High-cycle fatigue of hybrid carbon nanotube/glass fiber/polymer composites

Glass fiber polymer composites have high strength, low cost, but suffer from poor performance in fatigue. Mechanisms for high-cycle (>10⁴ cycles) fatigue failure in glass fiber composites consist primarily of matrix-dominated damage accumulation and growth that coalesce and propagate into the fibers resulting in ultimate fatigue failure. This investigation shows that the addition of small volume fractions of multi-walled carbon nanotubes (CNTs) in the matrix results in a significant increase in the high-cycle fatigue life. Cyclic hysteresis measured over each cycle in real time during testing is used as a sensitive indicator of fatigue damage. We show that hysteresis growth with cycling is suppressed when CNTs are present with resulting longer cyclic life. Incorporating CNTs into the matrix tends to inhibit the formation of large cracks since a large density of nucleation sites are provided by the CNTs. In addition, the increase in energy absorption from the fracture of nanotubes bridging across nanoscale cracks and nanotube pull-out from the matrix is thought to contribute to the higher fatigue life of glass composites containing CNTs. High-resolution scanning electron microscopy suggests possible mechanisms for energy absorption including nanotube pull-out and fracture. The distributed nanotubes in the matrix appear to inhibit damage propagation resulting in overall improved fatigue strength and durability.     

Impact behavior of aramid fiber/glass fiber hybrid composite: Evaluation of four-layer hybrid composites

Aramid fiber/glass fiber hybrid composites were fabricated to investigate the impact behavior of four-layer composites through the analysis of delamination area. The effect of position and content of aramid layer on the impact properties of hybrid composites was examined by using driven dart impact tester. The surface-treated composites were prepared by treating the surface of aramid fiber with oxygen plasma and silane coupling agent. The trend of total impact energy was correlated to that of delamination area in both untreated and treated composites. The impact energy and delamination area of hybrid composites depended on the position of aramid layer. When aramid layer was at back surface, the composite exhibited the higher impact energy and delamination area. In surface-treated composites, however, the position of aramid layer had a minor effect on the impact energy of hybrid composites. This was due to the restriction in deformation of aramid fiber. The impact behavior of four-layer hybrid composites was affected by the delamination area at each interface. The deformation at neighbored-aramid layers increased the deformation at adjacent interfaces.     

全保偏光纤直流磁场传感系统

采用保偏光纤耦合器和偏振器搭建了马赫-曾德尔型光纤干涉仪。在传感臂中接入铽镝铁材料被覆保偏光纤结构的光纤磁传感探头,在参考臂中接入保偏光纤PZT相位调制器进行工作点控制,得到了全保偏结构的光纤直流磁传感系统。该系统抑制了偏振诱导的信号衰落,实现了稳定的直流磁场信号检测。实验得到了系统对0.75mT~60mT的外加直流磁场响应特性,结果表明,该直流磁场传感系统的线性度达到了0.997,最小可检测的直流磁场达到3.4×10-6T。     

Enhancing thermal conductivity of glass fiber/polymer composites through carbon nanotubes incorporation

Carbon nanotubes were effectively incorporated into low-viscosity polyester/vinyl ester resins and then used for infusion of glass fiber textiles by high-pressure injection, resulting in carbon nanotubes/glass fiber/polymer multiscale composites. The nanotubes distribution in the composites was examined by measuring the local density of as-produced composites. The uniformity of local density and scanning electron microscope characterization verified the homogeneous morphology of as-produced composites. Both theoretical calculation and experimental characterization indicated thermal conductivity was significantly improved. Incorporation of 3 wt% carbon nanotubes has resulted in 1.5-folds enhancement of thermal conductivity. These results will further increase industrial application of the fiber composites.     

Damage characterisation of glass/textile fabric polymer hybrid composites in sea water environment

The results of the experimental analysis carried out on the glass/textile fabric reinforced hybrid composites under normal condition and sea water environments have been reported. The critical stress intensity factor, interlaminar shear strength and impact toughness have been evaluated, both in interlaminar and translaminar directions. The specimen preparation and the experimentations were carried out according to the ASTM standards. Results have revealed that the damage in hybrid composite under sea water environment is entirely different. The characterising parameters have shown changes in their magnitudes with the variation in immersion time. The nature of fracture as a function of the reinforcement volume, loading and environmental conditions has been analyzed with the aid of scanning electron microscopy. The SEM analysis has shown that the fibers pull out, matrix cracking and also the nature of crack growth is different in sea water environment. The fracture in individual fiber has also been identified.     

