1.4 Composites Flashcards
What is a composite?
Two or more materials combined by bonding
Has improved mechanical, functional, aesthetic properties
Most have excellent strength to weight ratios
Describe and explain the characteristics of Glass fibre (GPR)
Polyester or epoxy resin reinforced by fine fibres of glass in woven matting
Plastic resins - strong in compressive strength
Glass fibres - strong in tension, no compressive strength.
GRP combines both compressive and tensile strength
Resin starts liquid - solidifies when catalyst/hardener added
Glass fibre strands provide the basic structure - resin with additives bonds fibres create lightweight rigid structure
Describe and explain the usage of Glass fibre (GPR)
Two materials used uniformly or Glass placed strategically in areas with tensile loads
One surface is highly polished - other is extremely rough - due to glass matting
Gel coat applied first for smooth finish
Glass matting laid on top - provide basic structure
Explain the steps of GPR production
- Created from a mould
- Mould checked for defects
- Mould is polished with a wax polish to become smooth
- Thin film of liquid release agent applied to inside of mould - prevent glass fibre product from sticking to mould
4.Gel coat = first layer of resin applied to mould - mixture of polymer resin, hardener, pigment - exothermic reaction occurs - hardener reacts with the resin and heat - causes resin to cure + harden - Layer of glass fibre is laid inside mould + polyester resin mixed with hardener is stippled + rolled into reinforcing layer - again exothermic reaction occurs- bonding with gel layer
- After first GRP layer cured, another layer of fibre reinforcing material is laid in mould + resin stippled + rolled into it. As each layer cures, more layers applied until the required thickness
- When product IS fully cured, removed from mould. Coloured gel coat is now exterior covering of the product
- Blemishes in mould would be reproduced in the finished moulding
Describe and explain the usage of carbon fire
Made of carbon fibres + polymer resin
Carbon fibres take tensile loads.
Polymer resin takes compressive loads
Carbon fibre is woven into fabric
Fabric has strength only in tension
Woven fabric placed in different directions - covers tensile loads in all directions
Describe and explain the usage of carbon fibre
Carbon fibre = much stronger than GRP
Used in:
- Aircraft
- Sports equipment.
- F1 racing car manufacture.
4x tensile strength of best steel alloys
1/4 weight of steel - useful in weight sensitive situations
Much better fatigue life compared to metals.
What material is Medium Density Fibre Board (MDF) made from and how is it created?
Made from wood waste or specifically grown softwoods in form of wood chips
- Wood chips heated and applied pressure to soften fibres and produce a fine, fluffy, lightweight pulp
- Pulp mixed with synthetic resin adhesive to bond fibres
- Heat pressed to form fine-textured surface
- Cooled, trimmed, sanded after pressing
- Can be laminated for extra strength
Describe and explain the characteristics of MDF and safety concerns using it
can be worked like wood
No grain - provides consistency in workability
Finishes well - various surface treatments
Available with veneered surface for decorative effects
Hazards:
Fumes from glues and resins in MDF production
Very fine fibers pose risks during cutting, drilling + sanding.
Dust can cause skin irritation, throat + nasal passage irritation.
Use respiratory equipment + appropriate dust extraction
Describe and explain the characteristics of hardboard and where it is used
Type of fibreboard
Engineered wood product
Made from exploded wood fibers
Highly compressed for density, strength + hardness
Used in furniture, construction + temporary floor protector
Declining popularity - new environmental targets in construction industry
Describe and explain the characteristics of chipboard and where it is used
Common composite material
Wood particles glued together under heat and pressure
Comes in normal, medium, and high-density forms
Suitable for internal applications - Work surfaces, flat-pack furniture, internal fire doors
Prone to waterlogging, swelling + breakdown if exposed to moisture
Describe and explain the characteristics of plywood and where it is used
Made from bonded layers of veneers.
Thin sheets obtained from timber using the rotary cut process
Strong and stable due to layers bonded with grain direction at 90° to each other
Uneven number of layers makes it resistant to warping or distortion
Discuss the applications, advantages and disadvantages of GRP
Applications
- Rotor blades of wind turbines
- Canoes
- Fish ponds
- Vehicle bodies,
- Fairground rides
Advantages
- Excellent strength to weight ratio
- Resistant to corrosion and water
- Ideal for external shell structures
- Wide range of colours
- Can be repaired easily
Disadvantages
- Expensive material
- Specialised manufacturing process required
- High-quality mould needed
Discuss the applications, advantages and disadvantages of Carbon Fibre
Applications
- Tennis racquets
- Fishing rods
- Bicycle frames and wheels,
- Aircraft and vehicle components
Advantages
- Excellent strength to weight ratio
- Better tensile strength than steel alloys
- Can be formed into complex and
aerodynamic one-piece structures
Disadvantages
- Very expensive material
- Only available in black
- Highly specialised manufacturing processes required
- Cannot be easily repaired as sctructure loses integrity
- Cannot be easily recycled
Discuss the applications, advantages and disadvantages of MDF
Applications
- Flat-pack furniture,
- General joinery work
- Moulds for forming processes
Advantages
- Less expensive than natural timbers
- Available in large sheet sizes and range of thicknesses
- No grain, so no tendency to split
- Consistent strength in all directions
Disadvantages
- Heavier (the resins are heavy)
- Requires appropriate finishes to seal surface fibres
- Swells and breaks when waterlogged
- Warps or expands if not sealed
- Contains urea-formaldehyde – eye and lung irritant
Discuss the applications, advantages and disadvantages of Hardboard
Applications
- Furniture components,
- Wall panelling
- Moulded door skins
Advantages
Hardboards are available for specific purposes- they have either embossed, perforated, plastic-faced or veneer surfaces
Disadvantages
Cannot be used outside because it absorbs
water
