Carbon Fiber Reinforced Plastic Laminates Research Articles

Progressive damage modeling in open hole composite laminates with ultrasound-informed drilling-induced delamination

Insertion of fasteners, often used in aerospace and automotive industries, requires drilling that induces non-uniform delamination between lamina of a carbon fiber reinforced plastic (CFRP). Understanding the effect of drilling-induced delamination on the mechanical performance and associated damage mechanisms (progressive damage and failure) is critical to ensure joining integrity. The present work develops an ultrasound testing (UT) method to quantify the drilling-induced delamination at each individual ply interface for CFRP laminates. We then develop a mesoscale finite element (FE) model of an open hole tension specimen by incorporating the UT-obtained drilling-induced delamination at each interface. This delamination is modeled using cohesive zone elements with a bilinear traction-separation law with progressive damage in each ply modeled using the 3D Hashin along with a progressive damage model. Our FE model, with UT-informed delamination, accurately predicts experimental observations of the stress concentration around the hole, damage progression, and open hole tension strength.

Multi-objective optimization of variable-stiffness composite for CFRP-winding buckle arrestor by using NSGA-Ⅲ

This study introduces a multi-objective optimization method utilizing the NSGA-III algorithm to tailor the fiber shape of variable-stiffness CFRP (Carbon Fiber Reinforced Plastics) shell structures. Combined with offshore oil and gas engineering, this method is employed to perform fiber shape optimization design for CFRP-winding buckle arrestors. Based on cubic polynomial path functions' contour lines, curved fibers are represented and fitted using the Curvature Minimum Bi-Arc (CMBiArc) interpolation NURBS curve method. Employing the NSGA-III algorithm, the fiber shapes of a CFRP laminate are optimized under manufacturing constraints, targeting mean compliance, fundamental frequency, and fiber curvature. With the study of numerical modeling, buckling crossover mode and arresting efficiency, multi-objective optimization is carried out for fiber shape of CFRP-winding buckle arrestors designed for subsea pipelines. With the goal of maximizing arresting efficiency, structural fundamental frequency, and minimizing fiber curvature, the method yields an enhanced CFRP-winding arrestor design, which demonstrates a high practicability through a layered design approach. By parametric study of optimization result and comparison with slip-on arrestor, the feasibility of the optimization method and the practical value of the novel improved arrestor are substantiated.

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.

Tensile strength prediction of unidirectional polyacrylonitrile (PAN)-based carbon fiber reinforced plastic composites considering stress distribution around fiber break points

Recent advancements in enhancing the mechanical characteristics of carbon fibers open up new application possibilities for carbon fibre-reinforced plastic (CFRP) composites. Particularly in unidirectional CFRPs, which form the basal structure of CFRP laminates, developing a micromechanics model capable of predicting the tensile strength of unidirectional CFRPs based on carbon fiber mechanical characteristics is a current aspiration. This study conducted a stress distribution analysis around the fiber fracture point to predict the tensile strengths of unidirectional CFRPs prepared with five types of polyacrylonitrile (PAN)-based carbon fibers, each with unique mechanical characteristics. Numerical simulation results obtained using a unidirectional CFRP model that considered the stress concentration, fiber axial stress, and bimodal Weibull distribution were reasonably consistent with the experimental results for the tensile strengths of unidirectional CFRP composites, regardless of the differences in the mechanical characteristics of the fiber. Our findings can provide guidance for designing further enhanced high-performance CFRP materials.

Theoretical investigation on scattering of ultrasonic Lamb waves at damaged area in quasi-isotropic CFRP laminates based on Mindlin plate theory

ABSTRACT With the wide application of carbon fibre reinforced plastic (CFRP) structure, a structural health monitoring (SHM) system that can easily detect damages in CFRP structures is urgently needed. Since it is possible to detect damages effectively in a large area in CFRP by using the scattering of Lamb waves, in this research, we investigated the scattering of Lamb waves at an impact damaged area in quasi-isotropic (QI) CFRP laminate. By modelling the impact damage as a cylinder area with a uniform stiffness degradation, the scattering waves are calculated based on Mindlin plate theory, which is more precise than Kirchhoff plate theory. It is shown that in the low-frequency region, the calculation results based on Kirchhoff and Mindlin plate theory was similar, but in a higher frequency range, the results differed. The calculation results were compared with the simulation results, suggesting the validity of Mindlin plate theory within a practical frequency range. Moreover, we validated the analytical and simulation results experimentally using a QI CFRP laminate with a hole. We also conducted some parameter study based on the analytical calculation to clarify influential stiffness components. Since scattering behaviour of Lamb waves can be calculated in a fast and easy way using this method, this work is useful for the successful development of a scattering-based SHM system.

