REPORTE

Revista de Metalurgia

El efecto del calor de entrada sobre el comportamiento a la fractura de la zona afectada por el calor recalentada en uniones soldadas multipasos de acero ASTM A633 fue evaluado mediante la prueba de impacto, fractografía, microscopia electrónica de barrido y procesamiento digital de imágenes. Los resultados de impacto indicaron una reducción en la energía Charpy como función de la velocidad de alimentación de alambre, lo cual se confirmó mediante fractografias después del procesamiento digital de imágenes que mostraron una reducción en la fracción volumétrica de microhoyuelos en la fractura dúctil acompañada del incremento en la rapidez de alimentación, favoreciendo la fractura frágil con facetas de clivaje transgranular conteniendo marcas de rio. La fracción mínima de microhuecos y el tamaño más largo de facetas mostrando un mayor número de patrones de rio fueron encontrados a la máxima rapidez de alimentación de 200 mm·s-1. La microestructura heterogénea de la zona afectada por el...

Revista de Metalurgia, 2021

En el presente trabajo se analizan las variaciones resistentes y microestructurales de la fundición dúctil soldada mediante la técnica tungsten inert gas (TIG), sin tratamientos térmicos y utilizando diferentes materiales de aporte (fundición maleable perlítica, aleación Fe-Ni y aleación de bronce y manganeso). A partir de cada cupón soldado de dimensiones 100x100x6 mm, se obtienen las probetas para los ensayos mecánicos y microestructurales. Con el análisis cualitativo de las micrografías y el análisis cuantitativo de los resultados de los ensayos mecánicos, que han sido realizados en zonas bien diferenciadas de las uniones soldadas (metal base, interfase y cordón de soldadura), se concluye la idoneidad de este tipo de soldaduras y de la introducción nuevas variables como los tratamientos térmicos previos y/o posteriores a la soldadura. Se han correlacionando las características mecánicas y resistentes con las microestructuras obtenidas en las placas (probetas) para poder evaluar s...

Much more detailed information regarding the mechanism of fracture is available from microscopic examination, normally using scanning electron microscopy. Studies of this type are termed fractographic. The scanning electron microscope is preferred for fractographic examinations since it has a much better resolution and depth of field than does the optical microscope; these characteristics are necessary to reveal the topographical features of fracture surfaces.

