Shorter Fatigue Life Research Articles

Fatigue Analysis of Long-Span Steel Truss Arched Bridge Part II: Fatigue Life Assessment of Suspenders Subjected to Dynamic Overloaded Moving Vehicles

In a half-through steel arched bridge, the suspenders are the critical load transfer component that transmits the deck system and traffic load to the arch rib. These suspenders are subjected to traffic and environmental vibrations and are prone to fatigue failure, especially for overloaded moving vehicles. This paper aims to study the impact of moving vehicles’ overloaded rate on the fatigue performance of suspenders in a long-span three steel truss arch bridge. Based on the Mingzhu Bay steel arch bridge, a 3D finite element bridge model was first established and seven types of moving fatigue vehicle models were considered. Then the stress amplitude and dynamic response of the suspenders on the middle steel truss arch were studied under a standard, 25%, and 50% overloaded moving vehicles load. Following that, the Miner fatigue cumulative damage theory was employed to evaluate the fatigue life of the suspenders. The results show that the short suspenders in the middle steel truss arch have the shortest fatigue life but can still meet the design requirements under the standard load. However, the fatigue life of the suspenders decreases by 20% and 30% when the overloading rate reaches 25% and 50%. The fatigue life cannot meet the design requirement when the overload rate is 50%.

Fatigue analysis of hot recycled asphalt mixtures with RAP incorporation

Asphalt coatings are the most commonly used in paving services in Brazil, explained by the availability of material and the applicability of the technique. Throughout their service life, pavements are subject to traffic stresses that cause damage to the coating, most commonly fatigue cracking and permanent deformation. Thus, the need for new pavements and the need to perform rehabilitation services result in the generation of waste. Because of this, the allocation of this waste in the pavement was now performed more frequently, like this, and this research aimed to evaluate the fatigue life of hot recycled asphalt mixtures, with the incorporation of RAP (reclaimed asphalt pavement) at 25%, 45%, and 100% as a substitute for part of the materials. The dosing process, which occurred according to the Superpave specification, focused on the analysis of the mechanical behavior of the mixtures in aspects of strength, deformation, adhesion, and cohesion. The results indicated a good performance of the mixtures with proportionality in the values obtained with the incorporation of RAP. Because fatigue is associated with stiffness, mixtures with higher incorporations tended to have a shorter fatigue life. Above all, the results indicated a good mechanical performance, proving the feasibility of the technique in paving works.

A Study of Rolling Contact Fatigue in Bearings with Rolling Elements

Abstract: Excessive noise levels from wheels and brakes, tire wear levels, bearing hub wear, bearing humming, undercarriage noise, and other factors are considered in this study. According to the study findings, better design and fatigue life prediction are urgently needed to prevent accidents. Because the hub assembly on the left side of the vehicle experiences the most deformation and has the shortest fatigue life, the behavior of the wheel hub ball bearing under duty cycle loading conditions affects deformations and bearing life. Keywords: bearing, fatigue life, Wheel hub, duty cycle

Effects of temperature and microstructure on low cycle fatigue behaviour of a PM Ni-based superalloy: EBSD assessment and crystal plasticity simulation

The macro and mesoscale deformation and damage of the PM nickel-based superalloy FGH4098 under low cycle fatigue loading at elevated temperatures were investigated using both SEM/EBSD characterization and crystal plasticity finite element (CPFE) simulations. The results indicate that higher temperature leads to more severe macroscale damage i.e. larger areas of hysteresis loops and shorter fatigue life with transgranular failure mode at both 650 °C and 750 °C. The misorientation parameters derived from EBSD characterization show similar deformation at both temperatures, but more intense localized deformation in the crack initiation region at 750 °C. Based on the accumulated shear-strain energy dissipation density and Fatemi-Socie fatigue indicator parameter, the distribution and evolution of fatigue damage are shown to be strongly affected by local stress–strain state and temperatures, and more severe and homogeneous damage is found at 750 °C. The CPFE simulation results also show higher damage propensity, as indicated by the fatigue indicator parameters used here, in the vicinity of annealing twin boundaries with high difference in elastic modulus.

