Добірка наукової літератури з теми "Fatigue lifespan"

AbstractThe aim of the study is to compare flexible pavement design lifespans and the main factors which create their values for a standard structure and one with an anti-fatigue course AF at different parameter values of pavement and its load, relevant to their design processes. Depending on the mixture used for the anti-fatigue course or the course thickness, durability improvement of the pavement (compared to the durability of a standard structure) can be obtained by extending the design lifespan of the asphalt base course or by extending the design lifespan of the AF course. On sections with predominantly slow traffic, the lifespan decreases significantly compared to sections with typical vehicle speed - the relative decrease is greater if anti-fatigue course is applied.

In this paper, an efficacious and accurate method for analyzing random vibration and fatigue lifespan of coaches with high degrees of freedom is developed. Based on the design requirements for structure strength and fatigue lifespan of a coach, the finite element model of its body structure was used to investigate the dynamic behavior of the coach running on a randomly uneven road. The vibration characteristic was derived using the pseudo excitation method (PEM). The fatigue lifespan is discussed by means of the Miner rule, and the fatigue resistance is also studied. The reliability of the proposed method is numerically verified.

Bridge cables under traffic loads are more prone to failure during the service life due to the corrosion–fatigue coupling effect. In this study, a novel lifespan model based on the equivalent initial flaw size (EIFS) theory is established to analyze the various stages of the lifespan of steel wires. Additionally, a comprehensive corrosion-fatigue lifespan calculation method for parallel steel wire cable is established based on the series–parallel model. A case study of the Runyang Suspension Bridge is conducted to evaluate the evolution of corrosion-fatigue damage in bridge cables during the service life. The results indicate that under the action of corrosion-fatigue, steel wires are more prone to crack initiation, and their fracture toughness is further reduced. In cases where the corrosion level is relatively low, the steel wires of the bridge cables experience no corrosion-fatigue fracture. When the steel wires have initial defects and are subject to corrosion-fatigue conditions, their fracture lifespan is dependent on the severity of the corrosive medium. The reduction in the service life of the cables under the corrosion environment is much greater than that under heavy loads. This research may contribute to the understanding of corrosion-fatigue damage in bridge cables, involving assessment, maintenance, and replacement for bridge cables.

Abstract The fatigue properties of conventional and hydrostatic extruded AZ80 Mg alloy were fully studied under strain-controlled mode. The hydrostatic extrusion can effectively increase the tensile strength, but decrease the elongation. Consequently, the low cycle fatigue lifespan of the hydrostatic extruded specimens was shorter than that of the conventional extruded ones. The Manson-Coffin-Basquin relationship was adopted to describe the fatigue lifespan of the extruded AZ80 alloys. Finally, the fracture surfaces were observed by scanning electron microscope. The fatigue crack stable propagation zone of the hydrostatic extruded sample has decreased significantly compared with that of the conventional extruded sample. The hydrostatic extruded specimen has small reverse plastic zone size, which leads to microscopically rough fatigue crack propagation zone.

The spectrum of stresses at a hazardous point on bearing metal structures of mining, road-building and transporting machines, as a rule, is random by nature. Objective complexity of the fatigue process and variety of fatigue crack nucleation mechanisms are the main causes of errors in prediction of their lifespan, along with an experimentally untestable hypothesis of linear summation of damages. The method of complete stress-strain diagrams uses a representative parameter of the fatigue process, selected in accordance with the results of testing, carried out on trained thin specimens of a specific material. The summation of fatigue damages is based on experimental kinematic curves, whose intersection with a load vector is used as a criterion of fatigue failure. It is shown that the approach proposed to calculate the lifespan gives certain advantages, as far as individual properties of the material are concerned, and when it comes to describing the kinetics of the fatigue process and determining the limiting state of the material in a structure.

