Compsites Revision

Questions and Answers

What temperature is required for phenol-formaldehyde adhesives to cure?

Variable temperature

Low temperature

Room temperature

High temperature (correct)

Which two processes are essential parts of the adhesive process?

Wetting and setting (correct)

Wetting and gripping

Drying and bonding

Spreading and setting

Which types of adhesive joints are categorized under adhesive bonding?

Flexible and rigid

Cemented and specific

Mechanical and specific (correct)

Mechanical and cemented

What type of material is best suited for high temperature applications such as a firewall?

Ceramic fibres Signup and view all the answers

In which direction can overextended honeycomb bend?

Along the ribbon Signup and view all the answers

Where is the strength of fibre weave greatest?

Warp direction Signup and view all the answers

What is a necessary property of ceramic composites in high temperature applications?

Strength retention at high temperatures Signup and view all the answers

Which factor influences the choice of adhesive for specific applications?

Temperature resistance Signup and view all the answers

What is alumina?

A ceramic oxide of aluminium. Signup and view all the answers

Which core material is most commonly selected for a composite material flat panel?

Hexagonal core. Signup and view all the answers

Which application is best suited for a Perspex panel?

A passenger window. Signup and view all the answers

What type of composite are Kevlar and Nomex categorized as?

Advanced composite. Signup and view all the answers

Fiberglass strength is primarily oriented in which direction?

Along the fibre. Signup and view all the answers

Which non-destructive testing (NDT) method is preferred to detect structural damage in a composite flap panel?

Coin tap test. Signup and view all the answers

What material is best at absorbing sound?

Soft and porous material. Signup and view all the answers

To achieve the maximum tensile strength in fibre reinforced plastic, which configuration of fibres is recommended?

Unidirectional fibres. Signup and view all the answers

What is produced when polyester resin is combined with glass fibre cloth?

GRP. Signup and view all the answers

Which statement describes the behavior of thermoplastics?

They can be reheated and reformed multiple times. Signup and view all the answers

Which group does impact adhesive belong to?

Thermoplastic group. Signup and view all the answers

What is the identifying characteristic of acrylic plastics?

Zinc chloride has no effect on it. Signup and view all the answers

Which type of E-glass is commonly used in fiberglass reinforcement material?

High resistivity glass. Signup and view all the answers

Composite fabric material has maximum strength in which direction?

Warp. Signup and view all the answers

Which characteristic is true about Kevlar composites?

High tensile strength, stiffness and ability to conduct electricity Signup and view all the answers

What is a common characteristic of carbon/graphite fibre composites?

Stiffness, high compressive strength, and corrosive effect in contact with aluminium Signup and view all the answers

What should be done if hardener is forgotten in a composite repair?

Remove all resin and start again. Signup and view all the answers

What is a defining feature of thermosetting plastics?

Once moulded, they cannot be softened by reheating Signup and view all the answers

Why are microballoons used in composite repairs?

They are the lightest filler material. Signup and view all the answers

What material should be used for covering repairs in an autoclave?

High temp nylon. Signup and view all the answers

Which material is susceptible to moisture ingress?

Kevlar Signup and view all the answers

What types of tests are commonly performed on adhesive joints?

Shear and peel Signup and view all the answers

During vacuum bag lay-up, where is the vacuum gauge positioned for optimal results?

Opposite side to the vacuum port. Signup and view all the answers

When using a hot bonder for composite repairs, which adhesive is appropriate?

Synthetic resin adhesives Signup and view all the answers

What is the maximum repair dimension limit when using microballoons?

10 mm. Signup and view all the answers

During a composite repair lay-up, how much should each layer extend beyond the one below it?

1 - 2 inches Signup and view all the answers

How many arrest points does stepped curing have?

2 or more arrest points. Signup and view all the answers

What is used to apply pressure in an autoclave?

A vacuum bag. Signup and view all the answers

What happens to the pot life of a cold cure resin when heat is applied?

Decreases pot life Signup and view all the answers

What does MSDS stand for?

Material Safety Data Sheet. Signup and view all the answers

Which product poses a serious health hazard when handling?

Asbestos Signup and view all the answers

How does increasing the amount of catalyst in a resin mixture affect its pot life?

Decreases the pot life Signup and view all the answers

What is the correct method to prepare a thermoplastic fibre reinforced composite?

The corona method. Signup and view all the answers

What is the recommended method for cleaning aircraft transparent plastics?

Warm soapy water, rinsed and dried Signup and view all the answers

Which components of a three-part polyester resin should not be mixed directly?

