碳/环氧复合材料多向层间拉伸强度的研究

本文系统地研究了碳/环氧复合材料多向层间(0/θ)(θ=0°,15°,30°,45°,60°,75°,90°)拉伸强度,并利用S-570扫描电镜观察了其断口形貌,同时对纤维与基体界面处的应力进行了分析。结果表明:该复合材料层间拉伸强度较少受到铺层取向的影响,而由纤维与基体的界面结合强度所控制。     

高温下的金属基复合材料双剪切试样应力应变有限元分析

对金属基复合材料双剪切试样的应力应变分布进行蠕变有限元计算分析,得到受剪区的应力应变随时间的分布规律。通过典型取向试样分析,表明受剪区的应力应变与纤维随机分布平面和加载方向夹角θ之间存在很大的相关性:随角度θ的减小,其蠕变应力分布越均匀;当角度θ=45°时,其稳态蠕变率γ·最大。双剪切试样能得到较均匀的剪应力区域,适合研究材料纯剪应力状态下的蠕变行为。     

聚乙烯醇纤维增强聚乳酸复合材料的制备及性能研究

以聚乳酸(PLA)和高强高模聚乙烯醇(PVA)纤维为原料，通过熔融共混热压成型工艺制备了不同PVA纤维含量的PLA/PVA复合材料，研究了复合材料的相形态、玻璃化转变、结晶和熔融行为以及力学性能。结果表明：低含量的PVA纤维能均匀地分散在PLA基体中，当纤维质量分数达到20%时，纤维发生团聚。差示扫描量热仪测试结果表明PVA纤维在PLA结晶过程中起到了成核作用。随PVA纤维含量增加，PLA的结晶度增加。此外，动态力学行为表明PVA纤维含量的增加有助于提高复合材料储能模量和刚性。复合材料的拉伸和弯曲模量随PVA纤维含量的增加而增加，当PVA纤维质量分数为20%时，拉伸和弯曲模量达到最大，与纯PLA相比，复合材料的拉伸和弯曲模量分别提高了43.5%和38.6%。但是，PVA纤维的加入并没有使复合材料的拉伸和弯曲强度得到较大改善。     

甘蔗渣纤维增强可降解复合材料的制备与弯曲模量的预测

利用压制成型制备了甘蔗渣纤维增强可降解复合材料,分析了纤维的热分解性能,研究了纤维含有量和纤维长度对材料弯曲模量的影响,利用Cox剪滞法和材料的结构特点,探讨了一种新的修正模型对弯曲模量的预测。实验表明,随着纤维含有量和纤维长度的增加,材料弯曲模量呈递增趋势。扫描电镜的观察显示了甘蔗渣纤维的横断面呈现蜂窝状结构,成型后受到压缩而变得致密,导致了弯曲模量的提高。预测结果表明,导入了纤维压缩率的修正模型的理论计算值与实验值取得了良好一致。     

复合材料层板+θ/-θ层间断裂韧性研究

本文讨论了纤维增强复合材料层板沿+θ/-θ层间断裂韧性的研究方法;提出在满足一定力学条件时,可沿用机械载荷实验方法测得G_C中“纯机械部分”G_m;结合数值方法计算得出“纯温度部分”G_T,从而得到G_C.给出一个针对DCB试验的充分条件,据此设计铺层并对T300/648和T300/QY8911进行试验和分析(θ=0～30°)、讨论了大变形的影响并提出一个新的修正系数.结合θ对G_C的影响及断口微观形貌作了进一步讨论.     