Low cycle fatigue behavior of wire arc additive manufactured and solution annealed 308 L stainless steel

Wire arc additive manufacturing (WAAM) has attracted much attention for many industrial fields owing to its high productivity and flexibility. However, little is known about the fatigue behavior of WAAM austenitic stainless steel (SS). In this study, microstructural characterization, quasi-static tensile tests, and strain controlled low cycle fatigue tests were carried out on a 308 L SS fabricated by WAAM and solution annealing. Hot-rolled 308 L SS was also studied as a reference material. The quasi-static tensile properties, cyclic deformation behaviors, fatigue lives and fatigue failure mechanisms are comparably investigated and found to be dependent on their distinct microstructures. Compared with the hot-rolled counterparts, the WAAM specimens showed slightly longer fatigue life at relatively high strain amplitudes, but shorter fatigue life at low strain amplitudes, which is attributed to their worse crack initiation, but better crack propagation resistance.

Effect of Heat Treatment on the Cyclic Deforming Behavior of As-Extruded ZA81M Magnesium Alloy

In the present work, the effect of heat treatment on the cyclic deformation behavior of as-extruded ZA81M magnesium alloy was investigated. Two heat treatment conditions were applied to the as-extruded ZA81M alloy: a solution treatment (T4, 653 K for 40 h and quenched with 298 K water) and a solution treatment plus artificial aging (T6, 348 K for 32 h (pre-aging at low temperature) and 453 K for 8 h (the second aging) and quenched with 353 K water). The results showed that the fine second phase precipitated after the aging treatment, the tensile yield strength of the T6-treated specimens increased, and the stress amplitude of T6-treated specimens was always higher than that of T4-treated specimens. The T6-treated specimens had a higher total strain energy density and a shorter fatigue life at a strain amplitude of 0.4%, and a lower total strain energy density and a longer fatigue life at a strain amplitude of 0.8%, compared to the T4-treated specimens. All fatigue cracks of the T4 and T6 ZA81M alloy were initiated at the second phase or along the grain boundary and propagated perpendicular to the loading direction.

An investigation of hygrothermal effect on fatigue behavior of adhesively bonded anchorages for FRP tendon

The present study is concerned with the fatigue performance of the adhesively bonded anchorage for fiber reinforced polymer (FRP) tendons under hygrothermal environment. Series of static and fatigue tests were carried out to investigate the performance aging of the conditioned anchorage. The results show that the increase of the immersion duration and immersion temperature aggravates the fatigue performance's degradation. The tendon slippage is increased and the fatigue life is shortened. The extension of the immersion makes the anchorage’s fatigue life more sensitive to the stress amplitude. The initial stiffness is degraded as well. A decrease of the stress ratio increases the tendon slippage and speeds up the stiffness degradation during cyclic loading, regardless of the moisture conditions. For the specimens suffering from the same immersion conditions, the constant life diagram with a longer fatigue life is always below the CLD with a shorter fatigue life. But the CLDs may become distinctly different for the specimens subjected to different immersion conditions. Under any immersion conditions, it is applicable for the anchorage that the fatigue life can be improved by lowering the stress amplitude or the stress level.

