Fiber Reinforced Plastic Laminates Research Articles

Exploring the Impact of Drilling Parameters on Damage Morphology and Strength of Carbon Fiber-Reinforced Plastic Laminates

Exploring the Impact of Drilling Parameters on Damage Morphology and Strength of Carbon Fiber-Reinforced Plastic Laminates

Stress and energy release rate analysis of cross-ply carbon fiber-reinforced plastic laminate with transverse cracks subjected to ultrasonic vibration using a variational approach

Application of carbon fiber reinforced plastics (CFRP) to structures that are subjected to increasingly high numbers of cyclic loads is expected to expand, so evaluation of fatigue properties up to the very-high cycle regime is essential to prove their long-term reliability. Conventional fatigue testing is not practical for such conditions owing to the excessive time required; ultrasonic fatigue testing, which can be performed at a frequency of 20 kHz, is an effective alternative. Stress distribution in ultrasonic fatigue testing differs from that in conventional fatigue testing because the specimen is resonated. The stress distribution of cross-ply laminates with transverse cracks subjected to resonance was calculated using a variational approach. The energy release rate was calculated based on the results of a previous study on transverse crack initiation. The results of the stress analysis are in good agreement with those of finite-element analysis. Quantitative evaluation of transverse crack initiation was also conducted.

Achieving strong interfacial bonding of CFRP and magnesium alloy by modifying magnesium alloy surface via alkaline etching with EDTA addition

The interfacial properties of fibre metal laminates are closely related to the surface microstructure of metals. Herein, a hitherto unreported honeycomb-like micro/nano-porous structure was successfully fabricated on an AZ31B Mg alloy surface by incorporation of ethylenediaminetetraacetic acid disodium (EDTA-2Na) into an alkaline solution and achieved excellent interfacial bonding property between AZ31B and carbon fibre-reinforced plastic. The addition of EDTA-2Na can promote the formation of etched pores. The growing nano-scale etched pores join together to produce micro-scale pores and ultimately lead to the formation of a micro/nano-porous structure. The 60 min etched AZ31B/carbon fibre-reinforced plastic laminate exhibits a bonding strength of 25.87 MPa, which is an increase of 350.7% compared to that of the untreated sample. The significant increase in bonding strength is mostly ascribed to composite mechanical interlocking by the micro/nano-porous structure and chemical bonding through the formation of MgCO3 and MgO1+X. In addition, the characteristics of micro-pores also affect the bonding strength.

Multi-objective optimization of composite sandwich structures using Artificial Neural Networks and Genetic Algorithm

Sandwich structures offer significant opportunities to improve the performance of many industrial applications such as aerospace, automotive, and marine. The design of a composite sandwich structure is often challenging because it is driven by the balance between the weight and cost of these structures. In this paper, a multi-objective optimization model using a Genetic Algorithm (GA) and an Artificial Neural Network (ANN) is presented to evaluate a new optimization approach in terms of weight and cost minimization for the composite sandwich structures. Classical lamination and beam bending theories were used, along with Monte Carlo simulation, to generate the design data for the proposed composite sandwich structure, which is applied as a floor panel for a high-speed train. Multilayer feedforward neural networks were used for predicting safety factors, cost, and weight of the designed structure based on the following inputs: core density, core thickness, face sheet materials’ combinations, and applied load. The trained Neural Network model was able to predict the considered results with a good performance metric, namely the coefficient of determination (R2 = 0.99) and the Mean Square Error (MSE = 1.3·10−5).Multi-objective optimization for cost and weight minimization was performed with a Genetic Algorithm using the derived ANN model. The obtained Pareto front provided several non-dominated optimal points leading to insights on the optimization process. The Finite Element Method (FEM) was used to model the key points of the optimal designs (i.e. the design with the lowest cost, weight, and Pareto optimal points). The FEM and optimization results had a maximum deviation of about 8.9%, indicating a good agreement between the two techniques.The newly elaborated methodology demonstrates a new approach for obtaining the optimum design of the investigated composite sandwich structure constructed from honeycomb core and laminated face sheets in terms the cost and weight. The study concluded that the use of Carbon Fiber-Reinforced Plastic (CFRP) or Fiber-Metal Laminate (FML) face sheets results in significant weight savings of about 59.5% and 48.6%, respectively, compared to an all-aluminum sandwich structure.

