L’acquisition d'une identité cellulaire différenciée est souvent considérée comme définitive et figée dans le temps; or un nombre croissant d’études démontre que les cellules différenciées peuvent faire preuve de plasticité sous certaines conditions. Afin de mieux comprendre ces phénomènes, notre laboratoire a établi un modèle unique chez Caenorhabditis elegans (C. elegans) permettant l’étude d’un événement de transdifférenciation dans un contexte physiologique à l'échelle de cellules uniques. Au cours du développement, une cellule épithéliale du rectum de C. elegans, nommé Y, va migrer antérieurement puis changer d’identité pour devenir un motoneurone nommé PDA. Les travaux préliminaires du laboratoire ont montré que la voie de signalisation LIN-12/Notch est le signal le plus précoce nécessaire pour le bon déroulement de la transdifférenciation de Y en PDA. Nous avons pu mettre en évidence : i) que lors de l’embryogénèse, deux ligands canoniques (apx-1 et lag-2) semblent agir de façon redondante afin d’activer la voie Notch. ii) l’activation ectopique et contrôlée de la voie Notch est suffisante pour induire la formation d’un second neurone PDA. iii) Les facteurs nucléaires que le laboratoire a identifiés comme cruciaux pour l'initiation de cet évènement de TD sont également importants pour la reprogrammation induite de cette deuxième cellule en neurone PDA par l'activation ectopique de Notch. iv) La suractivation prolongée de la voie Notch dans la cellule Y maintien l’identité épithéliale de cette dernière, ayant pour conséquence le blocage de la transdifférenciation de Y en PDA. L’ensemble de nos résultats montrent que la voie Notch est nécessaire et suffisante afin d’établir la compétence à transdifférencier et que cela ne peut être réalisé que si la voie Notch est régulée de façon très précise dans la cellule Y. / The acquisition of a differentiated cell identity is often considered as final and frozen in time. However, a growing number of studies showed that differentiated cells can exhibit plasticity under certain conditions. To better understand these cell plasticity phenomena, our laboratory has developed a unique model in Caenorhabditis elegans (C. elegans) to study a transdifferentiation event in a physiological context and at the single-cell level. During the worm development, an epithelial rectal cell, named Y, will migrate anteriorly and change its identity to become a neuron named PDA. Preliminary work performed by our laboratory showed that the LIN-12/Notch signalling pathway is the earliest signal necessary for the proper conduct of the transdifferentiation of Y into PDA. In our study, we showed that: i) during embryogenesis, two canonical ligands (apx-1 and lag-2) appear to act redundantly to activate the Notch pathway in Y. ii) ectopic and controlled activation of the Notch pathway is sufficient to induce formation of a second PDA neuron. iii) Nuclear factors indentified in our laboratory as crucial for the initiation of this event are also important for transdifferentiation of the second PDA obtained by ectopic activation of Notch. iv) A prolonged activation of the Notch pathway in the Y cell maintains its epithelial identity, which results in the inhibition of the transdifferentiation of Y into PDA. Together, our results showed that the Notch pathway is necessary and sufficient to establish the competence to transdifferentiate. This can only be achieved if the Notch pathway is regulated very precisely in the Y cell.

