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1
Bellecave, Johan. „Stress Gradients In Fretting Fatigue“. Thesis, Cachan, Ecole normale supérieure, 2015. http://www.theses.fr/2015DENS0036/document.
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Cette thèse fait partie d’un programme de recherche international (IRG Cognac). Lancé par le motoriste SNECMA (groupe SAFRAN), ce projet regroupe l’ENS Cachan, UnB, ENSMA, CNRS, Snecma, Turbomeca et Messier Bugatti Dowti, et se concentre sur l’effet du gradient des contraintes sur endommagement par fretting fatigue. Le fretting-fatigue se réfère au processus d’endommagement localisés en bord de fuite entre deux corps en contact soumis à un chargement de fatigue. La maitrise de ce phénomène est d’une importance cruciale dans la détermination des durées de vie des disques de turbine. En bord de contact, le champ de contrainte hérité des forces de contact est maximal à la surface mais présente un fort gradient en s’éloignant du contact.Il a été montré dans cette thèse que pour l’alliage Ti-6AL-4V, les approches locales, basés sur le niveau de contrainte au points critiques ne sont pas applicable dans ces conditions. Une approche non locale, s’appuyant sur la théorie de la distance critique a donc été utilisée. En effet, des fissures courtes initiées au point critique peuvent propager jusqu’à rupture ou peuvent s’arrêter si la diminution des contraintes est suffisamment sévère. Une seconde difficulté réside dans la nature multiaxial et localement non proportionnel du chargement. Le fretting fatigue est généralement créé par la superposition d’un chargement de fatigue cyclique, d’une force normale à la surface souvent considérée constante, et d’une force cyclique tangentiel à la surface mais dont la fréquence peut être différente de celle de la fatigue.Les résultats des essais réalisés ont mis en évidence l’effet du gradient des contraintes sur la fissuration et ont étaient utilisés pour évaluer le potentiel de diffèrent critères pour le dimensionnement en fatigue des structures. La simulation du phénomène a en effet été réalisé en utilisant différente approches. La première s’appuie sur la Théorie de la distance critique et utilise un critère multiaxial. La seconde utilise l’amplitude du facteur d’intensité des contraintes, ΔK, pour prédire l’arrêt des fissures courtes. Finalement un récent modèle construit comme un critère de plasticité en pointe de fissure a été appliqué au problème de fretting fatigue. Ce critère a pour particularité de prendre en compte la contrainte T dans le développement asymptotique en pointe de fissureThis thesis is part of an international research program (IRG Cognac) initiated by the engine manufacturer SNECMA (SAFRAN group) involving ENS Cachan, UnB, ENSMA, CNRS, Snecma, Turbomeca et Messier Bugatti Dowty. The thesis focuses on the effect of a stress gradient in fretting fatigue. Fretting-fatigue refers to the damage process localized at the frontier of the contact between two contacting bodies subjected to fatigue loadings. The prediction of this phenomenon is of major importance in determining, for instance, the lifetime of fan's disc. In the vicinity of the contact front, the stress field inherited from the contact loads is maximal at the surface and displays a strong gradient from the surface. It was shown in this thesis, for a Ti-6AL-4V alloy, that local approaches, based on local stresses at the most critical point, are not appropriate to predict fretting fatigue lives. As a matter of fact, short cracks initiated at the most critical point may stop if the stress decay from the surface is strong enough or may continue their growth, up to the failure of the component, if the stress gradient from the surface is not string enough. A second difficulty is the multiaxial and non-proportional nature of the loading conditions. Fatigue-fretting stems from the combination of loads that have neither the same spatial distribution nor the same time-dependency. In fretting-fatigue tests, three loading components are considered, the fatigue loading of the component (cyclic), the normal part (assumed to be constant) and the in-plane part (cyclic) of the loads between the two contacting components. To quantify the effect of the stress gradient, tests were carried out on a fatigue testing contact bench developed at the University of Brasilia, with experimental conditions ensuring different stress gradient while keeping the maximal stress the same. Damage mechanisms were studied using post-mortem analysis and optical microscopy on the contact elements tested. The prediction of the fretting fatigue life was done using different approaches. The first one is based on the Critical Distance Method and a fatigue criterion. The second is based on a K-based short crack arrest method. Finally, a new criterion was proposed. This method considers a generalized von Mises yield criterion for the crack tip region and accounts for the T-stresses in the asymptotic LEFM development
2
Li, Henan. „Flexible Pipe Stress and Fatigue Analysis“. Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18646.
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Fatigue is an important character for the flexible pipes as they are always exposed to dynamic loading. For nonbonded flexible pipes, fatigue and stress analysis can be performed based on different assumptions of slip behaviour. Different slip assumptions used in estimating the slip stress always play a determinative role in the prediction of fatigue damage. Thus, this thesis will focus on the study of the slip behaviour between tensile armour layers of nonbonded flexible pipes. The results can be used to support the basic assumptions for further fatigue analysis. The main object of this thesis is to summarize the existing analytical methods for stress and slip analysis of nonbonded flexible pipe armouring layers and to verify that the improved finite element models can give adequate description of the flexible pipe slip behaviour.In previous version of BFLEX, the transverse slip effect for nonbonded flexible pipes has been neglected. In this thesis, transverse slip regime has been activated in the updated BFLEX by developing a new type of beam element hshear353 and a new type of contact element hcont453. Finite element models use these two elements have been made and several case studies have been carried out.For axisymmetric loading, two analytical solutions, one obtained from the equations by Witz&Tan[13], one from Sævik[2] have been compared with the result from numerical simulation. It has been found that Sævik’s solution matches better with the BFLEX solution comparing to Witz&Tan’s solution. For flexible pipes exposed to bending, influences on slip behaviour from several pipe parameters, namely friction coefficient, axial strain and global pipe curvature, have been investigated. The numerical results are also compared with analytical solutions obtained from Sævik[2]. It has been found that the numerical solutions can give excellent agreement with analytical solutions. It is further concluded that the outer tensile armour layer do not influence much on the inner layer slip behaviour.In addition, the cyclic bending effects on nonbonded flexible pipes have been investigated. It has been found that the tendon behaves differently from case to case. The inner and outer layers behave differently. Only a few cases have been studied for this problem due to time limitation. The overall conclusion is that the developed BFLEX model is capable of describing the stresses and local displacements of flexible pipe for simple cases. The developed numerical model can further be used in the study of fatigue in flexible risers. However, more studies on influence from multi-tensile layers and cyclic bending are needed in the future.
3
Nowak, William J. „Fatigue stress analysis of turbine blades /“. Online version of thesis, 2007. http://hdl.handle.net/1850/5467.
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4
Desmond, Paula A. „Fatigue and stress in driving performance“. Thesis, University of Dundee, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364944.
