TRATAMENTO TÉRMICO

TRATAMENTO TÉRMICO

3ª lista de exercícios

Prof.: Ricardo Nolasco de Carvalho

1. Explique os tratamentos de recozimento pleno, normalização e esferoidização. Compare as microestruturas e propriedades mecânicas produzidas por esses tratamentos.

2. Descreva as mudanças estruturais que ocorrem no revenimento em função da temperatura.

3. Quais são os mecanismos responsáveis pela “fragilização da martensita revenida”, TME?

4. Qual é o efeito do Cr, Mo e V sobre as propriedades mecânicas de um aço após têmpera e revenimento.

5. Para um aço com base 0,3%C e 0,8%Mn, estime a variação de dureza após revenimento a 540°C/1h, produzida por:

a. 0,8%Cr

b. 0,8%Cr e 0,15%Mo

c. 0,7%Cr, 0,20%Mo e 1,7%Ni

6. Na fabricação de uma determinada peça utiliza-se o aço 4130H, cujo padrão de fornecimento é: 0,31%C; 0,50%Mn; 0,015%P; 0,005%S; 0,25%Si; 1,05%Cr e 0,22%Mo.

a. Com base no artigo “Hardness in Tempered Martensite of Carbon and Low-Alloy Steels”, disponível no SGA, determine a sua curva de revenimento.

b. Considere que para atingir o nível de resistência mecâINTRODUÇÃO

Fire Fighting

Fires - of any size and cause - can be devastating if not contained and extinguished. Fire fighting and the management thereof, should be understood and taken seriously as fires can get out of control quickly. Onboard fires are a very real threat to life. Crew should at all times be aware of smells and other fire related signals, so that immediate action can be taken.

Background and History

From the beginning of aviation, uncontrolled in-flight fire has been an identified risk.

Aviation’s first fatal accident occurred due to an uncontrolled in-flight fire. In July

1785, Jean-François Pilâtre de Rozier’s hydrogen balloon ignited and burned over

the English Channel. Dr Pilâtre de Rozier became aviation’s first fatality.

A review of past incidents shows that in-flight fires have continued to occur despite

the efforts of manufacturers, regulators and operators. The FAA acknowledges in

several documents that this risk will continue to be of concern:

“We have concluded that we are unlikely to identify and eradicate all

possible sources of ignition.”

(Federal Aviation Administration, 2007)

“ the examinations of large transport aircraft …revealed many anomalies

in electrical wiring systems and their components, as well as

contamination by dirt and debris.” (Federal Aviation Administration, 2005)

The importance of such statements illustrates the need for several layers of

mitigation when addressing smoke and fire issues.

The FAA further acknowledges the inability to eliminate ignition sources in a

statement that reads as follows: “To address the first part of this comprehensive safety regime, we have

taken several steps to reduce the chances of ignition. Since 1996, we

have imposed numerous airworthiness requirements (including

airworthiness directives or ‘Ads’) directed at the elimination of fuel tank

ignition sources. Special Federal Aviation Regulation No. 88 of 14 Code of Federal

Regulations (CFR) part 21 (SFAR 88; 66 FR 23086, 7 May 2001) requires

the detection and correction of potential system failures that can cause

ignition. Although these measures should prevent some of the (report’s)

four forecast explosions, our review of the current transport category

airplane designs of all major manufacturers has shown that unanticipated

failures and maintenance errors will continue to generate unexpected

ignition sources.”

(Reduction of Fuel Tank Flammability in Transport Category Airplanes Final Rule,

Reducing the Chance of Ignition, Federal Aviation Administration, 2007)

The FAA recognizes that efforts to eliminate ignition sources will not eradicate the in-flight fire risk since there are three requirements for a fire to occur; fuel, oxygen, as well as the source of ignition.

Accident History

Several in-flight fires in transport aeroplanes have provided insight into the extent of the risk. One example is an uncontrolled fire that caused the crash of a Trans World Airline

Lockheed Constellation on 11 July 1946, near Reading, Pennsylvania (Civil

Aeronautics Board, 1946). Soon after departure on this training flight, the crew began to smell burning insulation. The flight engineer opened the flight deck door and reported to the Captain: “The whole cabin is on fire.” (Civil Aeronautics Board, 1946). The flight crew attempted to fight the fire without success. Dense smoke streamed into the flight deck and filled it, obscuring the instruments. The instructor captain opened the window in an effort to find the airport, but was unable to maintain control. The aeroplane crashed killing everyone on board, except the instructor captain. The accident report determined that:

“The reason for the loss of control of the aircraft immediately prior to impact and therefore the most immediate cause of the accident, was the inability of the pilots to maintain adequate control because of the denseness of the smoke within the crew compartment.”

(Civil Aeronautics Board,