2014

A stocky tubular tension-torsion specimen geometry was optimized to characterize the effect of the stress state (stress triaxiality and Lode angle parameter) on metals ductility, at low stress triaxialities. Biaxial tests (proportional and non-proportional) were performed on 36NiCrMo16 steel and 2024-T351 aluminum alloy. Strain fields were measured by stereocorrelation of digital images during the tests. Loading paths to fracture (evolution of the equivalent plastic strain, the stress triaxiality and the Lode angle parameter at the critical point) were determined. The evolution of aluminum ductility with respect to the stress triaxiality measured from tension-torsion tests differed substantially from that obtained by Bao and Wierzbicki in 2004. Indeed, the latter suggested a minimal ductility under shear, while the tension-torsion technique revealed a maximal ductility under shear. Nonproportional loading paths were shown to have an influence on ductility, by means of tests consisting in a pre-compression, pre-tension or pre-torsion, followed by a proportional loading sequence under combined tension-torsion. SEM observations of metallographic sections from biaxial interrupted tests, a real-time monitoring of the surface strain and damage during in-situ torsion tests in the SEM, and a crack propagation test coupled with in-situ Xray synchrotron laminography brought evidences of localization phenomena at different scales, and of the growth of some cavities, even under pure shear, by contrast with the total collapse predicted by unit cell models. This growth may be due to the significant axial elongation measured under pure torsion (Swift effect). Shear localization was identified as the main coalescence mechanism, which justifies the choice of the Hosford-Coulomb fracture initiation criterion. Used in conjunction with a non-linear damage indicator, it accounts for the measured ductilities, even under possibly non-proportional loadings. Je remercie le Laboratoire de Mécanique des Solides de m'avoir accueillie dans ses locaux. Je tiens à exprimer ma gratitude envers mes directeurs de thèse, Véronique Doquet et Dirk Mohr, qui m'ont encadrée et guidée tout au long de ces trois années de doctorat. Je remercie mes rapporteurs MM Benallal et Dragon, ainsi que MM Balan, Besson et Bouchard d'avoir accepté d'évaluer ce travail. Je souhaite ensuite remercier Vincent De Greef et Erik Guimbretière, qui m'ont beaucoup appris et aidée dans l'utilisation des machines d'essais et la réalisation des montages. Un très grand merci également à Daniel Caldemaison qui m'a fait faire mes premiers pas avec le MEB, et à Alexandre Tanguy qui a partagé avec moi son savoir et son expérience en microscopie et en préparation métallographique. Une mention spéciale pour Sébastien Lepeer, mon stagiaire, qui, par sa motivation, son efficacité, et son travail méticuleux, a largement contribué à certains résultats présentés dans le chapitre III de cette thèse. Merci, et bravo, Sébastien ! Je tiens également à remercier très chaleureusement Thilo Morgeneyer, chargé de recherche au Centre des Matériaux, qui m'a accueillie au sein de son équipe et m'a offert l'opportunité de réaliser des essais à l'ESRF de Grenoble, au cours des derniers mois de ma thèse. J'en viens maintenant aux personnes avec qui je n'ai pas travaillé, mais dont la présence a grandement contribué à la bonne ambiance et qualité de vie nécessaires à la réalisation d'un travail dans les meilleures conditions. Merci aux doctorants et post-doctorants du LMS qui ont partagé mon quotidien. Merci à Camille, Fabien, Gauthier qui ont été parmi les premiers « jeunes » du laboratoire dont j'ai croisé le chemin ; à mes chers co-bureau JB, puis Chus ; à mon voisin de bureau Clément ; à Armel dont les anecdotes et la culture ne cessent de m'impressionner ; à Barbara et Aurélie ; à Matthieu et Mathieu, Christian, Gongyao, Borja, David, Dennis ; bien sûr, à nos dignes représentants, Dimitri et Gwen. Merci aussi à l'ensemble du secrétariat du LMS : Alexandra, Anna, Christiane, Valérie, Danielle, dont le travail fantastique transforme les formalités administratives les plus fastidieuses en une promenade. Merci à mes amis musiciens Laurent, Pierre et Alexandra, pour nos répétitions qui ont rythmé une grande partie de cette période. Merci à mes amis Anne, Chloé et Charles. Un grand merci à ma famille, à mes parents. Vingt-cinq ans après s'être assise sur son premier banc d'école, votre fille a enfin terminé ses études ! Et merci à Raphaël, pour son soutien de tous les instants.

Revista de Metalurgia

Se ha observado una clara transición de la ductilidad a tracción con el tamaño de grano D del orden 15 μm - 20 μm (1,50 μm ≤ D < 50 μm) en un acero TWIP, 22% de Mn, 0,6% de C (% en masa). Este comportamiento es una combinación de un efecto intrínseco del tamaño de grano D en la resistencia y el endurecimiento por deformación del material, con un efecto extrínseco, proceso de descarburación superficial y pérdida de Mn ocurrido durante los tratamientos de recocido a T ≥ 1000 ºC. En el presente trabajo se ha estudiado en profundidad este efecto extrínseco sucedido en el acero TWIP. Se han realizado análisis por GDOES (Espectroscopia Óptica de Descarga Luminiscente) para estudiar cuantitativamente los perfiles de concentración de C y Mn. La profundidad de descarburación superficial se ha modelizado usando la teoría de Birks-Jackson. Se ha observado vía ferritoscopio que, en el volumen descarburizado, coexisten dos microconstituyentes: α’-martensita y γ-austenita. La ductilidad del ac...

Journal of Constructional Steel Research, 2000

The application of tensile load in increments until the failure of the material was the main purpose of this test. Change in the material's length was recorded after every increment. The data until the failure was recorded and used to find the material's yielding strength, ductility, tensile strength, toughness, true tensile strength, fracture strength, true fracture strength, modulus of elasticity and estimate its toughness. Then, an engineering stress-strain graph was plotted. Finally the conversion formulas were used to come up with the true stress-strain curve. The material's mechanic features were also compared with the theoretical results. The physical properties were in the expected interval.

