Comparison between the preparation,structure and mechanical properties of long fiber reinforced thermoplastics and short fiber reinforced thermoplastic

This article summarizes the comparison between the preparation, structure and mechanical properties of long fiber reinforced thermoplastics （LFT） and short fiber reinforced thermoplastics （SFT）. Both of the experiment and theory results showed that the mechanical properties of long glass fiber reinforced thermoplastics pellets （LGFRT） have been enhanced better than that of short glass fiber reinforced thermoplastics pellets （SGFRT） manufactured by molding procession. After regulation of the relative humidity by 50 % , the mechanical properties of 30 % （ weight percent） short glass fiber content in SFT （ SFT-PA6-SGF30 ） are similar to that of 40 % long glass fiber content in LFT. Howev- er, the density of the latter is about 17 % lower than that of the former. Thus, the corresponding weight of products is reduced by 13 % ;output rate is increased by 21% , and the cost is therefore significantly lowered. And it has the fol- lowing advantages： impact strength is increased by 87 % ; the proportion is reduced by 20 % ; molding cycle is short- ened by 10 % ;materials cost is saved by 20 % -30 % and the final total cost is saved by 30 % -40 %. So LFT （LFT-PP-LGF40） can replace SFT （SFT-PA6-SGF30） with the similar basic mechanical properties under normal tem- perature or 160 ℃ lower.

Preparation of long alumina fibers by sol-gel method using malic acid

The precursor sol of alumina was prepared by sol-gel method with aluminum nitrate and malic acid as raw materials.The effects of content of malic acid and polyvinylpyrrolidone （PVP） on sol spinnability were explored.The gel fibers with above 80 cm in length were obtained by mixing aluminum nitrate,malic acid and PVP on mass ratio of 10 3 1.5.Thermogravimetry-differential scanning calorimetry （TG-DSC）,Fourier transform infrared （FTIR） spectrum,X-ray diffractometry （XRD）,and scanning electron microscopy （SEM） were used to characterize the properties of the gel and ceramic fibers.The alumina fibers with a smooth surface and about 20μm in diameter were obtained by sintering at 1 200℃,and their main phase was indentified to be α-Al2O3.

High Sensitive Long Period Fiber Grating Sensor for Detection of Nitrite

A high sensitive long period fiber grating（LPFG） sensor for the detection of nitrite is proposed, which is realized by coating multiple poly（sodium 4-styrensulfonate）（PSS） and poly（diallyldimethylammonium） chloride （PDDA） layers on the fiber grating surface. The sensitivity of this LPFG sensor is maximum when the number of assembled layers is 70. Under this condition, a nitrite concentration of 3×10^-3 mol/L, which is lower than the National Food Additive Standard, 4.2×10^-3 mol/L, can be distinguished. The sensitivity is further increased by 30% when nitrite was determined in the sucrose solution with a concentration of 65%, which provides a new solution for the best refraction index approaching matched index of the fiber cladding. Compared with chemical methods, this nitrite detection technology offers some advantages, such as high accuracy, non toxicity, high speed, low cost, without chemical reagent, and is suitable for foodstuff security detection.

Fabrication of long-period fiber gratings by CO_2 laser in fiber under tension

We demonstrate experimentally fabrication of CO2 laser written long-period fiber gratings （LPFGs） in single-mode fiber （SMF） under tension. New transmission dips can be generated due to the frozen-in stress in the fiber under tension. Dynamics analysis of laser writing process is performed to study the mechanism of the grating inscription. Experimental results show that the wavelength shift of new generated resonance dips can shift towards the longer or shorter wavelength with the increase of laser scanning cycles for gratings with different pitches.

The mechanisms underlying long-term potentiation of C-fiber evoked field potentials in spinal dorsal horn

Long-term potentiation(LTP) of C-fiber evoked field potentials in spinal dorsal horn is first reported in 1995.Since then,the mechanisms underlying the long-lasting enhancement in synaptic transmission between primary afferent C-fibers and neurons in spinal dorsal horn have been investigated by different laboratories.In this article,the related data were summarized and discussed.

Numerical Analysis of Fiber Bragg Grating and Long Period Fiber Grating Undergoing Linear and Quadratic Temperature Change

The coupled-mode equations for fiber Bragg grating （FBG） and long period fiber grating （LPFG） undergoing linear and quadratic temperature change were given. The effects of temperature gradient and quadratic temperature change on the reflectivity spectrum of fiber Braggs grating and the transmission spectrum of long period fiber grating were investigated using the numerical simulation, and the dependence relationships of the central wavelength shift, the full-width-athalf-maximum, and the peak intensity upon temperature gradient were also obtained. These relationships may be used to design a novel fiber optical sensor which can simultaneously measure the temperature and temperature gradient.

