碳纤维表面物理结构对复合材料界面剪切强度的影响

以3种典型碳纤维为研究对象,通过碳纤维断面形貌的扫描电镜分析,采用Photoshop对纤维截面特征进行有效提取并由Matlab编写程序,获得了碳纤维表面沟槽深度、宽度、个数等参数的统计信息,据此进一步计算了圆形度、沟槽深宽比、表面不规整度以及沟槽密集程度等物理量,建立了碳纤维表面物理沟槽结构的定量表征方法。在此基础上研究了原丝制备过程中的凝固环境对碳纤维表面物理结构的影响,并发现:当凝固浴温度由25℃升高至45℃时,碳纤维表面的沟槽深度及宽度均会逐渐减小,深宽比降低,沟槽形状逐渐趋于平缓,同时碳纤维的表面不规整度减小了约7.5%,而沟槽密集程度增加了约50%。采用上述具有不同表面物理结构特征的碳纤维作增强体制备复合材料,微滴脱粘测试结果表明:碳纤维复合材料的界面剪切强度(IFSS)随纤维表面的沟槽尺寸、沟槽深宽比及表面不规整度的增大而逐渐提高。     

Interfacial shear behavior of 3D composites reinforced with CNT-grafted carbon fibers

This paper presents the Molecular Dynamic (MD) models and the simulation results for the shear deformation process of an interface representative cell to develop an understanding of the roles of multi-walled carbon nanotube (MWNT) in enhancing fiber–matrix interfacial properties such as shear modulus and strength. Based on the MD results and the two simple formulae of rule of mixture, the shear modulus and strength of the carbon nanotube (CNT) grafted interface can be predicted. It is shown that there exists a good agreement between the predicted fiber–matrix interfacial shear strength with and without grafted CNTs and these measured from single-fiber micro bond test and single-fiber fragmentation test. The MD simulation also shows the MWNTs’ shear stress cross-section distribution is similar to that of a circular beam in shear with a non-zero shear stress on the neutral plane.     

碳纤维增强聚醚醚酮复合材料的形状记忆效应

为推动形状记忆聚合物在空间等极端恶劣环境中的应用,以超薄碳纤维增强聚醚醚酮(Carbon fibers reinforced polyether-ether-ketone,CF/PEEK)预浸料为实验对象,采用薄膜叠层与热压成型工艺制备厚度为0.036 mm超薄预浸料的层合片材,研究了其在热应力驱动下的形状记忆行为。结果表明,在320℃加热-冷却热循环温度场的作用下,CF/PEEK复合材料超薄层合板的初始变形的形状回复率近似可达100%,当变形循环达到100次时,其形状回复率仍然可以保持在90%以上。此外,根据层合板变形的温度与应力-应变关系,解释了CF/PEEK复合材料的热应力驱动变形机制。在此基础上,改变CF/PEEK层合板厚度进行仿真设计,实现了初始状态与深海珊瑚形状、立方体、灯笼草形状之间的变形与回复。利用记忆变形产生的机械夹紧力,完成了硬币抓取实验,验证了CF/PEEK复合材料在主动变形结构应用的可行性。      

Fabrication and mechanical properties of Cu-coatedwoven carbon fibers reinforced aluminum alloy composite

Cu-coatedwoven carbon fibers/aluminum alloy composite (C_f/Al) was prepared by spark plasma sintering. Microstructure and mechanical properties of the composite were investigated. Microstructure observation indicates that the interface reaction is evidently inhibited by Cu coating. Woven carbon fibers are adhered to the matrix alloy by anchor locking effect of matrix alloy immersing into the interstices between carbon fibers. Under the quasi-static and dynamic compressive conditions, the composite exhibits excellent ductility even when the strain reaches 0.8. Adding carbon fibers into ZL205A alloy has no obvious influence on compressive flow stress of the composite. The compressive true stress–true strain curves show that the composite is a strain rate insensitive material. During the tensile tests, the elongation of the composite shows a sharp increase from 4.5% to 13.5% due to the adding of woven carbon fibers. Meanwhile, the tensile strength of the composite is increased slightly from 168 MPa to 202 MPa compared to that of ZL205A alloy. The good ductility of the composite is ascribed to the cracks deflection, fibers pulling out, debonding and breakage mechanisms.     