Recycling of wet carbon fiber-reinforced plastic laminates by thermal decomposition coupled with electrical treatment

The use of carbon fiber-reinforced plastics (CFRPs) produces moisture-absorbing CFRP waste, which is usually recycled via thermal decomposition treatment (TDT). However, the oxygen gas generated during heating can hardly penetrate dense CFRPs, resulting in nonuniform damage to the recovered carbon fibers (rCFs) collected from the outer (oCFs) and inner (iCFs) parts of CFRP waste. Herein, TDT was coupled with electrical treatment (ET) to improve the recycling performance of CFRP laminates waste. The tensile strength of the rCFs measured via the single-fiber tensile tests was analyzed using a two-parameter Weibull distribution. Absorbed water was preferentially evaporated from the laminates by Joule heating during ET, resulting in extensive pore formation. Following TDT, the oCFs and iCFs showed nearly identical average tensile strengths because the pores formed by ET served as efficient diffusion pathways for oxygen gas. The proposed recycling technology may potentially be applied to other types of moisture-absorption waste.

A dynamic constitutive model for carbon nanotubes (CNTs) modified unidirectional fibre reinforced plastic laminates

A constitutive model is developed herein for carbon nanotubes (CNTs) modified unidirectional fibre reinforced plastic (FRP) laminates subjected to impact loading. In the model, intralaminar damage is described by continuum damage mechanics (CDM) model which is modified by introducing two parameters (namely, matrix correction factor (S) and residual strength factor (RSF)); interlaminar damage (delamination) is depicted by cohesive element damage model. In order to verify the model, numerical simulations are carried out on the response and failure of unidirectional FRP laminates with or without CNTs modification under both ballistic and low-speed impact. Furthermore, parametric study is performed on the influences of impact velocity. It is demonstrated that the present model predictions are in good agreement with available experimental data in terms of residual velocity, energy absorption, failure patterns and delamination. It is also demonstrated that, with the same impact energy, larger mass impact causes greater intralaminar damage whilst lower mass higher velocity ballistic impact leads to more interlaminar damage and less intralaminar damage.

Ply-Blocking Phenomenon and Hole Size Effects in Modeling Progressive Damage in Fiber-Reinforced Plastics Laminates

Abstract This work presents a 3D progressive damage model based on Puck’s failure theory and linear damage evolution in fiber-reinforced plastic (FRP) laminates. It includes shear nonlinearity, in situ strengths, equivalent stress–strain, and mixed-mode fracture energy, and is implemented in abaqus/explicitTM through VUMAT subroutine. Various test cases were performed to validate the model and demonstrate its applications. The shear nonlinearity test shows that transverse compression retards matrix microcracking while transverse tension accelerates it. The open hole tension (OHT) test of laminates shows that delamination initiates around the holes and free edges, spreads the most, and propagates in different directions at different interfaces. Later, interfiber damage in 45 deg or −45 deg plies initiates and spreads at a slight inclination to the tip of the hole. Finally, fiber damage in 0 deg plies initiates at the tip of the hole, spreads the least, and propagates perpendicular to the loading direction. The ply-blocked laminates show around 30% higher strength and fracture strain than non-ply-blocked laminate due to delay in damage propagation, and are less sensitive to the hole size. Accordingly, their OHT strength reduces by 14.3% as opposed to 21.14% in the non-ply-blocked laminates, when the hole size increases from 6 to 9 mm. The damage location, magnitude, and propagation were corroborated with experimental findings in the literature.

