Aramid Fiber Reinforced Polymer Composites Research Articles

The effect of piercing and drilling processes on burr formation and delamination of aged carbon and aramid fiber-reinforced polymer composites

There are two major problems with fiber-reinforced polymer (FRP) composites during their machining that need to be addressed. The first concern is the delamination and formation of burrs at machined edges, and the second is the effects of aging leading to mechanical deterioration. In this study, carbon FRP (CFRP) and aramid FRP (AFRP) composites were manufactured by vacuum infusion method and aged for 2 years under natural environmental conditions. Piercing with three different clearances (1%, 5%, and 10% of sheet thickness) and speed of 4 m/s were performed. Additionally, conventional drilling was carried out at a feed rate of 0.2 m/min. The highest delamination factor difference between piercing and drilling processes was calculated as 7.3% and 13.9% for CFRP and AFRP, respectively. The highest burr amounts for AFRP and CFRP composites were obtained as 91.5% and 39% at 10% clearance for piercing process and 123% and 32.1% for drilling process, respectively. Compared with drilling, piercing generates less burr formation except for CFRP composites in the case of 10% clearance and more precise hole production. It is understood that piercing results significantly improve when smaller clearances up to 5% of the sheet thickness are utilized.

Investigation of friction performance and surface integrity of aramid fiber‐reinforced polymer matrix composite

AbstractBecause of its superior properties, aramid fiber‐reinforced polymer (AFRP) composite material is used in many sectors including the aerospace, automotive, and defense industries and maintains a stable and reliable coefficient of friction under the various conditions required by these industries. In this study, the friction coefficient of AFRP composites was determined by tests carried out using a ball‐on‐disc friction tester under 8 and 12 N loads at 300, 450, and 550 rpm. The wear traces were investigated and according to the results, the high friction forces negatively affected the wear and led to more prominent wear traces. It was concluded that oxidation, fatigue (thermal), and delamination wear were effective because the increase in the load increased the forces on the samples. In sample A1, the value obtained under the 8 N load was 287.5% lower than that measured under the 12 N load.

Thermal analysis of postcured aramid fiber/epoxy composites

Abstract In this study, aramid fiber-reinforced polymer (AFRP) composites were prepared and then postcured under specific heating/cooling rates. By dynamic mechanical analysis, the viscoelastic properties of the AFRP composites at elevated temperatures and under various frequencies were determined. Thermomechanical analysis (TMA), in the modes of creep-recovery and stress–relaxation tests, was also performed. Furthermore, differential scanning calorimetry was also used, and the decomposition of the AFRP composites, aramid fibers, and pure postcured epoxy, in two different atmospheres, namely, air atmosphere and nitrogen (N2) atmosphere, was explored by the thermogravimetric analysis (TGA). From this point of view, the aramid fibers showed remarkably thermal resistance, in N2 atmosphere, and the volume fraction of fibers (Φf) was calculated to be Φf = 51%. In the TGA experiments, the postcured AFRP composites showed very good thermal resistance, both in air and N2 atmosphere, and this characteristic in conjunction with their relatively high T g, which is in the range of 85–95°C, depending on the frequency and the determination method, classifies these composites as potential materials in applications where the resistance in high temperatures is a required characteristic.

Intrinsically conducting polymer (ICP) coated aramid fiber reinforced composites for broadband radar absorbing structures (RAS)

In this study, a composite radar absorbing structure (RAS) was developed using intrinsically conducting polymer (ICP)-coated aramid fiber reinforced polymer composites (AFRPs). Dielectric aramid fibers fabric were fabricated by simple dip-coating with PEDOT:PSS and PANI:CSA conducting polymers. The electrical conductivity, dielectric constant, radar absorbing performance in the X-band range (8–12 GHz) and mechanical properties of the ICP-coated AFRP RAS were investigated with respect to the type and composition ratio. As a result, the optimal type and composition ratio of the ICPs were presented. The facile process of the ICP coating on the reinforcing fibers will help further the exploitation of conducting polymers for RAS.

