Composite Materials In Automotive Brake Disc

Composite Materials In Automotive Brake Disc Abstract The aim of this paper is to explore the uses of ceramic matrix composites (CMCs) in the automotive industry, their advantages over current grey cast iron discs, their manufacturing processes and potential commercial applications. Cast iron brake discs consume much fuel due to its high specific gravity. As a result, a better and perhaps cheaper alternative is needed to fulfil the needs of high end automotive industries and even mid range consumer vehicles. INTRODUCTION Reducing green house gases and fuel consumption is a common goal for automotive industries and of paramount importance. Auto industries have dramatically increased the use of aluminium in light vehicles in order to reduce weight and help improve efficiency. Aluminium alloy based metal matrix composites (MMCs) with ceramic particulate reinforcement have shown great promise for such applications [1,2]. These materials having a lower density and higher thermal conductivity as compared to the conventionally used gray cast irons are expected to result in weight reduction of up to 50 60 % in brake systems [3]. Under severe service conditions like higher speed, higher load etc, these advanced materials have the potential to with stand these conditions. Basic mechanism of mechanical properties The high fracture toughness or crack resistance mentioned above is a result of the following mechanism: under load the ceramic matrix cracks, like any ceramic material, at an elongation of about 0.05%. In CMCs the embedded fibres bridge these cracks. This mechanism works only when the matrix can slide along the fibres, which means that there must be a weak bond between the fibres and matrix. A strong bond would require a very high elongation capability of the fibre bridging the crack, and would result in a brittle fracture, as with conventional ceramics. Thermal and electrical properties The thermal and electrical properties of the composite are a result of its constituents, namely fibers, matrix and pores as well as their composition. The orientation of the fibers yields anisotropic data. Oxide CMCs are very good  electrical insulators, and because of their high porosity their  thermal insulation  is much better than that of conventional oxide ceramics. The use of carbon fibers increases the  electrical conductivity, provided the fibers contact each other and the voltage source. Silicon carbide matrix is a good thermal conductor. Electrically, it is a  semiconductor, and its  resistance  therefore decreases with increasing temperature. Compared to (poly)crystalline SiC, the amorphous SiC fibers are relatively poor conductors of heat and electricity. CMC Brake Discs Disc brakes  are typically made out of grey cast iron. This material is has high tensile strength and can withstand a high temperature before failing. In high performance vehicles the amount of heat generated by friction when braking can be too great so the brakes fail or must be changed often. The failure is due to thermally induced fractures. Also these brakes can be heavy and susceptible to corrosion, which cause failure. Other composites have been tested such as Metal Matrix Composite, and Carbon Carbon Composites. The challenges with these materials are the ability to dissipate heat caused by friction isnt optimal at high enough temperatures. A typical grey cast iron disc brake can withstand a surface heat of 400 C before failure occurs. Type C/C-SiC is a Carbon fiber phase added to a Silicon Carbide matrix. The resulting material has increased strength with a lower density and high tribological characteristics. The most predominant feature is its ability to withstand high temperatures without failure. Due to its low coefficient of thermal expansion and high thermal conductivity, this CMC can retain its strength at high temperature. This CMC was manufactured as a disc brake with 2D reinforced discontinuous fibers. The fibers are placed perpendicular to the surface of friction to maximize Thermal conductivity. The result is a disc brake that can withstand surfaces temperatures of 1000 C with minimal wear. Problems There are multiple reasons for CMC disk brakes not being implemented among regular cars. Firstly, there is a low demand for high performance brakes due to the brakes themselves being rather expensive. As CMCs gain popularity, the cost of the raw material is expected to reduce, regardless of it being slightly expensive. Since regular cars arent used at high speeds, the amount of heat generated with low friction is small. As such, the Carbon Silicon Carbide brakes become inefficient and much weaker particularly in colder