Review of Turn around Point Long Period Fiber Gratings

Long period fiber gratings are emerging as a potential candidate in the list of surrounding refractive index optical fiber sensors. Their sensitivity can be enhanced greatly if the grating period, fiber dimensions and surrounding refractive index are optimized in a way to operate at a point called turn around point on phase matching curves of these gratings. Turn around point LPFGs are well known for their ultrahigh sensitivity to external parameters. Potential of operating LPFG at or near turn around point has been investigated by many researchers in various applications including physical parameter sensing, adulteration detection, radiation dose, etc. Since TAP LPFGs are in investigation phase therefore a lot of rigorous & efficient work in finding techniques for optimizing their potential as sensor in chemical, biochemical, structural health monitoring is still to be carried out. A brief review of work carried out in this domain till now is presented here and key findings from literature review are highlighted.

Long-term stabilization of the optical fiber phase control using dual PID

We propose an approach of long-term stabilization of optical fiber phase by controlling a piezo-based phase modulator and a Peltier component attached to the fiber via a phase-locked loop( PLL) circuit w ith dual proportional-integral- derivative( PID) adjustment. With this approach,we can suppress the fast disturbance and slow drifting of optical fiber to satisfy the requirements of optical phase long-term locking. In theory,a mathematical model of an optical fiber phase control system is established. The disturbance term induced by environment influence is considered into the PLL model. The monotonous and continuous changing environment disturbance w ill cause a steady-state error in this theory model. The experimental results accords w ell w ith the theory. The steady-state performance,adjusting time,and overshoot can be improved by using the dual PID control. As a result,the long-term,highly stable and low noise fiber phase locking is realized experimentally.

Filtering of long-term dependent fractal noise in fiber optic gyroscope

Stochastic noises of fiber optic gyroscope （FOG） mainly contain white noise and fractal noise whose long-term dependent component causes FOG a rather slow drift. In order to eliminate this component, a two-step filtering methodology is proposed. Firstly, fractional differencing （FD） method is introduced to trans-form fractal noise into fractional white noise based on the estima-tion of Hurst exponent for long-term dependent fractal process, which together with the existing white noise make up of a gener-alized white noise. Further, an improved denoising algorithm of wavelet maxima is developed to suppress the generalized white noise. Experimental results show that the basic noise terms of FOG greatly decrease, and especially the slow drift is restrained effectively. The proposed methodology provides a promising ap-proach for filtering long-term dependent fractal noise.

Long-Pulse Single-Frequency All-Fiber Amplifier

In this paper, we report a high power long-pulse single-frequency all-fiber amplifier at 1064 nm with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). By applying square wave pulse modulation to the diodes, with a frequency of 50 Hz and a pulse width of 668 μs, the peak power of the output laser reached 257 W with an average power of 8.65 W, linewidth of 10.6 kHz and M2 < 1.5. .

On the Validity of the Effective Index Method for Long Period Grating Photonic Crystal Fibers

This paper focuses on the investigation of modal characteristics and sensing properties of long period grating photonic crystal fibers (LPG-PCFs). An improved effective index method is employed with an objective to study its limitations for various designs of LPG-PCFs. Results so obtained with the above method are compared with the corresponding values of multiple multipole (MMP) method results which points the range of validity and applicability of the improved effective index method to LPG-PCFs. It is shown that this method is excellent when the surrounding media is assumed to be air. However, it becomes less accurate when the fiber is immersed into a liquid with a refractive index close to that of the cladding.

Foam Forming: An Effective Method to Prepare Polyimide Fiber-based Paper

Well-dispersed fiber suspension is the precondition of good paper formation. Compared with cellulosic fibers, synthetic fibers are prone to flocculate because of their long length and hydrophobic nature, resulting in poor paper formation. To solve this problem, dispersants and extremely low forming consistency are typically adopted during the traditional wet-forming process, which cause a large amount of water consumption and treatment cost. Therefore, increasing forming consistency without compromising paper formation remains a challenge for papermakers. In this work, foam forming was adopted to disperse polyimide fibers (PI) with high forming consistency. The results showed that the formation index of handsheets increased when the bubble size and distribution became small and narrow. Compared with traditional wet-forming process with the same consistency (0.4%), the formation index of handsheets by foam forming increased by approximately 100% when C8 alkyl glucoside (APG08) concentration reached 16 g/L. Notably, forming consistency could increase by eight times while keeping the same level of paper formation. Overall, foam forming exhibits great advantages in dispersing long fiber and reducing water consumption and environmental pressure, and has potential applications in specialty paper made of long fibers.

