Cycle Fatigue Life Research Articles

Fatigue reliability assessment and life-cycle cost analysis of roadway bridges equipped with weigh-in-motion systems

The fatigue safety assessment of critical details in steel bridges is dominated by several uncertainties mainly related to load modelling. The use of integrated weigh-in-motion (WIM) systems in roadway bridges allows to collect all the necessary information for tracking actual traffic conditions. Based on WIM data, the uncertainty associated to the evaluation of the probability of fatigue failure is reduced, allowing the optimal scheduling of repair and maintenance activities and thus improving safety and economic savings. The paper presents a methodology for estimating fatigue life cycle cost (LCC) of roadway bridges equipped with a WIM system that considers uncertainties in measurement and modelling errors. The procedure allows the quantification of the economic gain enabled by WIM systems, useful in assessing the cost/accuracy trade-off for a given WIM system. It is found that the continuous use of a WIM system may improve the rate of decrease of the structural reliability index, compared with temporally limited use of WIM data. The periodic update of the reliability index and of the probability of failure based on WIM measurements results in a rather accurate estimation of the fatigue life cycle cost, which is crucial in identifying the payback time of the WIM system.

Cyclic plasticity models and fatigue criteria for exhaust manifold life assessment in the context of limited material data available

ABSTRACT The work focuses on predictive capabilities of fundamental cyclic plasticity and fatigue life models, which can be calibrated using limited amount of experiments as specific ones needed for more advanced models are often absent. The analyses are conducted for the synthetic case of exhaust manifold made from cast iron. The thermal boundary conditions from the forced convection were obtained from the computational fluid dynamics considered as a conjugate heat transfer problem. Two rate-independent and temperature-dependent material models were calibrated for structural analyses. Both were validated with experiments on isothermal and anisothermal levels. Sequential thermal–mechanical finite element simulations were performed. Two fatigue life models were employed. The first was a temperature-dependent strain-based fatigue life criterion calibrated from uniaxial data. The second was a temperature-independent energy-based fatigue life criterion resulting in twice lower life than the strain-based criterion, while none of the plasticity models made a significant difference in that prediction.

Fatigue behavior of modified ZK60 magnesium alloy after pre-corrosion under stress-controlled loading

Three kinds of modified layers were prepared on the surface of ZK60 magnesium alloy (BM) by micro-arc oxidation (MAO), laser shock penning (LSP), and composite of LSP and MAO method. Four kinds of specimens (BM, MAO, LSP, LSP / MAO) were pre-corroded in a simulated body fluid (SBF) with pH7.4 for 12 h. Fatigue tests were performed for non-corroded and pre-corroded specimens under stress-controlled cyclic loading. The cyclic deformation behavior of the specimens at different stress ratios and different stress amplitudes involves four deformation mechanisms: dislocation slip, twinnig-detwinning transfer to dislocation slip, partial twinning-partial detwinning, complete twinning-complete detwinning. The correlation between the cyclic deformation mechanism and fatigue life is discussed using a proposed evaluation parameter, β. The fatigue life of the material decreases with the β values increasing when cyclic deformation is dominated by twinning-detwinning. The proposed total strain energy model can better predict the fatigue life of modified magnesium alloys under different loading conditions.

A comparative analysis of friction stir and tungsten inert gas dissimilar AA5082-AA7075 butt welds

The aluminium alloys AA5082 and AA7075 were welded using friction stir welding (FSW) and tungsten inert gas (TIG) welding. The effect of these two (FSW and TIG) welding processes on the tensile and fatigue properties of dissimilar AA5082-AA7075 butt welded joints were studied. The S-N curve for both, FSW and TIG, joints were established. The results exhibited that the tensile and fatigue properties of dissimilar FSW welded butt joints are better than those of dissimilar TIG welded butt joints. The fatigue strength for FSWed and TIG welded joint is determined as 40 MPa for 106 cycles and 30 MPa for 105 cycles of fatigue life, respectively. The micro-hardness of the joints is also studied for both joints. The hardness for TIG joint is lower than the FSWed joint in the welded zone.