In this paper, the fatigue response of fused filament fabrication (FFF) Acrylonitrile butadiene styrene (ABS) parts is studied. Different building parameters (layer height, nozzle diameter, infill density, and printing speed) were chosen to study their influence on the lifespan of cylindrical specimens according to a design of experiments (DOE) using the Taguchi methodology. The same DOE was applied on two different specimen sets using two different infill patterns—rectilinear and honeycomb. The results show that the infill density is the most important parameter for both of the studied patterns. The specimens manufactured with the honeycomb pattern show longer lifespans. The best parameter set associated to that infill was chosen for a second experimental phase, in which the specimens were tested under different maximum bending stresses so as to construct the Wöhler curve associated with this 3D printing configuration. The results of this study are useful to design and manufacture ABS end-use parts that are expected to work under oscillating periodic loads.

This article combines with finite element method and the rain flow count method, which is using the nominal stress method developed a wind turbine used for structural fatigue analysis method, with 2.0 MW wind and machine hub to analyze the fatigue, calculated the operation lifespan fatigue load of wind turbine in the 20 years. By choosing the hot point of hub, analyzes the wheels fatigue damage characteristics. The calculation results show that: the selection of hot point wheels meet with the requirements of GL standard Fatigue design. This paper can be used in large wind turbine development design and in the process of production design authentication.

More and more pressure is exerted on railway infrastructure due to an increasing transportation demand and population density. Instead of expanding the net, a possible solution could lie in the enlargement of the capacity by operating longer trains rather than more short ones. However, close attention has to be paid to the behaviour and the lifetime of the infrastructure under these changed loads. In special bridges are delicate aspects in this matter. In the current thesis the simply supported Banafjäl bridge located on the Bothnia Line in the North of Sweden is studied more in detail with regards to this aspect. It is a high-speed composite railway bridge with a span of 42 m. A detailed 3D finite element (FE) model is made available. However in order to make reliable predictions about the behaviour under increasing train length loads, it had to be further improved. Different methods of calibrating measured response data to an existing FE model, finite element model updating (FEMU), are available and a detailed overview is given at the beginning of this thesis. Next a sensitivity analysis was performed to select the material parameters which are most influential for the result and will be updated. In the following, FEMU is carried out by means of two iterative updating methods, genetic and gradient-based optimization, after which also a combination of these two is implemented. Two objective functions are chosen and it is shown that all methods converge to a global optimal solution. After adjusting the initial model with the updated parameter values, a fatigue analysis on this updated model is carried out for high-speed trains of multiple lengthsby means of the Palmgren-Miner rule. The fatigue is found to increase with increasing train length and in particular when the speed approaches resonance speed. By extension an operating chart is created to indicate the maximum amount of train passages per day in function of speed and train length for a type 4 fatigue train. Furthermore, damping has been shown to have a positive effect on the fatigue, the larger this effect for shorter trains. The static behaviour has been proven not to be a problem and so will solely the weight of trains induce little to no fatigue problems in this particular bridge.

