Shaft Fatigue Research Articles

An experimental investigation of ship propulsion system fatigue damage during crash astern maneuver

Marine propulsion shafts are exposed to fatigue due to various maneuvers. Among them, crash astern is considered to induce a high level of torsional stress on the shaft. Torsional stress is a dominant factor in shaft fatigue damage; however, there has been limited discussion on how much this maneuver impacts shaft fatigue life. So, this study aims to calculate fractional fatigue damage resulting from crash astern maneuvers, obtaining numerical results through a marine shaft fatigue analysis method. Firstly, shaft fatigue criteria were defined to establish S-N curves. Then, crash astern maneuvers were conducted to measure torsional stress as a loading history. Raw data were analyzed to apply alternating stress values to the S-N curve, enabling the calculation of cumulative fractional damage. The crash astern maneuver was executed under two different drafts: full laden and normal ballast, allowing for a comparison of shaft fatigue levels based on draft. Torsional stress was higher in the ballast condition than in full laden. Additionally, fatigue damage in ballast is approximately 1.7 times higher than in the other condition. The results suggest that the shaft is more affected by fatigue when sailing in shallow water than when sailing in deep sea.

Shaft fatigue estimation based on characteristics of transient torsional vibration for propulsion shafting system according to variation of passing time in barred speed range

Shaft fatigue estimation based on characteristics of transient torsional vibration for propulsion shafting system according to variation of passing time in barred speed range

Torsional Fatigue and Static Torsion Strength and Test Validations of Composite Tube Hybrid Drive Shafts

Drive shafts are the transmission components which transfer power from power source to required location. The connection may be between steering wheel and rack & pinion mechanism or gearbox to differential. As in gearbox to differential connection, operational conditions are harsh and high loads are generated, steel materials are mainly preferred to be used. Though steels have such advantages in cost, performance and durability, it is heavier compared to other engineering materials. Since international regulations dictate to decrease the carbon emissions rates due to global concerns, weight decrement of automobile components plays an important role in solving such problem. Considering the operational requirements and boundary conditions, weight reduction in steel parts might be tough. For this reason, alternative materials must be deeply investigated and implemented into the traditional technologies. In the scope of this study, fatigue and torsional strength of propeller shaft with composite tube and aluminum subcomponents were investigated.

Multiphysics and comparative analysis on failure detection in planetary gears

Gearbox monitoring is considered an important scientific focus for predicting preventative maintenance plans. In these systems, mechanical defects such as loading problems, eccentricity and torsional vibrations lead to shaft fatigue and other damage to various other mechanical components. Various methods have been developed to detect and identify the presence of defects in gearboxes. In this paper, we investigate the effect of gearbox faults on the current signal by defining an analytical correlation between the physical presence of the fault and the stator current. The theoretical development is supported by experimental measurements taken on a back-to-back planetary gearbox. Planetary gearbox faults result in the motor’s input torque oscillations, generating amplitude and frequency modulation (AM-FM). These modulations have an effect on stator current signals. The study of the stator current was followed by that of vibration signal and acoustic pressure taken simultaneously under the same operating conditions. This comparative investigation aims to present the differences between different techniques and highlight the efficiency of each.

Identifying the mechanism of the fatigue behavior of the composite shaft subjected to variable load

This paper presents a finite element analysis of a composite shaft under dynamic variable fatigue loading. The object of this study is the behavior of the fatigue life of a composite shaft under dynamic variable fatigue loading. The fatigue life of the shaft is then determined by analyzing the stress distribution and its effect on the material's fatigue strength. The investigation of fatigue behavior involves evaluating factors such as stress concentrations, fatigue crack initiation and propagation, and the cumulative damage caused by cyclic loading. The study explores the impact of biaxial loading on the shaft's fatigue performance and provides insights into its significance in predicting fatigue life and it is 10e7 cycles. Furthermore, a damage indicator is predicted to assess the accumulated damage and monitor the progression of fatigue-related degradation. This indicator serves as a valuable tool for predicting the remaining useful life of the composite shaft. The equivalent alternative stress is calculated to characterize the combined effect of different loading conditions on the fatigue life of the composite shaft. By quantifying the stress level and variations experienced by the structure, this parameter allows for a comprehensive assessment of the fatigue performance under variable loading scenarios 250 N. The findings of this research contribute to the understanding of fatigue behavior in composite shafts under dynamic variable fatigue loading. The insights gained from the fatigue life investigation, biaxiality indication, damage prediction, and equivalent alternative stress calculation can aid in optimizing design considerations, maintenance planning, and enhancing the reliability and durability of composite shafts in various engineering applications