Non-Destructive Evaluation of In-Plane Waviness in Carbon Fiber Laminates Using Eddy Current Testing

Non-destructive detection of the in-plane waviness of carbon fiber-reinforced plastic (CFRP) laminates is of interest in a wide variety of industries, as wrinkles and other fiber alignment defects significantly impact the mechanical performance of the composites. This work demonstrates a method to detect in-plane wrinkles on a 5-ply unidirectional CFRP laminate with a customized eddy current testing (ECT) system. The results show that the ECT system is effective in detecting and quantifying in-plane waviness, and the results are compared to conventional X-ray computed tomography (CT) and ultrasonic testing (UT) methods. Using the anisotropic conductive nature of the aligned CFRP lamina, the ECT system was able to clearly detect throughout the part changes in the local fiber orientation, wave tangent angle, and wrinkle width.

Investigation of the resin infusion process and mechanical performance of carbon fiber reinforced plastic composites from recycled carbon fiber

The disposal of Fiber Reinforced Composites (FRCs) waste is becoming a very critical aspect, from both a technical and an economic point of view, due to the continuous increase of the production of such a class of materials. Thus, the possibility to produce new composites by employing recycled materials is a crucial aspect both to guarantee the circularity of the manufacturing processes and the reduction of costs. In this work, the manufacturing process, together with the performance of a carbon fiber-reinforced plastic (CFRP) laminate obtained by employing into sandwich structures a novel commercial recycled non-woven carbon fabric with an epoxy resin, have been investigated. The fabrication process based on the Resin Infusion under Flexible Tooling (RIFT) has been selected and performed in different conditions. The mechanical behavior of the resulting laminates has been investigated by quasi-static tensile, and flexural characterization, to evaluate both the optimal conditions for the process, and the possible anisotropy of the product. Moreover, thermogravimetric analysis (TGA) was applied to complete the post-processing characterization of the resulting laminate by determining the actual carbon fibers (CFs) content, thus, to validate the reproducibility of the manufacturing process. The laminates obtained by the RIFT method exhibited good mechanical properties and isotropy if cross-ply stratification is adopted. The use of recycled CFs allows high sustainability and reduced cost for the composites, making the RIFT method investigated a scalable process and the so-manufactured products a valid candidate for numerous applications.

Progressive damage analysis in an open hole compression of FRP laminates including fiber kinking and pre-existing damage

Progressive damage and strength analysis in an open hole compression (OHC) test is crucial in designing components made of fiber reinforced plastics (FRPs) composites. In this work, a continuum damage mechanics based 3D progressive damage model (PDM) incorporating LaRC05 failure criteria is developed. It considers identification of fracture and kink-band plane, shear non-linearity, in-situ strengths, and mixed-mode fracture in the formulation. The proposed PDM is validated through single element tests and applied to analyze the damage patterns and strength during open hole compression (OHC) tests of three different layups with two different hole sizes and a pre-existing damage. It is observed that fiber kinking in 0∘ plies initiates at the location of maximum in-plane shear stress and propagates due to a combined action of longitudinal compression and in-plane shear stress. The final failure of 0∘ dominant and quasi-isotropic layup is governed by fiber kinking in 0∘ plies, whereas matrix cracking in ±45∘ plies is responsible for the final failure of the shear dominant layup. Furthermore, OHC strength of the layups reduces by 15%–20%, when the hole size increases from 6.35 mm to 9.525 mm. In the presence of a pre-existing kink or matrix damage, fiber kinking initiates at locations of the pre-existing damage. A small pre-existing damage reduces OHC strength of the layups up to 7%–11%. The results predicted by the model match well with the experimental results in the literature.