Physical Therapy
Ph.D.
Muscle performance, particularly muscle fatigue and muscle recovery, impact an individual’s function and participation in activities of life. Most notably, older adults with medical co-morbidities experience impaired muscle performance from the natural aging process, cumulative effects of a sedentary lifestyle, or imposed bedrest, contributing to a significant reduction in health and quality of life.1 Exercise, particularly muscle strength, endurance, and power training, is considered “medicine” and often prescribed to improve the health and well-being of older adults, as well as younger adults.2 An appropriate exercise prescription requires knowledge of muscle fatigue and recovery in order to optimize the exercise program without preventing further muscle damage. Muscle fatigue and recovery have been characterized using frequency analyses of surface electromyography (sEMG) during muscle activation.3 Surface EMG measures electrical activity of a muscle, providing insight into muscle activation patterns.4 Conveniently, the sensors for sEMG are noninvasive, wireless, and compact, allowing capture of movement in a multitude of environments with minimal impact on typical movement patterns. By using sEMG to assess patterns during and after sustained isometric and dynamic knee extension, we hoped to determine baseline muscle fatigue and recovery patterns in subjects with no physical limitations for comparison with adults who are critically ill. The primary objective of this study is to improve our understanding of muscle fatigue and recovery in adults who are critically ill using sEMG technology and experimental procedures to be used in an intensive care unit (ICU) environment. We proposed to study muscle fatigue and recovery using sEMG through muscle activation analysis. The specific aims were to 1) measure time to task failure (TTTF) after a sub-maximal isometric contraction and dynamic contraction in adults who were healthy younger (HY), adults who were healthy older (HO) adults, and adults who were critically ill (CI); 2) measure time to muscle recovery after a sub-maximal isometric contraction and dynamic contraction in HY, HO, and CI; and 3) characterize a relationship between TTTF and time to recovery. Our hypotheses were that 1) CI would demonstrate a shorter TTTF than healthy subjects during an isometric contraction and dynamic contraction; 2) HY would demonstrate a shorter time to recovery, followed by HO, then CI after both an isometric contraction and dynamic contractions; and 3) there was no relationship between TTTF and time to recovery within group. Muscle fatigue and recovery were measured in the rectus femoris and vastus lateralis using sEMG. During a single 90 minute session, subjects participated in a 3 phase protocol: baseline strength measures, fatiguing contraction, and recovery contractions. The fatiguing contraction and subsequent recovery measures were performed twice – under isometric and dynamic conditions. Recovery measures were taken at termination (analysis point C), 1 minute (analysis point D), and ≥ 5 minutes (analysis point E). Sub-maximal indicated that the individual decided how long to keep their knee extended and stopped the contraction on their own at any time. Time to task failure and time to recovery amongst all 3 groups (HY, HO, and CI) were the basis for analysis of the dependent variables of sEMG – time (seconds) and median frequency (Fmed). After the isometric contraction, CI fatigued first, followed by HY, then HO. There was a statistically significant difference among TTTF and group (chi-squared with two degrees of freedom, p = 0.03). A Wilxocon rank sum test showed statistically significant differences between HY and HO (p = 0.03) and HO and CI (p = 0.02), but no statistically significant difference between HY and CI (p = 0.45). After the dynamic contraction, CI fatigued first, followed by HO, then HY. There was a statistically significant difference among TTTF and group (chi-squared with two degrees of freedom, p = 0.04). A Wilxocon rank sum test showed statistically significant difference between HY and CI (p = 0.02) and HO and CI (p = 0.02), but no statistically significant difference between HY and HO (p = 0.73). Chi-squared analysis between time to recovery and age group for both an isometric and dynamic contractions was performed. There was not a statistically significant difference for time to recovery between groups. After the isometric contraction, for the rectus femoris, all groups had a high percentage of subjects finish at analysis point E, with HY and HO having the same percentage recover at analysis point C and D, respectively. For the vastus lateralis, among the three groups, the HY had the highest percentage recovered at analysis point C. However, the largest percentage of HY subjects recovered at analysis point E. The HO and CI had the same percentage of subjects within group recover at analysis point D and E. After a dynamic contraction, for the rectus femoris, the highest percentage of HY and HO recovered at analysis point C, and CI at analysis point E. For the vastus lateralis, all groups had the highest percentage of subjects recover at analysis point C, with the HO and CI having all subjects recover before analysis point E. Our third hypothesis was that there was no relationship between TTTF and time to recovery within group. For an isometric contraction, the HY’s rectus femoris and vastus lateralis demonstrated a very weak – weak, positive correlation between TTTF and time to recovery. For a dynamic contraction, all, with the exception of HO’s vastus lateralis and CI’s rectus femoris, showed no association. HO’s vastus lateralis showed a weak, positive correlation, while the CI’s rectus femoris showed a moderate, negative correlation. None were statistically significant. This was the first study, to our knowledge, that studied muscle fatigue and muscle recovery using sEMG in patients with critical illness. From a study design perspective, the use of sEMG using Bluetooth technology was safe and feasible in the ICU setting. No adverse effects and excessive soreness were reported in CI. From a clinical perspective, despite a small sample size, CI showed comparable time to task failure and recovery time frames to HY and HO, indicating that perhaps patients do not need extensive five to ten minute rest breaks as commonly provided. Consideration to applied weight, as well as muscle fatigue and muscle recovery, should be given when designing an exercise program to appropriately tax the vulnerable muscle, while still preventing further muscle damage. Future research warrant a larger, more homogenous group of subjects, including similar diagnosis, severity of illness, and supplemental oxygenation. Secondly, efforts should be made to conduct testing in the ICU around comparable days to their length of stay. Thirdly, ideal testing should be performed prior to initiation of early mobility to capture a more authentic representation of muscle fatigue and recovery, resulting from ICUAW. All three modifications would assist in making results more generalizable. In addition, follow up sEMG analysis should be conducted to assess the effect of therapeutic interventions on muscle strength, fatigue, and recovery. Consideration must also be given to medical management, including sedatives and paralytics, as well as pH, which if in a more acidotic state, has greater hydrogen ions, which could influence fatigue. Lastly, being that sepsis is a primary admitting diagnosis and these individuals may present with muscle weakness that is not necessarily ICUAW, efforts should be made to assess if there is a difference in sEMG signals between muscle wasting from sepsis and ICUAW.
Temple University--Theses