Enhancement of delamination fatigue resistance in carbon nanotube reinforced glass fiber/polymer composites

We show that the addition of small volume fractions of multi-walled carbon nanotubes (CNTs) to the matrix of glass–fiber composites reduces cyclic delamination crack propagation rates significantly. In addition, both critical and sub-critical inter-laminar fracture toughness values are increased. These results corroborate recent experimental evidence that the incorporation of CNTs improve fatigue life by a factor of two to three in in-plane cyclic loading. We show that in both the critical and sub-critical cases, the degree of delamination suppression is most pronounced at lower levels of applied cyclic strain energy release rate, ΔG. High-resolution scanning electron microscopy of the fracture surfaces suggests that the presence of the CNTs at the delamination crack front slows the propagation of the crack due to crack bridging, nanotube fracture, and nanotube pull-out. Further examination of the sub-critical fracture surfaces shows that the relative proportion of CNT pull-out to CNT fracture is dependent on the applied cyclic strain energy, with pull-out dominating as ΔG is reduced. The conditions for crack propagation via matrix cracking and nanotube pull-out and fracture are studied analytically using fracture mechanics theory and the results compared with data from the experiments. It is believed that the shift in the fracture behavior of the CNTs is responsible for the associated increase in the inter-laminar fracture resistance that is observed at lower levels of ΔG relative to composites not containing CNTs.     

An investigation into hybrid carbon/glass fiber reinforced epoxy composite automotive drive shaft

This paper examines the effect of fiber orientation angles and stacking sequence on the torsional stiffness, natural frequency, buckling strength, fatigue life and failure modes of composite tubes. Finite element analysis (FEA) has been used to predict the fatigue life of composite drive shaft (CDS) using linear dynamic analysis for different stacking sequence. Experimental program on scaled woven fabric composite models was carried out to investigate the torsional stiffness. FEA results showed that the natural frequency increases with decreasing fiber orientation angles. The CDS has a reduction equal to 54.3% of its frequency when the orientation angle of carbon fibers at one layer, among other three glass ones, transformed from 0° to 90°. On the other hand, the critical buckling torque has a peak value at 90° and lowest at a range of 20–40° when the angle of one or two layers in a hybrid or all layers in non-hybrid changed similarly. Experimentally, composite tubes of fiber orientation angles of ±45° experience higher load carrying capacity and higher torsional stiffness. Specimens of carbon/epoxy or glass/epoxy composites with fiber orientation angles of ±45° show catastrophic failure mode. In a hybrid of both materials, [±45°] configuration influenced the failure mode.     

苎麻纤维布和玻璃纤维布混杂铺层复合材料的力学性能

利用真空吸注成型(vacuum resin absorbable molding,VRAM)工艺制备苎麻纤维布与玻璃纤维布混杂铺层的环氧树脂基复合材料。测定复合材料的损耗因子、储能模量的温度谱和力学性能;利用单悬臂梁共振实验测量复合材料的共振频率和自由振动衰减曲线并计算出了阻尼因子。用有限元软件对其共振频率和自由振动衰减实验进行仿真分析。结果表明:通过苎麻纤维布/玻璃纤维布的混杂铺层,能够实现材料阻尼性能和力学性能的可控调节,充分发挥复合材料可设计性强的优势。其中RGR铺层的复合材料的损耗因子比纯玻璃纤维板提高了1.4倍,而拉伸强度比纯苎麻纤维板提高了3倍多;自由振动的有限元模拟曲线和实验曲线基本吻合,表明可以通过模拟软件实现复合材料的虚拟振动测试,从而为材料性能预测和设计提供方便。     

Fire retardancy of clay/carbon nanofiber hybrid sheet in fiber reinforced polymer composites

In this paper, two kinds of clay/carbon nanofiber hybrid sheets containing 0.05 wt% and 0.20 wt% of Cloisite Na⁺ clay, were fabricated through a high-pressure filtration system. These sheets were integrated onto the surface of laminated composites like traditional continuous fiber mats through vacuum-assisted resin transfer molding process. The fire performance of the laminated composites was evaluated with cone calorimeter tests under an external radiant heat flux of 50 kW/m². Their residues were analyzed with scanning electron microscopy and thermal gravimetric analyses. It was found that the clay/nanofiber hybrid sheets survived on the combustion surface of composites and significantly reduced the heat release rate by 60.5%. The protective clay layer reduces the heat release rates and the nanofiber network reinforces the clay layer against the air bubbling and melt flow of the products degraded from the polymer resin. The clay/carbon nanofiber hybrid sheet combines the barrier and insulator effects of the clays with the re-emitting heat effect of carbon nanofibers on the combustion surface of composites.     

