圆管状立体机织复合材料的多尺度分析

采用多尺度耦合的数值模型研究了圆管状立体机织复合材料的力学性能。建立了反映纤维束中纤维/基体二相材料的微观尺度单胞和反映周期性编织结构的细观尺度扇形单胞,并重点讨论了扇形单胞的周期性边界条件。通过逐级计算微观单胞、细观单胞的平均弹性常数,得到了圆管状立体机织复合材料的刚度参数,实现了由组分材料性能及编织参数预测圆管的宏观弹性性能,模型预测刚度与试验结果吻合。另一方面,研究了从大到小各尺度耦合的应力分析,对于圆管环向应力非周期分布的情况,建立了嵌入细观单胞的环状模型,进行了复杂荷载下从宏观圆管结构、到细观纤维束尺度、再到微观纤维尺度之间的逐级应力分析。     

二维机织复合材料弹性常数的有限元法预测

为了预测二维机织复合材料的弹性性能,建立了有限元力学分析模型。基于二维机织复合材料的几何特征,建立了参数化的单胞模型;考虑了织物纤维束呈现出的各向异性材料特征,将有限元中材料主方向转化到纤维屈曲方向,建立其力学分析有限元模型;分析了单胞边界面保持平面假设的不足,提出了对于二维机织复合材料通用的周期边界条件,获得了更为准确的二维机织复合材料的工程弹性常数。结果表明:织物衬垫单胞边界面,在单向拉伸载荷和纯剪切载荷下,呈凹凸翘曲变形,即为周期边界;应用给出的织物参数化几何建模方法与有限元求解方法,可以精确地获得工程弹性常数,数值计算结果与实验值吻合较好。      

基于结构参数的平纹机织复合材料等效弹性性能预测

经向纤维束与纬向纤维束纵横交错引起的纤维弯曲(也称为波纹)是平纹机织复合材料固有特征。首先,提出了一种精确描述平纹机织复合材料单胞3D结构特征的数学表达式。其次,基于经典层合板理论和等应力假设,考虑平纹机织复合材料厚度方向非对称引起的弯曲-拉伸耦合效应及单胞结构特征,建立了含结构参数的平纹机织复合材料等效弹性性能多参数解析模型。通过数个典型算例验证了建立的多参数解析模型,结果表明：该多参数解析模型预测值与相关文献中有限元模型预测值、解析模型预测值、实验值等均吻合较好;该多参数解析模型预测值尤其是Z向弹性性能预测值,比文献中解析模型预测值更接近于实验值。在此基础上,进一步探讨了纤维束波纹比(包括纤维束波动方向波纹比与纤维束横截面波纹比)、经向与纬向纤维束构成的预成形体厚度、纤维束中弯曲部分的长度、相邻纤维束之间间距等结构参数对平纹机织复合材料弹性性能影响。该多参数解析模型建模方法为研究纺织复合材料力学性能提供了参考。     

计及复合材料飞轮内孔卸载影响的多厚环套装的简化分析

纤维束张紧力缠绕的复合材料厚环固化成型以后,再抽出缠绕芯轴形成空心环,这一过程称为内孔卸载。本文作者在飞轮多环套装初应力分析和张紧力缠绕飞轮初应力分析的基础上,进一步给出了计及纤维束张紧力影响和复合材料厚环内孔卸载影响的多环过盈套装的简化分析,并给出了计算复合材料飞轮总体初应力场和变形场的公式。算例分析表明:内孔卸载后,纤维束缠绕的复合材料厚环的应力场和变形场均有明显的变化;和多厚环过盈套装的方法结合起来装配飞轮,可以有效地增大径向压应力,缓和环向应力;内孔卸载使得装配中的真实过盈量相对初始设定过盈量有较大的改变,必须充分考虑。      

