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Blade is one of the basic and key components in wind turbines. To get closer to the actual loading condition of blade under complex and extreme wind conditions to more accurately analyse the structural failure characteristics of large wind turbine blades. The structural collapse test of a 52.5 m wind turbine blade under combined loading was carried out. The entire process of damage under ultimate load was recorded and analysed in detail. The joint analysis of the failure region after the blade collapse and the failure mode during the test process were performed. The research shows that the geometrical nonlinear buckling of spar cap and shear web, the delamination result from non-uniform stress distribution and further fracture of Aft panel cause catastrophic failure of the blade. The torsional moment cause oblique cracks and oblique bulges, aggravates the expansion of the internal and external composite cracks of blade, affects the final failure mode after blade collapses (critical failure mode), and make the spar cap at suction side to clockwise twist from blade tip to root. The research results lay a theoretical foundation for subsequent model establishment and simulation analysis of large wind turbine blades under combined loading.

Wind turbine blades can experience mass collision events during operations, either due to bird strikes or with other flying objects. The rapid impact loadings due to these events can cause fatigue damage leading to subsequent blade loss or even wind turbine system failure. This paper addresses the effects of transient loadings resulting from a rapid mass reduction event from the rotating blade as well as an impacting mass onto the wind turbine blade, leading to transient vibration and unbalance within the turbine system. The novelty of the research is that it shows the coupling between the blade in-plane with tower transverse (Z-direction) vibrations, and blade out-of-plane with tower front (Y-direction) vibrations which have been identified through different experiments. Measurements from an experimental small-scale horizontal axis wind turbine test rig are reported, instrumented with contact and non-contact sensors and rotating and non-rotating sensors, to investigate the various transient impact loading events. Additionally, the drive shaft vibration for different conditions has been monitored by utilizing orthogonal laser measurement for detecting the main shaft displacements towards perpendicular axes. Subsequent orbit analysis is presented showing the analysis of different shaft orders during the rapid mass reduction and mass collision events. Complex orbit and filtering analysis of shaft orders during the transient mass impact loading events are used to demonstrate the sensitivity of the sensors for further fault detection.

The paper presents a comprehensive approach to the refurbishment of titanium turbine blades by direct laser deposition. Coatings based on titanium carbide with the introduction of boron carbide and tungsten carbide particles for airfoil shroud platform and based on the commercially pure Ti with the addition of fine particles of aluminum oxide for the turbine airfoil are proposed. It is shown that large refractory particles with a hardness of 1384 HV0.1 ÷ 5108 HV0.1 are crystallization centers and reinforcing particles, and melting fine particles form high-temperature phases of TiB and Ti3Al in the coating metal with a hardness of 520 HV0.1.

Extending blades of wind turbine in service is the most effective method for increasing energy production. Adhesively bonding technology increases less mass and has simpler operation process, which is more suitable for extending blades in service. But unsteady aerodynamic loads on the blades due to stochastic turbulent inflow may lead to fatigue damage and even failure. This paper presented a study on strain response and fatigue life of adhesively bonded extended composite wind turbine blade suffering unsteady aerodynamic loads. Firstly, a loading method that applies periodic distributed aerodynamic loads on the blade was proposed to accurately simulate the unsteady distributed loads on the real extended blades in service. Secondly, strain response behaviors to unsteady aerodynamic loads and strain distribution behaviors in the adhesively bonded area were revealed. Finally, fatigue damage was predicted with unsteady aerodynamic load spectrums, rainflow cycle-counting algorithm, Goodman diagram and Miner's linear superposition principle. Based on the findings obtained from this study, the feasibility of adhesively bonding technology for extending blade was affirmed and a few potential future directions of study were addressed to reduce the risk of adhesively bonded structures.

