Composites (it is a deck about composites) (composites) Flashcards
name the two types of composites and compare them
Particulates and fiber reinforced. The only difference is the shape of the reinforcment. Particulate examples are concrete of asphalt (the aggregates are ‘particles’ that reinforce the cement paste, whereas wood cells has fibers that reinforce the lignin (which acts as a matrix).
name and describe the main parts of a composite.
matrix: The bulk material surrounding the fibers, they maintain the shape of the composite, transfer the tensile stress to the fibers and support the compression.
fibers: The hard material that reinforces the composite. They provide strength, imporove toughness and increase stiffness (bending resistance)
Interface: Contact between the matrix and the fibers. It enables stress transfer. If the two materials consist of different phases, it is called interphase.
Additives: they just be adding to the composite lol (added in search of a specific effect)
Name the most common additives and describe their effects
Plasticizers: decrease glass transition temperature
Lubricant: improves mixing and lowers friction
stabilizer: improves heat resistance, UV light and oxidation
Fire Retardant: inhibits burning (toxic)
Filler: improves mechanical properties and reduces cost.
what are the chacteristics of good fibers
-good aspect ratio (surface area to volume ratio)
-small diameter (^tensile strength, due to size effect)
-High flexibility (workability, it enables many techniques such as weaving and filament winding)
what are advantages and disadvantages of using fiber reinforced polymers
Advantages: low density, high specific strength and stiffness, can be shaped however, low heat conductance
Disadvantages: Brittle at low temps, properties degradation at high temperatures, moisture sensitive.
name some fabrication techniques for FRPs
Pulltrusion, injection molding, hand lay up, spray up, filament winding
how can the fact that FRPs are composed of multiple fibers be advantageous?
They have good impact resistance since there are multiple fibers to take the hit. If fiber breaks due to the energy intake, the whole composite won’t suffer too much from it.
explain the pultrusion process for FRPs, and its advantages and disadvantages for construction use.
Multiple fibers are pulled through a heated die amd simutaneously getting coated by resin. The heat from the die cures the resin and the composite takes its final shape.
Advantages:
-high strength to weight ratio
- not likely to corrode (materials used already have good resistance
-Design flexibility: pultrusion allows the cration of complex shapes and profiles.
Disadvantages:
- Pultrusion has limited thickness, or to make thicker products it requires more processing
- High initial cost
- brittle behavior in cold temperatures.
In what situations is the spray up technique pertinent. How does it work and what are its shortcomings?
It is good for quick and cost effective production of large, simple shapes. It is a chopped glass and liquid resin mixture that is sprayed in a mold thanks to a chopper gun. The mixture is then compacted thanks to a roller in order to remove air pockets. It is not the best approach if complex shapes or high strength/stiffness is required.
