Miner Linear Cumulative Damage Research Articles

Fatigue assessment of a 100-year-old riveted truss railway bridge

Fatigue is one of the most common reasons for failure in existing steel railway bridges, particularly with a riveted structure. Therefore, fatigue assessment is always the most important part of the complex evaluation of existing steel railway bridges. Additionally, a reliable fatigue assessment is often decisive in estimating the remaining service life of a bridge. The purpose of the presented research is to assess the fatigue of a 100-year-old riveted truss railway bridge. The assessment was carried out to decide whether the existing truss superstructure is still suitable for rehabilitation in the context of the ongoing modernisation of the railway line. The fatigue assessment procedure is based on the safe life method in the convention of nominal stresses. The Miner linear cumulative damage theory and the S-N curves according to the relevant European recommendations were also applied. Bridge evaluation revealed that the fatigue life of the steel superstructure was almost exhausted and that its remaining service life is too short to be considered for rehabilitation. It was also confirmed by the presence of fatigue cracks in the deck joints, detected during bridge inspection. Taking into account the assessment results, it was revealed that the existing riveted truss superstructure was not suitable for further use, which was intended to extend the bridge service life by the next 50 years after the modernisation of the railway line.

Fatigue load spectrum generation of Indonesian high-speed trains

The high-speed trains designed and constructed in Indonesia will use Aluminum alloy Al 6061-T6 as a structural material. Aluminum alloys are prone to fatigue failure due to the absence of endurance limit of the material, hence fatigue life prediction has to be carried out. Fatigue cracks could initiate at the defects of welded joints. Analyzing the fatigue load spectrum of critical locations in the train structures is crucial to predicting fatigue life. These critical locations are selected from areas with high static stress and stress concentration. The loads are analyzed using the multibody dynamic with rigid body assumptions and track roughness following UIC Standard Code 518. The finite element method is used to calculate the stresses from the loads generated by the multibody dynamic. The load sequence is further analyzed with rainflow counting method, and the load exceedance curve can be constructed. Finally, the Miner Linear Cumulative Damage Model is used to predict fatigue life.

Simulation Study on Methods for Reducing Dynamic Cable Curvature in Floating Wind Power Platforms

As a key component connecting a floating wind turbine with static sea cables, dynamic cables undergo significant tensile and bending loads caused by hydrostatic pressure, self-weight, waves, and ocean currents during service, which can lead to fatigue failure. Thus, dynamic and fatigue analyses are necessary for the design and operation of dynamic cables. In this study, a fatigue analysis of the three-core four-layer armored dynamic cable used in a semisubmersible floating wind turbine was carried out at a water depth of 25 m. The Miner linear cumulative damage method, based on material S-N curves, was used to predict fatigue life. The results indicate that, at 10 times the safety factor, the dynamic cables meet the design requirement of a 30-year service life in the studied marine environment. The maximal curvature of the dynamic cable always appears at the exit of the bend stiffener, even beyond the allowed point. Adding weights to the section where the cable exits the bend stiffener and adjusting the bend stiffener’s hanging angle can both reduce the curvature at the bend stiffener exit. The scheme of adjusting the bend stiffener’s hanging angle is preferred, for it is easier for simultaneous adjusting and inducing much smaller extra stress in the cable. As the hanging angle increases, the curvature at the bend stiffener exit decreases, while the maximal effective tension and maximal von Mises stress gradually increase. For certain operating conditions, especially with higher waves, it is better to adjust the hanging angle to avoid excessive curvature and, meanwhile, ensure the increase in the stress within a reasonable range.

Study on fatigue life estimation method of welded structure of lifting machinery

The fatigue strength of lifting machinery structure has always been an important issue in ensuring safety. In order to effectively and accurately evaluate the fatigue life of lifting machinery structure, this paper based on Miner linear cumulative damage theory and S-N curve in British BS 7608 standard, the fatigue life calculation of metal welded structure is carried out. Taking the large-scale bridge crane of hydropower station as an example, the nominal stress of the corresponding key parts is obtained by applying the actual load in the finite element model, and the stress time history is calculated, and then the safe service life of the structure is estimated, which provides an effective and feasible method for evaluating the fatigue residual life of the crane. The example analysis shows that the calculation method is convenient and reliable, which provides a scientific basis for accurately estimating the fatigue life of welded structure of lifting machinery.