纤维束张紧力缠绕复合材料飞轮的预应力简化分析

在纤维束缠绕时施加张紧力,使得固化成型后的飞轮内部形成一定的预加径向压应力,这是提高飞轮径向强度的有效方法之一。基于过盈配合的思想建立了计算张紧力缠绕导致的复合材料飞轮内部预应力和变形的简化模型和方法。通过算例分析发现:等张力缠绕产生的环向应力在半径方向上先减小后增大,径向压应力不断变小;变张力缠绕过程中,张紧力由小逐渐变大时,飞轮的径向压应力增大,径向强度提高;飞轮设计中仅仅依靠张紧力缠绕是不够的,还必须和固化成型后的厚壁筒之间的过盈套装一起来设计合理的径向预加压应力。     

三维正交机织复合材料的单胞模型及应用

根据三维正交机织复合材料的结构特点,在假设纤维束横截面为矩形的基础上建立一种单胞模型,该模型由3组互相正交的纤维与基体组成。首先利用这一模型,推导出纤维体积分数与纤维粗度、机织密度等织物参数的关系式,通过测量单胞单元的单层厚度得到纤维体积分数,计算值和实验值较为吻合。然后在假定纤维和基体均为线弹性材料的基础上,利用材料力学方法推导出了3 个正交方向的杨氏模量表达式,该表达式简单明了,给出了三维正交机织复合材料杨氏模量与纤维和基体的杨氏模量以及纤维体积分数间的关系,算例的计算结果与实验值有良好的一致性,这说明所建立的单胞模型具有合理性。     

纤维束张紧力缠绕复合材料飞轮初应力的三维数值分析

利用平面应力型全弹性模型的思想(即将纤维束张紧力缠绕看成多层复合材料薄环连续过盈装配的过程) , 建立了三维纤维束张紧力缠绕复合材料飞轮初应力分析模型, 并给出了基于面-面接触算法求解张紧力缠绕复合材料飞轮初应力的三维数值方法。算例分析表明, 三维数值分析得到的飞轮的环向初应力及径向初始压应力(数值) 均略低于平面应力模型的结果, 且这种差距随着飞轮轴向长度的增加而缓慢增大; 三维分析证实了平面应力模型关于张紧力缠绕复合材料飞轮的初应力分析有足够的精度。最后给出了三维模型轴向效应的表征方法。      

三维五向管状织物纱束轨迹及纤维体积分数的分析与研究

针对四步法编织的三维五向管状织物,基于圆形编织的纱束运动过程及机理分析,研究了织物内部与表面纱束的几何拓扑关系,继而提出三维五向管状织物的单胞结构模型。在此基础上,分别用阿基米德螺旋线段和圆弧段近似预成型内部与表面的纱束轨迹投影,并给出相应的数学描述。根据单胞几何特征,提出了织物横截面上不同位置处的纤维体积分数计算方法。通过建立纱束数据结构及运用计算机可视化技术,对纱束空间轨迹及横截面纤维体积分数进行了模拟显示。这对表征三维五向管状织物的结构性质、实现编织参数优化设计有着重要的意义。      

计及纤维交叉起伏影响的缠绕复合材料刚度分析

针对缠绕复合材料交叉起伏区域的细观结构,建立了一种细观分析模型。首先,将纤维交叉起伏区域划分为环向交叉起伏区和螺旋交叉起伏区2种类型;然后,以缠绕面为基准,用平行横截面将起伏区域空间结构模型离散化为多个子模型,运用纤维束起伏角、富树脂区域尺寸、纤维束的体积分数、纤维束的横截面形状及尺寸等细观参数来描述缠绕复合材料交叉起伏区域的细观结构。基于所建立的细观模型及层合板理论,提出了缠绕复合材料交叉起伏区域的等效刚度计算方法。通过算例研究了纤维束截面、纤维束起伏角以及富树脂区体积分数等细观参数对局部区域等效刚度的影响。结果表明:环向交叉起伏区的弹性模量比螺旋交叉起伏区下降得更为明显;在富树脂区域,弹性模量和剪切模量降低较为明显,而泊松比则有所增大。纤维束厚度增加及纤维束截面变化对交叉起伏区域等效刚度会产生明显影响。      