Accelerator and free catalyst Signup and view all the answers

Which of the following is considered dangerous when mixing resin?

Adding accelerator and catalyst before resin. Signup and view all the answers

What is the effect of adding excessive hardener to a resin?

Makes the repair more brittle Signup and view all the answers

What characterizes a thermosetting adhesive?

It undergoes a chemical transformation and creates an insoluble substance Signup and view all the answers

Metal fasteners used with carbon/graphite composite structures must be made from which materials?

Titanium or corrosion-resistant steel Signup and view all the answers

What is the maximum size of a hole in honeycomb material that can be repaired with microballoons?

2.54 cm Signup and view all the answers

What tool is appropriate for removing honeycomb material during repair?

A router. Signup and view all the answers

Which methods are effective for inspecting fibreglass/honeycomb structures for entrapped water?

X-ray and back-lighting Signup and view all the answers

At what pressure should the vacuum alarm in an autoclave be set?

Lower than operating pressure. Signup and view all the answers

What is the purpose of an air-driven router in honeycomb repairs?

To remove honeycomb material when one outer skin is damaged Signup and view all the answers

Where is a Templestick used in composite repairs?

To indicate temperature during curing with heat lamps Signup and view all the answers

When cutting a plug from balsa wood to replace a honeycomb core, how should the grain be aligned?

Perpendicular to the skin Signup and view all the answers

What should be done if a composite repair does not fully cure?

Remove all resin and start again. Signup and view all the answers

What is the purpose of tapering the edges of a doubler during metal-faced laminated honeycomb panel repairs?

To ensure stronger adhesion Signup and view all the answers

Where should vacuum connections be placed during a fiberglass repair?

On the breather mat Signup and view all the answers

One of the best ways to confirm a properly prepared batch of matrix resin is to:

Have mixed enough for a test sample Signup and view all the answers

What does composite inspection via acoustic emissions monitoring analyze?

Noise indicative of corrosion or material degradation Signup and view all the answers

For effective inspection of composites, which technique is NOT typically used?

Chemical analysis Signup and view all the answers

What occurs during the curing cycle of thermosetting adhesives?

Heat is released. Signup and view all the answers

How does a lower temperature than ambient affect the curing time of a resin?

Curing time increases. Signup and view all the answers

Which material is primarily used as a base covering on a honeycomb repair?

Glass cloth or thin aluminium sheet. Signup and view all the answers

What type of drill is recommended when working with carbon fibre reinforced plastic?

A tungsten carbide drill. Signup and view all the answers

What is the purpose of an extra layer of fiber when laying up a glass fibre repair?

To provide additional strength. Signup and view all the answers

How are bubbles eliminated from a wet composite lay-up effectively?

By using a roller. Signup and view all the answers

What effect does excessive hardener in polyester resin have?

It shortens the pot life. Signup and view all the answers

When a hot bond repair's temperature increases, what is it known as when the heating is paused?

The arrest point. Signup and view all the answers

What does slight waviness on a fiber composite structure indicate?

It may be acceptable if lightly loaded. Signup and view all the answers

What term is used to describe the maximum time a component can be stored?

Shelf life. Signup and view all the answers

What happens to a pre-preg composite's life if stored below 10 °C?

It can be prolonged by 12 months. Signup and view all the answers

What occurs when a crack in a hot bond composite pane reaches the ribbon?

The crack stops. Signup and view all the answers

What method is used to remove air from an autoclave?

By creating a vacuum. Signup and view all the answers

What is the separation of aramid panel layers referred to as?

Delamination. Signup and view all the answers

How effective is tap testing a sandwich panel construction?

It is crude, but works remarkably well. Signup and view all the answers

What is the term for the length and time that a catalyzed resin will remain in a workable state?

Pot life Signup and view all the answers

What does a dull thud indicate when inspecting a composite panel using the ring test/tapping method?

Separation of the laminates Signup and view all the answers

Which component is essential for determining the fibre orientation in a ply or fabric?

Warp clock Signup and view all the answers

Which method can be employed to inspect a damaged laminated fibreglass structure?

Strip the damaged area of all paint and shine a strong light through it Signup and view all the answers

What is the generally accepted fibre to resin ratio for advanced composite wet lay-ups?

40:60 Signup and view all the answers

What layer is used in a vacuum bag pressure system to absorb excess resin during the curing process?

Bleeder Signup and view all the answers

Which type of cutting fluid is usually acceptable for machining composite laminates?