Cyclic deformation behavior and fatigue life prediction of an automotive cast aluminum alloy: A new method of determining intrinsic fatigue toughness

AbstractThe aim of this study was to identify cyclic deformation behavior of a high‐pressure die‐cast Silafont®‐36 automotive cast aluminum alloy consisting of heterogeneous composite‐like microstructures of nearly circular eutectic silicon particles embedded in Al matrix, with particular attention to fatigue life prediction. The alloy exhibited superior fatigue resistance at higher strain amplitudes, where cyclic hardening occurred. The fatigue life of the alloy could be well predicted via a strain‐energy density based accumulative damage model using a new method proposed to calculate the intrinsic fatigue toughness. The predicted fatigue life was in good agreement with the experimental life, and also lay in‐between the results obtained via other methods. Fatigue crack initiation was observed to occur from the sample surface or near‐surface defects and crack propagation was characterized by fatigue striations along with tear ridges in the primary Al‐grains.

Validation of materials-informed digital twin: Mapping residual strains in HSLA steel weldment using high energy X-rays

The shipbuilding industry has placed an emphasis on establishing digital twin prototypes to advance computational lifecycle analysis capabilities. However, material processing data is not currently included in simulations for structural performance, which could lead to inaccuracies. Integrated Computational Materials Engineering (ICME) techniques yield a path to solving this problem through linking digital information across multiple length scales in order to minimize the time and cost of physical testing needed for validation. This paper details the initial work of a larger materials-informed digital twin effort seeking to validate the need for fabrication inclusion in lifecycle analysis. First, the selection and fabrication of the “sister sample” specimens used for physical validation from a single plate of HSLA-100 steel. Second, the finite-element analysis (FEA)-based welding simulations of the reinforced dog-bone weldment. Third, comparison of predicted strain data from FEA simulations to two-dimensional (2D) strain maps using energy dispersive diffraction (EDD) techniques at the Cornell High-Energy Synchrotron Source (CHESS). The results showed high correlation between the measured EDD data and the FEA predictions, particularly for the high strain (>0.0015) fields of first principle strain vectors measured parallel to each welding pass. This computational validation is the first step towards validating the materials-informed digital twin method for increasing accuracy of structural analysis and fatigue lifecycle evaluation.

Analysis of the failure and remedial measures taken after the collapse of a historical bell

This paper describes the collapse analysis of the historical El Jaume bell, cast in 1429, one of the bells in the Cathedral of Valencia’s Micalet bell tower (Spain). In 1992 the yoke was completely restored and given a new steel axis. The failure occurred when the bells were being rung on Christmas Day 2014, fortunately without any casualties. After several field visits to assess the damage and failure ‘‘in situ”, a diagnosis was made of the causes of the failure. The diagnosis was the result of (1) a detailed visual inspection, (2) a metallographic and fractographic analysis of the fractured steel axis, (3) a fatigue damage analysis by finite element modelling software and (4) an estimation of the bell’s remaining fatigue life cycle using Whöler S-N curves. In view of the results obtained it was concluded that the fatigue life cycle should have been reached between 300,000 and 400,000 cycles, while the failure occurred at 346,500 cycles. Although these elements are usually designed to not fail during its life, they can sometimes suffer cracks during cyclic ringing. One of the main causes of the fatigue failure was the incorrect design of the steel gudgeon, which produced a high stress concentration and drastically reduced the fatigue strength at 106 cycles. The paper also describes the remedial measures taken to avoid fatigue failure in the other bells and the lessons that have been learned from the experience.

A 3-D numerical simulation of fatigue crack growth in an alumino thermite welded UIC60 rail joint under different loading conditions

In this article, a UIC60 rail AT weldment with appropriate rail and weld geometry on two-parent rail tracks as per Indian Railways is analysed separately under vertical and lateral loads, applying FEM. Stresses in an alumino-thermite welded rail is measured using finite element analysis. The results of operating condition on the development of fatigue cracks in rail welds are investigated. A 3-D elastoplastic material basis analysis has performed on a CAD assembly model for this purpose. A wheel-rail track model is used to simulate for the allocation of high stresses field in the weldment on the rail under intense service conditions for the welded straight track. Damage mechanics approaches are also used to assess the stress allocation on weld and wheel interaction along with the influence on fatigue lifecycle. The crack's variables like of displacement and stress intensity factors (SIFs) are calculated at crack tip in finite element model to measure crack propagation patterns and the rate of growth, considering two crack and its comparison for different modes. Also the trapped fluid condition due to weather and its influence on crack has been discussed. As friction rate of the contact area between rail weld and wheels increases, formation of crack 1 initiates, and the growth of crack-2 accelerates. Friction of contact patch and the fracture surface have opposite effects on fatigue life. Wet-lubrication are useful for crack friction reduction and can be used as a catalytic factor for SIF on mode II, but this liquid may flow into crack-1 and creates wedge effect. The SIF of opening mode in crack-1 abruptly rises as a result the crack's spread-up, and the fracture becomes deeper. Increasing friction force reduces slip on the fracture crack surfaces, thus reduction in crack propagation. Fracture mechanics fundamentals are used to find the growth of fatigue cracks in weld zone. To measure the progress rate of fatigue crack and SIFs, updated Paris model is used with ANSYS academic.