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This thesis attempted to provide a detailed theoretical understanding of the effects of task-induced fatigue on simulated driving performance. Previous research has shown that duration of driving has only a weak effect on driving performance. A series of studies were conducted to examine how fatigue effects interact with task demands, and to explore the psychological changes associated with fatigue. The research also explored links between fatigue and stress in terms of their affective reactions and the coping mechanisms which are central to them. The first phase of the research consisted of a series of simulated studies of fatigue. The first study developed an experimental paradigm to examine both task-specific and aftereffects of fatigue on driving performance. The findings showed that fatigue effects interacted with task demands such that drivers' lateral control of the vehicle and trajectory were impaired during low demand rather than in high demand driving episodes. The study also showed that the fatigue state is a multidimensional state which is principally characterised by a reduction in motivation. The second and third studies attempted to explore the role of motivational mechanisms in fatigue-related impairments. This phase of the research showed that impairments in low demand driving conditions may be reduced by enhancing the driver's motivational state. The fourth study explored the development of subjective fatigue in two types of task-induced fatigue. The study showed that there is a dissociation between subjective and objective fatigue. The second phase of the research examined the links between stress and fatigue in simulated and real-life driving environments. The studies showed that stress and fatigue are similar states but there are particular features which make them distinct states. The results from simulated and real-life driving environments showed a high degree of consistency.
5
Holmberg, Erik. „Stress and fatigue constrained topology optimization“. Licentiate thesis, Linköpings universitet, Mekanik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-88094.
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This thesis concerns structural optimization in conceptual design stages, for which constraints that are adapted to industrial requirements have been developed for topology optimization problems. The objective of the project has been to identify and solve problems that today prevent structural optimization from being used in a broader sense in the avionic industry; the main focus has been on stress and fatigue constraints in topology optimization. The thesis consists of two parts. The rst part gives an introduction to topology optimization and describes the developed methods for stress and fatigue constraints. In the second part, two papers are included, where the stress and fatigue constraints are evaluated, respectively. In the rst paper, a clustered approach is presented, where stress constraints are applied to stress clusters, rather than points on the structure. This allows for a trade-o between computational time and accuracy, as the number of clusters and thus constraints can be varied. Dierent approaches for how to sort stress evaluation points into clusters and how to update the clusters, such that the results are suciently accurate for conceptual designs, are developed and evaluated. The two-dimensional examples conrm the theoretical discussions and the designs that are obtained have managed to avoid large stress concentrations, even for problems with an initial stress singularity. Compared to the traditional stiness based designs, the stress constrained designs are considered to be closer to a nal design, which will decrease the total product development time. The second paper uses the methodology developed in the rst paper and applies it to high-cycle fatigue constraints. Using loads described by a variable load spectrum and material data from fatigue tests, the tensile principal stresses are constrained by a limit that is determined such that fatigue failure will not occur. In the examples, where the mass is minimized subjected to fatigue and static stress constraints, simple topologies are obtained and the structural parts are sized with respect to the critical fatigue stress and the yield limit. Stress concentrations are again avoided, for example by the creation of a radius around an internal corner. A comparison between static stress constraints based on the von Mises criterion and the highest tensile principal stresses is given and the examples clearly show the characteristics of the two formulations.
6
Chahardehi, Amir Ebrahim. „Fatigue Crack Growth in Complex Stress Fields“. Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/3481.
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Fatigue crack growth has been traditionally modelled using LEFM through the use of
the Paris law. This requires an accurate method for stress intensity factor (K)
calculation. Weight functions have been developed for one-dimensional cracks (e.g.
edge and through cracks); these are functions that enable separation of the loading and
geometry and considering the effect of each one of these two factors on the stress
intensity factor (SIF) separately. They have been proven to be useful for arbitrary stress
distributions where an accurate empirical formula for the stress intensity factor does not
exist. Such cases include residual stress fields due to surface treatments or welds.
However, in the case of surface cracks, or part-through cracks, the problem of
modelling the growth of these cracks poses two main questions, namely, how should the
Paris law be generalised to suit the two-dimensional scenario, and under arbitrary
loadings, how can the SIFs be calculated for these cracks. Current solutions involve
tedious mathematical calculations and are complicated functions.
In this thesis, the concept of root mean square (RMS) SIF is examined and by drawing
mathematical analogy with the one-dimensional case, a novel weight function is derived
which enables calculation of RMS SIF values for a range of semi-elliptical surface
cracks under arbitrary loadings. The accuracy of the weight function is verified through
comparisons with finite elements results for a variety of loadings/geometries. The
simplicity of the weight function construction method makes it a useful tool for fatigue
life predictions where incremental recalculations of SIF is required as the crack grows.
Surface treatments such as shot peening and laser peening are used for crack growth
retardation. It is generally believed that it is through the introduction of what is termed
‘beneficiary compressive residual stresses’ that crack retardation occurs. The
compressive residual stresses are superimposed on the ‘detrimental tensile stresses’ due
to loading and hence lead to a lower SIF level. By having such a strong tool as weight
functions, this general belief can be put to test. To this end, a set of experiments were
carried out to study the behaviour of cracks in residual stress fields arising from laser
peening. Edge cracks were grown in partially-peened specimens. Neutron diffraction
stress measurements were taken and stress profiles were obtained for these specimens.
Measurements of strain fields near the crack show the interaction between the crack and
the stress field induced by the peening process. The effect of laser peening on crack
growth is discussed and recommendations for future work are proposed.
Overall the thesis proposes a weight function for surface cracks the uniqueness of which
is in its simplicity, and develops an understanding of the nature of induced and transient
stresses in laser-peened components. The concept of ‘effective fatigue stress’ is
introduced and its calculation is described, and conclusions are drawn from the nature of
this stress distribution.
7
Johansson, Frida, und 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.
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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.
8
Hattingh, Daniel Gerhardus. „The fatigue properties of spring steel“. Thesis, University of Plymouth, 1998. http://hdl.handle.net/10026.1/2300.
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The nature and scope of this thesis can be divided into three categories, namely stress distribution modelling in coil springs; fatigue and failure analysis, an investigation into measurement of residual stresses and the relation to fatigue life. The operation of springs is directly concerned with the theories of torsion and bending which makes the better understanding of these theories essential. The first part of the thesis is involved with a mathematical evaluation of these theories and a case study of an isolated loop of a coil spring. The mathematical modelling is verified by measuring the strain levels in a coil spring with the aid of strain gauges located at different positions in the coil spring. This evaluation gave a better understanding of the operational stress distribution for input into the two methods currently used by industry for the fatigue testing, namely isolated loop and complete coil spring samples. The remaining part of the thesis revolves around the understanding of the relationship between fatigue life, process effects and residual stresses. The relationship between fatigue failures and process effects was investigated to reveal the mechanism responsible for component fatigue failure in a 55Cr3 automotive suspension spring steel. This was done by subjecting coil springs, withdrawn from different stages of the manufacturing process, to fatigue tests, ensuring that all possible sources of fatigue initiation in this material batch have been identified, including those not dominant in the finished component. Failures prior to shot peen process was mainly surface relate as where those withdrawn after this process were subsurface (inclusions) related. Fractographic analysis, using an XL30 scanning electron microscope, has revealed a number of sources of initiation, which are largely related to mechanical damage and inherent material defects. The results indicate that decreasing defect levels in the material would represent a valid method for enhancing the fatigue response, specifically levels of nonmetallic inclusions and surface mechanical damage, but also that certain manufacturing process stages (cold scragg) are responsible for drop in fatigue life.
