Effect of silane/nano-silica on the mechanical properties of basalt fiber reinforced epoxy composites

The present study explains the role of surface modification of constituent materials on composite material performance. The influence of silane and nano-hybrid coatings on mechanical properties of basalt fibers and composite materials on their base was investigated. Infrared spectroscopy indicated that modification of basalt fiber surface and nano-SiO₂ was successfully applied. The surface modification leads to the significant increase in the tensile strength of basalt fibers compared to the non-coated fibers. The tensile strength of silane-treated fibers was established 23% higher than the non-coated fibers, indicating that silane plays a critical role in the strength retention of basalt fibers. Also it was pointed out that silane coupling agents can be used for the preparation of the nano-hybrid coating. Addition of SiO₂ nanoparticles into the fiber surface was incorporated to enhance the interfacial bonding of basalt fiber reinforced epoxy composite.     

硼酸镁晶须增强镁基复合材料的谱学表征与性能研究

用X射线衍射谱分析了Mg2B2O5w/AZ91D镁基复合材料中的物相。研究了固溶处理和时效处理以及固溶处理加人工时效处理对复合材料组织演变的影响及组织与显微硬度之间的关系。结果表明,经过固溶处理后,共晶相的分解使复合材料的硬度值明显下降。时效处理使得复合材料的硬度逐渐增加并在时效处理16h后出现时效峰值201HV。然而随着时效时间的进一步增加,显微硬度值降低。经固溶处理24h,基体中β相基本溶解,形成过饱和的固溶体,接着时效处理8h,β相以弥散形式析出,从而使得复合材料的显微硬度值提高30%;而固溶处理24h及时效处理24h后,β析出相由细小片状的连续析出相向粗大的层片状非连续析出相过渡,使得复合材料的显微硬度下降到183HV。     

Moisture absorption characteristics and effects on mechanical properties of Kolon/epoxy composites

Para-aramid fibers (Kolon) are high performance polymeric fibers characterized by their high tenacity and impact resistance. They are used for the soft body armor structures in ballistics. In this study, the testing specimens were made from multilayered Kolon fabrics impregnated with epoxy resin where silicon carbide (SiC) microparticles or SiC nanofibers were added as reinforcement. The laminated composite samples were fabricated by hot compression and curing of epoxy resin.The tensile and impact strengths of the untreated specimens were compared with the ones that underwent water absorption in duration of 72 h (immersion or humidity) followed by desorption. The immersion of the specimens in water and exposure to high humidity (70%) were performed according to the ISO 62 standard while the tensile test was carried out in accordance with the ASTM D 3039 standard. In the end, the tensile test simulation of the laminated composite by using software Abaqus® was accomplished.     

Studies on wettability, mechanical and tribological properties of the polyurethane composites filled with talc

A series of polyurethane (PU)/talc composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The effect of the talc content on the mechanical, wettability and tribological properties of the PU composites was studied. Tensile strength of the PU composites reached to the maximum after adding 5% talc. The water contact angles (CA) of the original surfaces and worn surfaces of the polyurethane composites were measured. The experimental results indicated that the contact angles of the worn surface increased after friction. The friction and wear experiments were tested on a MRH-3 model ring-on-block test rig at different sliding speeds and loads under dry sliding and water lubrication. Experimental results revealed that the talc contributed to largely improve the tribological properties of the PU composites. The coefficient of friction (COF) of the composites increased with increasing talc. Scanning electron microscopic (SEM) investigations showed that the worn surfaces of the talc filled PU composites were smoother than pure polyurethane under given load and sliding speed.     

Optimizing mechanical and thermal expansion properties of carbon/carbon composites by controlling textures

The present study explored the effect of medium texture (MT) content on flexural properties and thermal expansion coefficients (CTE_S) of carbon/carbon (C/C) composites with multilayered pyrolytic carbon. The specimen with 39% MT exhibited maximum flexural strength of 221.55 MPa, increasing by 52% compared with pure high texture. While the flexural strength decreased when the MT content exceeded 39%. The excellent strength can be attributed to crack deflection between multilayered texture and the strong interface bonding between fibers and matrix. Moreover, the four specimens expressed a similar trend of CTE_S in the direction of XY and Z. In the direction of XY, the specimen with 39% MT had the lowest CTE_S from 800 °C to 2100 °C. Therefore, the C/C composites with 39% MT have the best mechanical and thermal expansion properties, which means that the properties of C/C composites can be optimized by controlling the texture.     

Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.     

