Project description:We aimed to embed silica optical fibers in composites (epoxy vinyl ester matrix reinforced with E-glass unidirectional fibers in mass fraction of 60%) in order to further monitor the robustness of civil engineering structures (such as bridges). A simple system was implemented using two different silica optical fibers (F1-double coating of 172 µm diameter and F2-single coating of 101.8 µm diameter respectively). The optical fibers were dynamically tensile tested and Weibull plots were traced. Interfacial adhesion stress was determined using pull-out test and stress values were correlated to fracture mechanisms based on SEM observations. In the case of the optical fiber (OF) (F1)/resin system and OF (F1)/composite system, poor adhesion was reported that may be correlated to interface fracture at silica core level. Relevant applicable results were determined for OF (F2)/composite system.
Project description:Recently, fiber-reinforced, epoxy-based, optically transparent composites were successfully produced using resin transfer molding (RTM) techniques. Generally, the production of structural, optically transparent composites is challenging since it requires the combination of a very smooth mold surface with a sufficient control of resin flow that leads to no visible voids. Furthermore, it requires a minimum deviation of the refractive indices (RIs) of the matrix polymer and the reinforcement fibers. Here, a new mold design is described and three plates of optically transparent glass fiber-reinforced polymers (tGFRP) with reproducible properties as well as high fiber volume fractions were produced using the RTM process and in situ polymerization of an epoxy resin system enclosing E-glass fiber textiles. Their mechanical (flexural), microstructural (fiber volume fraction, surface roughness, etc.), thermal (DSC, TGA, etc.), and optical (dispersion curves of glass fibers and polymer as well as transmission over visible spectra curves of the tGFRP at varying tempering states) properties were evaluated. The research showed improved surface quality and good transmission data for samples manufactured by a new Optical-RTM setup compared to a standard RTM mold. The maximum transmission was reported to be ≈74%. In addition, no detectable voids were found in these samples. Furthermore, a flexural modulus of 23.49 ± 0.64 GPa was achieved for the Optical-RTM samples having a fiber volume fraction of ≈42%.
Project description:Epoxy nanocomposites are widely used in various applications because of their excellent properties. Different types of manufacturing techniques are used to produce epoxy composites based on various fillers, molecular weight, and applications required. The physical properties and chemical structure of epoxy resin help in determining the method for its manufacturing. Coatings and adhesive formulations are prepared using high- molecular-weight epoxies, whereas epoxy nanocomposites require low-molecular-weight epoxies due to ease of manufacturing. A low-molecular-weight epoxy can provide high crosslink density to the epoxy but may also cause inherent brittleness in epoxy nanocomposites. Further, the addition of CNTs may also cause more brittleness in the final product. In this work, the authors have developed a method to process composites based on high-molecular-weight epoxy reinforced with high loading of CNTs (15 wt.%). The high molecular weight will bring lots of challenges during manufacturing. In this paper, a novel manufacturing technique based on separate molding and curing conditions to produce highly concentrated CNT-filled epoxy with high-molecular-weight epoxy resin is described, achieving excellent mechanical properties, good toughness, and high electrical conductivity in an efficient, low-cost, environmentally friendly, and high-volume way. The findings demonstrated improvements in these mechanical properties compared to conventional systems. They also highlight the potential of the novel method to develop advanced composite materials which can revolutionize industrial sectors such as aerospace, automotives, and electronics where structural integrity and thermal stability are important.
Project description:This study focuses on understanding the effect of cellulose nanocrystals (CNCs) on glass fiber/epoxy interfacial interactions. The glass fibers (GF) were coated with solutions containing cellulose nanomaterial. The parameters that were investigated were the CNC surface chemistry, concentration, and dispersing medium, i.e., aqueous solution only versus emulsions. To determine the effect of the CNC coatings on the interfacial adhesion, specimens of a single GF in an epoxy matrix were prepared for GF coating by varying the coating formulations. The interfacial shear stress (IFSS) was determined by the single fiber fragmentation test (SFFT). Following the SFFT, the samples were investigated by cross-polarized microscopy in order to understand the fracture modes which are related to the nature of the interphase. According to the SFFT data and photoelastic fracture patterns, both the emulsion and aqueous coatings containing cellulose nanocrystals functionalized with methyl(triphenyl) phosphonium (CNCPh) improve the IFSS in comparison to coated GFs without CNCs.