Cette thèse concerne l’étude de fiabilité des structures travaillant en fatigue. L’un des sujets importants tient à la compréhension et la modélisation des phénomènes de fatigue tant dans les situations normales qu’accidentelles. Dans les polycristaux, ces phénomènes sont de nature probabiliste : pour un même chargement cyclique, deux éprouvettes macroscopiquement identiques ont en effet des durées de vie différentes. Ceci provient du fait que les microstructures présentent une certaine variabilité. L’approche traditionnelle consiste à établir expérimentalement des courbes S-N. Du fait de la nature aléatoire des phénomènes de fatigue, cette procédure expérimentale doit être répétée un grand nombre de fois pour être statistiquement représentative. On considère en général que la prédiction sécuritaire de la durée de vie pour un niveau de chargement donné se situe à la moyenne du nombre de cycles à rupture moins deux fois l’écart-type. Cette approche est extrêmement lourde en termes d’efforts expérimentaux, mais aussi insuffisante du point de vue de l’analyse des risques. L’ objectif principal de ce travail est de développer un modèle d’évolution polycristallin intégrant plasticité et rupture, suffisamment rapide en temps de calcul pour permettre une analyse probabiliste et applicable à l’échelle d’une structure entière. Le modèle proposé repose sur un principe de minimisation de l’énergie incrémentale et cible les chargements de faible amplitude, pour lesquels la plasticité est confinée à quelques grains critiques supposés éloignés les uns des autres et sollicités selon un seul système de glissement. Dans un premier temps, nous nous plaçons dans le cadre d’un écrouissage isotrope et cinématique linéaire, en négligeant les interactions élastiques entre grains critiques. L’incrément de glissement plastique dans chaque grain critique est alors obtenu comme une fonction explicite des paramètres du matériau, du chargement, et d’un tenseur de localisation entièrement déterminé par la géométrie du grain et ses modules élastiques. Pour des grains ellipsoïdaux, ce tenseur de localisation s’identifie au tenseur d’Eshelby. La validité du modèle est étudiée par une comparaison avec des calculs aux éléments finis. Le modèle est ensuite étendu pour prendre en compte les effets dominants de l’interaction élastique entre grains. A partir d’une analyse des dislocations, on propose également une loi d’écrouissage non linéaire faisant apparaître l’effet de la taille des grains. Une extension du modèle polycristallin à ce type de loi est présentée. Pour un chargement cyclique, l’approche proposée permet de calculer l’évolution incrémentale d’un polycristal via des formules de récurrence analytiques, sans nécessiter aucune discrétisation spatiale. Dans la situation la plus simple où les interactions élastiques sont négligées, on obtient des formules directes donnant l’état stabilisé atteint au bout d’un grand nombre de cycles. Ce modèle polycristallin est exploité pour une analyse de la sensibilité de la durée de vie par rapport aux paramètres microstructuraux, tels que la taille des grains, les textures morphologiques et cristallographiques. L’influence du gradient de contraintes est également discutée. Enfin, l’applicabilité du modèle a des structures réelles est illustré sur l’étude des stents, dispositifs biomédicaux de petite taille qui sont soumis à un chargement cyclique en raison des battements cardiaques et pour lesquels la durée de vie en fatigue est cruciale
This thesis concerns the study of the reliability of structures working in fatigue. One of the most important subjects is the understanding and modelling of fatigue phenomena in both normal and accidental situations. In polycrystals, these phenomena are of a probabilistic nature: for the same cyclic loading, two macroscopically identical specimens have different lifetimes. This is because the microstructures exhibit a certain variability. The traditional approach is to establish S-N curves experimentally. Due to the random nature of the fatigue phenomena, this experimental procedure must be repeated a large number of times to be statistically representative. It is generally considered that the safe prediction of service life for a given loading level is the average number of cycles to failure minus twice the standard deviation. This approach is extremely cumbersome in terms of experimental effort, but also inadequate from the point of view of risk analysis.The main objective of this work is to develop a polycrystalline evolution model integrating plasticity and fracture, sufficiently fast in calculation time to allow probabilistic analysis and applicable on the scale of an entire structure. The proposed model is based on the principle of minimising incremental energy and targets low-amplitude loading, for which plasticity is confined to a few critical grains that are assumed to be distant from one another and loaded according to a single sliding system. Initially, we assume isotropic and linear kinematic strain hardening, neglecting elastic interactions between critical grains. The plastic slip increment in each critical grain is then obtained as an explicit function of the material parameters, the loading, and a localization tensor determined entirely by the grain geometry and its elastic moduli. For ellipsoidal grains, this location tensor is identified with the Eshelby tensor. The validity of the model is studied by comparison with finite element calculations. The model is then extended to take into account the dominant effects of elastic interaction between grains. Based on an analysis of dislocations, a non-linear strain-hardening law is also proposed, showing the effect of grain size. An extension of the polycrystalline model to this type of law is presented.For cyclic loading, the proposed approach makes it possible to calculate the incremental evolution of a polycrystal using analytical recurrence formulae, without requiring any spatial discretisation. In the simplest situation, where elastic interactions are neglected, direct formulae are obtained giving the stabilized state reached after a large number of cycles. This polycrystalline model is used to analyse the sensitivity of fatigue life to microstructural parameters such as grain size, morphological and crystallographic textures. The influence of the stress gradient is also discussed. Finally, the applicability of the model to real structures is illustrated by the study of stents, small biomedical devices that are subjected to cyclic loading due to heartbeats and for which fatigue life is crucial

