碳纤维织物力学性能和冲压成形实验研究

在实际成形过程中,碳纤维复合材料往往处于复杂的应力状态,开展近于真实载荷环境下的力学试验分析,能够更准确地认识实际应用中材料的成形性能和变形机理.为获得碳纤维织物的基本力学特性,设计了平纹碳纤维织物拉伸试样及成形试样,进行了单轴拉伸、双轴拉伸、镜框剪切试验和方盒冲压成形实验研究,对比了不同双拉比及纱线取向对力学性能及成形性能的影响.研究结果表明:碳纤维织物具有高度的非线性、各向异性和双拉耦合特性,即经纬向纤维的力学性能会相互影响;剪切变形是成形过程中的主要变形模式,当剪切角达到临界锁死角时,织物发生起皱现象;同种织物不同纱线取向试样表现出不同的成形性能,因此可以根据零件几何形状选择合适纤维取向的织物,从而减少缺陷,优化成形零件的力学性能.研究结果为后续建立碳纤维织物本构模型和成形仿真奠定了基础.     

Sheet hydroforming of woven FRT composites: non-orthogonal constitutive equation considering shear stiffness and undulation of woven structure

For the simulation of sheet hydroforming for the shaping of woven fabric reinforced thermo-plastic (FRT) composites, a non-orthogonal constitutive model was developed based on a homogenization method by considering the microstructures of composites including mechanical and structural properties of the fabric reinforcement. This model is modified to capture the wrinkling behavior due to the undulation geometry of the woven structure and shear stiffness at the crossover of the warp and weft yarns of woven FRT composites. The model was implemented in an explicit dynamic finite element code to analyze the forming behavior of woven FRT during the stamp thermo-hydroforming process. Wrinkling behavior was investigated based on the application of a counteracting fluid pressure and changes to the initial blank shape.     

碳纤维机织物增强热塑性树脂复合材料热冲压叠层模型

针对碳纤维增强热塑性树脂复合材料(CFRTP)在热冲压成型过程中涉及到大变形、各向异性和多场耦合的现象,为了表征CFRTP在成型中的力学特征,基于有限元方法与连续介质力学理论提出了一种热塑性树脂基体与碳纤维机织物的叠层模型。与单独采用碳纤维机织物超弹性本构模型预测CFRTP成型性能的方法相比,提出的叠层模型能够表征成型温度、压边力和纤维取向对CFRTP成型缺陷的影响,并能优化热冲压成型工艺参数。这一叠层模型具有简单实用和材料参数容易确定的优点,为碳纤维机织物增强热塑性树脂复合材料成型的数值模拟和成型工艺优化奠定了理论基础。     

A non-orthogonal constitutive model for characterizing woven composites

Thermoforming of woven fabric reinforced composites usually results in significant in-plane shear deformation in materials, and induces additional anisotropy into the composite. In this paper, a new constitutive model for characterizing the non-orthogonal material behavior under large deformation is proposed. On the basis of stress and strain analysis in the orthogonal and non-orthogonal coordinates and the rigid body rotation matrices, the relationship between the stresses and strains in the global coordinates is obtained. The equivalent material properties are then determined by fitting the numerical load vs. displacement curves to experimental results under biaxial tension and pure shear conditions. This model can be used to efficiently predict material responses under various loading paths for woven composites with different weave architectures. The geometrical non-linearity and the material non-linearity, as well as the complex redistribution and reorientation of the warp and weft yarns during deformation are taken into account. To demonstrate the performance of this model, numerical simulations using a commercial finite element package (ABAQUS/Standard) incorporated with our material model are conducted for various loading cases. Numerical results are in excellent agreement with experimental data.     