Elaboration of a Multi-Objective Optimization Method for High-Speed Train Floors Using Composite Sandwich Structures

The transportation industry needs lightweight structures to meet economic and environmental demands. Composite sandwich structures offer high stiffness and low mass, making them ideal for weight reduction in high-speed trains. The objective of this research is to develop a method of weight and cost optimization for floors of high-speed trains. The studied sandwich floor structure consists of Fiber Metal Laminates (FML) face sheets and a honeycomb core. Different variations of FMLs were investigated to define the optimal sandwich structure for minimum weight and cost. The Neighborhood Cultivation Genetic Algorithm (NCGA) was used to search the design space, and the Finite Element Method (FEM) was used to construct the optimal design of the train car floor panel. The FEM and optimization results had a maximum difference about 11%. The study concluded that using face sheets made entirely of Fiber-Reinforced Plastic (FRP) or Fiber Metal Laminates (FMLs) resulted in significant weight savings of approximately 62% and 32%, respectively, compared to a sandwich structure made entirely of aluminum, but a lighter structure was associated with higher cost. The main contribution of this study is the elaboration of a multi-objective optimization method that utilizes a wide range of constituent materials and structural components in order to construct weight- and cost-optimized sandwich structures.

Mechanical properties and damage behavior of tapered unidirectional CFRP laminates

An understanding of damage mechanisms induced by drop-off plies in tapered composite laminates is crucial. This study investigated the mechanical properties and damage behaviors of asymmetric tapered unidirectional carbon fiber-reinforced plastic laminates. Damage observations of laminates with simultaneous tapered and staggered tapered structures under monotonic and cyclic tensile loads were done by an optical microscope and X-ray radiography. Based on the results, matrix cracks in the resin pocket and delamination occurred earliest in the simultaneous tapered specimen due to a greater stress concentration in a single large resin pocket in the structure. Intralaminar damages in the staggered tapered specimen with a shorter step spacing occurred mainly in the lower dropped ply as there was a more significant interaction between the neighboring steps in the specimen. The drastic decrease in the stress concentration after the occurrence of damages in the neighboring step(s) then suppressed the occurrence of intralaminar damages in the upper dropped ply. This is in contrast to the specimen with a longer step spacing where the intralaminar damages occurred in both dropped plies due to the distributed stress distribution. Delamination propagated between the dropped plies and continuous (belt and core) plies for both staggered laminates regardless of the length of the step spacing at higher applied stress levels. The results showed that internal ply-drop configuration and step spacing in staggered tapered structures contribute to significant differences in the mechanical properties and damage behavior in the laminates.

3D progressive damage modeling of fiber reinforced plastics laminates including drilling-induced damage

This work focuses on developing a 3D progressive damage model (PDM) to predict drilling-induced damage and its effect on the load-carrying capacity of fiber reinforced plastics (FRP) laminates. The proposed PDM is based on 3D Hashin’s failure criterion and a linear damage evolution law. It was implemented as a VUMAT subroutine in an Abaqus/explicitTM. Specifically, the model allows defining pre-existing damage through state-dependent variables. The PDM was first validated with a single element, mesh dependency, and open hole tension tests. Subsequently, it was applied to model drilling and drilling-induced damage. Single element tests verify primary damages. Further, open hole lamina in tension fails with matrix cracking along the fiber direction irrespective of their fiber orientation. Furthermore, in open hole [45/−45/90/45/0/−45/0/45/−45/0]S laminate in tension, 0° plies fail with fiber damage, whereas other plies fail with matrix damage. In drilling of a carbon fiber reinforced plastics (CFRP) laminate, the damage at the exit ply significantly increases with an increase in feed, while it slightly reduces with an increase in speed. The drilling-induced damage was then incorporated as pre-existing damage in the open hole laminate using cohesive interaction and state-dependent variables. The presence of the pre-existing drilling-induced damage has lowered the load-carrying capacity of the laminate by 8%. The predictions are in excellent agreement with experimental data from the literature.

