AME 6 Q1

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Which of the following are four properties of carbon fiber that make it desirable for marine fabrication?

A. High tensile strength, low weight, high stiffness, and excellent resistance to corrosion.

D. High density, high thermal expansion, low cost, and ease of machining.

C. High impact resistance, high absorbency, low tensile strength, and ease of molding.

B. High flexibility, high thermal conductivity, low density, and low cost.

Correct Answer:

A. High tensile strength, low weight, high stiffness, and excellent resistance to corrosion.

Explanation:
1. High Tensile Strength: Carbon fiber has an exceptionally high tensile strength, making it ideal for withstanding significant forces and stresses in marine environments.
2. Low Weight: Its low weight relative to its strength helps reduce the overall weight of marine structures, which can improve performance and efficiency.
3. High Stiffness: The high stiffness of carbon fiber contributes to structural rigidity, which is crucial for maintaining the shape and stability of marine vessels.
4. Excellent Resistance to Corrosion: Carbon fiber is resistant to corrosion, which is particularly valuable in the harsh marine environment where exposure to saltwater and other corrosive elements is common.

Incorrect Answers:

B. High flexibility, high thermal conductivity, low density, and low cost.

Why it's incorrect:
1. High Flexibility: Carbon fiber is known for its rigidity rather than flexibility. High flexibility is not a characteristic of carbon fiber.
2. High Thermal Conductivity: Carbon fiber has low thermal conductivity. While this property can be beneficial in some applications, it is not a key factor for marine fabrication.
3. Low Density: Carbon fiber has low density, which is correct, but it is not the only factor that makes it desirable. The other properties listed are more relevant to marine applications.
4. Low Cost: Carbon fiber is relatively expensive compared to other materials. Its high cost can be a drawback, although its performance benefits often justify the expense.

C. High impact resistance, high absorbency, low tensile strength, and ease of molding.

Why it's incorrect:
1. High Impact Resistance: While carbon fiber is strong, it is not particularly known for high impact resistance. It is more focused on tensile strength and stiffness.
2. High Absorbency: Carbon fiber is not absorbent. It does not absorb moisture, which is actually a desirable property for marine applications.
3. Low Tensile Strength: This is incorrect; carbon fiber has high tensile strength, not low.
4. Ease of Molding: Carbon fiber is not particularly easy to mold compared to other materials. The molding process can be complex and requires careful handling.

D. High density, high thermal expansion, low cost, and ease of machining.

Why it's incorrect:
1. High Density: Carbon fiber has low density, which contributes to its lightweight nature.
2. High Thermal Expansion: Carbon fiber has low thermal expansion, which means it does not expand or contract significantly with temperature changes.
3. Low Cost: As mentioned earlier, carbon fiber is relatively expensive.
4. Ease of Machining: Carbon fiber can be challenging to machine due to its hardness and abrasiveness. It often requires specialized tools and techniques.

Correct Answer:

A. High tensile strength, low weight, high stiffness, and excellent resistance to corrosion.

Explanation:
1. High Tensile Strength: Carbon fiber has an exceptionally high tensile strength, making it ideal for withstanding significant forces and stresses in marine environments.
2. Low Weight: Its low weight relative to its strength helps reduce the overall weight of marine structures, which can improve performance and efficiency.
3. High Stiffness: The high stiffness of carbon fiber contributes to structural rigidity, which is crucial for maintaining the shape and stability of marine vessels.
4. Excellent Resistance to Corrosion: Carbon fiber is resistant to corrosion, which is particularly valuable in the harsh marine environment where exposure to saltwater and other corrosive elements is common.

Incorrect Answers:

B. High flexibility, high thermal conductivity, low density, and low cost.

Why it's incorrect:
1. High Flexibility: Carbon fiber is known for its rigidity rather than flexibility. High flexibility is not a characteristic of carbon fiber.
2. High Thermal Conductivity: Carbon fiber has low thermal conductivity. While this property can be beneficial in some applications, it is not a key factor for marine fabrication.
3. Low Density: Carbon fiber has low density, which is correct, but it is not the only factor that makes it desirable. The other properties listed are more relevant to marine applications.
4. Low Cost: Carbon fiber is relatively expensive compared to other materials. Its high cost can be a drawback, although its performance benefits often justify the expense.