复合材料纤维张力缠绕预应力场动态特性

复合材料纤维张力缠绕技术通过提高纤维的张力水平可充分发挥纤维高强、高模优势,在成型过程中对结构进行预紧,成为解决高速转动部件径向变形大、界面强度低等问题新的有效途径。将每一层纤维的张力缠绕等效为一个含预应力复合材料薄环的叠加,基于正交各向异性复合材料缠绕层和各向同性金属芯模弹性变形理论,建立了纤维张力缠绕力学解析模型,得到芯模和缠绕层预应力场随缠绕层数及缠绕张力的变化规律,并通过复合材料纤维张力工艺试验验证了力学解析模型的正确性。研究发现了纤维张力缠绕中预应力“饱和”现象,并确定了影响张力缠绕预应力场的两个主要参数:缠绕层环径向刚度比E_θ/E_r和张力大小T（r）,为复合材料纤维张力缠绕成型工艺提供理论支撑。      

三维正交机织物参数对纤维体积含量的影响

三维机织物设计的一个目标是满足要求的纤维体积含量。通过分析三维正交机织物单元体的结构,可以计算经纱、纬纱和捆绑纱的截面尺寸,建立纤维体积含量与织物参数间的关系。实际制织了一块6层经纱、5层纬纱的玻璃纤维三维正交机织布,测试了经纱、纬纱、捆绑纱以及织物的纤维体积含量,并与理论计算值进行了对比,分析了产生误差的原因。最后,分析了织物参数对纤维体积含量的影响,发现经纬纱粗度比的增大或间距比的减小,将使经纱和织物的纤维体积含量增大,纬纱的纤维体积含量减小;捆绑纱的引入,降低了经纱、纬纱和织物的纤维体积含量。      

Micro-CT analysis of the internal deformed geometry of a non-crimp 3D orthogonal weave E-glass composite reinforcement

An investigation at the unit cell level of the sheared geometry of a single layer E-glass non-crimp 3D orthogonal woven reinforcement (commercialized under trademark 3WEAVE® by 3Tex Inc.) is performed by X-ray micro-computed tomography (micro-CT) observations. The aim is to observe, understand and quantify the effect of in-plane shear deformation on the composite reinforcement geometry, at meso-scale (i.e. unit cell level). It was observed that, increasing the shear deformation, Z-yarns maintain unchanged the distance between the yarns and as consequence the yarn cross-section has a reduced variation of width, mainly in the weft direction.Furthermore, the effect of the shear angle on the textile thickness during compression is measured, this being an important parameter after the forming and molding phases of a composite component production. Compression tests and micro-CT measurements of the thickness show similar values and are in agreement with the prediction obtained assuming the theoretical invariance of the volume in the considered range of shear deformations.     

Consistent Finite Element mesh generation for meso-scale modeling of textile composites with preformed and compacted reinforcements

A new automated method to generate smooth Finite Element meshes for the meso-scale representation of textile composites unit cells with preformed and compacted reinforcements is presented. The reinforcement geometry is obtained from textile geometry preprocessors or by modeling of the preforming step. It is then transformed into a geometric model of the entire composite unit cell, taking into account the real yarn shape after preforming and compaction, the contact interactions between the yarns, as well as the resulting local variations of fiber volume fraction. A consistent mesh of the complete cell, conformal between the parts, is ensured, without the need for inserting artificial matrix layers between the yarns. The methodology is illustrated by mechanical modeling of the representative unit cell of a multi-layer composite with a compacted and nested woven reinforcement.     

The influence of distinct fiber arrangement on the thermo-mechanical behavior of steel fiber-reinforced thermoplastic matrix composites

The effect of different fiber arrangements on mechanical behavior was investigated by using both experimental study and finite elements analyses. In particular, this study examined resultant residual stresses and plastic strains of steel-fiber reinforced thermoplastic composite discs under constant convective air cooling conditions. Three composite discs were manufactured with an identical concentration of woven, circular and radial arrays. The thermal and mechanical properties of the composite discs were measured. The numerical and experimental cooling curves were converged to correctly describe the convective cooling condition of the finite element analyses. After the cooling, the residual stresses and plastic strains in each disc were compared with one another and the results were analyzed. No thermal residual stress or plastic strain was observed for the woven fiber array. Residual stress and plastic strain found in the circular fiber array was twice as high as those in the radial fiber array. It is concluded that the reinforcement fiber array of thermoplastic composites is an effective parameter to describe their thermo-mechanical properties for the formation of thermal residual stresses and plastic deformation.     