9
Barsoum, Zuheir. „Residual stress analysis and fatigue of welded structures /“. Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3872.
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10
Ackley, Jessica Lee. „Compassion Fatigue and Secondary Traumatic Stress in Nurses“. Thesis, The University of Arizona, 2014. http://hdl.handle.net/10150/318839.
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11
Newport, Andrew. „Stress and fatigue analysis of threaded tether connections“. Thesis, University College London (University of London), 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309364.
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12
Kiuru, Martti. „Magnetic resonance imaging of fatigue bone stress injuries“. Helsinki : University of Helsinki, 2002. http://ethesis.helsinki.fi/julkaisut/laa/kliin/vk/kiuru2/.
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13
Williams, Zachary. „Krouse Fatigue for Metals with Elevated Mean Stress“. Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1597075964521893.
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14
Holmberg, Erik. „Topology optimization considering stress, fatigue and load uncertainties“. Doctoral thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-123008.
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This dissertation concerns structural topology optimization in conceptual design stages. The objective of the project has been to identify and solve problems that prevent structural topology optimization from being used in a broader sense in the avionic industry; therefore the main focus has been on stress and fatigue constraints and robustness with respect to load uncertainties. The thesis consists of two parts. The first part gives an introduction to topology optimization, describes the new contributions developed within this project and motivates why these are important. The second part includes five papers. The first paper deals with stress constraints and a clustered approach is presented where stress constraints are applied to stress clusters, instead of being defined for each point of the structure. Different approaches for how to create and update the clusters, such that sufficiently accurate representations of the local stresses are obtained at a reasonable computational cost, are developed and evaluated. High-cycle fatigue constraints are developed in the second paper, where loads described by a variable-amplitude load spectrum and material data from fatigue tests are used to determine a limit stress, for which below fatigue failure is not expected. A clustered approach is then used to constrain the tensile principal stresses below this limit. The third paper introduces load uncertainties and stiffness optimization considering the worst possible loading is then formulated as a semi-definite programming problem, which is solved very efficiently. The load is due to acceleration of point masses attached to the structure and the mass of the structure itself, and the uncertainty concerns the direction of the acceleration. The fourth paper introduces an extension to the formulated semi-definite programming problem such that both fixed and uncertain loads can be optimized for simultaneously. Game theory is used in the fifth paper to formulate a general framework, allowing essentially any differentiable objective and constraint functions, for topology optimization under load uncertainty. Two players, one controlling the structure and one the loads, are in conflict such that a solution to the game, a Nash equilibrium, is a design optimized for the worst possible load.
15
SAXBY, DYANI J. „ACTIVE AND PASSIVE FATIGUE IN SIMULATED DRIVING“. University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1195507547.
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16
Meyer, Nicholas. „Effects of Mean Stress and Stress Concentration on Fatigue Behavior of Ductile Iron“. University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418332368.
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17
Bulusu, Prashant. „Rolling contact fatigue predictions based on elastic-plastic finite element stress analysis and multiaxial fatigue /“. abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1437664.
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Thesis (M.S.)--University of Nevada, Reno, 2006."August, 2006." Includes bibliographical references (leaves 38-45). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2006]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.
18
Gustafsson, Sara. „Sjuksköterskors erfarenhet av compassion fatigue“. Thesis, Mälardalens högskola, Akademin för hälsa, vård och välfärd, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-40012.
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Background: The societys requirements for nurses working in care are to achieve good qualitative, safe care for patients that experiencing several trauma and suffering. Todays medical care with high patient flow and pace, as well as savings and low nursing staffing. Reported to be contributing factors to nurses suffering from compassion fatigue. Problem:The combination of this and the inadequate guidelines or support for being able to handle these requirements as a nurse, this contributing factors to nurses developing compassion fatigue Purpose: The purpose of the thesis work is to highlight the nurses experience of compassion fatigue. Method: A qualitative literature study with descriptive synthesis, twelve articles has been analyzed according to Evans (2002). Results: To create a balance between working life and priva life, having knowledge and being read as well as taking care of yourself is considered essential to avoid compassion fatigue. A support from management and colleagues was considered important to counteract compassion fatigue. Conclusion: nurses who experience stress or compassion fatigue as well as lacking tools or knowledge about what counteracts compassion fatigue can have difficulty emotionally engaging in caring. Which contributes to stress and even poorer quality of care.
19
Morrissey, Ryan J. „Frequency and mean stress effects in high cycle fatigue of Ti-6A1-4V“. Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17095.
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20
Ahmed, Rehan. „Rolling contact fatigue of thermal spray coatings“. Thesis, Brunel University, 1998. http://bura.brunel.ac.uk/handle/2438/5469.
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The practical advantages of thermal spray coatings like high deposition rates, low cost and tribological properties of high wear resistance have enabled these coatings to become an integral part of aircraft and automobile industry. Recent advancements in thermal spraying techniques like high particle speed and temperature call for new applications for these coatings. This experimental study addresses the Rolling Contact Fatigue performance of thermal spray coatings deposited by a variety of techniques like High Velocity Oxy-Fuel (HVOF), Detonation Gun (D-Gun) and Plasma spraying. RCF tests were conducted using a modified four ball machine in conventional steel ball bearing and hybrid ceramic bearing configurations. Tribological conditions during the RCF tests were varied by changing the test lubricant and the lubrication mechanism, contact load and shape of the drive coated rolling element to vary the roll/slip ratio. RCF tests were analyzed on the basis of the performance, coating failures using surface and subsurface observations, and residual stress studies. Experimental and theoretical studies of the ball kinematics have also been included. These tests revealed that the performance of the coated rolling elements was dependent upon the coating and the substrate properties. The coating thickness, substrate hardness, tribological conditions during the test, coating and substrate material as well as the coating process and the substrate preparation significantly affect the coating performance and the failure modes. Three different failure modes of these coatings have been discussed along with the changes in the near surface residual stress behaviour of the coated rolling elements.
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De, Noronha Motta Carlos Henrique. „A fatigue crack growth model with mean stress effects“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq21163.pdf.
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LaRue, James Edward. „The Influence of Residual Stress on Fatigue Crack Growth“. MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04072005-095303/.
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This thesis discusses the analysis of fatigue crack growth in the presence of residual stresses to determine a suitable method for fatigue life predictions. In the research discussed herein, the prediction methodologies are compared to determine the most accurate prediction technique. Finite element analysis results are presented as well as laboratory test data. The validity of each methodology is addressed and future work is proposed.