Bending characteristics of partially reinforced aluminum/CFRP hybrid hat‐section beam structures with an adhesively bonded joint: An experimental, numerical, and analytical study

AbstractA significant feature about hybrid structures is the strengthening of critical areas in order to increase the load capacity of the beams. This research evaluates the energy absorption capability and bending collapse behavior of an aluminum hat‐section with adhesively bonded of carbon fiber reinforced plastic (CFRP) as a partial reinforcement (PR) hybrid beam. The aluminum layers and processed CFRP laminates were bonded with adhesive joints to produce the beams with varied layups for hybrid beams. The specimens showed a range of bending collapses, and the hybrid specimens' peak load and load drop differed depending on failure mechanism. The experimental results reveal that the amount of SEA of the hybrid beam specimens was higher compared with that of the aluminum beam, with Al/CFRP [0/90]S PR hybrid beam exhibiting an 85.9% improvement in SEA value. Subsequently, FE models of aluminum and hybrid beams were developed for bending collapse analysis, and the finite element results were consistent with the experimental specimens' validation. In addition, the consequences of progressive damage failure in the interface effect and transverse matrix damage in various layups were investigated. Eventually, the Kecman model is used to perform analytical modeling of hybrid and aluminum beams in order to examine the impact of CFRP partial reinforcing components based on various bending moment hinge lines.Highlight Bending characteristics of adhesively bonded partially reinforced Al/CFRP beam Experimental and numerical investigation on the beams under three‐point bending Analytical study for the prediction of energy absorption characteristics A good agreement between numerical, theoretical and experimental results

Ballistic performance of thin CFRP laminates under complex in-plane preload

In this research, we explore the effects of complex in-plane quasi-static loads on the high-velocity impact response of Carbon Fiber Reinforced Plastic (CFRP) composite laminates, grounded in the practical context of various working loads combined with potential high-velocity impacts experienced by aircraft. The specific complex in-plane loads studied include uniaxial tension and compression, biaxial tension and compression, and a combination of tension and compression preloading. The results show that the complexity of in-plane preloads, along with pre-compression, reduces the ballistic limit velocity. Biaxial preloading, especially in compression, greatly compromises the specimen's ballistic resistance. The study also proposes a theoretical model based on energy conservation principles to predict the ballistic limit velocity of CFRP laminates under various preloading conditions. The research provides valuable insights for designing composite structures and highlights the importance of considering in-plane preloads in assessing thin CFRP ability to withstand ballistic impacts.

Fracture mechanism of carbon fiber-reinforced thermoplastic composite laminates under compression after impact

Thermoplastic carbon fiber-reinforced plastics (CFRPs) are increasingly utilized in the aerospace industry owing to their beneficial properties and enhanced formability relative to thermoset CFRPs. Despite the extensive use of these materials, studies focusing on compression after impact (CAI) tests with impact energies exceeding 20 J for thermoplastic CFRPs remain scarce. This study examines CAI tests on quasi-isotropic laminates of thermoplastic CFRP, subjected to a low-velocity impact energy of 27.04 J. For comparison, quasi-isotropic laminates of thermoset CFRP were subjected to a low-velocity impact energy of 36.5 J. These tests reveal that the CAI strength of both materials is comparable, notwithstanding the lower fiber volume fraction in the thermoplastic CFRP. Further, this research incorporates a finite element (FE) analysis to investigate the damage mechanisms in thermoplastic CFRP. The FE model, integrating interlaminar damage observed during the impact tests, accurately predicted the relationship between compressive stress and strain, correlating closely with the experimental outcomes. It was observed that both interlaminar and intralaminar damage propagation were constrained until the point of maximum compressive stress. Prior to reaching this maximum, a region of elevated compressive stress in the fiber direction was noted in the 0° layer near the non-impacted side. These findings indicate that the compressive stress in the fiber direction in the 0° layer adjacent to the non-impacted side is pivotal in dictating the final failure, which determines the CAI strength of thermoplastic CFRP laminates.