Wear Study of Coated Mills during Circumferential Milling of Carbon Fiber-Reinforced Composites and Their Influence on the Sustainable Quality of the Machined Surface

Composite materials made of fiber-reinforced plastic laminates are highly susceptible to surface damage caused by wear during contour milling, especially with inappropriate tool and cutting material properties. Improper choice of tools and cutting conditions lead to delamination between applied layers, thermal damage of materials in the polymer matrix, and reduction of the edge quality of cutting tools. The study was devoted to circumferential milling of twill-bonded CFRP (carbon-fiber-reinforced polymer) sheets with a focus on cutting forces and tool flank face wear, including their effect on the machined surface structure, roughness, and topography of the laminate. The main objective of the study is to investigate the feasibility of applying conventional coated tools, which are not primarily designed for milling CFRP, in comparison to a dedicated DLC (diamond-like carbon) coated tool, due to economic and distribution availability and the possibility of providing suitable cutting conditions during milling. The study provides results confirming the possibility of using conventional tools for machining CFRP and provides relevant experimental results that can be implemented for optimal tool selection, tool life criteria, cutting conditions, and machining strategies including low energy consumption. The best values of the investigated parameters were obtained when using the ECSSF (instrument designation) tool with DLC coating.

Application of machine learning for improved accuracy of simultaneous temperature and strain measurements of carbon fiber-reinforced plastic laminates using an embedded tilted fiber Bragg grating sensor

Tilted FBG (TFBG) sensors exhibit capability for simultaneous measurement of temperature and strain. However, improving the measurement accuracy is difficult. This study examined the applicability of machine learning techniques for improving the accuracy of simultaneous measurement of temperature and strain of a TFBG sensor, and of a carbon fiber-reinforced plastic (CFRP) composite laminate using an embedded TFBG sensor. Temperature and strain were ascertained using machine learning methods, i.e. deep neural networks (deep NN) and support vector regression (SVR), from multiple peaks in the transmission spectrum. The results obtained using the machine learning methods were compared directly to those found using a conventional method with the simultaneous linear equation of strain and temperature cross-sensitivity by extracting two peaks from the transmission spectrum. Results demonstrated that the accuracy was improved significantly using deep NN method with Bayesian regularization compared to the conventional cross-sensitivity method.

Laser ablation of CFRP surfaces for improving the strength of bonded scarf composite joints

Repairing damaged composite parts using scarf technique requires a careful selection of treatment methods for composite surface. Laser treatment is one of the emerging techniques to treat the milled composite surface by unlocking various levels of morphological changes and, thus, optimizing joint strength. However, laser parameters, e.g., energy density (fluence), should be carefully determined to ensure the acceptable structural recovery. Here, the influence of CO2 laser with relatively high fluence (ablation effect) on the surface characteristics (roughness, morphology, wettability) and scarf joint strength with associated failure modes of unidirectional (UD) and quasi-isotropic (QI) carbon fiber-reinforced plastic (CFRP) laminates is studied. We found that the ablation effect using CO2 laser at 3.6 J/m2 was considered safe for UD laminates as their joint strength was comparable with that treated by manual sanding. The ablation at higher fluence (8.4 J/m2) reduced the joint strength in UD laminates due to severe damage occurred in 0∘ fibers that triggered adhesive failure. In QI laminates, 3.6 J/m2 laser fluence could improve joint strength since the cohesive failure was activated in off-axis plies (90∘, +45∘, −45∘).