Na primeira parte desta tese, estudamos os princípios operacionais das decisões celulares mediadas pelo sistema de sinalização Notch. Este sistema tem papel importante nas decisões celulares que ocorrem durante o desenvolvimento embrionário, cicatrização de feridas e na formação de tumores. O circuito de sinalização é ativado quando o receptor Notch de uma célula interage com um dos ligantes - Delta ou Jagged - de uma célula vizinha. O circuito Notch-Delta forma um comutador intercelular, e duas células vizinhas tendem a adotar estados diferentes - Emissor (muito ligante e pouco receptor) e Recebedor (pouco ligante e muito receptor). Neste manuscrito, apresentamos uma nova abordagem teórica que integra ambos Delta e Jagged no circuito Notch. Mostramos que o circuito Notch-Delta-Jagged permite um novo estado - um híbrido Emissor/Recebedor (E/R) com concentrações intermediárias de receptores e ligantes, e portanto o circuito é age como uma chave de três vias. Em seguida, observamos que a taxa de produção de ambos os ligantes, assim como a modulação assimétrica da afinidade de ligação do Notch com seus ligantes mediada pela glicosiltransferase Fringe, afeta severamente o intervalo de existência dos estados e sua relativa estabilidade - altos níveis de Jagged, mas não de Fringe ou Delta, promovem o estado híbrido E/R e o processo de indução lateral. Nós elucidamos o papel de Jagged na determinação dos estados celulares e discutimos sua possível implicação no entendimento da comunicação entre tumor e estroma, que frequentemente envolve comunicação via interações Notch-Jagged. Posteriormente, avaliamos a interação entre Notch, inflamação e a população de Células Cancerígenas Estaminais (CCE). Mostramos que inflamação pode expandir a população de CCE por meio do aumento dos níveis de produção de Jagged que posteriormente ativa o sistema de sinalização Notch em células vizinhas não-CCE. Nossos resultados sugerem que a inibição da produção de Jagged atenua o efeito da expansão de CCE devido a inflamação, indicando que inflamação cresce a população de CCE via interações Notch-Jagged. Nossos resultados são consistentes com observações em câncer de mama do subtipo basal (triplo negativo), onde a perda de Fringe e a ativação constitutiva do eixo NF-kB - Jag1 promove a expansão da população de CCE. Nossa abordagem computacional pode ser adaptada para incluir circuitos adicionais tais como p53 e hipóxia, que afetam a plasticidade celular, proporcionando assim uma plataforma útil para a projeção de novas terapias. Na segunda parte desta tese, introduzimos um novo método para seleção de características: Suvrel. Este é um método variacional, inspirado em aprendizado de relevância, para determinar tensores métricos para definição de distâncias baseadas em similaridades, para utilização em métodos de classificação. Nós introduzimos uma nova metodologia na qual o tensor métrico pode ser calculado analiticamente. O preprocessamento das características por uma transformação linear utilizando o tensor métrico calculado via Suvrel melhora a eficiência dos classificadores. Testamos nosso método para conjuntos de dados públicos, utilizando os classificadores mais comumente utilizados. Nós também aplicamos esta metodologia no estudo da relação entre parâmetros estruturais globais e o sistema de classificação de função enzimática. Por último, introduzimos uma nova metodologia para a identificação de genes diferencialmente expressos utilizando a tecnologia de microarranjos de DNA. Diferentemente das abordagens tradicionais, nossa metodologia evita passos intermediários de preprocessamento que são desnecessários e devido a isto não acumula erros destas análises, o que resulta em um método mais sensível e robusto. / In the first part of this thesis, we studied the operating principles of cell fate decisions mediated by Notch signaling pathway. This pathway have important role in cell fate determination during embryonic development, wound healing and tumorigenesis. Notch signaling is activated by binding of Notch receptor of one cell to either of its ligand- Delta or Jagged- of another cell. Notch-Delta circuit forms an intercellular toggle switch, and two neighboring cells tend to adopt different fates - Sender (high ligand, low receptor) and Receiver (low ligand, high receptor). Here, we present a new tractable theoretical framework that incorporates both Delta and Jagged in Notch signaling, and show that Notch-Delta-Jagged circuit enables an additional fate - hybrid Sender/Receiver (S/R) (medium ligand, medium receptor) and behaves as a three-way switch. Further, we found that production rates of both the ligands and the asymmetric modulation of binding affinity of Notch to its ligands by glycosyltransferase Fringe severely affects the parameter