C. High impact resistance, high absorbency, low tensile strength, and ease of molding.

Why it's incorrect:
1. High Impact Resistance: While carbon fiber is strong, it is not particularly known for high impact resistance. It is more focused on tensile strength and stiffness.
2. High Absorbency: Carbon fiber is not absorbent. It does not absorb moisture, which is actually a desirable property for marine applications.
3. Low Tensile Strength: This is incorrect; carbon fiber has high tensile strength, not low.
4. Ease of Molding: Carbon fiber is not particularly easy to mold compared to other materials. The molding process can be complex and requires careful handling.

D. High density, high thermal expansion, low cost, and ease of machining.

Why it's incorrect:
1. High Density: Carbon fiber has low density, which contributes to its lightweight nature.
2. High Thermal Expansion: Carbon fiber has low thermal expansion, which means it does not expand or contract significantly with temperature changes.
3. Low Cost: As mentioned earlier, carbon fiber is relatively expensive.
4. Ease of Machining: Carbon fiber can be challenging to machine due to its hardness and abrasiveness. It often requires specialized tools and techniques.

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How is the base raw material turned into usable carbon fiber?

D. The raw material is chopped into small pieces, mixed with a binder, and then compressed into sheets, which are later heated to form carbon fibers.

C. The raw material is woven into fabric, cured in a high-pressure chamber, and then coated with a protective gelcoat.

A. The raw material is first spun into fibers, then stabilized through a chemical process, carbonized at high temperatures, and finally treated with a surface finish before being combined with a resin matrix.

B. The raw material is melted and extruded into sheets, then cut into fibers, and finally coated with a protective resin.

Correct Answer:

A. The raw material is first spun into fibers, then stabilized through a chemical process, carbonized at high temperatures, and finally treated with a surface finish before being combined with a resin matrix.

Explanation:
1. Spinning into fibers: The base material, typically polyacrylonitrile (PAN), is spun into fibers. This step is essential to form the basic structure of carbon fiber.
2. Stabilization: The spun fibers are stabilized through a chemical process, which involves heating them to a lower temperature in the presence of air or inert gases to maintain their structure.
3. Carbonization: The stabilized fibers are then heated to extremely high temperatures (usually around 1,000 to 3,000°C) in an inert atmosphere (like nitrogen) to remove non-carbon elements and convert them into carbon fibers.
4. Surface treatment: The carbon fibers are treated with a surface finish to enhance bonding with resins and improve performance in composite materials.
5. Combination with resin matrix: The treated carbon fibers are then combined with a resin matrix to create a composite material with high strength and stiffness.

Incorrect Answers:

B. The raw material is melted and extruded into sheets, then cut into fibers, and finally coated with a protective resin.

Why it's incorrect:
1. Melting and extruding: Carbon fiber production does not involve melting and extruding the material into sheets. Instead, the base material (PAN) is spun into fibers.
2. Cutting into fibers: Fibers are not cut from sheets; they are spun directly. The process involves stabilization and carbonization rather than sheet extrusion.

C. The raw material is woven into fabric, cured in a high-pressure chamber, and then coated with a protective gelcoat.

Why it's incorrect:
1. Woven into fabric: Carbon fibers are not woven into fabric until after they are produced. The primary steps involve spinning, stabilization, carbonization, and surface treatment.
2. Cured in a high-pressure chamber: Carbon fibers are not cured in a high-pressure chamber. The curing process applies to the composite material (fiber and resin) rather than the raw fibers.

D. The raw material is chopped into small pieces, mixed with a binder, and then compressed into sheets, which are later heated to form carbon fibers.

Why it's incorrect:
1. Chopped into small pieces: Carbon fibers are not formed by chopping and binding. The production involves spinning, stabilization, and carbonization processes.
2. Compressed into sheets: The production of carbon fibers does not involve compression into sheets. Instead, the fibers are processed through stabilization and carbonization to create the final carbon fiber.

