Composite Structures And Transparent Plastic Materials

A thermoplastic is a category of plastic material that is capable of softening or flowing when reheated. Unlike thermosets, which undergo a chemical change when heated and cannot be reshaped, thermoplastics can be melted and reshaped multiple times without undergoing any chemical change. This property makes thermoplastics highly versatile and widely used in various industries for applications such as injection molding, 3D printing, and packaging.

Aramid fibers, also known as Kevlar fibers, are extremely strong and resistant to heat. Due to their unique properties, special scissors are required to cut aramid fibers effectively. Regular scissors may not be able to cut through the fibers or may cause damage to them. Therefore, it is true that special scissors are needed to cut aramid fibers.

Kevlar is DuPont's trademark name for aramid fibers. Aramid fibers are a type of synthetic fibers that are known for their high strength and heat resistance. They are commonly used in applications that require protection against abrasion, impact, and heat, such as in bulletproof vests, helmets, and tires. Kevlar is one of the most well-known and widely used brands of aramid fibers.

When inspecting a composite panel using the ring test/tapping methods, a dull thud may indicate separation of the laminates. This means that the layers of the composite panel are not properly bonded together and there is a gap or separation between them. This can be a sign of poor manufacturing or damage to the panel. It is important to identify and address this issue as it can compromise the strength and integrity of the panel.

Sandwich panels made of metal honeycomb construction are used on modern aircraft because they have a high strength to weight ratio. This means that they are able to provide a high level of structural strength while being lightweight, which is crucial for aircraft where weight is a critical factor. The honeycomb structure allows for the distribution of load and provides rigidity, making it a suitable choice for aircraft construction.

To prevent corrosion inside a repaired metal honeycomb structure, it is necessary to prime the repair with a corrosion inhibitor and seal it from the atmosphere. This is because metal structures are susceptible to corrosion when exposed to moisture and oxygen. By applying a corrosion inhibitor, it helps to protect the metal from chemical reactions that cause corrosion. Additionally, sealing the repaired area from the atmosphere helps to prevent moisture and oxygen from coming into contact with the metal, further reducing the risk of corrosion.

When fiberglass laminate damage extends completely through one facing and into the core, it is necessary to replace both the damaged core and facing. This is because the damage has compromised the structural integrity of the laminate, and simply patching it with a metal facing would not adequately restore its strength. Therefore, the only solution is to replace the damaged components entirely to ensure the structural integrity of the laminate is restored.

Repairing advanced composites using materials and techniques traditionally used for fiberglass repairs is likely to result in an unairworthy repair. This is because advanced composites have different properties and require specialized materials and techniques for proper repair. Using materials and techniques meant for fiberglass repairs may not provide the necessary strength, flexibility, and durability required for advanced composites, leading to a repair that does not meet the standards for safe and reliable aircraft operation.

A potted compound repair on honeycomb can usually be made on damages less than 1 inch in diameter. This means that if the damage to the honeycomb structure is smaller than 1 inch in diameter, it can be repaired using a potted compound method. This method involves filling the damaged area with a compound material to restore the structural integrity of the honeycomb. However, if the damage exceeds 1 inch in diameter, alternative repair methods may be required.

Composite fabric material is considered to be the strongest in the warp direction. The warp direction refers to the lengthwise threads in the fabric that run parallel to the selvage. In composite fabrics, the warp threads are typically stronger and more tightly woven than the weft threads, which run perpendicular to the selvage. This design allows the fabric to have greater strength and resistance to stretching in the warp direction, making it the strongest direction for composite fabrics.

A fiber to resin ratio of 60:40 is generally considered the best for strength in advanced composite wet lay-ups. This means that there is a higher percentage of fiber compared to resin in the composite. The higher fiber content provides better load-bearing capacity and stiffness, resulting in increased strength. The lower resin content also helps to reduce weight and improve overall performance.

MEK (methyl ethyl ketone) is the correct answer because it is a solvent that is commonly used for cleaning and preparing surfaces before applying adhesives or making repairs. It is effective in removing dirt, grease, and other contaminants from the fiberglass surface, ensuring a clean and proper bond. The use of a thixotropic agent or soap, water, and a scrub brush may not be as effective in removing all the contaminants, resulting in a weaker bond.