Fatigue life prediction of stay cables under vehicle load considering corrosion variability

The combined effect of environmental corrosion and fatigue loads can accelerate the failure of stay cables. To ensure the safe operation of stay cables, this paper proposed a method for evaluating the fatigue life of stay cables, considering the variability of steel wire corrosion within the cable. Firstly, the relationship between the mean value and the standard deviation of uniform corrosion depth was established based on the experimental data of the corroded steel wires under the artificial accelerated corrosion environment. Then, the model of cable time-vary corrosion under the actual service environment was substituted, and the distributions of the weight loss rate of steel wires were obtained. Subsequently, a method for calculating the fatigue life of stay cables considering the corrosion variability of steel wires in the cable was proposed based on the parallel system theory and the Miner linear cumulative damage criterion. Finally, the North Channel Bridge (NCB) of Hangzhou Bay Bridge was used as an example, and the fatigue life distribution of stay cable under the combined action of corrosion and vehicle load was predicted. The results indicate that considering the corrosion variation of steel wires in the cable leads to a reduction in the fatigue life of stay cables, and neglecting this variability in fatigue life prediction methods is unsafe and non-conservative.

Fatigue life prediction of orthotropic steel deck strengthened with UHPC under stochastic traffic load

In recent years, the ultra-high performance concrete (UHPC) has been increasingly used to strengthen orthotropic steel decks (OSD) to solve the cracking problems at fatigue-prone details and pavement damage. In this paper, the fatigue life of a cable-stayed orthotropic steel decks bridge under stochastic traffic loads is calculated before and after the orthotropic steel decks strengthened with the ultra-high performance concrete layer. The traffic data of the real bridge for 1 week is first obtained based on the weigh-in-motion system. Then, a stochastic traffic load on the bridge is simulated for its service life by the Monte Carlo method. A fatigue life analysis framework, which includes the traffic load simulation, a refined finite element model, the S-N curve and Miner linear cumulative damage criterion, is proposed for fatigue life prediction of orthotropic steel decks. For the bridge before reinforcement, the predicting results for the fatigue life of three fatigue-prone details, including the scallop cutout, rib-to-diagram and rib-to-deck joint are basically consistent with that of the actual bridge inspection results. After strengthening by ultra-high performance concrete, the fatigue life of the three structural details are increased from 15.87, 13.89, and 32.26 years to more than 100 years, respectively, as compared with the original orthotropic steel decks structure.

Dynamic Reliability Evaluation and Life Prediction of Transmission System of Multi-Performance Degraded Wind Turbine

Wind power is a kind of important green energy. Thus, wind turbines have been widely utilized around the world. Wind turbines are composed of many important components. Among these components, the failure rate of the transmission system is relatively high in wind turbines. It is because the components are subjected to aerodynamic loads for a long time. In addition, its inertial load will result in fatigue fracture, wear and other problems. In this situation, wind turbines have to be repaired at a higher cost. Moreover, the traditional reliability methods are difficult to deal with the above challenges when performing the reliability analysis of the transmission system of wind turbines. To solve this problem, a stress-strength interference model based on performance degradation is introduced. Based on considering the strength degradation of each component, the improved Monte Carlo method simulation based on the Back Propagation neural network is used to obtain the curve of system reliability over time. Finally, the Miner linear cumulative damage theory and the Carten-Dolan cumulative damage theory method are used to calculate the cumulative damage and fatigue life of the gear transmission system.

Dynamic Response and Service Life of Tunnel Bottom Structure Considering Hydro-Mechanical Coupling Effect under the Condition of Bedrock Softening.

