缝合参数对泡沫夹层结构复合材料力学性能的影响

采用真空辅助树脂注射(VARI)成型工艺制备不同缝合方式和缝合密度的缝合泡沫夹层复合材料,研究缝合参数对平面拉伸、三点弯曲、芯子剪切以及滚筒剥离性能的影响。结果表明:缝合使泡沫夹层复合材料的平面拉伸强度和芯子剪切强度明显降低,可以改善弯曲性能并大幅提高滚筒剥离性能,改进锁式缝合方式优于临缝式缝合方式;适当地增加缝合行距对力学性能有一定的积极作用,但不利于滚筒剥离性能的提高;与未缝合泡沫夹层复合材料相比,当缝合密度为30 mm×10 mm时,改进锁式缝合泡沫夹层复合材料的平拉强度和芯子剪切强度分别降低了14.75%和24.79%,弯曲强度和平均剥离强度分别提高了7.96%和80.78%。     

CF-CNTs多尺度增强体的制备及CF-CNTs/环氧树脂复合材料力学性能

利用化学气相沉积(CVD)法在碳纤维(CF)表面生长碳纳米管(CNTs),制备了CF-CNTs多尺度增强体,增强体与环氧树脂(EP)结合得到CF-CNTs/EP复合材料。采用场发射扫描电镜(FESEM)、高分辨透射电镜(HRTEM)等方法研究了不同CVD工艺参数对CF-CNTs多尺度增强体的影响,并研究了不同CVD时间对CFCNTs/EP复合材料力学性能的影响。结果表明:沉积温度为500℃、沉积时间为10min、反应压力为0.02 MPa时,制备得到的多尺度增强体性能最好。CF-CNTs多尺度增强体较未生长CNTs的碳纤维与环氧树脂的浸润性明显提高。在CVD时间为10min时,所得CF-CNTs/EP复合材料的界面剪切强度(IFSS)最大可提高90.6%,层间剪切强度(ILSS)最大可提高24.4%。同时,在制备环氧树脂复合材料过程中碳纤维的不加捻与加捻相比,其ILSS提高了11.3%。     

Manufacturing and mechanical properties of soy-based composites using pultrusion

Two primary cost driving factors for the composites industry are raw materials and labor. Inexpensive alternative epoxy resin systems based on epoxidized soyate resins are developed for fiber reinforced composite applications. This research investigated on the manufacturing and mechanical characterization of fiber/epoxy composites using chemically modified soy-based epoxy resins. Co-resin systems with up to 30 wt% soyate resins were used to manufacture composites through pultrusion. Mechanical tests show that the pultruded composites with soy based co-resin systems possess comparable or improved structural performance characteristics such as flexural strength, modulus, and impact resistance. Maximum mechanical properties enhancement is demonstrated by the enhanced epoxidized allyl soyate (EAS) formulation. Further property improvement is obtained through using a two-step prepolymer process. The EAS holds great potential as partial supplement for polymer and composites applications from renewable resources.     

Compression properties of fire-damaged polymer sandwich composites

The effect of fire-induced damage on the edgewise compression properties of polymer sandwich composites is investigated. Fire tests were performed using a cone calorimeter on sandwich composites with high or low flammability. The highly flammable composite had a poly(vinyl chloride) foam core, while the flame resistant composite had a phenolic foam core. The residual edgewise compression properties of the burnt composites were determined after fire testing at room temperature. The compression stiffness and strength of the two sandwich composites decreased rapidly with increasing heat flux and heating time of the fire due to thermal decomposition of the face skin and foam core. A large reduction to the edgewise compression properties of the phenolic-based sandwich composite occurred despite having good flame resistance, and the reasons for this are described. Preliminary analytical models are presented for estimating the edgewise compression failure load of fire-damaged sandwich composites that fail by core shear or buckling.     

Stochastic analysis of the fracture toughness of polymeric nanoparticle composites using polynomial chaos expansions

The fracture energy is a substantial material property that measures the ability of materials to resist crack growth. The reinforcement of the epoxy polymers by nanosize fillers improves significantly their toughness. The fracture mechanism of the produced polymeric nanocomposites is influenced by different parameters. This paper presents a methodology for stochastic modelling of the fracture in polymer/particle nanocomposites. For this purpose, we generated a 2D finite element model containing an epoxy matrix and rigid nanoparticles surrounded by an interphase zone. The crack propagation was modelled by the phantom node method. The stochastic model is based on six uncertain parameters: the volume fraction and the diameter of the nanoparticles, Young’s modulus and the maximum allowable principal stress of the epoxy matrix, the interphase zone thickness and its Young’s modulus. Considering the uncertainties in input parameters, a polynomial chaos expansion surrogate model is constructed followed by a sensitivity analysis. The variance in the fracture energy was mostly influenced by the maximum allowable principal stress and Young’s modulus of the epoxy matrix.     

