Composite Fan Blades Research Articles

Bioinspired ultra-fine hybrid nanocoating for improving strength and damage tolerance of composite fan blades in flexible manufacturing

The ultrafine mineral bridges/bio-polymer hybrid structure inspired by nacreous is applied to the interface structure design of composite, aiming to address the high brittleness and low damage tolerance problems of carbon fiber composite fan blades (CFCFB). Herein, we present a simple and efficient approach, called the "cationic copolymer-mono micelle-mediated" method, to translate the nacre-inspired structure for developing micelles/ZnO hybrid nanocoating. The hybrid nanocoating was demonstrated to have remarkable characteristics such as ultrafine ZnO sizes, monodispersity, uniformity, and core-shell structure (diameters: ≈45 nm). Additionally, the coating process is simple, solvent-free, and seamlessly integrates with scalable carbon fiber manufacturing. Based on the nacre-inspired interface structure, the CFCFB exhibits high interlaminar strength (99.3 MPa), high stiffness (79 GPa), and high toughness (41.2 MPa m1/2). This study provides a blueprint for bioinspired ultrafine nanostructure design in composites and inspires advanced manufacturing strategies for other promising engineering materials.

Bayesian Inference for the Calibration of Progressive Damage Model of Dovetail Specimens from Laminated Composite Fan Blade

Abstract Composite fan blades are the preferred alternative for the fan stage of most advanced high bypass ratio turbofan engines. The ability of the dovetail to safely bear this load is one of the key points of the multi-level “test pyramid” approach of compliance demonstration for special airworthiness regulation. Debonding between adjacent layers is the main damage mode of laminated composite fan blades. However, there is difficulty in measuring the as manufactured interlaminar mechanical properties used in finite element models. In this study, tensile loading was applied to simulate the interacting centrifugal force and capture mixed mode damage evolution. Structural responses and material damages were calibrated with measured tensile loads through Bayesian inversion. Posterior probability distributions of maximum interface tractions and contact stresses were solved using Markov chain Monte Carlo sampler. Results indicated the two bilinear cohesive material models had a capacity of predicting empirical means of longitudinal reaction forces as that in test considering additional discrepancy term (0.035 kN and 0.96 kN respectively), while they made an significant impact on the prediction of tensile load history especially when two delamination cracks initiated and propagated. Interface elements provided a higher matching quality in predicting loading history and capturing damage mechanism in association with in-plane progressive damage analysis. This calibrated parameter set could be functioned as benchmark in numerically determining the ultimate tensile load of dovetail elements and reducing the necessary number of physical tests at elemental length level.

Ultrasonic guided wave damage localization method for composite fan blades based on damage-scattered wave difference

Abstract Ultrasonic guided wave (UGW) has a wide monitoring range and high accuracy, holding promise for monitoring damage in engine large-area composite fan blades. However, the multi-curvature characteristics of engine composite fan blades with their anisotropic material properties make damage localization impossible with conventional UGW monitoring methods. In order to realize the UGW damage monitoring of the blade, this paper proposes a damage localization method based on damage-scattered wave difference. The method utilizes irregular sensing arrays to achieve localization of damage in multi-curvature composite blades with a small amount of data. First, the difference between the mutual excitation in a pair of sensors and the damage-scattered waves captured at reception was analyzed. It is concluded that the closer the damage is to the received sensor, the greater the damage index (DI). Next, a DI ratio of the mutually excited and received signals is computed for each sensor pair. This ratio is utilized to make a vertical line on the propagation path, which is identified as the damage likelihood line (DLL). Finally, a DLL corresponding to the three largest DIs was selected, and their intersections were used for damage localization. A time-domain truncated signal processing method is proposed to enable DI to more accurately represent the effects of damage, and improve the localization accuracy of the method. An experiment on damage localization was carried out on a homemade composite fan blade, where the damage was tested at various locations and sizes. The results show that the damage localization on the blade is good and 3mm tiny damage localization is achieved.

