Miner Linear Cumulative Damage Theory 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.

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.

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.

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.

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.

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.

Fatigue behaviour of blind bolts under tensile cyclic loads

This study presents an experimental investigation on the fatigue performance of a blind bolt under axial-tension cyclic loads. Static, constant-amplitude, and variable-amplitude fatigue tests on standard bolts and blind bolts are carried out. The bolt failure modes, static tensile force–displacement relationships, and fatigue life are presented. Based on the experimental results, S–N curves of the bolts under constant-amplitude fatigue tests are obtained by means of regression analysis, and the influence of the load amplitude as well as the load ratio on the fatigue performance of blind bolts are examined. It is found that S–N curves follow a power function with negative exponent, and exhibit similar S–N curves to standard bolts under higher load ratio. Meanwhile, the fatigue life of blind bolts under variable-amplitude loadings is estimated by using Miner's linear cumulative-damage theory. The fatigue strength of blind bolts under variable-amplitude fatigue loading is lower than the corresponding value for constant-amplitude fatigue tests. Finally, the fatigue strength of blind bolts is assessed by comparing the test results with existing specifications. It is concluded that the fatigue performance of blind bolts can be conservatively estimated by the corresponding specification of design codes.

Lightweight design of gears in the wheel-side reducer based on Shanghai road driving cycle

The development of wheel-side reducer with proper durability is important for electric vehicles equipped with a wheel-side reducer system. Based on the Shanghai road driving cycle, a novel conversion method is proposed from vehicle speed to load, which provides a theoretical foundation for lightweight design and a durability analysis of the key components of the wheel-side reducer system. With the gears of the wheel-side reducer as an example, an electric drive system durability test specification is also developed on the basis of the Miner linear cumulative damage theory considering the material strengthening under low-amplitude loads. The durability test shows that the second round of the prototype design no longer has an infinite life compared with the first round of the prototype design. The method based on active load spectrum is more effective than the traditional design method.

Durability Testing Method of a Hub-Reducer System Based on the Shanghai Standard Road Driving Cycle

Abstract Electric vehicles are equipped with electric-drive wheel systems, so the development of matching hub reducers with proper durability is important. Based on the Shanghai standard road-driving cycle, this paper forecasts the load spectrum for key components of the hub-reducer system. After considering the material strengthening under low-amplitude loads, the reducer system running-in test specification is issued. This paper also develops an electric-drive system durability test specification on the basis of the Miner linear cumulative damage theory, and estimates the hub-reducer durability mileage. The bench test for durability shows that the first round of the prototype design satisfied the durability mileage required, and the bending-fatigue strength of the gear is sufficiently reliable, which gives possibilities for further lightweight designs. This method can be applied for the lightweight designing of other key automotive components. It also provides empirical evidence for developing automotive products that meet the standard road-driving-cycle conditions.

Bi-Probability Fatigue Life Prediction for Bridge Crane Structures

Fatigue crack is very dangerous for safely operating of steel structures. To estimate precisely fatigue life of bridge cranes, the randomness of lifted load and trolley’s position should be considered. Therefore, bi-probability fatigue life prediction method, namely load and position probability, is put forward based on the miner linear cumulative damage theory. Stress cycle spectrum is constructed based on real-time monitoring data by rainflow counting method. This method can successfully explain the existence of girder cracks in a typical bridge crane RMG, so it would provide valuable reference for maintenance decision of in-service cranes.

Effect of Interactive Periods to Corrosion-Fatigue Life on LY12CZ Alloy

To study life differences between pre-corrosion fatigue and corrosion-fatigue test, LY12CZ standard specimens are selected in pre-corrosion fatigue test to get the C(t) curve at first. Then, combining with Miner linear cumulative damage theory, theoretical fatigue life is calculated by simulated corrosion-fatigue interactive process. Compared with actual corrosion-fatigue interactive test, theoretical life is rather conservative. Afterwards, a modified model based on C(t) curve method and actual interactive test at different periods of specific flight strength is established. The result shows that the modified C(t) curve method is in good agreement with corrosion-fatigue interactive test.

Life Degeneration Rule on 2A12 Aluminium Alloy with Corrosion and Fatigue Experiment

2A12 specimens are selected in pre-corrosion fatigue test to get the ground corrosion effect coefficient, namely C(t) curve. Then, combining with Miner linear cumulative damage theory, theoretical fatigue life model is established based on the simulated corrosion-fatigue interactive process. Compared with actual corrosion-fatigue interactive test, theoretical life in short interactive periods is almost same, but actual life is higher in long interactive periods. Afterwards, a modified model based on C(t) curve at different interactive periods is established. The calculation shows that the modified results are in good agreement with the corrosion-fatigue interactive test.

Experimental Determination of Aircraft Structural Material Life Envelope

A new approach to reflect the relation of aircraft structural calendar life and fatigue life is established by pre-corrosion and fatigue test with 2A12 alloy specimens. The corrosion factor curve is fitted from the test, and then aircraft structural corrosion and fatigue interactive process during actual in-service environment is simulated. Furthermore, combining with Miner linear cumulative damage theory and the method of ‘calendar life tending to minimum’, life envelope is found. The result shows that flight strength is the key factor for aircraft structural life, and the envelope can be used to realize single aircraft structural life surveillance.

Estimation of Random Sonic Fatigue Life Based on Peak Probability Density of Von Mises Stress

As to the random sonic fatigue problem of thin walled structure of aerospace flight vehicle, estimation method for fatigue life based on Von Mises stress peak probability density is investigated. Assuming that Von Mises stress process satisfies three-parameter Weibull distribution, the peak probability density function of Von Mises stress is derived through the threshold crossing analysis and the peak distribution analysis of stationary random process. According to the Miner linear cumulative damage theory, the method for estimating the fatigue life in the frequency domain is established with the Von Mises stress peak probability density function applied. As an example, an aero-engine Combustor liner is considered, using coupled Finite Element Method (FEM) and Boundary Element Method (BEM) method, the structure vibration response to limited bandwidth Gaussian white noise is calculated. Based on the results, fatigue life of the structure is estimated by using the proposed method. Further more, the influences of the probability density function which is characterized by three-parameter Weibull distribution and two-parameter Weibull distribution respectivily for Von Mises stress response of the Combustor liner structure subjected to random accoustic loadings are discussed.

Fatigue Analysis of a Self-Propelled Steel Bridge for Life-Customized Design

Structure design of a product under complex loads not only must meet the conditions of its strength and stiffness, but also must consider the requirements of its fatigue life. Due to the lack of historical data of actual loads and stress, it is usually difficult to predict the fatigue life of product structure in life-customized design. Taking self-propelled steel bridge as an example, which is used for spoil transportation of tunnel construction in the Beijing-Shanghai high-speed railway projects, this paper presents a method of fatigue analysis for product structure for life-customized design. The approach of this work includes steps of (1) simulating actual work and load conditions of the bridge based on finite-element (FE) method, and determining risk components of the bridge, (2) analyzing the stress time history of dangerous components of the bridge, and drawing out the stress spectrum to solve the bottleneck problem of fatigue life calculation in the bridge design, (3) correcting the material S-N curves and predicting the fatigue life of the bridge based on Miner linear cumulative damage theory. The results of this research will facilitate implementation of life-customized design, thus meet the requirements of expected life of the bridge, and also improve the reliability and security of the bridge in engineering application.