23
Escobar, Jose Alejandro. „Stress and fatigue analysis of svi-tested camshaft lobes“. Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36656.
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Nondestructive evaluation techniques were
employed to fully characterize three 2.3L
camshafts tested in an engine simulator for an
equivalent of 100,000 miles. Optical
microscopy, acoustic microscopy (SAM),
and profilometry were used to characterize
wear and fatigue, crack depth, and surface
roughness, respectively. Results show
cracking to occur mainly in the opening ramp
of the most abusively ground cam lobes. No
clear evidence was found for subsurface
cracking at depths as great as 200 mm from
the lobe's surface. Profilometry results show
no evidence of any major tribological effect
due to the sliding friction of the follower.
Fractography studies show a difference
between fracture surfaces among the cracks
examined; straight cracks exhibit features
resembling fatigue propagation, while fracture
surfaces from pitted cracks show a more
brittle behavior. Small grinding cracks
(approximately 300 mm in length) were found
in the opening ramps of the most abusively
ground lobes prior to testing. Knoop and
Nanoindenter microhardness indicate a
near-surface rehardening for the most
abusively ground lobe (confirmed by
metallography), and temper burn for the
remaining lobes. X-ray residual stress results
made in the opening ramp of the tested lobes
show evidence of residual stress relaxation.
X-ray line width data as a function of depth
does not correlate with residual stress.Master of Science
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Loriol, Marc. „La médicalisation de la fatigue et du stress : la sociogénèse de la notion de mauvaise fatigue“. Paris 5, 1998. http://www.theses.fr/1998PA05H055.
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Il est de plus en plus courant aujourd'hui de se plaindre d'une "mauvaise fatigue" dont seraient responsables les conditions de vie modernes. Les représentations sociales à l'origine de tels discours peuvent être comprises dans le cadre conceptuel du processus de civilisation défini par Elias ; l'autocontrôle des émotions et les nouvelles régulations s'accompagnent d'une individualisation et d'une autonomie qui rendent plus sensibles les défaillances individuelles. Les premières catégories à entrer dans ce processus sont le plus souvent situées en haut de l'échelle sociale et la conscience d'endosser de nouvelles valeurs les poussent à se distinguer des catégories inferieures. Le discours sur la mauvaise fatigue est à la fois un moyen de donner un sens aux souffrances nées de contraintes sociales qui ne sont pas encore vécues comme "naturelles", un vecteur de nouvelles normes, et une façon de se distinguer. Dans ce cadre, la médicalisation de la fatigue résulte de la rencontre entre les stratégies de spécialisation de certains médecins ou psychologues et les besoins d'une catégorie sociale particulière devant s'adapter à de nouvelles formes d'interdépendances. Une étude historique sur la sociogenèse de la notion de mauvaise fatigue - de l'acédie au moyen Age au stress contemporain - et une recherche menée à partir de près de 200 entretiens sur la constitution de la fatigue au travail comme problème médical permettent de vérifier ces hypothèses. L'exemple de l'épuisement professionnel des infirmières, notamment, montre comment le discours sur la fatigue exprime une demande de reconnaissance tout en étant le support d'une stratégie de professionnalisation soutenue par les élites de la profession ; ce discours représente enfin un moyen pour les directions de gérer les problèmes liés à la transformation du métier et aux conditions de travail a un niveau essentiellement individuel : gestion du stress, formation au travail relationnel, etc.
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Gustafsson, Lidström Hjalmar, und Victoria Öhrn. „Compassion fatigue : När empation tar slut för sjuksköterskor“. Thesis, Röda Korsets Högskola, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:rkh:diva-223.
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Bakgrund: En genomgång av aktuellt kunskapsläge visar att sjuksköterskor har en risk att utveckla compassion fatiguepå grund av sitt empatiska engagemang gentemot patienterna. Compassion fatigueär då en person som konsekvens av sitt empatiska engagemang gentemot en patient blir emotionellt utmattad. Syfte:Syftet med denna studie är att belysa riskfaktorer för sjuksköterskor att drabbas av compassion fatiguesamt för att undvika detta tillstånd. Metod:En litteraturstudie gjordes med både kvalitativ och kvantitativ forskning. Resultatet analyserades och sammanfattades. Resultat:Resultatet visade att risken att drabbas var störst hos sjuksköterskor inom hemsjukvården, akutsjukvården, hospices sjuksköterskor och de sjuksköterskor som arbetade med kroniskt sjuka barn. Ett flertal strategier och åtgärder pekar på vikten att behålla en professionell distans till patienterna samt säga nej till arbete som ej tillhör ens specifika arbetsområde. Majoriteten av sjuksköterskorna delgav även support som en strategi för återhämtning, både från kollegor men även i form av kurator eller psykolog, speciellt vid traumatiska händelser. Slutsats: Compassion fatigueär ett problem både för sjukvården i stort och för den enskilda sjuksköterskan. Det påverkar både omvårdnaden, arbetssituationen och den enskilda sjuksköterskan negativt. Ett flertal faktorer spelar in i utvecklandet av compassion fatigue, detta gör även att det krävs ett brett urval av möjliga åtgärder för att förhindra det.Background: A review of the field shows that nurses are at risk to develop compassion fatigueas a result of their empathic engagement with patients. Compassion fatigueis when a person as a consequence of their empathic engagement with patients suffers an emotional exhaustion. Purpose: The purpose of this study is to highlight risk factors in developing compassion fatigueand how to avoid this condition in the nursing profession. Method: A literature review with both qualitative and quantitative research. The result was then analysed and summarized. Result: The results showed that nurses in homecare, acute care, hospice and those working with chronically ill children were at the highest risk for Compassion fatigue.A number of strategies and preventive measures highlight the importance of having a professional distance to the patient as well as saying no to tasks that are not within the nurses specific profession. A majority of nurses stated support as a strategy for recovery, both from colleges as well as counselors or psychologists, especially after traumatic events. Conclusion: Compassion fatigue is a problem both for healthcare in general as well as for nurses themselves. It affects the patient care, the work situation and the nurse negatively. A number of factors contribute in the development of compassion fatigue, because of this a broad selection of possible preventive measures is required,
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Kramer, Loretta Rose, und Loretta Rose Kramer. „Compassion Fatigue Among Travel Nurses“. Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626351.
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Purpose: To describe an educational workshop delivered to travel nurses, with analysis of the shared discussion.
Background: Travel nurses work beyond the realm of traditional nursing positions as they typically are contracted for short periods of time, fill positions created by nursing shortages, and are willing to work in various capacities. As currently conceptualized, compassion fatigue is comprised of compassion satisfaction, burnout, and secondary traumatic stress. Travel nurses are at risk for compassion fatigue as they often work on high acuity units such as emergency room and ICU. Additionally, travel nurses lack natural support systems as they often work far from usual supports such as family, which may increase the risk of compassion fatigue.