Whipping motion of airplane composite fan blades due to bird strike

Composite fan blades made of CFRP have been developed and investigated to reduce the weight of aircraft engines. Aircraft fan blades are subjected to high-speed impact by foreign objects, such as bird strikes. Because CFRP has lower impact resistance than metal materials, it is necessary to focus on possible failure not only at the impact point but also at the tip and trailing edge of the fan blade. This paper developed a finite element analysis model of fan blade geometry and investigated the dynamic deformation that may induce peripheral fracture when a bird strike occurs on a composite fan blade. Natural vibration analysis and transient response analysis were performed to analyze the vibration behavior at the fan blade periphery. The natural vibration analysis showed that the vibration modes in the out-of-plane direction of the blade are of low order. In the transient response analysis, when a group of particles defined by the equation of state and the SPH method collided, a sudden deformation in the periphery, called a whipping motion, was observed immediately after the impact. The spanwise strain has a peak value at the trailing edge of the fan blade, while the chordwise strain has a peak value at the leading edge of the fan blade. Furthermore, the transient response analysis with the fan blades rotating showed an increase in the peak strain value. A comparison of the impact loads and displacements immediately below the impact indicated that the centrifugal force increased the geometric stiffness, which increased the reaction force due to the fan blade, increasing the peak value.

Hybrid joint interface in composite fan blade subjected to bird strike loading

An aircraft engine’s fan blades are one of the most important parts of the engine. Bird strikes on fan blades have always been an issue, as bird parts can strike other parts of the engine, potentially causing more damage. It is impossible to avoid being struck by a bird entirely. However, finite element analysis can be used to optimize the design of blade so that the overall impact of a bird on a jet engine is reduced. Even though current composite blades can withstand the impact of a bird strike, some delamination failures have been observed on the blade’s trailing edge side, probably due to vibration bending modes. Instead of the single fiber composite blade that is currently in use, this research proposes using two fibers (Carbon and Glass). For this to be possible, two fiber joints must be designed properly at different locations on the blade. At crucial joint locations, the minimum inter-laminar strain level was used as the design criteria. Blade deformation is simulated using coupon and sub-element level finite element analysis (FEA) models with appropriate boundary conditions with in-built hybrid joints inside. The first stage of this project involved using the Ansys Parametric Design Language (APDL) and linear static analysis to create coupon models for combinations of joint positions. In the present work, dynamic bird strike analysis on sub-element level models was performed with various joint location combinations. The best joint configurations based on static and dynamic analysis results will be suggested for use in the composite blade to prevent delamination.

Numerical modeling and experimental validation of lamina fracture and progressive delamination in composite dovetail specimens under tensile loading

In this work, a numerical simulation was conducted to investigate the lamina fracture and progressive interlaminar failure behavior of a dovetail specimen of composite fan blades. Through-thickness compression (TTC) will strengthen the interphase properties as the applied pressure increases and degrade the tensile strength combined with the in-plane shear stress, which greatly affects the overall tensile behavior on the composite dovetail specimen. This was realized with the aid of ABAQUS user subroutines VUSDFLD and VUMAT, along with an experimental validation. To demonstrate the performance of the proposed approach, two sets of tensile tests were conducted on specimens with different stacking sequences with a digital image correlation (DIC) device to investigate the deformation configurations, as well as the load–displacement curves of the gauge section. The obtained results exhibited a remarkable agreement with the simulation results, particularly in terms of the first delamination load and lamina fracture load. To further validate these observations, a sensitivity analysis was carried out. This analysis took into consideration the uncertainties associated with parameters such as the longitudinal Young’s modulus, interphase properties, friction coefficient, and the position of the contact pad.