The harsh operating environment, and the extreme working condition, of the steam turbine blades have led to the use of alloys with special characteristics. Of these properties are high corrosion resistance and excellent rupture strength. The most widely used alloys in this category are heat treatable martensitic stainless steels. They provide a wide range of mechanical properties. In that sense, this research is focused on one of the most commonly used alloys of these series; i.e. 410 alloy. In this study, a turbine blade made of 410 stainless steel was under operation for 72,000 h, and its possible damage mechanisms were explored. To define the damage causes, microstructural analyses were performed by Optical Microscopy (OM), and a Field Emission Scanning Electron Microscopy (FESEM) instrument equipped with Energy Dispersive Spectroscopy (EDS) detector. As well, mechanical properties evaluation was performed using hardness testing. Results showed that the existence of foreign particles in the environment of the turbine has led to the initiation of damage in the blade through the erosion mechanism. Alternatively, such a damage was intensified by corrosion attack due to the presence of the fuel impurities. Such damages eventually led to the formation of fatigue cracks on the trailing edge of the blade. The latest phenomenon substantially reduced the fatigue strength of the blade. Finally, it is predicted that the reduced fatigue strength would ensue shortened service life for the blade.

Nickel-based single crystal creep’s properties are commonly calculated according to the rupture strength under constant load. The creep deformation of turbine blades is not only occurred under constant loading but also the variable loading. The influence of variable load on creep deformation should also be considered. Based on this background, in the present study, gradient loading creep tests of DD6 nickel-based single crystal are carried out under two modes. Take load and holding times into account, the creep characteristics and microstructure evolution is studied. The results show that the load and holding time have significant effects on the creep properties of nickel-based single crystals. The change of load induces an instantaneous jump on the creep deformation and strain rate. The holding time of each loading stage mainly affects the evolution of the internal microstructure of nickel-based single crystal. The research on creep behavior of nickel-based single crystal under gradient load in this paper not only enriches the service performance evaluation of nickel-based single crystal under complex environment but also provides a reference for material design and performance optimization.

This paper presents an in-depth analysis of the failure mechanism for the blade trailing edge from the viewpoint of material damage. A 3 m long blade segment is made and subjected to the static load in the subcomponent test through a specially designed test rig. A finite element model is set up to predict the progressive failure in the trailing edge region. The simulation results are used for setting up the on-site test and further, compared with the test results. The initial damage location and evolution of each defect are elucidated by cutting the test subcomponent into slices. The damage details of the test subcomponent and sensors data show that the end force leads to the local buckling of the PS and SS surface near the blade tip side. The buckling induces the damage to trailing edge materials, especially the sandwich structure in SS, and further bonding failure of the adhesive joint, which reduces the global strength of the subcomponent structure. The fracture of the sandwich caused by continued pressure leads to the final collapse of the test subcomponent.

In this work, based on the ‘Fish-eye’ theory and EIFS method, a prediction model of the whole fatigue crack propagation life of the predictable structure under multi-axial stress fatigue is proposed. Then, the fatigue crack propagation life of single-hole nickel-based single crystal superalloy samples under nine working conditions was predicted and verified by finite element simulation. Finally, the effects of three loads and three initial crack lengths on the fatigue crack propagation life of single-hole nickel-based single crystal superalloy were discussed by finite element simulation. The results show that the analysis results of the theoretical model and the finite element model proposed in this work are basically consistent under certain conditions. It is found that the fatigue crack propagation life of the initial crack stage, short crack stage and long crack stage accounts for 2%, 6%–10% and 90% of the whole crack propagation fatigue crack propagation life, respectively. Under the same loading stress condition, the higher the proportion of short crack stage in crack propagation is, the faster the fracture speed of the sample is. At the same time, the progressive crack propagation process of single hole specimen under fatigue load can be seen through the calculation results of finite element model. The above conclusions provide a good theoretical reference for the design and fatigue crack propagation life prediction of nickel-based single crystal superalloy turbine blades with cooling film holes.