Laser induced graphene for in-situ ballistic impact damage and delamination detection in aramid fiber reinforced composites

Aramid fiber reinforced polymer composites have been shown to exhibit impressive mechanical properties, including high strength-to-weight ratio, excellent abrasion resistance, and exceptional ballistic performance. For these reasons, aramid composites have been heavily used in high impact loading environments where ballistic properties are vital. In-situ damage monitoring of aramid composites under dynamic loading conditions typically requires externally bonded sensors, which add bulk and are limited by size and space constraints. To overcome these limitations, this work presents a piezoresistive laser induced graphene (LIG) interface for embedded impact sensing in aramid fiber reinforced composites. Through the monitoring of electrical impedance during ballistic impact, information regarding time and severity of the impact is obtained. The impact velocity correlates with the impedance change of the composites, due to delamination between aramid plies and damage to the LIG interface. The delamination length in Mode I specimens also correlates to changes in electrical impedance of the composite. The interlaminar fracture toughness and areal-density-specific V50 of the LIG aramid composites increased relative to untreated aramid composites. This work demonstrates a methodology to form multifunctional aramid-based composites with a LIG interface that provides both improved toughness and imbedded sensing of impact and damage severity during ballistic impact.

Mechanical properties of fiber/graphene epoxy hybrid composites

The aim of this study is to determine the effect of graphene nanoparticle (GNP) reinforcement on the mechanical properties of glass fiber reinforced polymer (GFRP), carbon fiber reinforced polymer (CFRP) and aramid fiber reinforced polymer (AFRP) composites commonly used in the space and defense industry. Accordingly, GFRP, CFRP and AFRP composites were produced by using hot pressing method. In addition, hybrid fiber composites were produced by adding 0.1 %, 0.2 % and 0.3 % GNP to these fiber reinforced composites. The tensile strength and modulus of elasticity of the composites were determined. The tensile damage fracture regions were analyzed by scanning electron microscopy (SEM) and energy distribution spectrum (EDS). It was observed that the addition of 0.2 wt. % GNP to GFRP and CFRP composites increased tensile strength and modulus of elasticity. However, the addition of 0.2 wt. % GNP to AFRP composites had no effect on the tensile strength; on the contrary, it partially reduced the tensile strength but increased the modulus of elasticity. On the fracture damage surfaces of the GFRP and CFRP composites and the GNP/GFRP and GNP/CFRP hybrid composites, the fibers were completely separated. On the damage surfaces of AFRP composite and GNP/AFRP hybrid composites, the fibers were deformed but these fibers were not separated from each other. From the EDS analysis, it was observed that the element C increased in the composites with the addition of GNP to the fiber reinforced composites.

Experimental and numerical investigation on compressive and flexural behavior of structural steel tubular beams strengthened with AFRP composites

Aramid Fiber Reinforced Polymer (AFRP) composites provide a companionable and beneficial technique to strengthen structures and noticeable advantages in terms of fire and heat resistance and vapor permeability. AFRP also improves the corrosion resistivity of the structural members, and it delays the buckling. These characteristics of AFRP materials have been catching attention of the technical community to study the mechanical behavior to define comprehensive strengthening design guidelines. This research work studied the effect of AFRP on a steel beam with five types of strengthening and without strengthening pattern. Several tests were carried out to find the compressive and flexural behavior of structure considering with strengthening and without strengthening. From the experimental result, it can be concluded that the load carrying capacity and stiffness of structure considerably enhanced due to external bonding of normal modulus AFRP. The wrapping of AFRP effectively delayed the local buckling and punching for the compressive and flexural loading, respectively. Then, the beam was modeled by using ANSYS 16.0 to authenticate the experimental results and the numerical results such as deflection and maximum load carrying capacity for the different patterns of strengthening quite agreed with the experimental results. Finally, this study concluded with showing different experimental failure modes and comparison made with the numerical results. It is expected that the outcome of this research will be of significant help for the strengthening of the structure.