The given correct answer states that only statement No.1 is true. This means that when performing a ring (coin tap) test on composite structures, a change in sound may be due to damage or to transition to a different internal structure. However, statement No.2, which claims that the extent of separation damage in composite structures is most accurately measured by a ring (coin tap) test, is not true.

When machining composite laminates, water is usually the most acceptable type of cutting fluid. This is because water does not react with or damage the composite material. Water is also effective in cooling the cutting tool and reducing friction during the machining process. Additionally, using water as a cutting fluid helps to minimize any potential environmental and health hazards associated with other types of cutting fluids.

Laminating on new repair plies is the preferred way to make permanent repairs on composites. This involves applying new layers of composite material to the damaged area, which helps restore the structural integrity of the composite. This method ensures a strong bond between the new repair plies and the existing composite, resulting in a durable and long-lasting repair. Bonding on metal or cured composite patches and riveting on metal or cured composite patches may also be used for repairs but are not the preferred method as they may not provide the same level of strength and durability as laminating on new repair plies.

Satin weaves have fewer crimps, which means the yarns are more spaced out and have longer floats compared to plain weave fabrics. This results in a smoother and more lustrous surface. However, this also makes satin weaves more prone to distortion as the longer floats are more susceptible to being pulled out of shape. Therefore, it is true that satin weaves have less crimp and are easier to distort than plain weave fabrics.

Water or moisture in honeycomb structures can actually have a significant impact on the structure during the repair process. Moisture can lead to corrosion of the metal reinforcement within the honeycomb structure, weakening it and potentially causing further damage. Additionally, water can also interfere with the adhesion of repair materials, making it difficult to properly repair the structure. Therefore, it is important to remove any water or moisture from honeycomb structures before attempting repairs.

Pot life refers to the length of time that a catalyzed resin remains in a workable state. It is the time period during which the resin can be applied or manipulated before it starts to harden or cure. Pot life is an important consideration in various industries, such as construction and manufacturing, as it determines the time available for working with the resin before it becomes unusable.

Plexiglas is a type of acrylic plastic that is prone to cracking and chipping when drilled. Using a standard twist drill or a wood drill can cause damage to the material. Therefore, a specially modified twist drill should be used to drill holes completely through Plexiglas. This type of drill is designed to reduce the risk of cracking and produce clean and precise holes in the material.

Stripping the damaged area of all paint and shining a strong light through the structure is a method used to inspect a laminated fiberglass structure that has been subjected to damage. By removing the paint and illuminating the structure with a strong light, any cracks, delaminations, or other damage can be easily identified. This method allows for a thorough examination of the structure to determine the extent of the damage and assess its structural integrity. Using an eddy current probe or dye penetrant inspection procedures may be suitable for other types of inspections, but in this case, the most effective method is to strip the paint and use light to inspect the structure.

A warp clock or compass is used as a reference tool to determine how the fiber is to be oriented for a particular ply of fabric. The warp refers to the lengthwise yarns in a woven fabric, and the warp clock helps in ensuring that the fibers are aligned properly in this direction. By using a warp clock or compass, the fabric manufacturer can accurately determine the angle at which the fibers should be placed during the weaving process, resulting in a fabric with the desired strength and appearance.

An individual fiber is called a filament. Filaments are long, continuous strands of material, often used in textiles and manufacturing processes. They can be made from various materials such as silk, nylon, or carbon fiber. Filaments are known for their strength and flexibility, making them suitable for a wide range of applications including clothing, ropes, and industrial materials.

Metal fasteners used with carbon/graphite composite structures must be constructed of material such as titanium or corrosion resistant steel. This is because carbon/graphite composite structures are highly susceptible to galvanic corrosion when in contact with certain metals, such as aluminum. Titanium and corrosion resistant steel are chosen as they have a low galvanic potential and are less likely to cause corrosion when in contact with carbon/graphite composites.

