Effects of Accelerated Hygroscopic Ageing on Interlaminar Shear Strength and Glass Transition Temperature of CFRP

This study, which is undertaken in cooperation with Riba-COMPOSITES, investigates the effects of hygroscopic ageing on the Interlaminar Shear Strength and Glass Transition Temperature of short-beams made of carbon fibre reinforced polymer (CFRP) composites provided by two different vendors. The materials have the same weave pattern but differ in the epoxy resin formulation. The tests are done in accordance with ASTM. Accelerated ageing techniques are carried out by immersion of the specimens in deionized water at 70°C for different periods of time, developing different degrees of ageing. The results of the tests confirm that hygroscopic ageing causes a loss of properties and a depression of the glass transition temperature in both the materials. However, since one of the two materials shows more constant property degradation, its behaviour in service conditions should be more easily predictable.

On the characterization of the mechanical behaviour of bonded steel-CFRP adhesive joints

The use of adhesively bonded carbon fiber reinforced polymers (CFRP) is well established to repair metallic structural elements in the aerospace industry for more than three decades. Despite a few exceptions, this technology has yet not been exploited for the steel construction industry where there is a great need to rehabilitate old metallic bridges. For instance, in Europe more than 30% of the railway bridge stock operated for more than 100 years. These bridges are made of old mild steel or puddle iron that exhibits poor behaviour due to the quality of the material itself and degradation caused by the long-term loading or environmental effects. The modest results for Steel/CFRP joints obtained may be due to the type of adhesive used. In fact, most of the previous studies utilized brittle adhesives specially developed for concrete structures. Recent ductile adhesives that made for the automotive industry for metallic joints should be more appropriate. In this study, an experimental investigation on the behaviour of CFRP/steel adhesively bonded joints is presented. A comparison between brittle adhesives and ductile adhesives is conducted. The results show that the ductile adhesives achieve much higher performance than the brittle ones. The brittle adhesives provide more stiffness to the adhesive joint. In the specimens with the ductile adhesives, the failure pattern started by yielding the steel bars first then the adhesive joint which is promising since it can facilitate the design significantly if the steel yielding can be used as a design criterion. The main disadvantage of ductile adhesives is they are usually more expensive than brittle ones. In order to solve this issue, bi-adhesive joints, in which the joint is mainly made of (low cost) brittle adhesive and ductile adhesive in the stress concentration region, are proposed. The results revealed very high improvement up to the yielding strength of the steel bars and with a balanced stiffness.

CFRP modificati con membrane elettrofilate per il self-healing: ottimizzazione delle condizioni di cura e test di delaminazione

I compositi a matrice polimerica rinforzati con fibre di carbonio (Carbon fiber reinforced polymers, CFRP) posseggono proprietà meccaniche uniche rispetto ai materiali convenzionali, ed un peso decisamente inferiore. Queste caratteristiche, negli ultimi decenni, hanno determinato un crescente interesse nei confronti dei CFRP che ha portato a numerose applicazioni in settori come l’industria aerospaziale e l’automotive. Le sollecitazioni cui i CFRP laminati sono soggetti durante la vita d’uso possono causare fenomeni di delaminazione che, portando ad una drastica riduzione delle proprietà meccaniche del materiale, ne compromettono l’integrità strutturale. Nel presente lavoro di tesi, sono state integrate in laminati CFRP membrane elettrofilate da blend polimeriche con capacità di self-healing. Le migliori condizioni da applicare in fase di cura del composito sono state approfonditamente investigate mediante analisi termica (DSC). Per verificare la capacità di autoriparazione dei laminati modificati, è stata valutata la tenacità a frattura interlaminare in Modo I e Modo II prima e dopo il trattamento di attivazione del self-healing.