Turbine blade is one of the key parts in thermal power plant, its failure will bring the power plant out of operation. Premature failure of turbine blade in thermal power plant was reported frequently. The crack was detected on the top of the last stage turbine blade in a thermal power plant. The failure causes of turbine blade were determined based on the testing and analysis by different methods. The macro morphology of the crack was observed by optical light microscope (OLM) method. The fracture surface of crack was observed by scanning electron microscopy (SEM) method and the mechanical property of the failure turbine blade was analyzed by different mechanical testing methods. The analysis results showed that the high level microstructure stress existed in the heat affected zone in the part of the blade, which was the directly factor to cause the failure. The uneven distribution fine and course martensitic due to the unqualified heat treatment in the heat affected zone and the high-frequency hardening zone was the root cause of the failure. Suggestions were proposed to prevent the failure about turbine blade according to the testing and analysis results as well.

A steam turbine from a thermoelectric central was put into maintenance due to a forced outage for high vibrations. Visual inspection of the steam turbine of 300 MW showed blades fractured at the last stage, L-0 and these affected other blades. Some operating parameters demonstrated to be out of range such as flow steam, low vacuum, and several areas in blade result to be damaged by the implosions particle. Three blades were fractured and others with a considerable crack presence were detected. The damage and fracture in the blades joints are attributed to high vibrations stresses combined with high cycle fatigue. A metallographic study revealed that the fracture was initiated from a cavity due to particle erosion. Numerical calculation results have shown that stubs blades group are disconnected as a result of the firstly vibratory stresses during startup and shutdown of the turbine. Resonance phenomena are present in the first blade when this is a detachment of the group initializing a crack propagation process. Number cycles before crack propagation in the blades of the last stage of a steam turbine of 300 MW were calculated.

Failure of an un-cooled turbine blade in an aero gas turbine engine is analyzed to determine its root cause. The operational condition of the engine was studied and metallurgical investigations are carried out on the fractured blade. The failure has originated from the leading edge and has propagated towards the trailing edge. Thermal cracks due to surface oxidation leading to fatigue were found to be the cause of the blade failure. Operation at elevated temperatures due to malfunction of sensors in the engine control system was found responsible for initiating the thermal cracks.

A long-term test run followed by room-temperature fatigue test was performed for the first-stage high-pressure turbine blades of an aero-engine. The investigation showed the appearance of cracks at the trailing edge of the blade coated with AlSiY. The failure mechanism was investigated by macroscopic observation, fracture analysis, metallographic analysis, hardness testing and structural evolution analysis by electron backscatter diffraction (EBSD), kernel average misorientation (KAM) and strain analysis. The results showed that thermal fatigue cracks initiated and propagated on the trailing edge during the test run and cracks further propagated during the fatigue test. Brittle and hard phases including M23C6 carbides, μ phase and γ'(Ni3Al) phase precipitated in the inter diffusion zone with a high dislocation density and maximum hardness and strain, resulting in thermal fatigue cracks initiation during frequent start-stop of the aero-engine test run. The cracks propagated outward along the β-NiAl grain boundaries with interconnected γ'(Ni3Al) phases in coating, and propagated inward along the lathlike precipitates including M23C6 carbides, M6C carbides and μ phase in the secondary reaction zone to the grain boundaries of the substrate. Chainlike M6C carbides locally precipitated on the substrate grain boundary, causing grain boundary embrittlement and further promoting cracks propagation.

This work is about the evaluating creep characterizations of GTD-111 superalloy, and its weldment, which has high demand in use in turbine blades of aero-engines and land-based gas turbine industries. For this purpose, plates with a thickness of 3 mm have subjected to Nd:YAG pulsed-laser welding. Test specimens were machined from different parts of weldments and prepared in the shape of disks with a thickness of 0.5 mm, including weld metal, heat-affected zone, and base metal. Small punch creep tests were carried out at 700 °C with loads of 350 N and 450 N to find the weakest location in creep consideration of GTD-111 weldment. Analysis of creep diagrams based on time-displacement showed that the weld metal has the highest creep life due fine γ′ particles and MC carbide. The HAZ of the heat-treated specimen showed a longer creep life of about 17 h than the cast specimen. This was due to the reduction of harmful phases for welding, including γ′, γ-γ′, MC, and Cr-M, which were the leading cause of the defect and reduced creep life in HAZ.