考虑双拉耦合的复合材料编织物各向异性超弹性本构模型

为了准确描述复合材料编织物的各向异性力学特性,首先,基于纤维增强复合材料连续介质力学理论提出了一种考虑纤维双拉耦合的复合材料编织物各向异性超弹性本构模型,该模型中单位体积的应变能被解耦为便于参数识别的纤维拉伸变形能、双拉耦合引起的挤压变形能和纤维间角度变化产生的剪切变形能;然后,给出了模型参数的确定方法,并通过拟合单轴拉伸、双轴拉伸和镜框剪切实验数据得到了本构模型参数;最后,利用该模型对双轴拉伸和镜框剪切实验进行了数值仿真,并将模拟结果与实验结果对比分析。结果表明:提出的本构模型适用于表征复合材料编织物在成型过程中由于大变形引起的非线性各向异性力学行为。所得结论表明提出的本构模型具有简单、实用的优点,且材料参数容易确定,可为复合材料编织物成型的数值模拟和工艺优化奠定理论基础。      

复合材料用机织物非正交本构模型的半球形冲压成型验证

为了描述复合材料用机织物在大变形下由于经纱和纬纱之间角度变化所引起的非线性各向异性材料行为, 前期工作中建立了一个非正交本构模型。利用半球形冲头对复合材料用平纹机织物进行冲压模拟, 并将非正交本构模型和正交本构模型的模拟结果与实验结果进行对比, 对非正交本构模型进行验证, 以充分说明该模型的有效性和正确性。结果表明: 采用非正交本构模型模拟的复合材料用平纹机织物变形后的边界轮廓与实验结果基本一致, 并且剪切角都在实验结果的误差范围内; 而采用正交本构模型, 复合材料用机织物变形后的边界轮廓和剪切角与实验结果相差较大。研究表明, 与正交本构模型相比非正交本构模型能更好地描述复合材料用机织物在大变形下的材料属性。      

Numerical and Experimental Investigations on Deep Drawing of G1151 Carbon Fiber Woven Composites

This study proposes to simulate the deep drawing on carbon woven composites in order to reduce the manufacturing cost and waste of composite material during the stamping process, The multi-scale anisotropic approach of woven composite was used to develop a finite element model for simulating the orientation of fibers accurately and predicting the deformation of composite during mechanical tests and forming process. The proposed experimental investigation for bias test and hemispherical deep drawing process is investigated in the G1151 Interlock. The mechanical properties of carbon fiber have great influence on the deformation of carbon fiber composites. In this study, shear angle–displacement curves and shear load–shear angle curves were obtained from a bias extension test. Deep drawing experiments and simulation were conducted, and the shear load–displacement curves under different forming depths and shear angle–displacement curves were obtained. The results showed that the compression and shear between fibers bundles were the main deformation mechanism of carbon fiber woven composite, as well as the maximum shear angle for the composites with G1151 woven fiber was 58°. In addition, during the drawing process, it has been found that the forming depth has a significant influence on the drawing force. It increases rapidly with the increasing of forming depth. In this approach the suitable forming depth deep drawing of the sheet carbon fiber woven composite was approximately 45 mm.     

Experimental and computational composite textile reinforcement forming: A review

Preforming is an important step in the manufacturing of textile-reinforced composites with resin infusion processes. It is important to control the fiber orientation to avoid fiber misalignments and wrinkles, which would reduce the mechanical properties of the composite part. The objective of the present paper is to give an overview of the literature dedicated to the textile reinforcement forming process. Therefore, experimental tests for the determination of the basic fabric properties, the experimental characterization of the forming and the numerical approaches for the modeling of the textile forming are reviewed. A great part of the literature has been devoted to the characterization of the shear behavior since it is the most important property for textile reinforcement forming processes. The bending behavior was initially neglected in mechanical models but was found to be important for the simulation of wrinkles.     

A homogenization procedure for the numerical analysis of woven fabric composites

The paper presents a procedure for the numerical evaluation of the mechanical properties of woven fabric laminates. Woven fabrics usually present orthogonal interlaced yarns (warp and weft) and distribution of the fibers in the yarns and of the yarns in the composite may be considered regular. This allows us to apply the homogenization theory for periodic media both to the yarn and to the fabric. Three-dimensional finite element models are used in two steps to predict both the stiffness and the strength of woven fabric laminates. The model includes all the important parameters that influence the mechanical behavior: the lamina thickness, the yarn orientation, the fiber volume fraction and the mechanical characteristics of the components. The capabilities of the numerical model were verified studying the elastic behavior of a woven fabric laminate available in the literature and the ultimate strength of a glass fabric laminate experimentally investigated. The procedure, that can be implemented into commercial finite element codes, appears to be an efficient tool for the design of textile composites.     