Multiple Adaptive Model Predictive Controllers for Frequency Regulation in Wind Farms

Frequent and inadequate power regulation could significantly impact the main shaft mechanical load and the fatigue of wind turbines, which imposes a stringent requirement to perform frequency regulation. However, the existing work on frequency regulation mainly uses torque compensation to improve the frequency response, while few of them consider the mechanical fatigue of the main shaft caused by torque compensation of the frequency controller. In this paper, the mechanical fatigue of the main shaft can be mitigated in all of the speed sections thanks to the proposed frequency regulation controllers. Precisely, a multiple adaptive model predictive controller (MAMPC), which seamlessly integrates the multiple model predictive control (MMPC) and the real-time AutoRegressive with eXogenous inputs (ARX) model, is proposed. It nicely handles the rate of change in compensation torque to mitigate the mechanical load on the shaft in all of the speed sections. The effectiveness of our method is verified through extensive simulations. With the proposed method, the minimum frequency deviation can be reduced, and the number of fatigue cycles of the main shaft can be extended.

Reusable workflows for virtual testing of multidisciplinary products in system models

Developing increasingly complex multidisciplinary products in short development cycles is one major challenge in today’s product development. Model-based Systems Engineering (MBSE) approaches are well suited to address this challenge. With MBSE, products are virtually represented in central system models. For the efficient verification of customer requirements and to avoid exhaustive physical testing with prototypes, virtual domain models (e.g. FE-models) are integrated into the system model. To perform a virtual test, domain models need to be executed in a sequence, so-called workflows.Current workflows link several product system levels in one workflow and are often only valid for one specific system architecture. As the number of requirements and system complexity increases, these workflows become also more complex. The effort for creating new comprehensible workflows is currently high and the reusability cannot be ensured. To solve these deficits, a method for the systematic formalization of reusable workflows in system models as well as their structured integration is presented. Behavior diagrams in the modelling language SysML are used to control the execution order of the domain models of different purposes and fidelities. Modular sub-workflows are developed for each system level. These sub-workflows can be reused and combined modularly to form larger workflows. The approach shows a high potential to easily build and organize workflows in reusable libraries thereby supporting automated virtual testing in product development. To demonstrate the approach, workflows for bearing lifetime calculation and shaft fatigue testing of a wind turbine drive train as well as their integration into the SysML system model are presented.

Full-scale fatigue testing of a cast-iron wind turbine rotor shaft

Spheroidal graphite cast iron (EN-GJS), which provides a high degree of design flexibility and the possibility for lightweight design, has benefits as a material for use in structural parts in wind turbines. Comparing components made using the sand casting technique to those made using the chill casting process reveals significant potential to boost strength. However, at present, there is neither a proven design guideline nor reliable material input data for a lightweight component based on this material and fabrication process. This publication presents the results from the Gusswelleproject in chronological order. It starts with the explanation of the final setup and test plan for the full-scale rotor shaft fatigue experiment. The elaborated sensor and operational concept are then presented together with an adequate finite element method (FEM) model of the specimen and relevant neighboring components. The validation of this FEM model to ensure that the loading and the resulting local strains representing the real test bench situation is described. The usage of non-destructive testing to document the condition of the specimen from initial crack formation until integrity loss is explained followed by a comparison between the component fatigue test results and the material-based life-time forecast. A strength increase for chill-cast large components in the range of 50% is indicated. Simulation-based crack propagation studies are performed to qualitatively verify the loads responsible for the observed cracks of the component test and to further develop the possible method for crack predictions.

Analisa Analisa Kelelahan Dan Kekerasan Pada Logam Axle shaft Dengan Pengelasan Gesek

The axle shaft is a component of the power transfer system which often experiences mechanical failure. The purpose of this study was to determine the degree of fatigue and hardness of metal shafts with variations in frictional load as information on friction welding recommendations on metal shafts. The research method used is the experimental method, which is a way to compare specimens with variations in friction welding loads of 2 kg, 4 kg, and 6 kg using the Rockwell method of hardness testing and fatigue testing using a rotary bending machine. From the research results it is recommended that friction welding on metal axle shafts can be carried out with a friction load of 6 kg because from the results of the fatigue test SPBG6 has the highest average fatigue strength compared to SPBG2 and SPBG4. This was reinforced by the results of the SPBG6 hardness test which showed the lowest hardness level for the parent metal at 80.44 HRA.

