Relative Fatigue Life Research Articles

Effect of stick and slip zones on fatigue life of a slewing ball bearing

Prediction of fatigue life of slewing ball bearings is challenging due to the influence of large deformations and adverse lubrication conditions. The present study presents an elegant simulation model that considers the flexibility of the supporting elements of the slewing bearing along with stick/slip zones at the raceway-ball contact interface. Using the stresses predicted by the simulation model, relative fatigue life using stick/slip condition versus no-friction condition is computed. A sensitivity study of the ball contact force, ball contact angle, coefficient of friction and raceway conformity is also performed. The present study also evaluates the results in comparison with full-sliding assumptions. The final results show that the stick/slip zone determination at the contact interface is beneficial for accurate determination of fatigue life of slewing bearings.

Mechanical Properties of Carbon Fiber-Reinforced Plastic with Two Types of Bolted Connections at Low Temperatures.

Carbon fiber-reinforced plastic (CFRP) is frequently utilized as a bolted joint material in aircraft applications because of its high specific strength and specific modulus. Therefore, the performance of CFRP under -50° is significant. Here, we discuss the specimens of two bolted connections (single-nailed and double-nailed) used for static load tensile and tensile fatigue tests. We obtained the failure curves and fatigue life relationships of the specimens with two different connection methods at different tightening torques (2 N/m, 4 N/m, and 6 N/m) and low room temperatures. Our analysis reveals the effect of the bolt tightening torque and temperature on the structural mechanical properties of a CFRP bolted joint. It provides a data reference for researchers to design a composite bolted joint structure in an airplane flight environment.

Matching relationship of low-cycle fatigue life and fatigue design method of concentrically braced frames with H-section steel

Simulations on 192 concentrically braced frames with H-section steel (Q355B) are carried out to investigate their low-cycle fatigue performance. The fatigue life of a steel-braced frame is predicted using a multiaxial fatigue damage parametric model. To depict the fatigue failure sequence and the matching relationship of the fatigue life between the two components in the braced frame, the fatigue life ratio (β) is introduced. This ratio represents the gusset plate's fatigue life to the brace's fatigue life. Simulated results are analyzed, and β is found to be positively correlated with four influencing factors, the width-to-thickness ratio of the brace flange, connection coefficient, ratio of the column length to beam length, and slenderness ratio of the gusset plate. Also, β is found to be negatively correlated with the slenderness ratio of the brace. Based on the Bayesian updating method, a probabilistic model is formulated to predict β of a steel-braced frame. Accordingly, a fatigue design method is proposed, which contributes to avoiding the in-coordination of seismic capacity caused by the significant difference between the brace’s and gusset plate’s fatigue life within the steel braced frame. The proposed fatigue design method has the potential to serve as a reference for improving design specifications.

Finite element validation and model updating of beam in agricultural mower for fatigue assessment

Agricultural disc mowers are used to cut crops in the field and are exposed to cyclic loading during their lifetime. A cutterbar is an essential part of a disc mower and consists of multiple parts welded together. This paper aims to develop a finite element model of a cutterbar, which can be used for fatigue assessments of the welded joints. A quasi-static experiment has been performed to validate the finite element model based on strain measurements. The finite element model has been updated using a parameter based method as several discrepancies were observed. The updated model reduces the mean absolute error of strain values from 7.5 % to 4.7 %. The hot spot approach has then been used to analyze three different weld locations on the cutterbar. The fatigue criterion by the International Institute of Welding has been used to determine the relative fatigue lives of the weld locations. The back weld is shown to be most exposed, which fits well with results from prior experiments.

Load response and fatigue life of cement-stabilized macadam base structure considering dynamic and static load differences and tension-compression modulus differences

The conventional semi-rigid base asphalt pavement (SRBAP) construction is designed with the classical theory of linear elastic mechanics. There is a significant discrepancy between the calculation results of the pavement structure load response and the measured results, which leads to inaccurate structural resistance and load response calculations. For this reason, this work depended on the actual structure of the SRBAP, took the linear elasticity theory as a contrast, and considered the difference between dynamic and static loads or the difference between the compressive and tensile modulus of pavement materials. Thus, the pavement structure response to load under three conditions is calculated, and five mechanical indexes are selected for comparative analysis. Furthermore, based on the calculated mechanical response, the structural fatigue life of the cement-stabilized macadam (CSMB) was then calculated, replacing the design index in the fatigue cracking model with the underside tensile stress or equivalent stress. The results demonstrated 20–30% variations between the calculated mechanical responses to dynamic and static stresses. Additionally, there is a substantial discrepancy between the strain computed using the bimodulus theory and the traditional linear elasticity theory, with a maximum divergence of 40%. In the meantime, the fatigue life of the CSMB produced using various design indices is noticeably different, and the fatigue life achieved using equivalent stress as the design index is significantly higher than that obtained using underside course tensile stress. Following is a relationship between the CSMB's fatigue life calculated by underside course tensile stress: viscoelastic theory (dynamic load) > bimodulus theory (tension–compression modulus difference) > classical linear elastic theory; The relationship of fatigue life represented by equivalent stress is as follows: viscoelastic theory > classical linear elastic theory > bimodulus theory.