界面对硅酸铝短纤维增强AZ91D镁基复合材料蠕变性能的影响

界面对复合材料蠕变性能的影响很大。在试验分析的基础上建立了硅酸铝短纤维增强AZ91D镁基复合材料理论分析模型,利用三维有限元分析方法,系统研究了界面特性、界面上应力应变分布和短纤维位向变化对硅酸铝短纤维增强AZ91D镁基复合材料蠕变性能的影响。研究表明：界面特性,如厚度、模量,均对纤维最大轴应力和稳态蠕变速率有影响,当界面厚度增加,纤维最大轴应力减小而稳态蠕变速率增大;当界面模量增大,纤维最大轴应力增大而稳态蠕变速率减小,但当界面模量高于基体模量时,纤维最大轴应力和稳态蠕变速率均保持不变;纤维位向也影响轴应力分布和稳态蠕变速率,纤维在其末端界面上存在较大的应力和应变,此处容易产生微裂纹而使材料抗蠕变能力下降;界面对硅酸铝短纤维增强AZ91D镁基复合材料的蠕变曲线和蠕变断裂机制也有影响,其影响程度还与纤维位向有关。     

碳纤维复合材料的微波反射特性研究

研究了各种铺层（０°、０°／９０°、±３０°、±４５°、±６０°）方式碳纤维复合材料（ＣＦＲＰ）的皮反射特性。结果表明,单向纤维铺层ＣＦＲＰ的反射率与纤维方向及层板厚度有关;交叉铺层ＣＦＲＰ的反射率很大,但比金属略小,喷涂了防雷击层的单向纤维铺层ＣＦＲＰ,电性能基本上各向员性;喷涂了防雷击层的０°、±４５°、０°／９０°ＣＦＲＰ的反射率比喷涂前有所降低。     

孔洞在晶界上长大行为的模拟

通过编制率相关有限元用户子程序,运用晶体有限元,通过建立一个包含球形孔洞的双晶粒模型,对FCC晶体中孔洞在晶界的长大行为进行了分析。计算中,晶粒1的取向固定为(0°,45°,90°),晶粒2的取向分别为(35°,45°,90°),(60°,45°,90°),(0°,0°,0°),分别对应于单胞A,单胞B,单胞C,晶界与X轴方向的夹角θ分别取0°,45°,60°。计算结果表明:单胞的断裂模式与两晶粒的取向因子的差异有关,对于两晶粒的取向因子差异最大的单胞B,单胞沿晶界处的等效塑性应变比单胞其它地方的应变大,且最大等效塑性应变在三个单胞中为最大,单胞易于发生沿晶断裂。而对于两晶粒的取向因子差异最小的单胞C,沿晶界的等效应变较小,单胞易于发生穿晶断裂。晶界与X轴方向的夹角θ为45°时,单胞沿晶界处的等效应变较大,单胞易发生沿晶断裂。     

纤维增强复合材料黏弹性行为的预测模型

根据标准线性固体模型构造了一种预测纤维增强复合材料黏弹性行为的模型, 推导出该模型的本构方程与松弛模量和蠕变柔量表达式, 该模型经有限元仿真验证具有较高的精度。利用该模型研究了纤维几何特性对蠕变柔量和松弛模量的影响。结果表明, 复合材料蠕变柔量与纤维比长度呈线性关系, 而当纤维比半径增大到临界值后, 其变化对材料的松弛模量和蠕变柔量影响减小, 该临界值随纤维弹性模量的增大而减小; 当纤维模量与基体模量相差较大时, 复合材料的增强系数和减柔系数几乎不受时间变化的影响。      

玻璃微珠含量及粒径对填充聚丙烯复合材料动态力学性能的影响

应用动态力学分析仪,在－１５０￣１０１０℃的温度范围内,考察了玻璃微珠填充聚丙烯中微珠的含量及其粒径对复合材料动态力学性能的影响。结果表明,室浊下的贮能模量和 损耗模量随着微珠体积分数Φｆ的增加而呈非线性形式增大;在相同条件下,最大粒径微珠填充体系的动态模量高于较小粒径微珠填充体系;微珠含量和粒径对复合材料的阻尼的影响不明显;在Φｆ５％￣１５％范围内,玻璃化转变温度随着Φｆ的增加而增大,然后随之下     

An analytical characterization of the anisotropy of the elastic modulus of misaligned short-fiber-reinforced polymers

Short-fiber-reinforced polymers (SFRP) are very attractive because of their ease of fabrication, relatively low cost and mechanical properties which are superior to those of relevant polymer resins. Owing to the partial orientation distribution of the fibers in final components, SFRP composites show direction-dependence, namely anisotropy in their mechanical properties. The fiber-length distribution (FLD) and the fiber-orientation distribution (FOD) in SFRP composites play an important role in determining the composite mechanical properties. In the present paper, the FLD and the FOD are modelled with suitable probability density functions and the laminate analogy approach is used to derive the expression of the elastic modulus of SFRP as a function of any given direction, the FLD and the FOD. The direction-dependence, i.e. the anisotropy, of the elastic modulus of SFRP has been studied in detail by taking into consideration the effects of the FLD and the FOD. The present theory is applied to existing experimental results, and the agreement is found to be very satisfactory.     