Overview of existing methods of asynchronous motor diagnostics

The paper provides a review, analysis and research of existing diagnostic methods such as a vibroacoustic method based on the analysis of damped oscillations arising from dynamic loads of the system in friction nodes, the thermal method based on the analysis of thermal fields created by the object under study and the acoustic emission method, which includes an assessment of acoustic emission occurring in metals and welded joints. The advantages and disadvantages are identified and the conditions and areas of use of these methods are described. The applicability of these methods to such an electromechanical system as an asynchronous motor is also described. Vibroacoustic diagnostics can be used to assess shaft fatigue and wear of rolling bearings; thermal diagnostics can be used to diagnose the operation of the cooling system and assess the degree of aging of the insulation of the windings; the acoustic emission method is applicable in cases where it is necessary to assess the progressive wear of the shaft and bearing assemblies, as well as fatigue of gear elements in the gearbox.

A Predicted-Risk-Based Protection Approach for Turbine Generator Shafts against Fatigue Damage due to Islanding

A distributed generation steam turbine generator (hereafter referred to as turbine generator) improves the supply reliability of the local load when operated as a backup supply during islanding. Interconnection standards recommend removing the utility load from the island. Transient torques induced at the moments of islanding and removing the utility load from the island may cause shaft fatigue life loss and lead to fatigue damage. Therefore, a protection method is proposed in this work. The method is based on predicting the risk of shaft fatigue damage. Induced transient torque is first modeled. Fatigue study determines the local load size required to mitigate shaft torsional vibrations and avoid fatigue life loss during islanding. This is substituted in the torque function to obtain the critical torque. The risk of shaft fatigue damage is predicted by comparing the actual shaft torque with the critical torque. The turbine generator is shut down when the actual shaft torque during islanding exceeds the critical torque. Islanding on the local load is allowed when the actual shaft torque is smaller than the critical torque. The proposed method yields 0.011% shaft fatigue life loss under the most adverse islanding condition against 100% obtained with an online monitoring and protection system (OMPS).

The Fatigue Strength Analysis of ABS (Acrylonitrile Butadiene Styrene) Material Shaft Result of 3D Printing Process due to Rotating Bending Load

Prototyping a product using 3D (three-dimensional) printing process has been widely used. One of the materials commonly used is ABS (Acrylonitrile Butadiene Styrene). Currently, research did not refer to ASTM E-466 and tested specimens at 75% infill density without endurance limit analysis. The purpose of this research was to analyse the fatigue strength of 3D printed ABS material with infill density 100% due to rotating bending load according to ASTM E-466 standard, compare it with the 75% infill density test result and determine the value of its endurance limit. The research method used is experimental research by testing the fatigue strength of a number of ABS material specimens with four rotating bending load conditions until the specimen fails. The obtained result of the research is a S-N curve with maximum average cycle of 143702 at a stress of 26.87 MPa and minimum average cycle of 145 at a stress of 35.71 MPa. The shaft fatigue strength of ABS 3D printed with infill density 100% material has higher cycles at stresses below 37.1 MPa and lower cycles at stresses above 37.1 MPa compared to 75% infill density. The endurance limit obtained from the regression of the S-N curve is 16.25 MPa.

Fatigue analysis in rotor of a prototype bulb turbine based on fluid-structure interaction

Bulb turbine units are widely used in run-of river or dam projects with relatively low head, and can also be used for tidal energy utilization. Some types of bulb turbines have excessive vibration and fatigue failure problems, which threats their fatigue life. The model analyzed in this paper is a prototype bulb turbine rotor which suffered cracks, probably due to erosion and welding defects. The dynamic stress characteristics are analyzed under not only the non-cracked shaft condition but also the cracked one, to find possible causes of the failure.The computational fluid dynamics (CFD) simulation is performed to obtain reliable hydraulic load on the runner for performing the FEM analysis. The CFD results are verified by comparing with the site test for the prototype one. The linear elastic fracture mechanics theory combined with the fluid-structural interaction theory is applied to developing a cracked FEM model, to obtain the dynamic stress characteristics for the runner, shaft and rotor. The results reveal that the change in dynamic stress level on the shaft flange root significantly depends on the operating conditions, and the stress amplitude on the shaft mainly depends on the structural weight. The stress at the cracked zone could be up to 376.5 MPa in the best efficiency point, with only 1.5 years of fatigue life.Based on the numerical calculations and site inspection, it could be concluded that the insufficient sealing could lead to leakage flows with specific flow rates in flange root, which resulted in the occurrence of erosion; in addition, the welding at the flange root probably generated tiny defects. These two factors are likely lead to fatigue cracks and major failure of the shaft. Suggestions for solutions for the problems of the shaft are also discussed. Results of this study helps to find the reasons of the shaft fatigue failure. Furthermore, the analysis method could be used for an accurate calculation of fatigue life and providing guidance in future designs and operations of bulb turbine units.

