Relative humidity sensor with optical fiber Bragg gratings

A novel concept for an intrinsic relative humidity (RH) sensor that uses polyimide-recoated fiber Bragg gratings is presented. Tests in a controlled environment indicate that the sensor has a linear, reversible, and accurate response behavior at 10-90% RH and at 13-60 degrees C. The RH and temperature sensitivities were measured as a function of coating thickness, and the thermal and hygroscopic expansion coefficients of the polyimide coating were determined.     

Modeling of mechanical behaviors for natural fiber reinforced composites under hygrothermal ageing

<正>In recent years,natural fiber reinforced composites have been widely applied to various industrial products for their excellent environmental-friendly performance.It is essential to understand the mechanical properties of natural fiber reinforced composites under their in-service environment.Compared with synthetic fibers,the hydrophilicity of natural fibers could result in a much larger quantity of water absorption from the moisture atmosphere,which would have adverse consequences for the durability of natural fiber reinforced composites[1].The environmental temperature would affect the     

Effect of fiber content and surface treatment on the mechanical properties of natural fiber composites produced by rotomolding

In this study, natural fibers (agave, coir, and pine) were surface treated with maleated polyethylene (MAPE) with two main objectives: (1) to improve the mechanical properties of natural fiber composites produced by rotational molding and (2) to increase the fiber content in the composite. The rotomolded composites were produced at 0, 10, 20, 30, and 40% wt. of fiber contents (treated or untreated) and characterized in terms of morphology and mechanical properties (hardness, impact, tension, and flexion). The results showed that MAPE surface treatment was more successful for agave and coir than for pine fibers due to their respective chemical composition. In general, surface treatment led to better fiber distribution and a more uniform composite morphology allowing the possibility to use higher fiber contents in rotational molding. At low fiber contents (10 and 20% wt.), the mechanical properties were improved using treated fiber composites (TFC) compared to the neat polymer and untreated fiber composites (UFC). Although the mechanical properties of TFC decreased at high fiber contents (30 and 40% wt.), they were substantially higher (about 160, 400, and 100% for impact, tensile, and flexural properties, respectively) than for UFC.     

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.     

Relative humidity sensor based on SMS fiber structure with polyvinyl alcohol coating

A novel relative humidity (RH) sensor based on single-mode–multimode–single-mode (SMS) fiber structure is presented. The sensors are created through coating a thin layer of polyvinyl alcohol (PVA) on the multimode fiber deleted the cladding trough HF solution cauterization as the sensitive cladding film, whose refractive index varies as a function of humidity level. Due to the SMS fiber structure's sensitivity to ambient refractive index, the transmission spectra of SMS fiber structure coated PVA film are modified under exposure to different ambient humidity levels ranging from 30% to 80% RH. The related numerical simulations of transmission spectra of SMS fiber structure with different surrounding refractive index are also proposed. The sensitive of the RH measurement of 0.09 nm/% RH in the range from 30% to 80% RH is experimentally achieved. Meanwhile the intensity of wavelength at 1543 nm is decreasing as the humidity increasing. The experimental results obtained are consistent with the conclusion obtained by numerical simulating.     

Ultra-longer fiber cantilever taper for simultaneous measurement of temperature and relative humidity

An ultra-longer fiber cantilever taper for simultaneous measurement of the temperature and relative humidity (RH) with high sensitivities was proposed. The structure was fabricated by using the simple and cost-effective method only including fiber cleaving, splicing, and tapering. The length of the cantilever taper is about 1.5 mm. The dip A and dip B were measured simultaneously, owing to the ultra-long length and super-fine size, the temperature sensitivities of the dip A and dip B reached as high as 127.3 pm/℃ and 0 pm/℃ between 25 ℃ and 50 ℃, and the RH sensitivities are -31.2 pm/% RH and -29.2 pm/% RH with a broad RH interval ranging from 20% RH to 70% RH. Besides, the proposed structure showed good linearity in the sensing process and small temperature crosstalk. It will be found in wide applications in environmental monitoring, food processing, and industries.     

Length and temperature dependence of the mechanical properties of finite-size carbyne

Carbyne is an ideal one-dimensional conductor and the thinnest interconnection in an ultimate nano-device and it requires an understanding of the mechanical properties that affect device performance and reliability. Here, we report the mechanical properties of finite-size carbyne, obtained by a molecular dynamics simulation study based on the adaptive intermolecular reactive empirical bond order potential. To avoid confusion in assigning the effective cross-sectional area of carbyne, the value of the effective cross-sectional area of carbyne (4.148 Å²) was deduced via experiment and adopted in our study. Ends-constraints effects on the ultimate stress (maximum force) of the carbyne chains are investigated, revealing that the molecular dynamics simulation results agree very well with the experimental results. The ultimate strength, Young's Modulus and maximum strain of carbyne are rather sensitive to the temperature and all decrease with the temperature. Opposite tendencies of the length dependence of the overall ultimate strength and maximum strain of carbyne at room temperature and very low temperature have been found, and analyses show that this originates in the ends effect of carbyne.     

