Fatigue Life Calculation Methods Research Articles

Study on Mechanical Properties and Fatigue of Cold-rolled Steel Plate for Distribution Transformer

The oil tank steel plate of the distribution transformer is covered with welds, and the fatigue failure of the oil tank often occurs in the internal defects of fillet welds. Given the above problems, this paper puts forward the bearing capacity calculation formula of cold-rolled steel plate and carries on the force analysis of steel plate and the fatigue analysis of weld through finite elements. Based on the theory of plastic limit design, the ultimate flexural bearing capacity of the control section of steel plate members is proposed. The calculation formula of equivalent structural stress is given based on the calculation method of structural stress and linear elastic fracture mechanics, and the calculation method of fatigue life and fatigue cumulative damage is given. Then, the elastic-plastic equation is solved according to three criteria: Mises yield criterion, plastic flow criterion, and strengthening criterion. Based on the above numerical simulation analysis, the mechanical model of steel plate weld is constructed, the mesh is divided, the boundary conditions are restricted and the same load is applied. ABAQUS analysis results show that the stress distribution curve of the connector has a maximum value at X = 80 mm and X = 210 mm, that is, the top surface of the connector steel plate has an obvious stress concentration at 80 mm and 210 mm. When the length of the weld is not more than 60 times the size of the welding foot, the full section of the core plate will yield, and the maximum stress value of the weld element will not exceed the tensile strength value of the welding material. The error of the results calculated by the formula in this paper is mostly within 10%, and the rest is basically within 20%. Therefore, the bearing capacity formula of the steel plate in this paper has ideal calculation accuracy and can provide effective guidance for the design of distribution transformer oil tanks.

Fatigue performance of Q420C high-strength steel at room and low temperatures

Steel structures are frequently exposed to the environment with variable temperature, where the fatigue failure of steel is difficult to be predicted. In this paper, the standard Q420C high-strength steel specimens were tested to explore their fatigue performance at room (25°C) and low temperatures (0°C, −15°C and −30°C). Before fatigue tests, the tensile tests have been done, and the results indicate that the yield and ultimate strengths of Q420C steel significantly grew when the temperature decreased. The fatigue behavior of Q420C steel was discussed from different perspectives, including the crack initiation, crack growth, fracture mode and fatigue life. The fatigue failure was observed mainly near the arc transition section of specimen, with the fatigue crack initiated from the surface and internal discontinuity defects. Furthermore, the test fatigue life was compared with the recommended S-N curves provided by specifications from various countries. These comparison results suggest that recommended S-N curves were excessively conservative to evaluate the steel fatigue life at low temperature, leading to a potential economic cost for the steel structures at extremely cold conditions. To avoid needless loss, a calculation method of steel fatigue life considering the effect of low-temperature, stress range and yield strength was proposed.

Stochastic Vibration-Driven Fatigue Analysis for Steel Structure Bridges Considering Track Irregularity

This study proposes a method for assessing the effect of stochastic vibrations resulting from track irregularities which are rarely studied but significant on bridge fatigue. First, the pseudo-excitation method is utilized to determine the power spectrum density of stress. Subsequently, the trigonometric series method is employed to acquire the stress time history set. Then, a traditional fatigue life calculation method is employed for analysis. By utilizing a post-sampling method, the need for costly repetitive solutions of the vehicle-bridge coupling system is eliminated. Numerical simulations are conducted on a steel truss bridge, revealing the non-negligible effect of track irregularity on bridge fatigue performance. The study investigates the underlying mechanism, highlighting the pronounced influence of long-wave track irregularity. Moreover, the research explores the correlation between track smoothness and bridge fatigue performance, demonstrating that a decrease in track smoothness leads to an increase in fatigue loss. These findings emphasize the necessity of considering stochastic vibrations when evaluating bridge fatigue, providing valuable insights for bridge design and maintenance.

