Material and structural testing to improve composite tidal turbine blade reliability

Structural validation of a thermoplastic composite wind turbine blade with comparison to a thermoset composite blade

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.

The present work investigates structural response of tidal stream turbine blades subjected to impact loads from sea animals. A full-scale tidal turbine blade model was developed using a finite element modelling software ABAQUS, while a simplified geometry of an adult killer whale (Orcinus orca) was assumed in simulating impact on the blade. The foil profiles along the turbine blade were based on the NACA 63-8XX series, while the geometric and material properties of the sea animal were calibrated with experimental results. The numerical model simulated the dynamic response of the blade, accounting for radial velocities of the blade corresponding to real life scenarios. Different magnitudes and trajectories of the velocity vector of the sea animal were simulated, in order to investigate their influence on the turbine blade’s plastic deformation. Furthermore, multiple impacts were analysed, in order to monitor the accumulation of plastic strain in the material of the blade. Finally, the potential application of stainless steel material in tidal stream turbine blades for impact resistance was evaluated, through comparison of numerical results obtained from models using stainless steel and mild carbon steel materials.

The paper describes a computational simulation approach for durability, damage tolerance (D&DT) and reliability of composite wind turbine blade structures in presence of uncertainties in material properties. This computer-based prediction methodology combines composite mechanics with finite element analysis, damage and fracture tracking capability, probabilistic analysis and a robust design algorithm to reduce weight of turbine bales without loss in structural durability and reliability. A composite turbine blade was first assessed with finite element based multi-scale progressive failure analysis to determine failure modes and locations as well as the fracture load. Analysis D&DT results were validated with static test performed at Sandia National Laboratories. The work was followed by detailed weight analysis to identify contribution of various materials to the overall weight of the blade. The methodology ensured that certain types of failure modes, such as delamination progression, are contained to reduce risk to the structure. Probabilistic analysis indicated that composite shear strength has a great influence of the blade ultimate load under static loading. Weight was reduced by 12% with robust design without loss in reliability or D&DT. It was achieved by replacing a small volume of key materials with foam.

Simulation of buckling-driven progressive damage in composite wind turbine blade under extreme wind loads

Composite wind turbine blades may experience interlaminar damage, including adhesive failure, cracking, and interlaminar fracture failure, from manufacturing or external fatigue load. Among these, the adhesive failure of adhesive joints is critical. Therefore, it is important to identify the failure mechanism in the adhesive joints between the spar cap–shear web and trailing edge of composite blades. We calculated fracture toughness through Mode I, Mode II, and Mixed-mode tests for quantitative analysis of adhesive joints. Then, to select a modeling method for realizing the damage generated in the blade, the method was verified from the specimen level. A damage model was constructed, considering contact conditions of the spar cap–shear web and trailing edge for an NREL 5MW wind turbine blade. Finally, a damage model based on cohesive zone modeling was used to analyze the progressive failure behavior of debonding at adhesive joints according to the external force applied to the blade.

A computerized method has been developed to aid in the preliminary design of composite wind turbine blades. The method allows for arbitrary specification of the chord, twist, and airfoil geometry along the blade and an arbitrary number of shear webs. Given the blade external geometry description and its design load distribution, the Fortran code uses ultimate-strength and buckling-resistance criteria to compute the design thickness of load-bearing composite laminates. The code also includes an analysis option to obtain blade properties if a composite laminates schedule is prescribed. These properties include bending stiffness, torsion stiffness, mass, moments of inertia, elastic-axis offset, and center-of-mass offset along the blade. Nonstructural materials-gelcoat, nexus, and bonding adhesive-are also included for computation of mass. The code includes an option to format the output properties that can be directly input to advanced aeroelastic codes. This report summarizes the structural layout of composite laminates within the blade, the design approach, and the computational process. Finally, we present the results of two composite blades designed using this code in support of a project covering comparison of two- and three-blade rotors for a hypothetical turbine.

<div class="htmlview paragraph">Design studies supported by laboratory test data have shown that graphite fiber composite fan blades in subsonic turbofan engines offer significant potential reductions in weight for both the fan rotor and containment structure as well as reduced sensitivity to fatigue failure from foreign object damage. However, substantial progress in the application of composite material technology including mechanical properties, design, development, processing and inspection methods must be accomplished in order to realize these potential improvements over conventional titanium fan blade materials. Turbofan aircraft engines are subjected to foreign object impact by birds, ice balls, ice slabs, rocks, sand, rain, and miscellaneous objects like blown tire treads in addition to operation with inlet distortion. Graphite composite blades must be designed to tolerate these types of damage and still produce power comparable to current engines before they can seriously be considered for flight applications.</div> <div class="htmlview paragraph">In 1969, the General Electric Company selected a high bypass engine as the test vehicle for initial application of graphite fiber composite fan blades. A two phase design, manufacturing and development program was initiated to produce a graphite composite first stage fan rotor suitable for flight application. The first phase of this program, completed in 1970, was directed toward identifying the problems and producing graphite composite fan blades for engine test evaluation with unshrouded titanium blades in the same rotor.</div> <div class="htmlview paragraph">This report presents a status summary of the composite fan blade design, manufacturing and development effort including the results of the crosswind engine testing of these blades at General Electric's engine test facility at Peebles, Ohio.</div>

Weight reduction of turbofan engines is one of the main concerns of aero engine manufacturers in order to cut fuel burn. To achieve higher fuel efficiency, aero engine manufacturers develop turbofans with higher bypass ratio, which can only be achieved with larger (and heavier) fan sections. This makes weight reduction in fan components a major consideration and becomes a key driver for the use of composite materials in future engines. The objective of this project is to design, perform structural analysis and optimization of a Composite fan blade. Development of a fan blade is comparable to a future large aircraft engine fan blade. This thesis is about the structural analysis of a composite fan blade with a honeycomb sandwich construction with a polymer matrix composite and honeycomb Aluminium core compared with baseline solid basic fan blade made of titanium. The focus of this work is to design the sandwich composite blade with honeycomb core and conduct static and dynamic analysis.

