The uptake of renewable energy sources has increased dramatically in recent decades, in response to the contribution to climate change attributed to CO2 emissions from the burning of fossil fuels, the need for governments to maximise the use of domestic energy forms with depleting conventional sources, and to reduce exposure to fuel price volatility. Renewable energy targets set by the European Union have been supported by legislation and economic incentives, and have resulted in a sharp increase in installed wind power capacity in particular. Wind power is seen as a particularly attractive source of renewable energy capacity in the UK due to favourable resources and a competitive cost of energy for onshore sites, with 8.8 GW of capacity currently installed [1]. Constraints from visual and environmental impacts, together with improved wind resources, have led to the acceptance of greater financial costs and the exploitation of offshore sites, with over 5 GW installed to date [1]. Both onshore and offshore, the wind industry now has significant operational experience, with some of the earliest wind farms approaching the end of their design life. Material fatigue is a design critical factor which dictates the safe operational life of wind turbines, but is subjected to numerous areas of uncertainty in the level of environmental loading and structural response, as well as material properties and manufacturing methods. Therefore, a conservative design must be ensured from the outset, which presents the potential for fatigue life extension of installed assets if improved knowledge of their operational experience can be obtained. This thesis details the methodology for a fatigue load assessment of operational offshore wind turbine support structures using measured data, and attempts to quantify areas of loading which contribute to total fatigue damage. The methodologies developed build on existing recommendations for onshore wind turbines to incorporate the additional effects of the offshore environment. Results from measured loading suggest that design fatigue levels can be reduced if operational monitoring is included. Operational experience can allow design conservatism, which is necessary due to uncertainties in structural properties and in levels of stochastic loading, to be more accurately quantified.

O sucesso da terapia reabilitadora com implantes requer um equilíbrio entre fatores biológicos e mecânicos. Os fatores biológicos são inúmeros, já os mecânicos associam-se à instabilidade da interface implante-intermediário protético. Com base nestas informações, este estudo busca criar um aparelho com o qual será possível avaliar e comparar a resistência e a estabilidade da interface implante-intermediário protético em implantes de diferentes tipos de sistema de conexão e componentes protéticos, após a aplicação de carga simulada, que será realizada por meio de um ensaio dinâmico de fadiga rotacional, também conhecido como flexão rotativa. Para a criação deste aparelho, vários procedimentos com base em princípios de usinagem CNC (Controle Numérico Computadorizado), engenharia elétrica e física foram utilizados. Os futuros testes e resultados, utilizando-se esse aparelho para realizar o ensaio de fadiga, serão publicados em trabalhos futuros. Para o desenvolvimento dos modelos de corpos de prova a serem analisados na máquina de ensaio, foram utilizados implantes do tipo hexágono externo (Neodent) de 3,75mm de diâmetro x 11.5mm de comprimento. Ao término do desenvolvimento, obteve-se um aparelho confiável, resistente e extremamente versátil; podendo-se facilmente variar a carga exercida e a frequência de rotação, sendo assim possível executar inúmeras combinações de ensaios de fadiga. Esse estudo demonstrou a possibilidade e viabilidade de desenvolver um aparelho adequado para realizar um ensaio de fadiga, de pequena dimensão (portátil) e a um custo significativamente inferior do que comprar um aparelho próprio para tal fim. / The success of a rehabilitation therapy with implant fixtures requires a balance between biological and mechanical factors. The biological factors are innumerable, however the mechanics associate it whit instability of the implant-abutment interface. On the basis of these information, the aim of this study is to create a device which it will be possible to evaluate and to compare the resistance and the stability of the implant-abutment interface whith implants of different connection system and abutments, after the simulated load application, that will be carried through a dynamic assay of rotational fatigue load, also known as rotary bending. For the creation of this device, some procedures on the basis of principles of milling CNC (Computerized Numerical control), electric and physical engineering had been used. The future tests and results, using this device to carry through the fatigue assay, will be published in future works. For the development of the body test to be analyzed in the assay machine, implant fixtures of external hexagon type (Neodent) of 3,75mm of diameter x 11mm of length had been used. In the ending of the development, a trustworthy, resistant and extremely versatile device was gotten; being able itself easily to vary the exerted load and the frequency of rotation, being been thus possible to execute innumerable combinations of fatigue assays. This study demonstrated the possibility and viability of it developing an adequate device to carry through an assay of fatigue, of small dimension (portable) and the significantly inferior cost of what if to buy a proper device for such end.