Project description:The ability of graphene-based materials to act as strain sensors in glass fiber/epoxy model composites by using Raman spectroscopy has been investigated. The strain reporting performance of two types of graphene nanoplatelets (GNPs) was compared with that of graphene produced by chemical vapor deposition (CVD). The strain sensitivity of the thicker GNPs was impeded by their limited aspect ratio and weak interaction between flakes and fibers. The discontinuity of the GNP coating and inconsistency in properties among individual platelets led to scatter in the reported strains. In comparison, continuous and homogeneous CVD grown graphene was more accurate as a strain sensor and suitable for point-by-point strain reporting. The Raman mapping results of CVD graphene and its behavior under cyclic deformation show reversible and reliable strain sensing at low strain levels (up to 0.6% matrix strain), above which interfacial sliding of the CVD graphene layer was observed through an in situ Raman spectroscopic study.
Project description:The use of 3D printing technology for manufacturing new products based on sustainable materials enables one to take advantage of secondary raw materials derived from recycling. This work investigates the structural performances of 3D printing composite filaments based on polylactic acid (PLA), as a matrix, reinforced by recycled carbon fiber (rCF). Carbon fibers were recovered from industrial scraps by a patented thermal process and used to produce thermoplastic composite filaments for additive manufacturing without any additional treatment and additives. The influence of the recovered carbon fiber (rCF) content on the thermal properties, mechanical properties and microstructure of the composites was studied in the range of 3-20 wt%. The recorded TGA curves exhibited a one-stage weight loss within the temperature range 290-380 °C for all samples and the residual rCF content was in good agreement with the theoretical fiber loading. The Young modulus of the extruded filaments strongly increased below a critical content (5 wt%), while at higher content the improvement was reduced. An increase in the storage modulus of 54% compared to neat PLA 3D printed sample resulted in a printed specimen with a higher rCF content. SEM images highlighted a strong rCF prevailing alignment in the direction of the extrusion flow, creating almost unidirectional reinforcement inside the filament. These findings suggest that homogeneous composite filaments reinforced with well-dispersed recycled CF without additional chemical modification and additives are suitable materials for additive manufacturing. The effect of rCF topological distribution within the material on the mechanical performances has been discussed, highlighting that the isolated fibers could efficiently transfer loads with respect to the percolated 3D network and have been correlated with the microstructure.
Project description:For the first time, next to the flammability tests (LOI, UL-94 HB, VBB, TGA), experimental tests and computer simulation have been conducted on the flame spread and combustion of glass fiber-reinforced epoxy resins (GFRER) with 6% graphene and 6% DDM-DOPO flame-retardant additives. The downward rates of flame spread (ROS) in opposed flow with oxidizer and the upward ROS along GFRER composites have been first measured as well as the distribution of temperature over the combustion surface of the composites with flame-retardant additives and without them. The LOI and UL-94 HB tests showed a reduction in the flammability of GFRER when flame retardants were added and predicted a higher effectiveness of DDM-DOPO compared to graphene. Adding DDM-DOPO resulted in increasing the rate of formation of the volatile pyrolysis products and their yield, indicating, together with the other data obtained, the gas phase mechanism of the flame retardant's action. Adding graphene resulted in an increase in the soot release on the burning surface and an increase in the amount of non-volatile pyrolysis products on the burning surface, reducing the amount of fuel that participated in the oxidation reactions in the gas phase. The developed numerical combustion model for GFRER with a DDM-DOPO additive, based on the action of DDM-DOPO as a flame retardant acting in the gas phase, satisfactorily predicts the effect of this flame retardant on the reduction in downward ROS over GFRER for 45-50% oxygen concentrations. The developed model for GFRER with graphene additive, based on a reduction in the amount of fuel and increase in the amount of incombustible volatile pyrolysis products when graphene is added, predicts with good accuracy downward ROS over GFRER depending on oxygen concentration.
