Siga este link para ver outros tipos de publicações sobre o tema: Fatigue.
Teses / dissertações sobre o tema "Fatigue"
Crie uma referência precisa em APA, MLA, Chicago, Harvard, e outros estilos
Veja os 50 melhores trabalhos (teses / dissertações) para estudos sobre o assunto "Fatigue".
Ao lado de cada fonte na lista de referências, há um botão "Adicionar à bibliografia". Clique e geraremos automaticamente a citação bibliográfica do trabalho escolhido no estilo de citação de que você precisa: APA, MLA, Harvard, Chicago, Vancouver, etc.
Você também pode baixar o texto completo da publicação científica em formato .pdf e ler o resumo do trabalho online se estiver presente nos metadados.
Veja as teses / dissertações das mais diversas áreas científicas e compile uma bibliografia correta.
1
Swalla, Dana Ray. "Fretting fatigue damage prediction using multiaxial fatigue criteria". Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/17033.
Texto completo da fonte
2
Krinsky, Robin S. "Fatigue and Alarm Fatigue in Critical Care Nurses". Case Western Reserve University Doctor of Nursing Practice / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=casednp1428102757.
Texto completo da fonte
3
Lester, Charles Gilbert IV. "Analysis of fatigue behavior, fatigue damage and fatigue fracture surfaces of two high strength steels". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42795.
Texto completo da fonteResumo:
Building fuel efficient automobiles is increasingly important due to the rising cost of energy. One way to improve fuel efficiency is to reduce the overall automobile weight. Weight reductions using steel components are desirable because of easy integration into existing manufacturing systems. Designing components with Advanced High Strength Steels (AHSS) has allowed for material reductions, while maintaining strength requirements. Two Advanced High Strength steel microstructures investigated in this research utilize different strengthening mechanisms to obtain a desired tensile strength grade of 590MPa. One steel, HR590, utilizes precipitation strengthening to refine the grain size and harden the steel. The other steel, HR590DP, utilizes a dual phase microstructure consisting of hardened martensite constituents in a ferrite matrix. The steels are processed to have the same tensile strength grade, but exhibit different fatigue behavior. The central objective of this research is to characterize and compare the fatigue behavior of these two steels. The results show the dual phase steel work hardens at a low fatigue life. The precipitation strengthened microstructure shows hardening at low strain amplitudes, softening at intermediate strain amplitudes and little to no effect at high strain amplitudes. These different fatigue responses are characterized and quantified in this research. Additionally, observations showing the fracture surfaces and the bulk microstructure are analyzed.
4
Russell, Alice Elizabeth. "Fatigue and inflammation : a psychoneuroimmunological approach o chronic fatigue". Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/fatigue-and-inflammation(f592a66f-ddd9-4a29-a375-2295953a86d6).html.
Texto completo da fonteResumo:
Chronic Fatigue Syndrome (CFS) is characterised by severe fatigue, endured for at least six months, together with symptoms including impaired cognitive function, sleep disturbance, and musculoskeletal pain. The pathogenesis is still unknown, resulting in a lack of treatment options and the stigmatization of patients. Both psychological and biological factors have been implicated in the development of CFS. To date, evidence has come largely from cross-sectional studies, and there have been a paucity of longitudinal studies. The aim of this study was to explore interferon-alpha (IFN-α) induced persistent fatigue as a proxy model of CFS. IFN-α is an immunotherapy for chronic Hepatitis C Virus (HCV) infection. It induces a range of side effects including fatigue, which in some patients persists post-treatment. This model allows for the identification of risk factors and monitoring of biological and behavioural changes from the perspective of the trigger, to determine factors relevant to the persistence of fatigue after the original stimulus is no longer present. Fifty-five patients undergoing IFN-α treatment for chronic HCV were assessed at baseline, during treatment, and six-months post-treatment. Clinical, inflammatory and cortisol measures were obtained. Fifty-four CFS patients and 57 healthy volunteers completed the same measures at a one-off assessment, which were compared with post-treatment measures from HCV persistent and resolved fatigue patients. IFN-α induced persistent fatigue was associated with an exaggerated response to IFN-α, with increased fatigue, depressive symptoms, and perceived stress, a greater decline in health status, and higher inflammation. This higher symptomatology during treatment put these patients at a disadvantage for their subsequent recovery. Neither IFN-α induced persistent fatigue nor CFS was associated with continued peripheral inflammation, emphasising the importance of the response to the initial trigger. Future studies are needed to elucidate the mechanisms behind the exaggerated response, and the ‘conversion’ to chronic illness in the absence of peripheral immune activation.
5
Hu, Haiyun. "Fatigue and corrosion fatigue crack growth resistance of RQT501 steel". Thesis, University of Sheffield, 1997. http://etheses.whiterose.ac.uk/5999/.
Texto completo da fonteResumo:
This project is concerned with the fatigue response of roller quenched and tempered (RQT50I) steels. Three closely related aspects are considered: (i) the relationship between the microstructure and fatigue properties, (ii) the influence of the environment on fatigue properties, (iii) theoretical modelling of fatigue crack growth. The material used is an RQT501 grade steel. Two steels have been chosen: (A) without Mo and V additions, (B) with Mo and V additions. The second condition is chosen to evaluate the role of these elements, as hydrogen traps, on the resistance to corrosion fatigue crack growth. In order to evaluate these effects, tests have been carried out under freely corroding conditions and applied cathodic polarisation (-9 . SO mV/SCE). Metallographic examination has been carried out to evaluate grain size and inclusion distribution, size and morphology. To enable a comparison between short and long fatigue crack growth, smooth shallow hour-glass specimens have been used to study initiation and growth of short fatigue cracks, and compact tension specimens were used to monitor propagation of long fatigue cracks. The fatigue response (S - Nf curve) and fatigue crack growth rate behaviour has been studied in air (5 - 10 biz) and in 3.5%NaCI solution (0.2 Hz) or artificial seawater (0.2 Hz) with an applied stress ratio of 0. I and sinusoidal waveform. The generation and growth behaviour of cracks from smooth hour-glass specimens has been investigated through successive observation using the plastic replication method. Long fatigue crack lengths were measured using a Direct Current Potential Drop (DCPD) technique and monitored via a chart recorder. Based upon the results of these tests a fatigue crack growth model was developed based on non-equilibrium statistical theory incorporating a consideration of the influence of microstructure, e. g. grain boundaries and hydrogen embrittlement. A stochastic theory of corrosion has also been developed for the use with corrosion fatigue test data.
6
Russell, Charlotte. "The relationship between sleep and fatigue in Chronic Fatigue Syndrome". Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/the-relationship-between-sleep-and-fatigue-in-chronic-fatigue-syndrome(ea68da56-797b-40ae-ab27-a620da7aee6d).html.
Texto completo da fonteResumo:
This thesis has been prepared in a paper based format and includes an empirical paper, a systematic review and critical reflection. As a whole, the thesis focuses on the importance of sleep in Chronic Fatigue Syndrome (CFS). The systematic review is prepared for submission to 'Sleep Medicine Reviews'. The empirical paper is prepared for submission to the 'Journal of Consulting and Clinical Psychology'. Paper 1 is a systematic review and narrative synthesis of the current evidence for the effectiveness of Cognitive Behavioural Therapy (CBT) and Graded Exercise Therapy (GET) on sleep in CFS. Eight studies were found and their methodological quality varied. To understand heterogeneity in findings, information regarding intervention delivery, including the presence of sleep management components, methodology and sleep outcome measures was extracted and synthesised. We conclude that GET can improve sleep, when delivered by experienced therapists in outpatient settings. The evidence for CBT on sleep is limited, moreover, at present we know little about the effectiveness of adding sleep management components to interventions. We suggest that sleep outcomes used previously have not been sufficiently comprehensive and sensitive to measure change in sleep difficulties experienced in CFS. Implications for further research are discussed. Paper 2 presents an empirical study examining the relationship between sleep and fatigue in CFS using a daily diary approach. Sleep was measured objectively using actigraphy, and subjectively, using sleep diaries, in order to test which parameters better predict next-day fatigue. We also examined whether negative mood could mediate these relationships and whether subjective sleep variables were predicted by pre-sleep arousal. Using multilevel modelling, we found that subjective sleep, and not objective sleep, predicted next-day fatigue and these relationships were partially mediated by negative mood on waking. Pre-sleep cognitive and somatic arousal predicted subjective sleep variables including sleep efficiency and quality. Based on these findings, we suggest that interventions targeting subjective sleep, such as CBT for insomnia, may be useful in improving experiences of fatigue in CFS. Paper 3 is a critical reflection on the systematic review and empirical research, and on the process as a whole. Strengths and weakness of Paper 1 and Paper 2 are discussed, in addition to consideration of their contribution to wider research, and clinical practice.
