Vibration Fatigue Research Articles

Investigation on three-dimensional vibration model and response characteristics of deep-water riser-test pipe system

Under deep-water test conditions, a riser-test pipe system (RTS) is subject to the vortex-induced effect on the riser, flow-induced effect on the test pipe, and longitudinal–transverse coupling effect. Further, the system is prone to buckling deformation, fatigue fracture, and friction perforation. A three-dimensional (3D) nonlinear vibration model of deep-water RTS was established using the micro-finite method, energy method, and Hamilton variational principle. Based on the elastic–plastic contact collision theory, a nonlinear contact load calculation method between the riser and test pipe was proposed. According to field parameters in the South China Sea and the similarity principle, a vibration test bench for the RTS was designed. The experimental measurement results and the calculation results obtained from the proposed vibration model and the single tubing vibration model developed in our recent study were compared. Based on this comparison, the correctness and effectiveness of the proposed vibration model of the deep-water RTS were verified. Then, the vibration characteristics of the RTS for the BY5-2-1 well in the South China Sea were analysed. The results demonstrate that, first, in the vibration fatigue analysis of the test pipe, the influence of its own local high-frequency vibration cannot be neglected. Second, long-term collisions will cause friction and wear failure in the RTS. In the safety analysis of the RTS, the wear problem of the RTS caused by the collision between the riser and test pipe cannot be neglected. Third, the position where the test pipe is prone to strength failure is mainly located in the upper and lower parts. The field designer should focus on the safety of the pipe at these locations.

Numerical study of aeolian vibration characteristics and fatigue life estimation of transmission conductors.

The 2D computational fluid dynamics (CFD) model of transmission conductor is set up to simulate the aerodynamic forces varying with time on the conductor. Taking into account the geometrical nonlinearity of conductor lines, the finite element (FE) models of single span and two-span transmission lines discretized with beam elements are established. By means of the FE models, the aeolian vibrations of the conductor lines excited by the aerodynamic forces under different wind velocities are numerically simulated. The nonlinear resonant characteristics, the amplitude-frequency relations of the conductor lines during aeolian vibration are investigated, and the influences of the span length as well as the initial tension in conductors on the aeolian vibration characteristics are analyzed. Furthermore, a 3D FE model of a conductor segment and the suspension clamp is created to study the stress distributions of the 3D model corresponding to different lines during aeolian vibrations. Finally, based on the stress analysis of the 3D model, the fatigue lives of the transmission conductors during aeolian vibration under different wind velocities are estimated. The jump phenomenon induced by the nonlinear vibration is reflected by the numerical simulation considering the geometric nonlinearity, and it is found that the energy balance principle (EBP) overestimates the vibration amplitudes because it cannot take the influences of the geometrical nonlinearity and span length into account. The obtained results may provide some instructions for the prevention design of aeolian vibration.

A Method for Monitoring Vibrational Fatigue of Structure and Components

Abstract A vibrational fatigue monitoring system has been developed by Framatome to assess, in real-time, the evolution of industrial structures, systems and components lifetime expectancy. Its originality comes from the fact that only one or a few acceleration measurements are necessary to reconstruct the complete stress history in the whole structure, including on welds or bolted connections that could not have been directly instrumented. From this stress history, a fatigue analysis with a rainflow counting algorithm is conducted and the cumulative usage factor of each weld or bolt is determined. The remaining life duration is then estimated. The method has been numerically and experimentally validated in that sense that the reconstructed stress histories were successfully compared to direct stress calculations and measurements. The system was then installed on five industrial structures submitted to transient dynamic excitations. It is expected that it will soon find further applications notably in monitoring vibrations induced during power plants transients that may induce some temporary resonance of piping equipment. Finally, the vibrational monitoring system can also be combined with a thermal fatigue monitoring system, many of which are already deployed, at least on nuclear power plants, and the reconstructed stresses might include both thermal and mechanical effects. Installing such a fatigue monitoring on a set of sensitive systems and components could be a valuable brick in the present trend of building digital twins of power plants or other industrial structures.