Scarf repair is a method used to repair damaged or weakened structures by overlapping and bonding the damaged area with additional material. This technique allows for a larger contact area between the repair material and the structure, resulting in a more efficient load transfer. On the other hand, external bolted patches involve bolting an additional piece of material onto the damaged area. Although bolted patches can provide reinforcement, they may not distribute the load as effectively as a scarf repair due to a smaller contact area. Therefore, the statement that scarf repair is more efficient in load transfer than external bolted patches is true.

The ribbon direction is the correct answer because when replacing a honeycomb core, it is important for the new core to align with the adjacent original core. The ribbon direction refers to the orientation of the honeycomb cells, and ensuring that the ribbon direction matches helps maintain the structural integrity and strength of the overall honeycomb structure.

Crazing refers to the formation of fine cracks in transparent plastic enclosures of an aircraft. These cracks can extend in a network pattern over or under the surface or through the plastic. This condition is known as crazing.

The material layer used within the vacuum bag pressure system to absorb excess resin during curing is called a bleeder. This layer helps to remove any excess resin from the laminate, allowing for a more efficient and controlled curing process. The bleeder acts as a pathway for the excess resin to escape, preventing it from causing any defects or inconsistencies in the final product.

When installing transparent plastic enclosures, it is important to tighten the nuts to a firm fit. However, it is also necessary to back off the nuts one full turn after reaching the firm fit. This is because plastic materials can expand or contract due to temperature changes, and by backing off the nuts, it allows for any potential expansion or contraction without causing damage to the plastic or putting excessive pressure on the enclosure.

The classification for high tensile strength fiberglass used in aircraft structures is S.

In the installation of acrylic plastics, it is considered good practice to use adequate spacer or other satisfactory means when using rivets to prevent excessive tightening of the frame to the plastic. This is important because acrylic plastics are prone to cracking or breaking under excessive pressure or stress. By providing a spacer or other means, it helps distribute the pressure evenly and prevents damage to the plastic.

After cleaning transparent plastic enclosure materials, covering their surfaces with a thin coat of wax can help to prevent scratches from appearing. The wax creates a protective layer that adds an extra barrier between the plastic and any potential sources of damage. This ensures that the plastic remains in good condition and maintains its transparency.

When a fiberglass laminate is damaged, it can be repaired by filling the damaged area with a putty made of a compatible resin and clean, short glass fibers. This putty will help to restore the strength and integrity of the damaged laminate. Sanding the area until it is aerodynamically smooth and trimming the rough edges are also important steps in the repair process. However, these steps alone are not sufficient to fully repair the damage. Sealing the repaired area with paint is not mentioned in the explanation, so it is not necessary for this particular repair process.

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The strength and stiffness of a composite buildup depend primarily on the orientation of the plies to the load direction. This means that the arrangement of the layers of fibers in the composite material plays a crucial role in determining its mechanical properties. When the plies are properly aligned with the load direction, they can efficiently transfer stress and distribute it throughout the material, resulting in enhanced strength and stiffness. On the other hand, if the plies are misaligned, the load may not be effectively transferred, leading to reduced performance of the composite buildup.

Aramid fibers are known to be hygroscopic, meaning they have a tendency to absorb moisture from the surrounding environment. This can be a disadvantage as the absorbed moisture can weaken the fibers and reduce their overall strength and performance. Additionally, the absorbed moisture can also lead to dimensional changes, causing the fibers to expand or shrink, which can further affect their structural integrity. Therefore, the primary disadvantage of aramid fibers is their hygroscopic nature.

Unidirectional tapes are designed to have high tensile strength in the fiber direction. This means that they are strong and resistant to stretching or breaking when force is applied along the length of the fibers. The other physical properties mentioned in the options, such as high compressive strength across the fibers and high shear strength, may also be present in unidirectional tapes to some extent, but the primary and most important property is the high tensile strength in the fiber direction.

Using microballons when making repairs to laminated honeycomb panels provides several benefits. Firstly, it allows for greater concentrations of resin in edges and corners, which helps to strengthen these vulnerable areas. Secondly, it improves the strength to weight ratio of the panels, making them lighter without sacrificing durability. Thirdly, microballons have a lower density, which further contributes to reducing the overall weight of the panels. Lastly, their use helps to lower stress concentrations, which can help prevent cracks and other forms of damage. Therefore, the correct answer is 2, 3, and 4.