Formability of a non-crimp 3D orthogonal weave E-glass composite reinforcement

In this paper, the formability of a single layer E-glass non-crimp 3D orthogonal woven reinforcement (commercialized under trademark 3WEAVE® by 3Tex Inc.) is experimentally investigated. The study involves the forming process of the 3D fabric on two complex moulds, namely tetrahedron and double-dome. The tests are assisted by 3D digital image correlation measurement to have a continuous registration of the fabric local deformation. Moreover, the results of bending tests in warp and weft direction are detailed to enlarge the mechanical properties data set of the 3D reinforcement, necessary for understanding its deformability capacities in forming processes. The elevated bending stiffness of the 3D fabric means that use of a blank-holder during forming is not required. The reinforcement has a good drapability and it is able to form complex shapes without defects (wrinkles and fibre distortions). The collected experimental results represent an important dataset for numerical simulations of any complex shape with the considered 3D fabric composite reinforcement.     

The characterization of low cost fiber reinforced thermoplastic composites produced by the DRIFT™ process

A new, low cost process for hot-melt impregnation of continuous reinforcing fibers with thermoplastic polymers is described. This technique can be used to fabricate various product forms including discontinuous, long-fiber products for compression molded parts, continuous fiber products for pultrusion, filament winding, and woven fabric applications. Mechanical data are presented for composites with various fiber and polymer combinations. Effects of fiber orientation and length on mechanical properties are discussed, and the effect of fiber–polymer bonding on impact strength and microstructure are shown. It is shown that the low cost and high performance achieved with this approach has the potential to expand applications of thermoplastic composite materials.     

The effect of thermoplastic coating on the mechanical properties of woven fabric carbon/epoxy composites

The effect of a polyetherimide (PEI) coating on the mechanical properties of woven fabric carbon/epoxy composites was investigated by thermal mechanical analysis, fractographical analysis and mechanical properties measurements. PEI coating enhanced the mechanical properties of carbon/epoxy composites mainly through the improvement of matrix properties. This was because most of the PEI coated on the carbon fiber diffused into the bulk of epoxy matrix due to its good miscibility with epoxy resin. As for mechanical properties of woven fabric carbon/epoxy composites, the extent of improvement by PEI coating highly depended on the applied stress state. Among the mechanical properties, mode II delamination resistance of carbon/epoxy composites showed the highest increment because matrix shear property played an important role in delamination resistance of woven fabric carbon/epoxy composite. Because of the woven geometry of carbon fiber, the improvement in impact property of carbon/epoxy composite was trivial except the large amount of PEI coated case.     

平纹编织SiC/SiC复合材料多尺度建模及强度预测

连续SiC纤维增强SiC基体复合材料（SiC/SiC）具有优异的高温力学性能、辐照稳定性及较低的氚渗透率,在核工程结构领域具有良好的应用前景,掌握其承载状态下的损伤演化和强度性能,对SiC/SiC复合材料的应用具有重要指导意义。本文基于平纹编织SiC/SiC复合材料的制备过程和组分材料分布的多尺度特性,考虑复合材料微观结构的局部近似周期性,建立了纤维丝尺度和纤维束尺度单胞模型。使用有限元分析软件对纤维丝尺度模型的弹性性能和强度性能进行预测,将这些性能参数代入纤维束尺度模型,引入Tsai-Wu失效准则,根据材料的不同失效模式并对失效单元进行方向性刚度折减,模拟了平纹编织SiC/SiC复合材料在单轴拉伸载荷下的渐进损伤过程。数值模拟曲线与试验曲线吻合较好,实现了对平纹编织SiC/SiC复合材料强度的有效预测。      

Fractographical analysis on the mode II delamination in woven carbon fiber reinforced epoxy composites

Mode II delamination phenomena of woven fabric carbon/epoxy composites were investigated by scanning electron microscopy. End notch flexural (ENF) test was used to examine the mode II delamination. Woven fabric composites showed two peculiar crack propagation patterns due to the complexity of woven geometry. In warp yarn region, crack propagated with forming a shear band and breaking the fiber/matrix interface. In fill yarn region, however, no shear band was observed. Considering these crack patterns, matrix shear property and fiber/matrix interfacial strength played an important role in enhancing the delamination properties of woven fabric carbon/epoxy composites. Due to the woven geometry, matrix rich positions, which are interstitial and undulated region, were formed in woven carbon/epoxy composite. In these regions, matrix fracture and complex crack path were mainly observed.     