Monotonic properties of unidirectional glass fiber (U)/random glass fiber (R)/epoxy hybrid composites

The main objective of the present paper is to study the tensile and bending behaviors of unidirectional glass fiber (U)/random glass fiber (R)/epoxy hybrid composites with total fiber volume fraction (V_fT) = 37%. Six kinds of laminated composites of average thickness 5.5 mm were manufactured using hand lay-up technique; i.e. [R]₅, [U/R/U/R/U], [U/0.5R/U]_S, [0.5R/U/U]_S, [U/U/0.5R]_S, and [U]₅. In bending test, notched and unnotched specimens were tested. For this purpose different circular notch sizes (D = 3, 6, 9 mm) were drilled at the specimen center. Tensile strength, tensile modulus, Poisson’s ratio, bending strength and bending modulus were determined experimentally. The effect of stacking sequences, random fiber relative volume fraction (V_fR/V_fT), and notch diameter on the mechanical properties of the mentioned composite types were studied. Failure modes of all specimens were investigated.     

Field and laboratory performance of a rectangular shaped glass fiber reinforced polymer deck

Fiber reinforced polymer (FRP) composites have been favorably noticed as state-of-the art construction materials, but sufficient material and structural data about FRP applications are not available. This study was intended to evaluate the applications and safety of FRP deck systems, which are developed by laboratory testing (static and fatigue tests), field application and testing of glass fiber reinforced polymer (GFRP) deck systems made of glass fiber and vinyl ester resin. The results show that the developed FRP deck systems have the expected strength and stiffness to replace the existing systems. FRP deck systems can effectively shorten the construction time and reduce the equipment required. In addition, it is determined that there is a need to evaluate the long-term structural behavior and durability of FRP deck systems in order to obtain comprehensive data for preparing the future design, manufacturing and construction materials.     

Novel optoelectronic sensing system for thin polymer films glass transition investigation

The glass transition zone of thin polystyrene films on silica substrates has been investigated by using a novel optoelectronic integrated sensor involving simultaneous refractive index and temperature measurements. The sensor design is based on the deposition of thin polymer film by chemical dipping on the distal end of a standard silica optical fiber. Direct reflectometric interrogation and fiber-Bragg grating sensor integration have been used to simultaneously retrieve information about the refractive index variation over the glass transition region revealed by a temperature ramping. Sensor modeling and sensitivity have been investigated. The glass transition has been identified by measuring the change of the thermooptic coefficient in cooling down experiments. The comparison between refractive index transition and standard calorimetric analysis has been carried out to test the optoelectronic integrated sensor reliability. The proposed sensing system has demonstrated that it is able to measure the glass transition temperature of thin polymer films; moreover, the system and procedure can be readily implemented to investigate the effect of polymeric sample finite size and specific energetic interactions on the glass transition zone.     

Electric field sensing system using coherence modulation of light

This paper describes an experimental setup for detecting electric fields using electrooptic lithium niobate (LiNbO/sub 3/) sensors and coherence modulation of light. In this detection scheme, the sensed electric fields modulate optical delays, which are introduced by LiNbO/sub 3/ coherence modulators when associated to low-coherence optical sources. The optical delays act as coherence-multiplexed carriers of the sensed electric fields and are transmitted through an optical fiber channel. At the receiver, the electric fields are detected by measuring the auto-correlation of the received light by using two-wave interferometers, which are matched to the introduced optical delays on the sensing devices.     