Design optimization of composite fan blade in aircraft engine subjected to bird strike loading

Bird strike has been a perennial problem for all airline companies in the world. It is the most important design criteria for the fan blades of an aircraft engine. As it is not possible to manufacture and test aircraft engines again and again for small design changes, through the simulation analysis, it is possible to study the ways to reduce the impact of the bird on a jet engine by using appropriate design and manufacturing methods for the blade. This research suggests using two fibers (hybrid) in place of the single fiber composite blade which is currently in use to reduce the delamination issues. In the first stage of this research, representative composite coupon models for combinations of hybrid fiber joint positions were created and linear static analysis was performed. For the validation of simulation methodology, a few coupons were manufactured and tested in the laboratory. Further, dynamic bird strike analysis on sub-element level models was carried out in the second stage with various joint location combinations. Next, the plate-level representative blade model was designed with the original dimensions of the aircraft engine fan blade, and bird strike analysis was performed. The behavior of the representative plate with hybrid interface was studied, and the levels of inter-laminar shear strain were checked, by varying the joint location of the two composites. Some of the shortlisted cases do show significant promise of being damage tolerant under bird strike loading.

Bird-Strike Analysis on Hybrid Composite Fan Blade: Blade-Level Validation

Bird strikes have long been a source of concern for all airlines across the world. It is the most significant design criterion for aircraft engine fan blades. As it is not practical to manufacture and test aviation engines repeatedly for minor design modifications, simulation analysis can be used to investigate strategies to reduce the influence of a bird strike on a jet engine by employing proper design and manufacturing processes for blades. This study proposes using two fibers (hybrid) instead of the single-fiber composite blade presently in use to address delamination problems. As an idea validation test, the coupon-level analysis results are validated using a four-point bend test of similar-size coupons. Following this validation, dynamic analysis is used to investigate the impact behavior of a rectangular plate subjected to a bird strike. The current research focuses on analyzing bird strikes on a hybrid composite fan blade using blade-level models. This study concentrates on the position of the bird’s impact and the joint region length of two materials. The results show that the joint region with a 40% length of glass composite shows the optimum level of normalized interlaminar shear strain in all three impact locations.

A numerical study on damage characteristics in composite tapered laminates under cyclic loading with different stress ratios

The composite fan blade requires increased thickness near the root and often is designed with tapered sections to carry the load, but they can introduce local material and geometric discontinuities, resulting in large interlayer stresses and also being the site of damage initiation. Fatigue damage mechanisms of modestly tapered laminates, designed by composite laminate design approach, were investigated by high-fidelity finite element modelling and a constitutive equation within the cyclic cohesive interface model approach. Static damage and weak-link index assessment were proposed to predict the location of fatigue damage based on the composite constant life diagram model. The findings show the sites of maximum damage index can be recognized as the ply interface of ply to ply in continuous cohesive element plies, and as the location of resin pocket in dropped cohesive element plies. The maximum scaling factor is only the direction of S13 with different steady stress, which indicates interlaminar shear stress along the longitudinal orientations reaches its fatigue failure first, and also explains the reason why interlaminar failure is easier to break. The high-cycles fatigue site of damage initiation is different with different stress ratios by the weak-link index assessment approach, and it is different from the site of static damage. Fatigue crack growth rates are also quite sensitive at the first natural frequency under cyclic loading and the weak-link zone appears in a crack growth area.

Vibration prediction of rotating composite fan blades comprising viscoelastic damping treatments

To reduce the risk of fatigue problems and flutter phenomena, the structural damping of turbomachinery components is increased by integrating constrained viscoelastic patches into rotating composite blades. However, the temperature, the frequency (of the vibration mode to be damped) and the rotation speed are all parameters which may affect significantly the efficiency of the viscoelastic damping treatment.In the presented work, a numerical tool is developed to predict the structural damping of a dynamic rotating composite fan blade while varying the temperature and the rotation speed. This study is based on a finite element model of a fan disk sector equipped with constrained viscoelastic patches. This work will allow quantifying the influence of temperature and rotation speed on the efficiency of the passive damping treatment and contribute to the design of higher performing blades.

