This doctoral thesis concerns fatigue of welded structures. Welding is one of the world’s most common joining methods and it is frequently used in several structural applications in many fields. Some examples are construction vehicles, loader cranes, trucks, busses, forestry and agricultural machines, bridges and ships. Since these structures are subjected to repeated loading, fatigue is the most common cause of failure. A novel numerical algorithm has been developed which assesses the welded surface and calculates and quantifies weld quality parameters and the presence of defects which are critical in fatigue applications. The algorithm is designed for implementation in serial production. It will provide robust and reliable feedback on the quality being produced, which is essential if high strength steels are utilized. Two welding procedures which can increase the weld quality in as welded conditions have been assessed. These procedures utilize welding in different positions and pendling techniques, which can be accomplished using the existing welding equipment. It was found that by using these methods, the fatigue strength can be increased compared to normal weld quality. Furthermore, two fatigue assessment methods ability to account for increased weld quality in low cycle and high cycle fatigue applications has been studied. One of these methods showed sufficient accuracy in predicting the fatigue strength with small scatter and also account for increased weld quality. When implementing thinner high strength steels, the overall stress level in the structure increase. Therefore, other locations such as the steel cut edges may become critical for fatigue failure unless they are not designed and manufactured with the same quality as the welded joint. The influence of surface quality on cut edges was studied and the fatigue strength was estimated using international standards and a fatigue strength model for cut edges. / <p>QC 20160613</p> / WIQ / LIGHTSTRUCT / ONWELD

Background Stroke is a major cause of disability worldwide. After treatment in a specialized stroke unit, early supported discharge (ESD) followed by home rehabilitation has shown to be an effective way to improve patient outcome and quality of care for persons with mild to moderate stroke. ESD service is recommended in the national and international guidelines for stroke care, but has only partially been implemented in Sweden. Following stroke, fatigue is a common consequence that often becomes more evident when the patient comes home. Currently, there is insufficient evidence about how to measure, treat and handle post-stroke fatigue. The overall aim of this thesis was to evaluate and implement early supported discharge (ESD) based on stroke patients experience after discharge from the stroke unit and local conditions. The aim was also to evaluate post-stroke fatigue with a potentially valid and reliable scale and finally to prepare for a study to evaluate cardiorespiratory training as a part of ESD service for patients with post-stroke fatigue. Methods In paper I, nine strategically chosen patients were interviewed of their experience of falling ill, the hospital stay, discharge, contact with health care after discharge and their request of support. Papers II-III describe and evaluate the development, content, implementation and effects of a locally adopted method for early supported discharge (Umeå Stroke Center ESD) in modern stroke care. Paper II included 153 consecutive patients and paper III, 30 232 patients with first-ever stroke registered in the Riksstroke registry in Sweden. Paper II evaluated number of patients/year, clinical and functional health status, satisfaction in relation to needs, accidental falls/other injuries and resources with the result summarized in a value compass. The implementation process was evaluated retrospectively by means of Consolidated Framework for Implementation (CFIR). Paper III evaluated patient reported outcome measurements (PROMs) at 3 months. The primary outcome in paper III was satisfaction with the rehabilitation after discharge. Secondary outcomes were information about stroke provided, tiredness/fatigue, pain, dysthymia/depression, general health status and dependence in activities of daily living (mobility, toilet hygiene and dressing). Multivariable logistic regression models for each PROM was used to analyze associations between PROMs and ESD/no ESD. In Paper IV, the Fatigue Assessment scale (FAS) was translated into Swedish and evaluated regarding psychometric properties when self-administered by persons with mild to moderate stroke. 