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1.
This study focused on the fabrication and acoustic property evaluation of sandwich cover-ply-reinforced highresilience thermal-bonding nonwoven hybrid composites. P-phenyleneterephthalamides and bicomponent high-resilience bonding polyester intra-ply hybrid nonwoven fabrics were compounded with glass plain fabric to produce the high strength sandwich structural cover ply by means of needle punching and thermal bonding to reinforce the whole composites and dissipate energy when being impacted. Then, the acoustic absorption properties of the homogenous intra-ply hybrid meshwork layer were investigated before and after being reinforced with the aforementioned cover ply. The influencing factors, including areal density, fiber blending ratio, needle punching depth, and air cavity thickness between back plate of the impedance tube and composites, were comparatively investigated. Results revealed that hybrid composites exhibited exceedingly high acoustic absorption properties. Acoustic absorption coefficients were promoted with increases in areal densities and fiber blending ratio of 3D crimped hollow polyester, particularly at low-mid frequency range. In addition, needle punching depths and back air cavity thicknesses considerably affected the average absorption coefficients. The meshwork center layer reinforced with sandwich structural cover-ply perform high resilience properties. 相似文献
2.
This work investigates the effects of fibre content and fibre orientation on the damping of flax fibre-reinforced polypropylene composites. Laminates of various fibre contents were manufactured by a vacuum bagging process; their dynamic behaviour were then found from the vibration measurements of beam test specimens using an impulse hammer technique to frequencies of 1 kHz. The frequency response of a sample was measured and the response at resonance was used to estimate the natural frequency and loss factor. The single-degree-of-freedom circle-fit method and the Newton’s divided differences formula were used to estimate the natural frequencies as well as the loss factors. The damping estimates were also investigated using a “carpet” plot. Experiments were subsequently conducted on a range of samples with different fibre volume fractions and orientations. The results show significant variations in natural frequencies and loss factors according to the variations in fibre orientation. Composites containing 45°, 60° and 90° fibre orientation exhibit approximately the same natural frequencies. Composites with differing fibre orientations exhibit different loss factors for the various modes of vibration, and the maximum loss factor is obtained for the case of 45° fibre orientation, with the loss factor generally lying in the range of 2-7 %. It was found that the loss factor increases with increasing frequency and decreases slightly with increasing fibre content. These outcomes indicate that flax fibre-reinforced composite could be a commercially viable material for applications in which noise and vibration are significant issues and where a significant amount of damping is required. 相似文献
3.
This study prepared the novel laminated composites composed of a cushioning layer with double identical hybrid surface reinforcement laminates based on Kevlar fiber (KF)/carbon fiber (CF) and evaluated their acoustic and mechanical performance. The effects of reinforcing fiber type, fiber blending ratio, needle-punching frequency, and laminated sequence on the static bursting, dynamic cushioning and acoustic absorption ability of the composites were individually investigated. Results revealed that the cushioning capacity of the KF-hybrid composites was always superior to that of the CF-hybrid composites. The dynamic cushioning capacity of a hybrid composites with the cushioning layer at the intermediate position was superior to that of samples with a cushioning layer at the top and bottom positions. The CF-hybrid composites exhibited higher acoustic absorption coefficient at low (125 to 500 Hz) to mid frequencies (500 to 2000 Hz) but a lower value at high frequencies (2000 to 4000 Hz) than the KF-hybrid composites. The acoustic absorption curve and the corresponding sound absorption average were significantly affected by the needle-punching frequency. This influence diminished with an increase in needle-punching frequency. The cushioning layer at the top position enhanced the absorption ability at low to mid frequencies. Thus, the hybrid construction with a cushioning layer at the middle position and double hybrid laminated cover plies was the optimal structure for acoustic absorption. 相似文献
4.