The temperature dependence of internal friction in SicPCS/Al composites

In this study the relationship between Q^-1 and the microstructural characteristics of SiC_PCS/Al composites was investigated. Seven specimens made by various processes were divided into three groups and their Q^-1-T spectra were compared. The temperature dependence of internal friction up to 500°C was measured by vacuum inverse torsional pendulum apparatus. For the SiC_PCS/Al composite fabricated by the liquid infiltration method, Q^-1 increased more and more rapidly with rising temperature when the extent of fiber-matrix interfacial reaction intensified. For hot-pressed plates fabricated from preform wires and Al(1050) foils, poor diffusion bonding between the preform wires and A1 foils was introduced; this new interface is primarily responsible for the temperature dependence of Q^-1.     

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.     

Origin of temperature dependence of microbending attenuation in fiber optic cables

Abstract

Temperature-induced changes in the attenuation of multimode optical fiber cables are shown to be caused by mismatch between the thermal expansion coefficients of the fiber and the cabling materials. A quantitative theoretical model of low temperature loss, based on the formation of fiber microbends by microvariations in the jacket concentricity, is described. This model applies to tightly jacketed, soft buffered cable designs. An equation relating the low temperature optical attenuation to cable parameters is derived using this model. Good agreement is obtained between this theoretical prediction and experimental results. The theoretical model is used to compare the effectiveness of different cable designs on reducing excess loss at low temperature.     

Dynamic mechanical characterization of PMR polyimide/carbon fiber composites modified by fiber coating with silicones

Viscous and elastomeric silicones have been applied as interlayers to carbon fibers in order to develop a tougher, micro-crack resistant, thermally stable polyimide (PMR-15) composite. Carbon fiber is continuously coated with very high molecular weight polydimethylsiloxane (PDMS) and polyvinyl-methylsiloxane (PVMS). Dynamic mechanical properties of the composites have been determined and compared with uncoated carbon fiber reinforced PMR-15 polyimide composites. The presence of the interlayer is shown by the appearance of a new relaxation peak. The peak temperature is found to be a good indication of the degree of the cure of the silicone elastomer. Comparison of the storage moduli of uncoated and coated carbon fiber composites at the service temperature range of the composites indicates that the presence of the silicone interlayer affects the shear moduli of the composites. Apparent activation energy of the α transition of the matrix in the modified composites varies with the amount of interlayer and composition in concert with the impact strength.     

Interfacial mechanical properties of carbon nanotube-deposited carbon fiber epoxy matrix hierarchical composites

Functionalized multiwalled carbon nanotubes were successfully deposited on carbon fibers using four different techniques including dip coating, hand layup, spray up and electrophoretic deposition (EPD). A uniform coating of nanotubes was achieved from EPD in comparison to other coating techniques. Later nanotube-coated fibers by EPD were introduced in epoxy resin to investigate interfacial mechanical properties of the developed hierarchical composites by vacuum bagging technique. The increases in flexural and interlaminar shear properties up to 15% and 18% were observed in composites containing nanotube-coated carbon fibers than composites with virgin carbon fibers, respectively. Microscopic observation revealed the proper impregnation of multiscale reinforcements, i.e., carbon fibers and carbon nanotubes, in resin along with the modification of fiber/matrix interface due to the presence of nanotubes at interface. Finally, the mechanisms for improved mechanical properties were identified along with the presentation of a schematic model for better understanding of the improved performance of hierarchical composite after depositing uniformly dispersed nanotubes on carbon fibers.     

Interfacial adhesion of cellulose fiber and natural fiber filled polypropylene compounds and their effects on rheological and mechanical properties

Rayon fiber (RN) and pine wood fiber (PW) filled polypropylene (PP) compounds, PP/RN (90/05 and 75/25 wt%) and PP/PW (90/05, 75/25 and 50/50 wt%), are investigated for their interfacial adhesion, rheological properties, morphology, nucleation and mechanical properties. The interfacial adhesion of the RN-filled PP compounds is better than that of the PW ones. As the concentration of the RN and the PW particles is increased, the dynamic viscosity, the crystallization temperature, and the tensile modulus are increased; however, the tensile strain is decreased. The viscosity of the RN-filled compounds is higher than that of the PW ones at the same loadings. Significant differences are found in the elongation yield test. As the concentration of the particles is increased, the elongation yield stress of the RN compounds is increased. Elongation yield stress of the PW compounds is decreased and more spherulites are locally developed on the RN surface than the PW surface. The interfacial adhesion of the RN surface with PP is better than that of the PW surface. The elimination of extractives on the PW surface improves the mechanical property of the PW/PP compounds; however, it reduces processability of the PW/PP compounds.     