An investigation on static and fatigue life evaluation of grooved adhesively bonded T-joints

Adhesively bonded joints with T-shaped configurations are widely used in bonded components of engineering structures used in industries such as automotive, aircraft, and marine. In this paper, static strength and fatigue life of two T-joint configurations of flat and grooved types were evaluated. For this purpose, firstly, the effect of the specimen configuration of the bonded T-joints on the stress field has been calculated using the finite element method. For this purpose, a three-dimensional elastoplastic model is used for simulation. Then, static failure load of these joint types was examined under four loading rates of 1, 10, 50, and 100 mm/min. Also, fatigue tests were performed under maximum fatigue loads of 40%, 60% and 80% of average static failure loads. Results indicated that the average static failure load of grooved specimens was 37.3%, 26.5%, 14.4%, and 9.3% higher than that of the flat type T-joints under 1, 10, 50, and 100 mm/min loading rates, respectively. Moreover, fatigue life cycles of grooved T-joints were 40.2%, 25.3%, and 11.6% longer than that of the flat bonded specimens under 40%, 60%, and 80% maximum fatigue loads, respectively. It was also concluded that, under high fatigue loads, the groove effect can be ignored on improving the fatigue life.

Force Controlled Low Cycle Fatigue (LCF) Life Evaluation Methodology Based on Unstabilized Material Properties

Low Cycle Fatigue (LCF) is a prominent failure mechanism in many design components; therefore, an evaluation of cycles to failure in this regime is of high importance. Most international standards recommend a closed loop strain-controlled mode specimen testing in this regime. However, the ꜪN data obtained from this test is not suitable for life evaluation of parts enduring force-controlled history during actual service without correction for control mode. Many existing procedures, which accounts for cyclic strain stabilization during force-controlled loading may significantly complicate the finite elements analysis (FEA) at solving or post processing stages and are often an inherent source of uncertainty. A heuristic, cost effective and sufficiently accurate approach for LCF life estimation is advocated. The method involves only two force loading FEA simulations, one of the actual parts and the other of the test specimen, using initial unstabilized stress strain curve, followed by a limited number of force-controlled specimens testing. Actual part and specimen life correlation performed using first loading unstabilized equivalent plastic strain value Ꜫp1 under locality and similitude assumptions. Unstabilized strain vs. number of cycles to failure curve Ꜫp1N is constructed and discussion regarding specimen geometry considerations for providing sufficient accuracy is included. Method validation and crack propagation study are provided.

Fatigue life analysis of wheel-rail contacts at railway turnouts using finite element modelling approach.

The article deals with wheel-rail contact analysis at railway turnout using a finite element modelling approach. The focus is understanding the wheel-rail contact problems and finding the means of reducing these problems at railway turnouts. The main aim of the work reported in this article is to analyse fatigue life and simulate the wheel-rail contact problems for a repeated wheel loading cycle by considering the effect of normal and tangential contact force impact under different vehicle loading conditions. The study investigates the impact of tangential contact force generated due to different-angled shapes of the turnout and aims to reveal how it affects the life of contacting surfaces. The obtained results show that the maximum von-Mises equivalent alternating stress, maximal fatigue sensitivity, and maximum hysteresis loop stresses were observed under tangential contact force. These maximum stresses and hysteresis loops are responsible for rolling contact fatigue damage, and excessive deformation of the wheel-rail contact surface. At a constant rotational velocity, the tangential contact force has a significant impact on the fatigue life cycle and wheel-rail material subjected to fatigue damage at lower cycles compared to the normal contact force. The finite element modelling analysis result indicated that the contact damages and structural integrity of the wheel-rail contact surface are highly dependent on contact force type and can be affected by the track geometry parameters.