The dynamic mechanical properties such as storage modulus, loss modulus, and tan δ of banana fiber reinforced PF composites fabricated by RTM and CM techniques were investigated as a function of fiber content, fiber treatment, temperature and frequency. Storage modulus (E′) increases with increase in fiber content and records maximum for the composites having a fiber loading of 40 wt % at all temperature ranges. The loss modulus and damping increases to great extent by the addition of filler, a maximum was observed for filler with 10–20 wt % fiber content followed by a slight decrease in loss modulus and damping with increasing filler content. Alkali treatment of the fiber shows a great enhancement in E′ and T g of the composites. Comparison is made between the composites fabricated by RTM and CM. RTM composites exhibited higher storage modulus and lower damping compared to CM composites. 相似文献
5.
6.
Amir NourbakhshFoad Farhani Baghlani Alireza Ashori 《Industrial Crops and Products》2011,33(1):183-187
In this research, reinforcing effect of hybrid filler including rice husk (RH), beech bark (BB) and nano-SiO2, in polypropylene has been investigated. In the sample preparation, four levels of filler loading were used for waste lignocellulosic materials (55-58 wt.%) and nano-SiO2 (0-4 wt.%). In order to increase the interphase adhesion, polypropylene grafted with maleic anhydride was added as a coupling agent to all the composites studied. The physical properties, viz. the thickness swelling and water absorption, and mechanical properties, namely, the tensile, flexural and notched Izod impact strengths, of the composites were determined. Generally, high amount of filler content in composites can lead to the reduction of interfacial adhesion between matrix polymer and filler, and it limits their applications. The results showed that while flexural properties and elongation at break were moderately improved by the increase in the amount of filler in the matrix, tensile and Izod impact strengths decreased dramatically. However, the composites had acceptable mechanical strength levels. The mechanical properties of composites filled with RH are generally greater than BB composites. The thickness swelling and water absorption of the composites increased with the increase in the filler loading, but to a negligible extent as compared with the wood-based composites and the solid woods. Nano-SiO2 addition showed little positive effect on the mechanical properties. It can be concluded from this study that the used waste lignocellulosic materials are attractive reinforcements from the standpoint of their physico-mechanical properties. 相似文献
7.
In this research, we fabricated a series of PVA membranes loaded with 0 wt.%, 1 wt.%, 3 wt.%, 5 wt.% ZrC and 0 wt.%, 1 wt.%, 3 wt.%, 5 wt.% TiO2 using a spiral vane electrospun machine respectively. There were 2 sizes of TiO2 nano particles: 10 nm and 200 nm. We tested sound absorption properties of needle-punched nonwovens as well as the composite of nano membranes and needle-punched nonwovens by an impedance tube at the frequency range from 500 Hz to 6500 Hz. Besides, we tested morphological characterization of nano membranes by scanning electron microscope (SEM) and crystalline properties by X-ray diffraction (XRD). We investigated the sound absorption properties of composites as well as the effect of ZrC, TiO2, nano particle sizes and cavity depth on sound absorption properties. Results showed that sound absorption properties of composites increased at the whole range of frequency compared to those of needle-punched nonwovens. When loaded with ZrC nano particles, sound absorption properties of composite shifted to a higher frequency region, and with increasing content of ZrC, sound absorption properties were better above 2500 Hz. However, when loaded with TiO2, sound absorption properties were better at lower frequency. With 3 wt.% TiO2, sound absorption coefficient reached the best at the frequency range from 500 Hz to 1500 Hz. Besides, 200 nm TiO2 was more conductive to the increase of sound absorption properties at lower frequency region compared to 10 nm TiO2. Sound absorption properties of composites with air back cavity shifted to a lower frequency region, too. SEM showed that there was nano particle aggregation when loaded TiO2 nano particles. XRD showed that ZrC nano particles loaded in PVA nano fiber retained their crystalline structure while TiO2 didn’t. It appeared from the results that nano particles had an effect on sound absorption materials, with different kinds and different sizes, sound absorption properties will improve in different ranges of frequency 相似文献
8.
This paper presents the results of a current research of the tensile properties: ultimate strength and stiffness modulus in
composites using natural reinforcements. Hemp short fibres and pine sawdust were randomly distributed in polypropylene matrices
to produce composite plates with 5 mm thickness by injection moulding technique. The specimens were cut from these plates
with bone dog shape or plane bars, and tested in tensile and four points bending, respectively. Stiffness modulus and ultimate
stresses were obtained for different weight fraction content of reinforcement and discussed taking in account the failure
modes. Four series of pine sawdust reinforced specimens were immersed in water in periods up to 20 days. Periodically, the
specimens were removed from the water recipient and immediately tested. The damage effect of water immersion time was discussed
based in the tensile results and in the water absorption curves. 相似文献
9.