Method: A two-part educational workshop was developed to reduce the risk of compassion fatigue among travel nurses (N=3). Workshops included education and skills training. Participants discussed their experiences, symptoms, and strategies they used to cope with the negative constructs of compassion fatigue. They journaled and make notations of personal and professional experiences including symptoms, triggers, and self-reflection of compassion fatigue and skills learned.
Findings: Commonalities included symptoms of fatigue, isolation, disassociation, second-hand grief, physical pain, dysfunctional communication, and questioning role as a nurse. Triggers to compassion fatigue included limited resources, patient complexity, length of shift, patient influences such as gratitude for nursing service, and witnessing loss. Outcomes included self-medicating with alcohol, self-isolating, working extra shifts, and not debriefing with clinical professionals.
Implications: Travel nurses experience symptoms of compassion fatigue including burnout and secondary traumatic stress that is consistent with other nursing professionals. The participants did not understand the phenomenon and had no knowledge of how to protect against compassion fatigue. Travel nurses would benefit from incorporating skills and strategies to address the phenomenon of compassion fatigue, burnout and secondary traumatic stress. The data from this educational intervention project magnify the knowledge currently known about the impact and experience of compassion fatigue in nursing populations, specifically travel nurse populations. It provides insight into the possible benefit of focus group discussions and self-care strategies in lessening the impact of compassion fatigue in travel nurse populations.
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Fidder, Herman. „Characterising the stress-life response of mechanical and laser formed titanium components“. Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1018462.
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This dissertation involves the experimental investigation of commercially pure titanium (CP Ti) which was subjected to laser forming and mechanical forming processes. Commercially pure titanium grade 2 was formed to a radius of curvature of approximately 120 mm using three forming procedures, i.e. i) laser forming; ii) mechanical forming (stretched forming) and iii) a combined forming process (laser-mechanical forming). Fatigue testing revealed, for all the forming processes, that samples produced by laser forming performed the best at high load settings. However, mechanically formed specimens performed the best at low load settings, whereas the laser-mechanical process resulted in midway performance between laser and mechanical processing. Considering microstructure vs fatigue; impact vs fatigue; and residual stress vs fatigue; at high load settings it is evident that the microstructure is the dominant contributor to crack initiation and growth. Crack morphology of fatigue samples revealed that secondary cracks (parallel to main crack front) followed the grain boundaries of the Widmanstätten microstructure, whereas irregular secondary cracks grew parallel and through the twinning planes and along the grain boundaries of the equiaxed microstructure. Laser forming resulted in microstructural changes from equiaxed grains to a Widmanstätten structure due to fast cooling rates. Excessive twinning is developed within the equiaxed microstructure after the mechanical forming procedure. This is due to cold working / strain hardening. The combined process shows a combination of equiaxed grains and Widmanstätten microstructure. Residual stress relieved for all forming processes revealed an increase in the magnitude of the residual stress compared to the parent plate and that the maximum values were obtained at the inner radius of curvature (i.e. 118.4 mm). Laser forming revealed the highest values in residual stress whereas the other two processes i.e. mechanical and laser-mechanical forming exhibited an increase midway between the parent plate and laser forming. The second most influential factor with regards to fatigue was the magnitude of the residual stress, especially at medium to low load settings. When considering theoretical models to predict fatigue life it was found that the Goodman model showed the closest relation to the actual fatigue data when considering the entire theoretical curve. Vickers microhardness profiling was applied to the thickness of the samples for the parent plate and all forming processes. No significant hardening occurred due to the forming processes and differences in hardness were considered negligible. Charpy impact testing revealed that the laser formed specimens exhibited the most brittle behaviour when compared to the parent plate results. Mechanical formed specimens showed a slight increase in brittleness compared to parent plate whereas the combined process yielded results midway between the laser and mechanically formed specimens. Mathematical equations are formulated and presented for predicting the fatigue life of CP Ti grade 2 for the parent plate and the three forming processes. This study proved that the laser forming process can be successfully used as a production stage in the forming of CP Ti grade 2.
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Read, Paul John Charles Lewis. „Fatigue characterisation of FRP structural tee joints“. Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242730.
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EMO, AMANDA KATHLEEN. „FATIGUE AND WORKLOAD EFFECTS IN SIMULATED DRIVING“. University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1078513446.
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Rydberg, Niklas, und Ryan Barfield. „Stress och fatigue hos vårdpersonal : Hur påverkas vårdare och patienter?“ Thesis, Växjö University, School of Health Sciences and Social Work, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-6946.
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Vårdyrket ställer höga krav på individen resulterande i en överbelastning som leder till stress och fatigue. Syftet med studien var att beskriva hur stress och fatigue påverkar vårdpersonal och deras arbetsförmåga. För att besvara frågeställningarna gjordes en litteraturstudie med kvalitativ ansats där systematiskt uppsökta, vetenskapliga artiklar analyserades. Av resultatet framkom fyra huvudkategorier som beskriver påverkan på vårdpersonal och deras arbetsförmåga: Arbetets art, organisation och krav, vårdarens kropp och själ, förlust av kontroll samt att bibehålla vårdarens välbefinnande. Roterande skiftarbete och hög arbetsbelastning är de största bidragande faktorerna till stress och fatigue. En negativ inverkan kan ses på psykisk och fysisk hälsa, likväl som på arbetsförmåga och patientsäkerhet. Den slutsats som dras är att stress och fatigue är ett problem inom vården som har konsekvenser för både personal och patienter.
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Barsoum, Zuheir. „Residual Stress Analysis and Fatigue Assessment of Welded Steel Structures“. Doctoral thesis, Stockholm : Farkost och flyg, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4687.
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Ngiam, Shi Song. „The influence of surface residual stress on fatigue crack growth“. Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1444870/.
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Residual stress exists in most structures and although it has been recognised for a long time, its complex mechanism and characteristics are still being intensively studied. Residual stress can be stratified into damaging residual stress and beneficial residual stress. Surface tensile residual stresses are generally known to reduce the mechanical properties of materials while compressive residual stresses improve the fatigue performance of components. This Ph.D. thesis reports the analytical and experimental work conducted to investigate both the damaging and beneficial effects of residual stress on fatigue crack growth in structural components. The detrimental effect of tensile residual stresses is studied through large scale fatigue testing of T-butt welded plates fabricated from High Strength Steels (HSS). Despite the growing use of HSSs in the offshore industry, the fatigue performance and corrosion resistance of welded joints made from such steels are still not clear. Due to their complex metallurgy and relatively poor weldability, there is still a lack of understanding of the residual stresses that arise from the welding process. This study involved modification and development conducted on a variable amplitude (VA) load-time sequence generator for the investigation of long life fatigue performance of HSS. Emphasis was given to the generation of a stationary load-time history and numerous analyses were presented to demonstrate the importance of the long term statistical nature of the load-time sequence on fatigue testing. Fatigue test results obtained were extensively compared with previous HSS corrosion fatigue studies. The effect of tensile residual stress on fatigue crack growth was investigated using a SIF weight function-based fatigue crack growth model. Two newly developed preferential cold working techniques termed stitch cold rolling and stitch shot peening were explored to investigate the beneficial effect of surface compressive residual stress on fatigue crack growth in mild steel plates. One of the main objectives of this study was to control the fatigue crack shape by the manipulation of surface residual stress fields. The stitch cold rolling technique was implemented using a custom-built cold rolling jig. The feasibility of preferential cold working techniques was further investigated by the fatigue testing of stitch shot peened specimens. Both experimental programmes yielded unprecedented fatigue crack growth results. A residual stress monitoring programme was conducted to study the residual stress relaxation behaviour under cyclic loading. The experimental test results enabled the investigation of SIF solutions in non-uniform stress fields. A novel fatigue crack growth evolution model, which takes into account residual stress relaxation effects, was developed using the powerful SIF weight function methods.