Experimental study and life prediction on fatigue failure of NiTi shape memory alloy under multi-axial one-way shape memory cyclic loadings

In this paper, the thermo-mechanical coupling fatigue experiments of NiTi shape memory alloy (SMA) micro-tubes involving one-way shape memory effect (OWSME) are first carried out under the uniaxial and multiaxial stress-controlled cyclic loadings with some specific loading paths and stress levels. Experimental results show that the OWSME cyclic degradation and fatigue lives of NiTi alloy micro-tubes are dependent on the prescribed loading paths and stress levels; and the multi-axial loadings accelerate the reorientation-induced ratchetting, resulting in more obvious OWSME cyclic degradation in NiTi SMA micro-tubes. Based on the experimental results, the dissipation energy is defined as the damage variable, and the damage evolution equations of mechanical loading and thermal loading parts are established from the correspondent experimental results by considering the influence of loading path. Then, combined with the established failure criterion, the fatigue lives of the NiTi alloy presented during the multi-axial OWSME cyclic loadings are predicted. It is demonstrated that all the predicted lives are located within the twice scatter band, and most of them are within the scatter band of 1.5 times; the predicted lives of the proposed multi-axial fatigue life-prediction model agree with the experimental ones well.

Evaluation of Fatigue Potential for Crumb Rubber Modified Bitumen in Stone Mastic Asphalt Mixes

SMA is a gap graded mix composed of a high concentration of coarse aggregate that is held together in a thick asphalt film by a matrix of mineral filler and stabilizers. Since natural aggregates have become expensive, hence Reclaimed Asphalt Pavement (RAP) can be reused in pavement construction to reduce the environmental hazardous due to disposal problems. Since the RAP contains used aggregates, it is highly prone to fatigue, thermal and reflective cracking effect. Rheological and chemical properties of aged bitumen in RAP can be enhanced by use of untreated waste oils such as waste engine oil as rejuvenators. This research presents a study on fatigue performance of SMA mix with Reclaimed Asphalt Pavement (RAP) materials with and without rejuvenators and results were compared with conventional SMA mix. The materials used were first characterized by common laboratory tests. Then the three SMA mixes are tested using several laboratory test procedures: Marshall Stability, indirect tensile strength, moisture susceptibility, and indirect tension fatigue test. The optimum proportions of the of the mixes with highest stability are selected from the Marshall stability test. The indirect tensile strength test results show that the SMA mix replaced with RAP without rejuvenators showed higher tensile strength ratio and resistance to moisture damage when compared to conventional mix and optimum RAP replacement mix with rejuvenators. The fatigue test was conducted for the three optimum mixes at different temperature and stresses. The fatigue test results showed that at lower temperature and stresses, the RAP replaced SMA without rejuvenator offered better fatigue resistance than those with rejuvenator and conventional SMA mix. At higher temperatures, the RAP replaced SMA mix with rejuvenator offered similar fatigue lifecycle as conventional mix. However, at high stresses, conventional SMA mix offered better fatigue lifecycle. Increase in failure stresses resulted in decrease of number of fatigue cycles and increased in initial tensile strain of the mix. Thus, with the use of RAP substantial decrease in cost can be achieved without compromising the fatigue characteristic of the SMA mix.

Prediction of Cyclic Plastic Strain Energy Density and Fatigue Life of Non-Masing Behavior Materials Without Master Curve

Prediction of Cyclic Plastic Strain Energy Density and Fatigue Life of Non-Masing Behavior Materials Without Master Curve

CORR Insights®: Deep-freezing Temperatures During Irradiation Preserves the Compressive Strength of Human Cortical Bone Allografts: A Cadaver Study.

CORR Insights®: Deep-freezing Temperatures During Irradiation Preserves the Compressive Strength of Human Cortical Bone Allografts: A Cadaver Study.

Crack Growth Prediction on Critical Component for Structure Life Extension of Royal Malaysian Air Force (RMAF) Sukhoi Su-30MKM

The critical aircraft structure, being the load-bearing members, is a vital component for any aircraft. The effect of fatigue loading, operating conditions, and environmental degradation has caused the structural integrity of the airframe to be assessed for its airworthiness requirement. Using the fatigue design concept of Safe Life, the RMAF adopts the Aircraft Structure Integrity Program (ASIP) to monitor the structural integrity of its critical components. RMAF has produced the task card using the engineering analysis concept on the aircraft’s critical structure. Various Computer-Aided Engineering (CAE) methods were used, and for this analysis, the Crack Growth Prediction method was used to determine the crack growth behavior and its ultimate failure point in case of any crack occurrences. Although there are six critical locations, the wing root is chosen since it has the highest possibility of fatigue failure. The analytical methods which were discussed are Crack Growth Analysis and Low Cycle Fatigue. For the numerical method, NX Nastran was used for the simulation of crack growth. The result from the crack growth analysis was validated with the numerical result. The conclusion is that, based on the fatigue life cycle, the wing root structure condition is not affected by severe damage, and its failure is approximately around 30 to 100 years for both the through hole and through side crack. Thus, its structural life can be extended. The research outcome will be on the extension of the structure life of the aircraft wing.