O sucesso da terapia reabilitadora com implantes requer um equilíbrio entre fatores biológicos e mecânicos. Os fatores biológicos são inúmeros, já os mecânicos associam-se à instabilidade da interface implante-intermediário protético. Com base nestas informações, este estudo busca criar um aparelho com o qual será possível avaliar e comparar a resistência e a estabilidade da interface implante-intermediário protético em implantes de diferentes tipos de sistema de conexão e componentes protéticos, após a aplicação de carga simulada, que será realizada por meio de um ensaio dinâmico de fadiga rotacional, também conhecido como flexão rotativa. Para a criação deste aparelho, vários procedimentos com base em princípios de usinagem CNC (Controle Numérico Computadorizado), engenharia elétrica e física foram utilizados. Os futuros testes e resultados, utilizando-se esse aparelho para realizar o ensaio de fadiga, serão publicados em trabalhos futuros. Para o desenvolvimento dos modelos de corpos de prova a serem analisados na máquina de ensaio, foram utilizados implantes do tipo hexágono externo (Neodent) de 3,75mm de diâmetro x 11.5mm de comprimento. Ao término do desenvolvimento, obteve-se um aparelho confiável, resistente e extremamente versátil; podendo-se facilmente variar a carga exercida e a frequência de rotação, sendo assim possível executar inúmeras combinações de ensaios de fadiga. Esse estudo demonstrou a possibilidade e viabilidade de desenvolver um aparelho adequado para realizar um ensaio de fadiga, de pequena dimensão (portátil) e a um custo significativamente inferior do que comprar um aparelho próprio para tal fim. / The success of a rehabilitation therapy with implant fixtures requires a balance between biological and mechanical factors. The biological factors are innumerable, however the mechanics associate it whit instability of the implant-abutment interface. On the basis of these information, the aim of this study is to create a device which it will be possible to evaluate and to compare the resistance and the stability of the implant-abutment interface whith implants of different connection system and abutments, after the simulated load application, that will be carried through a dynamic assay of rotational fatigue load, also known as rotary bending. For the creation of this device, some procedures on the basis of principles of milling CNC (Computerized Numerical control), electric and physical engineering had been used. The future tests and results, using this device to carry through the fatigue assay, will be published in future works. For the development of the body test to be analyzed in the assay machine, implant fixtures of external hexagon type (Neodent) of 3,75mm of diameter x 11mm of length had been used. In the ending of the development, a trustworthy, resistant and extremely versatile device was gotten; being able itself easily to vary the exerted load and the frequency of rotation, being been thus possible to execute innumerable combinations of fatigue assays. This study demonstrated the possibility and viability of it developing an adequate device to carry through an assay of fatigue, of small dimension (portable) and the significantly inferior cost of what if to buy a proper device for such end.