range of the existence of these states and their relative stability - high levels of Jagged, but not that of Fringe or Delta, promote hybrid S/R state and lateral induction. We elucidate the role of Jagged in cell fate determination and discuss its possible implications in understanding tumor-stroma crosstalk, which frequently entails Notch-Jagged communication. We further evaluate the interplay among Notch signaling, inflamation and Cancer Stem Cell population. We show that inflammation can expand the population of Cancer Stem Cells (CSCs) by increasing the levels of Jagged in cells that can further activate Notch signaling pathway in neighboring non-CSCs. Our results suggest that, inhibiting the production of Jagged dampens the effect of inflammation in expanding the CSC population, indicating that inflammatory signal function through Notch-Jagged signaling to increase CSCs. Our results are consistent with observations in basal-like breast cancer, where loss of Fringe and constitutive activation of NF-kB-Jag1 axis promotes CSC population. Our computational framework can be tailored to include additional signals such as p53 and hypoxia that affect this plasticity to gain stemness, thus providing a platform that can be useful in designing novel therapies. In the second part of the thesis, we introduce a new method for feature selection: Supervised Variational Relevance Learning (Suvrel). This is a variational method to determine metric tensors to define distance based similarity in pattern classification, inspired in relevance learning. We propose a new methodology where the metric tensor can be calculated analytically. Preprocessing the patterns by doing linear transformations using the metric tensor yields a dataset which can be more efficiently classified. We test our methods using publicly available datasets, for some standard classifiers. We also applied this methodology to study the relationship between global structural parameters and the Enzyme Commission hierarchy. Lastly, we propose a new methodology for identifying the differentially expressed genes using DNA microarray technology. Unlike traditional approaches, our methodology skips intermediate unnecessary preprocessing steps and therefore does not accumulate errors due to these analysis, resulting in a more sensitive and robust method.

A paracoccidioidomicose é uma micose sistêmica de natureza profunda que afeta preferencialmente o tecido pulmonar podendo disseminar via linfo-hematogênica para outros órgãos e tecidos, sendo causada principalmente pelo Paracoccidioides brasiliensis, fungo que apresenta dimorfismo térmico. O sistema imune inato mediado por macrófagos é extremamente importante para o controle de infecções e está envolvido na indução e regulação da resposta imune/inflamatória. Estas células são capazes de reconhecer patógenos por meio de receptores de reconhecimento de padrões (PRRs), tais como receptores Toll-like (TLR). Além desses PRRs, recentemente, demonstrou-se a importância da via de sinalização Notch no sistema imune inato e na regulação da atividade dos macrófagos. Nossos dados demonstram que a cepa Pb18 do P. brasiliensis é capaz de ativar o receptor Notch1 em macrófagos J774. A ativação desse receptor concomitante com a ativação de TLR 4 (via LPS) induz a produção de IL-6, e apresenta elevada carga fúngica e menor fagocitose, o que favorece a patogenia. Ao utilizarmos um inibidor farmacológico da γ-secretase (DAPT) para inibir a ativação do receptor Notch1 em macrófagos, é possível observar diminuição da carga fúngica, diminuição de IL-6, aumento de TNF-α e aumento da fagocitose. Entretanto, a ausência do receptor TLR 4 em macrófagos derivados de medula óssea de camundongos TLR 4-/-, na presença de DAPT, percebe-se diminuição da capacidade fagocítica desses macrófagos e também diminuição da carga fúngica, evidenciando a relação entre TLR 4 e Notch1. Em adição, realizamos um tratamento em camundongos BALB/c com DAPT previamente à infecção com Pb18. Nossos resultados evidenciaram que animais com este tratamento apresentaram diminuição da carga fúngica dos pulmões, diminuição de IL-6, ativação de macrófagos e aumento de IgG, após 45 dias de infecção, indicando um perfil de cura desses animais. O mesmo tratamento foi realizado em camundongos BALB/c NUDE, seguido da infecção com Pb18. Nestes animais, verificamos que há maior produção de citocinas pró-inflamatórias no pulmão, aumento de células CD19+ e a carga fúngica dos animais tratados manteve-se similar ao dos animais não tratados, indicando que o perfil protetor observado em animais com DAPT é dependente da resposta das células T. Juntos, esses resultados evidenciam que o Pb18 é capaz de ativar o receptor Notch1 em macrófagos e utiliza a via de sinalização Notch-TLR 4 como um possível