Analysis and mitigation of the drive train fatigue load for wind turbine with inertial control

Wind turbine (WT) have attracted more and more attention as a potential way to compensate the fall of the power system inertia by participating in inertial control (IC). However, such inertial control would frequently change the generator torque of the WT according to the system frequency, which increases the fatigue load of the main shaft. However, previous studies have failed to demonstrate a connection between inertia control and WT fatigue load. Thus, this study mainly focuses on the shaft fatigue load caused by inertial control. First, the impact of inertial control on WT fatigue load is analyzed in details. A WT small signal model is established, by which the impact mechanism of inertial control on the shaft torque and tower bending moment could be illustrated. Then, to reduce the impact of inertial control on the WT fatigue load, a PI based mitigation control (PIMC) strategy for the WT fatigue load mitigation is proposed. Simulations in both frequency and time domain are performed to demonstrate the correctness of the proposed method. The results show that the proposed method could greatly reduce the fatigue load of the main shaft while improving the inertia response capacity of the WT.

High torque and excessive vibration on the induction motors under special voltage fluctuation conditions

Purpose Voltage fluctuation (flicker) is a power quality disturbance that can produce several undesirable effects on industrial equipment. This paper aims to present the methodology and results of investigations undertaken to examine the speed and torque of an induction motor (IM) under voltage fluctuation conditions. Design/methodology/approach The IM response to different characteristics of voltage fluctuations is presented. It will be shown that under a special condition the IM torque can even reach two times the rated torque. To show how this occurs, a qualitative discussion is given on the motor response by linearized equations. Findings The small-signal analysis was used to determine the frequency which leads to maximum speed fluctuations. It was shown that, if the motor is excited with a modulation frequency (resonant frequency) which is one of its natural frequencies (modes), the mode will act as a fluctuating amplifier and greatly increase the amplitude of torque and speed fluctuations. Sensitivity analysis is also carried out to evaluate the influence of motor parameters on the resonance frequency. The results show that the resonance frequency is not affected at all by the changes in magnetizing reactance. This has been shown that magnetic saturation does not have any impact on the resonance frequency. The most effective parameters are rotor and stator resistances. Originality/value With the increasing popularity and use of arc furnace loads in the metallurgy industry and due to the wide application of large IMs in the industry, it is possible that the frequency of torque pulsation locates near a natural frequency and then will create an oscillation with a large magnitude, potentially leading to accelerated fatigue or severe damage of shaft. However, if this phenomenon occurs in industries, the resonance frequency must be filtered from the input voltage. Experimental results on a 1.1 kW, 380 V, 50 Hz, 2 pole IM are used to validate the accuracy of simulation results.

Energy Analysis of the Propulsion Shaft Fatigue Process in a Rotating Mechanical System Part III Dimensional Analysis

Abstract This article presents the third and last part of the problem of diagnosing the fatigue of marine propulsion shafts in terms of energy with the use of the action function, undertaken by the authors. Even the most perfect physical models of real objects, observed under laboratory conditions and developed based on the results of their research, cannot be useful in diagnostics without properly transferring the obtained results to the scale of the real object. This paper presents the method of using dimensional analyses and the Buckingham theorem (the so-called π theorem) to determine the dimensionless numbers of the dynamic similarity of the physical model of the propulsion shaft and its real ship counterpart, which enable the transfer of the results of the research on the energy processes accompanying the ship propulsion shaft fatigue from the physical model to the real object.