conditions. Thermal expansion of the composite and ceramic matrix results in this weakness. Cracking can occur on the surface of the brakes as the material expands at different rates under different temperatures. ADVANTAGES The integration of long multi-strand fibres has drastically increased the crack resistance,  elongation  and  thermal shock  resistance, and resulted in several new applications. As a result this has overcome the common problems associated with the conventional technical ceramics like alumina, silicon carbide, aluminium nitride, silicon nitride, or zirconia. Elongation  to rupture up to 1% Strongly increased  fracture toughness Extreme  thermal shock  resistance Improved dynamical load capability Anisotropic  properties following the orientation of fibers In comparison to the conventional grey cast iron brake disk the carbon-ceramic brake disk Weighed round 50 per cent less reducing the unsprung mass by almost 20 kilograms Improved brake response and fading data High thermal stableness No hot judder Excellent pedal feel Improved steering behavior High abrasion resistance and this longer life time and the advantage of avoiding almost completely brake dust The table below shows the properties of grey cast iron and its advanced alternatives (SGL Group n.d.) Property Unit Material C/SiC material, general C/SiC for carbon- ceramic brake disk Gray cast iron (GG-20) Density g cm-3 1,8 2,9 2,45 7,25 Tensile strength MPa (=N mm-2) 10 240 20 40 200 250 Modulus of elasticity GPa 20 240 30 90 110 Flexural strength MPa (=N mm-2) 20 210 50 80 150 250 Elongation at break % 0.05 0.8 0.3 0.3 0.8 Thermal shock resistance   (second thermal coefficient K) W m-1 26.500 46.000 > 27.000 < 5.400 Thermal stability  °C 1350 1350 approx. 700 Maximum operating temperature   (brake disk)  °C 1400   non-oxidizing 900 700 Linear coefficient of thermal expansion K-1 1.0 3.5 2.6 3.0 9 12 Thermal conductivity W m-1K-1 20 150 40 54 Specific heat capacity (cp) kJkg-1K-1 0.6 1.7 0.8 0.5 Manufacturing Processes There are currently 5 known manufacturing procedures for matrix forming. They are: Matrix deposition from a gas phase Matrix forming via pyrolysis of C- and Si-containing polymers Matrix forming via chemical reaction Matrix forming via sintering Matrix formed via electrophoresis Matrix deposition from a gas phase involves a process known as chemical vapour deposition where in the presence of a fibre perform, the deposition takes place between the fibres and their individual filaments and thus called chemical vapour infiltration. Pyrolysis (Pyrolysis  is a  thermo chemical  decomposition  of  organic material  at elevated temperatures without the participation of  oxygen) of C- and Si-containing polymers involves hydrocarbon  polymers to shrink during  pyrolysis, and upon  out gassing  form carbon with an amorphous, glass-like structure, which by additional heat treatment can be changed to a more  graphite-like structure. Matrix formation via chemical reaction works by one material being located between the fibres that react with a second material to form the ceramic matrix. Sintering is used to manufacture oxide fibre/oxide matrix CMC materials. Special  precursor  liquids are used to infiltrate the pre-form of oxide fibres. In the  electrophoresis  process, electrically charged particles are dispersed in a special liquid are transported through an  electric field  into the preform, which has the opposite electrical charge polarity. Application in Brake Discs Carbon/carbon  (C/C) materials have found their way into the  disk brakes  of  racing cars  and  airplanes, and C/SiC brake disks manufactured by the LSI process were qualified and are commercially available for  luxury vehicles. The advantages of these C/SiC disks are: Very little wear, resulting in lifetime use for a car with a normal driving load of 300,000  km, is forecast by manufacturers. No  fading  is experienced, even under high load. No surface  humidity  effect on the friction coefficient shows up, as in C/C brake disks. The corrosion resistance, for example to the road salt, is much better than for metal disks. The disk mass is only 40% of a metal disk. This translates into less unsprung and rotating mass. The weight reduction improves shock absorber response, road-holding comfort, agility, fuel economy, and thus driving comfort. The SiC-matrix of LSI has a very low porosity, which protects the carbon fibers quite well. Brake disks do not experience temperatures above 500  °C for more than a few hours in their lifetime. Oxidation is therefore not a problem in this application. The reduction of manufacturing costs will decide the success of this application for middle-class cars.