A numerical study of fatigue life in high-speed angular contact ball bearings with thermal and centrifugal expansion

PurposeFix-position preloading, centrifugal force and higher temperatures cause the bearing units in angular contact ball bearings to expand, changing the contact load and affecting bearing life. This study aims to examine the effect of thermal and centrifugal expansion on the fatigue life of fix-position preloaded angular contact ball bearings in high-speed operating conditions.Design/methodology/approachThe contact loads on the inner and outer bearing rings were resolved according to the thermal and centrifugal expansion factors in the quasi-static position preloading model. The pressure and frictional stress distribution were used to calculate the subsurface stress in the contact area, while the Zaretsky model was used to determine the relative fatigue life of the inner and outer bearing rings.FindingsUnder fix-position bearing preloading, thermal and centrifugal expansion significantly affected the contact load and relative fatigue life. At the same axial preload, the inner ring contact load was higher than the outer ring contact load, with a maximum difference of 132.3%. The decrease in the inner ring relative life exceeded the outer ring contact load, with a maximum difference of 7.5%, compared to the absence of thermal and centrifugal expansion.Originality/valueThis study revealed the influence of thermal and centrifugal expansion on the fatigue life of angular contact ball bearings in high-speed service conditions.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0065/

Effect of negative Poisson’s ratio architecture on fatigue life and output power of flexible wearable thermoelectric generators

The negative Poisson’s ratio (NPR) structure is the typical metamaterial structure that has excellent mechanical performances and other functional properties. This paper employs the NPR structure to improve the fracture resistance and flexibility of the wearable thermoelectric generator (TEG). The analytical models of the fatigue life and power output of the NPR-TEG for powering the wearable electronics are proposed. Effect of the wearing position of the generator on the human body on the fatigue life is evaluated. It is found that the fatigue life of the traditional TEG is greatly enhanced by employing the NPR structure. Fatigue life of the NPR-TEG decreases with the thickness of the cell wall and the angle. The relative fatigue life between the NPR-TEG and the traditional TEG hardly varies with the wearing position of human body. The power output of the NPR-TEG is inversely linear proportional to length and number of the fatigue crack. The obtained results can be used to optimize and predict the fatigue life of the flexible wearable thermoelectric devices.

Investigation of the fatigue life relationship among different geometry combinations of the 3-point bending cylinder (3PBC) fatigue test for asphalt concrete

ABSTRACT Laboratory testing is widely used to characterise fatigue properties of asphalt mixtures for the design of asphalt pavements. The recently introduced Three-Point Bending Cylinder (3PBC) test has proven to be an advantageous laboratory testing alternative. However, the standard sample size for the 3PBC test may hamper its use for testing as-built thin lifts of asphalt pavement. In this study, the potential to alter the sample size for 3PBC test was investigated. Various numerical techniques were explored to relate the fatigue performance in terms of the number of cycles to failure (Nf) among varying specimen diameters. In addition to Nf of the tested 3PBC sample diameter Nf (Di), strain level; 3PBC test sample diameter Di; and dynamic modulus |E*|; were selected as input variables to correlate with the Nf for the reference geometry Nf(D.R.). Initially, multi-linear regression (MLR) analysis was applied to inspect if any cogent relation could be achieved among the Nf values for different 3PBC sample diameters. In addition, multigene genetic programming (MGGP) and artificial neural network (ANN) analyses were performed to check if a better fit could be achieved. Both these techniques, however, revealed similar statistical results to the MLR model, with the ANN model achieving higher statistics.

Fatigue Behavior of an AM50 Die-Casting Alloy Anodized by Plasma Electrolytic Oxidation.