Effetto della temperatura sull’aderenza e la delaminazione di rinforzi FRCM applicati su supporto in muratura

Negli ultimi tempi, i compositi FRCM (Fiber Reinforced Cementitious Matrix) sono largamente utilizzati per il rinforzo di costruzioni murarie esistenti, tuttavia rimangono dubbi riguardo la loro durabilità e le loro prestazioni meccaniche in condizioni ambientali avverse. L'obiettivo del presente lavoro di tesi è stato quello di analizzare il comportamento meccanico e l'aderenza di due diversi compositi FRCM applicati su supporto murario, sottoposti a prove di distacco condotte a temperatura. A tal proposito, le prove sono state eseguite all'interno di una camera climatica mediante la quale è stato possibile procedere al condizionamento termico dei campioni: le temperature indagate sono comprese nell'intervallo da 23 a 140°C. Dai risultati ottenuti è stato possibile notare come, all'aumentare della temperatura, il comportamento meccanico del generico composito cambiasse, presentando tensioni di picco via via inferiori e un progressivo cambiamento della modalità di rottura. Infatti, mentre i campioni testati a temperatura ambiente hanno mostrato un comportamento fragile con rottura del tessuto esterno al rinforzo, i campioni testati a temperature superiori hanno manifestato un comportamento meno fragile, caratterizzato dallo scorrimento del tessuto presente all'interno della malta.

Composite materials obtained from textile fiber residue

This article presents the use of fibers residue from textile industry to minimize environmental problems associated with material accumulation. Composite materials utilizing textile fiber residues and high density polyethylene were prepared. Effect of treatment with hot water on fibers to prepare composites was studied to provide an improvement in mechanical properties of these materials. This treatment on fibers was evaluated by X-ray diffraction and scanning electron microscopy techniques. Experimental results of mechanical properties indicated higher mechanical strength for treated fiber composites compared to the untreated fiber composites.

Digital versus Conventional Radiography for Imaging Fatigue Cracks in Riveted Lap Joints of Hybrid Glass Reinforced Fiber/Metal Laminate

A round robin program zoos conducted to assess the ability of three different X-radiographic systems for imaging internal fatigue cracks in riveted lap joints of composite glass reinforced fiber/metal laminate. From an engineering perspective, conventional film radiography and direct radiography have produced the best results, identifying and characterizing in detail internal damage on metallic faying surfaces of fastened glass reinforced fiber/metal laminate joints. On the other hand, computed radiographic images presented large projected geometric distortions and feature shifts due to the angular incident radiation beam, disclosing only partial internal cracking patterns.

Thermal and mechanical characteristics of polyurethane/curaua fiber composites

Polyurethane composites reinforced with curaua fiber at 5, 10 and 20% mass/mass proportions were prepared by using the conventional melt-mixing method. The influence of curaua fibers on the thermal behavior and polymer cohesiveness in polyurethane matrix was evaluated by dynamic mechanical thermal analysis (DMTA) and by differential scanning calorimetry (DSC). This specific interaction between the fibers and the hard segment domain was influenced by the behavior of the storage modulus E` and the loss modulus EaEuro(3) curves. The polyurethane PU80 is much stiffer and resistant than the other composites at low temperatures up to 70A degrees C. All samples were thermoplastic and presented a rubbery plateau over a wide temperature range above the glass transition temperature and a thermoplastic flow around 170A degrees C.

Influence of Filling Materials on the Bonding Interface of Thin-walled Roots Reinforced with Resin and Quartz Fiber Posts

