Materials Science: Wood and Composites

Questions and Answers

What is one of the primary uses of polypropylene in composite construction?

To improve electrical conductivity

To create airfoil shapes (correct)

As a structural load-bearing element

For enhancing thermal insulation

Why are wood cores used in composite sandwich construction?

They act as adhesives in composite layers

They are cost-effective alternatives to metals

They provide high tensile strength

They offer high compressive strength (correct)

What is the main function of the matrix in a composite material?

To hold the reinforcing fibers in position and transfer stresses (correct)

To enhance thermal properties

To provide flexibility to the composite

To determine the color of the composite

What type of resin is commonly associated with structural applications in airframes?

Thermosetting resin Signup and view all the answers

What characteristic distinguishes thermosetting resins from thermoplastic resins?

Thermoplastic resins can be reheated and reshaped, while thermosetting cannot Signup and view all the answers

Which type of resin matrix has been used predominantly in non-structural applications?

Polyester resin Signup and view all the answers

What is a key consideration when using matrix materials in composites?

Their ability to transfer stress to reinforcing fibers Signup and view all the answers

How do plastic matrixes contribute to structural composites?

They form high-strength, lightweight structures when reinforced Signup and view all the answers

What is the definition of a check in wood quality?

A crack running through or across the annual grain Signup and view all the answers

Which of the following is NOT a characteristic of decay in wood?

Is primarily caused by insects Signup and view all the answers

What is one of the advantages of using composites in aircraft construction?

High strength to weight ratio Signup and view all the answers

What is a disadvantage of using composites?

They require well-trained staff for repairs Signup and view all the answers

What purpose does the matrix material serve in composite structures?

Serves as the bonding substance Signup and view all the answers

How can decay in wood be minimized?

By properly drying the wood and applying varnishes Signup and view all the answers

Which of the following best describes a shake in wood quality?

A crack visible from detached annual rings Signup and view all the answers

What is a general property of plastics used in aircraft construction?

They include thermoset and thermoplastic materials Signup and view all the answers

What is a key characteristic of epoxy resin systems?

Outstanding adhesion and strength Signup and view all the answers

Which type of resin is known for improved corrosion resistance over standard polyester composites?

Vinyl Ester resin Signup and view all the answers

Which resin is commonly used for interior components due to low smoke and flammability?

Phenolic resin Signup and view all the answers

Which thermoplastic material is known for its transparency and lightweight but tends to shrink and turn yellow?

Cellulose Acetate Signup and view all the answers

What effect does acetone have when applied to acrylic resin?

It leaves a white residue but the material remains hard Signup and view all the answers

What is true about thermosetting resins during the A stage of curing?

The resin components have been mixed but not yet reacted Signup and view all the answers

What characteristic do polyimide resins excel in?

High-temperature environments Signup and view all the answers

Which statement about thermoplastic resins is accurate?

They can be reshaped upon reheating Signup and view all the answers

What is the main advantage of applying heat and pressure during the curing process of composites?

It enhances the saturation and speeds up curing. Signup and view all the answers

Which method of composite manufacturing uses a plastic bag to create a vacuum for repairs?

Vacuum Bagging Signup and view all the answers

What is a characteristic feature of the Compression Molding process?

It is suited for precise, large-scale production. Signup and view all the answers

Which of the following methods is considered the most flexible in composite manufacturing?

Wet Lay-up Signup and view all the answers

How does the Filament Winding process create strong structures?

Through the winding of continuous reinforcing fibers. Signup and view all the answers

The primary function of the pressure in the curing process of composites is to:

Remove excess resin and air pockets. Signup and view all the answers

What is the purpose of the heat application during the matrix curing process in composites?

To facilitate the curing process. Signup and view all the answers

What common challenge does the Vacuum Bagging method address in composite repairs?

Applying appropriate mechanical pressure. Signup and view all the answers

What happens to prepreg materials when stored in a freezer at 0 °F?

They remain in the B stage. Signup and view all the answers

What is the primary difference between the B stage and C stage of resin?

The B stage is tacky and thickened. Signup and view all the answers

What term describes the amount of time a catalyzed resin remains in a workable state?

Pot life Signup and view all the answers

Which of the following best describes a resin rich composite?

It has too much resin applied, weakening the part. Signup and view all the answers

What fiber to resin ratio is considered the best for strength in advanced composite lay-ups?

60:40 Signup and view all the answers

What is necessary for the curing process of some resins?

An elevated temperature cure cycle Signup and view all the answers

What is the role of the partition between the resin and catalyst containers?

To prevent curing before application Signup and view all the answers

Which factor does NOT affect the strength of the reinforcing material in a composite?

The color of the resin Signup and view all the answers

Study Notes

Quality of Wood

Checks, shakes, and splits are common defects in wood that affect its integrity.
A check is a longitudinal crack through the annual grain, while a shake is a separation visible between annual rings.
Wood stains indicate decay, often appearing as streaks; they can vary from red to white discoloration.
Decay reduces toughness and may render wood brittle due to fungal activity in damp conditions.
Proper drying (up to 20%) and varnishing can minimize decay and protect wood from environmental elements.

Plastics in Aircraft Construction

Plastics are vital in aircraft manufacturing, utilized in forms like thermoset plastic reinforced fiberglass and thermoplastic materials for windows.

Composites Overview

Composites consist of multiple materials differing in composition, enhancing performance through weight reduction and structural integrity.
They offer a high strength-to-weight ratio, reduce the number of parts needed, minimize wear, and provide corrosion resistance.
Disadvantages include high costs and challenging repair processes requiring specialized training and equipment.

Composite Structure Elements

Reinforcing materials and matrix materials are key components in composite structures.
Polypropylene is commonly used for airfoil shapes; it is compatible with adhesives and epoxy but dissolves in fuels.
Balsa wood and laminated hardwoods serve as wood cores, enhancing compressive strength in composite designs.

Matrix Material Functionality

The matrix holds reinforcing fibers, providing composite strength and transferring external stresses to improve overall structure performance.
Resin, as an organic polymer, is a common matrix material. Polyester resin is used for non-structural applications, whereas epoxy resin offers better adhesion and chemical resistance.
Thermosetting resins cannot be reshaped post-curing, playing a critical role in structural applications.
Vinyl ester resins enhance mechanical properties compared to standard polyester resins.

Resin Systems and Curing Stages

Curing of thermosetting resins involves three stages: A stage (mixing without reaction), B stage (thickened, tacky state), and C stage (fully cured).
Prepreg materials are stored at low temperatures to maintain the B stage, preventing further curing until needed.

Working with Resins

Pot life refers to the workable timeframe of catalyzed resin, while shelf life indicates how long unopened products remain usable.
A balanced fiber-to-resin ratio (60:40) optimizes strength in composite lay-ups.

Fiber Science

The effectiveness of reinforcing materials depends on weave pattern, matrix application, fiber strength, and part design.

Manufacturing Processes for Composites

Heat and pressure application during curing improves fiber saturation and accelerates the curing of the matrix.
Compression molding employs male and female molds for high-volume production of precision parts.
Vacuum bagging involves placing assemblies in plastic bags and removing air to apply pressure for repairs.
Filament winding involves wrapping continuous fiber around a mandrel to create durable structures.
Wet lay-up is a straightforward method combining fiber reinforcement with a matrix for curing, offering flexibility at the cost of precision.

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Description

This quiz covers the quality of wood, including defects like checks and shakes, as well as the importance of drying and varnishing. It also explores the role of plastics and composites in aircraft construction, highlighting their advantages. Test your knowledge on materials that enhance structural integrity and performance.