Enhancing CFRP damping with graphene nanoplatelets: experiments versus finite element analysis

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.

Carbon fiber reinforced polymer (CFRP) laminates exhibit limited fracture toughness due to characteristic interlaminar fiber-matrix cracking and delamination. In this article, we demonstrate that the fracture toughness of CFRP laminates can be improved by the addition of multi-walled carbon nanotubes (MWCNTs). Experimental investigations and numerical modeling were performed to determine the effects of using MWCNTs in CFRP laminates. The CFRP specimens were produced using an epoxy nanocomposite matrix reinforced with carboxyl functionalized multi-walled carbon nanotubes (COOH–MWCNTs). Four MWCNTs contents of 0.0%, 0.5%, 1.0%, and 1.5% per weight of the epoxy resin/hardener mixture were examined. Double cantilever beam (DCB) tests were performed to determine the mode I interlaminar fracture toughness of the unidirectional CFRP composites. This composite material property was quantified using the critical energy release rate, GIC. The experimental results show a 25%, 20%, and 17% increase in the maximum interlaminar fracture toughness of the CFRP composites with the addition of 0.5, 1.0, and 1.5 wt% MWCNTs, respectively. Microstructural investigations using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) verify that chemical reactions took place between the COOH–MWCNTs and the epoxy resin, supporting the improvements experimentally observed in the interlaminar fracture toughness of the CFRP specimens containing MWCNTs. Finite element (FE) simulations show good agreement with the experimental results and confirm the significant effect of MWCNTs on the interlaminar fracture toughness of CFRP.

In the present work, first an attempt has been made to prepare carbon, glass and carbon-glass fibre-reinforced polymer composites, and later, machining of these composites is done on abrasive water jet machine (AWJM) to compare and optimize the machining parameters. Actually, the carbon fibre-reinforced polymer (CFRP) composites, glass fibre-reinforced polymer (GFRP) composites and carbon-glass fibre-reinforced polymer (CGFRP) composites are prepared through vacuum bagging process by using epoxy resin as the polymer matrix. The machining experiments are conducted to analyse the effects of the predominant machining parameters, i.e. cutting speed rate, feed rate and stand-off distance on the required machining characteristics, i.e. surface roughness (Ra), kerf top width (kw) and material removal rate (MRR). The range of values of each parameter is set at three different levels, and Taguchi’s L9 orthogonal array is used to design factors so that all the interactions between the response variables and machining variables can be investigated. Based on the experimental values, second-order regression equations are fitted between each of the response parameters and the machining parameters using Minitab 18 software. The equations are then optimized by defining the three equations of Ra, kw and MRR as the three objectives of a multi-objective optimization problem (MOOP) using a multi-objective optimization algorithm called Elitist Non-dominated Sorting Genetic Algorithm (NSGA-II). Single best compromise solutions with respect to the MOOPs of GFRP, CFRP and CGFRP composites are also determined from the Pareto optimal solutions obtained by NSGA-II. Finally, confirmation tests are conducted on specimens of GFRP, CFRP and CGFRP composites machined at their corresponding optimum parameters given by the GA. It is observed that the optimum values of Ra, kw and MRR of all the optimization problems are closer to the corresponding experimental values of confirmation tests.

The manufacturing process of carbon fiber reinforced polymer (CFRP) composite structures can introduce many characteristic defects and flaws such as fiber misorientation, fiber waviness and wrinkling. Therefore, it becomes increasingly important to detect the presence of these defects at the earliest stages of development. Eddy current testing (ECT) is a nondestructive inspection (NDI) technique which has been proven quite effective in metallic structures. However, NDI of composite structures has mainly relied on other methods such as ultrasonics and X-ray to name a few, and not much on ECT. In this paper, we explore the possibility of using ECT in NDI of CFRP composites. We base our research on the fact that the CFRP displays some low-level electric conductivity due to the inherent conductivity of the carbon fibers. This low-level conductivity may permit eddy-current pathways that can be exploited for NDI detection. An invention disclosure describing our high-frequency ECT method is being progressed. We use multiphysics FEM simulation to simulate the detection of various types of manufacturing flaws and operational damage in CFRP composites such as fiber misorientation; waviness; wrinkling, etc. ECT experiments were conducted on CFRP specimens with manufacturing flaws using the Eddyfi Reddy eddy current array (ECA) system.