A Design Method on Durable Asphalt Pavement of Flexible Base on Anti-Rutting Performance and Its Application.

To solve the durability of flexible base asphalt pavement, especially its anti-rutting problem, a design method on durable asphalt pavement of flexible base on anti-rutting performance was put forward in the paper, based on many experiments and calculations. Firstly, a method that asphalt could be selected according to penetration and the anti-rutting factor of its base asphalt was found, which solved the problem of the asphalt selection of the flexible base asphalt mixture design. Meanwhile, a method of skeleton-density structure gradation design was proposed based on the fractal void ratio of coarse aggregate, fractal volume of fine aggregate in coarse aggregate, penetration, fractal dimension of gradation particle size, and rutting tests, which effectively solved in advance the rutting and fatigue performance of flexible base asphalt mixtures. Then, on the basis of the fatigue damage, a calculation method of fatigue life was suggested, which solved the problem that the fatigue damage of asphalt mixtures rarely considered the combined effects of creep damage and fatigue damage. In addition, a calculation method of rutting was formulated based on vehicle dynamic load and ANSYS 16.0 software. Lastly, the feasibility of the design method on durable asphalt pavement of flexible base on anti-rutting performance was verified combining with the real engineering of a supporting project and several numerical calculations and tests.

The influence of water vapor on the structural response of asphalt pavement

Abstract A series of water damage phenomena of asphalt pavement during service show that water is very important. To comprehensively analyze the influence of water vapor factors on the response of pavement structure, this article first tests the water vapor diffusion coefficient of asphalt pavement materials at different temperatures establishes the water vapor concentration field model of the pavement structure, and analyzes the actual water vapor distribution of the pavement structure; then, the relationship between viscoelastic parameters of the mixture and water vapor concentration is established. Based on this, the finite element model of the pavement structure considering the water vapor factor is established, and the influence of the water vapor factor on the pavement structure response and fatigue life is quantified. It is found that water vapor has an important influence on the mechanical response. On the hottest days in summer, the attenuation of surface modulus caused by water vapor has the greatest impact on the upper layer of the pavement structure. Under the influence of water vapor, the position just below the wheel of the upper layer at the bottom of the horizontal tension strain increases by 108.26%, and the horizontal tension strain of the other layers increases by about 5%, increasing the risk of upper layer cracking. At the same time, water vapor reduces the stress that can be borne by the surface layer, while the rest of the stress is borne by the base. Compared with the fatigue life calculation method in the specification, the actual non-uniform water vapor concentration field reduces the fatigue life of the surface layer by 12.246%. This shows that the current structural calculation does not consider the water vapor factor, which makes the pavement structure more dangerous, and the influence of the water vapor factor should be fully considered.

Investigation of the quality category approach for BS7910-based rapid fatigue assessment of welded structures containing cracks

PurposeThis study aims to extend the application of the quality category approach in rapid fatigue assessment of complex welded structures containing defects under arbitrary loadings, following the investigation of their core data and fatigue assessment procedures based on fracture mechanics.Design/methodology/approachThe analysis methods and procedures for calculating equivalent sizes of semi-elliptic cracks and initial sizes of through-width cracks at the weld toe were developed based on the life equivalence principle. Different stress concentration solutions, i.e. 2D-Mk and 3D-Mk solutions, and different bending ratios were considered. Then, approximate equations were proposed to calculate the crack size under combined stress. In addition, a procedure for calculating the fatigue life by interpolation was proposed and applied to engineering examples.FindingsThe fatigue lives of fillet and butt weld joints obtained with the 3D-Mk solution for large L/B are longer than those obtained with the 2D-Mk solution. The results of the fatigue life of the brake unit bracket show that the average error between the proposed approximation equations and the quality category approach is 1.6%.Originality/valueThe quality category and equivalent size curves of different stress concentration solutions under combined membrane and bending stresses are newly added, which further expands the application of the quality category approach. When the proposed fatigue life calculation methods are employed, the remaining life can be quickly derived in addition to the qualitative conclusion on the safety of the structure. These provide the necessary conditions to perform a rapid fatigue assessment adapted to engineering purposes.