At the turn of 2010/2011, Sweden went from designing structures according to nationaldesign codes to the new European standards Eurocode. For bridge engineers, this implieda change from a combination of BRO 2004 and BSK 07 to the Eurocode as the maindocuments, complemented by national documents such as TRVK Bro 11. The normtransition did not only change the calculation methods, but also turned a phenomenonthat never was of great importance for road bridges before into something that could limitthe carrying capacity of the structure. This phenomenon is called fatigue, i.e. repeatedload cycles, where each load is much lower than the ultimate limit state capacity, thatfinally results in collapse. This master thesis investigates why fatigue is significant in the design today. This is donethrough a comparison of how the new and old regulations assesses fatigue. A bridge builtin 2011, designed by ELU Konsult AB according to the old regulations, was modelledin the finite element program LUSAS. Several lorry crossings from different fatigue loadmodels were then simulated. The output from LUSAS was then used to calculate theutilization ratios for three critical points along the bridge. The result indicates that both regulations give rise to similar stress ranges, i.e. thedifference between the maximum and minimum stress obtained during a crossing. Thedifferences between the regulations are instead within the fatigue calculations, where themajor difference is the number of lorries crossing the bridge during its lifetime. Theutilization ratio according to the old regulations for the worst exposed point is 27.0 %,corresponding to 9.13 daily crossings by heavy lorries, which is the maximum numberof daily crossings provided by BRO 2004. The lowest utilization ratio according tothe Eurocode is 70.0 %, calculated for 137 daily crossings which is the lowest amountof crossings allowed. An interpretation of the Eurocode, which allows usage of fatigue loadmodel 5 even for smaller bridges, results in a utilization ratio of 56.0% which correspondsto 90.0 daily crossings, i.e. lower than the other fatigue load models provided by theEurocode but clearly above the old regulations. The conclusion is that an alternative way of deciding the number of crossings shouldbe provided by the Eurocode. Today, the classification consists of four steps, which arevery rough. Instead, a proposal is given in this thesis which advocates usage of a linearfunction for deciding the number of design crossings based on the number of daily crossingsby lorries. The proposed alternative design method is between the two regulations withrespect to daily crossings and utilization ratio. / Vid årsskiftet 2010/2011 övergick Sverige från att dimensionera byggnadsverk enligt nationellastandarder till den nya europastandarden Eurokod. För brokonstruktörer innebar dettaen övergång från en kombination av BRO 2004 och BSK 07, till att Eurokod blev dethuvudsakligt styrande dokumentet, med bland annat TRVK Bro 11 som ett dokumentmed tillhörande nationella val. Övergången medförde inte bara att verksamma konstruktörertvingades lära sig förändrade beräkningsmetoder, utan också att ett fenomen som tidigaresällan var dimensionerande för vägbroar nu kunde vara det som ställde högst krav påbärförmågan. Detta fenomen kallas utmattning, dvs. upprepade av- och pålastningar, varoch en betydligt lägre än brons maximala bärförmåga, som i slutändan resulterar i brott. I detta examensarbete utreds det varför utmattning numera är en betydande del avdimensioneringen. Detta sker genom en jämförelse av hur de gamla och nya normernautvärderar utmattning. Som modell har en befintlig bro invigd 2011, dimensioneradav ELU Konsult AB enligt de gamla normerna, använts. Denna bro har modellerats ifinita element programmet LUSAS, varpå en mängd olika lastbilsöverfarter simulerats ochutmattningsutnyttjandet för tre utvalda kritska punkter beräknats. Resultatet indikerar att båda normerna har liknande storlekar på spänningsvidderna,dvs. skillnaden på största och minsta spänningen som uppstår vid en överfart. Däremotråder det skillnader vid utmattningsberäkningarna, där den stora skillnaden är antalettunga fordon som passerar bron under dess livslängd. Enligt de gamla normerna ärutnyttjandegraden för den värst utsatta studerade punkten 27.0 %, vilket är beräknatpå det högsta antalet dagliga passager från tunga fordon som BRO 2004 tillåter, d.v.s.9.13 dagliga passager. Enligt Eurokod uppgår den lägsta utnyttjandegraden till 70.0 %,vilket motsvarar 137 dagliga överfarter vilket är det lägsta Eurokod tillåter. Vid ettalternativt sätt att tolka Eurokod, som tillåter användandet av utmattningslastmodell5 även för mindre broar, fås en utnyttjandegrad på 56.0% vilket motsvarar 90.0 dagligaöverfarter. Detta är något lägre än de andra utmattningslastmodellerna enligt Eurokodmen fortfarande högre än det gamla regelverket. Slutsatsen av uppsatsen är att ett alternativt sätt att bestämma antalet överfarter bordeerbjudas i Eurokod, då indelningen idag består av fyra stora trappsteg vilket ger en väldigtsnäv indelning. I detta examensarbete presenteras ett förslag som innebär att antaletdimensionerande överfarter istället bör bestämmas som en rätlinjig funktion av antaletdagliga överfarter från tung trafik. Det föreslagna sättet ligger mellan de båda normernamed hänsyn till passager och utnyttjandegrad.