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Hussey, I. W. „The influence of notch stress field on fatigue crack growth“. Thesis, University of Portsmouth, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372739.
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Nguyen, Olivier T. Ortiz Michael. „Cohesive models of fatigue crack growth and stress-corrosion cracking /“. Diss., Pasadena, Calif. : California Institute of Technology, 2002. http://resolver.caltech.edu/CaltechETD:etd-12032004-161201.
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Bruun, Oyvind Aleksander. „Fatigue Assessment of Components Subjected to Non-Proportional Stress Histories“. Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produktutvikling og materialer, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-24138.
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The fatigue assessment of components subjected to complex loading histories is a challenging topic. Several criteria intended for use under multiaxial stress-states and non-proportional loading have been proposed by many researchers throughout the years. This thesis is intended as a critical review of the fatigue assessment of both proportional and non-proportional stress histories. A database consisting of 268 experimental tests for biaxial fatigue limits were collected from various sources. The compiled database spans 20 materials, ranging from carbon steels to cast irons. The data were evaluated using five multiaxial fatigue criteria and two separate assessment methods. The first assessment method is here described as the proportional-method, which is the assessment of relevant stress-values based on extreme values occurring throughout a cycle. The second method, here simply called the ASME-method, is heavily inspired by the ASME-criterion as stated by the ASME Boiler and Pressure Vessel code. The latter method determines the relevant stress values based on relative differences in stress components over time. In addition to the fatigue test data, a stress cycle provided from the industry is examined and discussed.The lack of readily available fatigue test data for validating purposes is a serious concern that is discussed here. The database provided in the appendix is intended to partially remedy this, and serve as a starting point for future research. A comparison of predictions, both criteria- and methodology-wise is also provided. The results and findings are then critically discussed. The research shows that the predictability of a fatigue criterion depends on both material and stress-state. For brittle materials such as the cast irons included in the assessment, the normal stress criterion provides excellent results. For carbon and low alloy steels, as well as the aluminium alloy 76S-T61, shear stress criteria such as Findley yield more accurate predictions. The ASME-method increases the complexity of the fatigue assessment, but is shown to have a positive effect on predictions for the Findley criterion.
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Hobbs, James William. „Aspects of the stress and fatigue performance of threaded connectors“. Thesis, University of Sheffield, 1999. http://etheses.whiterose.ac.uk/14782/.
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Threaded connectors have been used in a variety of engineering structures for hundreds of years. Although stress analysis of threaded connectors has been performed since the early 1900's, there are still areas that are not fully understood. The way in which eccentricity affects the fatigue performance and stress distribution is one such area, and is the main area of research described in this thesis. The techniques of photoelasticity and fatigue testing were used to determine the effect of eccentricity on the stresses and fatigue performance of bolts. The results show that eccentric loading has a significant effect on the fatigue performance, but that this effect can be quantified if the local stress amplitude is considered. The photoelastic analysis results show the eccentricity slightly increases the stress intensity factors at the crack tip. A number of two-dimensional and three-dimensional finite element models were created to detennine the salient characteristics of the models. The models were validated against the resuh from the photoelastic analysis and the results agreed well. Accurate results can be obtained from a two-dimensional model, but the information obtained is limited unless many models are created. However, if a three-dimensional model is created more information can be obtained, but the nut thread run-out must be accurately modelled to obtain the correct stress distribution. The shape of cracks occurring in cyclically loaded steel bolts and the effect of crack shape on the stress distribution was also investigated. The photoelastic analysis of cracked bolts failed to predict the shapes of cracks occurring in cyclically loaded bolts. It is suggested that the inability of photoelasticity to model plasticity is the cause of this failure and this is supported by results from an elastic-plastic finite element model.
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Yakub, Gabriela, und 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.
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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.
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Brennan, Feargal Peter. „Fatigue and fracture mechanics analysis of threaded connections“. Thesis, University College London (University of London), 1992. http://discovery.ucl.ac.uk/1317863/.
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This thesis aims to develop a comprehensive usable engineering design approach to the fatigue analysis of threaded connections. Although primarily concerned with the fatigue-fracture mechanics behaviour of screw threads, a broad review of stress analysis investigations in such connections is reported. Connection types, their functions and standardisation authorities are presented with the purpose of familiarising the reader with the subject and the options available to the design of threaded fasteners. Fatigue crack initiation is discussed with reference to the specific setting of a critical thread root. A crack initiation model is adapted for employment in thread root design. A novel weight function approach is developed for use in the determination of stress intensity factors for threaded connections. A generic solution is proposed valid for the fatigue crack growth from any thread root under any symmetrical stress system. Its development and discussion is examined in detail, remaining close to its proposed application. Two engineering situations where the chief structural components are comprised of threaded members are taken as case studies. The background to each situation is elaborated in detail and full-scale fatigue tests were conducted on the critical components. In all, fourteen full-scale tests under constant and variable amplitude loading are reported. The results of these are analysed and used to validate the fatigue crack initiation and propagation models. Useful observations which are helpful to understanding the fracture mechanisms operating during the fatigue of threaded connections are reported. Material and environmental considerations are examined and a survey of relevant materials and their behaviour in environments associated with threaded fasteners is presented. The merits or otherwise of some common engineering practices are discussed with regard to fatigue. A method has been developed for predicting fatigue life in large threaded connections under random loading. Experimental results have been gathered on two types of components used on certain oil rigs, tether joints and drill strings. The agreement found between prediction and experiment is appreciably better than by previous methods of analysis and also points to aspects open to further improvement.
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Echard, Benjamin. „Assessment by kriging of the reliability of structures subjected to fatigue stress“. Thesis, Clermont-Ferrand 2, 2012. http://www.theses.fr/2012CLF22269/document.
