Fatigue Life Of Blade Research Articles

Fatigue Life Prediction of Fan Blade Using Nominal Stress Method and Cumulative Fatigue Damage Theory

Abstract Fan blade is one of the key parts used in aircraft engine and its failure is mainly caused by fatigue fracture. This paper aims to predict fatigue life of fan blade during its service operation. First, the effective load and stress of fan blade are obtained by using finite element analysis and simulation. Second, the fatigue notch factor of fan blade is determined by using the nominal stress method. Then, the material properties of fan blade are used to correct and obtain the S − N $S - N$ curve of fan blade. Finally, according to the actual load spectrum of three working loading cycles in 900h, the Miner’s damage accumulation rule is employed to predict the fatigue life of fan blade.

Comprehensive fatigue estimation and fault diagnosis based on Refined Generalized Multi-Scale Entropy method of centrifugal fan blades

Fan is widely used in industry as a very important component of pressure transmission and system cooling. Fan blade is the key part which decides the service life of fan and the whole system. In this paper, the research focuses on the centrifugal fan of high-speed train cooling system and the blades on it. The experimental system and research method of fatigue analysis and fault diagnosis are built. The fan can work in both steady and unsteady state conditions controlled and driven by the test system. At the same time, the signals of strain and acceleration at different positions can be obtained accurately. Based on the static tension and dynamic fatigue test of the material, the accurate simulation of the fan is carried out. By simulation analysis, steady-state test, long-time start-stop test and metallographic test, the prediction of fatigue life of fan blades is conducted with in-depth analysis and comprehensive evaluation. The results show that fan meets the requirements of actual working life. As the actual working state is more diverse and severe than the above test process, some phenomena of damage also appear in the blades after service. Based on real situation, the blade faults are classified. After determination of measuring point position, the vibration signals of four fault states of blade under rated speed are collected. This paper proposes a new fault feature extraction method – the Refined Generalized Multi-Scale Entropy (RMSEσ2) combined with Support Vector Machine (SVM). According to the results of the empirical mode decomposition (EMD), the effective intrinsic mode function (IMF) components are selected by energy distribution and correlation coefficient. The comparative analysis of multi-scale entropy (MSE), generalized multi-scale entropy (MSEσ2) and RMSEσ2 between the original signal and 1–8 IMF components are carried out. Results show the RMSEσ2 of IMF1 component of Z direction of point 1 is the best choice. And it is imported into SVM for pattern recognition with scale factor 20. The optimal SVM model is obtained by choosing kernel function and parameters that are optimized by Particle Swarm Optimization (PSO) method. The results show the faults of centrifugal fan blades can be classified accurately. A set of research flow and method is set up, which provides important reference for fatigue and fault pattern recognition of fan blades in the future.

Research on compressor blades fatigue life test under thermal-vibration combined load

Contrapose the fatigue life of compressor blades under thermal-vibration combined load, this article is described to carry out the fatigue life test of blades under the thermal-vibration load, the test device is designed in this article, the test conditions are determined, and the test results are analysed to obtain the conclusion that resonant frequency decreases gradually as fatigue life time goes on, and the extent of blades damage could be quantitatively described by calculating the drift distance of resonant frequency. It can also provide data support for life prediction.

Probabilistic-based combined high and low cycle fatigue assessment for turbine blades using a substructure-based kriging surrogate model

Fatigue assessment for gas turbine blades under combined high and low fatigue cyclic loading is very difficult. In this paper, we propose a probabilistic approach based on a substructure-based kriging surrogate model (SKM) that embeds substructure simulation into a kriging surrogate model (KSM). A distributed collaborative SKM (DCSKM) approach is, then, proposed based on the combination of a distributed collaborative strategy (DC) with SKM. Low-cycle fatigue (LCF) life and high-cycle fatigue (HCF) life of turbine blades are predicted with DCSKM. Based on the simulation data, the combined high and low cycle fatigue (CCF) life and damage assessment are performed with respect to the linear cumulative damage by DCSKM. Further, the relationships between the number of applied cycles and CCF reliability R with survival probabilities P=0.5, 0.9 and 0.95, for a confidence level of 0.95, are fitted. Finally, the DCSKM is compared with the Monte Carlo method (MCM) and response surface method (RSM). It is found that (1) the CCF reliability of turbine blades decreases with increasing survival probability for the same applied cycle and decreases with increasing applied cycles under the same survival probability; (2) LCF holds a significant influence on the CCF damage of gas turbine blades; (3) the proposed DCSKM is found to be an available probabilistic analysis approach for the CCF assessment of turbine blades.