Due to the long-term coupling effect of a train load and groundwater, the surrounding rock at the tunnel bottom will soften in a certain range and the mechanical parameters of the surrounding rock will decrease, causing the uneven distribution of the confining pressure at the tunnel bottom and affecting the base concrete structure service life. In this research, the method of combining field tests and numerical simulation is adopted, and the vertical displacement, vertical acceleration, and maximum and minimum principal stresses are used as evaluation indicators. The dynamic response law of the base structure with the softened surrounding rock of the heavy-duty train is analyzed, and the Miner linear cumulative damage theory is introduced to obtain the service life of the tunnel bottom structure under different softening conditions. The results show that with the decrease in the softening coefficient and the increase in the softening thickness of the bedrock, the displacement, acceleration, and principal stress response indexes of the structure increase by varying degrees, and the service life of the base structure decreases almost linearly. The maximum vertical displacement, acceleration, and tensile stress are located directly below the track, and the maximum compressive stress is located at the connection between the inverted arch and the side wall. According to the predicted value of the service life, the reliability of the base structure is divided into four levels: safety, warning, danger, and serious danger.

The Anti-Fatigue Design of 80 t Depressed-Center Gondola Car Body

In view of the problem that special gondola cars are generally insufficient for the actual transportation of coke, and in order to improve the transportation efficiency and reduce the transportation cost, the 80 t depressed-center gondola car for coke transportation is designed by the anti-fatigue design method in this paper. The car body with a supporting bar and the car body without a supporting bar are simulated and analyzed by the finite element method; the results show that there are stress mutations at the transition area of the two key welds, especially at the 110 mm of weld 1. The fatigue lives of the two car body schemes are evaluated by Miner linear cumulative damage theory, spectrum and S-N curve in AAR standard, and load spectrum of the Daqin line and S-N curve in BSI standard. The results show that the 80 t depressed-center gondola car body with a supporting bar is the best scheme. In addition, the fatigue damage results show that the vertical load spectrum of AAR is worse than that of the Daqin line, and the longitudinal load spectrum of the Daqin line is worse than that of AAR. This conclusion will provide a basis for an anti-fatigue design of heavy haul wagon bodies or bogies.

Research on thermomechanical fatigue life prediction of regenerative cooling thrust chamber

The ratcheting effect of the liner wall structure in the thrust chamber of liquid rocket engine under cyclic load is studied, and its service life is predicted. Firstly, the 3-D heat transfer analysis of the wall of the thrust chamber is carried out while explaining the mechanism of its "dog room" failure. Based on the results of the heat transfer analysis, the stress-strain evolution of the structure under cyclic load is analyzed by nonlinear plane strain finite element method. According to the finite element analysis results, the ratcheting effect of the liner wall structure is described and the ratcheting damage is calculated. The low cycle fatigue damage is calculated by using modified Morrow model, and the creep damage is also calculated using Norton model. Finally, the total damage of thrust chamber liner wall is calculated by using Miner linear cumulative damage law and the thermomechanical fatigue life of the structure is estimated. The result shows that the middle point of the lower surface of the liner wall will fail first, and the calculated service life is 33 times, which is good agreement with its actual service life. In the total damage of the weak point, ratcheting damage, creep damage and low cycle fatigue damage account for 52%, 32% and 16% respectively, indicating that the ratcheting effect is the main reason for the failure of the thrust chamber structure. The research results of this paper provide important engineering reference for the structural optimization design and rapid life prediction of regenerative cooling thrust chamber of liquid rocket engine and the future reusable aerospace power.

Random Vibration Fatigue Life Analysis of Airborne Electrical Control Box

To study the influence of random vibration on the fatigue life of airborne equipment, an aircraft electrical control box was selected as the research object. First, finite element software was used to model the dynamics of the airborne electrical control box to investigate its mode frequencies. The accuracy of finite element simulations was verified by performing mode experiments. Second, the mode superposition method was used to analyze the flight direction (X axis), side direction (Y axis), and altitude direction (Z axis) random vibration responses of the electrical control box. The analysis results were combined with the Miner linear cumulative damage criterion and the Gaussian-distribution Steinberg method to estimate the fatigue life of the electrical control box in the three directions. Finally, the calculation results were verified by performing the random vibration durability test on the electrical control box. The finite element mode analysis results show good agreement with the vibration experiment results, and the maximum error is 13.4%, indicating that the finite element model established in this paper is acceptable. The fatigue life of the electrical control box in the three axes meets the user requirements, and random vibration along the side direction (Y axis) has the greatest impact on the fatigue life, which is consistent with the results of the actual experimental data. The research method can be extended to predict the fatigue life of other airborne equipment and thus has practical significance for structural design and reliability analysis of airborne equipment.