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Les méthodes traditionnelles de dimensionnement à la fatigue s’appuient sur l’utilisation de coefficients dits de “sécurité” dans le but d’assurer l’intégrité de la structure en couvrant les incertitudes inhérentes à la fatigue. Ces méthodes de l’ingénieur ont le mérite d’être simples d’application et de donner des solutions heureusement satisfaisantes du point de vue de la sécurité. Toutefois, elles ne permettent pas au concepteur de connaître la véritable marge de sécurité de la structure et l’influence des différents paramètres de conception sur la fiabilité. Les approches probabilistes sont envisagées dans cette thèse afin d’acquérir ces informations essentielles pour un dimensionnement optimal de la structure vis-à-vis de la fatigue. Une approche générale pour l’analyse probabiliste en fatigue est proposée dans ce manuscrit. Elle s’appuie sur la modélisation des incertitudes (chargement, propriétés du matériau, géométrie, courbe de fatigue) et vise à quantifier le niveau de fiabilité de la structure étudiée pour un scénario de défaillance en fatigue. Les méthodes classiques de fiabilité nécessitent un nombre important d’évaluations du modèle mécanique de la structure et ne sont donc pas envisageables lorsque le calcul du modèle est coûteux en temps. Une famille de méthodes appelée AK-RM (Active learning and Kriging-based Reliability Methods) est précisément proposée dans ces travaux de thèse afin de résoudre le problème de fiabilité avec un minimum d’évaluations du modèle mécanique. L’approche générale est appliquée à deux cas-tests fournis par SNECMA dans le cadre du projet ANR APPRoFiTraditional procedures for designing structures against fatigue are grounded upon the use of so-called safety factors in an attempt to ensure structural integrity while masking the uncertainties inherent to fatigue. These engineering methods are simple to use and fortunately, they give satisfactory solutions with regard to safety. However, they do not provide the designer with the structure’s safety margin as well as the influence of each design parameter on reliability. Probabilistic approaches are considered in this thesis in order to acquire this information, which is essential for an optimal design against fatigue. A general approach for probabilistic analysis in fatigue is proposed in this manuscript. It relies on the modelling of the uncertainties (load, material properties, geometry, and fatigue curve), and aims at assessing the reliability level of the studied structure in the case of a fatigue failure scenario. Classical reliability methods require a large number of calls to the mechanical model of the structure and are thus not applicable when the model evaluation is time-demanding. A family of methods named AK-RM (Active learning and Kriging-based Reliability methods) is proposed in this research work in order to solve the reliability problem with a minimum number of mechanical model evaluations. The general approach is applied to two case studies submitted by SNECMA in the frame of the ANR project APPRoFi
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Du, Yong. „Thermomechanical stress studies for advanced copper metallization and integration“. Access restricted to users with UT Austin EID Full text (PDF) UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3031046.
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Pirouznia, Pouyan. „High cycle fatigue properties of stainless martensitic chromium steel springs“. Thesis, KTH, Materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103201.
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For many materials and components like in high speed trains and airplanes fatigue failures occur in the range of over 107 load cycles which is called the high cycle fatigue range. A modern version of the springs was invented which are applied in a certain application. Ultrasonic fatigue testing (20 kHz machine) was conducted for evaluating the steel of the springs. This research explores the fundamental understanding of high cycle fatigue testing of strip steel and assesses a stainless martensitic chromium steel at the high cycle fatigue range. Finite element modeling was conducted to gain knowledge about the effect of various parameters. Significant attention was devoted to the fatigue failure initiations by SEM/EDS. The work demonstrated that the method of investigation for high cycle fatigue test is reliable. Fatigue failure at this range was initiated by internal defects which all included non-metallic inclusion. A critical distance was defined Within the strip fatigue specimen where all the fatigue failure initiated. The 3D stress field in the specimen was determined by FEM modeling and the local applied stress at the whole of the flat part of specimen and critical distance was estimated. FEM was also employed to give additional information about the effect of parameters. It was established that damping had the largest influence. The local applied stress of the fatigue test was calculated by means of FEM and SEM analysis. It was used to adjust the S-N curve which resulted in 15% lower values than the nominal applied stress.
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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.
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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%
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Abu, Eid Anna, und Josefin Jonsson. „Förebyggande faktorer mot compassion fatigue : En allmän litteraturöversikt“. Thesis, Mälardalens högskola, Akademin för hälsa, vård och välfärd, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-42857.
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Bakgrund: Tidigare forskning visar att vårdtyngden på sjukhusen ökar vilket leder till att vården blir påverkad, då sjuksköterskor anser att de inte vårdar etiskt och moraliskt rätt. Detta på grund av att det inte finns tillräckligt med tid att ge varje patient ”det lilla extra’’ och prioriteringar måste ske. Stressen hos sjuksköterskor ökar på grund av att prioriteringar är medvetna men inte självvalda, medvetenheten leder till att de arbetar på ett sätt sjuksköterskan själv anser är etiskt fel. Denna etiskt betingade stress leder till att kvaliteten på vården påverkas. Stressen kan leda till självanklagelser som “borde jag ha sprungit snabbare mellan patienterna”. På grund av bristfällig återhämtning försvinner krafterna till att ge en god vård. Syfte: Att belysa skyddsfaktorer som förebygger Compassion fatigue (CF) hos sjuksköterskor. Metod: Allmän litteraturöversikt. Där vårdvetenskapliga artiklar av kvalitativa, kvantitativa och mixad metod har använts. Resultat: Få stöd av sina kollegor, ledning och familjemedlemmar var viktiga faktorer för att förebygga CF. Kunskap hur sjuksköterskorna själva fungerar för att kunna minska sin stress, samt att känna compassion satisfaction var viktiga aspekter för att kunna förebygga CF. Slutsats: När sjuksköterskorna kände en mening med vårdandet kunde CF förebyggas.
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Porteiro, John L. „Spring Design Optimization With Fatigue“. Scholar Commons, 2010. https://scholarcommons.usf.edu/etd/1742.
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The purpose of this work is to look into the fundamental issues regarding spring design and develop a new, easy to use software program that would allow for optimal, flexible spring designs. Most commercial programs that address this function are basic and do not allow the designer much control over the variables hindering design. This is so because most programs start from the premise that the spring is a general purpose part of the system or that other design parameters can be altered to accommodate the chosen spring. In cases where this is not so, such as in hydraulic cartridge valves, where the geometric constraints are severe, spring design may be a cumbersome process. This is particularly true when fatigue life is taken into account.
The solution chosen here is to tailor the software application to these particular design constraints, incorporating some ideas about spring optimization. In addition to this, a concerted effort was made to make the subject more accessible to the engineers using the program by automating the more technical aspects of the process allowing the designers to make intelligent decisions based on how the variables would affect design. To this end currently existing software was evaluated to determine where it was lacking and a new program was written and painstakingly tested. Finally, it was used to correct flaws identified in existing springs.
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Radonovich, David Charles. „Methods of Extrapolating Low Cycle Fatigue Data to High Stress Amplitudes“. Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3460.