7
Ndiaye, Mamadou. "Simulation de la fatigue par chocs, par la fatigue conventionnelle". Metz, 1994. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1994/Ndiaye.Mamadou.SMZ9423.pdf.
Texto completo da fonteResumo:
Le but de cette thèse est d'étudier la simulation de la fatigue par chocs, par la fatigue conventionnelle, à partir des matériaux suivants: 30 NCD 16, Marval 18H, composite Al/SiC. Dans une première approche, nous avions examiné l'évolution de la vitesse de propagation des fissures en fonction uniquement du pic maximal de chaque chargement. Cette étude a permis de montrer que l'influence de la vitesse de déformation propre à ces deux modes de chargements, n'est pas significative. L'ensemble des pics du chargement de fatigue par chocs, a été considérée dans une seconde approche cela a nécessité l'utilisation des méthodes de comptage pour transformer ce chargement, en plusieurs cycles d'amplitude constante. Le calcul de la vitesse de fissuration à partir des résultats de cette décomposition, a été faite par le biais du cumul des progressions de la fissure et du chargement équivalent. L'application de ces deux concepts, révèle l'effet négligeable des petites oscillations du signal de fatigue par chocs sur cette vitesse. Par ailleurs, les essais d'amorçage font apparaître que les nombres de cycles d'amorçage correspondant respectivement, au chargement équivalent et au chargement programme, sont assez proches. Enfin, les résultats d'amorçage ont été dépouillés selon le nouveau critère base sur le facteur d'intensité de contraintes d'entaille une dispersion des résultats relativement faible par rapport à celle obtenue par le critère lié au facteur d'intensité de contraintes, a été observée de ce point de vue, la validité de ce nouveau critère se trouve justifiéeThe aim of this thesis is to study the simulation of impact fatigue with the help of conventionnal fatigue, on the following materials : 30 NCD 16 steel, Marval 18 h steel, Al/SiC composite. In a first step, we have examined the evolution of crack growth rate with respect to the maximum peak value of each loading. This study has shown that the influence of the strain rate of both kinds of fatigue loadings, is no significant. All the loading peaks for impact fatigue has been considered in a second step. It has been necessary to make use of counting methods in order to transform this loading in a constant amplitude loading cycles. The computation of the crack growth rate from these results, has been made using cumulative growth length and equivalent loading methods. The application of both concepts, reveals that small oscillations in the amplitude of the impact fatigue signal has no effect on the crack growth rate. On another hand, initiation tests has shown that the numbers of cycles to initiation corresponding respectively to the equivalent loading and the programmed loading, are quite similar. Last, the results of initiation tests has been analysed using a new criterion based on the notch stress intensity factor. A quite reasonnable scattering of results with respect to that observed with an analysis using the crack stress intensity factor, has been noticed. From this point of view, the validity of this criterion has been emphasised
8
Ndiaye, Mamadou Pluvinage Guy. "SIMULATION DE LA FATIGUE PAR CHOCS, PAR LA FATIGUE CONVENTIONNELLE /". [S.l.] : [s.n.], 1994. ftp://ftp.scd.univ-metz.fr/pub/Theses/1994/Ndiaye.Mamadou.SMZ9423.pdf.
Texto completo da fonte
9
Kaemingk, Kristine Lynn. "Cardiovascular reflex function, fatigue and depression in chronic fatigue syndrome". Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185968.
Texto completo da fonteResumo:
Recently there has been increased interest in chronic fatigue syndrome (CFS), a syndrome of nonspecific symptoms and unknown etiology. The relationship between cardiovascular reflex function, fatigue, and depression in CFS was examined. Findings were as follows: First, there was no evidence of abnormal cardiovascular reflex function in the CFS group. Second, the CFS group had significantly higher systolic and diastolic blood pressure than the control group. Third, the CFS group scored higher on psychological measures of depression, fatigue, and confusion than the control group; the control group scored higher on a measure of vigor than the CFS group. Finally, the CFS group reported more CFS-related symptoms, but some members of the control group did endorse symptoms on a CFS symptom checklist. The possibility that increased peripheral resistance accounts for the elevated blood pressure in the CFS group, and the merits of exploring the role of interleukin-1 and other hormones or "hormone-like" substances in the etiology or maintenance of CFS symptomatology are discussed.
10
Warneboldt, Iona. "Multiaxial fatigue design of elastomeric parts using Equivalent Fatigue Loads". Electronic Thesis or Diss., Brest, École nationale supérieure de techniques avancées Bretagne, 2022. http://www.theses.fr/2022ENTA0002.
Texto completo da fonteResumo:
Trois étapes sont mises en oeuvre ici : la méthode de localisation, la fonction de dommage matériau et le processus de détermination des chargements équivalents en fatigue (CEF). De nombreux essais de fatigue ont été réalisés (415 au total) pour étudier le comportement en fatigue sous chargement multiaxial relaxant et non relaxant sur des éprouvettes de caoutchouc naturel. La durée de vie et les caractéristiques des fissures sont analysées pour finalement introduire un critère de fatigue approprié basé sur le plan critique et permettant de rendre compte de l'effet de déformation moyenne. Ce critère est généralisé à travers une méthode originale de recherche du plan critique. Pour estimer la réponse mécanique locale (méthode de localisation), une méthode de couplage des axes adaptée à la nature non linéaire des structures élastomères est proposée. Elle est basée sur la décomposition multiplicative des tenseurs du gradient de la déformation. Ces deux étapes sont ensuite mises en oeuvre dans le cadre du processus de détermination du CEF. Pour cela, une méthode d'optimisation globale est ajoutée pour déterminer les chargements simplifiés, induisant partout localement le même endommagement en fatigue dans la structure étudiée que le RLD. Le temps de calcul de cette optimisation est réduit en ne considérant qu'un sous-ensemble de points matériels, les plus endommagés, pour la détermination du CEF. Enfin, la méthode a été testée sur une éprouvette afin de souligner ses capacités et de valider l'approcheThis thesis introduces an Equivalent Fatigue Load (EFL) approach for the multiaxial fatigue design of elastomeric parts. As direct Finite Element Analysis (FEA) calculations of automotive in-service loads (Road Load Data (RLD)) are too expensive, the objective is to derive simplified load blocks as a realistic input for numerical damage calculations. Three streps are applied for this method: the localization method, the material damage function and the EFL determination process. Various fatigue tests have been conducted (415 samples) to study the fatigue behavior of this complex type of relaxing and non-relaxing multiaxial loading on natural rubber specimens. Lifetime and crack features are analyzed to eventually introduce an appropriate critical planebased fatigue measure and to establish a novel mean strain effect model. This criterion is generalized throughout an original critical plane search method. To estimate the local mechanical response (localization method), this thesis identifies an axes-coupling method that is fitted for the nonlinear nature of elastomeric structures. It is based on the multiplicative decomposition of the deformation gradient tensors. These two steps are then implemented in the framework of the EFLdetermination process. For this, a global optimization method is added to determine the simplified load blocks, causing locally the same fatigue behavior in the given structure. The computational costs of this optimization are reduced by only considering a subset of the most damaged material points for EFLdetermination. Finally, the method has been challenged on a specimen to outline its capabilities and to validate the approach
11
Wang, Junjian, e Shujun Xue. "FATIGUE DETECTING SYSTEM". Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-13509.
Texto completo da fonte
12
Connally, John Arnold. "Micromechanical fatigue testing". Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12756.
Texto completo da fonte
13
Ratecki, Tomasz. "Fatigue Monitoring System". ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/1141.