Performance of glass fiber reinforced polymer bars under elevated temperatures

This paper investigates the residual tensile properties of newly developed glass fiber reinforced polymer (GFRP) bars after being subjected to elevated temperatures for different periods. A total of 120 GFRP specimens were tested in this study. Half of the samples were covered with concrete while the other half were bare bars. The specimens were subjected to three different controlled temperatures (100, 200 and 300 °C) for three different periods (1, 2, and 3 h). Test results showed that almost no losses were observed in the tensile modulus after all exposure periods and temperatures. Losses in the tensile strength, proportional to the level of temperature and exposure period, were recorded. The bars with concrete cover showed higher residual tensile strength compared to their counterparts without coating. The concrete cover was more effective at the lowest temperature level (100 °C) and at the shortest time period (1 h). Scanning Electronic Microscopy (SEM) technique was also used to investigate the effect of elevated temperature on the degradation mechanism of the GFRP bars. The results showed that increasing the temperature level affected the resin matrix surrounding the glass fibers and consequently affected the bond between the fibers and the matrix.     

Wave-front sensing with a sampling field sensor

We present a new type of optical wave-front sensor: the sampling field sensor (SFS). The SFS attempts to solve the problem of real-time optical phase detection. It has a high space-bandwidth product and can be made compact and vibration insensitive. We describe a particular implementation of this sensor and compare it, through numerical simulations, with a more mature technique based on the Shack-Hartmann wave-front sensor. We also present experimental results for SFS phase estimation. Finally, we discuss the advantages and drawbacks of this SFS implementation and suggest alternative implementations.     

InP nanowire/polymer hybrid photodiode

A novel design is presented for a nanowire/polymer hybrid photodiode. n-InP nanowires are grown directly onto an indium tin oxide (ITO) electrode to increase carrier collection efficiency and to eliminate the need for an expensive substrate. Experiments show that an ohmic contact is achieved between the nanowires and the ITO electrode. The nanowires are then enveloped by a high hole mobility conjugated polymer, poly(3-hexylthiophene). Compared to the control polymer-only device, the inclusion of InP nanowires increases the forward bias current conduction by 6-7 orders of magnitude. A high rectification ratio of 155 is achieved in these photodiodes along with a low ideality factor of 1.31. The hybrid device produces a photoresponse with a fill factor of 0.44, thus showing promise as an alternative to current polymer solar cell designs.     

Tensile,impact and dielectric properties of three dimensional orthogonal aramid/glass fiber hybrid composites

Aramid/glass hybrid composites with three different stacking sequences and their corresponding single fiber type composites have been fabricated and their tensile, impact and dielectric properties were investigated. The trend of tensile strength and modulus of the composites followed the rule of mixture (ROM) closely and a small but positive hybrid effect for tensile strength of the hybrid composites was observed. The hybrid composites in general had a higher impact resistance than the single fiber type composites and the hybrid composite in which fiber volume fractions for glass and aramid fiber were the most balanced showed the highest impact ductility. The aramid fiber composite showed a lower dielectric constant and a higher dielectric loss than the glass fiber composites. However, the dielectric constant of the hybrid composites decreased first and then increased as the volume fraction of aramid fiber increased, which did not follow the mixing rule for dielectric constants of compounds. The dielectric loss of the composites increased monotonically as the volume fraction of aramid fiber increased which agreed well with the mixing rule.     

In-plane shear properties of unidirectional glass fiber (U)/random glass fiber (R)/epoxy hybrid and non-hybrid composites

The in-plane shear properties (shear strength τ_xy and shear modulus G_xy) of unidirectional glass fiber (U)/random glass fiber (R)/epoxy hybrid and non-hybrid composites have been investigated experimentally and theoretically. The effect of stacking sequence and random fiber relative volume fraction (V_fR/V_fT) in hybrid composites were reported. Laminates were fabricated by hand lay-up technique with a total of 5 plies, by varying the number and position of random glass layers so as to obtain four different hybrid laminates; i.e. [0.5R/U/U]_S, [U/0.5R/U]_S, [U/U/0.5R]_S, and [U/R/U/R/U]. All unidirectional fiber laminate [U]₅ and another of all random fiber laminate [R]₅ were also fabricated for comparison purpose. The average thickness of the manufactured laminates is 5.5 ± 0.2 mm and the total fiber volume fraction (V_fT) is 37%. Failure modes of all specimens were investigated. Results indicated that the in-plane shear properties (shear strength τ_xy and shear modulus G_xy) of unidirectional fiber composite can be considerably improved by incorporation of random glass fiber and forming hybrid composites.