Introduction: A common complication during the restoration of severely destroyed teeth is the loss of coronal root dentine. The aim of this study was to evaluate the influence of different sealers on the bonding interface of weakened roots reinforced with resin and fiber posts. Methods: Sixty extracted maxillary canines were used. The crowns were removed, and the thickness of root dentine was reduced in the experimental (n = 40) and positive control (n = 10) groups. The specimens of experimental group were assigned to four subgroups (n = 10) according to the filling material: gutta-percha + Grossmann`s sealer, gutta-percha + AH Plus (Dentsply De Trey Gmbh, Konstanz, Germany), gutta-percha + Epiphany (Pentron Clinical Technologies, Wallingford, CT), and Resilon (Resilon Research LLC, Madison, CT) + Epiphany. In the negative control group (n = 10), canals were not filled. After post space preparation, the roots were restored with composite resin light-activated through a translucent fiber post. After 24 hours, specimens were transversally sectioned into 1-mm-thick slices. Push-out test and scanning electron microscopic (SEM) analyses of different regions were performed. Data from push-out test were analyzed by using Tukey post hoc multiple comparison tests. The percentage of failure type was calculated. Data from SEM analysis were compared by Friedman and Kruskal-Wallis tests (alpha = 0.05). Results: The mean bond strength was significantly higher in the negative control group as compared with the other groups (P < .05). In all groups, the most frequent type of failure was adhesive. Overall, apical and middle regions presented a lower density of resin tags than the coronal region (P < .05). Conclusions: The push-out bond strength was not affected by sealer or region. The canal region affected significantly the resin tag morphology and density at the bonding interface. (J Endod 2011;37:531-537)

Stone-ground wood pulp-reinforced polypropylene composites: water uptake and thermal properties

Two of the drawbacks of using natural-based composites in industrial applications are thermal instability and water uptake capacity. In this work, mechanical wood pulp was used to reinforce polypropylene at a level of 20 to 50 wt. %. Composites were mixed by means of a Brabender internal mixer for both non-coupled and coupled formulations. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to determine the thermal properties of the composites. The water uptake behavior was evaluated by immersion of the composites in water until an equilibrium state was reached. Results of water absorption tests revealed that the amount of water absorption was clearly dependent upon the fiber content. The coupled composites showed lower water absorption compared to the uncoupled composites. The incorporation of mechanical wood pulp into the polypropylene matrix produced a clear nucleating effect by increasing the crystallinity degree of the polymer and also increasing the temperature of polymer degradation. The maximum degradation temperature for stone ground wood pulp–reinforced composites was in the range of 330 to 345 ºC

Studies on short nylon fiber - reclaimed rubber/elastomer composites

The thesis deals with the development of short nylon fiber-reclaimed rubber/elastomer composites. Three rubbers viz, natural rubber, acrylonitrile butadiene rubber and styrene butadiene rubber were selected and were partially replaced with reclaimed rubber. The blend ratio was optimized with respect to cure characteristics and mechanical properties. Reclaimed rubber replaced 40 parts of NR and SBR and 20 parts of NBR without much affecting the properties. These blends were then reinforced with short nylon fibers. The mechanical properties of the composites were studied in detail. In all the cases the tensile strength, tear strength and the abrasion resistance increased with increase in fiber content. In the case of NRlreclaimed rubber blends, the tensile strength-fiberloading relationship was non-linear where as in the case of NBRlreclaimed rubber blends and SBRlreclaimed rubber blends the tensile strength-fiber loading relationship was linear. All the composites showed anisotropy in mechanical properties. The effect of bonding system on the composite properties was also studied with respect to cure characteristics and mechanical properties. For this, a 20 phr fiber loaded reclaimed rubber/elastomer composites were selected and the effect of MDI/PEG resin system was studied. The resin used was 5 phr and the resin ratios used were 0.67: I, 1:1, 1.5:1 and 2:1. The bonding system improved the tensile strength, tear strength and abrasion resistance. The best results are with SBRlreclaimed rubber-short nylon fiber composites. The optimized resin ratio was 1:1 MDI/PEG for all the composites.