The trailing edge (TE) failure of a commercial wind turbine blade (WBT) is investigated in this article. The effect of adhesive thickness and band width on the TE failure is one of the most important issues in WTB production governing the integrity and soundness of the WTB structure. Different static load cases of a WTB are identified under various operating conditions as a case study. Static analysis is performed on a full 3-D finite element model of the blade and the critical region of its TE is determined. Then, sub-part modeling is performed focusing on the critical region of the TE. Adhesive joint in the constructed model is modeled using cohesive zone modeling (CZM). The failure of the adhesive joint with different dimensions of adhesive is examined under normal wind condition and gust condition. Taking into account the production limitations, the proper dimensions of the adhesive withstanding different conditions of the WTB are extracted.

Intergranular corrosion is one of the decisive tools for the life of turbine blade for its continuous use. The study was to ascertain the occurrence of Intergranular Corrosion (IGC) in the turbine blades of an aircraft. For this purpose 2nd stage turbine blades made up of Nickel Based Superalloy Udimet 500 were used to find out attack of IGC in the top & middle portion of blades as the same was detected during Eddy Current Testing. The turbine blades having different flying hours (700, 1700 & 2700) were selected for specimen while simulating actual conditions which the turbine blades encounter during flight & maintenance/overhaul. High temperature exposure (at 900 °C for 1min & 950 °C for 1min) and alkaline media exposure (at normal and aggressive condition) were introduced to find out the damaging results. It was found that Cr carbide is precipitated at GBs on exposure to 900 °C and an excessive Cr carbide precipitation at GBs on exposure to 950 °C due to Intergranular Corrosion. On exposure to alkaline media, pitting was observed within grains and at grain boundaries on the specimen of blades.

In the present work, a study and description of the wear damage of the first-stage compressor blades of a gas turbine were conducted. The type of the equipment was a gas turbine Centaur 40 GT and the deterioration of the blades was after around 8000 h of service. This equipment is located in the City of Campeche in Mexico where the weather conditions are extremely warm. The gas turbine combines high performance operation with rugged industrial construction. This design provides high efficiency, low maintenance and a long service life. For power generation, the components that are on direct contact with air at different stages of operation are the compressor blades which are exposed to severe wear damage for the impact of particles, environmental contaminants such as salts, sands and sulphur. Due to this fact, the wear damage on the turbine blades was analysed. Firstly, a tribological characterization was conducted for obtaining the chemical composition of the turbine blades, which were in operation, by using energy dispersive X-ray analysis (EDS). Atomic Force Microscopy (AFM) was used to measure the roughness and has a perspective of the degradation of the surfaces of the blades after real service. Hardness tests were also conducted to determine the material that was employed to manufacture the blades. Additionally, optical microscopy and scanning electron microscopy (SEM) were used to identify the wear mechanisms on the surfaces. This allowed obtaining a more complete failure analysis. The wear modes were severe pitting action, large craters similar to those observed in solid particle erosion when the samples are impacted at normal incidence, corrosion and a few irregular scratches similar to ploughing action in abrasive wear.

The aim of this study is to investigate the significance of residual stresses in fatigue analyses of micro gas turbine blades in order to attain accurate fatigue life estimates; such studies have not been adequately investigated. This was achieved by manufacturing test samples using Additive Manufacturing (AM). The samples were subsequently heat-treated in order to mimic the operating conditions of the engine and then evaluated experimentally for the presence of residual stresses. In order to incorporate these residual stresses into engine operating conditions, an ABAQUS Finite Element Analysis (FEA) was conducted to define stresses which are effective during operation. Subsequently, a fatigue software (Fe-safe) was used to determine the fatigue behavior of the bladed disk while taking into consideration the in-plane residual stresses. The results acquired from this study showed an average residual stress contribution of 70% towards the fatigue life estimated cycles to failure of engines undertaking short flight missions. As the flight time increases, the residual stress influence decreases due to stress relaxation. This study, therefore, concluded that the inclusion of in-plane residual stresses in fatigue life estimates is significant for turbine blades operating at short flight time intervals with less effect on long mission operations.

