Dr. Ing. Martin Duarte Guigou

Ciencia de los Materiales

Porqué Materiales…?Entender las propiedades de los materiales

es esencial para lograr el mejor uso de estos.

Y esto es así desde el uso prehistórico de la piedra hasta el Puente de Oresund.

El diseño de nuevos materiales REQUIERE el correcto entendimiento de la estructura de los mismos.

Estructura Propiedades

Esta relación debe comprenderse en cabalidad, desde la escala sub-nanométrica de las estructuras cristalinas y las dislocaciones hasta estructura de mucho mayor escala, tales como las fases de los materiales compuestos, del orden del mm.

Entender las estructuras (especialmente las microestructuras) permite cambiar las propiedades de los materiales de formas particulares, incluso por medio de campos eléctricos o simplemente calor.

Porqué Materiales…?

• Los materiales no siempre son perfectos. Los materiales no siempre son perfectos. Pueden fallar, y a veces lo Pueden fallar, y a veces lo hacen con consecuencias serias. Entender estos procesos debe ayudar hacen con consecuencias serias. Entender estos procesos debe ayudar a prevenirlosa prevenirlos

• La Ciencia e Ingeniería de los Materiales es un campo que cambia hasta demasiado rápidamente y afecta fuertemente el mundo a nuestro alrededor.

• Se aplican enormes esfuerzos en desarrollar materiales cada vez mas capaces, a la vez que amigables conel medio ambiente y si es posible, recicables.

• Ver el desarrollo de la Ingeniería de Materiales detras de la vida diaria es uno de los objetivos de este curso.

Porqué Materiales…?

 

Ciencia y Tecnología de los Materiales

Ashby - Engineering Materials (2nd ed. 1998) Volume 1 - An Introduction to their Properties and Applications

A veces la decisión no está en cual es el MEJORMEJOR material

para mi aplicación

La mayoría de las veces la decisión esta en

CUAL ES EL MATERIAL de CUAL ES EL MATERIAL de QUE PUEDE QUE PUEDE

HACER EL TRABAJO AL HACER EL TRABAJO AL MENOR COSTOMENOR COSTO

The pieces of steel were found to have very high content of P and S (4x and 2x respectively, compared to modern steel), with manganese-sulfur ratio of 6.8:1 (compare with over 200:1 ratio for modern steels). High content of High content of phosphorus initiates fractures, sulfur phosphorus initiates fractures, sulfur forms grains of iron sulfide that forms grains of iron sulfide that facilitate propagation of cracks, and facilitate propagation of cracks, and lack of manganese makes the steel lack of manganese makes the steel less ductile.less ductile.

Of a total of 2,223 people, only 706 survived; 1,517 perished. The majority of deaths were caused by hypothermia in the −2 °C water.

Early Liberty ships suffered hull and deck cracks, and a few were lost to such structural defects. During World War II, During World War II, there were nearly 1,500 instances of there were nearly 1,500 instances of significant brittle fracturessignificant brittle fractures. Twelve ships, including three of the 2710 Liberties built, broke in half without warning. At the present day, it is At the present day, it is thought that the low weldability of thought that the low weldability of steel was the main cause of the steel was the main cause of the accidents.accidents.

• Liberty ships were cargo ships built in the United States during World War II.

• The average ship took about 42 days to build.42 days to build. • The record was set by Robert E. Peary, which was launched 4

days and 15 1/2 hours after the keel was laid, although this publicity stunt was not repeated and in fact much fitting-out and other work remained to be done after the Peary was launched.

• The ships were made assembly-line style, from prefabricated sections. In 1943, three new Liberty ships were being completed every day.

• The fractures were not initiated by welding, but instead by the grade of steel used which suffered from embrittlement.

• The ships in the North Atlantic were exposed to temperatures that could fall below a critical point when the mechanism of failure changed from ductile to brittle, and thus the hull could fracture relatively easily.

• The predominantly welded (as opposed to riveted) hull construction then allowed cracks to run for large distances unimpeded.

The principal investigator concluded, "In the light of known properties of the aluminium alloy D.T.D. 546 or 746aluminium alloy D.T.D. 546 or 746 of which the skin was made and in accordance with the advice I received from my Assessors, I accept the conclusion of RAE that this is a sufficient explanation of the failure of the cabin skin of Yoke Uncle by fatigue after a small number, namely, fatigue after a small number, namely, 3,060 cycles of pressurisation. (1)3,060 cycles of pressurisation. (1)

Engineers subjected an identical airframe, G-ALYU ("Yoke Uncle"), to repeated re-pressurisation and over-pressurisation and after 3,057 flight cycles (1,221 actual and 1,836 simulated), Yoke Uncle failed due to metal fatigueYoke Uncle failed due to metal fatigue near the front port-side escape hatch. Investigators began considering fatigue as the most likely cause of both accidents and initiated further research into measurable strain on the skin. Stress around the window corners was found to be much higher than expected, "probably over 40,000 psi," and stresses on the skin were generally more than previously expected or tested. This was due to stress concentrationstress concentration, a consequence of the window's square shape.The problem was exacerbated by the punch rivetpunch rivet construction technique employed. The windows had been engineered to be glued and riveted, but had been punch riveted only. Unlike drill riveting, the imperfect nature of the hole created by Unlike drill riveting, the imperfect nature of the hole created by punch riveting may cause the start of fatigue cracks around the rivet.punch riveting may cause the start of fatigue cracks around the rivet.

(1) Report of the Public Inquiry into the causes and circumstances of the accident which occurred on the 10 January 1954, to the Comet aircraft G-ALYP, Part XI (a. 69)

2 accidents2 accidents56 killed56 killed

Tank ExplosionTank ExplosionSt Louis Hide & Tallow Co. Rendering Plant.St Louis Hide & Tallow Co. Rendering Plant.

St. Louis, Missouri, November 13, 1918St. Louis, Missouri, November 13, 19181 Killed, 1 Injured1 Killed, 1 Injured

2 Boilers Exploded2 Boilers Exploded1 Heine, 1 Sterling1 Heine, 1 SterlingMobile Electric Company Power PlantMobile Electric Company Power PlantMobile, Alabama, February 21, 1919Mobile, Alabama, February 21, 19194 Killed4 Killed

martin.duarte@ucu.edu.uy