Damage tolerance analysis of double strap joints with composite adherends

ABSTRACT Damages in composite structures are typically repaired using external bonded patches. In this work, the damage tolerance within external patches is studied using double strap joint (DSJ) with carbon fibre reinforced plastic (CFRP) specimens. The damage tolerance in this work refers to bond-line manufacturing-related defects such as debond or dry area. Both intact and pre-cracked DSJ specimens are numerically analysed using experiments for comparisons. DSJ specimens’ adherends were CFRP laminates with AS4/3501–6 plies and bonded using adhesive film FM 300–2. The pre-cracked specimens are monitored during experiments using high-speed digital image correlation to visualize damage propagation. The unsymmetric pre-crack influences in a clear way as shown by experiments. The numerical analyses reveal the effect of failure mechanisms on final failure and the maximum force during a test. The included parametric sensitivity analysis is performed using statistical methods. The normally distributed parameters are sampled using separate distributions for each analysed interface and fracture mode. UNCLASSIFIED Based on Foreground Information under EDA Contract No B.PRJ.RT.670 covering the Ad Hoc Project entitled ”PATCHBOND II”.

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.

Complete constitutive model of CFRP including continuous damage in low strain rate compression and temperature generation in high strain rate impact

AbstractThis paper reports a method to construct the complete constitutive model of carbon fiber‐reinforced plastic (CFRP) by distinguishing the strain rate state and modifying the material stiffness. In quasistatic (low strain rate) compression, the initial nonlinear effect caused by the material defects was described by introducing an nonlinear increasing factor. In dynamic (high strain rate) impact, the nonlinear strengthening effect was described by introducing the dynamic amplification factors of stress and strain based on the reference state. Considering the instantaneous temperature rise obtained from the impact work–temperature generation equation and the influence of temperature on modulus and strength, the coupled thermomechanical constitutive models combining the strain rate effect and the temperature effect were established. The user‐defined material subroutines (VUMAT) were developed, and then these constitutive models were verified by finite element analysis (FEA). Finally, the developed material subroutine was applied to predict the impact penetration of CFRP laminates, and the results show that the opening holes, damage and energy dissipation are in good agreement with the reference experiment. This work comprehensively analyzed the construction method of CFRP constitutive models, which would provide a guidance for the coupled thermomechanical behavior under dynamic impact.Highlights An anisotropic continuum mechanical constitutive behavior considering strain rate effect and damage evolution behavior was established. A macroscopic anisotropic constitutive model including the coupled impact temperature generation‐mechanical behavior was established. Combined with the incremental finite element method, the three‐dimensional user‐defined material subroutines (VUMAT) were developed and verified. The thermomechanical impact penetration behaviors of CFRP laminates was predicted, and the stress field, temperature field and failure characteristics were visualized.

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.

Enhancing adhesive bond strength of CFRP/titanium joints through NaOH anodising and resin pre-coating treatments with optimised anodising conditions

Adhesively Bonded Carbon Fibre Reinforced Plastic (CFRP) and titanium alloy have been extensively used as a hybrid structure in modern aircrafts due to their excellent combination of mechanical properties and chemical stabilities. This study utilised NaOH anodising method to create micro-rough titanium surfaces for enhancing adhesive bonding between titanium alloy and CFRP laminates. A special and simple technique named Resin Pre-Coating (RPC) was also employed to improve the surface wetting of anodised titanium and grinded CFRP substrates. The influences of anodising temperature and duration on the surface morphology, wettability and adhesive bond strength were investigated. The single lap shear test results showed that the bond strength of specimens anodised at 20 °C for 15 min improved by 135.9% and 95.4%, respectively, in comparison with that of acid pickled and grinded specimens (without RPC treatment). Although increasing the anodising temperature and duration produced rougher titanium surfaces, the adhesively bonded joints were not strong enough due to relatively friable titanium oxide layers.