Creep-fatigue interaction (CFI) is a common failure mode in turbine blades. However, this failure mode has rarely been reported in boiler superheaters. This article presents a failure analysis of CFI on a superheater in a black liquor-fired boiler. Two cracks in the HAZ of stitch weld were identified. The “beach marks” on fracture surfaces indicated the cyclic stress. Fractographic analysis distinguished the different fracture modes. Crack 1 initiated and propagated in the transgranular mode. Crack 2 initiated in intergranular mode and propagated in the mixture of intergranular and transgranular modes. On the base of the hoop stress and axial stress, the dynamic stress was the main root cause of CFI fracture. The dynamic stress can be calculated from the fracture orientation angle. The greater the fracture orientation angle, the higher the dynamic stress. The fracture-mechanism map was applied in this case study. In combination of fractographic analysis and stress calculation with the fracture-mechanism map, the crack fracture sequence was revealed. The two cracks did not initiate simultaneously, and their stress levels were significantly different. Through this case study the fracture-mechanism map was recommended as a guide to superheater fracture analysis.

The causes of many blade fractures of a steam turbine in a power plant were studied by means of macro analysis, mechanical tests, metallographic examination, SEM and X-ray fluorescence spectrum analysis (XRF). The results show that the blade cracks due to corrosion fatigue. Cl −,K +react with the turbine blades in the steam environment in physical, chemical and electrochemical ways, causing local spot corrosion on the blades, forming corrosion pits. In addition, the steam condensated has an erosion effect on the blades, both of which form a corrosion fatigue source. The autocatalytic process of block cell is formed when Cl −, K + react with the turbine blades. Under the action of combined load, the current density i of activation dissolution of metal can be expressed as a function of complex stress state.Crack growth has an important relationship with stress, depth and width of corrosion pits. The blade cracks are determined by threshold nominal stress range for crack elongation Δ σ t h , which depends on the depth and width of corrosion pit. The combined alternating stress directly promotes the crack propagation until the fracture fail under the external conditions of alternating stress formed by tensile force, bending force, torsion force, and exciting force.

This research establishes the cause of a severe failure in bolts in the low pressure (LP) section of a gas turbine in an oil and gas production plant. The failure in bolts was reported together with massive failures of turbine blades in the second stage in the hot section of the turbine. The failure was categorized as an unexpected premature failure, given that it was reported to take place after 20 k of service and that the expected service life for this turbine is beyond 100 k. This research had a two-fold purpose; i) to analyse the cause of failure in both components (failed bolts and blades) and ii) to come up with a scenario for the chain of events. Standard microscopic examination techniques (optical metallography and electron microscopy) were used to correlate microstructure of failed components with possible failure mechanisms. Results showed a clear corrosion-fatigue-induced failure in blades. Hardly is there any evidence of fatigue failure in bolts. Bolts appeared to have experienced an excessive load and have consequently been heavily deformed and broken. The failure scenario was proposed, based on the service history, observations, and microstructural examinations.

The impulse mode of operation and the supply of various types of fuels causes frequent failures even in the heavy duty gas turbines. The paper presents the ravages of second rotor stage failure in a gas turbine. The excessive thermal elongation rise caused by fuel change was indicated as the main cause. We applied nonlinear numerical analysis, preceded by thermodynamic calculations of the turbine and visual inspection of the effects of failure. Simulations were performed on undamaged blade geometry under load resulting from combustion: nominal fuel and the changed fuel. Thermodynamic calculations demonstrated a 70 °C increase in temperature using the changed fuel. The blade tip displacements demonstrated the possibility of abrasion. The amount of displacement of the tip of the turbine blade with increasing pressure or increasing rotational speed do not pose as great a threat, as does the increase in the temperature. To maintain long-term and safe operation of a gas turbine, it is necessary to strictly observe the manufacturer's guidelines regarding fuel composition. If during the operation of a gas turbine it is likely that it can be powered by various types of fuels, then the structure should have adequate effort reserves and working tolerances.