Fatigue life modelling of railway prestressed concrete sleepers

Railway sleepers, which transfer wheel loads to the formation, are an essential component of railway track systems. Prestressed concrete is the most commonly used type of railway sleepers around world. Crushing is a common damage (under resultant compressive stress) in concrete sleepers, which is attributable to excessive flexural, shear, pre-stress and bond actions. Dynamic impact loading conditions are often the cause of failure in the concrete sleepers. However, accumulated damage due to cyclic loads can also cause concrete crushing. Most previous research has investigated the impact load characteristics and the ultimate limit states of prestressed concrete railway sleepers. There is a knowledge gap with respect to serviceability limit states and fatigue failure of prestressed concrete sleepers. This study presents new results of extensive numerical, analytical, and experimental investigations aimed at predicting fatigue lives under cyclic loads. A numerical study validated by 30 full-scale experimental tests is executed and extended to assess fatigue limit states, while theoretical fatigue analysis methods based on S-N curve and Miner linear cumulative damage are additionally introduced for benchmarking. This paper is the world's first to demonstrate a remaining fatigue life assessment for prestressed concrete sleepers and benchmark with the theoretical methods. Parametric studies are conducted to unprecedentedly illustrate influences of support conditions, dynamic load distribution, and track stiffnesses on the remaining fatigue lives of prestressed concrete sleepers. This paper highlights the rationales associated with the development of fatigue limit states. The insights will provide design flexibility and improve railway sleeper maintenance and inspection criteria.

Fatigue Life Analysis of Bus Body based on User Target Load Spectrum‎

In this article, fatigue life of a bus body is analyzed based on the user target load spectrum. A finite element model of the bus body is built with characteristics. The static analysis result is obtained by using the inertia release method and a multi-body dynamic model is established by using the rigid flexible coupling method. According to user investigation, the user load spectrum is obtained through dynamic simulation. The average value and amplitude of each level of stress are extracted from the load spectrum information. With the fatigue properties of the material, the damage value of the bus body is determined by using the S-N curve method and Miner linear cumulative damage theory. The simulation gives the fatigue life and damage values of the most dangerous position of the body structure. Calculation shows that the fatigue life of the bus body meets durability requirements.

Fatigue Life Prediction for Semi-Closed Noise Barrier of High-Speed Railway under Wind Load

The fatigue state of the semi-closed noise barrier directly affects driving safety, and replacement after damage leads to train delays and increased operating costs. It is more eco-friendly and sustainable to predict the fatigue life of noise barriers to reinforce the structure in time. However, previous life prediction methods provide a limited reference in the design stage. In this study, a novel fatigue life prediction method for noise barriers was proposed. The computational fluid dynamics and finite element model of the semi-closed noise barrier were established and subjected to simulated natural wind and train aerodynamic impulse wind loads to calculate the stress time-history on the noise barrier. Based on the rain flow counting method and Miner linear cumulative fatigue damage theory, the fatigue life of noise barriers in three Chinese cities was predicted. The results show that the fatigue life of the noise barrier is closely related to the wind conditions and train operation modes. Targeted reinforcement for noise barriers in different fatigue states can save materials and reduce maintenance workload. Moreover, the influence of wind load on the noise barrier was summarized, and engineering suggestions on prolonging the fatigue life of noise barriers were put forward.

Random Vibration Fatigue Life Estimation of Power Controller

The power controller will be subjected to random external excitation loads during use. When subjected to high stress levels for a long time, the structure is prone to random fatigue failure, resulting in structural failure. Therefore, the prediction of the random vibration fatigue life of the power controller is very necessary. In this paper, Nastran software is used, Miner linear cumulative fatigue damage method combined with Gaussian three-interval method to calculate random fatigue of the structure. The final example shows the effectiveness of the method proposed in this paper.