Dynamic Response of a Composite Fan Blade Excited Instantaneously by Multiple MFC Actuators

The vibration characteristics of a composite fan blade are much more complex than those of a solid titanium fan blade due to the anisotropic material properties and complex excitations coming from unsteady flow and mechanically induced vibration. In this study, the dynamic response measurement of a wide-chord composite fan blade was carried out to study the vibration characteristics using multiple macro fiber composite (MFC) actuators, which can generate complex excitation forces with different frequencies and peak values at different locations. The measured mode shapes and natural frequencies were compared with the finite element simulation results. Based on these results, the responses of the blade under the instantaneous excitation of three MFC actuators with different combinations of several natural frequencies were measured and compared. The results show that the responses of the blade excited by different combinations of MFC actuators with different frequencies were significantly different from those excited by a single MFC actuator. The superposition of different mode shapes may cause the change of the vibration stress state, which indicates that the high cycle fatigue location of the blade under complex excitations may change to an unexpected location. The results will be helpful in understanding the vibration characteristics of the composite blades under complex excitations, and the MFC actuator could be a potential tool in vibration active control.

Comprehensive assessment of the strength of the composite fan blade of the main ventilation of the mine

The work is devoted to the development and calculation of the strength of a new composite fan blade of the main ventilation of the mine, including the static and modal analyzes, as well as the stability analysis. The studies took into account the pre-determined aerodynamic loads on the lateral surface of the blade airfoil. The research was carried out by means of the finite element analysis of the thin-walled airfoil structure using the theory of thick multilayer shells. Estimation of the static strength was performed using the Hashin strength criterion. Analysis of the airfoil shell buckling resistance under the action of bending aerodynamic loads was performed using the methods of the linear stability theory. The modal analysis was performed taking into account the prestressed state from the action of static loads. The analysis of the research results testifies to the sufficient static and dynamic strength of the composite airfoil and the possibility of its implementation in a real rotary machine with the correct design of the fastening between the metal part of the blade root and the composite airfoil. The method of designing and analyzing the strength of the fan blade composite airfoil can be used to create new composite elements of turbomachines: the correct selection of thicknesses of different parts of the airfoil allows obtaining a uniform design with rational use of material; the optimal location of the stiffeners inside the airfoil shell avoids its excessive displacement and stress and the buckling effects, as well as achieving the maximal detuning level from the bending natural frequencies of vibrations; the proposed integrated approach to the strength assessment, which takes into account the effect of aerodynamic loads on the blade airfoil in the static analysis and the prestressed state during the modal analysis can significantly improve the accuracy and correctness of calculations. The approach described in the paper is new for low-speed rotary machines, as at present there are no comprehensive methods for designing composite blades of fans and compressors, and there is no mention of specific examples of their implementation in the projects implemented by manufacturers.

Effectiveness of 2-D and 3-D modelling of dovetail joint of composite fan blade for choosing rational reinforcement schemes

Turbofan jet engines are among the most complex and responsible constructions in the world. The creation of modern globally competitive engines is impossible without the use of digital twin technologies: a set of computational models that fully describe the behaviour of the structure under any operating conditions. Today, composite materials are widely used in many industries. In aircraft engines, their use is very promising for fan blades and fan case to reduce the overall weight of the engine and inertial loads. The dovetail joint of the fan blade works in compound stress conditions. To assess the strength of this element, it is necessary to consider a three-dimensional formulation of the problem, which requires significant computational resources. The use of composite materials is complicated by the complexity of preparing mesh models. A correct choice of the material strength criterion is another important factor that must be taken into account during the analysis of the mechanical behaviour of the thick-walled composite structures. The chosen criterion largely determines the reliability and weight efficiency of the composite structure. This paper considers the possibility of replacing the three-dimensional statement of the problem with a two-dimensional one when choosing rational reinforcing schemes for the dovetail joint of a CFRP fan blade at the initial stages using Daniel strength criterion.