Efficient temporal resolution and spatial grids are important in simulation of the inflow turbulence for wind turbine loads analyses. There have not been many published studies that address optimal space-time resolution of generated inflow velocity fields in order to estimate accurate load statistics. This study investigates turbine extreme and fatigue load statistics for a utility-scale 5MW wind turbine with a hub-height of 90 m and a rotor diameter of 126 m. Load statistics, spectra, and time-frequency analysis representations are compared for various alternative space and time resolutions employed in inflow turbulence field simulation. Conclusions are drawn regarding adequate resolution in space of the inflow turbulence simulated on the rotor plane prior to extracting turbine load statistics. Similarly, conclusions are drawn with regard to what constitutes adequate temporal filtering to preserve turbine load statistics. This first study employs conventional Fourier-based spectral methods for stochastic simulation of velocity fields for a neutral atmospheric boundary layer. In the second part of this study, large-eddy simulation (LES) is employed with similar resolutions in space and time as in the earlier Fourier-based simulations to again establish turbine load statistics. A comparison of extreme and fatigue load statistics is presented for the two approaches used for inflow field generation. The use of LES-generated flows (enhanced in deficient high-frequency energy by the use of fractal interpolation) to establish turbine load statistics in this manner is computationally very expensive but the study is justified in order to evaluate the ability of LES to be used as an alternative to more common approaches. LES with fractal interpolation is shown to lead to accurate load statistics when compared with stochastic simulation. A more compelling reason for using LES in turbine load studies is the following: for stable boundary layers, it is not possible to generate realistic inflow velocity fields using stochastic simulation. The present study presents a demonstration that, despite the computational costs involved, LES-generated inflows can be used for loads analyses for utility-scale turbines. The study sets the stage for future computations in the stable boundary layer where low-level jets, large speed and direction shears across the rotor, etc. can possibly cause large turbine loads; then, LES will likely be the inflow turbulence generator of choice. / text

Les grues à tour sont des engins de levage utilisés de manière cyclique sur les chantiers de construction. De ce fait, la prise en compte du phénomène de fatigue dans le dimensionnement des charpentes de grue est primordiale. La fatigue est usuellement considérée dans les normes au moyen de règles déterministes ayant pour but de garantir l’intégrité de la structure sous diverses conditions d’utilisation. Bien que cette approche fournisse des résultats satisfaisants dans la plupart des cas, celle-ci ne permet pas d’évaluer le niveau de fiabilité des éléments de charpente en fonction de leur durée d’exploitation. De ce point de vue, les approches probabilistes permettent de pallier cette difficulté en proposant des outils pertinents servant à caractériser et à propager les incertitudes liées à la fatigue au travers d’un modèle mécanique. Une approche probabiliste originale permettant la prise en compte des incertitudes liées à la fatigue dans le dimensionnement des charpentes de grues à tour est proposée dans ce manuscrit. La méthode proposée est basée sur la définition de deux densités de probabilité représentant respectivement les variabilités liées à la résistance des joints soudés d’une part, et les nombreuses dispersions associées à la sollicitation des éléments de charpente d’autre part. La définition de la densité de probabilité de résistance repose sur la capitalisation d’un grand nombre de résultats d’essais d’endurance sur structures soudées, tandis que la définition de la distribution de sollicitation est basée sur une modélisation à deux niveaux tenant compte de divers jeux de données collectés sur chantier. Les résultats de l’analyse de fiabilité présentée dans ce manuscrit démontrent la pertinence des approches probabilistes dans le cadre du dimensionnement en fatigue des éléments de charpente de grue à tour. / Tower cranes are lifting appliances which are cyclically used on construction sites. Thus, the consideration of the fatigue phenomenon in the design of crane structural members is essential. This phenomenon is usually taken into account in standards by means of deterministic rules enabling to ensure structural safety under various operating conditions. Although it provides satisfactory results in most cases, the deterministic approach do not enable to evaluate the reliability of crane structural members according to their operating time. From this point of view, probabilistic approaches allow to overcome this difficulty by proposing relevant tools enabling to characterize and propagate uncertainties related to fatigue through a mechanical model. An original probabilistic approach enabling the consideration of the uncertainties related to crane members fatigue design is proposed in this manuscript. It relies on the definition of two probability density functions related respectively to the strength variability of crane welded joints on one hand, and the dispersion of operating conditions (stress) on this other hand. The definition of the strength distribution stems from the capitalization of various welded joint fatigue test results, while the characterization of the stress distribution relies on the analysis of various data sets coming from crane monitoring performed on different construction sites. The results coming from the reliability analysis presented in this manuscript show the relevance of probabilistic approaches in the frame of tower crane structural members fatigue design.

