Composites

Question 1

Compsites - definition/structure

Answer 1

• Plastics + fibers
• Definition: Reinforcing fillers (fibers) are integrated within a polymer matrix (plastics)
• Must have strong bonding between fillers and matrix to prevent debonding during loading

Question 2

Composites - types

Answer 2

• CFRP = carbon fiber reinforced plastics
• GFRP = glass fiber reinforced plastics
• Bio-composites = biobased matrixes and fibers

Question 3

Composites - properties

Answer 3

Non-biobased:
+Strong and stiff
+Light weight
-Expensive
-Brittle material sensitive to impact load

Bio-composites:
+Renewable sources
+Relatively cheap
-High moisture uptake
-Usually relatively low strength

Question 4

Carbon fiber - structure and types

Answer 4

• 7-8 micrometer thick
• Contracts when temp. increases
• IM, HM, UHM = Intermediate, high, ultra high modulus
• HS = high strength but very brittle
• HT = high tenacity

Question 5

Carbon fiber - properties

Answer 5

+High stiffness and strength
+Good fatigue properties

-Low failure strain (brittle)
-Expensive

Question 6

Carbon fiber - manufacturing and usage

Answer 6

• PAN process - most common: fiber is stretched and everything except carbon is burned away
• Pitch process: Fribers goes through a lot of heat treatments - high energy consumption

Usage:

• Orthoses
• Aircraft and space components
• Instruments

Question 7

Glass fiber - types

Answer 7

• Glass fibers are classified accoring to TEX number = weight (g) for 1000 m of material, high TEX means many fibers in the same bundle
• E-fibers = electrical grade: most common
• S-fibers = high stregnth garde: expensive

Question 8

Glass fibers - properties

Answer 8

+High strength
+Low price

-Low stiffness
-Sensitive to moisture and notches

Question 9

Glass fibers - manufacturing and usage

Answer 9

1. Sand gets melted into glass
2. Cure and stretch it

Usage:

• Pressure vessels
• Pipes
• Bridges

Question 10

Natural fibers - properties and types

Answer 10

+Low density and price
+Renewable source

-Low failure strain (brittle)
-High moisture uptake

• Flax, hemp, jute, wood, bamboo

Question 11

Fiber reinforcements - fiber organisation

Answer 11

• The orginisation of the fiber threads affects properties as well
• Short threads: random or oriented (not so common)
• Continous threads: random (lika cooked spaghetti) or oriented (parallel, like hard spaghetti)
• We can optimize properties based on direction of the thread and known loading

Question 12

Fibers - directions

Answer 12

• Unidirectional (UD) = alternating layers of continous threads along x-axis and y-axis ex. wings on planes
• Weave

Question 13

Fibers - weave forms

Answer 13

• Plain - not so strong
• Twill - good for draping
• Basket
• Eight-harness satin

Question 14

Polymer matrixes - types

Answer 14

• Epoxy
• Vinylester
• Polyurethane
• Unsaturated polyester (UP)

Question 15

Unsaturated Polyester - properties

Answer 15

• A thermoset

+Good mechanical properties
+Cheap

-Low temp. resistance
-Large shrinkage at cure

Question 16

Epoxy

Answer 16

• A thermoset
• Careful while working with it!
  -> Use gloves
  -> Developed allergy will stay for rest of life
• Used in AFOs

+Good mechanical properties
+Good thermal and chemical resistance

-Poor UV-resistance
-Expensive

Question 17

Polyurethane (PU) - properties

Answer 17

• A thermoset

+Good chemical resistance
+High impact tolerance

-Absorbs moistures (and becomes foam)
-Raw material can be dangerous (cancer)

Question 18

PEEK - General and usage

Answer 18

• Thermoplast (poly ether ether ketone)
• Used for implants

Question 19

Properties of composite orthoses

Answer 19

+High stiffness and strength
+Low weight
+Easy to costumize
+More “normal” gait

-Expensive
-Brittle
-Long manufacturing time
-Complicated design

Question 20

Vinylester

Answer 20

+Good mechanical
+Good chemical resistance

-More expensive than UP