Meshing characteristics and failure analysis of shearer walking wheel considering torsional deformation

The safe and efficient operation of the shearer is the key to coal mining. However, the walking wheel with wear and short fatigue life seriously restrict the improvement of the shearer’s reliability. And the failure effect of torsion deformation is mostly ignored. Therefore, to reveal the failure mechanism of the walking wheel and improve the haulage reliability of the shearer, the meshing model of the walking wheel and pin track considering torsional deformation was established. The meshing characteristics of the walking wheel and the damage mechanism of the tooth surface caused by the axial unbalanced load were analyzed, and the effects of the roll angle, the velocity, and the traction force were discussed. The results show that the peak force is close to the meshing-in area, the stress concentration on the tooth profile of the walking wheel is significant, but the stress distribution in the axial direction of the pin track is uniform; although the roll angle can restrain the meshing impact of the walking wheel, the axial unbalanced load and the wear on the load-bearing side increases with the appearance of the torsional deformation; with the velocity increasing, the stability of the walking wheel with roll angle decreases, the axial unbalanced load intensifies while the safety factor decreases; with the traction load increasing, the load distribution improves, but the bending fatigue strength of the tooth root and the safety factor decrease, and the plastic deformation and wear on the bearing-load side increase. The results provide a reference for exploring the meshing characteristics and failure mechanism of the walking wheel and improving the traction reliability of the shearer.

The relationship between inclusions characteristic parameters and bending fatigue performance of 20Cr2Ni4A gear steel

Common heavy-duty 20Cr2Ni4A gear steel is widely used in industrial systems, but there are still problems with its use, such as materials processing issues and a short fatigue life during use. These drawbacks prevent 20Cr2Ni4A from meeting the quality requirements for heavy-duty gear steel in modern industrial systems. Therefore, in practical engineering application, the fatigue life of steel will be predicted to ensure that the fatigue failure of gear steel will not occur in the normal service process. By analysis of the bending fatigue process of structural steel, researchers found that almost every failure is closely related to the size, location and mechanical state of inclusions in the steel. Therefore, in order to accurately characterize the impact of inclusions on fatigue performance, we first used ASPEX inclusion field detection instrument and nanoindentation analyser to make statistics of all inclusions in the two steels, and the contents, distribution, average size and mechanical properties of inclusions in 20Cr2Ni4A steel were accurately counted. Subsequently, the bending fatigue life of two differently processed steels was tested, and a P-S-N curve was drawn. Then, the fatigue fracture was analysed and four fatigue fracture models were summarized to determine the influence of inclusions in the fatigue process. Based on the models by Nisha S, the effects of the number, area, and types of the inclusions were added as corrections, and a new set of life prediction models was proposed. The model was verified by experiments, and the results have a high accuracy. Thus, this approach can be applied to the prediction of the fatigue life of 20Cr2Ni4A steel.

On the Evaluation of Energy Dissipation at the Beginning of Fatigue

The slope method is a popular energy dissipation estimation method, which ignores the influence of heat exchange. Within the framework of the zero-dimensional thermal diffusion model, this paper presents a calculation method for evaluating the energy dissipation of materials in the initial stage of fatigue, which can be called the optimization method. Different from the slope method, this method takes the influence of thermal boundary conditions into consideration. Numerical simulation showed that the optimization method has the ability to accurately estimate energy dissipation in different experimental environments and is not sensitive to measurement noise. Compared with the popular slope method, the newly proposed optimization method has certain advantages in adaptability to different environments and flexibility in parameter selection. A case study was also carried out to study a high-cycle fatigue life of an aluminum alloy which demonstrated that results predicted by the proposed method matched the experimental data in the range of short fatigue life.

Effects of Wheel-Rail Impact on the Fatigue Performance of Fastening Clips in Rail Joint Area of High-Speed Railway

In order to study the effects of wheel-rail impacts on the fatigue damage of the fastening clips at the rail joints of a high-speed railway, field tests were carried out on the wheel-rail impacts at the rail joints of a high-speed railway in China. On the basis of the track irregularities at the rail joints obtained from field measurements, a nonlinear vehicle-track coupling dynamics three-dimensional (3D) model with consideration of Timoshenko beam elements and a refined finite element model of WJ-8 fastening system were constructed. And combined with the theory of cumulative damage and the method of fatigue analysis, the effects of wheel-rail impact at the rail joints on the fatigue life of fastening clips were analyzed. The results showed that the impacts of the wheel-rail in the joint area caused high-frequency fluctuations in the stress-time curves of the clips, which significantly increased the amplitude of stress cycle and increased a lot of stress cycles, of which the amplitudes were reached at a large level; the clips in the area where a rail joint was located suffered the most serious fatigue damage and had the shortest fatigue life; in the actual operation line, besides the clips in the rail joint area, it is also necessary to be concerned about the fatigue performance of fastening clips near the rail joint area.