This paper presents results of dynamic deformation behavior of woven natural silk/epoxy sandwich composite panels. The specimens were prepared in configurations of reinforced woven natural silk fiber (RWNSF)/Epoxy/Foam, RWNSF/Epoxy/Coremat; RWNSF/Epoxy/Honeycomb and reinforced RWNSF/Epoxy (control material) using hand-lay-up method. Each of the three core material was sandwiched between reinforced woven natural silk fiber/Epoxy composite facesheet. Drop weight impact test was carried out under 32 J impact energy. Degree of damages inflicted on the contact surface, through thickness and rear surface were analyzed, sandwich composites performed better than the reinforced (control material). Failure mechanism involved interlaminar matrix cracking, layer debonding, delamination and fibre breakage. 相似文献
10.
In this paper, a novel strategy was used to prepare the bamboo fiber (BF)/polypropylene (PP) composites which greatly improved the distribution of BF. Both the raw and alkali treated BF were utilized for the fabrication of composites and silane coupling agent was used to improve the adhesion of BF and PP. The effects of BF content and the alkali treatment of BF on mechanical, thermal, morphological, dynamic mechanical properties and water absorption were studied. The Fourier transform infrared spectroscopy (FT-IR) analysis indicated that the hydrophilic nature of raw BF was significantly reduced by alkali treatment. In addition, the mechanical properties and the water absorption of the composites were found to increase with the increment of BF loading. Most importantly, the mechanical properties of the alkali treated BF showed much higher values than that of raw BF while the water absorption of alkali treated BF was much lower than that of raw BF. The results indicated the interaction of fiber-matrix was greatly improved by the alkali treatment. Moreover, from the Scanning Electron Microscopy (SEM) images, it further proved that the distribution of BF was improved by the way of papermaking to premix BF and PP fiber. The Dynamic mechanical thermal analysis (DMA) results showed that the storage modulus of the composites was increased with further increase in BF content. 相似文献
11.
Jin Zhang Yibing Cai Xuebin Hou Cong Huang Hui Qiao Qufu Wei 《Fibers and Polymers》2017,18(2):253-263
Porous cellulose acetate (CA) films by breath figure (BF) incorporated with capric acid as form-stable phase change materials (PCMs) were fabricated and characterized for storing and retrieving thermal energy. Effects of different solvents, CA concentration and film thickness on morphology, microstructure and thermal energy storage property of formstable PCMs were investigated by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analyzer and differential scanning calorimetry (DSC), respectively. The results indicated that the prepared CA films were porous with DMF, acetone, and dichloromethane (DCM) as the solvents, and capric acid absorption capacity was as high as 86.9, 75.0 and 82.2 % with the specific surface area of 4.8, 2.8 and 1.8 m2/g. Moreover, porous CA film with 5 % CA concentration and 0.5 mm thickness prepared by using DMF as solvent had larger specific surface area and higher thermal energy storage properties. The fabricated form-stable PCMs could well maintain their PCM characteristics and demonstrated great temperature regulation ability and had potential applications in building energy conservation. 相似文献
12.
水稻开花灌浆期间阴害形成的光谱辐射能特征初步研究 总被引：5，自引：0，他引：5
通过对水稻开花灌浆期间模拟阴天，自然阴天和晴天光谱辐射能特征，以及这三种天气型下水稻群体反射，透射和吸收光谱辐射能变化特征的分析，揭示了阴天对水稻此阶段产生危害的光质原因即阴天促使400-510 nm（蓝光）和610-725 nm（红光）两个波段辐射能大幅度减少与水稻群体反射和透射这两个波段辐射能的比例大大增加，因而导致水稻群体吸收此两个波段的光谱辐射能显著减少所致。 相似文献
13.