有一定取向性的碳纤维增强尼龙6复合材料弹性模量的实验和理论研究

纤维增强热塑性聚合物基复合材料注塑成型后往往被认为是各向同性复合材料。然而,注塑成型后纤维会具有一定的取向性,从而使复合材料试样呈现各向异性的特点。为了合理预测此类复合材料的弹性模量,本文对碳纤维增强尼龙6复合材料注塑试样内部的纤维长度和取向分布情况进行了测试和分析,得出了纤维取向的分布规律。随后结合单向纤维增强聚合物基复合材料力学模型和层叠理论,构造出了适用于有一定取向性的纤维增强树脂基复合材料弹性模量预测理论模型,其理论结果和拉伸实验结果吻合较好,表明该预测模型的准确性比较高。      

Interactions at fiber/matrix interface in short fiber reinforced amorphous thermoplastic composites modified with micro- and nano-fillers

This study aims at systematically extracting fiber/matrix interfacial strength in short-glass fiber-reinforced polymer composites using an experimental micromechanics approach which employs mechanical properties and residual fiber length distributions to derive the apparent interfacial shear strength. We started from neat high-impact polystyrene matrix short-glass fiber-reinforced composites (HIPS/GF) with varying fiber loading and proceeded toward HIPS/GF hybrid composites containing micro- and nano-fillers where complex fiber/matrix interfacial interactions exist. It was found that apparent interfacial shear strength does not vary with fiber content, while the presence of fillers with different length-scales alters fiber/matrix interactions depending on their influence on physical properties of the polymer matrix, particularly in the vicinity of reinforcing fiber surfaces.     

连续纤维增强树脂复合材料纵向压缩强度预测模型的发展及其影响因素

基于高强、高韧、高模和压拉平衡为特征的第三代先进复合材料的需求,综述了连续纤维增强树脂复合材料纵向压缩强度预测模型的发展历程。基于纤维微屈曲、纤维扭结带、联合预测模型及渐进损伤失效模型,分别讨论了连续纤维增强树脂复合材料压缩失效机制,并在联合预测模型基础上,探究了碳纤维（直径、模量、体积分数、初始偏角）、树脂基体（弹性模量、剪切模量）及纤维/树脂界面三要素对连续纤维增强树脂复合材料纵向压缩强度和压缩失效形式的影响。      

PP composites based on mechanical pulp,deinked newspaper and jute strands: A comparative study

In the present work, polypropylene-based composites reinforced with three types of randomly distributed short lignocellulosic fibers, namely mechanical pulp (MP), deinked pulp (DIP), and jute strands, were prepared and analyzed. Addition of 6% (wt/wt) of MAPP resulted in a significant enhancement in the tensile strength in line with the improvement of the fiber–matrix interfacial adhesion making more effective the transfer of stress from the matrix to the rigid reinforcement. The mechanical properties of these composites were analyzed in terms of Bowyer–Bader and Hirsch models to fit the obtained experimental data. From the stress/strain curves and the fiber length distributions, it was possible to access to the orientation factor, the interfacial shear strength, the intrinsic tensile strength and the modulus of the fibers.     

PP composites based on mechanical pulp,deinked newspaper and jute strands: A comparative study

In the present work, polypropylene-based composites reinforced with three types of randomly distributed short lignocellulosic fibers, namely mechanical pulp (MP), deinked pulp (DIP), and jute strands, were prepared and analyzed. Addition of 6% (wt/wt) of MAPP resulted in a significant enhancement in the tensile strength in line with the improvement of the fiber–matrix interfacial adhesion making more effective the transfer of stress from the matrix to the rigid reinforcement. The mechanical properties of these composites were analyzed in terms of Bowyer–Bader and Hirsch models to fit the obtained experimental data. From the stress/strain curves and the fiber length distributions, it was possible to access to the orientation factor, the interfacial shear strength, the intrinsic tensile strength and the modulus of the fibers.     

