Reliability Analysis Based on a Nonlinear Fatigue Damage Accumulation Model

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.

QoE Assessment and Prediction Method for HighDefinition Video Stream Using Image Damage Accumulation

The accuracy of the traditional assessment method of the quality of experience(Qo E) has been facing challenges with the growth of high-definition(HD) video streaming services.Image display-quality damage is the main factor that affects the Qo E in HD video services through UDP network transmission.In this paper,we introduce a novel objective factor known as image damage accumulation(IDA) to assess user's Qo E in HD video services.First,this paper quantitatively analyzed the effect on user quality of experience by IDA and established a mapping relationship between mean opinion scores and IDA.Furthermore,the probability of image damage caused by compression and transmission were analyzed.Based on this analysis,an objective Qo E assessment and prediction method for HD video stream service that evaluated the user experience according to IDA are proposed.The proposed method can achieve assessment and prediction accuracy on three distinct subjective tests.

Fatigue Damage Accumulation of Steel/rubber Composite

The fatigue damage accumulation of [±20°] laminated steel cord reinforced rubber composite under T-T loading was studied. Results indicate that the increase in the cyclic maximum strain exhibits three-stage tendency in the process of fatigue. The macroscopic fatigue damage initiates from the ends of steel cords in the form of cylindrical crack. Damage propagates along with the increase in crack numbers, the cord/matrix interface debonding and the growth of interply cracks. By using the dynamic creep as parameter, a linear fatigue damage accumulation model was established. This model can be used under dual loading conditions to estimate the residual fatigue life of the specimen.

Damage Accumulation in Rail Steel under Rolling with Slippage and Its Analysis

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.

A new method to predict fatigue crack growth rate of materials based on average cyclic plasticity strain damage accumulation

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.

Interference mechanism and damage accumulation in high-speed cross scratches on hard brittle materials

Precision and low damage grinding of aviation optical elements can effectively improve the overall processing efficiency.The mechanism of high-speed cross scuffing of multiple abrasive particles has become an important factor affecting the forming quality of workpiece.Interaction of abrasive trajectory determines machined surface and subsurface morphology and damage.According to the relative motion trajectory of wear particles on the workpiece surface,a theoretical model of the trochoidal trajectory intersection angle is proposed.High-speed scratches with different cross angles are experimentally obtained to explore the interference mechanism and damage accumulation of cross scratches.The results indicate that the Crack system I and Crack system II,produced by the two cross scratches,are mainly based on the stress principle and the strength principle,respectively.An increase in the damage radius is observed with a decrease in the crossing angle.Furthermore,as the duration of the normal cutting force decomposition curve at the entrance/exit of the intersection increases,the half-peak width also increases.The accumulation of cross-scratch damage promotes the propagation of deep subsurface lateral and median cracks.In other words,damage accumulation and interference mechanism formed by the cross scratches increase the longitudinal depth and lateral length of the damage.

Residual Life Prediction Based on Nonlinear Fatigue Damage Accumulation Model

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.

Fatigue research of metro car body based on operational loads

Purpose–The principle of infinite life design currently directs fatigue resistance strategies for metro car bodies.However,this principle might not fully account for the dynamic influence of operational loads and the inevitable presence of defects.This study aims to integrate methods of service life estimation and residual life assessment,which are based on operational loads,into the existing infinite life verification framework to further ensure the operational safety of subway trains.Design/methodology/approach–Operational loads and fatigue loading spectra were determined through the field test.The material test was conducted to investigate characteristics of the fracture toughness and the crack growth rate.The fatigue strength of the metro car body was first verified using the finite element method and Moore–Kommers–Japer diagrams.The service life was then estimated by applying the Miner rule and high-cycle fatigue curves in a modified form of the Basquin equation.Finally,the residual life was assessed utilizing a fracture assessment diagram and a fitted curve of crack growth rate adhered to the Paris formula.Findings–Neither the maximum utilization factor nor the cumulative damage exceeds the threshold value of 1.0,the metro car body could meet the design life requirement of 30 years or 6.6 million km.However,three out of five fatigue key points were significantly influenced by the operational loads,which indicates that a single fatigue strength verification cannot achieve the infinite life design objective of the metro car body.For a projected design life of 30 years,the tolerance depth is 12.2 mm,which can underscore a relatively robust damage tolerance capability.Originality/value–The influence of operational loads on fatigue life was presented by the discrepancy analysis between fatigue strength verification results and service life estimation results.The fracture properties of butt-welded joints were tested and used for the damage tolerance assessment.The damage tolerance life can be effectively related by a newly developed equation in this study.It can be a valuable tool to provide the theoretical guidance and technical support for the structural improvements and maintenance decisions of the metro car body.