This study investigates the hygrothermal aging behavior and thermomechanical properties of as-manufactured glass fiber-reinforced epoxy and thermoplastic composite tidal turbine blades. The blades were previously deployed in a marine environment and subsequently analyzed through a comprehensive suite of material characterization techniques, including hygrothermal aging, dynamic mechanical analysis (DMA), tensile testing and X-ray computed tomography (XCT). Hygrothermal aging experiments revealed that while thermoplastic composites exhibited lower overall water absorption (0.78% vs. 0.47%), they had significantly higher diffusion coefficients than epoxy (2.1 vs. 12.1 × 10−13 m2s−1), suggesting faster saturation in operational environments. DMA results demonstrated that water ingress caused plasticization in epoxy matrices, reducing the glass transition temperature and increasing damping (112 °C to 104 °C), while thermoplastic composites showed more stable thermal behavior (87 °C glass transition temperature). Tensile testing revealed substantial reductions in ultimate strength (>40%) for both materials after prolonged water exposure, with minimal change in elastic modulus, highlighting the role of matrix degradation over fiber reinforcement. XCT image analysis showed that both composites were manufactured with high quality: no large voids or cracks were present, and the degree of misalignment was low. These findings inform future marine renewable energy composite designs by emphasizing the critical influence of moisture on long-term structural integrity and the need for optimized material systems in harsh marine environments. This work provides a rare real-world comparison of epoxy and recyclable thermoplastic tidal turbine blades, showing how laboratory aging tests and advanced imaging reveal the influence of material and manufacturing choices on long-term marine durability.

Composite blades working underwater experience complicated loading conditions. Robust design of a composite blade for hydrokinetic applications should satisfy varying loading conditions and conservative failure evaluations. Blade manufacturing using composites requires extensive optimization studies in terms of composite materials, number of layers, stacking sequences, ply thickness and orientation. In the current study, particle swarm optimization (PSO) technique is adopted to conduct composite lay-up optimization for the turbine blade. Layer numbers, ply thickness and ply orientations are optimized using standard PSO (SPSO) to minimize weight. Composite failure criteria are applied using finite element method to generate the most conservative blade design. Based on the blade lay-up design with minimized weight, stacking sequence of the blade lay-up was optimized to maximum safety factor of the designed blade using permutation discrete PSO (PDPSO). To improve the efficiency of the algorithm, the concepts of valid/invalid exchange, and memory checking were introduced into PDPSO. Meanwhile, another discrete PSO using partially mapped crossover (PMX) technique was used to validate the simulation results optimized by PDPSO. A final composite blade design with minimized weight and maximized load-carrying capacity was presented.

A probabilistic stress analysis tool predicting reliability of composite wind turbine rotor blades was developed and validated by comparing with results from a three‐dimensional shell finite element model of a blade. Stress analysis was based on thin wall multicellular Euler–Bernoulli beam theory using as input section stress resultants directly from aeroelastic simulations; a finite strip method was implemented for elastic stability calculations. Reliability analysis was performed at the ply level of the multidirectional laminates implementing various methods such as the response surface method, β‐index and crude Monte Carlo simulation. Physical and statistical uncertainties of the basic variables was taken into account while several model uncertainties related to the material properties were further introduced and quantified in the light of appropriate test results. To prove the efficiency of the code as a design tool, the effect of various probabilistic assumptions concerning the material properties was directly investigated on the estimated reliability β‐index values for two rotor blade design cases typical of stall‐regulated and pitch‐regulated wind turbines. Copyright © 2014 John Wiley & Sons, Ltd.

This experimental study presents the Lamb wave based baseline-free diagnostics of damage in a carbon-fiber composite fan blade using the Modified Time Reversal Method (MTRM). A fan blade with delamination was selected as the test specimen and two piezoelectric transducers (PZT) were surface bonded using epoxy adhesive. The system (fan blade and transducers) was then waveform-tuned from which 5.5 cycle tone burst was selected as the optimum excitation waveform. The system was then mode-tuned in order to determine the optimum excitation center frequency. The 55 kHz, 5.5 cycle tone burst was used to generate fundamental asymmetric Lamb waves with high signal-to-noise ratio and low dispersion. Damage Index (DI) values for the fan blade was calculated at equidistant points on a line using both PZTs. Results show that magnitudes of the DI values have strong correlation with the severity of damage present in the fan blade. The procedure followed in this experimental study is directly applicable to the Non Destructive Evaluation (NDE) conducted on composite fan blades. Additionally, this method can be extended to develop a real-time structural health monitoring system for composite fan blades which employs embedded PZTs for actuating and sensing waves.

Structural integrity of offshore wind turbine blade under extreme gust and normal operating conditions

Some interesting studies are made in this paper on the life management of a composite wind turbine blade. It presents the details of finite element modeling and validation, blade response under service loading conditions, power coefficient evaluation for the optimum design parameters of the blade configuration, development of failure envelope and fatigue life estimations. Finite element analysis results are found to be in good agreement with existing test results on a typical composite blade configuration. The failure envelope generated from the present modified failure criterion correlates well with the test results on different composite materials. The procedure adopted in this paper can be utilized for optimum design of large size composite wind turbine blades.