Fatigue evaluation of FV520B-I shrouded impeller blade with fatigue crack based on FEA and fracture mechanics

The fatigue life prediction of FV520B-I blade with fatigue crack is a critical study in the fatigue analysis of shrouded impeller. However, the relationship between fatigue crack and fatigue life of FV520B-I blade has not been well studied. In this paper, finite element analysis (FEA) for FV520B-I blade with fatigue crack is conducted; both centrifugal load and aerodynamic load involved, and the stress distribution and the fatigue failure at decisive positions are analyzed. The new correlation between mean stress and fatigue crack is found based on the results of FEA, which is helpful to the development of fatigue life model of FV520B-I blade. Then fatigue test for blade material FV520B-I is performed to determine the fatigue limit. A fatigue life evaluation model for FV520B-I blade is then achieved, by taking fatigue crack as main variable, combining with the comprehensive application of FEA, fatigue test, actual operating parameters and existing fatigue modeling theory. The model is proved to be reliable by comparing the theoretical predicted life with simulated one. Study on fatigue life evaluation method of FV520B-I blade with fatigue crack is novel and essential to improve precision of fatigue life prediction of shrouded impeller in engineering practice.

Fatigue life estimation of hydrokinetic turbine blades

Fatigue analysis of hydrokinetic blades is essential as they are subjected to dynamic loads during their operation. This makes fatigue life estimation very important during turbine design. Therefore, this work investigates fatigue life of hydrokinetic turbine blades placed downstream of a hydroelectric power plant. The adopted methodology requires that variations in velocity, load, and stress need to be well established. Historical data of the river at the site are used as reference for variation in flow velocity. The blade element theory is implemented to calculate loads, while stresses are estimated from a finite element model. The S-N method, the rainflow count, and the Palmgren–Miner rule are used to calculate fatigue. This whole process is facilitated by the creation of computational tools to automate different steps. As a result, a life of approximately 20 years is predicted for the blade, neglecting the turbulence that occurs in the speed of the river. When considering a turbulence of 5%, the estimation is reduced to 17 years, indicating a reduction of 15% in life. The complete codes can be downloaded from https://github.com/engsergiocustodio/fatigueblades.

Spinning finite element analysis of longitudinally stiffened horizontal axis wind turbine blade for fatigue life enhancement

In this study, a proof-of-concept is presented for extending the fatigue life of modern multi-megawatt wind turbine blades. For this purpose, spinning finite element model of the blade is investigated which has longitudinal stiffener (i.e. a tendon along its length) made of shape memory alloy. The material behaviour of the tendon is characterized by Liang and Rogers constitutive model in combination with thermodynamic principles. Modal analysis of the stiffened blade shows significant improvement of bending stiffness. The response of the blade with and without the stiffener are simulated using aerodynamic loads, which are evaluated following modified blade element momentum theory from the wind field generated by TurbSim. The impact of the proposed longitudinal stiffener on the stress profile and fatigue life of the blade are presented to show its performance. A sensitivity analysis on the reduction of peak stress and fatigue life for different diameters of the tendon are also presented.

Turbulent length scales and budgets of Reynolds stress-transport for open-channel flows; friction Reynolds numbers R eτ = 150, 400 and 1020

Turbulence in open channel flows is ubiquitous to hydro-environmental applications and has recently increased in importance with the deployment of tidal stream turbines, as turbulence impacts both the turbine performance and the blade fatigue life. Tidal turbine analysis requires fully developed turbulence characteristics at the inlet of numerical simulations where generally the length scale information is limited. In this study, fully resolved large eddy simulations (LES) with flat beds were undertaken using an open source code at friction Reynolds numbers () of 150, 400 and 1020. It was found that the effects of the free surface on turbulence length scales were felt in approximately the uppermost 10% of the channel only, although the influence on Reynolds stresses extended further downwards. Furthermore, the cross-correlation length scales of both streamwise and spanwise velocities were found to be significantly affected by the free surface where turbulent eddies were flattened to the two-component limit.