mecanismo de escape, podendo fornecer uma nova abordagem de estudo da imunidade envolvida na paracoccidioidomicose experimental. / Paracoccidioidomycosis is a systemic mycosis of deep nature that primarily affects the lung and can spread via lymphatic and hematogenous to other organs and tissues. It is mainly caused by Paracoccidioides brasiliensis fungus which exhibit thermal dimorphism. The innate immune system mediated by macrophages is extremely important for the control of infection and is involved in the induction and regulation of immune/inflammatory response. These cells are able to recognize pathogens through pattern recognition receptors (PRRs) such as Toll-like receptors (TLR). Beyond these PRRs, the importance of Notch signaling has recently been demonstrated in the innate immune system and the regulation of macrophage activity. Our data demonstrate that the Pb18 strain of P. brasiliensis is able to activate the Notch1 receptor in J774 macrophages. Activation of this receptor with also activation of TLR 4 (via LPS) induces IL-6 production, induces phagocytosis and decreases fungal burden, which favors the pathogenesis. By using a γ-secretase pharmacological inhibitor (DAPT) for inhibiting the activation of Notch1 receptor on macrophages, it is possible to observe decreased fungal burden, less production of IL-6, and increased TNF-α and phagocytosis. However, due to the absence of TLR 4 receptor in bone marrow derived macrophages from TLR 4-/- mice, these macrophages showed decreased phagocytic ability and also reduced fungal burden in the presence of DAPT, showing a relationship between TLR 4 and Notch1. In addition, we made a treatment with DAPT in BALB/c mice prior to infection with Pb18. And our results showed that DAPT-treated animals exhibited a decrease of fungal burden in the lungs, and a decrease of IL-6. Furthermore, we observed an increase of IgG after 45 days of infection, indicating probably a healing of these animals. Same treatment was made in BALB/c NUDE mice, followed by infection with Pb18. In these animals, we observed an increased production of proinflammatory cytokines in the lung and increased CD19+ cells, but fungal burden was similar in both group (treated and untreated), which indicates that treatment with DAPT is dependent on T cell response. Taken together, these results showed that Pb18 is able to activate the Notch 1 receptor on macrophages and uses the Notch-TLR 4 signaling pathway as a possible escape mechanism, and may provide a new immunity study approach in experimental paracoccidioidomycosis.

Au cours de la tumorigénèse, les cellules tumorales accumulent plusieurs mutations. Chez les modèles animaux comme la drosophile ou la souris, il a été montré que la coopération d’au moins deux altérations génétiques permet de reproduire une croissance néoplasique dans des cellules épithéliales : la sur-activation d’une voie de signalisation comme Ras or Notch, et des mutations altérant l’adhésion cellulaires ou la polarité. Bien que cette coopération soit très décrite, ses mécanismes sous-jacents ne sont que peu étudiés. Deux principaux modèles peuvent être proposés : soit les altérations génétiques fonctionnent indépendamment (modèle additif), ou ils s’influencent l’un l’autre pour faire émerger de nouveaux comportements (modèle synergique). En utilisant un paradigme généré par Notch de croissance hyperplasique et néoplasique dans des disques larvaires d’aile de Drosophila melanogaster, nous cherchons à confirmer l’un de ces deux modèles.En combinant des analyses de RNAseq et de ChIP, nous avons pu identifier des ensembles de gènes directement activés par Notch dans des disques hyperplasiques (Notch activé) et néoplasiques (Notch activé et perte de polarité). Bien que des cibles directes de la voie Notch soient partagées par les deux types de croissances, nos analyses ont montré qu’une grande partie de ces cibles sont spécifiques de chacune des conditions ce qui suggère que l’état polarisé ou non d’une cellule influence le contrôle transcriptionnel de la voie Notch. Enfin en réalisant un screen centré sur les gènes les plus affectés en néoplasie, nous avons identifié un ensemble de gènes qui contrôlent la transition entre l’hyperplasie et la néoplasie. / During tumourigenesis, tumour cells accumulate many mutations. In animal models such as Drosophila or mouse, the cooperation of at least two genetic insults has been shown to recapitulate neoplastic transformation of epithelial cells: an overactive signalling pathway such as Ras or Notch, and mutations affecting cell adhesion or polarity. While this cooperation is well documented, the mechanisms underlying it are still poorly understood. Two main models could be proposed: either the genetic alterations act independently (additive