In the modern era of metal-free minimally-invasive dentistry, there is a growing tendency toward using metal-free restorative alternatives that provide not only excellent aesthetics but also enable superior durability. Fibre-reinforced composite (FRC) is one cost-effective alternative that fulfils the requirements of aesthetics and durability, and offers favourable physico-mechanical properties. Many FRC applications are well-documented in the literature, such as crowns and fixed partial dentures (FPD); however, their clinical implementation is still limited, owing to the lack of significant knowledge about their longevity, deterioration signs, optimum design and overall performance. This in-vitro research aimed to address these uncertainties by investigating the performance of FRC restorations, and the influence of fibre reinforcement on particular physcio-mechanical properties, including surface hardness, edge-strength, shear bond strength, fatigue and wear resistance. Basic testing models were used to investigate the effect of incorporating differently-oriented FRCs on the surface hardness, edge-strength and shear bond strength of particulate-reinforced composite (PRC). The results revealed that the incorporation of FRC significantly enhanced surface hardness (by 12 - 19 %) and edge-strength (by 27 -75 %). However, this incorporation significantly reduced the shear bond strength (SBS) between PRC and other restorative materials, including lithium disilicate ceramic (10.9±3.1 MPa) and Co-Cr metal alloy (12.8±2.3 MPa), compared to the control (15.2±3.6 MPa, 15.0±3.7 MPa). The orientation of FRC was also found to affect the efficiency of reinforcement as bidirectional FRCs exhibited significantly higher hardness (76.8±1.2 VHN), edge-strength (67.7±8.2 N) and SBS (14.1±3.9 MPa) values than unidirectional FRCs (72.4±1.2 VHN, 56.8±5.9 N, 9.8±2.3 MPa).Clinically-relevant testing models, employing accelerated aging techniques, were performed to investigate the fatigue and wear behaviours of anatomically-shaped FRC restorations in-vitro. Direct inlay-retained FRC-FPDs with two framework designs, were tested for their fatigue behaviour and load-bearing capacity. Type-I design (with an additional bidirectional FRC layer incorporated perpendicular to the loading direction) yielded significantly higher fatigue resistance (1144.0±270.9 N) and load-bearing capacity (1598.6±361.8) than Type-II design (with a woven FRC embedded around the pontic core) (716.6±72.1 N, 1125.8±278.2 N, respectively). However, Type-19II design exhibited fewer delamination failures. Both framework design and dynamic fatigue were found to have a significant influence (p < 0.05) on the load-bearing capacity of FRC-FPDs. Additionally, the in-vitro fatigue and wear behaviours of FRC crowns, fabricated conventionally from bidirectional FRC and indirect PRC (Sinfony), were compared with those made of two CAD/CAM alternatives, namely Lava Zirconia (LZ) and Lava Ultimate (LU). A chewing simulator was employed to induce some fatigue wear in crowns, while an intraoral 3D scanner was used to quantify the resultant morphological changes. The results showed that FRC crowns had significantly lower mean cumulative wear (233.9±100.4 μm) than LU crowns (348.2±52.0 μm), but higher than LZ crowns (16.4±1.5 μm). The mean load bearing-capacity after fatigue simulation was also the highest for LZ crowns (1997.8±260.2 N) compared with FRC (1386.5±258.4 N) and LU crowns (756.5±290.9 N).Accordingly, the incorporation of FRC in resin-composite restorations is advocated since it increases surface hardness and marginal integrity, improves fatigue and wear behaviours, and enhances load-bearing capacity and overall performance.