Experimental investigations of impact behavior and milling performance of T700-CFRP under cryogenic conditions

The carbon fiber reinforced plastic (CFRP) composite is a reliable body material for modern airplanes, and extremely difficult to cut owing to its complex structure and special mechanical characteristics. In cutting CFRP, fiber breakage and delamination defects very frequently appear on the machined surface. The use of cryogenic cooling in CFRP cutting has proven to be an advanced approach to improving the machined surface quality of CFRP composites. To reveal the mechanism of milling CFRP under cryogenic conditions, this study investigates the impact behavior and cutting performance of T700-CFRP at low temperatures. The impact test of T700-CFRP unidirectional laminates with 0°, 45°, and 90° fiber directions was performed at various temperatures ranging from 20 °C to −196 °C, to analyze the impact toughness and the fracture morphology. Side milling experiments of CFRP laminates of 0°, 45°, and 90° fiber directions with the PCD endmill were conducted at the same temperatures used in the impact test. Experimental findings revealed that for 0° specimens, the impact toughness increased at lower temperatures, and the impact damage worsened as the temperature dropped from −120 °C to −196 °C. There were no evident changes in the impact toughness or impact damage of 45° and 90° specimens with the decrease in temperature. The feed force and radial force increased as the cooling medium temperature lowered during milling CFRP. The machined surface of 45° workpieces was the roughest among all the workpieces and covered with numerous pits and craters. The machined surface roughness Ra of 0° workpieces decreased as the cooling medium temperature was lowered from 20 °C to −160 °C and then increased at −196 °C, while the Ra value of both 45° and 90° workpieces rose as the temperature dropped from 0 °C to −196 °C.

Numerical simulation on addition of Kevlar as reinforcement in CFRP (Carbon fiber reinforced plastic) laminates under low velocity impact

Fibre Reinforced Polymer (FRP) laminates are used extensively in automotive and aerospace components because to their reduced weight, increased design freedom, increased durability, and reduced susceptibility to corrosion. The research of impact damage is crucial for composite materials utilised in these components. Impact circumstances and laminate designs play the biggest roles in determining how laminates react to impacts. The hybrid composite laminates in this work (made of CFRP and Kevlar) are subjected to an explicit numerical analysis of the low velocity impact damage behaviour for three distinct thicknesses. Modelling is done using ABAQUS/CAE on the composite laminate and impactor. Modelling is done using ABAQUS/CAE on the composite laminate and impactor. The laminates' characteristics were coded in a VUMAT subroutine, and the analysis was done using ABAQUS/Explicit. Numerical analysis results for the absorbed energy are compared to laminates reinforced simply with carbon. In comparison to bare CFRP laminates, the simulation results indicated that hybrid laminates had a better energy absorption capability.

Effect of span/thickness ratio on fatigue properties of thick quasi-isotropic CFRP laminates subjected to three-point bending loading

In this study, three-point bending fatigue tests were conducted to investigate damage growth behavior of thick quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates. The span/thickness ratio L/h was varied for both static tests and fatigue tests to determine failure mechanisms. In the static tests, the failure mode changed from delamination to compressive buckling as span/thickness ratio increases. The apparent interlaminar shear strength was higher for the specimens with lower span/thickness ratios, and the shear failure was likely to be caused by oblique crack in 90° plies. In the fatigue tests, the specimens with span/thickness ratio L/h=7 caused delamination regardless of stress level. For the specimens with span/thickness ratio L/h =15, three types of failure modes were obtained depending on stress level; delamination near the neutral plane, buckling at compressive area and matrix crack at tensile area. During the fatigue tests, stiffness of specimens with different span/thickness ratios which fail in shear was compared using digital image correlation (DIC) method. The specimens with span/thickness ratio 4 suddenly decreased in stiffness without increasing normal strain over cycles. Both specimens with span/thickness ratio 4 and 11 finally failed by delamination but they showed different failure process in how normal or shear strain developed.