An Open-Water Efficiency Based Speed Change Strategy With Propeller Lifespan Enhancement in All-Electric Ships

In recent years, utilizing the electrical propulsion system in the marine industry has become widely popular. Control of the propeller has been a high-priority design challenge in this industry. One of the essential issues in propeller control is the speed control of the ships. A suitable control strategy for the propeller should be economically-efficient while ensuring stability, reliability, and power quality of the ship’s power system. This article proposes an improved propeller control strategy for increasing/decreasing the ship’s speed. This scheme consists of two strategies: a maximum acceleration strategy and an efficient operation strategy. The maximum acceleration strategy aims to quickly reach the final speed setpoint. On the other hand, the efficient operation strategy is deemed to increase the reliability and power quality of the ship power system, as well as having a slightly more acceleration than the conventional method. Moreover, a mechanical index is employed for comparing the performance of the various speed change strategies. By utilizing this index, which is known as loss of life (LoL), the effects of a speed change maneuver on the propeller shaft fatigue are analyzed and the advantage of the proposed method in enhancing the propeller lifespan is discussed. Simulations show that utilizing the proposed speed change scheme decreases the propeller mechanical wear and tear to about 1.8 percent of the conventional methods and consequently will increase its lifespan.

Fatigue Life Analysis and Experimental Study of the Input Shaft of 6-Speed Automatic Transmission

The input shaft of gearbox usually bears a cyclic variation of torque, which may lead to the risk of experiencing a fatigue fracture. To evaluate the fatigue life accurately and identify the weak parts, the ANSYS is used to simulate the torsional fatigue of the input shaft for the gearbox, and the fatigue life of the weak part is obtained, which is then tested and verified by the torsional fatigue testing in the MTS torsional fatigue test rig. The test results show that the maximum difference is 14% between the calculated life and the testing results, indicating that the simulation value can reflect the actual fatigue life accurately. Notably, the cracks appear in the large oil holes, and its life is mainly concentrated in the crack initiation stage, accounting for 99.2% of the total life. The analysis results show that the fatigue life of the software simulation has the guiding significance for the life evaluation. The fatigue life of the shaft can be quickly calculated by the simulation to reduce the number of fatigue tests and achieve cost-effectiveness.

Energy Analysis of the Propulsion Shaft Fatigue Process in a Rotating Mechanical System Part II Identification Studies – Developing the Fatigue Durability Model of a Drive Shaft

Abstract The article presents a continuation of research carried out concerning identification of energy consequences of mechanical fatigue within a propeller shaft in a rotating mechanical system, while working under conditions of the loss of the required alignment of shaft lines. Experimental research was carried out on a physical model reflecting a full-sized real object: i.e., the propulsion system of the ship. It is proven, by means of an active experiment, that changes in propeller shaft deflection are reflected in the amount of dissipated kinetic energy of masses in rotational motion and the accumulated internal energy in its construction material. Adoption of a high-cycle fatigue syndrome, consisting of diagnostic symptoms determined from the action of the propeller shaft associated with the transformation of mechanical energy into work and heat, as well as with the generation of mechanical vibrations and elastic waves of acoustic emission, is proposed. To assess the diagnostic information quantity brought about by the defined features of propeller shaft fatigue, an experimental research program was developed and implemented, in which two statistical hypotheses are verified: the significance of the impact of the values enforcing the fatigue process, presented in the first part of the article, and the adequacy of the regression equation describing the fatigue durability of the propeller shaft in the energy aspect, constituting the second part of the article. This finally gives us the opportunity, after the appropriate translation of the model test results into full-sized real objects, to develop a methodology to diagnose marine propeller shaft fatigue in operating conditions. The third part of the article is devoted to this issue

Online Evaluation of Turbo-Generator Shaft Fatigue Damage Caused by Subsynchronous Oscillation

Subsynchronous oscillation (SSO) fault can cause torsional vibration and fatigue damage of the shafting system, thereby endanger the safe operation of the turbo-generator set. A novel framework for the online evaluation of shaft fatigue damage suffered from SSO is proposed in this paper. The main ingredients of the framework are a calculation method of the turbo-generator shaft torque, rain-flow counting method, S-N curves and linear damage accumulation law. The shaft torque calculation method, based on the measured torsional angle and generator voltage and current data, is mainly discussed. The effects of damping and electromechanical coupling under complex operating conditions are included in the measured data, and the calculated results of the torque are accurate. The novel framework was used to evaluate the fatigue damage of a 1000 MW turbo-generator shaft that suffered an actual SSO fault caused by a high-voltage direct current (HVDC) transmission system and some meaningful conclusions were given.