Analysis of fretting inception for marine propeller by single blade loads measurement in realistic operating conditions. Straight ahead and turning circle maneuver

Controllable pitch propeller (CPP) is a versatile solution to fulfill high hydrodynamic efficiency and low environmental emissions for different operative scenario of a seagoing vessel because it allows the most suitable matching between the prime mover and the propulsor. In contrast, this configuration is a complex mechanical system and, therefore, it may be subjected to a wide range of failures related to the automation system of blade pitch variation, strength and fatigue life of the various mechanical components. This paper focuses on blade fretting, that is a small amplitude vibratory motion of the blade with respect to its lodging in the hub; this motion causes the wear between the contact surfaces, reducing the fatigue life of the material as well. The prediction of this phenomenon in realistic sailing conditions during the design stage is of utmost importance to prevent damages and failures during ship operations, by developing suitable control laws. The analysis is based on single blade loads measurements, obtained with a novel set–up installed on a free running maneuvering, self–propelled model of a twin screw ship. The experimental campaign was aimed to characterize single blade loads during different ship operations, with particular effort on maneuvering (standard and safety maneuvers) and motion in waves. This paper is focused on the straight ahead motions as well as steady and transient phases of the turning circle maneuver, performed at different rudder angles and speeds. The results show that the onset of fretting is sensitive to the wake evolution, and, hence, to the rudder angles; moreover, consistently to the asymmetric behavior of the propellers, fretting is differently triggered on the port and starboard propeller.

Investigation on geometric precision and surface quality of microholes machined by ultrafast laser

The geometric precision and surface quality of film cooling holes has significant influence on the cooling efficiency and fatigue life of turbine blades. In this paper, the investigation about fabrication process of film cooling holes on the single crystal superalloy DD6 plate specimen by ultrafast laser is carried out. By comparing three different processing paths, minimum roughness of hole wall could be obtained by concentric circular scanning, which was used in the followed-up experiment. The influence of process parameters on the geometric precision and surface quality of microholes was analyzed, and the physical mechanism was examined. The results show that among several process parameters, focus position has the most significant influence on the microholes geometric precision and surface quality, and that the divergent beam (where the focal plane is above the machined surface) can lead to smaller taper, roundness, and surface roughness. In addition, besides a layer of solidified debris adheres to the inner wall at the hole entrance, the microholes machined by ultrafast lasers have no other defects such as a recast layer, microcrack or heat affected zone.

Forecasting spare parts demand using condition monitoring information

Purpose The control of an inventory where spare parts demand is infrequent has always been difficult to manage because of the randomness of the demand, as well as the existence of a large proportion of zero values in the demand pattern. The purpose of this paper is to propose a just-in-time (JIT) spare parts availability approach by integrating condition monitoring (CM) with spare parts management by means of proportional hazards models (PHM) to eliminate some of the shortcomings of the spare parts demand forecasting methods. Design/methodology/approach In order to obtain the event data (lifetime) and CM data (first natural frequency) required to build the PHM for the spares demand forecasting, a series of fatigue tests were conducted on a group of turbomachinery blades that were systematically fatigued on an electrodynamic shaker in the laboratory, through base excitation. The process of data generation in the numerical as well as experimental approaches comprised introducing an initial crack in each of the blades and subjecting the blades to base excitation on the shaker and then propagating the crack. The blade fatigue life was estimated from monitoring the first natural frequency of each blade while the crack was propagating. The numerical investigation was performed using the MSC.MARC/2016 software package. Findings After building the PHM using the data obtained during the fatigue tests, a blending of the PHM with economic considerations allowed determining the optimal risk level, which minimizes the cost. The optimal risk point was then used to estimate the JIT spare parts demand and define a component replacement policy. The outcome from the PHM and economical approach allowed proposing development of an integrated forecasting methodology based not only on failure information, but also on condition information. Research limitations/implications The research is simplified by not considering all the elements usually forming part of the spare parts management study, such as lead time, stock holding, etc. This is done to focus the attention on component replacement, so that a just-in-time spare parts availability approach can be implemented. Another feature of the work relates to the decision making using PHM. The approach adopted here does not consider the use of the transition probability matrix as addressed by Jardine and Makis (2013). Instead, a simulation method is used to determine the optimal risk point which minimizes the cost. Originality/value This paper presents a way to address some existing shortcomings of traditional spare parts demand forecasting methods, by introducing the PHM as a tool to forecast spare parts demand, not considering the previous demand as is the case for most of the traditional spare parts forecasting methods, but the condition of the parts in operation. In this paper, the blade bending first mode natural frequency is used as the covariate in the PHM in a laboratory experiment. The choice of natural frequency as covariate is justified by its relationship with structural stiffness (and hence damage), as well as being a global parameter that could be measured anywhere on the blade without affecting the results.

Fatigue Life of Megawatt-Scale Composite Wind Turbine Blades with Shallow-Angled Laminates

The fatigue life of megawatt-scale composite wind turbine blades implemented with shallow-angled laminates is investigated. Full dynamic simulations of a 5-MW 3-bladed horizontal-axis wind turbine were carried out to estimate the incident fatigue loads. The fatigue stress histories experienced by lay up materials were then computed using a finite-element model of the composite blade developed to ply-level details. Thereafter, the fatigue life of blade was estimated considering the 100% availability of the turbine for the site-specific annual wind distribution related to the wind turbine class IB. It is demonstrated that the application of shallow-angled laminates leads to a more durable design.

