‐oxide fibre/fabric‐reinforced boron nitride ceramic matrix composite (SiNO/BN) is applied to simulate the failure of specimens that are observed in situ during diametral compression testing. Measurements of deformation by image correlation of two‐dimensional optical surface observations and three‐dimensional X‐ray computed tomographs are used to fit the simulation's elastic properties for the matrix and fibre tows. The observed patterns of damage nucleation and propagation are correctly simulated using a local tensile strain criterion.     

Finite element analysis of damaged woven fabric composite materials

Since fiber reinforced composite materials have been used in main parts of structures, an accurate evaluation of their mechanical characteristics becomes very important. Due to their anisotropic nature and complicated architecture, it is very difficult to reveal the damage mechanisms of these materials from the results of mechanical tests. Therefore, there is a need to conduct reliable simulations and analytical evaluations. In this paper, the damage behavior of FRP is simulated by finite element analysis using an anisotropic damage model based on damage mechanics. The proposed procedure is applied to an example; the finite element analysis of microscopic damage propagation in woven fabric composites. Experimental tests have been conducted to evaluate the validity of the proposed method. It is recognized that there is a good agreement between the computational and experimental results, and that the proposed simulation method is very useful for the evaluation of damage mechanisms.     

预浸织物剪切变形时树脂细观分析模型

为了更好地研究在发生剪切变形时预浸织物材料的力学性能,建立了在像框剪切试验时未固化的树脂对织物发生剪切变形时的阻碍作用的细观分析模型.通过对材料的单胞进行分析,得到了织物单胞变形前、后各质点间的运动学关系,进而得到了树脂材料对整个织物单胞的阻力矩,即树脂的阻尼作用.此阻尼作用较好地说明了树脂在预浸织物材料中的作用.此外,通过树脂的流变试验得到其粘性系数,该粘度系数确定,即该材料的阻尼作用确定.