A modified nonlinear fatigue damage accumulation model based on the Manson-Halford theory was presented,and the new model was developed for fatigue life prediction under constant and variable amplitude loading, which ...A modified nonlinear fatigue damage accumulation model based on the Manson-Halford theory was presented,and the new model was developed for fatigue life prediction under constant and variable amplitude loading, which took the effects of the load interactions and the phenomenon of material's strength degradation into account. The experimental data of the 30 Cr Mn Si A and the LY-12 cz from literature were used to verify the proposed model. And from the good agreement between the experimental data and predicted results,we can see it clear that the proposed method can be applied to predicting fatigue life under different loadings.展开更多
In order to solve the problem of insufficient exciting force of equipment for large full-scale wind turbine blade fatigue testing,the influence of gravity on the performance of excitation equipment and fatigue damage ...In order to solve the problem of insufficient exciting force of equipment for large full-scale wind turbine blade fatigue testing,the influence of gravity on the performance of excitation equipment and fatigue damage evaluation of the different positions of wind turbine blades are analyzed.With the multi-excitation loading in the horizontal direction,the actuator force of the excitation equipment does not need to overcome the gravity of the dynamic mass,which directly outputs the exciting force of the system vibration.The excitation efficiency of the equipment is 77%higher than that of the vertical load.The gravity moment of the horizontal loading mode is perpendicular to the loading direction.That is,the mean load in the flapwise direction is zero.The weight of excitation equipment could replace the tuning mass on the condition that the self-weight of equipment is reduced by the multi-excitation mode,which helps the excitation equipment play the comprehensive function of excitation equipment and tuning mass.At the same time,the gravity moment in the edgewise direction will be decreased by 17.0%22.5%under the multi-excitation horizontal loading mode.In the vertical loading mode,the gravity moment is the mean load,which only increases fatigue damage accumulation by 15.6%.By comparing the role of gravity in the excitation equipment and fatigue damage evaluation,the multi-excitation horizontal loading mode has more advantage to performance the exciting force than the contribution of gravity to the fatigue damage accumulation in the vertical loading mode.Through the fatigue testing of multi-excitation horizontal loading,the potential of excitation equipment is explored,and the problem of insufficient exciting force in large full-scale wind turbine blade fatigue testing will be solved.展开更多
By introducing a fatigue blunting factor, the cyclic elasto-plastic Hutchinson-Rice-Rosengren (HRR) field near the crack tip under the cyclic loading is modified. And, an average damage per loading-cycle in the cycl...By introducing a fatigue blunting factor, the cyclic elasto-plastic Hutchinson-Rice-Rosengren (HRR) field near the crack tip under the cyclic loading is modified. And, an average damage per loading-cycle in the cyclic plastic deformation region is defined due to Manson-Coffin law. Then, according to the linear damage accumulation theory-Miner law, a new model for predicting the fatigue crack growth (FCG) of the opening mode crack based on the low cycle fatigue (LCF) damage is set up. The step length of crack propagation is assumed to be the size of cyclic plastic zone. It is clear that every parameter of the new model has clearly physical meaning which does not need any human debugging. Based on the LCF test data, the FCG predictions given by the new model are consistent with the FCG test results of Cr2Ni2MoV and X12CrMoWVNbN 10-1-1. What's more, referring to the relative researches, the good predictability of the new model is also proved on six kinds of materials.展开更多
When a nonlinear fatigue damage accumulation model based on damage curve approach is used to get better residual life prediction results, it is necessary to solve the problem caused by the uncertain exponent of the mo...When a nonlinear fatigue damage accumulation model based on damage curve approach is used to get better residual life prediction results, it is necessary to solve the problem caused by the uncertain exponent of the model. Considering the effects of load interaction, the assumption that there is a linear dependence between the exponent ratio and the loading ratio is established to predict fatigue residual life of materials. Three experimental data sets are used to validate the rightness of the proposition. The comparisons of experimental data and predictions show that the predictions based on the proposed proposition are in good accordance with the experimental results as long as the parameters that represent the linear correlativity are set an appropriate value. Meanwhile, the accuracy of the proposition is approximated to that of an existing model. Therefore, the proposition proposed in this paper is reasonable for residual life prediction.展开更多