In-situ polymerization and covalent modification on aramid fiber surface via direct fluorination for interfacial enhancement

Poor adhesive performance is considered to be a major disadvantage of aramid fibers in the fabrication of aramid fiber reinforced polymer composites, and it's a main drawback to restrict its wide application. In this paper, fluorine-related free radicals induced by direct fluorination were detected by Electron Paramagnetic Spectrum (EPR), which were considered as active spots to initiate copolymerization between acrylic acid (AA) and divinylbenzene (DVB), and the copolymer was chemically grafted onto AF surface, thus aramid fiber was covalently decorated by plenty of –COOH groups. Furthermore, amine-functionalized carbon nanotubes were devised to undergo the condensation reaction with the –COOH groups on fiber surface so that high density of carbon nanotubes could be chemically grafted on aramid fiber surface. Testing of mechanical properties showed that there was almost no damage to the mechanical property of aramid fibers, and interfacial shear strength of modified fiber increased by 53.1% and 69.1% after grafting polyacrylic acid-divinylbenzene copolymer and carbon nanotubes in sequence, respectively. Mathematical analysis for the changes and relationships between surface energy, surface roughness of fibers and their IFSS revealed that specific surface energy made a greater contribution to the enhancement of IFSS than surface roughness, which proved that surface energy was more helpful to the interfacial properties of the composites. Additionally, electric conductivity of organic aramid fiber improved obviously with a conductivity of 0.48 S/m.

FATIGUE BEHAVIOUR STUDY ON REPAIRED ARAMID FIBER/EPOXY COMPOSITES. doi: 10.5028/jatm.2009.0102217221

Aramid fiber reinforced polymer composites have been used in a wide variety of applications, such as aerospace, marine, sporting equipment and in the defense sector, due to their outstanding properties at low density. The most widely adopted procedure to investigate the repair of composites has been by repairing damages simulated in composite specimens. This work presents the structural repair influence on tensile and fatigue properties of a typical aramid fiber/epoxy composite used in the aerospace industry. According to this work, the aramid/epoxy composites with and without repair present tensile strength values of 618 and 680MPa, respectively, and tensile modulus of 26.5 and 30.1 GPa, respectively. Therefore, the fatigue results show that in loads higher than 170 MPa, both composites present a low life cycle (lower than 200,000 cycles) and the repaired aramid/epoxy composite presented low fatigue resistance in low and high cycle when compared with non-repaired composite. With these results, it is possible to observe a decrease of the measured mechanical properties of the repaired composites.

Evaluating and proposing models of circular concrete columns confined with different FRP composites

Commonly used fiber-reinforced polymer (FRP) includes Carbon, Glass, and Aramid FRP composites. Meanwhile, some new FRPs such as PBO (Polypara-phenylene-Benzo-bis-Oxazole), PET (Polyethylene Terephthalate/Polyester), Dyneema, and Basalt have been gradually applied in recent years. Over the past 20 years, there has been extensive research on modeling of stress–strain response of confined concrete using the common types of FRP. In this study, most popular and recent models are investigated to evaluate their general practical application in predicting the response of FRP-confined concrete with strain-hardening performance without any restriction on the fiber used. The aim of the study is twofold. In case of different types of FRP composites, providing equivalent confinement modulus (lateral stiffness), five models are employed to find the FRP-confined concrete stress–strain relationship of three scale-model circular columns. Second ascending part (second stiffness) of the stress–strain relationship of FRP-confined concrete with strain-hardening performance is evaluated in the light of available database from the existing literature using these analytical models. The results showed that the examined models do not satisfy the fact that the slope of the second ascending branch of the stress–strain curve of FRP-confined concrete is independent of its types, provided the design confinement modulus is the same. A comparison of predicted values of the second stiffness with the collected test results of 257 cylinder specimens confined with the common types of FRP composites revealed the necessity for a more accurate model. Based on the discussion of the features and accuracy of these models, a model considering the effect of FRP lateral stiffness is proposed. Because of the variability observed in the test data, however, it appears impossible to develop simple empirical models based on the current database with less than approximately 27% mean absolute error for the second stiffness, and 16% mean absolute error for ultimate strength.