72 consecutively patients selected from the stroke unit admission register received a letter including three questionnaires: the FAS, the Short Form Health Survey (SF-36) subscale for vitality and the Geriatric Depression Scale GDS-15. A second letter with FAS was sent within 2 weeks, for re-test evaluation. Paper V is a study protocol for a planned randomized controlled trial (RCT) of 50 consecutive stroke patients will who receive stroke unit care followed by ESD-service at Umeå Stroke Center, University Hospital, Umeå, Sweden. Paper V will investigate if a structured cardiorespiratory interval training program (CITP) added to the ESD-service may result in relieved post-stroke fatigue and increased oxygen uptake. Results The interviews in Paper I revealed three main categories with subcategories: “Responsible and implicated”, “Depersonalized object for caring measures” and “The striving for repersonalization and autonomy”. The findings indicate that coming home gave the informants’ important insights and understanding of the stroke, its consequences and was also an important factor for the recovery. Paper II-III showed that it is possible to develop and implement an adapted ESD service for stroke patients based on the patients’ experiences and requests, evidence-based recommendations and local conditions. The ESD service reduced dependence of activity, increased mobility with seemingly no increased risk of accidental falls or other injuries. The patient satisfaction in relation to needs regarding the ESD was high. Paper III showed that patients that received ESD were more satisfied with rehabilitation after discharge, had less need for assistance with ADL and less dysthymia/depression compared to patients that did not receive ESD. Study IV showed that the Swedish FAS used at home as a selfadministered questionnaire is a reliable and valid questionnaire for measuring fatigue in persons with mild to moderate stroke. The internal consistency was good, the agreement between the test and retest reliability for individual items (weighted kappa) was for the majority of items good or moderate. The relative reliability for total scores was good and the absolute reliability was 9 points. The Swedish FAS had no floor nor ceiling effects and correlated both with the SF-36, subscale for vitality and the GDS-15 indicating convergent construct validity, but not divergent construct validity. Conclusion It is possible to develop and implement ESD care for stroke patients based on patients’ experience and needs, evidence-based principles and local conditions. Early supported discharge (ESD) in the setting of modern stroke unit care appears to have positive effects on rehabilitation in the subacute phase. The Swedish FAS used at home as a self-administered questionnaire is reliable and valid for measuring fatigue in persons with mild to moderate stroke.

This thesis is investigating how the effective notch method can be used for fatigue assessment of welded joints.  The effective notch method is based on a finite element analysis where the joint is modeled with all notches fictitiously rounded with a radius of 1 mm. Analyses are performed on a cruciform fillet welded joint where parameters such as, load case, steel plate thickness and weld size, are varied. The achieved lifetime estimations are then compared to calculations with other fatigue assessment methods, linear elastic fracture mechanics and the nominal method. The goal is to draw conclusions about pros and cons of the effective notch method. The results are also compared to experimental fatigue tests performed on the same geometry. The results indicates that the effective notch method tends overestimating the lifetime, especially when the steel plate thickness is small. This leads to a non conservative method that is dangerous to use as guidance when designing. The estimations are though better when considering a toe crack then when considering a root crack. Due to a large scatter in experimental test results, it is hard to validate a fatigue assessment method in an absolute sense. That is also the case for the effective notch method, and more results from experimental fatigue tests are needed before the effective notch method can be fully used. For relative analysis, when variations of the same design needs to be compared, the effective notch can be a very powerful tool. This is because of the flexibility for different geometries that this method grants.

The installed capacity of offshore wind turbines in Europe is increasing with the monopile being the most common type of foundation. During its lifetime an offshore wind turbine is exposed to high dynamic loads which eventually can result in the fatigue of the substructure. This thesis will show how the linear damage accumulation approach based on the Miner’s rule can be used to estimate the damage induced on the substructure of an offshore wind turbine using measurements from strain gauges. Furthermore, the most important environmental influences will be illustrated and the different stress concentration factors and the size effect introduced in the industry guideline DNVGL-RP-C203 will be analysed towards their effect on the calculated lifetime.