Assessment of thermal fatigue induced by dryout front oscillation in printed circuit steam generator

A printed circuit steam generator (PCSG) is being considered as the component for pressurized water reactor (PWR) type small modular reactor (SMR) that can further reduce the physical size of the system. Since a steam generator in many PWR-type SMR generates superheated steam, it is expected that dryout front oscillation can potentially cause thermal fatigue failure due to cyclic thermal stresses induced by the transition in boiling regimes between convective evaporation and film boiling. To investigate the fatigue issue of a PCSG, a reference PCSG is designed in this study first using an in-house PCSG design tool. For the stress analysis, a finite element method analysis model is developed to obtain the temperature and stress fields of the designed PCSG. Fatigue estimation is performed based on ASME Boiler and pressure vessel code to identify the major parameters influencing the fatigue life time originating from the dryout front oscillation. As a result of this study, the limit on the temperature difference between the hot side and cold side fluids is obtained. Moreover, it is found that the heat transfer coefficient of convective evaporation and film boiling regimes play an essential role in the fatigue life cycle as well as the temperature difference.

Mechanical behavior and fatigue life prediction of fiber metal laminates with inclined edge cracks at elevated temperatures

Mechanical properties and load vs. displacement diagrams, and fatigue life, mechanisms and load vs. cycles curves were received for fiber metal laminates (FMLs) with original and inclined edge cracks at room and elevated temperatures. The mixed mode stress intensity factors and J-integral of cracked FMLs were obtained. The bridging stresses was considered in the modified Paris Law to predict fatigue life of inclined crack FMLs. The predicted results of fatigue life with vertical cracks at room temperature were satisfactorily well. The fatigue life of samples with inclined cracks at elevated temperature the scatter was also acceptable within minor errors.

Fretting fatigue behavior and failure characteristics of 35CrMoA steel under elliptical loading path

Purpose This study aims to understand the multiaxial fretting fatigue, wear and fracture characteristics of 35CrMoA steel under the elliptical loading path. Design/methodology/approach By keeping the contact pressure and torsional shear cyclic stress amplitude unchanged; the axial cyclic stress amplitude varied from 650 MPa to 850 MPa. The fretting fatigue test was carried out on MTS809 testing machine, and the axial cyclic strain response and fatigue life of the material were analyzed. The fretting zone and fracture surface morphology were observed by scanning electron microscope. The composition of wear debris was detected by energy dispersive X-ray spectrometer. Findings In this study, with the increase of axial stress amplitude, 35CrMoA steel will be continuously softened, and the cyclic softening degree increases. The fretting fatigue life decreases unevenly. The fretting scars in the stick region are elongated in the axial direction. The area of fracture crack propagation zone decreases. In addition, the results indicate that wear debris in the slip region is spherical and has higher oxygen content. Originality/value There were few literatures about the multiaxial fretting fatigue behavior of 35CrMoA steel, and most scholars focused on the contact pressure. This paper reveals the effect of axial cyclic stress on fretting fatigue and wear of 35CrMoA steel under the elliptical loading path.

Cyclic fatigue life characteristics of ceramic balls under variable thermal shock loadings

Ceramic balls made of silicon nitride (Si3N4) exhibited excellent mechanical properties are used in high-end components operating at ultra-high speeds, and high and low temperatures. Previously, studies have involved the cyclic mechanical and thermal fatigue tests of ceramic balls under a constant temperature. However, the thermal fatigue characteristics of brittle materials have not been theoretically or experimentally investigated under variable thermal shock loadings to date. Herein, cyclic thermal shock fatigue (CTSF) life characteristics of Si3N4 ceramic balls subjected to single- and two-stage cyclic thermal shock loadings were theoretically and experimentally investigated using a probabilistic model based on slow crack growth concept in conjunction with Weibull distribution. Consequently, the fracture criterion derived from the probabilistic model was related to the linear cumulative damage law (Miner’s rule). Thereafter, the predicted CTSF life of the ceramic balls was compared with the experimental results to validate the proposed probabilistic model. Therefore, the proposed model accurately reproduced the experimental results to a certain extent.