While an anodizing process is essential for magnesium alloys to be used under corrosive environments, it sometimes stimulates a fatigue fracture that initiates at the interface between the coating layer and the substrate. In this study, a plasma electrolyte oxidation (PEO) technique was employed to provide excellent adhesion between the anodizing layer and the AM50 die-cast by applying an extremely high dielectric discharge in an alkaline phosphate electrolyte, and its effect on corrosion and fatigue behaviors was investigated. The stress intensity factor at the fatigue limit was estimated to be 0.28 MPam0.5. The specimen anodized using the PEO technique exhibits enhanced strength and corrosion resistance compared to the unanodized counterpart. Furthermore, it shows a relative fatigue life in spite of the thick anodizing layer because the crack initiates from the interface, not from the pore near the interface.

Experimental Study of Fatigue Damage Accumulation in Laminated Carbon Reinforced Fiber Plastics

It is necessary to achieve high fatigue strength in order to apply carbon reinforced fiber plastics (CRFP) for critical elements subjected to vibration. Gradual accumulation of fatigue damage is accompanied by changes in the material stiffness and natural frequencies. The purpose of this work is to found experimental data on the change of the elastic characteristics of layered CRFP as fatigue damage accumulates. The object of the study is standard samples made of unidirectional carbon/epoxy fiber with different layering schemes. The samples were subjected to fatigue tests under cyclic tension with constant amplitude. The test of each sample was stopped several times at different loading stages to execute experimental modal analysis and non-destructive inspection of the appeared defects. The found natural frequencies were used to solve the inverse problem of identifying the elastic parameters of the laminate monolayer: two Young’s modulus, shear modulus and Poisson’s ratio. As a result, the dependences of these parameters on the relative fatigue life were obtained. These dependences, together with the results of non-destructive testing, can be used to describe the process of fatigue damage accumulation and for the subsequent development of methods for the fatigue life prediction.

Investigation on stress microcycles and mild wear mechanism in gear contact fatigue

AbstractGear contact fatigue is becoming a primary limitation for the growing demand of power density and service life in gear‐driven equipment. The unchecked surface fatigue crack could further cause premature failure and put a serious risk to the safety and reliability of mechanical systems. In this work, an attempt is made to investigate the effects of rolling‐sliding and mild wear on contact fatigue behavior. A contact model is developed to capture the variation of instantaneous pressure and stress field, which are calculated with the transient mixed elastohydrodynamic lubrication (EHL) approach. Rolling‐sliding contact is simulated with the time‐varying roughness topography, which is updated by Archard wear equation. The stress cycles are extracted, and the relative contact fatigue life is obtained by using the Zaretsky criterion. Results suggest that in rolling‐sliding contact, the contact fatigue life is obviously lower compared with pure rolling. The increases in the number and amplitude of stress microcycles is found to be the main contributors to the reduction of fatigue life. Mild wear tends to smooth the surface, subsequently mitigates the stress concentration, and reduces stress cycles, and then decreases the risk of surface contact fatigue.

Degradation of elastic characteristics of the CFRP used in the design of a gas turbine engine as a result of high-cycle fatigue damage

Carbon fiber reinforced polymers (CFRP) are increasingly being used in heavily loaded parts of aircraft engines. CFRP fan blades, vanes must successfully resist fracture due to high-cycle fatigue. One of the consequences of fatigue damage is a decrease in the rigidity of the material and a drop in the natural vibration frequencies of parts. These effects are of interest when developing fatigue fracture models and predicting durability. The purpose of this article is to develop a method and obtain experimental data on the decrease of elastic characteristics of CFRP as a result of progressive fatigue damage. The developed technique consists of two stages. During the first one, the natural frequencies and eigenmodes of the samples during their fatigue testing are experimentally obtained. During the second stage, the four elasticity parameters of the CFRP laminate monolayer are identified via the natural frequencies. The inverse numerical/experimental technique for material properties identification is applied. The dependences of elastic characteristics on the relative fatigue life are obtained as experimental results of both modal and fatigue tests. The results can be useful in studying the fatigue behavior of the examined materials and in creating methods for calculating fatigue life.

