[pt] Uma relação direta onde a vida em fadiga Número de ciclos por falha pode ser descrita como função das amplitudes macroscópicas de tensão normal e cisalhante, Amplitude de tensão normal macroscópica e Amplitude macroscópica da tensão de cisalhamento, é obtida. Utilizando o critério de Carpinteri e Spagnoli (CeS) como uma ferramenta de inspeção, foram obtidas curvas de nível elípticas sobre um domínio Amplitude de tensão normal macroscópica x Amplitude macroscópica da tensão de cisalhamento. A expressão das curvas de nível obtidas foi generalizada, proporcionando uma ferramenta capaz de prever o número de ciclos para falha associado a qualquer combinação (Amplitude de tensão normal macroscópica, Amplitude macroscópica da tensão de cisalhamento). As previsões obtidas através do método da curva elíptica foram comparadas às observações experimentais, bem como a previsões obtidas a partir de versões adaptadas de modelos consagrados na literatura, a saber: Findley (F), Matake (M), McDiarmid (McD), Susmel e Lazzarin (SeL), Carpinteri e Spagnoli (CeS) e Papadopoulos (P). O modelo proposto forneceu previsões em boa concordância com as observações experimentais, e sua capacidade de avaliar o comportamento em fadiga se revelou o melhor dentro todos os critérios considerados. Por fim, uma leve tendência conservadora do modelo foi atenuada através da introdução de um parâmetro de ajuste, melhorando ainda mais sua capacidade de avaliação de comportamento em fadiga. / [en] A direct relation where fatigue life Number of cycles to failure can be determined as function of macroscopic normal and shear stress amplitudes Macroscopic normal stress amplitude and Macroscopic shear stress amplitude is established. Using the Carpinteri and Spagnoli (CandS) criterion as a survey tool, elliptical level curves in the Macroscopic normal stress amplitude x Macroscopic shear stress amplitude domain were revealed and further generalised, providing means to determine the number of cycles to failure for any given (Macroscopic normal stress amplitude, Macroscopic shear stress amplitude ) combination. Predictions obtained through the elliptical curve method (E) were compared to experimental observations, as well as to predictions obtained from adapted versions of popular fatigue criteria, namely Findley (F), Matake (M), McDiarmid (McD), Susmel and Lazzarin (SandL), Carpinteri and Spagnoli (CandS) and Papadopoulos (P). The proposed model delivered predictions in fair agreement with experimental observations and its predictive capability was seen to be the best among all the considered criteria. Finally, a slight bias towards conservativeness was attenuated with the introduction of an adjusting parameter, further improving the predictive capability of the model.

Le mémoire vise à proposer une épistémologie pragmatique de la science scolaire à l’école primaire. Un défaut de compréhension de la nature de la science pourrait en effet justifier en partie les difficultés de l'enseignement des sciences par démarche d'investigation. Une étude des représentations de la science chez les enseignants et futurs enseignants confirme qu’ils n‘en ont pour la plupart qu‘une vision assez floue, relevant majoritairement d'une forme d'empirisme naïf. Un jeu opératoire de critères de scientificité adapté au contexte de l’école est développé dans une approche "bottom-up" partant des pratiques de classe effectives. Sa capacité à discriminer pratiques scientifiques et non scientifiques est discutée, de même que les implications didactiques et épistémologiques de son utilisation. Il est en particulier possible d‘en déduire des définitions évolutives d‘une science scolaire normative mais subsidiaire par rapport à la “science des scientifiques”. Cet outil épistémologique s’avère bien reçu par les enseignants auxquels il a été présenté. Le test en situation de différentes stratégies pédagogiques fait apparaître que les plus efficaces pour l'appropriation de critères de scientificité ajoutent à la démarche d’investigation une composante épistémologique explicite. Certains éléments de méthode scientifique peuvent être travaillés dès la Grande Section de maternelle (5-6 ans) : des élèves ayant vécu des démarches d’investigation s’avèrent capables de revendiquer la primauté de l’expérience, mais aussi de mettre en œuvre des tests relatifs à plusieurs critères de scientificité et de s‘approprier les rudiments de la modélisation scientifique. / The purpose of this thesis is to propose a pragmatic epistemology of school science in primary school. Indeed, some of the difficulties encountered by inquiry-based science education may be attributed to a lack of understanding of the very nature of science. A survey on the perception of science by incumbent teachers and teachers in training confirms that most of them have a relatively vague vision grounded in a form of naive empiricism. A practical set of criteria of scientificity adapted to the school context is developed through a “bottom-up” approach based on actual classroom practices. Its efficiency at discriminating scientific and non-scientific practices is discussed, as well as the didactical and epistemological implications of its use. It is thus possible to deduce evolutive definitions of a school science that is normative yet subordinated to the “science of scientists”. Teachers responded positively to this epistemological tool when it was presented to them. Among the different teaching strategies tested in a classroom, the most efficient for the acquisition of criteria of scientificity were those which supplemented the inquiry process with an explicit epistemological component. Some elements of scientific method can be introduced as early as kindergarten (5-6 y.o) : after experimenting with inquiry processes, pupils have proved able not only to claim the primacy of experiment but also to run tests related to different criteria of scientificity and acquire the basics of scientific modeling.

Geometrical discontinuities, like sharp notches, appear in constructions and engineering structures and lead to stress concentrations. These technical objects are very dangerous due to the fact that they reduce the structural conformity and can lead to crack initiation. Technical objects are not always designed as homogenous bodies but can consist of two or more materials with sharp notches on the interface of these materials. The influence of free surface on crack initiation conditions is studied and assessed by means of 3D model of sharp and bi-material notches with finite thickness. Stress fields around the singular stress concentrators are calculated with finite element method and the results are evaluated by means of criterion of critical quantity. This approach is easy applicable and can be used in combination with the knowledge of basic material properties and results of finite element analysis of the assessed notches. In order to estimate weather crack will initiate from the middle of the observed notched specimen or from its free surface, the value of averaged critical applied stress was introduced. With this value it’s possible to determine the location of crack initiation thru the sample thickness. Thru the ratio of values of critical applied stress in the middle and on the free surface of the observed specimen it’s possible to quantify the influence of the free surface on the location of crack initiation. With the use of this approach it’s shown, that the location of crack initiation depends on more parameters, loading direction, the notch opening angle and the sample thickness. In case of bi-material notches it depends also on the ratio of young modulus.