Quantification of vertical, lateral, and longitudinal fastener demand in broken spike track: Inputs to mechanistic-empirical design

To address a recent challenge related to broken spikes in premium elastic fastening systems that have led to at least ten derailments and require manual walking inspections as well as build upon mechanistic-empirical (M-E) design principles for future fastening system component design, this paper quantifies the vertical, lateral, and longitudinal fastening system loads under revenue service traffic in a curve that has regularly experienced spike fastener fatigue failures. Previous data has indicated that the high rail of Track 3 experienced the most failures at this location. The data from this investigation sheds light into why failures are more predominant at this location than others and how the vertical, lateral, and longitudinal loads cannot be considered independently. Specifically, while the magnitude of the applied loading was the lowest on the high rail of Track 3, the threshold for failure was also the lowest given the operations at this location led to unloading of the high rail, thus indirectly highlighting the importance of friction within a fastening system. The data also show the high rail of Track 3 was subjected to the highest L/V load ratios and was an outlier in the typical lateral load reversals applied likely leading to spike stress reversals and thus a shorter fatigue life. Finally, based upon the data, it is recommended that to mitigate spike failures, as well as similar fastener challenges in other track types (e.g. rail seat deterioration, etc.) railroads should ensure trains operate close to the balance speed and use fastening system that transfer loads through friction. This study also provides novel data for M-E design of fastening systems.

Fatigue Variability of Alloy 625 Thin-Tube Brazed Specimens

As an advanced heat exchanger for aero-turbine applications, a tubular-type heat exchanger was developed. To ensure the optimum performance of the heat exchanger, it is necessary to assess the structural integrity of the tubes, considering the assembly processes such as brazing. In this study, fatigue tests at room temperature and 1000 K were performed for 0.135 mm-thick alloy 625 tubes (outer diameter of 1.5 mm), which were brazed to the grip of the fatigue specimen. The variability in fatigue life was investigated by analyzing the locations of the fatigue failure, fracture surfaces, and microstructures of the brazed joint and tube. At room temperature, the specimens failed near the brazed joint for high σmax values, while both brazed joint failure and tube side failure were observed for low σmax values. The largest variability in fatigue life under the same test conditions was found when one specimen failed in the brazed joint, while the other specimen failed in the middle of the tube. The specimen with brazed joint failure showed multiple crack initiations circumferentially near the surface of the filler metal layer and growth of cracks in the tube, resulting in a short fatigue life. At 1000 K, all the specimens exhibited failure in the middle of the tube. In this case, the short-life specimen showed crack initiation and growth along the grains with large through thickness in addition to multiple crack initiations at the carbides inside the tube. The results suggest that the variability in the fatigue life of the alloy 625 thin-tube brazed specimen is affected by the presence of the brazed joint, as well as the spatial distribution of the grain size and carbides.

Fatigue reliability evaluation of aging prestressed concrete bridge accounting for stochastic traffic loading and resistance degradation