Analysis of pipeline fatigue performance under random vibration load

As one of the most important equipments in power plant, the mechanical properties of steam pipe were analysed in this paper. Random vibration theory and Miner linear cumulative damage theory as well as frequency-domain fatigue analysis method were adopted, modal analysis and fatigue performance analysis of the in-service steam pipe were carried out with ANSYS, calculated first ten natural frequencies and cumulative damage under random excitation use Steinberg three-interval method. Results show that no fatigue failure will occur under this excitation load, the random vibration frequency-domain fatigue analysis method can effectively evaluate the fatigue performance of steam pipe, and provide a reference for the pipeline random vibration fatigue analysis.

Fatigue Life Analysis of Longitudinal Welding Seam for Wind Turbine Tower

Tower is an important fundamental component of large-scale wind turbines. The fatigue performance of the tower welded part directly affects the running safety and reliability of wind turbines. A fatigue life predicting method for the longitudinal welding seam of the tower is proposed in this paper. Under the precondition of satisfying the limit strength, the time series stress of each working condition is obtained by DIN18800-4 section stress calculation. Combined with the rain-flow counting method and the Miner linear cumulative damage theory, the fatigue life of the tower longitudinal weld is predicted. The results show that the tower structure meets the design requirement, and the feasibility and effectiveness of the method are verified.

Strength Evaluation of a Bogie Frame by Different Methods

Some crucial loads that current strength design specifications have not taken into account are also considered when assessing the strength of a bogie frame. Calculation methods of these loads come from load analysis. Finite element simulation and fatigue test rig have been used to assess static strength and fatigue strength of a bogie frame. In addition to the two methods, actual running test is also used to assess bogie frame fatigue strength. In finite element simulation method, endurance limit and modified Goodman fatigue limit diagram are two important tools to judge whether fatigue strength of a bogie frame meets requirement. In actual running test method, Miner linear cumulative damage rule is used to assess bogie frame fatigue strength.

A method of determining test load for full-scale wind turbine blade fatigue tests

Full-scale fatigue test is an effective method for validating the fatigue performance of wind turbine blade. Its primary problem is how to design the test load. The conventional approach to determine test load requires a complicated and time-consuming process. Thus, a simplified method for directly converting load spectrum of blade into test load is proposed in this paper. Firstly, beam theory is used to obtain the relationship between stress, strain and bending moment of blade cross section. Based on the assumption of local stress concentration and linear relationship between stress and strain, M-N curves (applied moment vs. allowable number of cycles to failure) is defined. Secondly, based on Miner's linear cumulative damage theory and constant life diagram, the equivalent fatigue cumulative damage of load spectrum which is equal to the damage of full-scale fatigue test is obtained. Then, in the case of the selected test load ratio and cycles, the mean and amplitude of test load can be solved. Finally, the validity of the proposed method is verified by an illustrative example. The result indicates that the error of the calculated results between this method and the traditional method is close to 5 %, and it can be used for fatigue test and improve the efficiency of test load design.

Effects of welding residual stresses on the vibration fatigue life of a ship's shock absorption support

The shock absorption support of a ship is a type of welding structure for reducing vibrations. In this paper, the vibration modal and frequency responses are first analysed using the finite element method, which is helpful to obtain exciting loads and the high stress areas of the support. Then, the vibration fatigue life of the support is analysed according to the power spectral density method and Miner linear cumulative damage theory. Based on the experimentally measured welding residual stresses of the support, the S–N curves are modified. The vibration fatigue life of the support is then calculated considering the welding residual stresses, and the key areas prone to cause vibration-fatigue damage are obtained. Finally, by improving the local structure of these key areas, the vibration fatigue strength of the support is increased. The results show that the vibration fatigue failure of the ship's shock absorption support usually occurs at the places where the structure suffers from larger stresses, defects, or stress concentrations. The welding residual stresses greatly influence the vibration fatigue of the support. Consequently, the welding residual stresses must be minimized or eliminated at the key areas of the support.