Applications of continuum fatigue risk monitoring in riser connectors system integrity management

This paper discusses the effects of marine riser connectors (MRCs) on fatigue failure risk using multi-coupling models. When MRCs are subjected to vortex-induced fatigue, a risk early warning strategy is used for effective risk monitoring as a preventive measure for the operation of MRCs. To ensure safe marine oil and gas production and to improve fatigue failure prevention and control, research on offshore structural fatigue risk failure theory criteria and evaluation and the vibration fatigue characteristics of MRCs over time and frequency is characterized. By coupling data-driven technological means, including rain-flow counting (RFC), Hilbert–Huang transform (HHT), power spectral density (PSD), artificial neural network (ANN), risk-based inspection (RBI), and risk management measures (RMM) to assess the fatigue risk characteristics of in-service members in special offshore environments. The fluid-structure interaction characteristics of MRCs and a load spectrum are analysed by empirical mode decomposition (EMD) to determine the changes in the components of an intrinsic mode function (IMF) and investigate the degree of fatigue damage. The fatigue damage of MRCs is predicted using the PSD of the IMF and the RFC of the IMF-coupled ANN time series prediction model. The results show that using any IMF component or combined component data as input to the ANN and training set facilitates cross-validation of the analysis. When the input layer and a hidden layer of the ANN are optimized and properly trained, the predicted performance is suitable. Through early warnings and coordination, the spread of fatigue failure risk trends can be predicted, and warning information is issued accordingly.

Fatigue behavior of 2.5D woven composites based on the first-order bending vibration tests

The 2.5D woven composite material has good resistance to delamination and impact load. However, its fatigue behavior is lack of investigation. In this work, first-order bending vibration fatigue tests were conducted on cantilever beam specimens made of 2.5D woven composites under different nominal stress levels. Test results showed that rapid damage evolution and accumulation occurred in the woven composites under a high stress level. However, under a low stress level, crack growth showed arrest behavior. The square root of residual stiffness showed a linear relation with resonance frequency, so the normalized full-time domain curves can be used to characterize the residual stiffness. On that basis, a residual stiffness model for the studied vibration fatigue specimens under other stress levels was proposed. Besides, a formula of ɛ-N curve was established for guiding the design and analysis of the 2.5D woven composite. To further reveal the failure mechanism, a multi-scale model of the woven composite was proposed. Numerical results showed that the high interlaminar shear stress between the yarn and the matrix near the compressed surface of the specimen caused material damage. This was consistent with the observed fracture topography, which verified the applicability of the multi-scale model.

Effects of insufficient sampling on counting algorithms in vibration fatigue

This paper investigates and quantifies the effects of insufficient sampling on counting algorithms in vibration fatigue. Even though a stress series upholds the Nyquist-Shannon theorem, insufficiently sampled series lead to discrepancies in the fatigue damage estimation, if their peaks are not well resolved in the time domain. Therefore, these discrepancies are investigated by relating the fatigue damage potential of stress series to its up-sampled series using popular signal reconstruction algorithms. In order to find suitable parameters for describing and specifying the error due to insufficient sampling (up to 35%) time series are considered that represent synthetic and realistic PSDs. A best-fitting error formula is obtained that estimates from a PSD whether and to what extent a stress series is subjected to insufficient sampling. This provides more accurate results for lifetime estimation without changing the computational of cycle counting algorithms.

Актуальні проблеми фізики динамічних пошкоджень в елементах першого контуру реакторів типу ВВЕР

In the context of the actual problems of the physics of operational damage of modern reactor steels produced in the leading countries of the world (USA, Russia, Western Europe) and used for the manufacture of nuclear reactor vessels and other equipment of the first circuit of nuclear power plants, the characteristic features of possible dynamic damage in the responsible elements of this are considered. The mentioned problems are systematized from the standpoint of analyzing the effects of radiation embrittlement, as well as physical and chemical processes that, under certain conditions, are capable of developing in the operating equipment of Ukrainian NPPs, which are already working out their design operational resource. The characteristic features of possible dynamic damage in the operating reactor equipment of Ukrainian and foreign nuclear power plants are considered. The problem is systematized, first of all, from the standpoint of analyzing the operational stability of domestic and foreign reactor steels in relation to their radiation embrittlement. The peculiarities of the course of this physical process have been analyzed, which should be taken into account when determining the maximum possible terms of extension of safe operation of nuclear power units with reactors of the VVER type at the NPP of Ukraine. The main metal-physical properties of reactor steels of various types and possible problems caused by neutron irradiation, physical and chemical processes, vibrational and thermomechanical fatigue, which threaten the unexpected sudden destruction of reactor vessels, are considered. Special attention is paid to mechanical damage and processes accompanying the operation of reactor housings under conditions of cyclic and dynamic loads. A warning has been given regarding the unjustified extension of the period of reactors safe operation. The significant technological lag of the former Soviet, and now Russian, metallurgy from the level of metallurgy of the leading Western countries was noted. Data are provided on the high operational properties of the latest American steels, from which modern reactors of the AR1000 type are manufactured in the USA, and the safety, technical, economic and environmental advantages of using these reactors in Ukraine in comparison with new models of reactors of the VVER-1000 and VVER-1200.