Medical mistakes made during the fatigue state result in the spread of infection, diagnostic error, psychological distress, poor patient outcomes, and ultimately, loss of life. Alarmingly, the fatigue-management systems put forth by government agency have failed to reduce the risks of fatigue in physicians. A shift from “one size fits all” approaches for fatigue management, to individualized fatigue assessment and training, is required. To date, no validated measures of fatigue are feasible for use as portable, on-site assessments. Here, I propose the use new portable EEG technologies recently validated for the collection of ERP data, as a basis for a portable fatigue assessment that is cost effective, portable, and efficient enough to be used in medical professionals. Over the course of three experiments I have provided data to support the use of the MUSE portable EEG headband, in combination with short oddball task to assess fatigue related neural impacts. Results of these experiments indicate that the P300 component is reduced in fatigued subjects in comparison to non-fatigued, and further that there is a strong correlation between subjective fatigue severity and P300 amplitude. / Graduate

Background: Cancer-related fatigue is one of the most common symptom experienced by cancer patients throughout their cancer trajectory. However, very little effort has been made within many oncology practices to assess this clinical problem and to provide timely nursing interventions to reduce its impact. While there have been tremendous advancements in the treatments of the disease aspects of cancer in term of medicine and advanced technology, basic assessment of related physiological concerns, such as fatigue, have not seen the same progress. Purpose: The purpose of this quality improvement project was to develop an evidence-based cancer-related fatigue assessment guideline and a screening protocol adopted from the National Comprehensive Cancer Network algorithm to assess cancer-related fatigue for oncology patients at their initial visit to the oncology unit toward timely intervention. Theoretical Framework: The ADAPTE collaboration model was used. This is an international framework that provides guidance on guidelines development and modification for healthcare providers. Method: This initiative began with a series of formal and informal conversations with major key stakeholders who were primarily the front-line oncology nurses at the practice unit. Based on the need of the unit, a consensus was reached to modify an existing clinical tool currently used to screen patients for emotional distress and to develop a clinical tool and guideline to screen cancer patient to reduce cancer-related fatigue as well. Outcome and Result: A clinical assessment tool was developed based on the patient population needs and the nursing staff concerns to yield an outcome that met the needs of this patient population. An evidence-based assessment guideline was introduced to key stakeholders and recommendations were made to integrate the new revised guideline into practice. The research department, professional practice, and the performance leadership continue to revise the current protocol to include continuous assessment of cancer-related fatigue into policy and procedure. Conclusion: This quality improvement project once implemented will benefit cancer patients as well as oncology practitioners by use of available resources and evidence-based guidelines to improve nursing practice and patient quality of life.

This thesis treats virtual sensing for fatigue assessment of steel bridges. The purpose is to develop avirtual sensing method to use in the fatigue assessment process. The aim for the virtual sensing method is to only depend on strain measurements located on the bridge structure. The service life of bridges is often limited by fatigue and amending bridge design to improve fatigue resistance was developed in the 1970s. There are several bridges in Sweden, Europe and other countries that have exceeded their theoretical service life with regard to fatigue, and the need to replace them isboth a environmental and economical issue. The bridge over Rautasjokk north of Kiruna, Sweden is a specific example where the theoretical service life is limited by fatigue. Uncertainties in the theoretical fatigue assessment of bridges can be reduced by measuring strains atthe fatigue critical details, and therefore lead to a longer theoretical service life. Monitoring is, however,an expensive method and the procedure of installation and administration requires working time, and monitoring can only provide information at the gauge location. Hence, it is of great interest to optimizethe monitoring system. Virtual sensing is a method that could provide an alternative to conventionalmeasuring techniques. Virtual sensing combine measurement data with information from a model. Virtual sensing for fatigue assessment of the Rautasjokk Bridge was evaluated developing two methods. Both methods uses a finite element model of the bridge combined with strain measurements. The measurements were obtained on February 14 2018 and included a time signal and strain variations at six different locations of the structure. The accuracy of the virtual sensing methods were evaluated by comparing the fatigue damage of virtual sensing with the fatigue damage calculated using measured strains. The fatigue calculations were based on methods presented in the Eurocode EN-1993-1-9. The first method was based on the idea to find a relation between groups of stress ranges for two gauge locations on the bridge. The stress ranges were established by loading influence lines obtained from the finite element model with a fictitious train and the difference between two gauges was stored in a vector, the correlation vector. The correlation vector was applied on the measured stress ranges of the first gauge to estimate the actual stress ranges of the second gauge. No relation between groups of stress ranges for different loading cases was found and the correlation vector method for virtual sensing is not a sufficiently accurate method to apply in the fatigue assessment of the Rautasjokk Bridge. The second method was based on finding a relation between each stress range instead of a group of stress ranges. Influence lines from the finite element model were used to find a relation between each stress range of two gauges. Their relation was stored in a matrix, the correlation matrix. The matrix was applied on the measured stress ranges of the first gauge to estimate the actual stress ranges of the second gauge. The correlation matrix method for virtual sensing estimate the fatigue damage sufficiently accurate at the bridge locations where local stress ranges have the greatest impact on the fatigue damage. Results obtained through virtual sensing only include the same parameters that were used as inputs in the method. A credible virtual sensing method is crucial in order to achieve reliable results. In general, a virtual sensing method requires an extent amount of input data to validate its reliability. Further studies are required to investigate how the uncertainties of the correlation matrix affect the fatigue assessment.