Correct Answer:

A. The raw material is first spun into fibers, then stabilized through a chemical process, carbonized at high temperatures, and finally treated with a surface finish before being combined with a resin matrix.

Explanation:
1. Spinning into fibers: The base material, typically polyacrylonitrile (PAN), is spun into fibers. This step is essential to form the basic structure of carbon fiber.
2. Stabilization: The spun fibers are stabilized through a chemical process, which involves heating them to a lower temperature in the presence of air or inert gases to maintain their structure.
3. Carbonization: The stabilized fibers are then heated to extremely high temperatures (usually around 1,000 to 3,000°C) in an inert atmosphere (like nitrogen) to remove non-carbon elements and convert them into carbon fibers.
4. Surface treatment: The carbon fibers are treated with a surface finish to enhance bonding with resins and improve performance in composite materials.
5. Combination with resin matrix: The treated carbon fibers are then combined with a resin matrix to create a composite material with high strength and stiffness.

Incorrect Answers:

B. The raw material is melted and extruded into sheets, then cut into fibers, and finally coated with a protective resin.

Why it's incorrect:
1. Melting and extruding: Carbon fiber production does not involve melting and extruding the material into sheets. Instead, the base material (PAN) is spun into fibers.
2. Cutting into fibers: Fibers are not cut from sheets; they are spun directly. The process involves stabilization and carbonization rather than sheet extrusion.

C. The raw material is woven into fabric, cured in a high-pressure chamber, and then coated with a protective gelcoat.

Why it's incorrect:
1. Woven into fabric: Carbon fibers are not woven into fabric until after they are produced. The primary steps involve spinning, stabilization, carbonization, and surface treatment.
2. Cured in a high-pressure chamber: Carbon fibers are not cured in a high-pressure chamber. The curing process applies to the composite material (fiber and resin) rather than the raw fibers.

D. The raw material is chopped into small pieces, mixed with a binder, and then compressed into sheets, which are later heated to form carbon fibers.

Why it's incorrect:
1. Chopped into small pieces: Carbon fibers are not formed by chopping and binding. The production involves spinning, stabilization, and carbonization processes.
2. Compressed into sheets: The production of carbon fibers does not involve compression into sheets. Instead, the fibers are processed through stabilization and carbonization to create the final carbon fiber.

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How does the internal structure of carbon fiber contribute to its unique strength properties?

A. Carbon fibers have a crystalline structure with carbon atoms arranged in hexagonal lattices, which provides high tensile strength and stiffness.

B. Carbon fibers have a porous structure that allows for lightweight and flexible properties, enhancing their overall strength.

C. Carbon fibers consist of a random arrangement of carbon atoms, which provides a high degree of impact resistance and flexibility.

D. Carbon fibers are composed of multiple layers of woven carbon sheets, which increase their flexibility and reduce their tensile strength.

Correct Answer:

A. Carbon fibers have a crystalline structure with carbon atoms arranged in hexagonal lattices, which provides high tensile strength and stiffness.

Explanation:
1. Crystalline Structure: Carbon fibers have a crystalline structure where carbon atoms are arranged in hexagonal lattices within the fiber. This structure is known as graphene sheets, and it contributes to the material’s exceptional tensile strength and stiffness.
2. High Tensile Strength: The strong covalent bonds between carbon atoms in the hexagonal lattice provide high tensile strength, making carbon fibers very strong under tension.
3. Stiffness: The alignment of these lattices along the fiber direction ensures that the fibers are stiff and resistant to deformation.

Incorrect Answers:

B. Carbon fibers have a porous structure that allows for lightweight and flexible properties, enhancing their overall strength.

Why it's incorrect:
1. Porous Structure: Carbon fibers do not have a porous structure. They are solid and composed of tightly packed carbon atoms. Porosity would decrease strength and stiffness, not enhance them.
2. Lightweight and Flexibility: While carbon fibers are lightweight, the strength comes from their solid crystalline structure rather than porosity.