The relevant factors of work-related fatigue for occupational vibration-exposed employees

BackgroundTo date, little is known about the effects of factors linked to work-related fatigue on vibration-exposed workers. Thus, the purpose of this study was (1) to assess the effects of vibration exposure time per week and work-related fatigue on workers and (2) to identify factors associated with work-related fatigue caused by long-term exposure to occupational vibration.MethodsThis study used data collected from the 5th Korean Working Conditions Survey. A total of 34,820 non-vibration-exposed and 10,776 vibration-exposed employees were selected from the data. The χ2 and multiple logistic regression were used to determine the effect of vibration exposure time per week and the effects of factors of work-related fatigue on workers.ResultsThe prevalence of work-related fatigue in vibration-exposed workers (30.5%) was higher than that of non-exposed workers (15.9%). The prevalence of work-related fatigue was higher for female and workers with depression, anxiety, and shift work, and those with authority to control their work pace had statistically significantly higher odds than those who did not. The employees who had the authority to control their order of work (odds ratio [OR]: 0.88; 95% confidence interval [CI]: 0.81–0.95) and method of work (OR: 0.90; 95% CI: 0.82–0.98) had statistically significantly lower odds than those who did not. The OR of work-related fatigue symptoms was highest among employees whose vibration exposure time per week were 30.0%–40.0% (OR: 2.36; 95% CI: 1.96–2.83). Lower OR was observed as vibration exposure time per week decreased.ConclusionsThe results of the present study suggest an association between occupational vibration and work-related fatigue and longer vibration exposure time per week, causing an increased prevalence of work-related fatigue symptoms. Measures to protect workers exposed to occupational vibration from work-related fatigue must be taken.

Vibration Fatigue Analysis of Interface Enclosure with Cantilever Structure for Charging Commercial Electric Vehicles

The interface enclosure for charging commercial electric vehicle (CEV), which is an alternative to the fuel filler of internal combustion engine vehicle, was studied. It supplies the power and the communication signal for charging between the power supply (EVSE) and the battery. It should be long to match the exterior of the vehicle for easy charging, and it requires space between the vehicle frame and the enclosure to connect the charging cable. In order to design the interface enclosure with the cantilever structure which is vulnerable to vibration, analysis-based design through vibration fatigue analysis was conducted, and the reliability of analysis results was reviewed through experiments.

Vibration fatigue analysis through frequency response function of variable amplitude loading

Vibration fatigue analysis through frequency response function of variable amplitude loading

Study on high frequency vibration-induced fatigue failure of antenna beam in a metro bogie

This paper investigated on the high frequency vibration-induced fatigue failure of antenna beam through both field tests and numerical simulation. In the field tests, the dynamic stress, acceleration, and operational modal of bogie system as well as the short pitch irregularities of rail were measured to identify the primary contributor to the fatigue failure of antenna beam. The result suggested that the rail corrugation- induced impact with the passing frequency of 78 Hz serves as the main driving force of the modal resonance for bogie frame and antenna beam in the bogie system, which can emphasis the bending of antenna beam and further contribute to the reduced fatigue lifetime. To better understanding the failure mechanism and the associated mitigation method, a rigid/flexible coupled dynamic model of rail vehicle, considering the flexibility of bogie frame, wheelset and antenna beam as well as coil spring, was developed by using the modal synthesis method. Based on the developed model, the influence of elastic rubber mounts located on both ends of antenna beam was investigated, and a new design was proposed to relief the bending movement- induced stress concentration in the antenna beam. This is expected to mitigate the vibration fatigue problem of antenna beam arising from the rail corrugation-induced high frequency wheel/rail impact.