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Modern gas turbine component design applies much effort into prediction and avoidance of fatigue. Advances in the prediction of low-cycle fatigue (LCF) cracks will reduce repair and replacement costs of turbine components. These cracks have the potential to cause component failure. Regression modeling of low-cycle fatigue (LCF)test data is typically restricted for use over the range of the test data. It is often difficult to characterize the plastic strain curve fit constants when the plastic strain is a small fraction of the total strain acquired. This is often the case with high strength, moderate ductility Ni-base superalloys. The intent of this project is to identify the optimal technique for extrapolating LCF test results into stress amplitudes approaching the ultimate strength. The proposed method to accomplish this is by finding an appropriate upper and lower bounds for the cyclic stress-strain and strain-life equations. Techniques investigated include: monotonic test data anchor points, strain-compatibility, and temperature independence of the Coffin-Manson relation. A Ni-base superalloy (IN738 LC) data set with fully reversed fatigue tests at several elevated temperatures with minimal plastic strain relative to the total strain range was used to model several options to represent the upper and lower bounds of material behavior. Several high strain LCF tests were performed with stress amplitudes approaching the ultimate strength. An augmented data set was developed by combining the high strain data with the original data set. The effectiveness of the bounding equations is judged by comparing the bounding equation results with the base data set to a linear regression model using the augmented data set.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering MSME
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Fjeldstad, Arne. „Modelling of Fatigue Crack Growth at Notches and Other Stress Raisers“. Doctoral thesis, Norwegian University of Science and Technology, Department of Engineering Design and Materials, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1811.
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This thesis consists of an introduction and eight papers [1–8]. Paper 1 presents simple and flexible methods to enhance the fatigue life of welded aluminium components. The key element of the methods is to change residual stresses from tension to compression at locations vulnerable to fatigue crack growth. This is accomplished by mechanical pre-stressing using elastic pre-deformation or thermal pre-stressing using induction heating. Based on fatigue test results induction heating tuned out to be the most promising method.
In Paper 2, an approximate method based on asymptotic solutions for estimating the stress intensity factor for cracks at stress concentrations is presented. The proposed solution makes use of the near-notch and remote-notch solution to interpolate over the entire range from shallow to deep cracks. Paper 3 extends the theory presented in Paper 2 to cover through-cracked plates of finite width subjected to bending or tension. Paper 4 examines how a decreasing stress field influences the fatigue crack growth. Even though the stress generally decreases from a maximum at some critical point, fatigue crack growth analyses are often performed assuming a homogeneous stress state to avoid the difficulties related to crack growth analyses in complex components. The degree of conservatism has been determined by comparing the calculated fatigue life of cracks growing in a homogeneous stress field with the fatigue life of cracks growing in a gradient stress field. In Paper 5, an approximate method based on asymptotic solutions for estimating the stress intensity factor for cracked V-notched plates is presented. The proposed solutions make use of a reference solution to interpolate from shallow to deep cracks. The reference solution is obtained by considering the current crack emanating from the associated specimen with a sharp notch. It is showed how the proposed theory can be used for estimating the stress intensity factor for a crack located at the root of a weld toe in a T-joint.
Paper 6 and 7 presents the probabilistic fatigue assessment tool, P•FAT, for the fatigue analysis of arbitrary components. General concepts which have to be considered for the accomplishment of a 3D fatigue crack simulation by postprocessing results from a standard finite element analysis are introduced. General features such as determination of the life controlling defect, fatigue strength and fatigue life distribution, and probability of component failure, have been presented. Furthermore, a new short crack growth model that accounts for short crack growth is presented. In Paper 8, the short crack growth model is used to predict the arrest of cracks growing in stress gradient fields. The predictions have been compared with experimentally obtained data for notched specimens and found to agree well.
Paper I and II reprinted with kind permission of Elsevier, sciencedirect.com
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McKinnon, Peter Laurence, University of Western Sydney, College of Social and Health Sciences und of Nursing Family and Community Health School. „Tired of dying : fatigue and stress in long distance road transport“. THESIS_CSHS_NFC_McKinnon_P.xml, 2004. http://handle.uws.edu.au:8081/1959.7/657.
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In this thesis, the author has drawn on a large body of international research and his own surveys, interviews and experience to examine the interrelated issues of Fatigue and Stress in the long distance sector of the Australian road transport industry. Two major Australian studies are studied in some detail: House of Representatives Standing Committee on Communications, Transport and the Arts: Beyond the Midnight Oil, Report into an Inquiry into Managing Fatigue in Transport, Parliament of the Commonwealth of Australia October 2000 (The Neville Report) and Quinlan, Michael, Report of an Inquiry into Safety in the Long Haul Sector of the Road Trucking Industry, Motor Accident Authority of NSW, Nov 2001 and the United States of America: Belzer, Michael H., Sweatshop on Wheels: Winners and Losers in Trucking Deregulation, Oxford University Press, New York, 2000, has direct relevance to this study, especially as it relates to the underlying causes of much of the fatigue and stress suffered by long distance drivers. An extensive literature review was undertaken to help form an understanding of the issues and developments relating to workplace fatigue and stress, in several different settings, including the military, aviation and general industry. The author has surveyed a number of long distance drivers and interviewed managers and others linked to this industry, analysed their responses and reported on the findings. Since the commencement of this study, several significant changes have occurred in the relevant legislation and its application, and where possible these have been incorporated into the studyMaster of Science (Hons)
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Fellows, Lesley. „Fatigue crack growth under variable stress ratios and complex load history“. Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325898.
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Mock-McLaughlin, Jessica. „STRESS, FATIGUE AND WORKLOAD: DETERMINING THE COMBINED AFFECT ON HUMAN PERFORMANCE“. Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3526.
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This research generated a model that will help to predict, prevent, control and mitigate the occurrence of task related factors that negatively influence stress, fatigue, and workload; thus enhancing human performance. Past research efforts involving stress, fatigue and workload identified factors that influence a change in performance (Lan, Ji and Looney, 2003, and Hancock & Warm, 1989). Also, while some mathematical models have been developed within each respective area, however, there is no evidence of an integrated model describing the combined affect of stress, fatigue and workload. To respond to this research gap, a quantitative model representing the state of stress, fatigue and workload experienced under task conditions was developed. This model was derived using fuzzy set theory with data inputs from both objective and subjective measures such as heart rate, NASA TLX, blood pressure and a variety of additional factors. The resultant mathematical model included both subjective and objective measures that can be collected in an occupational environment. Control rooms at the flight centers for large space craft were utilized to validate the quantitative model developed in this research. Data was gathered during launch simulation exercises. Fuzzy Set Theory was applied to develop the mathematical model to describe the changes in stress, fatigue and workload. FST provides a means to model many real-world environments.Ph.D.
Department of Industrial Engineering and Management Systems
Engineering and Computer Science
Industrial Engineering PhD
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Han, Sungkon. „Fatigue and fracture mechanics analysis of components containing residual stress fields“. Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407985.
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