C. Carbon fibers consist of a random arrangement of carbon atoms, which provides a high degree of impact resistance and flexibility.

Why it's incorrect:
1. Random Arrangement: Carbon fibers do not have a random arrangement of carbon atoms. Their strength comes from the ordered crystalline structure of hexagonal lattices.
2. Impact Resistance and Flexibility: The unique strength properties of carbon fibers are due to their crystalline structure, not a random arrangement. Carbon fibers are not particularly flexible; they are known for their rigidity and strength.

D. Carbon fibers are composed of multiple layers of woven carbon sheets, which increase their flexibility and reduce their tensile strength.

Why it's incorrect:
1. Woven Carbon Sheets: The structure of carbon fibers involves single filaments or strands, which can be woven into fabrics. However, the strength of the fibers themselves comes from their internal crystalline structure, not the weaving process.
2. Flexibility and Strength: Woven carbon sheets might provide some flexibility in composite materials, but the individual carbon fibers have high tensile strength due to their internal crystalline structure, not reduced strength.

Correct Answer:

A. Carbon fibers have a crystalline structure with carbon atoms arranged in hexagonal lattices, which provides high tensile strength and stiffness.

Explanation:
1. Crystalline Structure: Carbon fibers have a crystalline structure where carbon atoms are arranged in hexagonal lattices within the fiber. This structure is known as graphene sheets, and it contributes to the material’s exceptional tensile strength and stiffness.
2. High Tensile Strength: The strong covalent bonds between carbon atoms in the hexagonal lattice provide high tensile strength, making carbon fibers very strong under tension.
3. Stiffness: The alignment of these lattices along the fiber direction ensures that the fibers are stiff and resistant to deformation.

Incorrect Answers:

B. Carbon fibers have a porous structure that allows for lightweight and flexible properties, enhancing their overall strength.

Why it's incorrect:
1. Porous Structure: Carbon fibers do not have a porous structure. They are solid and composed of tightly packed carbon atoms. Porosity would decrease strength and stiffness, not enhance them.
2. Lightweight and Flexibility: While carbon fibers are lightweight, the strength comes from their solid crystalline structure rather than porosity.

C. Carbon fibers consist of a random arrangement of carbon atoms, which provides a high degree of impact resistance and flexibility.

Why it's incorrect:
1. Random Arrangement: Carbon fibers do not have a random arrangement of carbon atoms. Their strength comes from the ordered crystalline structure of hexagonal lattices.
2. Impact Resistance and Flexibility: The unique strength properties of carbon fibers are due to their crystalline structure, not a random arrangement. Carbon fibers are not particularly flexible; they are known for their rigidity and strength.

D. Carbon fibers are composed of multiple layers of woven carbon sheets, which increase their flexibility and reduce their tensile strength.

Why it's incorrect:
1. Woven Carbon Sheets: The structure of carbon fibers involves single filaments or strands, which can be woven into fabrics. However, the strength of the fibers themselves comes from their internal crystalline structure, not the weaving process.
2. Flexibility and Strength: Woven carbon sheets might provide some flexibility in composite materials, but the individual carbon fibers have high tensile strength due to their internal crystalline structure, not reduced strength.

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How are carbon fibers turned into a usable product?

B. Carbon fibers are chopped into short lengths, mixed with a binder, and compressed into sheets, which are then heated to achieve the desired properties.

D. Carbon fibers are extruded into long filaments, woven into a mesh, and then treated with a chemical hardener to enhance strength.

C. Carbon fibers are spun into a continuous thread, coated with a protective gelcoat, and then used directly without further processing.

A. Carbon fibers are first woven into fabric, then impregnated with resin, and finally cured in an autoclave to form a composite material.

Correct Answer:

A. Carbon fibers are first woven into fabric, then impregnated with resin, and finally cured in an autoclave to form a composite material.