短纤维橡胶基复合材料模量的理论预测

基于Ｈａｌｐｉｎ－Ｔｓａｉ方程，引入短纤维平均长度和取向因子ｆｐ考虑尼龙短纤维／氯丁橡胶天然橡胶复合材料中短纤维的长度分布和纤维取向对纵向杨氏模量的影响，提出直接用ｆｐ修正ζ来考虑取向影响的新方法，ζθ（ｆｐ）＝Ｌｄ＾－１（ｆｐ＋１）。结果表明，纵向模量的理论预测值和实验值的相关性较好，对横向模量，用ζ＝２＋Ｋｖｆ（Ｋ为决定于体系的常数）考虑取向的影响，预测也较成功。     

Influence of processing methods and fiber length on physical properties of kenaf fiber reinforced soy based biocomposites

Biocomposites from kenaf fiber and soy based bioplastic were fabricated by extrusion, followed by injection or compression molding. The impact of fiber length and the processing method on the thermal and mechanical properties of the composites were characterized with dynamic mechanical analysis (DMA) and mechanical properties measurements. The morphology was studied with optical and electron microscopy. Compression molded specimens have a similar modulus to injection molded specimens at room temperature, but exhibit a higher heat deflection temperature (HDT) and notched Izod impact strength. The improved HDT and impact strength are derived from an increase in modulus at high temperature and fiber bridging effects, respectively. The modulus, impact strength and HDT of kenaf fiber reinforced soy based biocomposites increase with increases in fiber length, fiber content and fiber orientation. Through microscopy observations, it was found that the fractured fiber length on the impact fracture surface increased with increasing fiber length and fiber content. This indicates that the role of fiber bridging effects is predominant on impact strength of the biocomposites.     

Continuous carbon nanotube reinforced composites

Carbon nanotubes are considered short fibers, and polymer composites with nanotube fillers are always analogues of random, short fiber composites. The real structural carbon fiber composites, on the other hand, always contain carbon fiber reinforcements where fibers run continuously through the composite matrix. With the recent optimization in aligned nanotube growth, samples of nanotubes in macroscopic lengths have become available, and this allows the creation of composites that are similar to the continuous fiber composites with individual nanotubes running continuously through the composite body. This allows the proper utilization of the extreme high modulus and strength predicted for nanotubes in structural composites. Here, we fabricate such continuous nanotube polymer composites with continuous nanotube reinforcements and report that under compressive loadings, the nanotube composites can generate more than an order of magnitude improvement in the longitudinal modulus (up to 3,300%) as well as damping capability (up to 2,100%). It is also observed that composites with a random distribution of nanotubes of same length and similar filler fraction provide three times less effective reinforcement in composites.     

Analysis of effect of fiber orientation on Young’s modulus for unidirectional fiber reinforced composites

Young’s modulus of unidirectional glass fiber reinforced polymer (GFRP) composites for wind energy applications were studied using analytical, numerical and experimental methods. In order to explore the effect of fiber orientation angle on the Young’s modulus of composites, from the basic theory of elastic mechanics, a procedure which can be applied to evaluate the elastic stiffness matrix of GFRP composite as an analytical function of fiber orientation angle (from 0° to 90°), was developed. At the same time, different finite element models with inclined glass fiber were developed via the ABAQUS Scripting Interface. Results indicate that Young’s modulus of the composites strongly depends on the fiber orientation angles. A U-shaped dependency of the Young’s modulus of composites on the inclined angle of fiber is found, which agree well with the experimental results. The shear modulus is found to have significant effect on the composites’ Young’s modulus, too. The effect of volume content of glass fiber on the Young’s modulus of composites was investigated. Results indicate the relation between them is nearly linear. The results of the investigation are expected to provide some design guideline for the microstructural optimization of the glass fiber reinforced composites.