UV-Inscribed Optical Fiber Gratings in Mid-IR Range and Their Laser Applications

We have UV-inscribed fiber Bragg gratings （FBGs）, long-period gratings （LPGs） and tilted fiber gratings （TFGs） into mid-IR 2μm range using three common optical fiber grating fabrication techniques （two-beam holographic, phase mask and point-by-point）. The fabricated FBGs have been evaluated for thermal and strain response. It has been revealed that the FBG devices with responses in mid-IR range are much more sensitive to temperature than that in near-IR range. To explore the unique cladding mode coupling function, we have investigated the thermal and refractive index sensitivities of LPGs and identified that the coupled cladding modes in mid-IR range are also much more sensitive to temperature and surrounding medium refractive index change. The 45° tilted fiber gratings （45°-TFGs） as polarizing devices in mid-IR have been investigated for their polarization extinction characteristics. As efficient reflection filters and in-cavity polarizers, the mid-IR FBGs and 45°-TFGs have been employed in fiber laser cavity to realize multi-wavelength 2μm Tm-doped CW and mode locked fiber lasers, respectively.

Temperature Compensated Solution Concentration Measurement Based on a Cascaded SMS/LPFG Fiber Structure

In this paper, a hybrid optical fiber structure for solution concentration measurement with the temperature compensation is proposed. The structure consists of long period fiber grating (LPFG) and single mode-multimode-single mode (SMS) fiber structures. The sensing mechanism of the device is studied and verified by experiments. LPFG is sensitive to solution concentration and is affected by temperature crosstalk. SMS structure is not affected by solution concentration, but sensitive to ambient temperature. It can be used as a temperature compensation system. The sensitivity coefficients of LPFG and SMS on temperature and concentration were measured experimentally, and a dual-wavelength matrix was established to realize simultaneous measurement of solution temperature and concentration.

复合材料尾门结构的拓扑-参数一体化轻量化设计

以某新能源车型的尾门为研究对象,结合注塑长玻纤增强复合材料,提出了一种结构拓扑参数一体化轻量化设计方法,并为尾门性能仿真和优化设计分别建立了联合仿真和常规仿真模型,提高了仿真精度和优化效率。首先,基于常规仿真模型通过三步式结构概念设计优化并重新设计了复合材料尾门结构。然后,建立了用于后续多目标优化的联合仿真模型,并通过样件试制和性能试验进行了验证。最后,利用带精英策略的非支配排序遗传算法(NSGA-Ⅱ)对尾门的筋条厚度、关键位置厚度、截面尺寸进行了详细优化。优化后的复合材料尾门质量比原钢制尾门减小了27.2%,同时尾门扭转刚度、横向刚度、弯曲刚度及自由模态满足应用要求。

长余辉海藻酸钠纤维的制备及其性能

为了制备出具有长余辉功能的海藻酸钠纤维,拓宽海藻酸钠纤维和长余辉发光材料的应用领域,文章首先以硝酸锶、二氧化硅、氧化镁、氧化硼、氧化铕和氧化镝为原料,通过高温固相法制备了长余辉发光材料,再采用共混方式结合海藻酸钠制备出纺丝液,最后通过湿法纺丝制备了不同浓度的长余辉海藻酸钠纤维。利用扫描电子显微镜、红外光谱仪、荧光光谱仪、荧光余辉亮度测试仪和多功能力学测试仪对长余辉海藻酸钠纤维的微观形貌、化学结构、余辉性能及力学性能进行分析。结果表明:随着加入的长余辉发光材料质量增加,长余辉海藻酸钠纤维的余辉性能在不断提高,但纤维的强力呈下降趋势;当加入的长余辉发光材料质量分数为2.0%时,所制备的长余辉海藻酸钠纤维的综合性能达到最优。所制备的长余辉海藻酸钠纤维在夜行服和防伪标志等方面具有良好的应用前景。

长玻纤/高密度聚乙烯复合材料的制备

以N406作为偶联剂,向双螺杆挤出机中连续加入玻璃纤维(玻纤GF),再经剪切、混合工艺,共混制备了长玻纤增强高密度聚乙烯(HDPE)复合材料。采用万能拉伸测试仪、冲击强度测试仪和熔体流动速率(MFR)测试仪,测试了复合材料的力学性能和流动性能;采用差式扫描量热仪(DSC)表征了复合材料的结晶温度、熔融温度;用热失重分析仪(TG)测量了复合材料的玻纤含量。研究结果表明,N406的用量对HDPE的拉伸强度的影响不大,但对冲击强度和MFR的影响较明显。偶联剂用量为8%时,相较未用偶联剂的长玻纤,增强HDPE复合材料的冲击强度提高了64.34%,MFR降低了40.07%。随着玻纤含量增加,拉伸强度、冲击强度升高,MFR降低;HDPE的结晶温度降低,熔融温度增加。玻纤含量为31.26%的复合材料,拉伸强度达到62.88MPa,较纯HDPE提高了180.97%。