In the future, hydropower plants are expected to operate more flexibly. This will lead to a more varied operation of the turbine and the generator, such as more start and stop in order to stabilise the frequency in the grid. Studies show that these transient operations are more costly in terms of fatigue degradation, i.e. consumption of fatigue life. Vattenfall has developed a methodology with the aim to analyse fatigue loads, acting on the runner and the rotor in hydropower units during operation. With a numerical model, the loads are assessed with input data gathered from measurements together with given data on several parameters. Some of the input data are bearing structure stiffness, bearing oil properties, and point of action of forces, etc. Several of these input parameters are subject to a degree of uncertainty, which affect the assessed fatigue load, determined with the methodology. This study will focus on analysing one fatigue force component acting on the runner. The aim with this study is to answer the following research questions: (i) Which input parameters, that are subject to a degree of uncertainty, contribute the most to the combined standard uncertainty in the assessed fatigue force? (ii) How much does the combined standard uncertainty in the assessed fatigue force amount to? (iii) How does the uncertainty in the assessed fatigue force affect the fatigue damage?. The combined standard uncertainty in the fatigue force is determined with methods in uncertainty propagation. In order to evaluate the effect from the uncertainty in the fatigue load on the fatigue damage, a statistical analysis of the ratio between the fatigue damage associated with a probability of exceedance and the expected fatigue damage is conducted. From the results it can be observed that the governing uncertainty parameter is the offset of the shaft displacement signal, which amount to 40 % of the combined standard uncertainty in the fatigue force. Of the nine analysed uncertainty parameters, three parameters are bearing properties parameters, i.e. the bearing clearance, the oil film temperature and the point of action of bearing forces, which amount to 47.5 % of the combined standard uncertainty in the fatigue force. Therefore, in order to decrease the uncertainties, focus should be kept on the bearing properties. Given each parameters uncertainty, the ratio between the combined standard uncertainty in the fatigue force and the expected fatigue force amount to 7 %. This corresponds to a ratio between the standard uncertainty in the fatigue damage and the expected fatigue damage of 35 %, due to the value of the index of S-N curve of five. Given the standard uncertainty in the fatigue force together with the index of S-N-curve, the ratio between the fatigue force associated with a probability of exceedance and the expected fatigue force can be assessed, i.e. the fatigue force ratio. Consequently, the fatigue force ratio amount to 1.32 for a probability of 0.0032 %, 1.09 for a probability of 10 % and 1.04 for a probability of 30 %. These probabilities correspond to the fatigue damage ratios, i.e. the ratios between the fatigue damage associated with a probability of exceedance and the expected fatigue damage of 4, 1.56 and 1.20. Thereby, the uncertainty in the fatigue force can greatly affect the uncertainty in the fatigue damage, dependent on the value of the index of S-N-curve. The results from this study imply the importance of considering the uncertainties in fatigue load assessments. These results provide support for assessing load levels for runner dimensioning to finally, be able to derive a correct margin of safety. This in order to not underestimate fatigue damage and thereby decrease the risk for unexpected fatigue failure. / Det finns ett förväntat behov av att kraftproduktionen i vattenkraftverk skall vara mer flexibel i framtiden. Detta leder till mer varierande driftlägen för turbinen och generatorn, såsom fler start och stop med syfte att stabilisera frekvensen i elnätet. Studier påvisar att transienta driftlägen är mer kostsamma i form av utmattningsdegradering, d.v.s. konsumtion av utmattningsliv. Vattenfall har utvecklat en metodik för att analysera inverkan av utmattningslaster verkande på löphjulet och rotorn i vattenkraftsaggregat under drift. Med en numerisk modell kan utmattningslasterna bedömas. Den ingående datan till modellen är bland annat är uppmätta storheter och given data på parameterar. Några av de ingående storheterna är lagerstyvhet, angreppspunkter för lagerkrafter och lageroljans egenskaper, etc. Flera av dessa ingående parametrar innehar osäkerheter, vilket påverkar bedömningen av utmattningslasterna. Denna studie kommer att fokusera på en kraftkomponent verkande på löphjulet. Malet med detta arbete är att svara på följande forskningsfrågor: (i) Vilka ingående parametrar, som innehar en osäkerhet, bidrar med en styrande