Objectives: To determine the followings 1. The relation between the engineering stress and engineering strain according to the results obtained from the tensile test. 2. The yield stress and offset yield stress. 3. Modulus of elasticity or young's modulus. 4. Tensile strength or ultimate tensile strength. 5. Percentage elongation and percentage reduction in area. 6. Indications to understand some important properties of material, such as ductility, brittleness and toughness.

examples of structures and devices showing how we select the right material for the job 3 A. Price and availability 2. The Price and Availability of Materials 15 what governs the prices of engineering materials, how long will supplies last, and how can we make the most of the resources that we have? B. The elastic moduli 3. The Elastic Moduli 27 stress and strain; Hooke's Law; measuring Young's modulus; data for design 4. Bonding Between Atoms 36 the types of bonds that hold materials together; why some bonds are stiff and others floppy 5. Packing of Atoms in Solids 45 how atoms are packed in crystalscrystal structures, plane (Miller) indices, direction indices; how atoms are packed in polymers, ceramics and glasses 6 . The Physical Basis of Young's Modulus 58 how the modulus is governed by bond stiffness and atomic packing; the glass transition temperature in rubbers; designing stiff materialsman-made composites 7. Case Studies of Modulus-limited Design 66 the mirror for a big telescope; a stiff beam of minimum weight; a stiff beam of minimum cost vi Contents C. Yield strength, tensile strength, hardness and ductility 8. The Yield Strength, Tensile Strength, Hardness and Ductility definitions, stress-strain curves (true and nominal), testing methods, data 9. Dislocations and Yielding in Crystals the ideal strength; dislocations (screw and edge) and how they move to give plastic flow 10. Strengthening Methods and Plasticity of Polycrystals solid solution hardening; precipitate and dispersion strengthening; work-hardening; yield in polycrystals 11. Continuum Aspects of Plastic Flow the shear yield strength; plastic instability; the formability of metals and polymers 12. Case Studies in Yield-limited Design materials for springs; a pressure vessel of minimum weight; a pressure vessel of minimum cost; how metals are rolled into sheet D. Fast fracture, toughness and fatigue where the energy comes from for catastrophic crack growth; the condition for fast fracture; data for toughness and fracture toughness 13. Fast Fracture and Toughness 14. Micromechanisms of Fast Fracture ductile tearing, cleavage; composites, alloysand why structures are more likely to fail in the winter 15. Fatigue Failure fatigue testing, Basquin's Law, Coffin-Manson Law; crack growth rates for pre-cracked materials; mechanisms of fatigue 16. Case Studies in Fast Fracture and Fatigue Failure fast fracture of an ammonia tank; how to stop a pressure vessel blowing up; is cracked cast iron safe? E. Creep deformation and fracture high-temperature behaviour of materials; creep testing and creep curves; consequences of creep; creep damage and creep fracture 17. Creep and Creep Fracture 77 93 104 111 119 131 140 146 155 169 Contents vii 18. Kinetic Theory of Diffusion 1 79 Arrhenius's Law; Fick's first law derived from statistical mechanics of thermally activated atoms; how diffusion takes place in solids 19. Mechanisms of Creep, and Creep-resistant Materials 187 metals and ceramicsdislocation creep, diffusion creep; creep in polymers; designing creep-resistant materials 20. The Turbine Blade -A Case Study in Creep-limited Design 197 requirements of a turbine-blade material; nickel-based super-alloys, blade cooling; a new generation of materials?metal-matrix composites, ceramics, cost effectiveness F. Oxidation and corrosion 21. Oxidation of Materials the driving force for oxidation; rates of oxidation, mechanisms of oxidation; data 22. Case Studies in Dry Oxidation making stainless alloys; protecting turbine blades 23. Wet Corrosion of Materials voltages as driving forces; rates of corrosion; why selective attack is especially dangerous 24. Case Studies in Wet Corrosion how to protect an underground pipeline; materials for a light-weight factory roof; how to make motor-car exhausts last longer G. Friction, abrasion and wear 25. Friction and Wear surfaces in contact; how the laws of friction are explained by the asperity-contact model; coefficients of friction; lubrication; the adhesive and abrasive wear of materials 26. Case Studies in Friction and Wear the design of a journal bearing; materials for skis and sledge runners; 'non-skid' tyres 211 219 225 232 241 250