Low cycle fatigue life consumption analysis was carried out in this work. Fatigue cycles accumulation method suitable even if engine is not often shut down was applied together with the modified universal sloped metho...Low cycle fatigue life consumption analysis was carried out in this work. Fatigue cycles accumulation method suitable even if engine is not often shut down was applied together with the modified universal sloped method for estimating fatigue cycles to failure. Damage summation rule was applied to estimate the fatigue damage accumulated over a given period of engine operation. The concept of fatigue factor which indicates how well engine is operated was introduced to make engine life tracking feasible. The developed fatigue life tracking method was incorporated in PYTHIA, Cranfield University in-house software and applied to 8 months of engine operation. The results obtained are similar to those of real engine operation. At a set power level, fatigue life decreases with increase in ambient temperature with the magnitude of decrease greater at higher power levels. The fatigue life tracking methodology developed could serve as a useful tool to engine operators.展开更多
A novel method is presented to evaluate the complicated fatigue behavior of gears made of20Cr2Ni4 A.Fatigue tests are conducted in a high-frequency push-pull fatigue tester,and acoustic emission(AE)technique is used...A novel method is presented to evaluate the complicated fatigue behavior of gears made of20Cr2Ni4 A.Fatigue tests are conducted in a high-frequency push-pull fatigue tester,and acoustic emission(AE)technique is used to acquire metal fatigue signals.After analyzing large number of AE frequency spectrum,we find that:the crack extension can be expressed as the energy of specific frequency band,which is abbreviated as F-energy.To further validate the fatigue behavior,some correlation analysis is applied between F-energy and some AE parameters.Experimental results show that there is significant correlation among the Fenergy,root mean square(RMS),relative energy,and hits.The findings can be used to validate the effectiveness of the F-energy in predicting fatigue crack propagation and remaining life for parts in-service.F-energy,as a new AE parameter,is first put forward in the area of fatigue crack growth.展开更多
Firstly, constant amplitude P-S_a-S_m-N_c surface family is established.Secondly, four basic assumptions, i.e., monotonically increasing, non-coupling, separability andnonintersecting of fatigue damage accumulation ar...Firstly, constant amplitude P-S_a-S_m-N_c surface family is established.Secondly, four basic assumptions, i.e., monotonically increasing, non-coupling, separability andnonintersecting of fatigue damage accumulation are proposed from the viewpoint of both damagemechanics and fracture mechanics. Then the individual isodamage D-S_a-S_m-N surface under constantamplitude loading is constructed and the two-dimensional individual Miner's rule is derived.Consequently, the two-dimensional probabilistic Miner's rule (TPMiner) is established and proved fora population subjected to variable amplitude loading. Finally, with successfully experimentverification, TPMiner proves be to very useful and feasible in fatigue reliability theory.展开更多
Purpose–In view of the difficulty in determining the key parameters d in the Corten-Dolan model,based on the introduction of small loads,damage degrees and stress states to the Corten-Dolan model and the existing imp...Purpose–In view of the difficulty in determining the key parameters d in the Corten-Dolan model,based on the introduction of small loads,damage degrees and stress states to the Corten-Dolan model and the existing improved model,the sequential effects of the adjacent two-stage load were further considered.Design/methodology/approach–Two improved Corten-Dolan models were established on the basis of modifying the parameter d by two different methods,namely,increasing stress ratio coefficient as well as considering the effects of loading sequence and damage degree as independent influencing factors respectively.According to the test data of the welded joints of common materials(standard 45 steel),alloy materials(standard 16Mn steel)and Q235B steel,the validity and feasibility of the above two improved models for fatigue life prediction were verified.Findings–Results show that,compared with the traditional Miner model and the existing Corten-Dolan improved model,the two improved models have higher prediction accuracy in the fatigue life prediction of welding materials whether under two-stage load or multi-stage load.Originality/value–Because the mathematical expressions of the models are relatively simple and need no multi-layer iterative calculation,it is convenient to predict the fatigue life of welded structure in practical engineering.展开更多
The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring f...The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring forces, which are induced by wave excitation and transferred by the YOKE and the mooring support frame, may cause fatigue damage to the bow structure. Different from direct wave-in duced-forces, the mooring force consists of wave frequency force (WF) and 2nd dr aft low frequency force (LF) [3] , which are represented by two sets of short-term distribution respectively. Based on two sets of short-term distribution of moor ing forces obtained by the model test, the fatigue damage of the bow structure of FPSO is analyzed, with emphasis on two points. One is the procedure and position selection for fatigue check, and the other is the application of new formulae for the calculation of accumulative fatigue damage caused by two sets of short-term distribution of hot spot stress range. From the results distingui shed features of fatigue damage to the FPSO’s bow structure can be observed.展开更多