The gamma irradiation of PBO fiber on the mechanical and tribological properties of PTFE composites

The mechanical and tribological behavior of gamma irradiated poly(p-phenylene benzobisoxazole) (PBO) fiber filled polytetrafluoroethylene (PTFE) composites was investigated. The gamma irradiated PBO fiber composite had the highest inter-laminar shear strength value of all the combinations because its higher bond strength may have hindered a large fiber/matrix debonding. X-ray photoelectron spectroscopy results indicate that the contents of polar groups on the surface of gamma irradiated PBO fiber increase compared to PBO fiber. The wear tests were conducted on a ring-on-block apparatus using composite block against polished metal counterparts under dry sliding conditions. It can also be found that gamma irradiation treatment was helpful to the improvement of the anti-wear ability of the PTFE composite which was related to the abrasive wear mechanism.     

Size and temperature dependence of the tensile mechanical properties of zinc blende CdSe nanowires

The effect of size and temperature on the tensile mechanical properties of zinc blende CdSe nanowires is investigated by all atoms molecular dynamic simulation. We found the ultimate tensile strength and Young?s modulus will decrease as the temperature and size of the nanowire increase. The size and temperature dependence are mainly attributed to surface effect and thermally elongation effect. High reversibility of tensile behavior will make zinc blende CdSe nanowires suitable for building efficient nanodevices.     

Enhanced mechanical and thermal properties of two-dimensional SiC and GeC with temperature and size dependence

Two-dimensional materials with novel mechanical and thermal properties are available for sensors, photodetectors,thermoelectric, crystal diode and flexible nanodevices. In this investigation, the mechanical and thermal properties of pristine Si C and Ge C are explored by molecular dynamics simulations. First, the fracture strength and fracture strain behaviors are addressed in the zigzag and armchair directions at 300 K. The excellent toughness of Si C and Ge C is demonstrated by the maximal fra...     

Enhanced mechanical properties of bamboo fiber/HDPE composites by grafting poly(amido amine) onto fiber surface

The mechanical properties of bamboo fiber composites depend on the interfacial strength between fiber and high-density polyethylene (HDPE) matrix. Different poly (amido amine) (PAMAM) dendrimers were grafted onto bamboo fiber to improve the interfacial strength of the resulting composites. The surface morphology of the resulting materials was characterized by scanning electron microscopy and atomic force microscope. Surface characteristic the bamboo fiber surface were examined by X-ray photoelectron spectroscopy and Fourier transform infrared (FT-IR). The characterization results revealed that PAMAM were chemically grafted onto the surface of bamboo fiber.     

Dynamic mechanical analysis of the interphase in bacterial polyester/cellulose whiskers natural composites

Nanocomposite materials were prepared from an elastomeric poly(hydroxyoctanoate) (PHO) latex as a fully amorphous or semi-crystalline matrix using a colloidal suspension of hydrolyzed cellulose whiskers as natural and biodegradable filler. After stirring, the preparations were cast and evaporated. High performance materials were obtained from these systems, preserving the natural character of PHO. Interfacial phenomena were assumed to be noticeable owing to the high specific area of this filler. Dynamic mechanical analysis was performed on these systems to test the influence of the interphase on the molecular mobility of the amorphous phase. To quantify the distance away from the surface at which the molecular mobility is restricted, a physical model was used to predict the mechanical loss angle. This allows removal of the filler reinforcement effect keeping only the interfacial effect. It was shown that the local motion at the filler-matrix interface of amorphous PHO chains is strongly affected when an amorphous PHO was used as the matrix. No significant change was observed when a semi-crystalline PHO was used as the matrix. This result was ascribed to a possible trancrystallization phenomenon of semi-crystalline PHO in contact with cellulose whisker surface, which prevents any contact between amorphous PHO chains and filler surface.     

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.     

基于光纤锥和纤芯失配的Mach-Zehnder干涉湿度传感器

介绍了一种简单且灵敏度较高的Mach-Zehnder干涉湿度传感器.将单模光纤和多模光纤渐变熔接光纤锥,色散补偿光纤被熔接在两个多模渐变光纤之间,形成了单模光纤-光纤锥-多模渐变光纤-色散补偿光纤-多模渐变光纤-光纤锥-单模光纤结构的传感器.光纤锥起到了增加包层模能量的作用,两个多模渐变光纤节点作为光耦合器,从而形成光纤Mach-Zehnder干涉仪.外界环境湿度的变化,将使得传感器透射谱能量发生变化,通过测量干涉谱波峰峰值能量实现对湿度的测量.实验结果表明干涉谱波峰峰值能量与环境湿度之间存在良好的线性关系.当环境湿度在35%RH—85%RH范围内变化,一段由20 mm色散补偿光纤组成的传感器,其灵敏度为-0.0668 dB/%RH,相关度为0.995.该传感器结构紧凑、尺寸小、制造工艺简单,这使其可以被广泛用于湿度测量.