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Budzik Michal - One of the best experts on this subject based on the ideXlab platform.

  • Fracture in asymmetric bonded joints
    2020
    Co-Authors: Budzik Michal
    Abstract:

    Des Tests de fissuration ont été réalisés sur des joints collés asymétriques. Ces assemblages asymétriques sont constitués de deux substrats de nature et/ou d’épaisseur différentes liés par un adhésif. Cette géométrie d’éprouvette semble peu utilisée pour effectuer des essais de fissuration. Elles présentent certains inconvénients et de ce fait n’ont fait l’objet d’aucune normalisation. Dans le cadre cette géométrie d’éprouvette d’essai a été néanmoins été retenue et utilisée dans trois configurations différentes pour la caractérisation mécanique des assemblages collés. Des protocoles d’essai et les schéma d’analyse associés ont été définis pour des essais de fissuration à vitesse de déplacement imposé (CRT : Constant Rate Test), à force imposée (CFT : Constant Force Test) ainsi qu’à déplacement imposé (CDT : Constant Displacement Test). Les analyses ont pu être étalonnées au moyen d’un étau matérialisant artificiellement la position d’un fissure. De nombreuses configurations ont été étudiées à l’occasion de ce travail tant du point de vue des adhésifs utilisés (epoxy, cyanoacrylate, acrylic mastic, PSA) que du point de vue des substrats encollés (alliage d’aluminium, composite à matrice organique, polycarbonate). Ces nouveaux Tests s’avèrent prometteurs car ils permettent de suivre de façon continu et précision la propagation de fissure au sein de la liaison. En outre, l’analyse des déformations mesurées par extensométrie lors d’essai réalisés à déplacement imposé (CDT) permet un suivi précis de la réponse de la couche adhésive dans la zone contrainte et d’estimer la taille de cette dernière, y compris lorsque la colle est dans un état métastable. Un autre résultat important de ce travail concerne l’analyse de la modification du front de fissure celle-ci voit une diminution de l’adhésion entre les deux substrats. Enfin, un calcul plus précis du taux de restitution d’énergie a été proposé pour prendre en compte le caractère élastique de la couche adhésive, mais permettant aussi de mieux appréhender la redistribution des contraintes dans la colle, et ainsi mieux interpréter les essais mécaniques réalisés. Des analyses par Microscopie à Force Atomique (AFM) ainsi qu’au microscope électronique à balayage (MEB) ont été effectués sur les substrats encollés pour évaluer l’impact des traitements de surface. Des simulations numériques par la method des éléments finis ont été réalisées pour determiner l’état de contrainte dans nos éprouvette d’essai et ainsi expliquer la courbure du front de fissure et les faciès de rupture observés. Les nouvelles configurations expérimentales décrites dans ce manuscript nous paraissent prometteuses car elle offrent une amelioration très significative en terme de fiabilité et précision comparativement aux Tests présentés habituellement pour ce type de travaux.Adhesion was studied in asymmetric bonded joints using fracture mechanics Tests. The asymmetric bonded joints consist of two different type and/or thickness materials bonded by an adhesive. Mentions of asymmetric bonded joint Tests employed so far are rare in the literature. They are imperfect and therefore are not standardized. Accordingly three new Tests were introduced in this work to study bonded joints. The new metrological routines and models were built for the CRT (Constant Rate Test), CFT (Constant Force Test) and the CDT (Constant Displacement Test). The routines were validated with the new Artificial Crack Tip Test developed in this thesis. Different bonded systems were examined: the adhesives - epoxy, cyanoacrylate, acrylic mastic, PSA; the bonded adherends - aluminium alloys, CFRP composites and polycarbonate. The results obtained in the new Tests are very promising in terms of the accuracy and continuous observation of crack kinetics. In addition it was found that the novel strain gauge technique, introduced in the CDT, Test allows precise joint monitoring when the adhesive is in a metastable state and a precise estimation of process zone. Another interesting achievement of this work was describing the phenomenon of double crack curvature in the vicinity of the strong – weak adhesion transition zone. The next achievement was derivation of the strain energy release rate from the elastic foundation model, which gives better understanding of the mechanics and the measurements behind adhesive bonding. Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) studies were made of the bonded substrates to estimate the surface treatment effects. The stress state in asymmetric geometry was studied using finite element analysis (FEA), which explained the formation of the curved crack front and the origin of river patterns. The new Tests developed in this study appear promising since they offer accurate and reliable results for the materials Tested

Bertoncello, João Carlos Brancher - One of the best experts on this subject based on the ideXlab platform.

  • Avaliação de revestimento de alumínio obtido por aspersão térmica aplicado em fios de alta resistência da armadura de tração de dutos flexíveis
    2020
    Co-Authors: Bertoncello, João Carlos Brancher
    Abstract:

    Dutos flexíveis são equipamentos fundamentais para a produção offshore de óleo e gás em todo o mundo. Um ambiente ácido poderá se formar no espaço anular, devido a permeação de H2S e a condenção de água ou alagamento pela ruptura da capa externa em conjunto com a permeação de H2S, expondo os fios da armadura de tração a um ambiente sour, o que pode levar ao trincamento induzido por sulfetos (TIS) e/ou trincamento induzido por hidrogênio (TIH). O objetivo do trabalho é avaliar, através de Testes eletroquímicos e de carga Constante, a eficiência de um revestimento de alumínio obtido por aspersão térmica em mitigar os fenômenos de TIS e TIH em aços de alta resistência, utilizados para a fabricação dos fios da armadura de tração de dutos flexíveis. Os Testes eletroquímicos confirmaram o comportamento anódico do revestimento em relação ao aço e estimaram uma vida útil de 2,5 anos. Além disso, a permeação eletroquímica revelou uma redução significativa do hidrogênio que se difundiu pelo revestimento e chegou ao substrato. Os Testes de carga Constante indicaram que as amostras não revestidas falharam por TIS e também por TIH. Para as amostras totalmente revestidas, não foram observados os fenômenos de TIS e TIH. O revestimento de alumínio apresentou um efeito de dupla barreira, dificultando a corrosão do aço e a absorção de hidrogênio, eliminando o TIS e o TIH. As amostras revestidas com defeito foram catodicamente protegidas e não foram observadas trincas do tipo TIH.Flexible risers are critical equipment for the production of oil and gas in offshore fields around the world. An acidic environment may be formed in the annular space, due to H2S permeation and water condensation or flooding due to rupture of the external sheath, exposing the tensile armour steel wires to a sour environment, which may promote sulphide stress cracking (SSC) and/or hydrogen-induced cracking (HIC). This work aims to evaluate through electrochemical and Constant Displacement Tests the effectiveness of thermal spray aluminium (TSA) coating to mitigate SSC and HIC in high strength steel used to manufacture the tensile armour of a flexible riser. Electrochemical Tests confirmed the anodic behaviour of the coating against the steel and estimated a service life of 2.5 years. In addition, electrochemical permeation revealed a significant reduction in hydrogen that diffused through the coating and reached the substrate. The Constant Displacement Test indicated that the non-coated samples failed by SSC although some cracks were also found in the samples mid-section due to HIC. For Al-coated samples, no signs of SSC and HIC were observed. The TSA coating showed a dual barrier effect, hindering either corrosion of steel or hydrogen up-taking, and neither SSC nor HIC was observed. Samples with a coating defect were cathodically protected and no HIC was observed