The nonlinear cumulative damage model is modified to have high prediction accuracy when the high-low cycle stress frequency ratio m is large(m500).The low cycle fatigue(LCF)tests,high cycle fatigue(HCF)tests and combi...The nonlinear cumulative damage model is modified to have high prediction accuracy when the high-low cycle stress frequency ratio m is large(m500).The low cycle fatigue(LCF)tests,high cycle fatigue(HCF)tests and combined high and low cycle fatigue(CCF)tests of TC11 titanium alloy were carried out,and the influencing factors of CCF life were analysed.The CCF life declines with the decrease of the ratio of high-low cycle stress frequency m.Both linear and nonlinear cumulative damage models are used to predict the CCF life.The CCF life prediction error of the linear cumulative damage model is great and the predictions tend to be overestimated,which is dangerous for engineering application.The accuracy is relatively high when the high-low cycle stress frequency ratio m500.The accuracy of nonlinear cumulative damage model is higher than that of linear model when the high-low cycle stress frequency ratio m500.Based on the relationship between high cycle average stress rmajor and material yield limit rp,0.2,a correction term is added to the nonlinear cumulative damage model and verified,which made the modified model more accurate when m500.展开更多
Experime ntal research results of surface damage accumulation in rail steel under rolling with slippage are presented. Hertz contact for two rollers made of rail and whe el steels was realized in the test. The influe...Experime ntal research results of surface damage accumulation in rail steel under rolling with slippage are presented. Hertz contact for two rollers made of rail and whe el steels was realized in the test. The influence of loading regime upon wear of rail is considered. The estimation of characteristics of surface fracture resis tance for rail steel is made. The method to predict the life of rail steel under given conditions of regular loading is proposed.展开更多
Rolling contact fatigue(RCF)issues,such as pitting,might occur on bevel gears because load fluctuation induces considerable subsurface stress amplitudes.Such issues can dramatically affect the service life of associat...Rolling contact fatigue(RCF)issues,such as pitting,might occur on bevel gears because load fluctuation induces considerable subsurface stress amplitudes.Such issues can dramatically affect the service life of associated machines.An accurate geometry model of a hypoid gear utilized in the main reducer of a heavy-duty vehicle is developed in this study with the commercial gear design software MASTA.Multiaxial stress–strain states are simulated with the finite element method,and the RCF life is predicted using the Brown–Miller–Morrow fatigue criterion.The patterns of fatigue life on the tooth surface are simulated under various loading levels,and the RCF S–N curve is numerically generated.Moreover,a typical torque–time history on the driven axle is described,followed by the construction of program load spectrum with the rain flow method and the Goodman mean stress equation.The effects of various fatigue damage accumulation rules on fatigue life are compared and discussed in detail.Predicted results reveal that the Miner linear rule provides the most optimistic result among the three selected rules,and the Manson bilinear rule produces the most conservative result.展开更多
The brake unit bracket of a bogie frame is an important load-carrying component, particularly under emergency start/stop conditions. Conventional infinite/safe life approaches provide an over-conservative recommendati...The brake unit bracket of a bogie frame is an important load-carrying component, particularly under emergency start/stop conditions. Conventional infinite/safe life approaches provide an over-conservative recommendation for the allowable strength and lifetime, which hinders the lightweight design of modern railway vehicles. In this study, to ensure the reliability and durability of a brake unit bracket, an attempt was made to integrate the nominal stress method and an advanced damage tolerance method. First, a complex bogie frame was modelled using solid elements instead of plate and beam elements. A hot spot stress region on the bracket was found under an eight-stage load spectrum obtained from the Wuhan–Guangzhou high-speed railway line. Based on the probability of foreign damage, a semi-elliptical surface crack was then assumed for residual life assessment. The results obtained by the cumulative damage and damage tolerance methods show that the brake unit bracket can operate for over 30 years. Moreover, even if a 2-mm depth crack exists, the brake unit bracket can be safely operated for more than 2.27 years, with the hope that the crack can be detected in subsequent maintenance procedures. Finally, an appropriate safety margin was suggested which provides a basis for the life prediction and durability assessment of brake unit brackets of high-speed railways.展开更多