An unexpected hardening behaviour of carbon-fiber epoxy composites under flexural fatigue loading and its intensification by graphene nano-fillers

Hybrid filler systems of carbon-based nanoparticles with different geometry shapes, one-dimensional (1D-) carbon nanotubes (CNTs) and two-dimensional (2D-) graphene nanoplatelets (GnPs), were dispersed into epoxy matrix, using an intensive mixer, to evaluate their promising synergistic effects. In this work, the influence of different CNT/GnP ratios on the dispersion level, electrical and mechanical performance of epoxy-based nanocomposites was investigated. It was found that the size and number of GnP agglomerates are significantly reduced with the incorporation of CNTs, due to the formation of a co-supporting three-dimensional (3D-) architecture that delays re-agglomeration of the nanoplatelets. The combination of CNTs and GnPs, at an overall concentration of 0.043 wt. %, synergistically increase the mechanical performance and reduce the electrical percolation threshold of nanocomposites comparatively to the single filled systems. The transversal tensile properties, including elastic modulus – E2 and failure strength – Yt, of carbon fibre reinforced polymer (CFRP) composites were studied and synergetic effects were also found when combining CNTs with GnPs.

The use of carbon fiber-reinforced polymer (CFRP) composites having low weight and high strength provides the substantial energy savings in space and aerospace industry. The disadvantage of these composites is that the carbon fiber is not firmly bonded to the epoxy resin and the toughness of the produced materials is low. Graphene (G) and Graphene Oxide (GO) nanoparticles are used to functionalize CFRP composites. The CFRP composites functionalized with G and GO improve the strength of these composites by improving the fiber/matrix interface bond. In this study, the effect of type of nanoparticles, feed rate, cutting speed and number of flutes on machinability (cutting force, delamination factor and surface roughness) were experimentally investigated in the milling of CFRP composites, G-CFRP (CFRP functionalized with G) and GO-CFRP (CFRP functionalized with GO) nanocomposites. Cutting force, delamination factor, and surface roughness were found to be strongly impacted by feed rate, cutting speed, number of flutes, and type of nanoparticles. The increase in the number of flutes contributed to decrease of cutting force, delamination factor and surface roughness, while the increase in the feed rate caused to increase of them. By increasing cutting speed, surface roughness reduced, delamination factor and cutting force increased. In addition, compared to the CFRP composite, the cutting forces and surface roughness were higher, and delamination factor was lower in the CFRP composites functionalized with G and GO.

In order to leverage the advantages of the hot isostatic pressing (HIP) process and efficiently and stably manufacture carbon fiber reinforced polymer (CFRP) hollow load‐bearing structures, an evaluation and optimization of three processes were carried out. Based on material testing, mathematical models for the curing and rheological behaviors of the prepreg were developed, and simulation calculations were conducted using the established material model. Finally, CFRP composites were manufactured using the HIP process based on the process from the simulation calculations. The results show that process 3 is the best choice among the three forming processes, with a compaction displacement of 0.374 mm and a fiber content of 71 vol%, demonstrating better compaction performance. Samples prepared according to process 3 exhibit a high degree of consistency with the simulation results. The wall compaction displacement is 0.29 mm, with slight differences in the edge compaction conditions. The overall fiber content reaches 62–65 vol%, and the internal morphology and defects are characterized, confirming a good compaction effect. Highlights New mathematical models for resin curing and flowing were developed. Mathematical models were used to simulate and optimize the HIP process. CFRP specimens were manufactured to validate the superiority of the process.