Change of the Elastic Characteristics of a Fiber-Reinforced Laminate as a Result of Progressive Fatigue Damage

It is a widely known fact that the stiffness of polymer composite materials decreases with the accumulation of fatigue damage under cyclic loading. The purpose of this article is to develop a method and obtain experimental data on decrease of the elastic characteristics of a fiber-reinforced laminate, as a result of progressive fatigue damage. The developed technique consists of two stages. At the first one, the natural frequencies and eigenmodes of the samples during their fatigue testing are experimentally obtained. The dependences of the natural frequencies of the samples on the number of loading cycles are found. At the second stage, the four elasticity parameters of the laminate monolayer (two Young modules, the shear module and Poisson's ratio) are identified via the natural frequencies. The inverse numerical/experimental technique for material properties identification is applied. The dependences of the natural frequencies and mentioned elastic characteristics on the relative fatigue life are obtained as experimental results of both modal and fatigue tests. The results can be useful to study the fatigue behavior of the investigated materials and to create methods for calculating fatigue life.

Fatigue behaviour of conventional and rubber-modified gap-graded asphalt mixtures using bending and axial fatigue tests

ABSTRACT The study presented in this paper assesses and compares the laboratory fatigue performance of two gap-graded asphalt concrete (AC) mixture: one using crumb rubber (CR) (rubber-modified) and without using CR (conventional). The rubber-modified and conventional gap-graded mixtures were sampled from the E18 highway located in the Stockholm area of Sweden. The testing program consisted of dynamic modulus, |E*|, bending beam, and axial fatigue tests. The |E*| master curves of the respective AC mixtures and their generalised fatigue model coefficients (k 1, k 2, k 3) from the axial fatigue tests were used to predict and compare the long-term pavement performance of each mixture using the AASHTOWare Pavement ME Design software. This analysis was performed systematically using parametric variations to assess the sensitivity of the predicted performance to individual material factors. Fatigue test results from both bending beam and axial fatigue tests showed clear evidence of improved fatigue behaviour for the rubber-modified gap-graded mixture compared to the conventional gap-graded mixture. The Pavement ME design analysis showed that the rubber-modified gap-graded mixture outperformed the conventional mixture. The parametric sensitivity analysis showed that this improved behaviour was the result of an increase in k 1 and decrease in k 2 of the fatigue life relationships at individual test temperatures of the rubber-modified gap-graded mixture. It was also found that the |E*| and the fatigue coefficient k 3 of the rubber-modified gap-graded mixture has an adverse impact on its fatigue performance compared to that of the conventional gap-graded mixture.

Determination of wind farm life consumption in complex terrain using ten-minute SCADA measurements

Measured ten-minute mean turbine performance characteristics are used to characterize the turbulence within wind farms. A neural network is trained to reproduce turbulence at each mean wind speed, given the ten-minute mean power production, blade pitch angle and rotor speed. The predicted turbulence from the neural network is verified using simulated wind turbulence that is input to aeroelastic simulations. The neural network is further trained to predict loads time series, given SCADA input time series. The load predictions are validated using an instrumented turbine. Based on the verified ability to predict wind turbulence and loads, the methodology is extended to reproduce loads on the blade and tower of wind turbines within wind farms in complex terrain. The input to the neural network is reduced to only the ten-minute mean measurements from the wind turbines, which are converted to 10-minute time series using Principal Component Analysis (PCA). The output of the neural network is the load time series, which are processed to damage equivalent loads. The standard deviation of measured power is used as a proxy for loads, to validate the predicted damage equivalent loads. The methodology is shown to provide a useful indication of relative fatigue life consumption within the wind farm, even when only mean SCADA measurements are available.

Experimental study on interface bonding fatigue behavior of C-FRCM composites in ICCP

This paper mainly deals with interface fatigue behavior of Carbon-Fabric Reinforced Cementitious Matrix (C-FRCM) composites in Impressed Current Cathodic Protection (ICCP) system. Fatigue pull-out tests were launched on a total of 18 C-FRCM composites. Two bonding lengths of 60 and 125 mm, three current densities of 0, 100 and 150 mA/m2 and three cyclic stress ratios of 0.55, 0.65 and 0.75 of the specimens are considered. The interface slip versus cycle number and load amplitude versus fatigue life relationships of the specimens are presented. The interface stiffness and its damage evolution are further analyzed with simplified models, wherein key parameters are calibrated against experimental results. It is found that C-FRCM composites with higher stress ratio showed less fatigue life due to a pre-matured damage accumulation. The interface fatigue performance at high stress level significantly varied when it suffered from different current densities in ICCP system. A linear relationship between the load amplitude and common logarithms of the cycle number is found for C-FRCM composites in the fatigue pull-out tests. Moreover, the relationship between the fatigue damage index at the carbon fiber (CF) yarn-cementitious matrix interface and cycle number is tri-linear. The damage mainly developed at the early stage and the cycle number in the stable damage development stage accounted for great proportion of the whole fatigue life for the C-FRCM composites.