Laser shock peening is a new method employed to increase the fatigue life of metals by inducing in-depth Compressive Residual Stress to about 1 mm. This helps prevent superficial failures, stress corrosion cracking and elongate the fatigue life and this has provided varying applications in the aviation industry. This study investigates the effect of pulse energy on fatigue lifespan of AA 2024-T351 and the results validated by the finite element method. When compared with the as-received specimen, the result confirms that LSP can significantly produce higher residual compressive stress, and elongate fatigue life of alloys marginally at the superficial layer while decreasing in-depth. The FE analysis of the laser peened specimen produced a good correlation with the experimental work. The fracture morphologies also show visible signs of fatigue striations in the micro-scale. The layout between each striation space is large for the as-received specimen, demonstrating a rapid fatigue growth rate whereas relatively small in the LSP-treated specimen indicating a stable fatigue growth.

This chapter presents a new alternative approach to the analysis of the fatigue life of aircraft fuselage parts considering the compliance of internal elements to replace the classical model of critical crack size. In this case, from a global–local analysis using the boundary element method (BEM), induced stresses at a macro model, and their effects on micro models are evaluated. The BEM enables efficient simulations of the propagation of initial defects to assess the damage tolerance. For this purpose, computational techniques were developed that allowed evaluating these models, through a probabilistic treatment to assess damage tolerance and fatigue life. Finally, this technique is shown as an alternative to ensure the integrity and proper operation of fuselage panels avoiding reaching a Limit State during its projected lifespan.