Problematik med utmattningsbrott är känt sedan början på 1800-talet och fenomenet har studerats sedan dess. Efter lång tids arbete har man hittat en metodik för att ta fram analytiska beräkningsmodeller samt säkra och noggranna livslängdsberäkningar för stålkonstruktioner. Syftet med detta arbete har varit att undersöka en marin ångpannas utmattningshållfasthet under loppet av dess ekonomiska livslängd. I den här studien har en analytisk beräkning gjorts på en marin ångpannas utmattningslivslängd med hjälp av DNV ́s regler för klassifikation av fartyg samt Europeiska tryckkärlsnormen. I studien har författarna tagit hänsyn till ångpannans tryckvariationer, temperaturvariationer samt den marina ångpannans yttre påverkan från fartygets rörelse i vattnet och de resulterande hävkrafterna. Detta för att med hög tillförlitlighet (konfidens) kunna värna om människoliv, natur och miljö, fysisk egendom (fartyg samt last), operativa tillgänglighet samt lagar och regler. / Problems with fractures due to fatigue have been known since the early 19th century, and the phenomenon has been studied since then. After long periods of work, a methodology has been found to develop analytical fatigue calculation models for steel structures. The purpose of this work has been to investigate the fatigue assessments of marine boilers during it ́s economic lifetime. In this study, an analytical calculation has been made of the marine boiler using DNV's ship classification rules and the European pressure vessel standard. In the study, the authors have taken into account the boilers pressure variations, temperature variations, and the marine boiler's external impact from the vessel's motion in the water and the resulting forces. In order to be able to protect human life, nature and the environment, physical property (ships and cargo), operational availability as well as laws and regulations, with high reliability (confidentiality).

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As pontes rodoviárias metálicas e mistas (aço-concreto) são submetidas a um grande número de carregamentos repetitivos de diferentes magnitudes, ao longo do tempo. Estas ações dinâmicas podem causar a nucleação de fraturas ou mesmo a propagação destas sobre o sistema estrutural. A depender da magnitude, estes efeitos podem comprometer o sistema estrutural e a sua confiabilidade, além de reduzir a vida útil das pontes. Assim sendo, neste trabalho de pesquisa foi investigada a resposta dinâmica de uma ponte mista (aço-concreto), simplesmente apoiada, com vão de 40,0 m, submetida ao tráfego de veículos sobre a superfície irregular do pavimento. Para tal um modelo numérico representativo do sistema estrutural foi desenvolvido com base no emprego do programa ANSYS, por meio do uso de técnicas usuais de discretização, via método dos elementos finitos. Um estudo paramétrico foi desenvolvido para identificar, de forma qualitativa e quantitativa, o efeito das irregularidades do pavimento sobre o comportamento dinâmico da ponte mista investigada. Em seguida, a verificação do projeto à fadiga do sistema misto foi realizada, com base no emprego do algoritmo de contagem de ciclos Rainflow e em curvas S-N associadas às principais normas de projeto sobre o tema. As conclusões deste trabalho de pesquisa alertam aos engenheiros estruturais para a possibilidade concreta acerca do aumento do dano por fadiga, relacionado às ações dinâmicas de veículos trafegando sobre o tabuleiro de pontes em aço e mistas (aço-concreto). / Steel and steel-concrete composite highway bridges are currently subjected to dynamic actions with variable magnitudes due to the action of vehicles crossing on the deck. These dynamic actions can generate the nucleation of fractures or even their propagation in the structures. Depending on the magnitude, these effects can compromise the structural system response and the reliability, which may also lead to a reduction of the expected bridge service life. This way, the dynamic response of a steel-concrete composite bridge