An approach in modeling the temperature effect in thermo-stamping of woven composites

Made with high-strength continuous fibers, textile composites are of increasing interest in automotive and aerospace industries due to their high-strength/weight performance as compared to sheet metals. Nevertheless, significant reduction in manufacturing cost is required to use textile composites for mass production applications. Highly efficient thermo-stamping operations possess the potential to substantially reduce fabrication time and cost compared to the much slower autoclave forming process. In this paper, thermo-forming of woven fabric-reinforced thermo-plastic composites is simulated using a non-orthogonal material model. The temperature effect is taken into account by modifying the equivalent material properties for the composite sheet based on the contact status between the tooling and the blank. The approach is exemplified on the hemispherical thermo-stamping of a plain weave composite sheet.     

Free vibration analysis of orthogonal-woven fabric composites

This paper presents a study on the free vibration analysis of orthogonal-woven fabric composites. The fabrics are composed of two sets of mutually orthogonal yarns of either the same material (nonhybrid fabrics) or different materials (hybrid fabrics). We focus on the repeating unit of the woven structure, known as a `unit cell'. Based upon the one-dimensional (1D) elasto-dynamic analysis developed by the authors for such a woven fabric composite, the free vibration problem is formulated and solved for four basic boundary conditions. Natural frequency equations and natural modes are obtained analytically. For the special case of two bonded isotropic layers, closed-form solutions of natural frequencies and natural modes are given. It has been shown that numerical solutions can readily be carried out for woven fabric composites with arbitrary combinations of material and geometrical parameters. As an example, the first ten natural frequencies for plain weave composites based upon graphite/epoxy and glass/polyester are presented and discussed.     

Initial fracture behavior of satin woven fabric composites

Final fractures of composites is considered to be caused by cumulation of the microfractures, so that, the initiation of microfracture, namely, initial fracture is important factor to know the mechanical properties. Microfracture behaviors in textile composites were regarded to be decided by the geometry of textile fabric quantitatively. In this study, initial fracture in plain and satin woven fabric composites was investigated and the effect of weaving structure on initial fracture behavior was clarified. First, in order to investigate the geometry of textile fabric, crimp ratio and aspect ratio were measured. Tensile testing was performed and knee point on the stress–strain curve was identified. Fracture process of composites was observed by replica method. Initial fracture in plain woven fabric composite was confirmed as transverse crack in weft fiber bundle, on the other hand, in satin woven fabric composites both transverse crack and filament fracture at the same time was observed. The effects of changes in crimp ratio and aspect ratio on the initial fracture of woven fabric composites were discussed.     

Geometrical analysis of woven fabric microstructure based on micron-resolution computed tomography data

The global mechanical properties of textiles such as elasticity and strength, as well as transport properties such as permeability depend strongly on the microstructure of the textile. Textiles are heterogeneous structures with highly anisotropic material properties, including local fiber orientation and local fiber volume fraction. In this paper, an algorithm is presented to generate a virtual 3D–model of a woven fabric architecture with information about the local fiber orientation and the local fiber volume fraction. The geometric data of the woven fabric impregnated with resin was obtained by micron-resolution computed tomography (μCT). The volumetric μCT-scan was discretized into cells and the microstructure of each cell was analyzed and homogenized. Furthermore, the discretized data was used to calculate the local permeability tensors of each cell. An example application of the analyzed data is the simulation of the resin flow through a woven fabric based on the determined local permeability tensors and on Darcy’s law. The presented algorithm is an automated and robust method of going from μCT-scans to structural or flow models.     

考虑拉剪耦合的二维编织物各向异性超弹性本构模型

基于连续介质力学理论,提出了一种考虑二维编织物拉剪耦合作用的各向异性超弹性本构模型。该模型中应变能被分解为纤维拉伸应变能和拉剪耦合作用下的剪切应变能两部分。给出了模型参数的确定方法,通过拟合实验数据,得到了本构模型参数。利用确定的本构模型对文献中不同预拉状态下的镜框剪切实验进行了预测,通过与实验结果对照,验证了所提出的本构模型正确性。该模型不仅具有明确的物理意义且参数确定简单,为更加全面精确的二维编织物成型有限元分析奠定了理论基础。