The effect of interface on fracture mechanism of GF/PP composites using O2 plasma treatment

Polypropylene sheets are treated with oxygen plasma for the interfacial control of GF/PP composites. The interfacial strength between glass fabric and PP resin is estimated by the T-peel test method. The evaluation of T-peel test data is done by both the T-peel strength method and the T-peel amplitude method. The T-peel strength value and T-peel amplitude value were respectively increased to about 50% and 120% compared with each value of non-treated specimens. The T-peel strength relates to the surface energy on the PP-sheet and the T-peel amplitude relates to the fracture pattern of the delamination surface. From SEM observations on the delamination surface, many voids in the space enclosed with fiber bundles are observed in the case of non-treated specimen and no void and fiber bridging are observed on the plasma treated specimens. It is found that interfacial properties between fiber and resin are improved by this plasma process.     

Polyaniline-coated kenaf core and its effect on the mechanical and electrical properties of epoxy resin

Novel conducting kenaf core/polyaniline (KC-PANI) biofibers were successfully prepared via in situ oxidative polymerization. The newly developed conducting KC achieved enhancement in DC conductivity up to seven fold compared to the raw KC. Enhanced interaction was obtained between the acetylated KC-PANI surfaces compared to untreated KC-PANI, without significant loss in the cellulose crystallinity. The morphological analysis revealed uniform layers of PANI deposited on the surface of acetylated KC. Epoxy resin (EP) containing KC-PANI (EP/KC-PANI composites) showed that the electrical percolation of KC-PANI occurred at 20?wt.%. The tensile strength of the EP/KC-PANI composites was slightly reduced compared to that of EP/KC composites at the same loading fraction. However, the flexural test revealed that the presence of KC-PANI increased the flexural strength of the EP composites by up to 15?wt.% loading. Electron micrograph of the EP/KC-PANI composite indicated favourable adhesion between components.     

Morphology,mechanical, rheological,and thermal properties study on the PTT/ABS/SCF composites

In order to improve the mechanical properties of the poly(trimethylene terephthalate) (PTT), both maleinized acrylonitrile–butadiene–styrene (ABS) and short carbon fiber (SCF) were melt-blended with PTT to prepare the composites and their morphology and properties were investigated in detail. When ABS content is fixed at 5?wt.% in composites, SCF can significantly improve the tensile and flexural strength as well as the impact strength of the matrix. The SCF has good interface adherence with the matrix. At glassy state, the storage modulus increases much with increasing SCF content. At rubbery state, the composites have larger cold-crystallization rate. At molten state, SCF first serves as lubricants and then as viscosity reinforcing agent for the matrix with increasing SCF. The composites melt exhibits increasing elastic behaviors with SCF. The composites have larger crystallization rate, but this accelerating effect decreases with excessive SCF content. The crystals formed in different composites are quite different in size or perfection.     

Effects of particle/matrix interface and strengthening mechanisms on the mechanical properties of metal matrix composites

A randomly distributed multi-particle model considering the effects of particle/matrix interface and strengthening mechanisms introduced by the particles has been constructed. Particle shape, distribution, volume fraction and the particles/matrix interface due to the factors including element diffusion were considered in the model. The effects of strengthening mechanisms, caused by the introduction of particles on the mechanical properties of the composites, including grain refinement strengthening, dislocation strengthening and Orowan strengthening, are incorporated. In the model, the particles are assumed to have spheroidal shape, with uniform distribution of the centre, long axis length and inclination angle. The axis ratio follows a right half-normal distribution. Using Monte Carlo method, the location and shape parameters of the spheroids are randomly selected. The particle volume fraction is calculated using the area ratio of the spheroids. Then, the effects of particle/matrix interface and strengthening mechanism on the distribution of Mises stress and equivalent strain and the flow behaviour for the composites are discussed.     

Study on the surface properties of wood/polyethylene composites treated under plasma

Wood/polyethylene (PE) composites are widely used in many fields for its excellent properties, but they are hard to adhere for the surface lacking of polarity. So low-pressure glow discharge of air plasma was used to improve the adhesion properties of wood/PE composites. The composites were treated by plasma under different discharge power. And the changes on the surface properties of the treated and untreated composites were studied by contact angle, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) analysis. The measurement showed that the contact angle decreased after plasma treatment, and the contact angle decreased gradually with the increasing of discharge power. The FTIR analysis results showed that the polar groups such as hydroxyl, carbonyl and carboxyl were formed on the surface of the composites treated under plasma. SEM and AFM results showed that the roughness of plasma treated samples increased. XPS analysis results indicated that the content of carbon element decreased while the content of oxygen element in the composition of wood/PE composites surface element increased and it reached a balance in a higher power, meanwhile a lot of carboxyl groups were formed. The newly formed polar groups are benefit for the adhesion of composites. The shear bonding strength test showed that the adhesion properties of wood/PE composites improved effectively after plasma treatment.     