model), or they influence each other to allow the emergence of new behaviours (synergistic model). Using Notch driven paradigms of hyperplastic and neoplastic growth in Drosophila wing discs, we sought to distinguish between these two models.Combining RNAseq and ChIP analysis, we were able to identify the repertoires of genes directly activated by Notch in hyperplastic discs (Notch activation) and in neoplastic discs (Notch activation and polarity loss). While some Notch direct targets are shared between the two types of growth, our analysis revealed that the majority of Notch targets are actually specific to each condition, suggesting that a correct polarity has a major influence on the transcriptional output of the Notch signalling pathway, and strongly supports the synergistic model. Our studies further revealed that histone composition changes and polycomb mark changes are amongst the mechanisms that redirect the Notch pathway. Finally, using a small scale functional screen centred on the most affected genes in neoplasia, we identified a core set of genes controlling the transition from hyperplastic to neoplastic growth.

La croissance musculaire postnatale chez la souris s’effectue principalement par une hypertrophie et un allongement des fibresmusculaires. L’augmentation de l’aire des fibres est contrôlée par plusieurs voies de signalisation telle que la voie Notch, qui est impliquée dans l’activation des cellules satellites (CS) en début de croissance musculaire postnatale chez la souris. La O-fucosylation, médiée par la protéine O-fucosyltransférase 1 (POFUT1), des répétitions EGF-like de la partie extracellulaire des récepteurs NOTCH joue un rôle déterminant dans la modulation des interactions récepteur-ligand (R-L), nécessaires à l’activation de la voie Notch.Les souris Pofut1cax/cax sont hypomorphes pour le gène Pofut1 et nosrésultats montrent, en plus de malformations squelettiques, unehypertrophie musculaire post-natale, pas d’hyperplasie et une réduction du pool de CS. Pour comprendre l’origine de cette hypertrophie, des cultures primaires de myoblastes dérivés de CS (MDCS) de muscles squelettiques ont été réalisées dans des conditions de prolifération ou de différenciation. Les MDCS Pofut1cax/cax présentent une activité réduite de la signalisation Notch, due à une moins bonne interaction R-L provoquée par une O-fucosylation amoindrie des répétitions EGF-like. Il en résulte une diminution de l’expression de Pax7, marqueur de l’état indifférencié, et une dérégulation de l’expression des facteurs régulateurs de lamyogenèse (Myod, Myf5 et Myogénine). La conséquence ultime est laréduction de la proportion en progéniteurs Pax7+/MyoD- au profit decellules Pax7-/MyoD+ engagées dans la différenciation. Ces observations sont en accord avec la différentiation précoce des MDCS Pofut1cax/cax. Nos résultats indiquent que cette hypertrophie musculaire post-natale chez les souris Pofut1cax/cax est due à une propension plus importante des CS activées à se différencier et à fusionner avec des fibres pré-existantes plutôt que retourner à l’état de quiescence. / Postnatal muscle growth in mice mainly occurs by hypertrophy and by anincrease of myofibres length. This increase in myofibres area is controlled by multiple signaling pathways such as Notch signaling, which is involved in activation of satellite cells (SC) at the beginning of postnatal muscle growth in mice. The O-fucosylation of EGF-like repeats within the extracellular domain of NOTCH receptors, mediated by protein O-fucosyltransferase 1 (POFUT1), plays a key role in the modulation of receptor-ligand interactions (R-L), necessary for activation of Notch signaling. Pofut1cax/cax mice are hypomorphic for the Pofut1 gene. In addition to skeletal defects, our results show postnatal muscular hypertrophy, no hyperplasia and a reduced pool of SC. To understand the origin of this hypertrophy, primary cultures of myoblasts derived from SC (SCDM) from skeletal muscles were studied in proliferating and differentiating conditions. Pofut1cax/cax SCDM showed a reduced Notch signaling due to aless efficient R-L interactions provoked by a low O-fucosylation of EGF-like repeats. This results in decreased expression of Pax7, a marker of undifferentiated state, and a change in the expression of myogenic regulatory factors (Myod, Myf5 and Myogenin). Subsequently, the proportion of Pax7+/MyoD- progenitors decreased while the proportion of Pax7-/MyoD+ cells committed in differentiation increased. These findings corroborate early differentiation of Pofut1cax/cax SCDM.Our results indicate that this postnatal muscle hypertrophy in Pofut1cax/caxmice is due to the fact that activated satellite cells are more prone todifferentiate and fuse with pre-existing myofibres that returning toquiescence.