The structural properties of a composite laminate, such as stiffness, dimensional stability, and strength, depend on the stacking sequence of the plies. The arrangement and order in which the plies are layered greatly affect the overall performance of the laminate. The stacking sequence determines the distribution of forces and load transfer within the material, impacting its mechanical properties. Therefore, selecting the appropriate stacking sequence is crucial in optimizing the desired characteristics of the composite laminate.

The given correct answer suggests that fiberglass damage that extends completely through a laminated sandwich structure can be repaired. This implies that the damage is not beyond repair and can be fixed using appropriate methods. It is important to fill the damaged area with resin to eliminate dangerous stress concentrations and ensure the structural integrity of the laminated sandwich structure. Additionally, the option of filling the damaged area with putty that is compatible with resin is also mentioned as a possible repair solution.

Plastic enclosure materials have a higher coefficient of expansion compared to steel and aluminum. This means that when exposed to heat, plastic materials will expand more than steel and aluminum. Therefore, the statement "greater than both steel and aluminum" is correct.

The correct answer is E. Fiberglass reinforcement material with high resistivity is commonly classified as E.

Carbon fibers have a high potential for causing galvanic corrosion when used with metallic fasteners and structures. Galvanic corrosion occurs when two dissimilar metals come into contact in the presence of an electrolyte, causing one metal to corrode more rapidly than it would on its own. Carbon fibers, being electrically conductive, can act as a catalyst for galvanic corrosion when in contact with metals. Therefore, the statement that carbon fibers have a low potential for causing galvanic corrosion is false.

Hole filling fasteners should not be used in composite structures primarily because of the possibility of causing delamination. Delamination refers to the separation or splitting of layers within the composite material, which can weaken the structure and compromise its integrity. Hole filling fasteners, such as MS20470 rivets, do not adequately distribute the load across the composite layers, leading to stress concentration and potential delamination. Therefore, alternative fastening methods that minimize the risk of delamination should be used in composite structures.

The most common method of cementing transparent plastics is the soak method. This involves immersing the plastic parts in a solvent that can dissolve the surface of the plastic, creating a bond when the solvent evaporates. This method is commonly used because it allows for a strong and seamless bond between the plastic parts, without causing any damage or distortion to the transparency of the material. The bevel method involves creating a beveled edge on the plastic parts and joining them together, while the heat method involves using heat to melt the plastic parts and fuse them together. However, the soak method is the preferred choice for cementing transparent plastics.

Using short strips of fiberglass in the bonded repair helps to reduce warping of the surface when repairing large, flat surfaces with polyester resins. The fiberglass strips provide additional reinforcement and support to the repair, preventing excessive warpage.

To assure that a properly prepared batch of matrix resin has been achieved, it is important to have mixed enough resin for a test sample. This ensures that there is an adequate amount of resin available for testing purposes, allowing for accurate analysis of its properties and performance. By having a sufficient quantity of resin, any potential issues or inconsistencies in the mixing process can be identified and addressed before using the resin in actual applications. This step helps to ensure the quality and reliability of the final product.

Composite inspections conducted by means of acoustic emission monitoring involve using sensors to detect and pick up the "noise" generated by corrosion or other forms of deterioration occurring in the inspected areas. This technique allows for the early detection of potential issues before they become more severe. It does not involve creating sonogram pictures or analyzing ultrasonic signals, but rather focuses on detecting and monitoring the acoustic emissions produced by the deterioration process.

Carbon/graphite fiber composites are known for their stiffness, high compressive strength, and the ability to corrode aluminum when in contact with it. They are not typically flexible and have the ability to conduct electricity. Therefore, the correct answer is 2, 3, and 4.

Acrylic plastics are known for their resistance to chemicals, including zinc chloride. This means that when exposed to zinc chloride, acrylic plastics will not undergo any noticeable changes or reactions. Therefore, the fact that zinc chloride will have no effect on acrylic plastics is an identifying characteristic of this type of plastic.

Bonded scarf repairs are not quicker and easier to carry out than bolted repairs. This statement contradicts the given information, indicating that the correct answer is False.