Water only Signup and view all the answers

What is the primary factor that the strength and stiffness of a composite lay-up depend on?

Orientation of the plies to the load direction Signup and view all the answers

What type of repairs can generally be done for superficial damage on fibreglass laminates?

Applying one or more coats of suitable resin Signup and view all the answers

For what size damage can a potted compound repair on honeycomb typically be performed?

1 inch in diameter Signup and view all the answers

What is the advantage of using microballoons in repairs to laminate honeycomb sandwich panels?

Lower weight and stress concentrations Signup and view all the answers

What Surface preparation method is generally used for repair of fibreglass laminate damage?

Sanding until smooth Signup and view all the answers

What type of composite repair generally requires filling with compatible resin and glass fibers?

Fibreglass laminate not exceeding the first layer Signup and view all the answers

What characterizes a well-constructed composite lay-up regarding fibre and matrix?

Optimized fibre orientation for stress transfer Signup and view all the answers

What must be done to fibreglass damage that penetrates completely through a laminated sandwich structure?

It requires a stepped-joint or scarfed repair. Signup and view all the answers

What is necessary when repairing fibreglass laminate damage that reaches the core?

Replace both the damaged core and facing. Signup and view all the answers

Which materials are effective for strengthening repairs of fastener holes in composite panels?

Cotton flock and chopped fibres. Signup and view all the answers

Which part of a replacement honeycomb core must align with the original?

Ribbon direction. Signup and view all the answers

How is cure time defined in composite materials?

Time to reach an initial rubbery state. Signup and view all the answers

To avoid dermatitis from polymer resin, what is the recommended action?

Use barrier cream or disposable gloves. Signup and view all the answers

What type of repair is appropriate for fibreglass laminate damage?

Stepped-joint or scarfed repair. Signup and view all the answers

Which of the following strategies is least appropriate for repairing core damage in fibreglass?

Ignoring small cracks if the surface looks intact. Signup and view all the answers

Which of the following indicates a successful repair of fastener holes?

The surface is even with no gaps. Signup and view all the answers

What happens to the adhesive properties of a compound during the cure process?

They fully disappear once cured. Signup and view all the answers

Study Notes

Adhesives and Bonding Processes

Phenol-formaldehyde adhesives cure at high temperatures.
The adhesive process consists of wetting and setting.
Adhesive joints can be classified as mechanical and specific.

Materials and Applications

Ceramic fibres are used in high-temperature applications, such as firewall construction.
Honeycomb structures can bend along the ribbon direction when extended.
The strength of fiber weave is greatest along the warp direction.

Material Properties

Alumina is a ceramic oxide of aluminium.
Hexagonal core is utilized in composite material flat panels.
Perspex panels are best suited for passenger windows.

Fibres and Composites

Kevlar and Nomex are classified as advanced composites.
Fiberglass strength is primarily along the fibre direction.
Carbon/graphite composites are known for their stiffness and high compressive strength.

Repair Techniques and Procedures

Coin tap test is used for detecting structural damage in composite flap panels.
Sound absorption is most effective in soft and porous materials.
Unidirectional fibres achieve maximum tensile strength in fibre-reinforced plastics.

Characteristics of Materials

GRP (Glass Reinforced Plastic) is formed by polyester resin and glass fibre cloth.
Thermoplastics can be reheated and reshaped multiple times.
Thermosetting plastics become set upon moulding and cannot be softened again.

Composite and Non-Metallic Materials

Kevlar is prone to moisture ingress.
Shear and peel tests assess adhesive joint performance.
Synthetic resin adhesives are ideal for repairs utilizing a hot bonder.

Composite Lay-up Techniques

Each layer in a composite repair lay-up should extend 1-2 inches beyond the layer below.
The effect of heat on cold cure resin decreases pot life.
Microballoons serve as the lightest filler material in repairs, effective for holes up to 2.54 cm.

Repair and Measurement Tools

Templesticks indicate temperature during composite curing with heat lamps.
Vacuum connections must be placed on the breather mat in fiberglass repairs.
Honeycomb material can be removed for repairs using an air-driven router.

Autoclave Procedures

In an autoclave, the vacuum alarm is set below operating pressure to alert pressure drops.
Repairs must be covered in high-temperature nylon within the autoclave.
Using a vacuum bag applies pressure in the autoclave process.

Safety and Handling

Mixing resin is dangerous when accelerator is added before resin.
Material Safety Data Sheet (MSDS) provides essential safety information.
Pot life of cold cured resin decreases with increased temperature.