The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears.Meanwhile,the coexistence of tooth contact fatigue damage and tooth profile wear leads t...The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears.Meanwhile,the coexistence of tooth contact fatigue damage and tooth profile wear leads to a complicated competitive mechanism between surface-initiated failure and subsurface-initiated contact fatigue failures.To address this issue,a fatigue-wear coupling model of an aviation gear pair was developed based on the elastic-plastic finite element method.The tooth profile surface roughness was considered,and its evolution during repeated meshing was simulated using the Archard wear formula.The fatigue damage accumulation of material points on and underneath the contact surface was captured using the Brown-Miller-Morrow multiaxial fatigue criterion.The elastic-plastic constitutive behavior of damaged material points was updated by incorporating the damage variable.Variations in the wear depth and fatigue damage around the pitch point are described,and the effect of surface roughness on the fatigue life is addressed.The results reveal that whether fatigue failure occurs initially on the surface or sub-surface depends on the level of surface roughness.Mild wear on the asperity level alleviates the local stress concentration and leads to a longer surface fatigue life compared with the result without wear.展开更多
Based on Tanaka and Mura’s fatigue model and Griffith theory for fracture,an energy-equilibrium model was proposed to explain the complex stress effect on fatigue behavior.When the summation of the elastic strain ene...Based on Tanaka and Mura’s fatigue model and Griffith theory for fracture,an energy-equilibrium model was proposed to explain the complex stress effect on fatigue behavior.When the summation of the elastic strain energy release and the stored strain energy of accumulated dislocations reach the surface energy of a crack,the fatigue crack will initiate in materials.According to this model,for multiaxial stress condition,the orientation of the crack initiation and the initiation life can be deduced from the energy equilibrium equation.For the uniaxial fatigue loading with mean stress,the relation between the maximum stress or the minimum stress and the stress amplitude is in agreement with an ellipse equation on the constant life diagram.If the ratio of the mean stress to stress amplitude is less than a critical value-0.17,and the stress amplitude keeps constant,the fatigue crack initiation life will decrease with the increase of the compress mean stress.In this model,the mean stress does not cause damage accumulation with the fatigue cycles in crack initiation.For this reason,the loading sequence of different load levels would induce the cumulative damage to deviate from the Palmgren-Miner cumulative damage rule.The procedure of estimating the damage under random loading is also discussed.展开更多
基金National Natural Science Foundation of China(No.11272082)Fundamental Research Funds for the Central Universities(No.E022050205)the Open Research Fund of Key Laboratory of Fluid and Power Machinery of Xi Hua University,China(No.szjj2013-03)
文摘A modified nonlinear fatigue damage accumulation model based on the Manson-Halford theory was presented,and the new model was developed for fatigue life prediction under constant and variable amplitude loading, which took the effects of the load interactions and the phenomenon of material's strength degradation into account. The experimental data of the 30 Cr Mn Si A and the LY-12 cz from literature were used to verify the proposed model. And from the good agreement between the experimental data and predicted results,we can see it clear that the proposed method can be applied to predicting fatigue life under different loadings.
基金The authors gratefully acknowledge the financial support by the National Natural Sciece Foundation of China under grant No. 10302008the Science Foundation of Heilongjiang Province under project No. A0309.
基金National Key Research and Development Program of China(No.2018YFB1501200)。
文摘In order to solve the problem of insufficient exciting force of equipment for large full-scale wind turbine blade fatigue testing,the influence of gravity on the performance of excitation equipment and fatigue damage evaluation of the different positions of wind turbine blades are analyzed.With the multi-excitation loading in the horizontal direction,the actuator force of the excitation equipment does not need to overcome the gravity of the dynamic mass,which directly outputs the exciting force of the system vibration.The excitation efficiency of the equipment is 77%higher than that of the vertical load.The gravity moment of the horizontal loading mode is perpendicular to the loading direction.That is,the mean load in the flapwise direction is zero.The weight of excitation equipment could replace the tuning mass on the condition that the self-weight of equipment is reduced by the multi-excitation mode,which helps the excitation equipment play the comprehensive function of excitation equipment and tuning mass.At the same time,the gravity moment in the edgewise direction will be decreased by 17.0%22.5%under the multi-excitation horizontal loading mode.In the vertical loading mode,the gravity moment is the mean load,which only increases fatigue damage accumulation by 15.6%.By comparing the role of gravity in the excitation equipment and fatigue damage evaluation,the multi-excitation horizontal loading mode has more advantage to performance the exciting force than the contribution of gravity to the fatigue damage accumulation in the vertical loading mode.Through the fatigue testing of multi-excitation horizontal loading,the potential of excitation equipment is explored,and the problem of insufficient exciting force in large full-scale wind turbine blade fatigue testing will be solved.