Characterization of rhodamine 6G doped polymer optical fiber by side illumination fluorescence

The length-dependent tuning of the fluorescence spectra of a dye doped polymer fiber is reported. The fiber is pumped sideways and the fluorescence is measured from one of the ends. The excitation of a finite length of dye doped fiber is done by a diode pumped solid state laser at a wavelength of 532 nm. The fluorescence emission is measured at various positions of the fiber starting from a position closer to the pumping region and then progressing toward the other end of the fiber. We observe that the optical loss coefficients for shorter and longer distances of propagation through the dye doped fiber are different. At longer distances of propagation, a decrease in optical loss coefficient is observed. The fluorescence peaks exhibit a redshift of 12 nm from 589 to 610 nm as the point of illumination progresses toward the detector end. This is attributed to the self-absorption and re-emission of the laser dye in the fiber.

Fabrication and characterization of dye-doped polymer optical fiber as a light amplifier

The fabrication and characterization of a Rhodamine 6G-doped polymer optical fiber amplifier have been carried out. Two different schemes were employed to characterize the optical fiber: the stripe illumination technique to study the fiber as a gain medium and another technique to study its performance as an amplifier. We observed a spectral narrowing from 42 to 7 nm when the pump energy was increased to 6 mJ in the stripe illumination geometry. A gain of 18 dB was obtained in the amplifier configuration. The effects of pump power and dye concentration on the performance of the fiber as an amplifier were also studied.

Side illumination fluorescence emission characteristics from a dye doped polymer optical fiber under two-photon excitation.

Two-photon excited (TPE) side illumination fluorescence studies in a Rh6G-RhB dye mixture doped polymer optical fiber (POF) and the effect of energy transfer on the attenuation coefficient is reported. The dye doped POF is pumped sideways using 800 nm, 70 fs laser pulses from a Ti:sapphire laser, and the TPE fluorescence emission is collected from the end of the fiber for different propagation distances. The fluorescence intensity of RhB doped POF is enhanced in the presence of Rh6G as a result of energy transfer from Rh6G to RhB. Because of the reabsorption and reemission process in dye molecules, an effective energy transfer is observed from the shorter wavelength part of the fluorescence spectrum to the longer wavelength part as the propagation distance is increased in dye doped POF. An energy transfer coefficient is found to be higher at shorter propagation distances compared to longer distances. A TPE fluorescence signal is used to characterize the optical attenuation coefficient in dye doped POF. The attenuation coefficient decreases at longer propagation distances due to the reabsorption and reemission process taking place within the dye doped fiber as the propagation distance is increased.

Multimode laser emission from dye doped polymer optical fiber

Multimode laser emission is observed in a polymer optical fiber doped with a mixture of Rhodamine 6G (Rh 6G) and Rhodamine B (Rh B) dyes. Tuning of laser emission is achieved by using the mixture of dyes due to the energy transfer occurring from donor molecule (Rh 6G) to acceptor molecule (Rh B). The dye doped poly(methyl methacrylate)-based polymer optical fiber is pumped axially at one end of the fiber using a 532 nm pulsed laser beam from a Nd:YAG laser and the fluorescence emission is collected from the other end. At low pump energy levels, fluorescence emission is observed. When the energy is increased beyond a threshold value, laser emission occurs with a multimode structure. The optical feedback for the gain medium is provided by the cylindrical surface of the optical fiber, which acts as a cavity. This fact is confirmed by the mode spacing dependence on the diameter of the fiber.

Fabrication and characterization of dye mixture doped polymer optical fiber as a broad wavelength optical amplifier

Rhodamine 6G and Rhodamine B dye mixture doped polymer optical fiber amplifier (POFA), which can operate in a broad wavelength region (60 nm), has been successfully fabricated and tested. Tunable operation of the amplifier over a broad wavelength region is achieved by mixing different ratios of the dyes. The dye doped POFA is pumped axially using 532 nm, 10 ns laser pulses from a frequency doubled Q-switched Nd: YAG laser and the signals are taken from an optical parametric oscillator. A maximum gain of 22.3 dB at 617 nm wavelength has been obtained for a 7 cm long dye mixture doped POFA. The effects of pump energy and length of the fiber on the performance of the fiber amplifier are also studied. There exists an optimum length for which the amplifier gain is at a maximum value.