osäkerhet i den bedömda kraften? (ii) Hur mycket uppgår den kombinerade standardosäkerheten i den bedömda kraften till? (iii) Hur påverkar kraftens osäkerhet utmattningsskadan? Den kombinerade standardosäkerheten i kraften är beräknad med metoder i fortplantning av osäkerheter. För att kunna bedöma påverkan på delskadan givet osäkerheten i kraften, så sker en statistisk analys av förhållandet mellan delskadan sammanhängande med en sannolikhet för överskridande och den förväntade delskadan. Resultatet påvisar att den styrande ingående parametern är offset i signalen för axelförskjutning, vilken uppgår till 40 % av den kombinerade standardosäkerheten i utmattningskraften. Av de nio analyserade parametrarna härrör tre av dessa lageregenskaper, d.v.s. lagerspel, oljetemperatur och angreppspunkter för lagerkrafterna, vilka tillsammans uppgår till 47.5 % av den kombinerade standardosäkerheten i utmattningskraften. Därför, för att reducera den totala osäkerheten bör fokus ligga på lageregenskaperna. Givet alla standardosäkerheter i de analyserade parametrarna så uppgår förhållandet mellan standardosäkerheten i utmattningskraften och den förväntade utmattningskraften på löphjulet till 7 %. Detta motsvarar att förhållandet mellan standardosäkerheten i delskadan och väntevärdet för delskadan uppkommer till 35 %, givet ett index av S-N-kurvan på fem. Givet standardosäkerheten i kraften och index av S-N-kurvan, kan förhållandet mellan utmattningskraften förenad med en sannolikhet för överskridande, och den förväntade utmattningskraften, d.v.s. kvoten av utmattningskraften, utvärderas. Detta resulterar att kvoten av utmattningskraften uppgår till 1.32 för en sannolikhet för överskridande på 0.0032 %, 1.09 för en sannolikhet på 10 % och 1.04 för en sannolikhet på 30 %. Dessa sannolikheter motsvarar att kvoten av delskadan, d.v.s. kvoten mellan delskadan förenad med en sannolikhet för överskridande, och den förväntade delskadan uppgår till 4, 1.56 och 1.20. Därför kan osäkerheten i utmattningskraften påverka osäkerheten i delskadan med en betydande faktor, beroende på värdet på index av S-N-kurvan. Således, resultaten från denna studie påvisar betydelsen att beakta osäkerheterna i de ingående parameterna vid bedömning av utmattningslast. Dessa resultat tillhandahåller stöd vid bedömning av lastnivåer för dimensionering av löphjul, för att slutligen kunna erhålla en korrekt säkerhetsmarginal. Detta för att inte underskatta utmattningsskadan och därmed minska risken oför oväntat utmattningshaveri.

Worker fatigue has been the focus of research for many years. However, there is limited research available on the evaluation and measurement of fatigue for prolonged mentally demanding activities. The objectives of the study are (1 )to evaluate fatigue for prolonged, mentally demanding work-tasks by considering task-dependent, task-independent and personal factors, (2) to identify effective subjective and objective fatigue measures, (3) to establish a relationship between time and factors that affect fatigue (4) to develop models to predict fatigue. A total of 16 participants, eight participants with western cultural backgrounds and eight participants with eastern cultural backgrounds, currently employed in mentally demanding work-tasks (e.g., programmers, computer simulation experts, etc.) completed the study protocols. Each participant was evaluated during normal working hours in their workplace for a 4-hour test session, with a 15-minute break provided after two hours. Fatigue was evaluated using subjective questionnaires (Borg Perceived Level of Fatigue Scale and the Swedish Occupational Fatigue Index (SOFI)); and objective measures (change in resting heart rate and salivary cortisol excretion). Workload was also assessed using the NASA-TLX. Fatigue and workload scales were collected every 30 minutes, cortisol at the start and finish of each 2-hour work block, and heart rate throughout the test session. Fatigue significantly increased over time (p-value <0.0001). All measures, except cortisol hormone, returned to near baseline level following the 15-minute break (p-value <0.0001). Ethnicity was found to have limited effects on fatigue development. Poor to moderate (Rho = 0.35 to 0.75) significant correlations were observed between the subjective and objective measures. Time and fatigue load (a factor that impacts fatigue development) significantly interact to explain fatigue represented by a hyperbolic relationship. Predictive models explained a maximum of 87% of the variation in the fatigue measures. As expected, fatigue develops over time, especially when considering other factors that can impact fatigue (e.g. hours slept, hours of work), providing further evidence of the complex nature of fatigue. As the 15-minute break was found to reduce all measures of fatigue, the development of appropriate rest breaks may mitigate some of the negative consequences of fatigue.