基金co-supported by National Natural Science Foundation of China (No. 11072205)College Students' National Innovation Foundation of China (No. 101061323)
文摘By introducing a fatigue blunting factor, the cyclic elasto-plastic Hutchinson-Rice-Rosengren (HRR) field near the crack tip under the cyclic loading is modified. And, an average damage per loading-cycle in the cyclic plastic deformation region is defined due to Manson-Coffin law. Then, according to the linear damage accumulation theory-Miner law, a new model for predicting the fatigue crack growth (FCG) of the opening mode crack based on the low cycle fatigue (LCF) damage is set up. The step length of crack propagation is assumed to be the size of cyclic plastic zone. It is clear that every parameter of the new model has clearly physical meaning which does not need any human debugging. Based on the LCF test data, the FCG predictions given by the new model are consistent with the FCG test results of Cr2Ni2MoV and X12CrMoWVNbN 10-1-1. What's more, referring to the relative researches, the good predictability of the new model is also proved on six kinds of materials.
基金the National Natural Science Foundation of China(No.11272082)
文摘When a nonlinear fatigue damage accumulation model based on damage curve approach is used to get better residual life prediction results, it is necessary to solve the problem caused by the uncertain exponent of the model. Considering the effects of load interaction, the assumption that there is a linear dependence between the exponent ratio and the loading ratio is established to predict fatigue residual life of materials. Three experimental data sets are used to validate the rightness of the proposition. The comparisons of experimental data and predictions show that the predictions based on the proposed proposition are in good accordance with the experimental results as long as the parameters that represent the linear correlativity are set an appropriate value. Meanwhile, the accuracy of the proposition is approximated to that of an existing model. Therefore, the proposition proposed in this paper is reasonable for residual life prediction.
文摘Low cycle fatigue life consumption analysis was carried out in this work. Fatigue cycles accumulation method suitable even if engine is not often shut down was applied together with the modified universal sloped method for estimating fatigue cycles to failure. Damage summation rule was applied to estimate the fatigue damage accumulated over a given period of engine operation. The concept of fatigue factor which indicates how well engine is operated was introduced to make engine life tracking feasible. The developed fatigue life tracking method was incorporated in PYTHIA, Cranfield University in-house software and applied to 8 months of engine operation. The results obtained are similar to those of real engine operation. At a set power level, fatigue life decreases with increase in ambient temperature with the magnitude of decrease greater at higher power levels. The fatigue life tracking methodology developed could serve as a useful tool to engine operators.
基金Supported by the National Natural Science Foundation of China(50975030)
文摘A novel method is presented to evaluate the complicated fatigue behavior of gears made of20Cr2Ni4 A.Fatigue tests are conducted in a high-frequency push-pull fatigue tester,and acoustic emission(AE)technique is used to acquire metal fatigue signals.After analyzing large number of AE frequency spectrum,we find that:the crack extension can be expressed as the energy of specific frequency band,which is abbreviated as F-energy.To further validate the fatigue behavior,some correlation analysis is applied between F-energy and some AE parameters.Experimental results show that there is significant correlation among the Fenergy,root mean square(RMS),relative energy,and hits.The findings can be used to validate the effectiveness of the F-energy in predicting fatigue crack propagation and remaining life for parts in-service.F-energy,as a new AE parameter,is first put forward in the area of fatigue crack growth.
基金This project is supported by National Natural Science Foundation of China(No.59605010,No.59979015)Selected from Proceedings of 2000 the First International Conference on Mechanical Engineering
文摘Firstly, constant amplitude P-S_a-S_m-N_c surface family is established.Secondly, four basic assumptions, i.e., monotonically increasing, non-coupling, separability andnonintersecting of fatigue damage accumulation are proposed from the viewpoint of both damagemechanics and fracture mechanics. Then the individual isodamage D-S_a-S_m-N surface under constantamplitude loading is constructed and the two-dimensional individual Miner's rule is derived.Consequently, the two-dimensional probabilistic Miner's rule (TPMiner) is established and proved fora population subjected to variable amplitude loading. Finally, with successfully experimentverification, TPMiner proves be to very useful and feasible in fatigue reliability theory.