Ovarian cancer is the most common cause of death from gynecological malignancy. Taxanes and platinum derivatives are most used therapeutics for its treatment. Development of multi drug resistance to chemotherapy represents a serious complication of the treatment. Therefore, new chemotherapeutic and therapeutic targets are investigated, which could help to overcome tumor cell resistance. The main objectives of the thesis were to study: i) the efficiency of new derivatives of conventional taxanes in vitro with the aim to determine the potentially most effective taxane derivatives in resistant tumor ovarian cells and, ii) the gene expression profile of the Notch signaling pathway, as a possible therapeutic target for the treatment of ovarian cancer. Specifically, the thesis focused on the relationship between levels of Notch signaling gene expression in patients with ovarian carcinoma and their prognosis, progression and survival. This thesis revealed that Stony Brook Taxanes - "SB-T"; SB-T-121402, SB-T-121605, and SB-T-121606 derivatives are very effective in NCI/ADR-RES tumor carcinoma cells resistant to conventional taxane - paclitaxel, and should be further studied in more advanced models, e.g. in vivo patient derived xenografts. In a study of the importance of the Notch signaling pathway in...

Fatigue life estimation of welds is a complex issue since the characteristics of each weld are unique depending on load case, geometry and properties. Fatigue life estimation on weld ends is limited and often the weakest point of a weld. There are five different methods for evaluation of fatigue life as following: nominal stress method, hot-spot method, effective notch method, fracture mechanics and lab testing. To evaluate fatigue life on weld ends, only lab testing can be used.   The purpose with this thesis is to determine a method for evaluation of fatigue life weld ends for a load carrying weld joint. This is done by comparing finite element calculations to mechanical testing and adapt the existing calculation method to have a better correspondence to the test results. The focus will be to analyse the fatigue through mechanical testing and develop a new fatigue class (FAT) and slope of the S/N-curve for weld ends.   The research was conduct through different parts with fatigue testing in form of mechanical testing, strain gauge measurements and creating different modelling techniques for finite element calculations. The development of the different modelling techniques has been carried out using linear misalignment, increasing the depth of fusion by extension of the weld root gap, changing plate edge radius at the weld toe notch and decreasing the throat thickness on a finite element model on the continues weld design.   The result from the mechanical testing indicates that the continues weld has a higher fatigue strength than the discontinues weld and that the initial crack mainly in both weld designs mainly propagating from the weld root. The fatigue strength when the initial crack starts at the weld root is higher than when the crack starts at the weld toe.   The conclusion is that the tested modelling techniques can’t be used to analyse the real-life weld end design. from the comparison between the mechanical test results the FE analysis result the fatigue life can be approximated with the effective notch method using FAT 340  and slope  at 50 % failure probability for weld ends, if the calculated root stress is used even if the toe stress is higher. / Livslängsberäkningar för utmattning av svetsar är ett komplext problem, då varje svets har unika kännetecken som är beroende av lastfall, geometrin och andra egenskaper från svetsprocessen. Livslängdsuppskattning av svetslut är ett område där det inte finns så mycket forskning, trots att svetsluten ofta har högst spänningskoncentration och lägst livslängd. Det finns fem olika beräkningsmetoder för att utvärdera livslängden, nominell spänning, hot-spot, effective notch, brottmekanik och labbprovning. För att utvärdera livslängden på svetslut kan endast labbprovning användas som utvärderingsmetod.   