Elaboration of aluminum-matrix composite materials reinforced with inorganic fibers

This article is a literature survey concerning the different methods presently known for producing fiber-reinforced aluminum-matrix composites. The elaboration problems are discussed in terms of wettability between aluminum or aluminum alloys and inorganic fibers. The fibers involved are continuous monofilaments about 100 μm diameter such as boron or silicon carbide fibers, and tows of 500–6000 endless thinner filaments 5–15 μm as graphite fibers, alumina fibers and Nicalon silicon carbide fibers. The typical mechanical properties (strength, modulus, fatigue) attained with these reinforcing fibers are also reported.     

碳纳米管增强PA6纤维的性能

将碳纳米管(CNT)在分散剂或分散剂和聚合物(PA6)载体中处理后制备出两种母粒,将其作为增强材料分别和PA6切片熔融共混纺丝,制备出碳纳米管的增强PA6纤维,研究其结构和力学性能.CNT含量低于0.5%(质量分数)时,使用两种母粒制备出的纤维强度和模量都提高,NT含量为0.03%时增强的效果最好.由碳纳米管和分散剂组成的母粒增强效果更好,NT的含量为0.03%时就能使PA6纤维的强度和模量分别提高23%和76%.这种增强纤维是一种微纤增强纤维,纳米CNT在纤维中均匀分散且沿着纤维轴的方向取向.这种结构能有效地转移载荷,具有增强作用,且取向性越好,增强效果越好.     

Modified shear lag theory based fatigue crack growth life prediction model for short-fiber reinforced metal matrix composites

Closed form expressions for the low cycle and high cycle fatigue crack growth lives have been derived for the randomly-planar oriented short-fiber reinforced metal matrix composites under the total strain-controlled conditions. The modeling was based on fatigue-fracture mechanics theory under both the small scale and the large scale yielding conditions. The modified shear lag theory was considered to describe the effect of yielding strength. The present model is essentially a crack growth model because crack initiation period in short fiber reinforced metal matrix composite is much shorter; hence, not assumed to play a dominant role in the calculation of fatigue crack growth life. The effects of short-fiber volume fraction (V_f), cyclic strain hardening exponent (n′) and cyclic strain hardening coefficient (K′) on the fatigue crack propagation life are analyzed for aluminum based SFMMCs at different levels of cyclic plastic strain values. It is observed that the influence of fatigue crack growth resistance increases with increase in cyclic strain hardening exponent (n′) and decreases when volume fraction (V_f) or cyclic strain hardening coefficient (K′) increases. The present MSL theory based fatigue crack growth life prediction model is an alternative of modified rule of mixture and strengthening factor models. The predicted fatigue life for SFMMC shows good agreement with the experimental data for the low cycle and high cycle fatigue applications.     

碳纤维混杂纤维混凝土抗冲击性能研究

对比美国混凝土学会的混凝土落锤冲击试验装置,自行设计了混凝土落锤弯曲冲击试验装置,进行了不同几何尺寸及弹性模量的碳纤维、钢纤维和聚丙烯纤维混凝土的抗冲击力学性能试验研究。分析比较了不同纤维几何尺寸和弹性模量、种类和掺量对混杂纤维混凝土抗冲击性能的影响和增强机理。本文通过定义混杂效应系数,可定量评价混凝土抗冲击力学性能的正混杂效应。研究表明纤维可以明显提高混凝土的抗冲击强度,其中碳纤维混杂纤维混凝土的提高幅度更为显著。     

An inclusion model for crack arrest in a composite reinforced by sliding fibers

The inclusion model of Mori and Mura for crack arrest in fiber reinforced materials is extended. The analysis is restricted to short fibers. The sliding of fibers is allowed along fiber-matrix interfaces. Analytical expressions for energy release rate and extra energy dissipation during crack extension are obtained. Sliding fibers result in a larger energy release rate than non-sliding and perfectly bridging fibers. However, the energy dissipation accompanied by sliding offers additional resistance to the extension of a crack. Fibers of smaller radius decrease the energy release rate and raise the energy dissipation more efficiently.     