基金the National Natural Science Foundation of China(10802015)the Joint Fund of Natural Science Foundation of Liaoning Province(2015020119)+1 种基金the Liaoning Province Graduate Education and Teaching Reform Research Project(2017)the Liaoning Province Transformation and the Innovation and Entrepreneurship Education Project(2017).
文摘Purpose–In view of the difficulty in determining the key parameters d in the Corten-Dolan model,based on the introduction of small loads,damage degrees and stress states to the Corten-Dolan model and the existing improved model,the sequential effects of the adjacent two-stage load were further considered.Design/methodology/approach–Two improved Corten-Dolan models were established on the basis of modifying the parameter d by two different methods,namely,increasing stress ratio coefficient as well as considering the effects of loading sequence and damage degree as independent influencing factors respectively.According to the test data of the welded joints of common materials(standard 45 steel),alloy materials(standard 16Mn steel)and Q235B steel,the validity and feasibility of the above two improved models for fatigue life prediction were verified.Findings–Results show that,compared with the traditional Miner model and the existing Corten-Dolan improved model,the two improved models have higher prediction accuracy in the fatigue life prediction of welding materials whether under two-stage load or multi-stage load.Originality/value–Because the mathematical expressions of the models are relatively simple and need no multi-layer iterative calculation,it is convenient to predict the fatigue life of welded structure in practical engineering.
文摘The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring forces, which are induced by wave excitation and transferred by the YOKE and the mooring support frame, may cause fatigue damage to the bow structure. Different from direct wave-in duced-forces, the mooring force consists of wave frequency force (WF) and 2nd dr aft low frequency force (LF) [3] , which are represented by two sets of short-term distribution respectively. Based on two sets of short-term distribution of moor ing forces obtained by the model test, the fatigue damage of the bow structure of FPSO is analyzed, with emphasis on two points. One is the procedure and position selection for fatigue check, and the other is the application of new formulae for the calculation of accumulative fatigue damage caused by two sets of short-term distribution of hot spot stress range. From the results distingui shed features of fatigue damage to the FPSO’s bow structure can be observed.
基金This study was co-supported by the National Natural Science Foundation of China(No.51301090).
文摘The nonlinear cumulative damage model is modified to have high prediction accuracy when the high-low cycle stress frequency ratio m is large(m500).The low cycle fatigue(LCF)tests,high cycle fatigue(HCF)tests and combined high and low cycle fatigue(CCF)tests of TC11 titanium alloy were carried out,and the influencing factors of CCF life were analysed.The CCF life declines with the decrease of the ratio of high-low cycle stress frequency m.Both linear and nonlinear cumulative damage models are used to predict the CCF life.The CCF life prediction error of the linear cumulative damage model is great and the predictions tend to be overestimated,which is dangerous for engineering application.The accuracy is relatively high when the high-low cycle stress frequency ratio m500.The accuracy of nonlinear cumulative damage model is higher than that of linear model when the high-low cycle stress frequency ratio m500.Based on the relationship between high cycle average stress rmajor and material yield limit rp,0.2,a correction term is added to the nonlinear cumulative damage model and verified,which made the modified model more accurate when m500.
基金SupportedbytheNationalNaturalScienceFoundationofChina (No .5 9935 10 0 )
文摘Experime ntal research results of surface damage accumulation in rail steel under rolling with slippage are presented. Hertz contact for two rollers made of rail and whe el steels was realized in the test. The influence of loading regime upon wear of rail is considered. The estimation of characteristics of surface fracture resis tance for rail steel is made. The method to predict the life of rail steel under given conditions of regular loading is proposed.
基金The work was supported by the National Natural Science Foundation of China(Grant No.U1864210)the Open Foundation of the State Key Laboratory of Mechanical Transmissions(Grant No.SKLMT-KFKT-201701)Chongqing Research Program of Basic Research and Frontier Technology(Grant No.cstc2017jcyjAX0103).