Fatigue life analysis of rotary drill pipe

In this paper, the crack problem of a certain type of rotary drill pipe in use is studied, and a simplified calculation method for the fatigue life of rotary drill pipe is proposed. The bench test device built can be used for the fatigue life test of all tubular structures by analogy. The calculation method of fatigue life of rotary drill pipe is studied through field test and bench test of drill pipe. Firstly, a simplified model of the drill pipe was established with the outer rod of the rotary drill pipe as the research object, and the model was verified. Then, the difference between the hot spot stress extrapolation method recommended by the IIW standard and the DNV standard was compared, and the hot spot stress of the drill pipe was calculated by the two-point linear extrapolation method recommended by the IIW standard, and the equivalent fatigue limit of the drill pipe was obtained by the Von Mises criterion. Finally, the equivalent load was deduced according to the stress level of the actual work test, and the constant amplitude load test was carried out on the bench, and the fatigue life of the drill pipe under the constant amplitude load was obtained. The results show that both the simplified model of the drill pipe and the bench test drill pipe can well reflect the stress level of the field test. The rotary drill pipe mainly bears torsional load, and the crack position of the bench test corresponds to the actual drill pipe crack position. The fatigue life of drill pipe is calculated by applying the Von Mises criterion and Basquin's SN curve power function. The calculated fatigue life is consistent with the results of the bench test. The calculation method can be well applied to the life analysis problem of multiaxial fatigue of large structural parts.

Analysis of dynamic fatigue characteristics of critical parts of highly strengthened single cylinder diesel engine

In this paper, the strength analysis and fatigue life calculation of multi-component coupling of crankshaft, connecting rod and engine body of highly strengthened single cylinder diesel engine are carried out. The stress of crankshaft, connecting rod and engine body in two working cycles is calculated by multi-component coupling transient dynamics, and the strength is analyzed based on the third strength theory firstly; Then, the accuracy of the transient calculation results is verified by the strength experiment of the crankshaft and connecting rod reduced scale model and the calculation of the static stress of the body; Finally, according to the stress fatigue life calculation method, the fatigue life of crankshaft, connecting rod and engine body is calculated. The maximum stress of crankshaft, connecting rod and body is less than the yield limit of corresponding materials; The fatigue life calculation results show that the damage accumulation of the engine body is very little, which meets the design requirements of infinite life. The damage accumulation of the crankshaft at the fillet of the main journal and the connecting rod at the side of the rod is 32005.6 hours and 102841.7 hours respectively, which meeting the design requirements of 20000 hours.

Fatigue Life Analysis of Main Reducer Gears for Battery Electric Bus Considering Regenerative Braking

The braking mode of the battery electric urban bus (BEUB) is different from the friction braking of the traditional fuel bus due to the introduction of a regenerative braking system. The intervention of electromagnetic braking changes the working condition of the main reducer gears, thus affecting their service lives. Based on the Urban Dynamometer Driving Schedule (UDDS) driving cycle condition, the stress–time history of the main reducer gears is calculated. Combined with the static analysis results and the S-N curve of the material, the fatigue lives of the main reducer gears considering electromagnetic braking and traditional friction braking are analyzed. The reverse torque on the driving axle during electromagnetic braking is taken into account to be closer to the real situation. Results show that, under the electromagnetic braking mode, the bending fatigue lives of the tooth root on the convex and concave surfaces of the pinion are 78.5% and 78.9% of that under the traditional friction braking mode, respectively, while the contact fatigue life of the pinion working surface is 78.2% of that under the friction braking mode, indicating that the introduction of the regenerative braking system into the BEUB will cause a significant reduction in the service life of the main reducer gears. This study provides a high-precision fatigue life calculation method for the BEUB main reducer gears and the accurate prediction of their remaining life.