The flexspline, as a core component of the harmonic drive, is highly susceptible to fatigue failure due to elastic deformation and alternating stress during operation. Its performance directly affects the working life of the harmonic drive. In this paper, finite element modeling and analysis were carried out on the polyoxymethylene flexspline (POM FS), resulting in stress, displacement, and strain cloud maps. Then, using the control variable method, the influence of structural parameters such as cylinder length L, wall thickness d, and chamfer radius r on the maximum stress of POM FS was studied, and the structural parameters were optimized. Finally, the fatigue life of POM FS was analyzed based on the S-N curve of POM. The results show that the optimized POM FS has a fatigue life of 18,300 hours, which is 24% higher than the original POM FS with the initial parameters. This paper provides a technical reference for the optimization and improvement of the lifespan of POM FS.

Eye health is essential to national health and involves all age groups throughout the lifespan. Visual impairment seriously affects people’s physical and mental health and quality of life, increases the burden on families and society, and is a public health and social problem involving people’s well-being. Our method of combining acupuncture and physiotherapy to stimulate acupoints was found to relieve eye muscle fatigue and reduce eye tendon contracture and blood stasis. It also causes bio-stimulation within the tissues and improves local blood circulation. On this basis, using a laser instead of a silver needle was improved to stimulate the acupoints. The laser is low-intensity laser irradiation through the laser beam deep inside the tissue, which can play the proper bio-thermal effect and does not damage the body’s normal biological tissues.

Abstract Traditionally, the industry benchmark for determining the lifespan of a coiled tubing string has relied on conventional parameters like running meters or fatigue analysis. This study will highlight the benefits of utilizing frequent coiled tubing string inspections as a key factor in assessing the effective remaining operational life of coiled tubing strings. The study aims to provide valuable insights that can enhance decision-making in asset management and maintenance procedures. A sample of coiled tubing strings across various operational environments underwent inspections at key intervals during their respective operational lifespans. Rigorous inspection protocols were implemented, capturing data on factors like corrosion, material degradation, and stress-induced deformities. A comparative analysis was conducted using historical data obtained from running meters and fatigue analysis to highlight the unique insights provided by frequent inspections. The findings of this study underscore the significance of frequent string inspections in assessing the operational lifespan of coiled tubing strings. While traditional methods such as running meters and fatigue analysis remain informative, they often overlook localized stressors and gradual deterioration that can compromise string integrity. In contrast, frequent inspections offer insights into the evolving condition of the strings, enabling timely interventions to prevent catastrophic failures. Furthermore, the data collected from frequent inspections can be utilized in an effective manner to anticipate future wear patterns and potential failure points. This proactive approach to maintenance and asset management enhances operational efficiency, reduces downtime, and optimizes resource allocation. This study sheds light on a significant departure from the traditional industry practice of assessing the lifespan of a coiled tubing string through conventional means. Shifting the service industry's focus toward frequent inspections as a new perspective for assessing coiled tubing string lifespan holds positive implications for asset management and maintenance strategies. By embracing this approach, service companies can make more informed decisions about when to replace or repair coiled tubing strings, ultimately prolonging their service life and minimizing operational disruptions.

The aim of the present work is the evaluation of the fatigue lifespan of a horizontal stiffened panel of an offshore structure subjected to random wave slamming. In order to achieve this objective, a methodology for time-domain slamming prediction was developed. Time series for the relative distance and velocity between the bottom panel and sea surface and the angle between the panel and the sea surface are simulated to provide a way to evaluate when the slamming occurs and the loads associated with slamming, using factor calibrated after a model test on ocean basin. With the loads obtained from these simulations, the structural analysis is then performed, considering all the shell plating, main stiffeners as well as other main supporting structures, by using a finite element structural analysis. The fatigue lifespan is estimated in a complete stochastic analysis, considering all possible sea states during the lifetime of the offshore structure as well as each probability of occurrence associated. All phases of the methodology used for the evaluation of the slamming loads and the fatigue analyses are presented.