The effect of filler on the temperature coefficient of the relative permittivity of PTFE/ceramic composites

High permittivity and low-loss ceramic fillers have been prepared by means of the solid state ceramic route. Ceramic-filled composites were prepared by the Sigma Mixing, Extrusion, Calendering, which was followed by the Hot pressing (SMECH) process. The microwave dielectric properties of the composites were studied using X-band waveguide cavity perturbation technique. The temperature coefficient of the relative permittivity of the composites was investigated in the 0-100 °C temperature range using a hot and cold chamber coupled with an impedance analyzer. The temperature coefficient of the relative permittivity of the composites showed strong dependence on the temperature coefficient of the relative permittivity of the filler material. In the present study, a high-permittivity polymer/ceramic composite, having τ_εr ∼63 ppm/K, has been realized. This composite is suitable for outdoor wireless applications.     

The role of interface modification on the mechanical properties of injection-moulded composites from commingled polypropylene/banana granules

Commingled polypropylene (PP)/banana granules were fabricated from slivers by mixing PP fibers and banana fibers by textile equipment. By twisting the sliver, the reinforcing fibers were compacted and bonded with the molten matrix material. PP/banana composites were prepared from commingled PP/banana granules by injection moulding method with special reference to the effect of maleic anhydride modified polypropylene (MAH-PP) concentration. The mechanical properties of the composites were found to depend on the concentration of MAH-PP. The tensile and flexural properties of the composites increased with the addition of MAH-PP up to 2 wt%. After 2 wt% addition of MAH-PP, these properties tend to be stabilized. On the other hand the unmodified composites showed the maximum impact strength. Fourier transform infrared spectroscopic (FTIR) analysis of the MAH-PP modified composites showed evidence of a chemical bridge between the hydroxyl group of the banana fiber and maleic anhydride of the MAH-PP through an esterification reaction. The feature peak of the esterification occurred in the range ～ 1743 cm^?1. In order to confirm the esterfication reaction further, FTIR spectra of the banana microfibrils and MAH-PP modified PP/banana microfibril composites were taken and compared. The tensile fracture surfaces of the unmodified and MAH-PP modified PP/banana composites were studied by scanning electron microscopy (SEM). An improvement in adhesion between the fiber and the matrix was observed in the case of MAH-PP modified composites. Two different processing methods, both injection and compression mouldings were performed to prepare the PP/banana composites. Tensile properties of the composites prepared by these two methods were compared. The enhancement of tensile properties for injection-moulded composites compared to the compression-moulded composites is owing to the occurrence of orientation, better mixing and interaction between the fiber and the matrix during injection moulding. Finally, experimental results of the tensile properties of the injection-moulded composites have been compared with theoretical predictions.     

Comparative experimental studies on the mechanical and degradation properties of natural fibers reinforced polypropylene composites

Coir/silk fiber-reinforced polypropylene (PP) based unidirectional composites (40 wt.%) were manufactured by compression molding. Coir/silk fibers and PP sheets were treated with ultraviolet radiation at different intensities and then composites were fabricated. It was found that mechanical properties of irradiated silk/irradiated PP composites were found to increase significantly compared to the untreated ones and even higher than that of irradiated coir/irradiated PP composites. Soil degradation tests indicated that irradiated coir/irradiated PP composites significantly lost much of its mechanical properties, but irradiated silk/irradiated PP composites retained their strength of its original integrity. Scanning electron microscopy and water uptake of both types of composites were also investigated.     

Surface modification of recycled carbon fiber and its reinforcement effect on nylon 6 composites: Mechanical properties,morphology and crystallization behaviors

Recycled carbon fiber (RCF) was employed as a reinforcement material for preparation of nylon 6-based thermoplastic composites. An effective approach was developed to clean and modify the surface condition of RCF with nitric acid and then with an epoxy macromolecular coupling agent. The interfacial adhesion between RCF and nylon 6 matrix was improved significantly as a result of such a surface modification. Consequently, the reinforcing potential of the RCF was enhanced substantially, and thus, the mechanical properties and thermal stabilities of nylon 6 composites were improved remarkably. The morphologies of fracture surfaces indicated that RCF achieved a homogeneous dispersion in nylon 6 matrix due to good interfacial boding between fibers and matrix. The studies of non-isothermal and isothermal crystallization behaviors showed that RCF acted as a nucleation agent for the crystallization of nylon 6; therefore, the crystallization rate and nucleation density increased notably due to the heterogeneous nucleating effect of RCF in the matrix. These crystallization features may be advantageous for the enhancement of mechanical performance and processability of nylon 6-based composites. This study may provide a design guide for RCF-reinforced nylon 6 composites with a great potential as well as a low cost for industrial and civil applications.     