Fatigue damage accumulation is a critical factor resulting in the failure of prestressed concrete (PC) bridges. The fatigue damage is usually caused by the coupled effect of cyclic vehicle loading and environmental corrosion. This study investigated probabilistic fatigue damage on aging PC bridges considering both stochastic traffic loading and corrosion. A stochastic traffic model was derived based on long-term monitoring data aiming to simulate fatigue stress spectra of critical rebar. The effect of cracks on the fatigue stress spectra was investigated in order to model the fatigue stress state more realistically. A three-stage traffic growth model was established based on traffic volume histories of three highways in China. A fatigue limit state function considering traffic growth and corrosion effect was deduced for fatigue reliability assessment of PC bridges. Numerical results show that the stress amplitude of rebar considering cracks is 1.53 times greater than the rebar with no-cracks, resulting in a decrease of fatigue life by 68 years. In addition, the three-stage traffic growth models lead to 25 years shorter fatigue life than the one considering a linear traffic growth model. Finally, the corrosion effect results in a fatigue life of 44 years. The numerical results provide a theoretical basis for fatigue life estimation and maintenance of aging PC bridges.

Crack growth models for multiaxial fatigue in a ship’s propeller shaft

A premature fatigue failure of a large intermediate propeller shaft in a shuttle tanker is discussed and analyzed. The short fatigue life consists mainly of a crack growth phase. Life predictions are carried out by crack growth modelling based on engineering fracture mechanics. The purpose of the present investigation is to identify the most likely loading modes based on the evolution of the crack propagation. A Linear Elastic Fracture Mechanics Model (LEFM) is applied with the stress intensity factor range entering the Paris law as a key parameter. Existing formulas for the geometry functions are supplemented by more detailed stress intensity factor calculations pertaining to small semi-elliptical surface cracks subjected to stress mode I. Enhanced geometry functions are proposed as a function of the relative crack depth and the crack shape aspect ratio. The ability of the fracture mechanics model to reconstruct the observed crack path and crack shape development is emphasized. Various loading modes and multi-axial stress states are applied to pursue the observed crack behavior. The observed semi-elliptical crack shapes and the shift in crack planes are included in the analysis.

Effects of Stress Amplitude Ratio and Phase Angle on Short Fatigue Crack Behavior and Fracture Mode of EA4T Steel

The loads on railway axles in actual service conditions are complex and variable, which may lead to local changes in the fatigue performance, which then affect the fatigue reliability and safety evaluation results of the components and structures. At present, studies on the short fatigue crack behavior and fracture failure mode of EA4T steel, a common material for high-speed trains, are limited. Therefore, fatigue tests on smooth funnel solid round bar specimens under different stress amplitude ratios and different phase angles were performed. Replica technology was used to record the initiation and propagation information of short fatigue cracks. Due to the homogenous and fine microstructure of all the specimens, the same short fatigue crack behavior was observed regardless of the loading condition. The fracture morphology observed by a scanning electron microscope shows that the cracks initiated on the surface of the specimens, and the specific fracture morphology was exceedingly distinct in each region. In addition, the short fatigue crack growth rate and fatigue life were compared and analyzed. The results show that the stress amplitude ratio and phase angle have a considerable influence on the fatigue life and short crack growth rate of the specimens. The results of this research can provide a reference for practical engineering applications.

A comparative study of thermal fatigue life of Eutectic Sn-Bi, Hybrid Sn-Bi/SAC and SAC solder alloy BGAs

Low melting temperature solders are becoming a hot topic in Pb-free solder studies. Among these solders, SnBi has attracted more attention because it can not only reduce the energy for reflow, but more importantly, increase the reliability of joints by minimizing warpage. In this study, the board-level reliability of the assembly of BGA components was investigated. Three types of assemblies are compared: mixed (hybrid) Sn-Bi/SAC305 assembly, which is made by soldering BGAs with SAC305 solder balls using eutectic SnBi solder pastes so that the low reflow temperature avoids the SAC305 solder joints from being molten; homogeneous eutectic SnBi assembly, which is made with solder balls and pastes that are both eutectic Sn-Bi; and homogenous SAC305 assembly as a control group. An accelerated thermal cycling test shows that homogeneous eutectic SnBi assembly exhibits the best cycling reliability while the mixed assembly has the shortest fatigue life. The failure mechanism of the mixed assembly is also different from the other two types. Based on the experimental fatigue life results, the parameters of constitutive equation of eutectic SnBi are calculated to evaluate the fatigue life of the solder joints. The study shows the better thermal cycling reliability of eutectic SnBi assembly and help predict the fatigue life of different assemblies.