Due to the special working environment of steam turbine blades, such as high temperature and cyclic stresses, they are routinely under heavy damage conditions. Of the most applicable of the alloy used in such blades are martensitic stainless steels which are heat and corrosion resistance and have high strength creep characteristics. In this investigation, a 410 stainless steel type of steam turbine blade, which was damaged after working for about 165,000 h, was studied to define the possible failure mechanisms involved. Optical microscopy and Field Emission Scanning Microscopy (FE-SEM) Analyses, together with hardness measurement, were performed to differentiate the various modes of failure. Results pointed to the presence of fatigue signs on the fracture surfaces. As well, the presence of foreign particles of SiO2 and Fe2O3 could bring about the effect of corrosion and lead to an increase in failure speed. Finally, it was suggested to perform shot peening or apply some protective coatings to increase the service life of these types of turbine blades.

FBG sensors are often packaged within composites before they are pasted on the blade surface, and many studies have shown that the materials, fatigue properties, geometric parameters, etc. of intermediate layer have influences on the measuring accuracy of the FBG sensors. Thus, this paper established an reliability calculation model based on strain transfer efficiency for the measuring accuracy of FBG sensors packaged by composites, analyzed the influences of material properties and geometric parameters of the adhesive layer on the performance of FBG sensors based on finite element analysis (FEA) method, and then compared the differences of strain transfer efficiency and reliability of the FBG sensors under different load conditions. The results show that the bond length and the bond thickness of the adhesive layer have greater influences on the performance of the FBG sensors compared with other parameters, both the strain transfer efficiency and the reliability of the FBG sensors will reduce over time under suddenly applied load and increase with increasing frequency of the alternating load.

This study provides a new perspective on the failure of sandwich panels in a composite wind turbine blade. Fractographic characteristics of fracture regions are examined thoroughly using optical microscopy and X-ray computed tomography. The detailed fractographic analysis leads to the identification of the failure modes and failure sequence. This study addresses an important but rarely studied failure process in the sandwich panels cored with grooved foams. The partially resin-filled grooves lead to large voids in the foams that cause crack migration of skin/core debonding from one side of sandwich panels to the other. In this study, the adverse effects of the partially resin-filled foams are addressed and the associated challenges in the blade design are highlighted. It is found that the fracture of skin laminates under biaxial compression is characterized by a shear-dominated failure mode in the form of kink bands in two directions. The whitening of skin laminates under tension is caused by micro-cracks in the matrix and the fiber/matrix interface. Moreover, fiber breakage also occurs in the whitening region although it is not visually apparent. These fractographic characteristics could help the identification of the root causes of blade failure if similar observations are found.

A metallographic study is performed on a turbine blade from a land-based gas turbine in an industrial environment. The aim of the present work is to study the degradation of the turbine blade. The gas turbine has been running for about a month before shut down, which has established steady-state temperature gradients around the cooling holes, causing tensile stresses as a result of cold spots. The tensile stresses cause creep damage, which, in turn, plastically deformed the material, generating substructures and twins near the crack. Furthermore, by comparing substructures from the turbine blade formed during service with substructure from test bars subjected to thermal mechanical fatigue testing gives a strong indication that the damage of the turbine blade is not caused by thermal mechanical fatigue. The turbine blade is also exposed to chemical degradation by type I hot corrosion and internal corrosion/nitridation. Type I hot corrosion has formed Ti-sulfides in grain boundaries and nearby surroundings. Ti-sulfides are also found ahead of the crack tip region. The internal corrosion/nitridation has established TiN, AlN and simultaneously formed a depletion zone near the crack.