Atomic-Scale Insights into Damage Mechanisms of GGr15 Bearing Steel Under Cyclic Shear Fatigue

Alternating shear stress is a critical factor in the accumulation of damage during rolling contact fatigue,severely limiting the service life of bearings.However,the specific mechanisms responsible for the cyclic shear fatigue damage in bearing steel have not been fully understood.Here the mechanical response and microstructural evolution of a model GGr15 bearing steel under cyclic shear loading are investigated through the implementation of molecular dynamics simulations.The samples undergo 30 cycles under three different loading conditions with strains of 6.2%,9.2%,and 12.2%,respectively.The findings indicate that severe cyclic shear deformation results in early cyclic softening and significant accumulation of plastic damage in the bearing steel.Besides,samples subjected to higher strain-controlled loading exhibit higher plastic strain energy and shorter fatigue life.Additionally,strain localization is identified as the predominant damage mechanism in cyclic shear fatigue of the bearing steel,which accumulates and ultimately results in fatigue failure.Furthermore,simulation results also revealed the microstructural reasons for the strain localization(e.g.,BCC phase transformation into FCC and HCP phase),which well explained the formation of white etching areas.This study provides fresh atomic-scale insights into the mechanisms of cyclic shear fatigue damage in bearing steels.

An Approach to Online Reliability Evaluation and Prediction of Mechanical Transmission Components

New development trends in electronic operating data logging systems enable classification, recording and storage of load spectrums of mechanical transmission components during usage. Based on this fact, the application of online reliability evaluation and reliability prediction procedures are presented. Different methods are considered to calculate reliability, depending on actual load spectrum and a Wohler curve. The prediction of a reliability trend is analyzed by the application of time series models. For this purpose, exponential smoothing model, regression model, and the ARIMA model are considered to evaluate data and predict an decreasing reliability trends during usage.

Investigating fatigue behavior of gear components with the acoustic emission technique

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.

PROBABILISTIC MINER’S RULE IN FATIGUE RELIABILITY

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.

Multi-Excitation Fatigue Testing for Large Full-Scale Wind Turbine Blade

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.

Frame property of unequal storey height with specially shaped columns under cyclic loading

A 1/3-scale reinfored concrete(RC) frame of unequal storey height with specially shaped columns was tested under low frequency cyclic loading.The damage characteristic,bearing capacity,deformation capacity and ductility were analyzed.The restoring force model of the frame was obtained based on the study of the hysteresis curve measured in experiment,and the stiffness degeneration characteristics of every storey of the frame were analyzed.Finally the accumulated damage was analyzed with the damage assessment model.It is shown that the seismic behavior of this frame of unequal storey height with specially shaped columns is generally good,but the bottom of first floor column is a weak part,which should be paid more attention in design,and the restoring force model derived from this experiment can be seen as a valuable guide for design and non-linear finite element analysis for this kind of structure.

Fatigue analysis of the bow structure of FPSO

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.

An improved fatigue life prediction model based on loading sequence

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.

Prediction of combined cycle fatigue life of TC11 alloy based on modified nonlinear cumulative damage model

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.

Experimental Analysis and Damage Modeling of High-Density Polyethylene under Fatigue Loading

In this study,an experimental analysis for determining the fatigue strength of HDPE-100 under cyclic loading is presented.The curve of cumulative fatigue damage versus number of cycles（D-N） was deduced from stiffness degradation.Based on the three stage damage trend,the remaining fatigue life is numerically predicted by considering a double term power damage accumulation model.This model is found to be accurate,both in modeling the rapid damage growth in the early life and near the end of the fatigue life.Numerical results illustrate that the proposed model is capable of accurately fitting several different sets of experimental data.

Accumulated damage process of thermal sprayed coating under rolling contact by acoustic emission technique

The accumulated damage process of rolling contact fatigue （RCF） of plasma-sprayed coatings was investigated. The influences of surface roughness, loading condition, and stress cycle frequency on the accumulated damage status of the coatings were discussed. A ball-on- disc machine was employed to conduct RCF experiments. Acoustic emission （AE） technique was introduced to monitor thc RCF process of the coatings. AE signal characteristics were investigated to reveal the accumulated damage process. Result showed that the polished coating would resist the asperity contact and remit accumulated damage. The RCF lifetime would then extend. Heavy load would aggravate the accumulated damage status and induce surface fracture. Wear became the main failure mode that reduced the RCF lifetime. Frequent stress cycle would aggravate the accumulated damage status and induce interface fracture. Fatigue then became the main failure mode that also reduced the RCF lifetime.

Validation of a particle impact breakage model incorporating impact number effect

This paper presents validation of a particle impact breakage model i.e.Vogel and Peukert model with a focus on the impact number.The Vogel and Peukert model developed based on mechanical and sta-tistical foundation has been widely used in various fields such as mineral engineering and chemical engineering but is barely studied in the application of repeated impact.The selective breakage data in the literature is collected to provide the database for model validation.It has shown that the Vogel and Peukert model is generally applicable to all the breakage cases considering the impact number.The effect of impact number is further elaborated in the population balance model(PBM)whereas the particle dynamics are provided from Discrete Element Method(DEM)simulation of an impact pin mill.The global system analysis of impact number is carried out with the synergic effect from impact velocity.The successful validation of Vogel and Peukert model incorporating the effect of impact number demon-strates its versatility whilst other key parameters such as impact energy and particle size can be considered in parallel.