Abstract In this paper, a method to simulate deformation of a shield braid of a cable, which is useful for predicting its lifespan, is proposed. A shield braid in a shielded cable used in a robot may break due to repetitive movement of the robot. For avoiding that, the lifespan of the shield braid must be known. However, fatigue testing to measure its lifespan requires much time and cost. Predicting the lifespan of a shield braid by simulation would reduce such time and cost. As a shield braid is composed of many strands, each strand is modeled based on the differential geometry at first. After that, a method to predict the shape of one strand from that of another strand adjacent is proposed for reduction of computation time. Then, the deformed shape of the whole braid can be simulated when a shield cable is bent. Furthermore, strain at any point on the braid can be estimated from the deformed shape of the braid simulated. Estimated strain is useful for prediction of the lifespan of the braid when the cable is bent repeatedly.

Fretting damage occurs in mechanisms submitted to vibrations which result in small amplitude oscillatory sliding motion between surfaces. The damage is either crack initiation (fatigue damage) or wear, adhesion, transfer (wear damage) depending on displacement amplitude. Aircraft and helicopters design methods tend to lighten mechanical parts, thus increasing the vibratory levels generated by engines, aerodynamic flow or during taking off and landing phases. Higher displacement amplitude may cause a slip from fatigue oriented damage to wear dominant fretting modes, dramatically decreasing the structures lifespan.

In offshore facilities, the most widely spread way to transport fluids in relatively short distances is through submarine pipelines. These structures are subject to internal and external forces. Nowadays, most of the proposed models to study submarine pipelines subjected to vortex induced vibrations feature a circular cylinder, submitted to a cross-flow, and are able to display oscillations in just the transverse direction to the fluid flow velocity. In this paper three different models that consider a two-dimensional fluid flow around a pipeline were studied via ANSYS CFX®, for Reynolds numbers between 100 and 700, with the purpose of determining the limitations of the 1-DOF models based on the Strouhal number and lift and drag coefficients and account its influence in fatigue lifespan. These models consisted of a static cylinder — i.e. no oscillations —, a cylinder with 1-DOF — i.e. cross-flow oscillations — and a cylinder with 2-DOF — i.e. cross-flow and inline oscillations —. It was found that, although fluid flow Reynolds numbers were very small as to make the submarine pipeline models fall within the finite-life region, a 1-DOF model is accurate enough to predict fatigue lifespan, since it presents respect to the 2-DOF model little deviation in the chosen comparison parameters.

While the deformation and damage behavior of aluminum cylinder heads under complex thermal mechanical loading has been the subject of numerous studies in the past, cast iron cylinder heads have been in the focus of thermomechanical fatigue (TMF) only to a minor extent. In this paper, a feasible procedure is presented to set-up material models and estimate service life of cast iron cylinder heads under variable thermomechanical loading conditions by the use of CAE tools. In addition, the influence of thermal load and mechanical constraints on TMF life span is shown. A specimen model is used for parameter identification in material model set-up and a cylinder head model is used for correlation with cracking phenomena. Investigation of different thermomechanical load influences is conducted on the cylinder head model. The principal strain and energy based fatigue criteria are used in assessment of TMF lifetime for the cast iron family and material specific evaluation procedures are pointed out. The results highlight the importance of exact definitions of the boundary conditions and underline the sensitivity of TMF lifespan of cast iron cylinder heads with respect to the defined boundary conditions. Considering this sensitivity, an approach conforming to the engine development requirements is proposed. It is shown that both the crack location and fatigue lifetime are predicted with high accuracy.