Texto completo da fonteResumo:
This work provides an innovative solution for monitoring fatigue for users behind workstations. A web camera was adjusted to work in near infrared range and a system of 880 nm IR diodes was implemented to create an IR vision system to localize and track the eye pupils. The software developed monitors and tracks eyes for signs of fatigue by measuring PERCLOS. The software developed runs on the workstation and is designed to draw limited computational power, so as to not interfere with the user task. To overcome low-frame rate imposed by the hardware limitations and to improve real time monitoring, two-phases detection and tacking algorithm is implemented. The proposed system successfully monitors fatigue at a rate of 8 fps. The system is well suited to monitor users in command centers, flight control centers, airport traffic dispatches, military operation and command centers, etc., but the work can be extended to wearable devices and other environments.
14
Larsson, Julia, e Sofia Mattsson. "Post Stroke Fatigue". Thesis, Malmö högskola, Fakulteten för hälsa och samhälle (HS), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-24401.
Texto completo da fonteResumo:
Bakgrund: Stroke är ett samlingsnamn på de symtom som uppstår när hjärnans nervvävnad skadas på grund av hämmad syretillförsel. Stroke kan påverka vilken funktion som helst i hjärnan, vilket leder till fysiska och kognitiva funktionsnedsättningar. En av de vanligaste konsekvenserna efter stroke är fatigue. Syfte: Att undersöka hur fatigue som konsekvens av stroke påverkar individens dagliga liv. Metod: En systematisk litteraturstudie där tio stycken vetenskapliga artiklar med kvalitativ ansats använts och kvalitetsgranskats utifrån SBU´s granskningsmall för kvalitativa studier. Resultat: Att leva med post stroke fatigue innebär en förändring i det dagliga livet. Individerna tvingas avstå helt eller göra större förändringar i aktiviteter som tillhör vardagen. Att vara beroende av andras hjälp och att inte kunna möta de krav som ställs på individerna medför både skuldkänslor och försämrat självförtroende. Slutsats: Det finns starkt vetenskapligt stöd för att post stroke fatigue har inverkan på arbetsliv, det sociala livet, aktiviteter och synen på identitet och självbild.Nyckelord: Dagligt liv, Fatigue, StrokeBackground: Stroke is a disease that affects the arteries leading to and within the brain and occurs when the tissue of the brain doesn´t get oxygen enough. Stroke can have an impact on any of the functions of the brain, leading to both physical and cognitive deficits. One of the most frequent consequences after stroke is fatigue. Aim: To explore how fatigue as a post stroke condition impacts on the daily life of the individual. Method: A systematic literature review where ten qualitative scientific articles have been examined and reviewed according to the template for qualitative research by SBU. Results: Living with post stroke fatigue means making several changes in activities of daily living or completely having to give up on the activity. To be dependent on others causes a negative effect on self-confidence and feelings of guilt. Conclusion: Strong evidence supports that fatigue has impact on daily life in terms of occupational performance, activities of daily living, social life and self-confidence. Keywords: Daily life, Fatigue, Stroke
15
Joenoes, Ahmad T. "Quantitative analysis of fatigue behavior, fatigue damage and fatigue fracture surfaces of low carbon bainitic steel (SAE 15B13)". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19671.
Texto completo da fonte
16
Wärner, Hugo. "High-Temperature Fatigue Behaviour of Austenitic Stainless Steel : Influence of Ageing on Thermomechanical Fatigue and Creep-Fatigue Interaction". Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-153100.
Texto completo da fonteResumo:
The global energy consumption is increasing and together with global warming from greenhouse gas emission, create the need for more environmental friendly energy production processes. Higher efficiency of biomass power plants can be achieved by increasing temperature and pressure in the boiler section and this would increase the generation of electricity along with the reduction in emission of greenhouse gases e.g. CO2. The power generation must also be flexible to be able to follow the demands of the energy market, this results in a need for cyclic operating conditions with alternating output and multiple start-ups and shut-downs. Because of the demands of flexibility, higher temperature and higher pressure in the boiler section of future biomass power plants, the demands on improved mechanical properties of the materials of these components are also increased. Properties like creep strength, thermomechanical fatigue resistance and high temperature corrosion resistance are critical for materials used in the next generation biomass power plants. Austenitic stainless steels are known to possess such good high temperature properties and are relatively cheap compared to the nickel-base alloys, which are already operating at high temperature cyclic conditions in other applications. The behaviour of austenitic stainless steels during these widened operating conditions are not yet fully understood. The aim of this licentiate thesis is to increase the knowledge of the mechanical behaviour at high temperature cyclic conditions for austenitic stainless steels. This is done by the use of thermomechanical fatigue- and creepfatigue testing at elevated temperatures. For safety reasons, the effect of prolonged service degradation is investigated by pre-ageing before mechanical testing. Microscopy is used to investigate the microstructural development and resulting damage behaviour of the austenitic stainless steels after testing. The results show that creep-fatigue interaction damage, creep damage and oxidation assisted cracking are present at high temperature cyclic conditions. In addition, simulated service degradation resulted in a detrimental embrittling effect due to the deterioration by the microstructural evolution.
17
Stewart, Calvin. "A Hybrid Constitutive Model For Creep, Fatigue, And Creep-Fatigue Damage". Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6023.
Texto completo da fonteResumo:
In the combustion zone of industrial- and aero- gas turbines, thermomechanical fatigue (TMF) is the dominant damage mechanism. Thermomechanical fatigue is a coupling of independent creep, fatigue, and oxidation damage mechanisms that interact and accelerate microstructural degradation. A mixture of intergranular cracking due to creep, transgranular cracking due to fatigue, and surface embrittlement due to oxidation is often observed in gas turbine components removed from service. The current maintenance scheme for gas turbines is to remove components from service when any criteria (elongation, stress-rupture, crack length, etc.) exceed the designed maximum allowable. Experimental, theoretical, and numerical analyses are performed to determine the state of the component as it relates to each criterion (a time consuming process). While calculating these metrics individually has been successful in the past, a better approach would be to develop a unified mechanical modeling that incorporates the constitutive response, microstructural degradation, and rupture of the subject material via a damage variable used to predict the cumulative “damage state” within a component. This would allow for a priori predictions of microstructural degradation, crack propagation/arrest, and component-level lifing. In this study, a unified mechanical model for creep-fatigue (deformation, cracking, and rupture) is proposed. It is hypothesized that damage quantification techniques can be used to develop accurate creep, fatigue, and plastic/ductile cumulative- nonlinear- damage laws within the continuum damage mechanics principle. These damage laws when coupled with appropriate constitutive equations and a degrading stiffness tensor can be used to predict the mechanical state of a component. A series of monotonic, creep, fatigue, and tensile-hold creep-fatigue tests are obtained from literature for 304 stainless steel at 600°C (1112°F) in an air. Cumulative- nonlinear- creep, fatigue, and a coupled creep-fatigue damage laws are developed. The individual damage variables are incorporated as an internal state variable within a novel unified viscoplasticity constitutive model (zero yield surface) and degrading stiffness tensor. These equations are implemented as a custom material model within a custom FORTRAN one-dimensional finite element code. The radial return mapping technique is used with the updated stress vector solved by Newton-Raphson iteration. A consistent tangent stiffness matrix is derived based on the inelastic strain increment. All available experimental data is compared to finite element results to determine the ability of the unified mechanical model to predict deformation, damage evolution, crack growth, and rupture under a creep-fatigue environment.Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
18
Mohin, Ma. "Fatigue crack growth assessment and fatigue resistance enhancement of aluminium alloys". Thesis, University of Hertfordshire, 2018. http://hdl.handle.net/2299/20824.