Size effect on the structure and magnetic properties of SmMn2O5 nanorods

Three sizes of SmMn₂O₅ nanorods that are labeled with (<L_C>) × axial lengths of 58(17) nm × 25(6) nm, 92(21) nm × 32(8) nm, and 126(25) nm × 52(13) nm were fabricated by the hydrothermal method. All the samples exhibited an antiferroicmagnetic (AFM) peak at approximately 6 K, which was associated with Sm magnetic ordering and no size independence. Another AFM magnetic ordering that belongs to the Mn ion was found with <L_C> = 58 nm, 92 nm, and 126 nm at 26 K, 28 K, and 30 K, respectively. The spin-orbit interaction increases with size in the magnetic susceptibility experiment. All the samples displayed a hysteresis loop at 2 K. The coercivity decreases as the size increases. The effects of the size on the crystal structure were elucidated from the Raman spectra of the <L_C> = 92 and 126 nm samples at various temperatures. The 126 nm sample displayed a red-shift for the Ag mode with warming, revealing that the Mn–O bonds are more sensitive to temperature in larger SmMn₂O₅ nanorods. These results demonstrate that the size effect importantly affects the structure and magnetic properties in SmMn₂O₅ multiferroic nanorods.     

Effects of plasma surface modification on the mechanical properties of carbon fiber and carbon fiber/epoxy composite

_The effect of surface treatment on mechanical properties of carbon fibers has been investigated by application of plasma polymerization of selected monomers in the vapor phase. The role of the fiber-matrix interface on carbon fiber-reinforced epoxy resin composites has also been studied. Composites have been prepared separately by the use of plasma-modified and unmodified carbon fibers in the epoxy resin matrix. The mechanical properties of carbon fibers (Hercules and Grafil) as well as of fiber/epoxy composites were examined by using single filament and three-point bending tests, respectively. It was observed that plasma polymerization treatment at selected plasma conditions led to significant improvement of interlaminar shear and flexural strength values of composites.     

The interface structure of nano-SiO2/PA66 composites and its influence on material's mechanical and thermal properties

The PA66-based nanocomposites containing surface-modified nano-SiO₂ were prepared by melt compounding. The interface structure formed in composite system was investigated by thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The influence of interface structure on material's mechanical and thermal properties was also studied. The results indicated that the PA66 chains were attached to the surface of modified-silica nanoparticles by chemical bonding and physical absorption mode, accompanying the formation of the composites network structure. With the addition of modified silica, the strength and stiffness of composites were all reinforced: the observed increase depended on the formation of the interface structure based on hydrogen bonding and covalent bonding. Furthermore, the differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that the presence of modified silica could affect the crystallization behavior of the PA66 matrix and lead to glass transition temperature of composites a shift to higher temperature.     

第一性原理研究压力对Fe2B的结构、机械性质的影响

基于密度泛函理论的第一性原理方法,系统研究了0～30 GPa压力下四方相Fe₂B的结构,稳定性和力学性质等.随着压力的增加,计算得到的晶格参数逐渐减小,所有结构均满足热力学稳定性,体积模量和剪切模量逐渐增大,韧性得到有效改善.硬度呈现先增大后减小的趋势,并在18 GPa压力时达到最大值,各向异性先增大后减小.德拜温度变化趋势与杨氏模量的变化趋势相同.同时还研究了相变结构——正交相的相关性质,结果表明其结构满足热力学稳定性但不满足力学稳定性,是否稳定存在还需要进行后续实验研究.     

Effect of processing temperature on the micro- and macro-interfacial properties of carbon fiber/epoxy composites

Three different temperature schemes were applied on carbon fiber/epoxy composite to elucidate the effect on interfacial shear strength (IFSS) and inter-laminar shear strength (ILSS). It showed that carbon fiber/epoxy IFSS was significantly influenced by the processing temperature, while ILSS was only slightly changed. Moreover, the mechanical properties revealed no necessary relationship between the micro- and macro-interfacial strengths with the properties of epoxy matrix. Among all the temperature schemes, Pro2 (the one-platform curing scheme with relatively rapid heating rate) produced highest IFSS and ILSS. Fourier transform infrared spectroscopy analysis demonstrated that the sizing agent can chemically react itself and also react with epoxy resin at temperature 180?°C. The resin rheological data showed that different temperature schemes can considerably impact diffusion behavior of the resin molecules. Hence, the highest interfacial strengths for Pro2 scheme were ascribed to large extent of chemical reactions and good inter-diffusion between components, at the interface region.