Miscellaneous

Advanced composites, including aramid fibres, provide high tensile strength and varying characteristics.
Stepped curing processes involve multiple arrest points, typically two or more.
The maximum size for repair with microballoons is approximately 10mm.### Resin Curing and Temperature
Lower ambient temperatures increase curing time for resin.
A colder environment slows down the chemical reactions needed for curing.

Honeycomb Repair Materials

Glass cloth or thin aluminum sheet is preferred as a base covering for honeycomb repairs.
This choice ensures compatibility with honeycomb sandwich structures.

Drilling Carbon Fibre

A tungsten carbide drill is recommended for drilling carbon fibre reinforced plastics.
This ensures precise drilling and minimizes damage to composite materials.

Glass Fibre Lay-Up

An additional layer of fibre in a glass fibre repair provides extra strength rather than serving as a sacrificial layer.

Composite Lay-Up Processing

Use a roller to remove large bubbles from a wet composite lay-up, enhancing the finish and strength of the composite.

Polyester Resin and Hardener

Excessive hardener in polyester resin reduces pot life, limiting the time the resin can be worked with.
Over-hardening can also lead to brittleness of the final product.

Hot Bond Repairs

An "arrest point" occurs during hot bond repairs when the temperature increase is paused, allowing for a controlled curing process.

Composite Panel Inspections

Slight waviness in fibre composite structures may be tolerable if the load is light, but could lead to potential fatigue cracks if not managed properly.

Shelf Life of Components

The maximum duration a component can be stored before use is referred to as shelf life.
This is crucial for maintaining the integrity and safety of materials.

Pre-preg Composite Storage

Storing pre-preg composites above 40 °C can extend their usable life by up to 12 months.

Crack Behavior in Hot Bond Repairs

A crack may stop at a ribbon in a hot bond composite panel, preventing further damage propagation.

Autoclave Operation

Air is evacuated from an autoclave using a vacuum system, crucial for creating the optimal environment for curing composites.

Delamination of Aramid Panels

Separation of layers in aramid panels is termed delamination, a critical point in composite integrity assessments.

Acoustic Emission Testing

Acoustic emission monitoring in composite inspections detects deterioration and may produce sonogram images for analysis.

Strength to Weight Ratio in Repairs

Microballoons in laminate honeycomb repairs provide benefits such as reduced density and lower stress concentrations.

Pot Life Definition

Pot life is the duration a catalyzed resin remains workable; critical to planning application processes.

Visual Inspection Techniques

A common method for inspecting laminated fibreglass structures is to remove paint and shine light through the area, revealing damage.

Tapping Method for Composite Panels

The "ring test" may indicate separation of laminates if a dull thud is heard, suggesting integrity concerns.

Surface Repairs on Fibreglass

Superficial damage can often be repaired by applying resin and may involve additional techniques such as heating for curing.

Core Replacement in Honeycomb Structures

If replacing a damaged honeycomb core, the plug must be aligned correctly with the original core’s grain for structural stability.

Fibre Orientation Reference

The warp clock is utilized to determine the correct fibre orientation during composite ply application.

Composite Lay-Up Strength

The performance of a composite lay-up relies heavily on the orientation of plies relative to the load direction.

Ideal Fibre to Resin Ratio

A 40:60 fibre to resin ratio is generally viewed as optimal for advanced composite wet lay-ups.

Vacuum Bagging Process

A bleeder layer in the vacuum bagging process absorbs excess resin during curing, ensuring optimal resin content in the final product.

Cutting Fluids for Machining

Water is typically the acceptable cutting fluid for machining composite laminates, promoting necessary cooling without contamination.

Fiberglass Laminate Damage Assessment

Damage that penetrates beyond the first layer in fibreglass must be repaired properly to maintain structural integrity.

Honeycomb Core Compatibility

When repairing with a replacement honeycomb core, the new cell must align with the original core's structure to ensure strength and stability.

Cure Time Definition

Cure time refers to the duration necessary for a mixed compound to develop its initial rubbery state, impacting its effectiveness in applications.

Dermatitis Prevention

To prevent dermatitis from polymer resin, it's crucial to use gloves or barrier cream, minimizing skin contact with hazardous materials.

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Description

This quiz explores key concepts in adhesive technology, including the curing temperature for phenol-formaldehyde adhesives and essential processes in adhesive application. Additionally, it covers types of adhesive joints and materials suitable for high-temperature environments. Test your knowledge on how material properties affect adhesive strength and performance.