文摘Rolling contact fatigue(RCF)issues,such as pitting,might occur on bevel gears because load fluctuation induces considerable subsurface stress amplitudes.Such issues can dramatically affect the service life of associated machines.An accurate geometry model of a hypoid gear utilized in the main reducer of a heavy-duty vehicle is developed in this study with the commercial gear design software MASTA.Multiaxial stress–strain states are simulated with the finite element method,and the RCF life is predicted using the Brown–Miller–Morrow fatigue criterion.The patterns of fatigue life on the tooth surface are simulated under various loading levels,and the RCF S–N curve is numerically generated.Moreover,a typical torque–time history on the driven axle is described,followed by the construction of program load spectrum with the rain flow method and the Goodman mean stress equation.The effects of various fatigue damage accumulation rules on fatigue life are compared and discussed in detail.Predicted results reveal that the Miner linear rule provides the most optimistic result among the three selected rules,and the Manson bilinear rule produces the most conservative result.
基金Supported by National Natural Science Foundation of China(Grant No.11572267)Sichuan Science and Technology Program(Grant No.2017JY0216)+1 种基金Open Research Project of State Key Laboratory for Strength and Vibration of Mechanical Structures of China(Grant No.SV2016-KF-21)Open Research Project of State Key Laboratory of Traction Power of China(Grant No.2018TPL_T03)
文摘The brake unit bracket of a bogie frame is an important load-carrying component, particularly under emergency start/stop conditions. Conventional infinite/safe life approaches provide an over-conservative recommendation for the allowable strength and lifetime, which hinders the lightweight design of modern railway vehicles. In this study, to ensure the reliability and durability of a brake unit bracket, an attempt was made to integrate the nominal stress method and an advanced damage tolerance method. First, a complex bogie frame was modelled using solid elements instead of plate and beam elements. A hot spot stress region on the bracket was found under an eight-stage load spectrum obtained from the Wuhan–Guangzhou high-speed railway line. Based on the probability of foreign damage, a semi-elliptical surface crack was then assumed for residual life assessment. The results obtained by the cumulative damage and damage tolerance methods show that the brake unit bracket can operate for over 30 years. Moreover, even if a 2-mm depth crack exists, the brake unit bracket can be safely operated for more than 2.27 years, with the hope that the crack can be detected in subsequent maintenance procedures. Finally, an appropriate safety margin was suggested which provides a basis for the life prediction and durability assessment of brake unit brackets of high-speed railways.
基金The work was supported by the National Key R&D Program of China(Grant No.2018YFB2001300).
文摘The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears.Meanwhile,the coexistence of tooth contact fatigue damage and tooth profile wear leads to a complicated competitive mechanism between surface-initiated failure and subsurface-initiated contact fatigue failures.To address this issue,a fatigue-wear coupling model of an aviation gear pair was developed based on the elastic-plastic finite element method.The tooth profile surface roughness was considered,and its evolution during repeated meshing was simulated using the Archard wear formula.The fatigue damage accumulation of material points on and underneath the contact surface was captured using the Brown-Miller-Morrow multiaxial fatigue criterion.The elastic-plastic constitutive behavior of damaged material points was updated by incorporating the damage variable.Variations in the wear depth and fatigue damage around the pitch point are described,and the effect of surface roughness on the fatigue life is addressed.The results reveal that whether fatigue failure occurs initially on the surface or sub-surface depends on the level of surface roughness.Mild wear on the asperity level alleviates the local stress concentration and leads to a longer surface fatigue life compared with the result without wear.
基金supported by the National Basic Research Program of China (Grant No. 2012CB937500)the National Natural Science Foundation of China (Grant Nos. 11072243 and 11202210)
文摘Based on Tanaka and Mura’s fatigue model and Griffith theory for fracture,an energy-equilibrium model was proposed to explain the complex stress effect on fatigue behavior.When the summation of the elastic strain energy release and the stored strain energy of accumulated dislocations reach the surface energy of a crack,the fatigue crack will initiate in materials.According to this model,for multiaxial stress condition,the orientation of the crack initiation and the initiation life can be deduced from the energy equilibrium equation.For the uniaxial fatigue loading with mean stress,the relation between the maximum stress or the minimum stress and the stress amplitude is in agreement with an ellipse equation on the constant life diagram.If the ratio of the mean stress to stress amplitude is less than a critical value-0.17,and the stress amplitude keeps constant,the fatigue crack initiation life will decrease with the increase of the compress mean stress.In this model,the mean stress does not cause damage accumulation with the fatigue cycles in crack initiation.For this reason,the loading sequence of different load levels would induce the cumulative damage to deviate from the Palmgren-Miner cumulative damage rule.The procedure of estimating the damage under random loading is also discussed.