The present paper is concerned with the effect of cork and rice husk ash micro particles fillers on the mechanical properties
(flexural resistance, fracture toughness, impact absorbed energy, elastic and viscous moduli) of polyester based composite.
Composite sheets were hand molded using weight filler fractions of 1, 2.5, and 5 %. Flexural strength of filled materials
was much lower than the polyester matrix, with more pronounced effect for cork powder, decreasing significantly with filler
content increases. Fracture toughness decreases also on the filled composites. Using cork powder fracture toughness decreases
significantly when filler content increases, while for rice husk ash filler a slight increase was observed. Both fillers improve
absorbed impact energy, peaking at about 2.5 % of filler content. Best improvements were obtained using rice husk ash powder,
reaching about 30 %. Both fillers increase glass transition temperature and the maximum use temperature and also the elastic
modulus compared with polyester. It can be concluded from this study that the used agro-waste materials are attractive reinforcements
from the standpoint of their mechanical properties. 相似文献
14.
In this study, the ballistic impact performance of woven kenaf-Kevlar hybrid and non-hybrid composites against fragment simulating projectiles (FSPs) was investigated. All the composites were prepared using the hand lay-up technique, method, followed by static load compression. The hybrid composites consist of Kevlar fabric and woven kenaf layers. The results obtained indicate that the energy absorption, ballistic limit velocity (V 50) and failure behaviour of the composites during the impact event were affected by the woven kenaf hybridisation. The additional kenaf layers in hybrid composites resulted in the increase in composites thickness and areal density, thus increased the energy absorption (14.46 % to 41.30 %) and V 50 (5.5 % to 8.44 %). It was observed that the hybrid composites failed through a combination of fibre shear, delamination and fibre fracture in the impacted surface, woven kenaf-Kevlar interface and rear surface respectively. Although the specific energy absorption was lower for the hybrid composites, further investigations need to be carried out to utilise the great potential natural fibres. 相似文献
15.
Tao Yang Xiaoman Xiong Rajesh Mishra Jan Novák Jiří Chaloupek Filip Sanetrnik Jiří Militký 《Fibers and Polymers》2016,17(12):2078-2084
This work deals with the study of acoustic performance of struto nonwovens and their relation to fabric air permeability. In order to achieve the objective of the research, sound absorption coefficient of struto nonwovens was determined via impedance tube method, the average value of sound absorption coefficient (α?) was calculated. Air permeability of struto nonwovens was examined by using FX3300 Textech Air Permeability Tester. Results showed that struto nonwoven exhibited good absorption ability at frequency bands 3000-6400 Hz while it was ineffective for frequency lower than 3000 Hz. Struto nonwovens with high GSM and fabric thickness showed better acoustic performance and lower air permeability. It was observed that α? was inversely proportional to air permeability, with correlation coefficient 0.95. It was concluded that air permeability can be used as a criterion of sound absorption behavior of struto nonwovens. A lower air permeability suggests a better sound absorption performance for struto nonwoven fabrics. 相似文献
16.
The effects of damping on the bending and twisting modes of flax fibre-reinforced polypropylene composites are investigated. The laminate was manufactured by a vacuum bagging process; its dynamic behaviour was then found from the vibration measurements of a beam test specimen using an impulse hammer technique to frequencies of 1 kHz. The frequency response of a sample was measured, and the bending and twisting responses at resonance were used to estimate the natural frequency and loss factor. The single-degree-of-freedom circle-fit method and Newton’s divided differences formula were used to estimate the natural frequencies as well as the loss factors. The damping estimates were also investigated using a “carpet” plot. The results show significant variations in loss factors depending on the type of mode. The loss factor generally lies in the range of 1.7-2.2 % for the bending modes, while 4.8 % on average for the twisting modes. Numerical estimates of the response, and in particular the natural frequencies, were made using a Mechanical APDL (ANSYS parametric design language) finite element model, with the beam being discretised into a number of shell elements. The natural frequencies from the finite element analysis show reasonably good agreement (errors < 5 %) with the measured natural frequencies. 相似文献
17.