Processing of hybrid wood plastic composite reinforced with short PET fibers

Poly(ethylene terephthalate) (PET) fibers (virgin, waste, and mixed) were incorporated in the composite poly(methyl methacrylate) (PMMA)–wood. Hybrid composite panels were prepared by pressure molding. Toluene-2,4-diisocyanate (TDI) and (3-mercaptopropyl)trimethoxysilane (MPTMS) were used as cross-linking bonding agents for modification of wood fibers. Influence of cross-linking bonding agents, structure, and composition of PET fibers was examined by studying thermomechanical properties as well as moisture absorption. Moisture absorption was lower for composites with bonding agents. Mechanical testing revealed that the addition of PET fibers drastically enhances properties of the composites. Covalent and hydrogen bonds formed with the addition of bonding agents have also improved mechanical properties compared to the untreated composites.     

Sandwich panels with Kagome lattice cores reinforced by carbon fibers

Stretching dominated Kagome lattices reinforced by carbon fibers were designed and manufactured. The sandwich panels were assembled with bonded laminate skins. The mechanical behaviors of the sandwich panels were tested by out-of-plane compression, in-plane compression and three-point bending. Different failure modes of the sandwich structures were revealed. The experimental results showed that the carbon fiber reinforced lattice grids are much stiffer and stronger than foams and honeycombs. It was found that buckling and debonding dominate the mechanical behavior of the sandwich structures, and that more complaint skin sheets might further improve the overall mechanical performance of the sandwich panels.     

Ferromagnetic composite coatings on carbon fibers

Alumina- and titania-based composite coatings containing ferromagnetic nanoparticles have been produced on UKN-5000P carbon fibers by an in situ organo-inorganic hybrid sol-gel process using appropriate aqueous metal chloride solutions containing Fe(III) and Co(II). The morphology, phase composition, and elemental composition of the coatings have been studied by high-resolution electron microscopy, X-ray diffraction, and energy-dispersive X-ray microanalysis. The results demonstrate that the oxide coatings containing ferromagnetic nanoparticles are uniform in thickness along and across the fibers and adhere well to the fiber surface. The coatings range in thickness from 100 to 500 nm. In all of the systems studied, the coatings produced on carbon fibers differ in phase composition from powders prepared from identical hydrosols.     

Experimental study of carbon fiber reinforced plastic with embedded optical fibers

Structural differences of interface between the embedded optical fiber and the resulting smart composite were studied. Quasi-isotropic composite laminated specimens were produced from T300 Carbon/epoxy prepregs. Optical fibers were embedded within the specimens at different locations. Micro photos of the specimens showed that ‘bridges’ formed around the embedded optical fibers. The configuration and the size of the ‘bridges’, namely, the interfacial structures, varied with the locations where the optical fiber was embedded. Tensile tests showed that the ultimate strength of the smart material was affected by different interfacial structures. As the location of the embedded fiber moved to the middle plane of the specimen, the size of the interface increased. This caused the drop of the tensile strength. Observation of the broken sections of different specimens showed that imbibitions between the coating of the optical fiber and the clad were not good enough, therefore, damages could originate at the interface between the coating and the clad foremost.     

Damage model for concrete reinforced with sliding metallic fibers

This contribution presents an effective and practical three dimensional (3D) numerical model to predict the behaviour of concrete matrix reinforced with sliding metallic fibers. Considering fiber-reinforced concrete (FRC) as two-phase composite, constitutive behaviour laws of plain concrete and sliding metallic fibers were described first and then they were combined according to anisotropic damage theory to predict the mechanical behaviour of FRC. The behaviour law used for the plain concrete is based on damage and plasticity theories able to manage localized crack opening in 3D. The constitutive law of the action of sliding metallic fibers in the matrix is based on the effective stress carried by the fibers. This effective stress depends on a damage parameter related to on one hand, on the content and mechanical properties of fibers and on the other hand, on the fiber–matrix bond which itself depends on the localized crack opening. The proposed model for FRC is easy to implement in most of the finite element codes based on displacement formulation; it uses only measurable parameters like Young’s modulus, tensile and compressive strengths, fracture energies and strains at peak stress in tension and compression. A comparison between the experimental data and model results has been also provided in this paper.     