Development of a mathematical model to demonstrate the impact on the fan blades of a high dual-circuit turbofan engine

A mathematical model describing the impact of a foreign object (bird) on the fan blades of a turbofan engine with a high degree of dual circuitry was developed. The validation of the calculation studies was evaluated based on the examination on the prototype engine. Considering the increasing application of composite materials in the designs of prospective aviation gas-turbine engines and assuming the importance of the issue related to providing a sufficient level of airworthiness special attention is paid to the modeling and assessment of the condition of composite fan blades. In this connection the developed model allows to investigate the stress-strain state of the blades made of different, including composite materials, of the fan under the influence of foreign objects and birds on them.

Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss—Part II: Experimental Assessments and Applications

AbstractPart II describes the experimental assessment and the application of the ideas in Part I concerning the mechanisms that determine the role of blade surface waviness on laminar-turbulent transition and their consequent effect on civil aircraft fan performance. A natural transition wind tunnel was designed and constructed to characterize the impact of surface waviness on transition, using both hotwire anemometry and infrared thermography. The experimental results support the new hypothesis presented in Part I, concerning the way in which blade surface waviness affects fan performance through motion of the transition onset location due to interaction between surface waviness and Tollmien–Schlichting (TS) boundary layer instability. In particular, the theoretical amplification of the TS waves, and the corresponding transition onset location movement due to surface waviness, was borne out over a range of variations in Reynolds number, nondimensional surface wavelength, nondimensional surface wave height, and location of surface wave initiation, relevant to composite fan blade parameters. Further, the increase of receptivity coefficient, and thus, the initial amplitude of disturbances due to geometric resonance between surface wavelength and TS wavelength was also confirmed by the experiments. Surface waviness was estimated, in some cases, to result in a nearly 1% decrease in fan efficiency compared to a nonwavy blade. Suggestions are given for mitigation of the effects of waviness, including the idea of blade curvature rescheduling as a method to delay transition and thus decrease loss.

Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss—Part I: Methodology and Computational Results

AbstractThis two-part paper describes a new approach to determine the effect of surface waviness, arising from manufacture of composite fan blades, on transition onset location movement and hence fan profile losses. The approach includes analysis and computations of unsteady disturbances in boundary layers over a wavy surface, assessed and supported by wind tunnel measurements of these disturbances and the transition location. An integrated framework is developed for analysis of surface waviness effects on natural transition. The framework, referred to as the extended eN method, traces the evolution of disturbance energy transfer in flow over a wavy surface, from external acoustic noise through exponential growth of Tollmien–Schlichting (TS) waves, to the start and end of the transition process. The computational results show that surface waviness affects the transition onset location due to the interaction between the surface waviness and the TS boundary layer instability and that the interaction is strongest when the geometric and TS wavelengths match. The condition at which this occurs, and the initial amplitude of the boundary layer disturbances that grow to create the transition onset is maximized, is called receptivity amplification. The results provide first-of-a-kind descriptions of the mechanism for the changes in transition onset location as well as quantitative calculations for the effects of surface waviness on fan performance due to changes in surface wavelength, surface wave amplitude, and the location at which the waviness is initiated on the fan blade.

Collaborative optimization of conical cutter sequence for efficient multi-axis machining of deep curved cavities

As an essential part of the composite fan blade, the leading edge protection cap (LPC) has a very narrow and deep cavity which, in order to avoid the interference, requires the conical ball-end cutter to be long and thin. It calls to improve the cutter’s stiffness so to increase the roughing efficiency of the whole cavity. Targeting this important problem, this paper proposes a novel method to collaboratively optimize a conical cutter sequence, the machining ranges, and the cutting parameters for achieving the highest material removal efficiency. The main difficulty is that all the relevant entities – i.e., the LPC cavity geometry, tool size, tool axis, machining ranges, minimum tool length, tool stiffness, and cutting performance – collaboratively affect the total cutting efficiency. To facilitate decoupling them, the 3D LPC cavity is characterized by its medial surface. To identify all the geometrically accessible conical tools of each medial point, an efficient algorithm is proposed, which is featured by searching characteristic points on the cavity surface. By considering both the geometric and physical accessibilities, the tool sequence domain is constructed. To obtain the appropriate cutting parameters, the best cutting performance of a weak conical cutter is modeled under the constraint of deflection due to the cutting force. Finally, the complicated collaborative optimization model aiming for the minimum cutting time is established and solved by a PSO-based algorithm. The experimental results confirm that the proposed model and algorithm are practicable for improving the roughing efficiency of LPC cavity.