番木瓜片的微波真空干燥特性与动力学模型 总被引：1，自引：0，他引：1
研究了番木瓜片在不同微波功率、相对压力、切片厚度和装载量等干燥参数条件下的微波真空干燥特性,并建立微波真空干燥数学模型。结果表明:番木瓜片微波真空干燥过程可分为加速、恒速和降速过程;番木瓜片的干燥主要集中于恒速干燥阶段;番木瓜片的微波真空干燥过程同时受到微波功率、相对压力、切片厚度和装载量的影响;Page方程关于番木瓜片干基含水量和水分比的预测值与试验值均拟合较好,能较准确地反映番木瓜片微波真空干燥过程中的水分变化规律。 相似文献
18.
Shruti S. Devangamath Blaise Lobo Saraswati P. Masti Shivayogi Narasagoudr 《Fibers and Polymers》2018,19(7):1490-1499
Cobaltous sulfate heptahydrate (CoSO4·7H2O) was incorporated as filler into diglycidyl ether of bisphenol A (DGEBA) based epoxy resin system, to prepare organic-inorganic polymer hybrid materials. Mechanical tensile studies and dynamic mechanical analysis (DMA) were carried out in order to study the static and dynamic mechanical properties of the prepared hybrid films. Mechanical tensile studies were carried out at room temperature, at a test speed of 30 mm/min. Highest tensile strength of 24.74±2.42 MPa was achieved for 4.44 wt% filler level (FL), along with an increase in the value of Young’s modulus. Storage modulus (E′), loss modulus (E″), damping factor (tan δ) were obtained by DMA studies. Glass transition temperature (Tg) was obtained for pure epoxy and filled epoxy, for various FLs varying from 0.28 wt% to 5.00 wt%. Pure epoxy showed highest Tg value compared to filled epoxy hybrids. Highest storage modulus of 9.5 GPa was obtained for 2.22 wt% FL, which also showed highest loss modulus peak. Parameters like effectiveness coefficient (C) and crosslink density were calculated from the storage modulus data. Loss modulus and tan δ curves were analyzed to study the energy dissipation properties of prepared hybrid films. Activation energy (Ea) value for glass transition was obtained from damping factor (tan δ), which showed highest Ea value of 630.5 kJmol-1, for 4.44 wt% FL. DMA studies for various FLs were carried out at different test frequencies in order to study the changes in dynamic mechanical properties of the prepared hybrid materials with respect to frequency 相似文献
19.
Sorghum was germinated for different time (12, 24, 36 and 48 h) at different temperatures (25, 30 and 35 °C) and the changes in their nutritional and functional properties of germinated sorghum flour were assessed and compared with native sorghum flour. Germination inversely affects the crude protein, fat, fibre and ash content. A decrease in water absorption and swelling power and increase in oil absorption capacity was observed due to enzymatic starch modification as the germination duration progressed. Germination of sorghum increased the gel consistency while paste clarity was decreased as compared to native flour. Proteins were modified by action of enzymes during higher germination time and temperature conditions, which results in significantly higher protein solubility of germinated sorghum flour, which also result in enhancing the foaming and emulsifying properties of the flour. Lowest % synersis value and least gelation concentrations were observed in native sorghum has, which increased during germination and were highest in sorghum germinated for 48 h at 35 °C. Germination in overall can be used as low cost natural bio-processing technique for the preparation of modified flour with enhanced function properties without chemical modification or genetic engineering. 相似文献
20.
外施脱落酸和赤霉素对海南岛落叶树木韧皮部的作用 总被引：5，自引：3，他引：2
将脱落酸（０．２％ＡＢＡ和１％ＡＢＡ羊毛脂）和赤霉素（０．５％ＧＡ３和１％ＧＡ３羊毛脂）涂到树干树皮的刮皮伤口上，经过８ｄ后用光学显微镜技术观察堵塞筛管的固定胶胝体在韧皮部中形成的位置，以确定有功能韧皮部的厚度。对于无叶期筛管破坏型的树种苦楝树（Ｍｅｌｉａ ａｚｅｄａｒａｃｈ Ｌ．），在生长季开始时期之后施用ＡＢＡ，能使有功能韧皮部大量减少，但在生长季开始时期施用，对韧皮部几乎没有作用；在生长季晚 相似文献