Texto completo da fonteResumo:
Fatigue damage of aluminium alloys is one of the key concerns in transport industries, particularly in the aerospace industry. The purpose of the project is to develop new knowledge and techniques against fatigue failure for these industries through a systematic investigation of fatigue resistance and crack growth behaviours of aluminium alloys. Fatigue and fracture mechanics have been investigated analytically, numerically and experimentally in this project. Overload transient effect on fatigue crack growth has been examined by considering various parameters including crack closure, overload ratio (OLR), load ratio (R ratio), baseline stress intensity factor range, (∆K)_BL and geometry. It was found that crack closure can be correlated qualitatively and quantitatively to all other parameters associated with overload transient behaviour. It is proposed that the effect of crack tip plasticity on the non-linearity of the compliance curve can be separated to obtain reliable crack closure measurement. In this project, different methods are used to better understand the transient retardation process so that the damage tolerance design (DTD) of the components made of aluminium alloys can be enhanced. Another important parameter for fatigue and damage tolerance design (DTD) of engineering components is the threshold stress intensity factor range for fatigue crack growth, ∆K_th. A small variation in identification of ∆K_th can lead to a big change in overall estimation of fatigue life. In this project, an analytical model has been developed for aluminium alloys by fitting an analytical curve with raw crack growth data in order to identify the ∆K_th. This model has the capacity to identify ∆K_th for different aluminium alloys at various R ratios. There is a great demand for enhanced fatigue life of aluminium alloys in the transport industry. This project has carried out a detailed investigation of electromagnetic treatment (ET) in the form of electropulsing treatment to develop an efficient technique for fatigue resistance enhancement. ET parameters including the treatment intensity, treatment time and the number of applications have been optimised. It is suggested that the duration of ET treatment can be used as the main parameter among all these to control the fatigue resistance of the aluminium alloy. The improvement in fatigue resistance has been explained by the change in microhardness and conductivity of aluminium alloy due to ET. Additionally, the fracture morphology was analysed using scanning electron microscopy (SEM). The precipitates and dislocation characteristics were also studied using transmission electron microscopy (TEM). The outcomes of this investigation will help improve structural integrity by enhancing fatigue resistance of aluminium alloys.
19
Johansson, Frida, e Rebecka Karlsson. "Compassion Fatigue : En litteraturöversikt om compassion fatigue hos sjuksköterskor inom akutsjukvård". Thesis, Högskolan i Skövde, Institutionen för hälsa och lärande, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-16804.
Texto completo da fonteResumo:
Bakgrund: Det råder idag ett högt tempo inom akutsjukvård och sjuksköterskan förväntas vara mångkunnig genom göra snabba bedömningar, möta patienters lidande samt prioritera akuta patienter i en stressig arbetsmiljö. Att ständigt arbeta i en påfrestande arbetsmiljö med lidande patienter och ett högt arbetstempo kan bidra till att sjuksköterskan utvecklar compassion fatigue vilket innebär att empatiförmågan avtar. Syfte: Att belysa faktorer som orsakar compassion fatigue hos sjuksköterskor inom akutsjukvård. Metod: En litteraturöversikt bestående av 11 vetenskapliga artiklar med kvantitativ forskningsmetodik. Artikelsökning utfördes i databaserna CINAHL, MEDLINE, PubMed samt WorldCat Discovery. Resultat: Tre huvudteman kunde utläsas genom analys vilket var demografiska faktorer, arbetsrelaterade faktorer samt psykosociala faktorer. Demografiska faktorer som kunde orsaka compassion fatigue var ålder, kön och civilstånd. Arbetsrelaterade faktorer var arbetsmiljö som bestod av minskat socialt stöd från chefer och kollegor, hög arbetsbelastning, minskad teamkänsla samt yrkesrelaterade faktorer som bestod av utbildningsnivå, yrkeserfarenhet och arbetstider. De psykosociala faktorerna som uppdagades var stressorer, patienters lidande och trauman. Konklusion: Compassion fatigue behöver uppmärksammas och prioriteras både individuellt, kollegialt samt på chefsnivå inom hälso- och sjukvård. Det uppdagades även att fokus på att skapa compassion satisfaction förebygger uppkomsten av compassion fatigue vilket är relevant att anamma inom personalutveckling.Background: There´s a high speed in the emergency care and the expectation of the nurse seems to be versatile with quick assessment, confront the patients suffering and to prioritize the most acute patient in a stressful work environment. Untenable work environment with suffering patients and a high work speed for the nurse can developed compassion fatigue which means a lost of the ability to feel empathy. Purpose: To illustrate factors that causes compassion fatigue for nurses in emergency care. Method: A literature review consisting of 11 scientific articles with quantitative research. The search of the articles was performed in the databases CINAHL, MEDLINE, PubMed and WorldCat Discovery. Result: Three head themes was seen with analysis which was demographic factors, work relatable and psychosocial factors. Demographic factors which could cause compassion fatigue was age, gender and civil state. Work relatable factors was work environment which consisted less social support from managers and colleges, high workload, less team spirit and work relatable factors which consisted level of education, work experience and working hours. The psychosocial factors that was observed was stressors, patients suffering and trauma. Conclusion: Compassion fatigue needs to been seen and prioritize by individuals, colleges and managers in the healthcare. It was discovered that focus should be to create compassion satisfaction which prevent the appearance of compassion fatigue, which is relevant to embrace in staff development.
20
Knipling, Keith Edward. "High-cycle fatigue / low-cycle fatigue interactions in Ti-6Al-4V". Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/41290.
Texto completo da fonteResumo:
The largest single cause of failure in fan and compressor components in the cold frontal sections of commercial and military gas turbine engines has been attributed to high cycle fatigue (HCF). Additionally, both high-cycle fatigue (HCF) and lowcycle fatigue (LCF) loadings are widely recognized as unavoidable during operation of these components and because the classic Linear Damage Rule (LDR) neglects to account for the synergistic interaction between these damage contributors, dangerous over predictions of lifetime can result.
Combined low-cycle fatigue / high-cycle fatigue (HCF/LCF) loadings were investigated in smooth Ti-6Al-4V. The specimens were subjected to a variable amplitude block loading history comprised of completely-reversed (R = -1) tensioncompression overloads followed by constant-amplitude zero-tension (R = 0) minor cycles. Axial specimens were excised from forgings representative of turbine engine fan blade forgings, and consisted of approximately 60% primary α in a matrix of lamellar α + β.
Data are reported for smooth specimens of Ti-6Al-4V subjected to both constant amplitude and variable amplitude loadings. The axial specimens were prepared according to two distinct specimen conditions: low stress ground and longitudinallypolished (LSG+LP) and stress-relieved and chemically milled (SR+CM) conditions. Significantly longer lives were observed for the LSG+LP specimen condition under both constant and variable amplitude loading, due to the presence of a beneficial compressive surface residual stress. The presence of this residual stress was confirmed by x-ray diffraction, and its magnitude was of the order of 180 MPa (~20% of the yield stress). In either specimen condition, no appreciable effect of periodic overloads on the life of subsequent minor cycles was observed.Master of Science
21
Gaur, Vidit. "Fatigue and corrosion-fatigue in Cr-Mo steel in biaxial tension". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX027/document.