Design and Optimization of Hybrid Interface Joint in a Composite Fan Blade of Aircraft Engine

Fan blades are one of the most important components of an aircraft engine. Bird strikes on fan blades have always been a cause of worry and it can cause slices of birds hitting other parts of the engine which may lead to greater damages. Bird strikes cannot be completely avoided. However, reduction of the impact of a bird on jet engines can be achieved by suitable design and manufacturing, through the simulation analysis. Although current composite blades can withstand the bird strike impact, some delamination failures are still observed on the trailing edge side of the blade, possibly due to vibration bending modes This paper talks about using two fibers in composite blade instead of the current single fiber one. For this to be feasible, two fiber joints at various locations on the blade have to be properly designed. The design criteria used here is the lowest inter-laminar shear strain level at critical joint locations. Suitable size coupon models in FEA with hybrid joints inside are used to simulate the blade bending with appropriate boundary conditions. The coupon models were developed by using the ANSYS APDL and linear static analysis was performed for different repetitive layups and varying layer by layer joint locations. The coupon joint designs with minimum inter-laminar shear strains are shortlisted to be recommended for use in sub-element and blade models.

A Study on Stacking Sequence Design of Composite Fan Blades Using Multi-level Optimization

In this paper, the multi-level optimization method is proposed to design the optimal stacking sequence of composite fan blade more efficiently. The fan blade model used is a laminate with inconsistent stiffness because the thickness is not uniform throughout the model. This feature complicates the optimization problem and makes it difficult to apply optimal design algorithms that use only continuous or discrete variables. For this reason, we conducted the literature survey about combining the optimal design algorithm with continuous and discontinuous variables and developed optimization algorithm for the composite fan blade. Moreover, the design space of discrete variables is reduced through the optimal design of continuous variables. In the first-level, response surface method is used, with the design variables being the volume fraction of plies of the predefined angles of [0°/±45°/90°]. The optimization problem in the first-level aims at minimizing the tip displacement of the fan blade and constraints on other structural responses are imposed. At the second-level, the permutation genetic algorithm is used with the fiber orientation of each ply as design variables. In this level, we perform the optimal design of the stacking sequence using the results determined by prior level, while the composite design rule and compliance constraints are applied.

Innovative designs of embedded foam inserts in aerospace composite structures

Abstract There have been many attempts to redesign the aerospace composite structures in recent times to further improve their performance and reduce the weight. As part of these efforts, it has been proposed here that lightweight polymeric foam can be used as an embedded insert inside the fiber reinforced composite structure to further reduce its weight. The target application here is composite fan blade of aircraft engine This paper describes the analysis led design (FEA) and experimental efforts to optimize the shape of this embedded foam insert inside the composite structure under both representative static and dynamic loading so that weight reduction is achieved without affecting the structural performance of the aerospace composite structure. Different geometrical parameters like taper of foam tip, blunting level of the foam tip, use of dual or multiple foam inserts, use of continuous ply layer and other parameters like use of softer material like glass near foam tip, thickness of adhesive (which is used to bond foam with carbon composite) are investigated and their effect on the level of shear stress near the foam tip has been observed. The level of shear stress near the foam insert tip is found to be the major indicator of the possible crack initiation near tip. This study helped optimize the shape of the foam insert inside the composite structure to avoid the initiation of cracks, which is validated by manufacturing the lab level carbon fiber epoxy composite specimens with optimized foam insert geometry and testing them under representative staggered four point bend boundary conditions.