A Multi-Scale Submodel Method for Fatigue Analysis of Braided Composite Structures.

A multi-scale fatigue analysis method for braided ceramic matrix composites (CMCs) based on sub-models is developed in this paper. The finite element shape function is used as the interpolation function for transferring the displacement information between the macro-scale and meso-scale models. The fatigue failure criterion based on the shear lag theory is used to implement the coupling calculation of the meso-scale and micro-scale. Combining the meso-scale cell model and the fatigue failure criterion based on the shear lag theory, the fatigue life of 2D SiC/SiC is analyzed. The analysis results are in good agreement with the experimental results, which proves the accuracy of the meso-scale cell model and the fatigue life calculation method. A multi-scale sub-model fatigue analysis method is used to study the fatigue damage of 2D SiC/SiC stiffened plates under random tension–tension loads. The influence of the sub-models at different positions in the macro-model element on the analysis results was analyzed. The results shows that the fatigue analysis method proposed in this paper takes into account the damage condition of the meso-structured of composite material, and at the same time has high calculation efficiency, and has low requirements for modeling of the macro finite element model, which can be better applied to the fatigue analysis of CMCs structure.

Fatigue life prediction for locomotive bogie frames using virtual prototype technique

Current research papers use simulated load spectrums to assess bogie frames’ fatigue life but seldom consider traction and braking loads. Traction and braking loads play important roles in predicting fatigue life in high-speed and heavy haul operational scenarios. Hence, there is a research gap in terms of the consideration of longitudinal load spectrums while assessing bogie frames’ fatigue life. This paper presents research about this topic. A virtual prototype technique available in literature has been extended for this purpose; it uses multibody dynamics and finite element techniques to simulate the behaviour of bogie frames under real operational service loads. As a result, the special simulation methodology has been developed in this work and it includes the unique integration of simulation approaches that includes train dynamics, locomotive dynamics with the consideration of a traction control algorithm and the adopted fatigue life calculation method. This paper gives numerical examples of a rigid-flexible coupled dynamic railway vehicle model subjected to longitudinal forces. Road Environment Percent Occurrence Spectrum (REPOS) load spectrums of the bogie frame were developed from a whole-trip train simulation on a real route. The spectrums are then used to predict locomotive the bogie frame’s fatigue life. The results of the bogie frame fatigue life evaluation performed in this paper show that fatigue lives at the roots of traction rod seats under longitudinal load spectrums are shorter than their fatigue life under vertical load spectrums.

Effect of Non-metallic Inclusions on Subsurface Stress and Fatigue Life of High-speed Railway Bearings

The contact simulation model of high-speed railway train axle box bearing is simplified into a two-dimensional plane with an elastic semi-infinite body subjected to semi-elliptical cylindrical compressive stress in one direction. The ANSYS software was used to solve the effects of single inclusion size, the depth of the contact surface and the elastic modulus on dynamic shear stress and Von Mises stress of high-iron bearing subsurface, and compared with the calculation results of bearing material uniformity assumption. Using the modified Basquin equation, the relevant assumptions are made. The maximum Von Mises stress is used as the key stress for fatigue life calculation. The bearing fatigue life calculation method is established to study the influence of the inclusion size, the depth of the contact surface and the elastic modulus on the bearing fatigue life.

Contact fatigue model and life prediction of the compound motion curve-face gear pair

Different from the common face gear pair fixed rotation motion between intersecting axes, the compound transmission of the curve-face gear is a new motion form, which can convert rotational motion into rotation and movement motion. To solve the contact fatigue life problem of this new motion form gear pair, a new contact fatigue life calculation method of the compound transmission curve-face gear pair was proposed. Based on the space gear engagement principle and the fracture mechanics theory, the theoretical contact fatigue model of the curve-face gear composite transmission was established. Considering that the contact load for every tooth is time-varying in the half-period of the curve-face gear, the contact fatigue life stage of the curve-face gear was divided into crack initiation and crack growth, and the crack growth fatigue life for each tooth was calculated using the finite element method. The curve-face gear pair was processed in the five-axis NC machining center and the compound transmission experiment platform of the curve-face gear was set up to measure the tooth surface dynamic contact stress, and the overall life of the curve-face gear was predicted. The comparison analysis between theoretical and experimental results verified the correctness of the theoretical contact fatigue calculation model.