Impact resistance and damage mechanism of polyurea coated CFRP laminates under quasi-static indentation and low velocity impact

In this study, polyurea coating has been applied to improve the impact resistance of carbon fiber reinforced plastics (CFRP) battery pack housing under automotive crash condition. The quasi-static indentation test and low velocity impact test were carried out to study the impact response of polyurea coated unidirectional and plain woven CFRP laminates with three coating methods. The impact velocity was selected from 10−4 m/s to 4.5 m/s. In addition, damage mechanism and failure modes of the laminates were analyzed, focusing on the identification of dominant damage modes and crack evolution. It was demonstrated that thin polyurea coating can improve the impact resistance of both unidirectional and plain woven CFRP, while the former was more significant than the latter. The specific energy absorption had 94% and 51% increment under low velocity impact and quasi-static indentation. The front coating method was the best polyurea coating method. Results also revealed that the polyurea coating increased the damage area and fracture crack of polyurea coated CFRP laminates with different damage mechanisms. This study confirms that the use of polyurea coated CFRP laminates is an interesting and promising structure candidate for crash safety design and lightweight design of battery pack housing.

Improving hole quality of thick CFRP laminates through a laser-mechanical compound drilling process

Conventional mechanical drilling of thick carbon fiber reinforced plastic (CFRP) composite laminates is prone to machining-induced defects such as burrs, delamination, and severe tool wear. However, pulsed laser drilling as an improved strategy results in hole taper and the formation of a heat-affected zone (HAZ). Herein, a new laser-mechanical composite drilling process is proposed, which combines the advantages of pulsed laser drilling for avoiding tool wear and twist drilling for achieving high dimensional accuracy, significantly improving the drilling quality of thick CFRP laminates. The evolution mechanism of the hole taper and HAZ with processing conditions in pulsed laser drilling is investigated. Furthermore, a theoretical model is established to reveal the material removal mechanism during the reaming process. The thrust force variation, drilling quality and tool wear are analyzed and verified by comparative experiments. The results show that due to the shielding effect from the surface materials, the maximum hole taper and HAZ at the hole exit reach up to 37.5° and 650 μm, respectively, which can be removed effectively by subsequent reaming operations. Due to its small amount of material removal, the peak thrust force and the average thrust force in laser-mechanical drilling are only 53.8 % and 37.6 % of the critical thrust force of delamination, respectively, which can effectively inhibit delamination. Compared with direct twist drilling, the average wear of the main cutting edge in laser-mechanical drilling is decreased by 60.87 %, which greatly reduces the size of the delamination by 55 %.

Fastening solutions on composite structures: Progressive damage analysis of a unique bolted joint design for single-lap CFRP laminate

This study tested a unique assembly method using single and multi-body sleeves with carbon fiber-reinforced plastic (CFRP) to improve load-carrying capacity in single-lap joints. Advanced techniques were implemented into FE code to simulate progressive material degradation behavior. Ti6-4 bolt, insert, and washers with AISI 304L sleeve joint were conceptually designed to keep bolt and nut together with less relative motion. Failure indices were reduced by 16–54%, damage initiation force was improved by 8–40%, and inter-plate clamp loss was reduced by 18% compared to the sleeveless design. Lateral load-carrying capability of joint and inter-plate clamp load significantly improved.

Prediction of Impact Information of Composites Laminates Considering the Practicality

Recently, carbon fiber reinforced plastics (CFRP) have been used in various applications, including aircraft. Because they are vulnerable to out-of-plane loads, internal and externaldamage occurs when foreign objects impact them. Internal damage that can affect residual properties is difficult to find and judge from the outside without special devices, which arehighly costed and are sometimes difficult to conduct in some locations. In this study, surface contour information was obtained from impact tests on CFRP laminates, and thepredictability of compression after impact (CAI)strength was investigated using a conventional single-task random forest model, and a decision tree-based multi-task learning model with other objective variables related to impact tests. The models estimated CAI strength with around 75% R2, and the conventional single-task learning model showed the highest value. The importance of each model indicated that factors that contribute to impact-related objective variables (impactor shape, delamination area, and delamination length) and those to CAI strength do not have a strong relationship.