大跨越架空输电导线铝部应力分布试验

为了掌握大跨越架空输电导线铝部应力空间分布特性,以JLHA1/G6A-500/280型特强钢芯铝合金导线为研究对象,采用铝股丝表面激光刻槽,内嵌高灵敏、超大复用容量超弱光纤光栅,搭建了大跨越输电导线铝部应力试验平台,研究了不同张力条件下大跨越架空输电导线铝部应力分布规律,建立了大跨越导线实体有限元模型,分析了铝股应力分布特征,并验证了试验结果的正确性。结果表明:导线承受张力作用时,外层铝股和次外层铝股应力不同,外层铝股应力小于次外层铝股应力,导线同层铝股应力基本相同;铝股应力随导线张力的增大呈线性增大趋势,张力每增大1%,铝股应力增大约10%。不同导线张力作用时钢股和铝股应力均呈现环状分层特性,铝股平均应力小于钢股平均应力,铝部和钢股应力比约为3∶7;外层和次外层铝合金股丝应力沿圆周向分布不均匀,建议大跨越导线线型设计时考虑铝股丝分层特性。

乙纶分子结构及热变性三级长波近红外-中红外光谱研究

长波近红外-中红外(LW-NIR-MIR)光谱开展乙纶分子结构研究。红外模式主要包括:2ν_(asCH3-去卷积-乙纶)、2ν_(asCH2-去卷积-乙纶)、2ν_(sCH3-去卷积-乙纶)、2ν_(sCH2-去卷积-乙纶)、(ν_(asCH2-去卷积-乙纶)+ν_(CH-去卷积-乙纶))、(ν_(asCH2-去卷积-乙纶)+ν_(sCH2-去卷积-乙纶))、ν_(asCH3-去卷积-乙纶)、ν_(sCH3-去卷积-乙纶)、ν_(asCH2-去卷积-乙纶)、ν_(sCH2-去卷积-乙纶)、δ_(CH2-去卷积-乙纶)和ρ_(CH2-去卷积-乙纶)。进一步开展了变温LW-NIR-MIR光谱研究。在303 K~393 K的温度范围内,结构官能团(2ν_(sCH2-去卷积-乙纶),ν_(asCH2-去卷积-乙纶)和ρ_(CH2-去卷积-乙纶))对应频率及强度都有明显改变。最后开展二维LW-NIR-MIR光谱研究。LW-NIR区间,5835 cm^(-1)(2ν_(asCH2-2-二维-乙纶))>5700 cm^(-1)(2ν_(sCH2-二维-乙纶))>5867 cm^(-1)(2ν_(asCH2-1-二维-乙纶))>5800 cm^(-1)(ν_(asCH2-二维-乙纶)+ν_(CH-二维-乙纶))>5762 cm^(-1)(ν_(asCH2-二维-乙纶)+ν_(sCH2-二维-乙纶))>5894 cm^(-1)(2ν_(asCH3-二维-乙纶))。MIR区间,2915 cm^(-1)(ν_(asCH2-二维))>2845 cm^(-1)(ν_(sCH2-二维-乙纶))>2945 cm^(-1)(ν_(asCH3-二维-乙纶))>2885 cm^(-1)(ν_(sCH3-二维-乙纶))。1452 cm^(-1)(δ_(CH2-2-二维-乙纶))>1475 cm^(-1)(δ_(CH2-1-二维-乙纶))。LW-NIR-MIR区间,5835 cm^(-1)(2ν_(asCH2-2-二维-乙纶))>2915 cm^(-1)(ν_(asCH2-二维-乙纶))>2845 cm^(-1)(ν_(sCH2-二维-乙纶))>5894 cm^(-1)(2ν_(asCH3-二维-乙纶))。乙纶分子结构主要官能团对热的敏感程度及变化快慢顺序都存在着较大的差异性。研究拓展了三级LW-NIR-MIR谱在乙纶分子结构及热变性的研究范围。

基于双峰谐振长周期光纤光栅的海水盐度传感器

为研制高灵敏海水盐度传感器,本文基于CO_(2)激光技术成功制备出一种工作在色散转折点(DTP)附近的长周期光纤光栅(LPFG)。首先,利用CO_(2)激光器在80μm细单模光纤上制备出工作在DTP附近的LPFG,证明了采用CO_(2)激光微加工技术制备较短周期LPFG的可能性。其次,通过调控CO_(2)激光器的制备周期,使高阶包层模式LP_(1,9)工作在DTP附近,从而显著提高了LPFG的折射率灵敏度。在双峰谐振增敏效应的作用下,当海水盐度从5.001‰变化到39.996‰时,光栅周期为115.4μm的双峰谐振LPFG平均灵敏度高达0.279 nm/‰。研究结果表明,本文制备的LPFG海水盐度传感器具有谐振损耗大和灵敏度高的优点,其在海水盐度监测领域具有较好的应用前景。