Evaluation of fatigue cracking of hot-mix asphalts containing recycled concrete aggregates coated with waste plastic bottles using thermodynamic parameters

ABSTRACT Coarse recycled concrete aggregates (CRCAs) were used as substitutes in asphalt mixtures. These aggregates have a layer of porous cement mortar on their surfaces that impairs their physical and mechanical properties. Therefore, their surfaces were coated with waste plastic bottles to improve their quality. Fatigue cracking, as a critical failure, in asphalt mixtures containing 0, 15, 30, and 50% coarse recycled concrete aggregate was evaluated using the indirect tensile fatigue test in wet and dry conditions. Also, the adhesion of mixture ingredients (bitumen and aggregates) to each other was determined using the sessile drop test based on the surface free energy concept. According to the results, the asphalt mixes containing CRCA had a higher optimum bitumen content compared to the control mixture. The modified asphalt mixtures had a shorter fatigue life in wet and dry conditions. Furthermore, moisture reduced the fatigue resistance of the control and modified asphalt mixtures, and this rate of decline was greater in the mixtures containing CRCA due to their high absorption.

Low Cycle Fatigue of an Ultrafine Grained AA5083 Aluminum Alloy Composite Produced by Cryomilling

Low cycle fatigue (LCF) properties were investigated for a novel cryomilled AA5083 aluminum composite with duplex coarse and ultrafine grain sizes and reinforced with boron carbide particulates, referred to as trimodal material. Fully reversed cyclic tests were conducted under plastic strain control at plastic strain amplitudes from 0.15 to 0.6 pct using a constant plastic strain rate in a servo-hydraulic testing system. A nonlinear elastic modulus was used to calculate the elastic contribution to the measured total strain. The LCF performance of this trimodal material is compared to previous results for unreinforced AA5083 aluminum alloy with bimodal grain size (85/15 pct CM/UM) and its coarse-grained wrought counterpart, AA5083-H131. Stress response curves for the trimodal material revealed slow hardening until failure associated with the presence of particulate reinforcements. The very small asymmetry between tension and compression stresses reflects a lack of strain localization beyond the initial cycles. The trimodal and 85/15 pct CM/UM alloys have similar and superior low cycle fatigue strength compared to AA5083-H131. From the Coffin-Manson plot, the trimodal material has a shorter fatigue life than 85/15 pct CM/UM alloy and AA5083-H131 for high plastic strain amplitudes, but nearly identical life at low amplitudes. Microcracks were observed near the dominant crack on trimodal specimen surfaces at failure. Back-scattered images revealed that particulates altered the crack propagation direction; cracks nearly always propagated around particulates.

Experiment on Corrosion Fatigue Life of Steel Strands under the Coupling Effects of Chloride Environment and Alternating Loads

Corrosion pits will lead to local stress concentration on the surface of steel strands and even shorter fatigue life and worse mechanical properties of steel strands. In order to explore the corrosion mechanics of steel strands to predict the fatigue life, accelerated salt spray corrosion test is carried out to simulate the corrosion laws of steel strands and record the changes of the corrosion degrees during the experiment, considering the coupling effects of alternating loads and chloride environment. Besides, the impact of stress amplitudes on the corrosion degrees of steel strands is quantitatively studied by the corrosion weight loss, and corroded steel strands in experiment are graded according to the corrosion weight loss to test the mechanical properties, respectively; the results show that the corrosion weight loss and tensile strength of steel strands obey the exponential distribution, and the relationship with elongation is linear. In addition, the relationships between the stress concentration coefficient and the pit length, width, and depth are obtained; with the three-dimensional linear regression theory, the accuracy of the regression model is verified by t-value test, laying a foundation for predicting the corrosion life of the cables.