Syftet med detta examensarbete är att bestämma en analysmetod för utvärdering av livslängden av svetslut för en lastbärande svetsfog. Detta görs genom jämförelse mellan provresultat på detaljer med och utan svetslut och resultat från finita elementberäkningar. Fokus kommer att vara att analysera utmattningen för svetsförbandet genom mekanisk provning och ta fram ett nytt FAT-värde och en lutning på S/N-kurvan motsvarande resultaten från den mekaniska provningen av svetslut.   Forskningen har genomförts i olika steg, genom utmattningsprovning i form av mekanisk provning, genom mätning med trådtöjningsgivare och genom beräkningar med finita elementmetoder. I beräkningarna har olika modelleringsmetoder testats för att se om det gick att få bättre överenstämmelse med provresultatet.   Resultatet från de mekaniska testerna indikerar att de svetsförband med kontinuerlig svets har en högre utmattningsstyrka än svetsförbanden med svetslut. De mekaniska testerna indikerar att utmattningssprickan för båda designerna huvudsakligen sker från svetsroten. Livslängden då spricktillväxten sker från svetsroten är högre än då spricktillväxt sker från svetstån.   De olika modelleringsmetoderna som provades gav inte högst spänningskoncentration vid provobjektens sprickstart. Ingen av dessa metoder fångar därför det verkliga beteendet. Utifrån en jämförelse mellan provresultaten och resultatet från FE analysen kan utmattningshållfastheten i svetsluten approximeras med effective notch metoden om ett FAT-värde 340  och en lutning på  vid 50 % brottrisk används, förutsatt att den beräknande rotspänningen används även om tåspänningen är högre.

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Welding is one of the most applied technics in the world for joining steel. Welds are liable to the phenomenon of fatigue, which is, primarily, the formation of a crack and consequently reduction of strength due to the action of time varying loads. Fatigue is one of the main causes of failure in steel structures. The aim of this thesis is to do static and dynamic analyses of a forestry crane with the purpose of using the analyses to determine the lifetime due to fatigue of welded components. Two methods for fatigue assessment are used in this work, the Hot-Spot Method and the Notch Stress Method. The first boom, which is a key component for the crane, is analyzed in a Finite Element Method (FEM) software. The found principal stress in accordance with the notch stress method in the first boom is ±165 MPa for the analyzed load case, rendering in a stress range of 330 MPa. The fatigue strength class FAT-225 (m=3), leads to an expected number of 633000 cycles, with a probability of survival of 97,7% for this case. / Svetsning är en av de vanligaste teknikerna för sammanfogning av stål. Svetsar är känsliga för utmattning. Utmattningsfenomenet består primärt av en initial dislokation som genom tidsvarierande belastning formar en spricka som växer och därmed reducerar styrkan i konstruktionen. Utmattning är en av de vanligaste orsakerna till skador i stålkonstruktioner. Målet med detta arbete är att genomföra både statiska och dynamiska analyser av en skogsmaskins kran i avseende att bestämma utmattningslivslängden för dess svetsade konstruktioner. Två metoder för utvärdering används i detta arbete, hot-spot-metoden och notch-stress-metoden. Kranens första bom (lyftarmen) som är en huvudkomponent i kranen analyseras med hjälp av ett Finita Element program i enlighet med notch-metoden. Högsta funna spänningsvariationen i första huvudspänningsriktningen var ±165 MPa för ett av de analyserade lastfallen. Utmattningsklass FAT 225 (m=3) ger en uppskattning om utmattningslivslängd på 633000 cykler med en sannolikhet för överlevnad på 97.7% i detta fall.