三维机织结构的几何模型

根据三维机织结构中纱线系统的组成和相应纱线的几何形态,建立了具有普适意义的几何模型,获得了组成三维机织结构各纱线系统在一个结构单元内的纱线长度和取向角,进而计算出纤维体积分数。随后,选择了基于11种不同接结组织的三维机织复合材料试样,测试了试样的纤维体积分数,所得的测试结果与模型输出的预测值有很好的一致性。利用所建立的模型还定量讨论了接结组织对纤维体积分数和取向角的影响。结果表明:分层接结可以提供比正交接结高的纤维体积分数;而正交接结中接结经具有较大的取向,有利于增强三维机织复合材料在厚度方向上的力学性能。     

Meso-macro approach for composites forming simulation

The F.E. analysis of woven composite reinforcement forming is an alternative to geometrical draping computation. It permits to account for mechanical behaviours of the fabric and static boundary conditions of the process. In this paper, macroscopic forming simulations of woven composite reinforcements are performed using finite elements composed of woven cells, the mechanical behaviour of which are computed by F.E. analyses at mesoscale i.e. on the unit cell of the fabric. The objective is to only calculate the relevant quantities in the woven finite element. The in-plane biaxiale tensile behaviour and the in-plane shear behaviour are obtained by 3D analyses of the woven cell submitted respectively to tension and shear. They need to take the specificities of the mechanical behaviour of the yarn (made of thousand of fibres) into account. Especially an objective derivative based on the fibre rotation is used. These computations on the unit woven cell have proved to be consistent with experimental tests. An example of deep drawing of a square box using the proposed approach is presented. Angles between warp and weft directions are computed as well as wrinkles.     

Modeling and analyses of thermo-elastic properties of radially grown carbon nanotubes-based woven fabric hybrid composite materials

Carbon nanotubes (CNTs) may be useful due to their sound thermo-mechanical properties. The present work deals with the evaluation and analysis of elastic properties and coefficient of thermal expansions (CTEs) of a CNTs-based 2D plane woven fabric composite material system where the CNTs are radially grown on the surface of the carbon fiber. Detailed constructional features of the proposed trans-scale composite material system is explained in detail. The mathematical modeling for the material properties of each constituent or building block of the hybrid composite is developed. The mathematical model for the thermo-elastic properties of yarns is also formulated based on strength of material method whereas the thermo-elastic properties of representative unit cell is based on the unit cell method. Various numerical results have been obtained by varying the CNTs content, carbon fiber contents, and temperatures. Effects of different geometrical parameters (such as yarn thickness, yarn width, and the ratio of gap length to yarn width of the yarn) on the elastic properties as well as the CTEs are also investigated.     

管道修复用涤纶-苎麻复合机织物性能试验

针对传统管道内衬修复材料施工中易出现内壁塌陷等问题,结合目前快速发展的绿色纤维复合材料,提出在涤纶机织物内衬材料中加入苎麻纱线,制作涤纶-苎麻复合机织物材料来提高树脂对管道修复用内衬机织物的浸透性能,增强内衬材料和管壁的粘结性能。以纤维外观、抽拔实验后纤维断面形貌的电镜观察,并通过树脂与织物接触角的测试、粘结实验,综合分析了涤-麻复合机织物的树脂浸透性,同时对涤纶-苎麻复合机织物力学性能进行测试来保障内衬复合材料满足强度的要求。实验结果表明,采用上述涤-麻复合织造的方法,可以显著提高树脂的浸透性能,有利于携带更多的树脂粘结剂提高树脂与管壁的粘结性,减少塌陷发生的可能性。同时加入麻复合的机织物,拉伸顶破性能都满足高压燃气管道的修复要求。