The mechanical performance of 3D woven sandwich composites

Composite sandwich structures were manufactured from a 3D woven fabric consisting of two face fabrics interconnected by pile yarns (Distance Fabric). Specimens were produced from Distance Fabric (DF) consolidated with vinyl ester resin with and without a polyurethane foam core and compared to specimens produced from a precast polyurethane foam core with composite skins added separately. Flatwise compression, edgewise compression, climbing drum peel and flexure tests were conducted and all demonstrated a dramatic improvement in properties from the combination of DF and foam core. These improvements are postulated to arise from the mutual reinforcement of the pile yarns and foam core.     

玻璃纤维立体织物增强环氧树脂泡沫夹层复合材料的制备及力学性能

为了进一步提高泡沫夹层复合材料的承载能力和综合性能,实现其在轨道交通及汽车等工业领域的应用,开展了玻璃纤维立体织物增强环氧树脂泡沫(GF-Fabric/EP)复合材料的制备及其力学性能的研究。制备GF-Fabric/EP复合材料及其夹层结构,探索了GF-Fabric/EP复合材料及其夹层结构的失效行为,以揭示立体织物的增强机制。结果表明：立体织物的引入可显著改善GF-Fabric/EP复合材料的强度、刚度及破坏应变;但在不同承载条件下,各纱线发挥承载作用和效果不同。面板、芯材各自的性能、尺寸及面/芯界面性能均是影响GF-Fabric/EP夹层复合材料力学性能及失效特征的重要因素。以三点加载下的弯曲性能为例,针对不同的GF-Fabric/EP夹层复合材料,需调整跨厚比和试样尺寸并获得理想的失效特征,方可对其弯曲性能或层间剪切性能进行有效、合理的评价。     

Glass-fibre-reinforced composites with enhanced mechanical and electrical properties - Benefits and limitations of a nanoparticle modified matrix

Nanoparticles and especially carbon nanotubes (CNTs) provide a high potential for the modification of polymers. They are very effective fillers regarding mechanical properties, especially toughness. Furthermore, they allow the implication of functional properties, which are connected to their electrical conductivity, into polymeric matrices. In the present paper, different nanoparticles, as fumed silica and carbon black, were used to optimise the epoxy matrix system of a glass-fibre-reinforced composite. Their nanometre-size enables their application as particle-reinforcement in FRPs produced by the resin-transfer-moulding method (RTM), without being filtered by the glass-fibre bundles. Additionally, an electrical field was applied during curing, in order to enhance orientation of the nanofillers in z-direction. The interlaminar shear strengths of the nanoparticle modified composites were significantly improved (+16%) by adding only 0.3 wt.% of CNTs. The interlaminar toughness G_Ic and G_IIc was not affected in a comparable manner. The laminates containing carbon nanotubes exhibited a relatively high electrical conductivity at very low filler contents, which allows the implication of functional properties, such as stress-strain monitoring and damage detection.     

The interlaminar fracture of organic-matrix,woven reinforcement composites

A study has been made of the interlaminar (transverse) fracture of glass and graphite fabric composites. A double cantilever beam specimen was used and was width-tapered for constant change in compliance with crack length so that the fracture energy calculation is independent of crack length. It was found that the interlaminar fracture energy could be significantly increased either by the addition of elastomeric toughening agents to the epoxy matrix or by using a thermoplastic matrix resin instead of an epoxy. The largest increase in interlaminar fracture energy (approximately eight-fold) was obtained for an epoxy matrix/graphite fabric composite by the addition of elastomeric modifiers.     

Alfa fibres for unsaturated polyester composites reinforcement: Effects of chemical treatments on mechanical and permeation properties

In this study, composite materials were prepared using unsaturated polyester resins reinforced by Alfa fibres. The fibres were previously modified by chemical treatments, maleic anhydride (MA), styrene (S), acrylic acid (AA) and acetic anhydride (Ac). The Ac and the S treatments allowed an increase in the moisture resistance and the mechanical properties of the fibres. The preliminary S or MA treatment of the fibres allowed a decrease of the water permeability of the composite. A slight increase of the stiffness of the composite was observed due to the presence of the fibres (treated or not), whereas the resistance (breaking strength and strain) was not improved. The mechanical behaviour of the composites appeared similar whatever the treatment of the fibres except with S treatment which seemed to improve the breaking strength.     

Mechanical properties of chemically-treated hemp fibre reinforced sandwich composites

In this study, hemp fabrics were used as reinforcements with polyester resin to form composite skins while short hemp fibres with polyester as a core for making composite sandwich structures. To improve the fibre matrix adhesion properties, alkalisation, silane and acetylation treatments on the fibres surface were carried out. Examinations through fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were conducted to investigate the physical and thermal properties of the fibres. Mechanical properties such as flexural and compressive strengths of the sandwich structures made by treated and untreated hemp fibres were studied. Based on the results obtained from the experiments, it was found that the fibre treated with alkalic solution and post-soaked by 8% NaOH exhibited better mechanical strength as compared with other treated and untreated fibre composite samples. Besides, DSC and TGA analysis showed that the thermal stability of all treated fibre was enhanced as compared with untreated samples.     