Texto completo da fonteResumo:
Les connecteurs clips utilisés pour assembler les tubes de riser pour le forage pétrolier offshore subissent un chargement cyclique dû aux vagues. 90% de la durée de service est passée en mode connecté, avec une contrainte moyenne élevée, alors que 10% est passé en mode déconnecté, avec une faible contrainte moyenne. Des calculs numériques montrent qu’un chargement cyclique de tension biaxiale en phase prévaut dans la zone critique de la structure. Les effets de contrainte moyenne et de biaxialité doivent tous deux être pris en compte pour un design approprié. Les critères de fatigue multiaxiale de la littérature sont basés sur des données de traction-torsion et ne discriminent pas bien l’influence de la tension biaxiale de celle d’une contrainte moyenne. Un des objectif de cette étude est donc de caractériser séparément ces deux effets.Pour étudier les effets de contrainte moyenne, des essais de fatigue uniaxiale ont été menés avec différents rapports R. Les durées de vie diminuent avec l'augmentation de R, et la limite d'endurance suit la parabole de Gerber. À faible contrainte moyenne et amplitude de contrainte élevée, les fissures s’amorcent en surface, tandis que pour des rapports R élevés et des amplitudes faibles, les fissures s’amorcent à partir de défauts internes ou coupant la surface. Cette transition est analysée à partir de calculs élasto-plastiques des champs de contrainte et déformation autour des défauts. Les fissures internes se propagent sous un faible ΔK indépendant de R, ce qui est attribué à la quasi absence d’effets de fermeture.Pour étudier l'effet de biaxialité, des essais cycliques de tension et pression interne combinées en diverses proportions ont été effectuées à rapport R fixe (0,25). Un taux de biaxialité modéré (B = 0,25 et 0,5) a un effet bénéfique, attribué à un retard de l'amorçage des fissures, alors que la tension équibiaxiale a un effet légèrement nuisible, attribué à un "pseudo effet de taille" (probabilité plus grande qu’une microfissure se propage le long de deux plans principaux équivalents, au lieu d’un seul).De facettes intergranulaires révélatrices de fragilisation par l'hydrogène ont été observées sur les surfaces de rupture. L’évolution de leur fraction avec ΔK et la biaxialité suggèrent une réduction de la vitesse de fissuration à B≤0.5, mais l'effet néfaste de la tension équibiaxiale ne peut être attribué à une accélération de la propagation.Plusieurs des critères de fatigue existants échouent à décrire toutes les données de cette étude. Les critères d'endurance avec un terme linéaire de contrainte moyenne ou de tension hydrostatique ne parviennent pas à prédire les variations de la limite d'endurance. Un nouveau critère de fatigue a été proposé sur la base de la parabole de Gerber. Il décrit bien les effets combinés d'une contrainte moyenne et d’un taux de biaxialité positif.Des essais biaxiaux ont également été effectués dans l’eau salée (3.5% NaCl) pour étudier l'influence de ce milieu sur les durées de vie en fatigue, en corrosion libre et avec une protection cathodique qui amplifie le dégagement d’hydrogène.En corrosion libre, l'eau salée réduit fortement les durées de vie et supprime la limite d'endurance. Cela est dû à la formation de piqûres de corrosion qui favorisent l’amorçage précoce et multiples de fissures. La tension équibiaxiale n’accentue pas l’effet nocif de l'eau salée, malgré des mécanismes de fissuration différents: décohésion fragile transgranulaires en tension uniaxiale, mais principalement intergranulaire en tension biaxiale.La protection cathodique annule l'effet néfaste de l'eau salée pour tous les taux de biaxialité, en dépit d'un net accroissement de la fragilisation par l’hydrogène des joints de grains. Les surfaces de rupture deviennent presque entièrement intergranulaire, tandis qu’à l'air, le taux de rupture intergranulaire ne dépasse pas 45%The clip connectors used to join the riser tubes for offshore oil drilling undergo cyclic loading due to sea waves. 90% of the service life is spent in the “connected mode” with a high mean stress and 10% in the “disconnected mode” with a lower mean stress. Finite element computations revealed in-phase biaxial tension in the critical areas of the clip connector along with high mean stresses. Thus, both the mean stress effect and the biaxiality effect need to be addressed for proper design of these structures. However, most of the multiaxial fatigue criteria are based on tension-torsion fatigue data and do not discriminate the influence of biaxial tension from that of a mean stress. This study investigates separately these two effects.For investigating the mean stress effect, uniaxial fatigue tests were run on Cr-Mo steel with various R ratios (σmin/σmax). The fatigue lives, as well as the slope of the S-N curves were found to decrease with increasing R, and the endurance limit to follow Gerber’s parabola. At low R ratios and thus relatively high stress ranges, fatigue cracks initiated from the surface, while for high R ratios, and thus low stress ranges, cracks initiated from internal or surface-cutting defects. This transition was analyzed based on elastic-plastic computations of stress-strain fields around the defects. The threshold for internal fatigue crack growth from defects was found to be quite low and independent from the R ratio. This was attributed to a nearly closure-free propagation.To investigate the effect of positive stress biaxiality, combined cyclic tension and internal pressure tests with various proportions of each loading were run on tubular specimens, at fixed R ratio (0.25). Moderate stress biaxialities (B= 0.25 and 0.5) had a beneficial effect on fatigue lives, attributed mainly to a retardation of crack initiation, while equibiaxial tension had a slightly detrimental effect, attributed to a “pseudo size effect” (higher probability for an incipient crack to grow along two possible planes, compared to a single one).Intergranular facets associated with temper and H2 embrittlement were observed on the fracture surfaces. The evolutions of their surface fraction with ΔK and load biaxiality suggested a possible reduction in crack growth rate at moderate biaxialities, but the detrimental effect of equibiaxial tension could not be explained in terms of crack growth rate.Several popular fatigue criteria failed to describe all fatigue data. Endurance criteria that include a linear mean stress term or contain a hydrostatic tension term fail to predict the variations of the endurance limit of this material with the R ratio and biaxiality ratio. Thus, a new fatigue criterion based on Gerber’s parabola was proposed. It captured the evolution of the endurance limit under the combined effects of positive mean stress and biaxiality.Similar tests were run to investigate the influence of salt water (3.5% NaCl) on fatigue lives under two types of test conditions: 1) free corrosion and 2) cathodic protection.In free corrosion, salt water strongly reduced the fatigue lives and suppressed the endurance limit. This was due to the formation of corrosion pits that favor early, multiple crack initiations. The detrimental effect of salt water was not enhanced by equibiaxial tension, which did not modify the size and density of corrosion pits. Fatigue lives in uniaxial and biaxial tension were nearly the same, although the crack growth mechanism was different: transgranular brittle decohesion in uniaxial loading and mostly intergranular in biaxial tension.Cathodic protection cancelled the detrimental effect of salt water for all biaxialities, in spite of a clear enhancement of H-induced embrittlement of the grain boundaries. The fracture surfaces were nearly fully intergranular, irrespective of load biaxialities, while in air the proportion of intergranular fracture was less than 45%
22
Lynch, Sean Patrick Jeremy. "The nature of fatigue in the chronic fatigue syndrome : a longitudinal study". Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/7496.
Texto completo da fonte
23
Berchem, Klaus Herbert Hans. "High cycle fatigue and corrosion fatigue performance of two car body steels". Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414711.
Texto completo da fonte
24
Storey, Dawn J. "Fatigue and prostate cancer". Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/29383.
Texto completo da fonteResumo:
Methods: Four studies were conducted: Study A, was a pilot study which examined fatigue over 3 months after different treatments for localised prostate cancer (radiotherapy, brachytherapy and androgen deprivation, n=45). Study B focussed on fatigue over 12 months after brachytherapy (n=51). Two cross sectional postal surveys explored fatigue in recurrence free prostate cancer survivors (Study C, n=443) and hormone controlled prostate cancer (Study D, n=198). Throughout, fatigue was assessed using the Brief Fatigue Inventory and a case definition of clinically significant fatigue (CSF) was also constructed and applied in Studies A and B. Results: Study A found CSF increased after treatment but returned to baseline 3 months after radiotherapy, whereas it appeared to be prolonged after brachytherapy. CSF was not associated with C reactive protein or interleukin-6. Study B found CSF increased between baseline and 1 month after brachytherapy (6 vs.29%, p=0.001) and was higher than the non-cancer comparison group (29 vs. 4% p=0.001). CSF returned towards baseline levels of 6 months. There were no baseline predictors of developing CSF. Study C found 29% of recurrence free prostate cancer survivors had fatigue after radiotherapy or radical prostatectomy (33 vs. 22% p=0.024) but it was not independently associated with treatment received after controlling for other factors 43% of men with hormone controlled prostate cancer had fatigue in Study D. Conclusions: Fatigue is an important symptom in men treated for prostate cancer but resolves within months of brachytherapy. Almost one third of recurrence free survivors have fatigue but it does not appear to be related to the type of treatment received. Fatigue is most prevalent in men with hormone controlled prostate cancer.
25
Ninic, Dejan Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Fatigue in automatic transmissions". Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2006. http://handle.unsw.edu.au/1959.4/28056.
Texto completo da fonteResumo:
A novel method of predicting the multiaxial high-cycle fatigue strength of metallic components is proposed and verified for various steel, aluminium and cast iron alloys. The proposed Fatigue Damage Function shows superior multiaxial fatigue strength prediction compared to the established methods of Gough and Pollard, McDiarmid and Carpinteri and Spagnoli. A new material property, the Normal Stress Sensitivity Factor, is also introduced and its applicability is verified according to published test results of sixteen different structural alloys. To highlight the effectiveness of the proposed criterion, for industrial applications, a case study has been conducted on heat-treated and not heat-treated automatic transmission output shafts.
26
Runquist, Jennifer Jo. "Persevering Through Postpartum Fatigue". Diss., Tucson, Arizona : University of Arizona, 2006. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1458%5F1%5Fm.pdf&type=application/pdf.