Comparing and Contrasting E.L. Doctorows Billy Bathgate and William Kennedys Legs :: Comparison Compare Contrast Essays

Comparing and Contrasting E.L. Doctorow's Billy Bathgate and William Kennedy's Legs The many similarities between E.L. Doctorow's Billy Bathgate and William Kennedy's Legs suggest that Doctorow used Legs as a starting place for the creation of his own novel. Certain scenes are so similar that it seems that they did not originate independently. Marcus Gorman and Billy Bathgate had almost indistinguishable experiences while firing target practice and later when Jack Diamond and Dutch Schultz died. Doctorow did not, however, merely copy Kennedy's story; he instead used it as a building block to begin from. Billy Bathgate had many elements that Legs did not which expanded the story's significance. The pistol firing scene in Billy Bathgate palpably mimics the machine gun practice in Legs. Not only are the literal actions very similar to each other, but their impact on the characters is almost identical as well. The excitement and power gained by firing weapons lures both characters further on their descent into the criminal underworld. After shooting, Marcus thinks, "Do something new and you are new. How boring it is not to fire machine guns" (Kennedy 41). And Billy said, "I will never forget how it felt to hold a loaded gun for the first time and lift it and fire it, the scare of its animate kick up the bone of your arm, you are empowered there is no question about it, it is an investiture, like knighthood" (Doctorow 145). In the case of Marcus Gorman, the exhilaration of firing the machine gun was the benefit that would outweigh the risks of associating with Jack Diamond. Billy had already been attracted to the gang life. However, the power he gained from firing his automatic amplified his attraction. He finally understood why the other gang members had such closeness with their guns. Doctorow saw Marcus' introduction to the gang life through guns as an organic element in the story that worked properly. Therefore, he chose to borrow for Billy rather than trying to come up with something different that may not have worked as well. After their gun firing experiences, Marcus and Billy experienced many strikingly similar events. The most dramatic of these were the death scenes of Jack Diamond and Dutch Schultz. In both cases, mentor and protà ©gà © were together at the time of departure, and each protà ©gà © received a privileged transmission of information that no one else did.