Impact of winding parameters on the fiber bandwidth in the cylindrical area of a hydrogen pressure vessel for generating a digital twin

AbstractThe wet winding process is an established manufacturing technology for the production of rotationally symmetrical components made of fiber‐reinforced plastic (FRP), such as type‐IV hydrogen pressure vessels. In this process, the FRP laminate is produced by continuously depositing an impregnated fiber band on the winding core in a winding pattern adapted to the component stress. Despite a long history of the process, there are shortcomings in the understanding of the process, without which further optimization in terms of cost and material efficiency will reach its limits in the future. Currently, the fiber band is assumed to have a constant rectangular cross‐section in most simulations, which neglects manufacturing influences such as fiber spreading. The investigations carried out aim to extend the process understanding by a realistic description of the fiber bandwidth when deposited on the winding core. The investigations show that the fiber spreading, as well as the absolute fiber bandwidth, depend on the resin loading and the fiber band tension, independent of the winding pattern in the cylindrical area of a pressure vessel shaped winding core. In addition, the fiber bandwidth changes by 15%–20% during circumferential winding, depending on the machine movement.

The Effect of Carbon Fiber Types on Tool Wear During Edge Trimming of 0 deg, 45 deg, 90 deg, and 135 deg Carbon Fiber-Reinforced Plastic Laminates

Abstract Carbon fiber-reinforced plastics (CFRP) composites are difficult-to-machine materials due to extensive tool wear. This article investigates the impact of carbon fiber types on tool wear in edge-trimming CFRPs, each with the ply angle of 0 deg, 45 deg, 90 deg, or 135 deg, using uncoated tungsten carbide endmills at the high spindle speed of 6000 rpm and the constant feed of 0.0508 mm/rev. Three distinct types of carbon fiber tows, including T300 as standard modulus (SM), IM-7 as intermediate modulus (IM), and K13312 as high modulus (HM), have been vacuum infused into CFRP laminates and edge trimmed to investigate wear characteristics. Three wear criteria measured are flank wear, edge rounding radii, and worn area. The results show that tool wear is influenced by carbon fiber properties, such as fiber tensile strength, tensile modulus, and fiber microstructure. Overall, IM carbon fibers with the highest tensile strength produced the most extensive tool wear due to the abrasive carbon fibers. Of four fiber directions, the largest tool wear was obtained from the 45 deg angle, while the lowest tool wear occurred in the 0 deg angle.

Experimental Manufacturing Methods of Glass Fiber Composites Considering Flexural Behaviour

Fiber-reinforced plastic laminates (FRPL) and sandwich composites are outstanding materials due to its mechanical properties (i.e., light weight, low density and high strength to weight ratio). These applications are widely used in the fields of aviation, automotive and construction industries. The superior mechanical properties depend on the properties of reinforcing materials, matrixes and manufacturing processes. This research proposes the comprehensive study of mechanical properties of epoxy resin reinforced by glass fibers under different processes. Glass-fiber sandwich composites were manufactured by the hand lay-up process and cured in different methods (i.e., with and without vacuum bagging). The comparison between curing temperature and pressure is investigated using the vacuum bagging process to determine the mechanical properties under flexural tests. Experimental tests are performed using the universal testing machine (UTM). As a result, it is confirmed that the hand lay-up process affects the flexural stress, deflection and internal force of both fiber-reinforced plastic laminates and sandwich composites. At the high curing temperature, the vacuum bagging method significantly provides the greater flexural stress, deflection and load

Blister tests on thin-walled composite structures at different temperatures

Blister tests are widely used to characterize adhesives on substrates. In this paper, pressurized blister tests are performed at different temperatures between −40 °C and 180 °C with two different glass fiber-reinforced plastic laminates. The paper examines the influence of surface pretreatment and geometric features of the substrate. The resulting burst pressures vary between 1 bar and 150 bar. Our studies show that the main influences on burst pressures at high temperatures are glass-transition temperature and storage modulus, and at low temperatures brittleness of the epoxy. Surface pretreatment of corundum blasting results in the highest burst pressures. While the gap width has a big impact on burst pressures, gap spacings show little influence. • A method and results of pressurized blister tests up to 150 ​bar at temperatures from −40 ​°C to 180 ​°C are presented. • Investigations on the impact of surface pretreatment and geometric features of the substrate are reported. • Empirical investigations on elastic and strength properties of two GFRP systems are shown.