Texto completo da fonte
27
McCord, Barbara Norton. "Fatigue of atherosclerotic plaque". Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/15890.
Texto completo da fonte
28
Syed, Mujtaba [Verfasser], e Jürgen [Akademischer Betreuer] Wilde. "Fatigue analysis of microstructures". Freiburg : Universität, 2016. http://d-nb.info/1122743335/34.
Texto completo da fonte
29
Cooper, J. F. "Fatigue of spot-welds". Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383069.
Texto completo da fonte
30
Chen, K. C. "Fatigue of dovetail joints". Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355721.
Texto completo da fonte
31
Dyer, K. P. "Fatigue of composite materials". Thesis, Swansea University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636755.
Texto completo da fonteResumo:
A study has been undertaken of fatigue in glass fibre reinforced composites. Two matrix resins were tested; an isophthalic polyester and a polyurethane-vinyl-ester, which was designed to have superior properties, including toughness and resistance to hydrolytic attack. Three different types of glass fibre fabrics were used for reinforcement, a conventional woven roving and two novel stitch-bonded cloths. The resins and cloths were combined into eight lay-ups in order to consider the effects of matrix, cloth and lay-up on fatigue strength and lifetime. The fatigue study was extended to evaluate the micromechanisms that occur in these composites during fatigue and how damage accumulated throughout the sample lifetime. This involved measuring stiffness changes during fatigue cycling combined with microscopic study of the samples. The damage mechanisms that occurred were similar to those seen by previous authors on different materials and from this, it was concluded that the same mechanisms occur independent of material and lay-up but these parameters affect the point in the specimen lifetime at which the damage occurs. After the data had been obtained, two experimental models were compared against data obtained in the S-N and damage accumulation studies to evaluate whether existing models would predict the behaviour of these composites. It was found that modelling of the linear portion of the S-N curve was fairly accurate but the damage accumulation model was not suitable. The composites were also fatigue tested in various environments and compared against the results obtained in air. Distilled water, sea water and dilute HCl were chosen as being the most likely encountered in the service of these materials. It was found that distilled water and sea water have minimal effect on fatigue in these composites during the short lifetimes used in this study, but it is suggested that the effect would increase with lifetime. The dilute HCl acid also had a smaller than expected effect. This study was backed with various tests which studied methods of water transport into these materials and the effects of the environments on matrix and fibre properties. Finally, initial studies have been made into methods of fabricating these materials into composite tubes with the aim of studying their properties in torsion and possibly tension-torsion.
32
Luo, Renfan. "Fatigue of dented pipes". Thesis, University of Nottingham, 2002. http://eprints.nottingham.ac.uk/13984/.
Texto completo da fonteResumo:
A dented pipe fails either through being punctured or by fatigue damage accumulation due to internal pressure fluctuation. Increasing the wall thickness may prevent these failures but is impractical. As a pipe is punctured, transmission services must be cut off and repair processes have to be made immediately. However, when a dent depth is not large enough to puncture the pipe, the pipe can safely continue in service for a long time until a fatigue crack initiation occurs. Therefore, the fatigue life assessment has attracted much attention in the pipe industries for economic and safety reasons. The severe tensile residual stress concentration and the large plastic strain deformation in the dented region are the main causes of the pipe failure due to fatigue damage. Accurate calculation and prediction of the residual stress and variations resulting from internal pressure fluctuation can lead to safety assessments and prediction of the remaining life of the dented pipe. Due to the complex nature of the contact process, the deformed pipe geometry and the elastic-plasticity, analytical approaches are incapable of obtaining stress solutions. Therefore, FE modelling is employed in the present work. Experimental tests are employed to investigate the indenter force-dent depth behaviour which can be compared with the FE solutions to confirm and validate the FE models. The rigid perfect elastic-plastic limit load method and an energy-based method are also used to analytically calculate the limit load and the indenter force/deflection relationship of indented rings to predict damage. Two dimensional FE modelling is performed to calculate the contact and residual stress and strain distributions on the outer, inner surfaces and through the wall thickness. These FE solutions show that high stress concentrations occur in the indented region, which give the potential for fatigue damage. As the 2D FE modelling requires only limited resources, the indenter size and indentation position can be changed to analyse their effects on stress and strain distributions in the indented region. This forms the foundation of later 3D FE modelling. Stress sensitivity and the validation of shell models are investigated and confirmed through the 2D and 3D FE modelling and by comparing experimental test data with the FE solutions. Based on this work, the decision is made to use shell element modelling to perform the residual stress and stress range calculations in a 3D pipe. Semi-empirical formulations are developed to predict stress and stress range values if the residual dent depth, the pipe and indenter geometries, material property, internal pressure and pressure range are known. These FE solutions and semi-empirical formulae can be used to calculate the stress range and mean stress.
33
Chen, Zheng. "Torsional fatigue of wood". Thesis, London South Bank University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271780.
Texto completo da fonte
34
Abu, Kasim Noor Hayaty. "Fatigue of dental composites". Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281886.
Texto completo da fonte
35
Hu, Zhihua. "Spectral fatigue analysis techniques". Thesis, University College London (University of London), 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362446.
Texto completo da fonte
36
Kawamoto, Jiro. "Fatigue of rubber composites". Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14566.
Texto completo da fonte
37
Yakub, Gabriela, e Enoz Issa. "Compassion fatigue hos sjuksköterskor". Thesis, Mälardalens högskola, Akademin för hälsa, vård och välfärd, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-40022.
Texto completo da fonteResumo:
Background: Compassion is to know how another person feel, fatigue is a condition of constant tiredness. Compassion fatigue occurs among caregivers and is characterized by nurses’ empathetic ability to nurture patients and appears physically, mentally and spiritually in nurses and can have a negative outcome on their well-beings. Problem: Compassion fatigue can occur within care giving professions which can affect the nurse and patient negatively. To prevent it, awareness of compassion fatigue should be highlighted in a larger context. Purpose: To describe aspects of compassion fatigue from the nurse perspective. Method: A general literature review has been applied in the thesis work, as eight quantitative articles, two qualitative articles and three articles of mixed method have been used. Findings: Compassion fatigue has shown to affect nurses working in different care departments caused by high work load, stress, time shortage and critically ill patients. Strategies for coping with compassion fatigue turned to be physical activity and support from family, friends and colleagues. Time for recovery was considered important for nurses as they could disconnect their negative thinking. Conclusion: Knowledge about compassion fatigue and its risk factors should be noted to prevent the condition.
38
Andersson, Filip, e Rhodel Bengtsson. "Spot-Weld Fatigue Optimization". Thesis, KTH, Hållfasthetslära (Avd.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-232529.
Texto completo da fonteResumo:
The purpose of this thesis project is to develop a methodology that can be used to minimize the number of spot-welds in a mechanical structure, this is done in a reliable manner via optimization methods. The optimization considers fatigue life in spot-welds and also stiffness and eigenfrequency values. The first chapter of this thesis presents a spot-weld fatigue model proposed by Rupp (1995), common FEmodels of spot-welds and also important aspects about structural optimization in general. The second chapter further describes how topology optimization and size (parameter) optimization are applied on a simple multi-weld model with respect to the aforementioned structural constraints. The topology optimization is later used on a full-size car model, while the size optimization is used to optimize the multiweld model by adding an non-linear structural constraint - a crash indentation constraint. The spot-weld fatigue model proposed by Rupp (1995), is also verified by comparing FE results using different FE-models of spot-welds compared to fatigue data by Long and Khanna (2007). Both optimization methods successfully minimize the total amount of spot-welds on the multi-weld model. The topology optimization,accompanied with thegradient based MFD algorithm,minimizes th etotal spot-welds with around 15% and 3% on the multi-weld model and car body respectively. The size optimization, using design of experiments and response surfaces, manage storeduce the number of welds in the multi-weldmodel by 25%. However, with the size optimization the computational time is several orders of magnitude longer-even without the formulation of the crash constraint. The fatiguespot-weld model fares reasonably well compared to the experimental fatigue data, regardless of the FE model of the spot-weld. It is concluded that the ACM model would be recommended based on its compatibility with fatigue and optimization methods, mesh-independence and also other studies have shown its ability to represent stiffness and eigenfrequency correctly.