Notch fatigue behavior of needled C/SiC composite under random vibration loading

In order to study the properties of needled C/SiC composite under random vibration loading, a kind of plate specimen with arc notch was designed. Random vibration tests were carried out on a vibration table, the vibration fatigue life and vibration response signal at the dangerous position of each specimen were obtained. The strain amplitude probability distribution of vibration response signal was obtained by rainflow counting method, which can be approximately described by the Dirlik distribution. The attenuation history curve of natural frequency for the specimen presented obvious nonlinearity. In addition, the microscopic fracture morphology of failed specimens showed that the major failure mode of fibers in axial and transverse direction are pull-out and splitting, respectively. And the fiber bundles adhering strongly to the matrix can form a neat fracture surface.

Investigation of axial impact behavior of adhesively bonded joints after vibratory fatigue

In this study, the mechanical behaviours of adhesively bonded composite joints were investigated applying different mechanical tests such as vibration and axial impacts. In the first step of this study, the vibration tests were applied to adhesively bonded composite plates with different cycles (1.5 × 105, 3 × 105, 12 × 105 and 24 × 105) via vibration motor. After the vibration tests, as a second step of the study, these plates were cut as a single lap adhesively bonded composite joints and axial impact tests with different impact energy values as 5, 10, 15 and 20 Joules were applied to these joints. Subsequently, quasi-static tensile tests were implemented to adhesively bonded composite joints. According to experimental results, the strength of adhesively bonded composite joints decreased with the increasing of axial impact energy and vibration cycles. The experimental results showed that the strength was higher only at 10 J energy when compared to other impact energy values.

Flow-Induced Vibration Fatigue Damage of A Pair of Flexible Cylinders in A Staggered Array

Flow-Induced Vibration Fatigue Damage of A Pair of Flexible Cylinders in A Staggered Array

Fatigue Damage Evaluation of Compressor Blade Based on Nonlinear Ultrasonic Nondestructive Testing

Nonlinear ultrasonic testing is highly sensitive to micro-defects and can be used to detect hidden damage and defects inside materials. At present, most tests are carried out on specimens, and there are few nonlinear ultrasonic tests for fatigue damage of compressor blades. A vibration fatigue test was carried out on compressor blade steel KMN, and blade specimens with different damage degrees were obtained. Then, the nonlinear coefficients of blade specimens were obtained by nonlinear ultrasonic testing. The results showed that the nonlinear coefficient increased with the increase in the number of fatigue cycles in the early stage of fatigue, and then the nonlinear coefficient decreased. The microstructures were observed by scanning electron microscopy (SEM). It was proven that the nonlinear ultrasonic testing can be used for the detection of micro-cracks in the early stage of fatigue. Through the statistical analysis of the size of the micro-cracks inside the material, the empirical formula of the nonlinear coefficient β and the equivalent crack size were obtained. Combined with the β–S–N three-dimensional model, an evaluation method based on the nonlinear ultrasonic testing for the early fatigue damage of the blade was proposed.

Numerical Study on Vibration Response and Fatigue Damage of Axial Compressor Blade Considering Aerodynamic Excitation

Axial compressor blades with a deformed initial torsion angle caused by aerodynamic excitation resonated at the working speed and changed the rule of fatigue damage accumulation. The fatigue life of a blade has a prediction error, even causing serious flight accidents if the effect of torque causing damage deterioration of the blade fatigue life is neglected. Therefore, in this paper, a uniaxial non-linear fatigue damage model was modified using the equivalent stress with torsional shear stress, and the proposed fatigue model including the torsional moment was used to study the compressor blade fatigue life. Then, the blade numerical simulation model was established to calculate the vibration characteristics under complex loads of airflow excitation and a rotating centrifugal force. Finally, the blade fatigue life under actual working conditions was predicted using the modified fatigue model. The results show that the interaction between centrifugal and aerodynamic loads affects the natural frequency, as the frequencies in modes dominated by bending deformation decreased whereas those dominated by torsional deformation increased. Furthermore, the blade root of the suction surface showed stress concentration, but there is an obvious difference of stress distribution and amplitude between the normal stress and the equivalent stress including torsional shear stress. The additional consideration of the torsional shear stress decreased the predicted fatigue life by 4.5%. The damage accumulation rate changes with the loading cycle, and it accelerates fast for the last 25% of the cycle, when the blade fracture may occur at any time. Thus, the aerodynamic excitation increased the safety factor of blade fatigue life prediction.