INVESTIGATION OF TIME AND FREQUENCY DOMAIN FATIGUE LIFE CALCULATION METHODS USING FINITE ELEMENT METHOD

Maruz kalınan titreşim nedeni ile meydana gelen yorulma hasarı ve ömrünü tespit etmek için zaman düzleminde ve frekans düzleminde hesaplama yapan yöntemler bulunmaktadır. Bu yöntemler sonlu eleman analizleri ile birlikte kullanılarak mekanik tasarımın şekillendirilmesi sürecinde kritik rol oynamaktadır. Bu çalışmada zaman düzleminde yorulma hesaplayan Rainflow yöntemi ve frekans düzleminde yorulma hesaplayan Dirlik yöntemi sonlu elemanlar analizleri yardımı ile incelenmiş ve minimum yorulma ömrünü Dirlik metodunun verdiği görülmüştür. Herhangi bir test ile tasarım doğrulama imkânı bulunmadığında ve tasarım yalnızca sonlu elemanlar yöntemi ile değerlendirileceğinde, Dirlik metodu sonuçları referans alınarak yapılacak tasarımın en güvenli tasarımı vereceği için en avantajlı yöntem olduğu tespit edilmiştir.

Fatigue Life Assessment Approaches Comparison Based on Typical Welded Joint of Chassis Frame

There are many approaches to the durability calculation that are used in engineering practice. At the same time the existing accident studies show that the leading position is still hold by fatigue failures. This means that there is still no universal approach to fatigue problem solution, and the existing approaches have their limitations. In addition, there is lack of information about the comparison between the precision of the obtained results using different approaches. In this paper different fatigue life calculation methods, like nominal stress, hot spot stress, notch stress and fracture mechanics are used to calculate the durability of T-type welded joint. The obtained results are compared with the fatigue test ones and the approaches, which give the closest results, are found.

Fatigue Life Estimation with Mean Stress Effect Compensation for Lightweight Structures-The Case of GLARE 2 Composite.

This paper describes the current state-of-the-art in fatigue life assessment for lightweight composite structures with the use of the frequency domain fatigue life calculation method. Random stationary gaussian loading signals have been generated and served in the process of fatigue calculation. The material information that is being used in the calculation process has been obtained from literature for the Glare 2 composite. The effect of nonzero mean stress and different fiber orientations have been taken into account. The calculations have been performed for two mean stress compensation models by Goodman and Gerber. The proposed procedure gives satisfying results for the high-cycle fatigue region for Goodman and an overall good comparison in both regimes for the Gerber model.

Analysis and calculation of bending fatigue life of curve-face gear

The curve-face gear pair is a new type of gear pair, and it has not been widely applied in many occasions as other kinds of gear pairs. In order to solve the bending fatigue life problem of this new gear pair with time-varying characteristics, a new theoretical calculation model was established. According to the loading state in actual operation, the single-tooth force model of curve-face gear pair was built, the effective loading of curve-face gear was analyzed, and loading spectrum in a period tooth was obtained. By building tooth equivalent cantilever beam model, the single-tooth bending stress calculation formula was derived, and the bending stress spectrums in tooth different sections were analyzed, meanwhile stress spectrum of bending fatigue hazard section in a period tooth was obtained. Combining the Miner’s rule and bending stress spectrum of dangerous section position, the bending fatigue life calculation method of curve-face gear was proposed. Through concrete example analysis, the bending fatigue life of curve-face gear was calculated. According to dynamic load spectrum extracted by ADAMS and bending stress calculated by ANSYS Workbench, the fatigue damage distribution of curve-face gear was obtained by nCode DesignLife. By constructing curve-face gear pair running experimental platform, the dynamic tooth root bending stress was measured. Comparing the theoretical calculation, simulation, and experimental results, the error between experiment and theory is within 10%, so the theoretical calculation method of bending fatigue life of curve-face gear was verified.