Multi-axis low-cycle creep/fatigue life prediction of high-pressure turbine blades based on a new critical plane damage parameter

To study the multi-axis low-cycle creep/fatigue life of high-pressure turbine blades, a multi-axis low-cycle fatigue life prediction model based on a new critical plane damage parameter is proposed in this paper. Firstly, based on the thermal-structural coupling analysis of high-pressure turbine blades, the law of stress-strain distribution under the complex load of centrifugal load, temperature load and the aerodynamic load is obtained. Secondly, the multi-axis low-cycle fatigue life prediction model and the L-M equation are applied to predict the fatigue life and creep life of blade respectively. Furthermore, different experimental loading schemes are used to study the fatigue damage mechanism for the creep/fatigue interaction under high temperature condition, and a creep/fatigue interaction life prediction model is simultaneously provided. And finally, the experiment results demonstrate the rationality of the multi-axis low-cycle fatigue life prediction model and the creep/fatigue interaction should not be ignored.

Corrosion fatigue failure of steam turbine moving blades: A case study

This paper describes the failure of a rotor of a condensing industrial steam turbine installed in a fertilizer production plant. There was a fracture of the two adjacent rotor blades in their roots. An analysis of the failure cause was carried out, which included the analysis of the fracture location on the steam flow path, the corrosion deposit analysis and the modal analysis of the rotor blades. Modal analysis was performed using the finite element method. It was concluded that the cause of the blades failure was a phenomenon known as corrosion fatigue. To extend the useful fatigue life of rotor blades in the future, the entire turbine stage of broken blades was redesigned. The modified design of the turbine stage has increased the fatigue safety factor by about 50% compared to the original design.

Reduction of aerodynamic forces on turbine blading by asymmetric layout of struts based on flow interaction between rotor-strut-volute

The flows in the power turbine and nonaxisymmetric exhaust volute with struts are closely coupled and inherently unsteady for marine gas turbines, and the flow interactions between them have a significant influence on the rotor and strut blade aerodynamic force characteristics; however, the asymmetric flow interactions have not been taken into account properly in current turbine design approaches. This paper is a continuation of the previous work and aims to clarify effects of different symmetrical and asymmetric layouts of struts on the flow interactions between power turbine and exhaust volute, in an attempt to seek an optimal layout of struts with the objective of making use of the mentioned asymmetric flow interactions to reduce the rotor and strut blade aerodynamic forces. This work was carried out using coupled unsteady simulations with the full annulus computational domain including 76 rotor blades, 9 strut blades, and an exhaust volute. Results show that the level of aerodynamic force at specific frequencies on the power turbine blade surface can be reduced by applying a proper distribution of asymmetric layout of struts; using the asymmetric strut design, although the reduction of the rotor blade aerodynamic force is weak, the strut blade aerodynamic force has been reduced significantly; the asymmetric layout of struts does not improve the overall flow characteristics of turbines very much. The present results indicate that it is possible to reduce vibration and increase blade fatigue life by asymmetric strut designs.

The structural optimum design of laminated slender beam section with arbitrary material distribution using a genetic algorithm

In this paper, a study on optimum design methodology of a section structure of a composite material rotor blade using genetic algorithm is conducted, in order to calculate repetitive optimum design, analysis of strength, fatigue and vibration on blade section. In the analysis, the minimum mass of the rotor blade was defined as objective function; stress damage index, center of mass on blade section and fatigue life of blade were set as constraints. By applying genetic algorithm, laminate angle and thickness of skin, thickness, location and width of torsion box were established as design variables; the optimum design methodology on section structure of the composite material rotor blade was validated. The integrated design program of the section structure of the composite material rotor blade based on this study deals with designing the optimal rotor blade section which meets the design load and constraints given by the random position of rotor blade. By using blade’s section design variables derived from this, it can be facilitated for basic information on detailed design of rotor blade.