spanning 40 m was investigated in this work. The computational model, developed for the composite bridge dynamic analysis, adopted the usual mesh refinement techniques present in finite element method simulations, and was implemented in the ANSYS program. A parametric study was performed to identify the effect of vehicle speed and roughness pavement on the investigated bridge dynamic behaviour. The proposed methodology for evaluate the bridge service life to fatigue was based on a linear cumulative damage rule, Rainflow-counting algorithm and S-N curves from main design codes. Results of a parametric analysis are presented to verify the extension of the dynamical effects on highway bridges due to vehicles crossing on the irregular pavement surface. The main conclusions of this work focuses on alerting structural engineers to the possibility of increase of fatigue damage, related to steel and composite highway bridges when subjected to vehicle dynamic actions.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As pontes rodoviárias metálicas e mistas (aço-concreto) são submetidas a um grande número de carregamentos repetitivos de diferentes magnitudes, ao longo do tempo. Estas ações dinâmicas podem causar a nucleação de fraturas ou mesmo a propagação destas sobre o sistema estrutural. A depender da magnitude, estes efeitos podem comprometer o sistema estrutural e a sua confiabilidade, além de reduzir a vida útil das pontes. Assim sendo, neste trabalho de pesquisa foi investigada a resposta dinâmica de uma ponte mista (aço-concreto), simplesmente apoiada, com vão de 40,0 m, submetida ao tráfego de veículos sobre a superfície irregular do pavimento. Para tal um modelo numérico representativo do sistema estrutural foi desenvolvido com base no emprego do programa ANSYS, por meio do uso de técnicas usuais de discretização, via método dos elementos finitos. Um estudo paramétrico foi desenvolvido para identificar, de forma qualitativa e quantitativa, o efeito das irregularidades do pavimento sobre o comportamento dinâmico da ponte mista investigada. Em seguida, a verificação do projeto à fadiga do sistema misto foi realizada, com base no emprego do algoritmo de contagem de ciclos Rainflow e em curvas S-N associadas às principais normas de projeto sobre o tema. As conclusões deste trabalho de pesquisa alertam aos engenheiros estruturais para a possibilidade concreta acerca do aumento do dano por fadiga, relacionado às ações dinâmicas de veículos trafegando sobre o tabuleiro de pontes em aço e mistas (aço-concreto). / Steel and steel-concrete composite highway bridges are currently subjected to dynamic actions with variable magnitudes due to the action of vehicles crossing on the deck. These dynamic actions can generate the nucleation of fractures or even their propagation in the structures. Depending on the magnitude, these effects can compromise the structural system response and the reliability, which may also lead to a reduction of the expected bridge service life. This way, the dynamic response of a steel-concrete composite bridge spanning 40 m was investigated in this work. The computational model, developed for the composite bridge dynamic analysis, adopted the usual mesh refinement techniques present in finite element method simulations, and was implemented in the ANSYS program. A parametric study was performed to identify the effect of vehicle speed and roughness pavement on the investigated bridge dynamic behaviour. The proposed methodology for evaluate the bridge service life to fatigue was based on a linear cumulative damage rule, Rainflow-counting algorithm and S-N curves from main design codes. Results of a parametric analysis are presented to verify the extension of the dynamical effects on highway bridges due to vehicles crossing on the irregular pavement surface. The main conclusions of this work focuses on alerting structural engineers to the possibility of increase of fatigue damage, related to steel and composite highway bridges when subjected to vehicle dynamic actions.