Research on Bearing Stress Characteristics of Stacking Robot Base under New Engineering Background

Under the background of the continuous development of new engineering, more and more researches are aiming at new cutting-edge technologies, among which industrial robots have attracted much attention. Based on typical trajectory and a given load condition of the palletizing robot, the dynamics analysis and calculation was accomplished by using the dynamics analysis and calculation module of Adams software under the condition that the palletizing robot was working normally, then obtained the dynamic load variation when rolling bearing was running, furthermore, the contact stress change rule was obtained by using the finite element analysis calculation method, and the rule was regard as the basis of rolling bearing fatigue life analysis and evaluation. Judging from the results of analysis and calculation, the contact stress distribution of rolling bearing under the combined effect of both external load and dynamic load, which was similar to the phenomenon of commonly used rolling bearing stress fatigue destruction, this method can effectively overcome the deficiencies of traditional rolling bearing fatigue life calculation method that only consider static load, and reference for relevant engineering and technical personnel.

Influence of distribution parameters of rough surface asperities on the contact fatigue life of gears

The influence of the distribution parameters of asperities, i.e. mean radius of curvature of asperities β, density of asperities η, and standard deviation of asperity heights σ, on the contact fatigue life of gears is first studied in this paper. Based on the elastic–plastic contact model of asperities, the surface contact pressure and subsurface stress field during the gear meshing process are calculated by the iterative calculation method. According to the multi-axis fatigue life model, the calculation method of fatigue life under different distribution parameters of asperities in the gear meshing process is obtained. The quantitative calculation results of fatigue life and measured distribution parameters of asperities are analyzed. The relationship between the fatigue life and the distribution parameters of asperities on the measured gear surface is calculated and analyzed quantitatively. The following conclusions are drawn: (1) when the roughness value Ra is less than 0.3 µm, the contact fatigue life of gears with rough surfaces is close to that of smooth surfaces; (2) when the roughness value Ra ranges from 0.5 µm to 0.9 µm, the contact fatigue failure occurs near the surface (micro-pitting); (3) under the same roughness value Ra, the contact fatigue life of the gear decreases with the decrease of the density of the asperity and the mean curvature radius of the asperity. The mean radius of curvature of the asperity has a greater influence on the contact fatigue life than the density of the asperity.

Fatigue life analysis of slewing bearings in wind turbines

Wind energy is a type of green renewable energy that has received increased attention. Wind turbines use wind power to generate electricity. As important components of wind turbines, slewing bearings are large and expensive, and these properties make bearing tests challenging. The theories and methods of slewing bearing design in wind turbines are not perfect, and the field lacks long-term engineering verification. To ensure the service life of slewing bearings, an accurate fatigue life estimation in the design stage is essential. This paper presents a method of testing the fatigue life using a small sample test. Experiments were conducted to determine the actual fatigue life of a small sample, and the changes in local raceway damage, vibration acceleration, and lubrication were monitored. A finite element model of the slewing bearing was established in ABAQUS to obtain the contact stress between the ball and raceway. The calculation results were imported into FE-SAFE to analyse the fatigue life. The Morrow mean stress correction in conjunction with the Brown-Miller strain-life method were used in the analysis. The simulation results were compared with the experimental results to validate the effectiveness of the experiment. Three fatigue life calculation methods have distinct advantages and can be mutually referenced to improve the accuracy of bearing life calculations.