Flexural fatigue properties of a polyvinyl alcohol-engineered cementitious composite

The flexural fatigue properties of a recently developed polyvinyl alcohol-engineered cementitious composite (PVA-ECC) using local dune sand were investigated. Fatigue flexural tests were conducted under a four-point bending setup. Normal concrete beams were also tested as a benchmark. To determine the stress range versus fatigue life relationship, five and four stress ranges were applied to the PVA-ECC and the normal concrete specimens, respectively. It was found that, compared with normal concrete specimens, the PVA-ECC specimens showed much superior flexural fatigue performance in terms of fatigue strength and deformation capacity, with a more ductile failure mode. Furthermore, typical fatigue performance indicators of the PVA-ECC specimens, including evolution of the midspan deflection, total crack mouth opening displacement, crack width and crack depth of the critical crack that led to final failure, with number of cycles as well as total dissipated energy, were recorded and compared with those of normal concrete specimens. It was observed that the PVA-ECC specimens tested under a stress range of 3 MPa (32% of the flexural strength) did not fail by fatigue after 5·6 million cycles; subsequent static tests demonstrated that they still had good residual flexural properties, including residual flexural strength, deformation capacity, stiffness and energy absorption capacity.

Experimental Investigation on the Effect of Shot Peening and Deep Rolling on the Fatigue Response of High Strength Fasteners

Shot-peening and deep rolling are mechanical surface treatments that are commonly applied to enhance the fatigue performances of components, owing to their capacity to generate compressive residual stresses and induce work hardening. However, literature is still poor of published data concerning the application of these treatments to high strength steels fasteners, although these represent a class of components among the most widespread. In the present work, the impact of deep rolling and shot-peening performed in the underhead radius of two set of fasteners made of 36NiCrMo and 42CrMoV for fatigue life enhancement has been investigated. The experimental tests consisted of six combinations of shot-peening and deep rolling, including the non-treated state. Two test campaigns have been sequentially carried out with different process parameters and treatment sequences. The results always showed a beneficial impact of the deep rolling on fatigue, especially for the 42CrMoV steel. Conversely, the effect of the shot-peening strongly depended on the selected set of parameters, alternatively leading to an improvement or a worsening of the fatigue life in relation to the level of induced surface roughness.

A fatigue life prediction method from magnetic pole material to simulation part

Due to the higher reliability needs of the large moving component motor-generator rotor, the assessment of the service life has drawn more and more attention. After finite element analysis of the rotor, the simulation part which can represent the magnetic pole with the most dangerous position of the rotor was designed to investigate the S–N curves. Compared with the conventional specimen, considering the main influencing factors of fatigue life for simulation part, the comprehensive factor was proposed to establish the fatigue life relationship between magnetic pole material and simulation part. It was found that the calculation method of fatigue notch factor based on the notch sensitivity factor is relatively simple and practical, and there is no significant effect of surface roughness on high and low cycle fatigues for low roughness ( R a is about 1 µm), and the dimension factor changes linearly with the scale factor. Based on those results, a fatigue life prediction method was proposed and validated, and the predicted results were in good agreement with the experimental data. This study will provide a reasonable reference to determine the fatigue life prediction of large moving components.

Mechanisms of interior crack initiation in very-high-cycle fatigue of high-strength alloys

Tension-compression and tension-tension fatigue tests were conducted on a high-strength steel and a titanium alloy in the very-high-cycle fatigue (VHCF) regime. A shared interior crack initiation mechanism for high strength steel and titanium alloy was proposed based on the common nanograins and facet formation, i.e., (i) cleavage of local brittle microstructure; (ii) gradual growth of originated cracks (facets), and the coalescence of adjacent facets, facets disappear and nanograins form for the cyclic pressing in the cases of tension-compression fatigue and (iii) coalesced crack forming a main crack. The experimental results indicate that the stress ratio magnitude has a substantial effect on the fatigue strength, which decreases with the increasing of stress ratio. The tendency of the S-N curves from low cycle fatigue to VHCF regime is similar for the high-strength steel and the titanium alloy with different stress ratios. It is shown that the relationship of fatigue strength, fatigue life, inclusion size and stress ratio in the VHCF of high-strength steel and Ti-6Al-4V are correlated by the Sun model. The predicted results are in good agreement with the experimental data.