Development of deep learning-based detection technology for vortex-induced vibration of a ship's propeller

Vortex-induced vibration (VIV) resulting lock-in phenomenon which is the vibration frequency of the structure immersed in a fluid is locked in its resonance frequencies within a flow speed range is a potential cause of vibration fatigue and/or singing of the propellers of large merchant ships. A deep learning-based indirect VIV detection algorithm that works by vibration measurement data of a hull structure instead of a propeller during the sea trial phase is proposed in this study. RPM-frequency representations of the vibration signal by stacking the vibration frequency spectrum relative to various propeller RPM's, so-called waterfall chart of 2-dimensional data like an image, are measured and fed into the proposed convolutional neural network (CNN) architecture for VIV detection i.e. VIV frequency and RPM range. To generate the large data set, artificial data looks real, for learning, a method based on the modal superposition method instead of time-consuming fluid-structure interaction analysis is proposed. 10k set data for training, 1k set for hyper-parameter tuning, and 1k set for the test were generated. After the training, it showed a diagnosis success rate of 82% for the test set. To test the proposed VIV detection algorithm, investigations were carried out in a laboratory on a small-scale ship propulsion system designed in such a way that the vortex shedding frequency and the underwater natural frequency match each other. The proposed VIV detection algorithm was tested using the structural vibration signals measured at stationary structures in the air instead of the rotating propeller immersed in water. Lastly, the validity of the proposed algorithm was tested using the structural vibration signal measured at the hull structure of a crude oil carrier in which a propeller singing occurred during her sea trial.

Fatigue life calculation of notched specimens by modified Wöhler curve method and theory of critical distance under multiaxial random loading

AbstractReformulation of a critical plane‐based multiaxial fatigue criterion named as Modified Wöhler Curve Method (MWCM) in the frequency domain is proposed; moreover, it is combined with the theory of critical distance (TCD) to implement vibration fatigue lifetime prediction of notched specimens subjected to complex multiaxial random loading. Firstly, a frequency‐domain formulation of the maximum variance method (MVM) is proposed for determining the critical plane with high computational efficiency. Then, a reference fatigue curve is defined through the frequency‐domain formulation of the reference stress ratio corresponding to the critical plane. Finally, the power spectral density (PSD) function of the resolved shear stress along the maximum variance direction is applied with the Bendat/Tovo–Benasciutti (TB) method to implement fatigue damage estimation of mechanical components. Both the time‐domain formulation and the proposed frequency‐domain formulation of the MWCM combined with the TCD are applied to the experimental results from the literature, concerning notched specimens made of 2024‐T4 aluminum alloy tested under various nonproportional bending‐torsion random vibration fatigue loading.

Damage comparative analysis of needled C/SiC composite under vibration fatigue loading and monotonic tensile loading

Needled C/SiC composite is composed of fiber and matrix, witch fatigue limit is related to the vibration loading frequency. A kind of plate specimen made of needled C/SiC composite was tested on a shaking table, and the vibration fatigue life of each specimen was obtained. In addition, the monotonic tensile test of needled C/SiC composite specimen was also carried out. Furthermore, the fracture morphologies from vibration test and monotonic tensile test were compared by scanning electron microscope. And the mechanism causing these differences was also explained.

Fatigue life analysis of aero-engine blades for abrasive belt grinding considering residual stress

Abrasive belt grinding technology is widely used in the processing of aero-engine blades. Residual stress is used as an indicator of grinding gauge integrity, which has a significant impact on the fatigue performance of aero-engine blades. In fatigue life research, experiments are mainly used to explore the influence of residual stress on fatigue life. Restricted by factors such as experimental efficiency and cost, it is necessary to simulate the influence of residual stress in the process of fatigue failure. Based on the theory of crack initiation and propagation, this paper proposes a life prediction algorithm considering residual stress; carries out a bending vibration fatigue experiment and simulation fatigue life analysis of aero-engine blade grinding with abrasive belt; compares the results of experiments and simulations and proposes a residual stress equivalent calibration method. Used theory, simulation, and experiment to verify the effectiveness of the method, and uses this equivalent calibration method to analyze the effect of residual stress on the fatigue life of aero-engine blades ground by abrasive belts. The experimental results show that the surface residual compressive stress will optimize the size and distribution of the surface stress during the service process of the aero-engine blade. Under the same external load and surface roughness conditions, a larger surface residual compressive stress will increase the aero-engine blade stiffness, reduce the aero-engine blade’s vibration amplitude, and reduce Surface stress, which in turn, has a beneficial effect on fatigue life. The proposed calibration method considering residual stress can accurately predict the fatigue life of aero-engine blades with a prediction accuracy up to 90%.