Explanation:
1. Woven into fabric: After carbon fibers are produced, they are often woven into fabric or other forms such as uni-directional sheets. This step organizes the fibers into a usable format for further processing.
2. Impregnated with resin: The woven fabric is then impregnated with resin, which acts as a matrix to hold the fibers together and provide additional mechanical properties.
3. Cured in an autoclave: The resin-impregnated fabric is cured in an autoclave, a high-pressure and high-temperature chamber, to harden the resin and form a strong, durable composite material. This curing process solidifies the composite structure, enhancing its strength and performance.

Incorrect Answers:

B. Carbon fibers are chopped into short lengths, mixed with a binder, and compressed into sheets, which are then heated to achieve the desired properties.

Why it's incorrect:
1. Chopped into short lengths: Carbon fibers are typically used in continuous or woven forms rather than chopped lengths for high-performance applications. Chopping fibers into short lengths is more common in other materials or less demanding applications.
2. Mixed with a binder: While binders are used in some composite materials, the standard process for high-strength carbon fiber products involves resin impregnation rather than binder mixing and compression.

C. Carbon fibers are spun into a continuous thread, coated with a protective gelcoat, and then used directly without further processing.

Why it's incorrect:
1. Spun into a continuous thread: Carbon fibers are indeed spun into continuous filaments, but they are not typically used directly in this form. They need to be woven into fabric or other structures for effective use.
2. Coated with a protective gelcoat: Gelcoat is not used in carbon fiber processing. Gelcoat is applied to the surface of composite materials for protection and aesthetics, but carbon fibers are processed into fabric and combined with resin rather than gelcoat.

D. Carbon fibers are extruded into long filaments, woven into a mesh, and then treated with a chemical hardener to enhance strength.

Why it's incorrect:
1. Extruded into long filaments: Carbon fibers are not typically extruded; they are spun and then processed. The extrusion process is more relevant to materials like plastics.
2. Treated with a chemical hardener: The standard process involves resin impregnation and autoclave curing rather than using chemical hardeners. The resin system used in carbon fiber composites is crucial for forming the final product.

Correct Answer:

A. Carbon fibers are first woven into fabric, then impregnated with resin, and finally cured in an autoclave to form a composite material.

Explanation:
1. Woven into fabric: After carbon fibers are produced, they are often woven into fabric or other forms such as uni-directional sheets. This step organizes the fibers into a usable format for further processing.
2. Impregnated with resin: The woven fabric is then impregnated with resin, which acts as a matrix to hold the fibers together and provide additional mechanical properties.
3. Cured in an autoclave: The resin-impregnated fabric is cured in an autoclave, a high-pressure and high-temperature chamber, to harden the resin and form a strong, durable composite material. This curing process solidifies the composite structure, enhancing its strength and performance.

Incorrect Answers:

B. Carbon fibers are chopped into short lengths, mixed with a binder, and compressed into sheets, which are then heated to achieve the desired properties.

Why it's incorrect:
1. Chopped into short lengths: Carbon fibers are typically used in continuous or woven forms rather than chopped lengths for high-performance applications. Chopping fibers into short lengths is more common in other materials or less demanding applications.
2. Mixed with a binder: While binders are used in some composite materials, the standard process for high-strength carbon fiber products involves resin impregnation rather than binder mixing and compression.

C. Carbon fibers are spun into a continuous thread, coated with a protective gelcoat, and then used directly without further processing.

Why it's incorrect:
1. Spun into a continuous thread: Carbon fibers are indeed spun into continuous filaments, but they are not typically used directly in this form. They need to be woven into fabric or other structures for effective use.
2. Coated with a protective gelcoat: Gelcoat is not used in carbon fiber processing. Gelcoat is applied to the surface of composite materials for protection and aesthetics, but carbon fibers are processed into fabric and combined with resin rather than gelcoat.

D. Carbon fibers are extruded into long filaments, woven into a mesh, and then treated with a chemical hardener to enhance strength.

Why it's incorrect:
1. Extruded into long filaments: Carbon fibers are not typically extruded; they are spun and then processed. The extrusion process is more relevant to materials like plastics.
2. Treated with a chemical hardener: The standard process involves resin impregnation and autoclave curing rather than using chemical hardeners. The resin system used in carbon fiber composites is crucial for forming the final product.

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