Improvement of interleaving Aramid pulp micro-fibers on compressive strengths of carbon fiber reinforced polymers with and without impact

Highly protective and functional strengthening strategies for 3D printed continuous carbon fiber reinforced polymer composites: Manufacturing and properties

Graphene nanoplatelets (GNPs) are of particular interest to the field of nano-reinforced composites since they possess superior mechanical, fracture, thermal, and barrier properties. Due to their geometrical characteristics, high aspect ratio (AR)/specific surface area (SSA) and their planar structure, GNPs are considered as high-potential nanosized fillers for improving performance of composites. The present study investigates the effect of SSA of GNPs on fracture properties of carbon fiber reinforced polymers (CFRPs). For this reason, two nano-doped CFRPs were produced by using two types of GNPs (C300 and C500) with different SSAs, 300 and 500 m2/g, respectively. Both types of GNPs, at the same content of 0.5 wt%, were added into the epoxy matrix of composites by applying a three-roll milling technique. The nanomodified matrix was used for the manufacturing of prepregs, while the final composite laminates were fabricated through the vacuum-bag method. Mode I and II interlaminar fracture tests were carried out to determine the interlaminar fracture toughness GIC and GIIC of the composites, respectively. According to the results, the toughening effect of C500 GNPs was the strongest, resulting in increases of 25% in GIC and 33% in GIIC compared with the corresponding unmodified composites. The activation of the absorption mechanisms of C500 contributed to this outcome, which was confirmed by the scanning electron microscopy (SEM) analyses conducted in the fracture surfaces of specimens. On the other hand, C300 GNPs, due to disability to be dispersed uniformly into the epoxy matrix, did not influence the fracture properties of CFRPs, indicating that probably there is a threshold in SSA which is necessary to achieve for improving the fracture properties of CFRPs.

The application of carbon fiber reinforced polymer (CFRP) composites for rehabilitation of steel structures has become vital in recent years. This paper presents an experimental program and a finite element (FE) modelling approach to study the effectiveness of CFRP patch for repair of notch damaged circular hollow sectional (CHS) steel beams. The proposed modeling approach is unique because it takes into account the orthotropic behavior and stacking sequence of composite materials. Parametric study was conducted to investigate the effect of initial damage (i.e., notch depth) on flexural performance of the notched beams and effectiveness of the repair system using the validated FE models. Results demonstrated the ability of CFRP patch to repair notched CHS steel beams, restoring them to their original flexural stiffness and strength. The effect of composite patch repair technique on post-elastic stiffness was more pronounced compared to the elastic stiffness. Composite patch repair becomes more effective when the level of initial damage of beam increases. Copyright © 2018 Techno-Press, Ltd.

Efficient recycling of carbon fibers from amine-cured CFRP composites under facile condition

Influence of curing on the mechanical performance of FRP laminates

Carbon fiber-reinforced polymer (CFRP) composites have been increasingly used in spacecraft applications. Spacecraft may encounter highenergy-density X-ray radiation in outer space that can cause severe damage. To protect spacecraft from such unexpected damage, it is essential to predict the dynamic behavior of CFRP composites under X-ray radiation. In this study, we developed an in-house three-dimensional explicit finite element (FEM) code to investigate the dynamic responses of CFRP composite under X-ray radiation for the first time, by incorporating a modified PUFF equation-of-state. First, the blow-off impulse (BOI) momentum of an aluminum panel was predicted by our FEM code and compared with an existing radiation experiment. Then, the FEM code was utilized to determine the dynamic behavior of a CFRP composite under various radiation conditions. It was found that the numerical result was comparable with the experimental one. Furthermore, the CFRP composite was more effective than the aluminum panel in reducing radiation-induced pressure and BOI momentum. The numerical results also revealed that a 1 keV X-ray led to vaporization of surface materials and a high-magnitude compressive stress wave, whereas a low-magnitude stress wave was generated with no surface vaporization when a 3 keV X-ray was applied.