Punching shear behavior of concrete flat plate slab reinforced with carbon fiber reinforced polymer rods

Flat plate slab system is widely adopted by engineers as it provides many advantages . The system can reduce the height of the building, provide more flexible spatial planning due to no beams present, and further reduce the material cost. However, the main problem in practice is the brittle failure of flat plate slab under punching shear. In this paper, the punching shear behavior has been studied and an experimental work using carbon fiber reinforced polymer (CFRP) rods as shear reinforcement has been conducted in flat plate slab system.This exploratory research is to study the behavior of the flat plate slab with CFRP-rods reinforced in punching shear zone under constant gravity load and lateral displacements in a reversed cyclic manner. Three specimens of interior column-slab connection specimens were tested including one standard specimen without any shear reinforcement, the second one reinforced with CFRP-rods and the third one reinforced with stud rails as the reference to the second one. The slabs were 3000 mm long × 2800 mm wide × 150 mm deep, and were simply supported at four corners. Punching shear failure occurred for the standard specimens at a lateral drift-ratio, lateral drift divided by the length of vertical member, of approximately 5%. The specimen reinforced by CFRP-rods had significant flexural yielding and sustained deformations up to a drift ratio of approximately 9% without significant losses of strength, and punching shear was not observed in this specimen. The displacements increased up to 1.79 times larger than that of the standard specimen. And this specimen showed 42% superior ductile performance than the standard specimen and even the same capability with the stud-rail reinforced specimen. The results of the experiment indicate that CFRP-rods using in the flat slab has a better foreground.     

Thermal expansion behaviors of aluminum composite reinforced with carbon nanotubes

The coefficient of thermal expansion (CTE) of aluminum matrix composite reinforced with 1.0wt.% multi-wall carbon nanotubes (MWNTs) fabricated by cold isostatic pressing and hot squeeze technique was measured between 25 and 400 °C with a high-precision thermomechanical analyzer, and compared with those of pure aluminum and 2024Al matrix fabricated under the same processing. The results show that the CTE of the composite obviously reduces in relation to those of pure aluminum and 2024Al matrix due to the introduction of MWNTs. The addition of 1.0wt.% MWNTs to 2024Al matrix decreases the CTE by as much as 12% and 11% compared with those of pure aluminum and 2024Al matrix at 50 °C, respectively, which indicates that carbon nanotube reinforced metal matrix composite may be a promising materials with low CTE.     

Friction and wear behavior of hydroxyapatite based composite ceramics reinforced with fibers

The HA-based composites reinforced with multi-component fibers were prepared by hot pressing. The friction properties of the composite at different temperatures were investigated by a block-on-disc tester. The results show that the addition of Cu has a significant positive effect on the friction and wear behaviors of HA-based composites. The improvements in the friction and wear properties of HA-based composites depend on the formation of an interfacial layer. The plastic deformation and the mending effect of Cu benefit the formation of the interfacial layer. The wear mechanism of the composites changes from the delamination and abrasive wear to the adhesive wear with increasing Cu.     

Mechanical property improvement of unsaturated polyester composite reinforced with admicellar-treated sisal fibers

Sisal fiber was treated by admicellar polymerization with a poly(methyl methacrylate) film coating in order to enhance the interfacial adhesion of the fiber/polymer composite for mechanical property improvement. Properties of the admicellar-treated sisal fiber were investigated by measuring its moisture absorption and electrostatic charge. Thermal stability study by thermogravimetric analysis and film identification by FTIR was also carried out. The treatment was shown to improve the tensile and flexural properties, impact strength, and hardness of the composite. SEM micrographs of the tensile fracture surface of sisal/unsaturated polyester composites also show interfacial adhesion improvement of the composite prepared with admicellar-treated sisal.