Project description:This paper aims to assess experimentally the mechanical and tribological behavior of conventional and functionally graded (FG) polymeric matrix composites reinforced with continuous glass fibers. The small punch test (SPT) and a pin-on-disc device were used in the present work to examine the mechanical and wear behavior, respectively. The hand lay-up technique was used in the present investigation to manufacture the conventional and FG composites. Various wooden looms with different nailed spacing were employed to manufacture the FG composites. According to test type, the FG composite is composed of four and ten layers, with a different glass fiber volume of fraction (Vf%) for each layer. In addition, the finite element simulation based on Hashin's failure criterion and cohesive zone modeling was used to show the progressive failure and give more explanation regarding the flexural behavior of such composites. The present results indicate that the wear rate of an FG composite could be affected by many factors, including the disk speed, applied load, the composite layers number, and average glass fiber volume fraction. On the other hand, the arrangement of layers in the composite materials by variation of Vf% for each layer can improve the wear rate and value of the ultimate load before the fracture of the composite material when subjected to SPT. The experimental and numerical results for all SPT specimens showed that the fracture of the SPT specimens began beneath the punch tip and grew along the fiber direction. The ultimate flexural capacity of FG composites increased by 30% compared with the conventional composites.
Project description:The development of an energy-saving method to recycle expensive carbon fibers (CFs) from end-of-life thermosetting resin-based CF-reinforced composites (CFRCs) is strongly desired because of the environmental and economic issues. The replacement of traditional thermosetting matrixes with controllably degradable epoxy resins provides a promising solution to this challenging task. In this work, a liquid acetal-containing semi-cycloaliphatic epoxy resin (H-ER) is designed and synthesized. After curing, H-ER shows simultaneously increased thermal stability, shearing strength, flexural strength, strain at break, and critical stress intensity factors by 126%, 26.5%, 17.0%, and 29.5%, respectively, in comparison with ERL-4221. Particularly, the cured H-ER is sufficiently resistant to organic solvents, bases, and weak acids but degrades rapidly in a modestly strong acidic aqueous solution, and the rate of degradation is controlled by modulating the acidity. GC-MS and FTIR spectra demonstrate that the degradation is indeed due to the cleavage of acetal linkages in the network, and the degradation-generated benzaldehyde may be reused as a raw material for the synthesis of the H-ER resin. More importantly, for the CFRCs using H-ER as a matrix, the CFs are readily recovered without detectable damage and are able to be recycled for CFRC fabrication.
Project description:Long Fiber Spray-up Molding (LFSM) deviates from the conventional approach in liquid composite molding (LCM) processes by utilizing extremely long chopped strands of fibers as the primary reinforcement material in its fabrication process. In LFSM, chopped fibers are impregnated with resin that is sprayed vertically downwards before reaching the mold surface. The spraying mechanism is mounted on an actuator, which is capable of spraying freely in any specified pattern or direction. Under LFSM, it is extremely difficult to fabricate a composite part with uniformly distributed fiber content throughout its volume. The consequences of the non-uniform fiber volume distribution arise from the fiber entanglement as the length of the fiber reaches up to 100 mm in LFSM. In this study, the effect of fiber entanglement during LFSM was analyzed through various approaches. This included measuring the coefficient of friction between fibers in contact and examining the correlation between fiber lengths and the number of intersections. Furthermore, the viscoelastic properties of the uncured composite part were assessed by experimenting with the influence of viscosity on fiber length during compression molding. The results were then computed, modeled, and visualized in MATLAB, considering variations in viscosity and fiber length, both before and after compression molding.