In civil engineering, fatigue can be referred to as the loss in structural performance of engineering components when subjected to repeated cyclic loads. Fatigue is identified as one of the leading factors that determines the lifespan of an engineering structure. Fatigue develops in the form of small and localized cracks which gradually propagates subcritically until the engineering component is structurally incapable to satisfy the serviceability conditions and ultimately fails. Due to the engineering importance of the phenomenon, fatigue is studied extensively in order to obtain a better understanding of the phenomenon and its manifestation in different engineering components. Over the years a number of mechanisms and models have been developed in order to explain, analyze and predict the effects of the phenomenon on various components. The three key factors that have been identified to have influenced the fatigue life of engineering components include the material properties of the engineering component, the geometry of the engineering component and the load pattern to which the engineering component is subjected. This paper aims to give a brief and consolidated overview of the various mechanisms, the different models and the influence of the various factors on the fatigue performance of components composed of ductile materials.

This paper focuses on the fatigue crack growth resulting from an aeroelastic behavior of a fan blade when operating under upstream distortion. The forced response of the first bending mode of the blade due to the inlet distortion is analyzed and the mechanical stability of blades is investigated. The forced response of one blade is evaluated using an uncoupled approach. In this approach, the forced response is calculated in four steps. First, the modal analysis is obtained using Finite Element (FE) calculations. In the second step, the aerodynamic damping is obtained by performing the CFD (Computational Fluid Dynamics) simulation for a single rotor blade with a prescribed harmonic forced motion. The next step is the estimation of the excitation forces when the unsteadiness of the inlet flow has a frequency close to the eigenfrequency of the blade. In the end, by solving the equations of equilibrium forces of the structure, the forced response is computed. Afterwards, a fatigue crack growth analysis is performed. The crack is assumed to initiate in the area of the maximum principal stress. The crack is inserted into the FE model using the Extended Finite Element Method (XFEM) [1, 2] which is implemented in an in-house plugin “Morfeo-crack” for Samcef (commercial finite element analysis software package). This method allows for easily inserting a crack while minimizing the difficulties inherent to the mesh adaptation since the crack does not need to be explicitly meshed. The calculations are performed under the Linear Elastic Fracture Mechanics hypothesis. Finally, the crack path as well as the lifespan are estimated.

Composite production risers in deep sea condition operate in harsh environment induced by wind and waves together with large axial tension fluctuations. Therefore, a suitable fatigue analysis of the riser stress joints must be undertaken at the structural design stage to ensure their adequate lifespan of 25–30 years. The composite riser, under study, is considered to be a part of Tension Leg Platform (TLP) to be installed at a depth of 2000 m. The probabilistic records of twelve sea states are used to simulate the expected loads for its entire service life. The response time histories are obtained by implicit time domain analysis of the composite riser for each sea state of random nature, duly considering the nonlinearities involved. Each stress time history is decomposed into equivalent stress blocks. A stress range histogram is generated in terms of the number of cycles in each block. The rain flow cycle counting method is hence used to estimate the cumulative fatigue damage. Palmgren-Miner rule is used to calculate the damage caused by stress signals of variable amplitudes. The damage fractions are then summed linearly to give an estimate of the total fatigue life for a particular stress history. The cumulative estimate for its entire service life is hence estimated considering all expected sea states.

In this paper, axial-tensile, constant-amplitude fatigue experiments are performed on M24 high-strength bolts with grade 8.8 fabricated from 20MnTiB steel with a stress ratio (R) of 0.3, and their crack development is simulated. The stress range-fatigue life (S–N) curve is derived by using the experimental results. The fatigue mechanism is then investigated through strain and fractographic analyses. Moreover, the extended finite element method (XFEM) is applied for assessing the fatigue crack propagation behavior of the high-strength bolts. The findings reveal that the 20MnTiB steel bolt exhibits a threshold fatigue strength of 140.77 MPa at two million loading cycles, which is 1.68 times greater than the corresponding value for 35K steel bolts at the same stress ratio. The bolt's stable deformation stage constitutes 87% of its total fatigue life. The XFEM is capable of accurately predicting the fatigue crack propagation trajectory and the lifespan of the high-strength bolts. Our analysis indicates that the crack initially propagates predominantly along the bolt's circumferential direction, accounting for 85% of the overall crack propagation life, before transitioning to unstable growth and experiencing an exponential increase in length.