Multidisciplinary Design Optimization Based on Parameterized Free-Form Deformation for Single Turbine

In a traditional multidisciplinary design optimization loop for complex-shaped structures, the regeneration of structure geometry and its associated analysis grids may be unsuccessful or of poor quality, which will reduce the result validity and efficiency of multidisciplinary design optimization. In this Paper, an improved multidisciplinary design optimization method based on parameterized free-form mesh deformation is proposed. Using this method, the analysis grid can be directly updated with high quality instead of regenerating the geometry model when design variables change during optimization. To achieve the mesh deformation of a blade in a single turbine stage, three-dimensional control volume needs to be constructed using two-dimensional control planes at different blade heights, where the control points in the two-dimensional control plane are arranged and parameterized according to the definition of profile design variables. The grids for both computational fluid dynamics and structural analysis are controlled by the same control volume to ensure grid consistency on the fluid–structure interface. Results for an example single turbine stage show that the proposed method can guarantee good controllability and high grid quality when updating design variables in optimization loop. Multidisciplinary design optimization for the single turbine stage is performed, and the optimization results indicate a significant improvement of isentropic efficiency and turbine blade fatigue life. Therefore, the proposed multidisciplinary design optimization method based on parameterized mesh deformation provides an efficient tool for the design of complex and high-performance engineering structures.

Fatigue Strength and Life Prediction of a MAR-M247 Nickel-Base Superalloy Gas Turbine Blade with Multiple Carbide Inclusions

Casting of a gas turbine blade from MAR-M247 nickel-base superalloy is followed by multiple carbide precipitates as a result of solidification. The microstructure of carbide was established with scanning electron microscopy and energy spectrum analysis. A finite element model simulating the blade with a random carbide precipitate is constructed using ANSYS software, and stress-strain evaluation is performed. The blade operation conditions are realized in a vibratory-tensile combined test setup with stress measurements using strain gauges arranged on different parts of the blade. The respective von Mises equivalent stresses obtained in simulation and test measurements are found to be comparable and can be used to assess the blade fatigue life based on the available fatigue curves and Palmgren–Miner rule of damage accumulation. Simulation and experimental results are the basis for plotting the relationship between the volumetric ratio of precipitates in the blade and its fatigue life. The results obtained at room temperature can; be extrapolated to the elevated ones to provide more reliable prediction of the superalloy blade fatigue and creep-fatigue life values.

BTT & RFLB - THE OPTIMUM SET FOR STEAM TURBINE BLADES MONITORING

BTT, Blade Tip Timing system, is a commercially available system generating files of precise times of blade tips when passing sensors attached in a machine stator. RFLB, Residual Fatigue Life of Blades, is a postprocessor of those files evaluating estimates of fatigue lives of all blades fitted to the wheel. The set reduces a danger of unexpected blade failures.

Study on wake-induced fatigue on wind turbine blade based on elastic actuator line model and two-dimensional finite element model

Atmospheric and wake turbulence have a great and immediate impact on the fatigue life of wind turbine blades. Generally speaking, wake-induced fatigue accounts for 5%–15% increase of fatigue load on the wind turbine rotor, which definitely threats the safety and economy of the whole wind farm. However, this effect is difficult to simulate which involves multi-wake interaction and fluid structure interaction. To better simulate the wake-induced fatigue on wind turbine blades, a novel elastic actuator line model is employed in this study. The elastic actuator line is a two-way coupling model, consisting of traditional actuator line model and one-dimensional implicit or explicit finite difference method beam structural model, among which the beam model takes gravitational force, aerodynamic force and centrifugal force into consideration. Large eddy simulation method in the NREL SOWFA code is employed to model the turbulence effect, including wake-induced turbulence and atmospheric turbulence. For the fatigue analysis part, the fatigue life of an NREL 5MW turbine blade subjected to upstream wind turbine wake effects is studied using the elastic actuator line model and laminate data available from Sandia Laboratory in the United States. First, the strain and stress on different composite materials, such as uniaxial carbon fibre and biaxial composite material, are recovered by using the sectional force and moment obtained with the one-dimensional beam model and two-dimensional finite element method model, namely BECAS. Second, the stress-life method, rain-flow counting method, shifted Goodman diagram (constant life diagram) and Miners rule are employed to estimate the fatigue life for different composite materials. Noticeably, elastic actuator line largely reduces the computational efforts compared with a high-resolution computational fluid dynamics model, in which each wind turbine blade is fully resolved. Both the characteristics of different composite materials and airfoil geometries will be considered during fatigue analysis. As a result, the above procedure makes the fatigue life estimation more reliable and feasible. In the case studies, the moment time series predicted by elastic actuator line and FAST are compared. The fatigue damage of NREL 5MW wind turbine under turbulent neutral atmospheric boundary layer is calculated, and the fatigue critical section is determined to be at 10.25 m section from root. Finally, in the study of two in-line turbines, the fatigue damage increase by wake flow is 16%, which is close to the results from previous studies.