The Greek Mythology

Greek Mythology is a group of teachings and myths that were originated by the ancient Greeks, when they were trying to understand the origin of things in the sky and on earth. This myth was a big part of the religion of the Greeks. Hesiod offers the theogony, which tells of the dealings with the creation of the world, and the origin of the gods, titans, and giants. Athena, also called Athene, was a goddess of many things like wisdom, and courage. She was born to Zeus and Metis in Mount Olympus. She was fully grown and wearing armor from head to toe. Athena is said to be a pre-Hellenic goddess that was taken by the Greeks. Her story shows that the people were looking for closure over wisdom and war during this time. This myth seeks to explain some countless inventions. She has a major influence on today's culture. For instance, her helmet is featured on the crest of West Point Academy, as well as represented the first branch of the United States Army just for women. Although there are many different stories of how Athena came to be, most known one is that Zeus swallowed Metis and Athena sprang from his head. Because she is the goddess of many things, Athena is featured on many modern crests, was praised by the Greeks in their time, and was supposedly the origin of many great inventions. Although classical Greek culture was during the period of the 4th and 5th centuries, ancient Greek culture and myths are tremendously influential in many aspects like, language, politic, educational system, philosophy, science, the arts, and the gods. For instance, our country is a democracy. Democracy is said to originate from Greece. Not only that, we use the gods and goddesses in our everyday life. Athena's helmet is featured on the West Point Military Academy crest. Her head is represented on the first branch of the United States Army that is for women. Hellenic polytheists worship the Greek gods, olympians, nature divinities, underworld deities, and heroes. Hellenic religion is any systems of beliefs and practices of the ancient Greeks during the Hellenic period and the Roman Empire. Religion was very important to the Greeks because they believed that religion would make their lives better. This Hellenistic world was made after conquest that went from India to Egypt and took about 20 to complete after Alexander the Great's death. (Hellenistic Culture) Athena was born to Zeus and Metis, at Mount Olympus, fully grown and wearing full armor from head to toe. Athena is said to be a pre-Hellenic goddess that was taken from kgjhjv by the Greeks. There are many different versions of how Athena came to be. Most say that Zeus and Metis conceived a baby girl. Before Metis gave birth, Mother Earth told Zeus that a child born to Metis would one day overthrow his throne. He became worried because that is the same thing he did to his own father. Zeus challenged her in a shapeshifting contest; she turned herself into a fly and taking the advice of Gaea and Uranus, Zeus swallowed her up. A few days later, he started to get dreadful headaches and asked his son, Hephaestus, to take an axe and crack his head open.(Temple)Some versions say that Palamon and Hermes helped Zeus give birth. Others regard her to be his daughter, but also as the daughter of Pallas, whom she killed later because he tried to desecrate her chastity. Another that was transplanted to Libya, says that she is the daughter of Poseidon and Tritonis. According to Athena, herodotus became enraged with her father and went to Zeus, who later stepped in as her father. These were regarded more as Hellenistic Myths (â€Å"Athene†) Athena was a goddess of many aspects like wisdom, courage, inspiration, civilization, law and justice, strategic warfare, mathematics, strength, strategy, the arts, crafts, and skill. She was the goddess of arts and crafts because of her spinning and weaving. She was the goddess of war and wisdom because she sprang from Zeus's head and she was a ruthless warrior. She was very strategic and skilled during warfare. She is often portrayed as the companion of heroes is the patron goddess of heroic endeavour. (â€Å"Athene†)Athena was featured in many heroic stories. One being, when she assisted Odysseus in his adventures. Odysseus and Athena were similar. He was the Greek King of Ithaca just as she was a great goddess. They had some of the same qualities. They were both nondiscriminatory, and clever. When it came to helping Odysseus in the Trojan War, she was there. Other gods didn't like that he was helping the Trojans. Most of all, she helped him on his way home, because he ran into many obstacles. He was imprisoned by Calypso then, when he escaped, he went sailing through storms, which later resulted in many shipwrecks. He then found himself in trouble with many other gods like, Poseidon and Polyphemus. Athena did not want to make the other gods angry, so she only offered Odysseus wisdom. When he returned safely to Ithaca, Athena helped him disguise as a beggar.(Temple) A less heroic story of Athena, is when she accidentally killed her friend, Pallas. As a young woman, Athena didn't quite fit in on Mount Olympus. So she went out to find a friend, Pallas. Her new friend was the daughter of Triton, the sea god. The often practiced their combat skills with each other. On time they were doing their session when Pallas took a fatal blow from Athena. Feeling sorrowful, Athena put a statue of Pallas near Zeus's throne Mount Olympus.(Temple) Athena has a major influence on today's culture; her helmet is featured on many things of the United States. One being the West Point Academy crest. Her helmet represents her wisdom, while her sword represents a warrior. The seal of California also features her head. It symbolizes the goddess of wisdom overlooking the scene. (Seal of California) The US Women Army Corps shows her head as their insignia. Athena is said to be the origin of many things that make up Greek culture. She made the statue of Pallas that sits near Zeus's throne. She helped many heros on adventures, like the one with Odysseus. She also has tremendous influence on modern culture. For instance, she is featured on the Seal of California, the U.S. Women's Army Corp, and the West Point crest. Its is clear that Athena is relevant in both ancient times and modern day culture. She is, many times, the symbol of power, wisdom, and valor. This is what makes her so influential in the world.

Sexual Harrasment - 709 Words

Throughout the 1840’s and 1850’s a growing tension developed between the Northern and Southern states of America. That tension was primarily focused on the existence of slavery in the Southern states. Most Northern states had abolished slavery by 1850 and made a promise to the people to end slavery completely. They wanted the South to begin to become similar to the North, and to live under the concept of free labor, and not rely on slavery for productivity. The resentment for the interference of the North angered southerners because they felt that it was not the place of the federal government to interfere. Ever since the American Revolution sectional differences arose, the first being those favoring greater states rights and those†¦show more content†¦By 1860, one quarter of all Northerners lived in urban areas. Between 1800 and 1860, the percentage of laborers working in agricultural pursuits dropped drastically from 70% to only 40%. Slavery had died out, rep laced in the cities and factories by immigrant labor from Europe. In fact an overwhelming majority of immigrants, seven out of every eight, settled in the North rather than the South. Transportation was easier in the North, which boasted more than two-thirds of the railroad tracks in the country and the economy was on an upswing. Far more Northerners than Southerners belonged to the Whig/Republican political party and they were far more likely to have careers in business, medicine, or education. In fact, an engineer was six times as likely to be from the North as from the South. Northern children were slightly more prone to attend school than Southern children. The fertile soil and warm climate of the South made it ideal for large-scale farms and crops like tobacco and cotton because agriculture was so profitable few Southerners saw a need for industrial development. Eighty percent of the labor force worked on the farm. 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