39
Yazdanpanah, Amir. "Computer aided fatigue design". Thesis, Sheffield Hallam University, 1990. http://shura.shu.ac.uk/20587/.
Texto completo da fonteResumo:
Today's competitive market requires engineers to produce reliable light weight products at low cost. This can be achieved by more effective use of computer aided engineering tools during early stages of the design process. A research programme has been undertaken to investigate the data requirements of integrating commercially available software packages (finite element analysis and fatigue life evaluation) to evaluate the integrity and durability of engineering components at the conceptual design stage. A real engineering component, in the form of a steering arm, supplied by a European truck manufacturer was used as a basis for the investigation. This is a typical vehicle component, in which, under service loading conditions, a multiaxial state of stress occurs. A geometric model of the component was created using the Prime "MEDUSA" software suite. The model was used to locate the boundary co-ordinates necessary for the development of a PAFEC Finite Element model. By imposing the conditions experienced during the service, the critical areas of the component were identified by analysing the F.E. model and a detailed description of the elastic stress/strain fields were also established. These were incorporated in an energy density approach and Neuber's uniaxial analysis to predict total local elastic/plastic strains at these critical- locations. These were compared with strain gauge measurements. The calculated results were used to plot a number of load/local strain calibration curves for the development of a load history, suitable for experimental fatigue life assessment. Fatigue crack initiation tests were performed on the steering arm using a computer controlled DARTEC multiaxial fatigue testing machine. Fatigue life assessment based on full service loading was carried out using a software package based on the critical location approach. A comparison of computerised, experimental and actual test circuit fatigue lives has been made. The work enabled a specification to be produced for the integration of the two items of software. This integrated software was developed by third parties and used to produce a computerised life map of the steering arm.
40
Hunter, Angus Murray. "Manipulations of neural fatigue". Doctoral thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/4402.
Texto completo da fonte
41
Liu, Mu-Hsin. "Multiaxial Fatigue Testing Machine". Ohio University / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1266241731.
Texto completo da fonte
42
Kirsch, Franck. "Fatigue-fluage du bois". Metz, 1998. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1998/Kirsch.Franck.SMZ9835.pdf.
Texto completo da fonteResumo:
L'ensemble de ce travail a pour objectif de déterminer le comportement mécanique du matériau bois lorsque celui-ci est soumis à des efforts de fatigue-fluage. On va donc s'intéresser à l'évolution de la déformation d'une éprouvette au cours de plusieurs cycles de charge et de décharge. On peut aussi se demander comment s'endommage le matériau en fatigue-fluage. On va pour cela essayer de comparer le comportement du matériau en fatigue-fluage par rapport à son comportement en fatigue pure et en fluage pur. On peut aussi s'interroger s'il y a un effet mémoire du chargement et si tel est le cas ou se loge cet effet mémoire. Toutes les constructions, notamment dans le bâtiment, sont soumises à des efforts de fluage et parfois ceux-ci sont combinés à des efforts de fatigue. Indépendamment, ces deux types d'efforts ont été étudiés sous de nombreux aspects mais il existe peu de références lorsque l'on approche ce problème de manière simultanée. L'on souhaite vérifier si la responsabilité de la rupture est due au fluage, à la fatigue ou alors si elle est due à une combinaison des deux phénomènes. Pour ce faire, on détermine un modèle d'endommagement à partir d'essais de flexion quatre points en fluage, fatigue et fatigue-fluage.
43
KIRSCH, FRANCK Jodin Philippe. "FATIGUE-FLUAGE DU BOIS /". [S.l.] : [s.n.], 1998. ftp://ftp.scd.univ-metz.fr/pub/Theses/1998/Kirsch.Franck.SMZ9835.pdf.
Texto completo da fonte
44
Vaughan, Claire. "Cognitive fatigue in MS : an investigation of 'pacing' as a fatigue management strategy". Thesis, Royal Holloway, University of London, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604643.
Texto completo da fonteResumo:
Fatigue is a disabling symptom in Multiple Sclerosis (MS), but fatigue management strategies have not been systematically evaluated. The objective of this study was to investigate the effects of 'Pacing', on the experience of fatigue measured by self-report ratings and cognitive performance decrement. Using an experimental design, 29 MS participants and 31 matched healthy control participants were separately randomised to one of three conditions: continuous verbal list learning, alternating verbal list and visual memory tasks, or verbal list learning alternating with rest ("pacing"). Participants were assessed on parallel forms of the Brief Repeatable Neuropsychological Battery (BRB-N) before and after the intervention. Baseline depression (CES-D) and fatigue (FSS) questionnaires and 4 Fatigue Visual Analog Scale (FVAS) ratings spaced through the 90- minute schedule were completed. Results revealed the MS group had significantly higher baseline depression and fatigue scores. A mixed ANOV A (group x condition x cognition time I, time 2) for cognitive performance revealed: the MS group's performance was worse than the healthy control group's (p<.OOI); both groups' performance was worse after the mental effort (p<.OOI) required by the intervention, whilst experimental condition had no effect upon cognitive performance. A mixed ANOV A (group x condition x self-reported fatigue at 4 time points) for FVAS ratings revealed both groups reported increased fatigue over time (p<.OOI) yet fatigue did not differ significantly between groups or conditions. The conclusion drawn was effortful mental tasks increased self-reported fatigue and reduced cognitive performance equally in both MS and healthy participants. This supports cognitive fatigue as an inducible and measurable construct. In this study, ' Pacing' had no effect on cognitive performance decrement or self-reported fatigue. With direct clinical implications for MS fatigue management courses that incorporate these strategies further systematic evaluation is warranted.
45
Gillisdotter, Anna. "Att delta i en Fatigue Management kurs – upplevelser från personer med MS-fatigue". Thesis, Luleå tekniska universitet, Hälsa och rehabilitering, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-67521.
Texto completo da fonteResumo:
Syftet med denna studie var att beskriva hur personer med MS-fatigue upplever upplägg och innehåll i FM-kursen, samt vilken betydelse de upplever att kursen haft för deras möjligheter att hantera sin MS-fatigue i vardagen. En kvalitativ metod med semistrukturerade intervjuer användes. Data är analyserad med riktad kvalitativ innehållsanalys. Resultatet visade att deltagarna upplevde att kursen var lärorik men ansträngande. Samtidigt gav kursen dem kunskap och strategier för att hantera MS-fatigue i vardagen. Huvudfyndet anses vara hur deltagarna upplever kursen stöttat dem hantera MS-fatiguen i vardagen genom användning av strategier och hjälpmedel. I diskussionen tas aspekten av resultatet om hur deltagarna blivit mer aktiva trots de infört vila i relation till aktivitetsbalans. Även aspekten om arbetsterapeutens expertis inom hjälpmedel och stödja deltagarna i användning av detta kunde möjliggöras i kursen. Konklusionen är att fler studier behövs för att studera Fatigue Management påverkan på aktivitet ur aktivitetsbalansperspektivet.The purpose of this study was to describe how people with MS fatigue experience the structure and content of the FM course, and if the course helped them to handle their MS fatigue in their daily lives. A qualitative method of semi structured interviews was used. Data is analysed with directed qualitative content analysis. The result shows that the participants felt that the course was educative but strenuous. The course gave them knowledge and strategies for managing MS fatigue in everyday life. The main finding is considered how the participants experience the course supported them managing the MS fatigue in everyday life through the use of strategies and tools. In the discussion, the aspect of the result of how participants became more active, despite the added rest in relation to the activity balance, is taken. The aspect of the occupational assistant's expertise in assistive devices and supporting participants in using this could also be made possible in the course. The conclusion is that more studies are needed to study Fatigue Management's impact on activity from the activity balance perspective.
46
Fair, G. H. "The effect of shot peening on fatigue and fretting-fatigue of aluminium alloys". Thesis, University of Nottingham, 1988. http://eprints.nottingham.ac.uk/12723/.