Synergistic reinforcement effect of aramid nonwoven fabrics and PVDF on mechanical and damping properties of bismaleimide matrix composites

A new type of structural damping composite was prepared by interleaving aramid nonwoven fabrics (ANF) modified with semi-crystalline polyvinylidene fluoride (PVDF) between carbon-fibre-reinforced bismaleimide (BMI) laminae. The co-cured composite exhibited an increase of 108% and 2.72% in loss factor and flexural modulus, respectively, compared with the original carbon-fibre-reinforced BMI composite. The damping behaviour of the co-cured composites was experimentally investigated using the single cantilever beam test and dynamic mechanical analysis. Furthermore, the composite interlaminar shear strength and flexural strength and modulus were also investigated. The results indicated that the composite interleaved with ANF/PVDF possessed higher flexural modulus and loss factor than the composites interleaved with ANF or PVDF films alone as a result of synergistic reinforcement of ANF and PVDF. Finally, the reinforcement mechanism of ANF/PVDF was investigated by analyzing the composite microstructure and the dynamical mechanical properties of ANF, PVDF, and ANF/PVDF interlayers.     

Structure and mechanical properties of polyethylene-fullerene composites

The microhardness of films of fullerene-polyethylene composites prepared by gelation from semidilute solution, using ultrahigh molecular weight polyethylene (PE) (6×10⁶), has been determined. The composite materials were characterized by optical microscopy and X-ray diffraction techniques. The microhardness of the films is shown to increase notably with the concentration of fullerene particles within the films. In addition, a substantial hardening of the composites is obtained after annealing the materials at high temperatures (T _a=130 °C) and long annealing times (t _a=10⁵s). The hardening of the composites with annealing temperature has been identified with the thickening of the PE crystalline lamellae. Comparison of X-ray scattering data and the microhardness values upon annealing leads to the conclusion of phase separation of C₆₀ molecules from the polyethylene crystals within the material. The temperature dependence is discussed in terms of the independent contribution of the PE matrix of the C₆₀ aggregates to the hardness value.     

Microstructure and mechanical properties of Mg-HAP composites

In the present study, it has been attempted to develop biodegradable Mg-HAP (magnesium-hydroxyapatite) composite materials for bone replacement. At first the HAP powders were prepared by chemical synthesis process and synthesized powders were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Synthesized powders contain HAP as a major phase with tricalcium phosphate (β-TCP) as a minor phase. The Mg-HAP composites were prepared by adding different amounts of HAP powders to Mg melts and finally the billets were extruded. The microstructure of Mg-HAP composite was examined by optical microscope (OM). The presence of HAP in Mg matrix results in decrease of grain size of Mg-HAP composites. The theoretical and experimental hardness of the composites are compared with the addition of HAP. The tensile strength of composites is found to decrease with the addition of HAP, whereas compressive strength increases with HAP.     

Mica-EVA-AR弹性体复合材料动态力学性能

将乙烯醋酸乙烯酯共聚物(EVA)、 丙烯酸酯弹性体(AR)和云母(Mica)熔融共混制备了一系列复合材料。动态力学分析发现, EVA与AR共混后, tanδ在5℃附近出现了新峰; 在EVA-AR(80/20)中加入聚合级空间受阻酚MPDI(4-甲基-苯酚与二环戊二烯和异丁烯的反应产物), tanδ峰值逐渐增大, 且峰位置逐渐向高温方向偏移。云母的加入使EVA-AR-MPDI共混物的tanδ峰位置明显向高温方向偏移, 而且峰宽拓宽明显。随着云母含量的增加, 高温区tanδ数值逐步变大, 损耗模量E″大幅度提高, 当云母含量为58.8wt%时E″峰值由未加云母时的79MPa增加至280MPa, 并且E″峰位置向高温偏移。氢键红外光谱和扫描电镜分析结果表明, 复合材料阻尼性能有所提高。      

基体粉末与增强粒子的粒度级配对SiCp/Fe性能的影响

使用不同粒度的铁粉,采用电流直加热动态热压烧结工艺制备了10%(体积分数)的SiC颗粒增强铁基复合材料,研究了铁粉与SiC粒子颗粒级配对复合材料显微组织和力学性能的影响.结果表明,SiC粒子与铁粉的颗粒级配,显著影响复合材料基体中增强粒子的分布状况和力学性能.建立了粒子分布的双基体颗粒级配模型,只有铁粉中一次颗粒与二次颗粒的粒径比为6.5、二次颗粒含量为4.6%、铁粉一次颗粒与SiC的粒度比值为15.9时,SiC颗粒才能很好地填充铁粉间隙并均匀地分布在基体中,复合材料将具有较高的力学性能.模型计算的结果和实验结果相符合.