Texto completo da fonteResumo:
Plain-fatigue and fretting-fatigue tests have been carried out on the two peak-aged, high-strength aluminium alloys, 7010 and 8090, in the unpeened and shot peened conditions. Shot peening produced a highly deformed surface containing many deep dimples and folds from which fatigue cracks rapidly initiated. Although initiation was early, propagation through the peened surface layers was retarded by the residual compressive stresses introduced by the peening treatment; this retardation being greatest at a depth corresponding to that of the peak residual compressive stress. Shot peening improved the plain-fatigue properties of the 7010 alloy at high applied stresses and this improvement decreased as the applied stress was reduced. A reversed trend was observed in the 8090 alloy with shot peening being beneficial to the fatigue properties at low applied stresses and detrimental at high applied stresses. The poor resistance of the 7010 alloy to fretting-fatigue was eliminated by shot peening and this was again attributed to the residual compressive stress induced by the peening treatment. Since the 8090 alloy in the unpeened condition is relatively insensitive to the effects of fretting, shot peening resulted in only a minor improvement in the fretting-fatigue behaviour of this alloy.
47
Connaughton, M. D. "A study of cumulative fatigue and creep-fatigue damage in Type 316 steel". Thesis, Open University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234153.
Texto completo da fonte
48
Wallström, Maria, e Nadia Axelsson. "Med fatigue som följeslagare : upplevelsen av att leva med MS-relaterad fatigue/trötthet". Thesis, Högskolan i Borås, Institutionen för Vårdvetenskap, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-18610.
Texto completo da fonteResumo:
Multipel skleros, MS, är en neurologisk autoimmun sjukdom som drabbar centrala nervsystemet. Trötthet/fatigue upplevs av många som ett av de svåraste symptomen som inverkar starkt på det vardagliga livet. MS-relaterad fatigue/trötthet ger en känsla av utmattning och brist på energi som kan vara överväldigande. Tröttheten är orimlig i förhållande till de aktiviteter som utförs. Syftet med uppsatsen var att beskriva hur det är att leva med MS-relaterad fatigue/trötthet. Metoden som användes var litteraturstudie med kvalitativ innehållsanalys som baserats på åtta vetenskapliga artiklar. Dataanalysen skedde med hjälp av Fribergs (2006) beskrivning. Ur resultatet framkom fyra teman varav det första var upplevelsen av kroppen som ett fysiskt hinder. Detta tema belyser hur ett antal intervjupersoner upplever sin kropp som ett hinder och hur fatigue/trötthet begränsar och påverkar det dagliga livet. Tema två och tre beskriver hur relationer till familj och vänner kan förändras samt hur den psykiska hälsan påverkas. Det fjärde och sista temat handlar om hur personer som lever med denna trötthet lägger upp strategier och på bästa sätt planerar sin vardag för att orka mer. I diskussionen diskuteras begrepp som hälsa och sjukdom. Vi belyser också hur fysisk träning och annan självhjälp kan minska fatigue/trötthet och öka en människas psykiska hälsa. I de praktiska implikationerna tar vi upp vikten av information och kommunikation som vi anser är grunden till en god vårdrelation.Program: Sjuksköterskeutbildning
Uppsatsnivå: C
49
Fares, Youssef. "Dimensionnement en fatigue des assemblages boulonnés à l'aide de critères de fatigue multiaxiale". Toulouse, INSA, 2006. http://www.theses.fr/2006ISAT0016.
Texto completo da fonteResumo:
Le principal objectif de ce travail de thèse est d'utiliser les critères de fatigue multiaxiale pour dimensionner les assemblages boulonnés. A partir d'une étude comparative des différents critères, nous en avons sélectionné deux : celui de SINES et celui de DANG VAN dont nous avons généralisé la formulation pour prendre en compte le domaine de l'endurance limitée. L'utilisation de ces critères nécessite la détermination de l'état de contrainte au fond du premier filet en prise, lieu privilégié de l'amorçage de la rupture des boulons. Nous avons donc réalisé des modèles éléments finis d'un boulon. Parallèlement, plusieurs campagnes d'essais fatigue ont été réalisées : les nombres de cycles à rupture obtenus couplés aux états de contrainte en fond de filet obtenus par simulation ont permis de caractériser le comportement en fatigue multiaxiale des boulons. Une fois cette caractérisation réalisée, l'usage de ces critères à été validé par un essai sur un assemblage de type bride. Puis, afin de s'affranchir de la phase modélisation EF, nous avons utilisé la règle de NEUBER et la méthode ESED pour déterminer l'état de contrainte en fond du premier filet en prise lors d'un chargement cyclique. Les essais de fatigue ont été faits sur deux types de boulons : des boulons roulés à froid puis trempés-revenus et des boulons trempés-revenus puis roulés à froid. Les performances améliorées de ces derniers a permis de bien mettre en évidence l'influence de la chronologie des opérations. Cette amélioration est à mettre sur le compte des contraintes résiduelles que nous avons essayé d'évaluer par modélisation du roulageThe aim of this thesis is the use of multi-axial fatigue criterion in bolted assemblies design. From a comparative analysis of several criterion, we chose those of SINES and DANG VAN that we generalised to limited fatigue life. These criterion require the knowledge of the stress level in the screw at the bottom of its first thread in contact with the nut, where fatigue failure occurs. For this, we used a finite elements model of the bolt. On the other hand, several fatigue tests were undertaken; with the number of cycles to failure related to the stress level at the bottom of threads obtained by simulation, we characterised the multiaxial fatigue behaviour of the tested bolts. Then, the use of these criteria to industrial bolted joints was experimentally validated on a flanged type assembly. To overpass the finite elements model of the bolted joint, we used NEUBER's generalised rule and ESED method to determine the stress level at the bottom of the first thread under a cyclic loading. The fatigue tests were carried on two types of bolts: cold rolled then heated-tempered bolts, and heated-tempered then cold rolled bolts. The improved performance on this last type of bolts has put in evidence the influence of chronology of the different manufacturing operations. This improvement is explained by the residual stresses induced by rolling that we tried to simulate
50
Aref, Fathema, e Marina Fryxell. "Fatigues påverkan på barn vid behandling av leukemi under vårdtiden och förändringar av fatigue över tid : En litteraturöversikt". Thesis, Uppsala universitet, Institutionen för folkhälso- och vårdvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-434105.
Texto completo da fonteResumo:
Background: Leukemia is the most common form of cancer in children, with eight out of ten children surviving the disease. Children who develop leukemia are usually between two and six years old. Fatigue is one of the most common side effects in children undergoing treatment for leukemia. Fatigues can reduce the mental, physical and social well-being of the patient. Aim: The purpose of this study was to investigate how fatigue affects children with leukaemia during care and changes in fatigue over time. Method: A literature review that includes ten scientific articles that have been quality reviewed according to the Swedish Agency for Medical and Social Evaluation (SBU) review template and according to Willman, Stoltz och Bahtsevani (2011) template. Result: The results from 10 articles are reported in two different categories. These were; impact on quality of life during care and sleep. The results show that children with leukaemia rated their quality of life low during the care period. Fatigue also had negative effects on children's sleep. Conclusion: Sleep and quality of life in children with leukemia are negatively affected by fatigue. Changes in the degree of fatigue could be demonstrated in several articles.SAMMANFATTNING Bakgrund: Leukemi är den vanligaste cancerformen hos barn där åtta av tio barn överlever sjukdomen. Barn som insjuknar i leukemi är oftast mellan två och sex år gamla. Fatigue är en av de vanligaste biverkningarna som förekommer hos barn som genomgår behandling av leukemi. Fatigues kan minska det psykiska, fysiska och social välbefinnandet hos patienten. Syfte: Syftet med denna studie var att undersöka hur fatigue påverkar barn med leukemi under vårdtiden samt förändringar av fatigue över tid. Metod: En litteraturöversikt som har en deskriptiv design och de vetenskapliga artiklarna har kvalitetsgranskats efter Statens beredning för medicinsk och social utvärderings (SBU) granskningsmall samt Willman, Stoltz och Bahtsevani (2011) granskningsmall. Resultat: Resultatet från tio artiklar redovisas i två olika kategorier. Dessa var; påverkan på livskvalitén under vårdtiden och sömn. Det framkom i resultatet att fatigue hade en negativ inverkan på livskvalitén hos barn med leukemi där barnen skattade sin livskvalité som låg under vårdtiden. Fatigue hade även negativa effekter på barns sömn. Slutsats: Livskvalitén och sömnen hos barn med leukemi påverkades negativt av fatigue. Förändringar av graden fatigue kunde påvisas i ett flertal artiklar.