Ceramics And Polymers

Question 1

Why don’t we use a a tensile test for ceramics (3)

Answer 1

They’re brittle
Difficult to prepare required geometry
Difficult to grip without fracturing

Question 2

Ceramics show no…. before fracture

Answer 2

Plastic deformation

Question 3

Fractography for impact/point loading

Answer 3

Crack lines 180 degrees around origin X

Question 4

Fractography for bending

Answer 4

180 degree across origin then splits in 2 with 45 degree between
V
I

Question 5

Fractography for torsion

Answer 5

180 degree across origin then splits in 2 with 15 degree between

Question 6

Fractography for internal pressure

Answer 6

180 degree then splits then splits 90 degree between

Question 7

Characteristic fracture behaviour of glass (4regions)

Answer 7

Origin
Smooth mirror region
Mist
Hackle

Question 8

How do ceramics fail in tension

Answer 8

Worst flaw propagates to failure

Crack normal to force

Question 9

How do ceramics fail in compression

Answer 9

Crack extend in a stable manner

Failure when crush band collapses

Question 10

How to measure tensile strength in ceramics

Answer 10

3 point bend test
Top in compression
Bottom in tension

Question 11

How much stronger are ceramics in compression than tension

Answer 11

X10

Question 12

Porosity….. fracture strength and elastic modulus of ceramics

Answer 12

Decreases

Question 13

At what strain does the stress strain curve of a polymer become non-linear (yield)

Answer 13

1%

Question 14

The behaviour of polymers beyond the yield point depends on the temp relative to

Answer 14

The glass transition temperature

Question 15

Drawing…. and increases…..

Answer 15

Aligns polymer chains

Increases strength and stiffness

Question 16

Affects of temperature increase on polymers (4)

Answer 16

Strength decreases
Elastic modulus decreases
Reduces tensile strength
Increases ductility

Question 17

Why are polymers more sensitive to changes in temperature

Answer 17

Room temperature is closer to their melting point

Question 18

Strain rate=

Answer 18

How fast you deform the material

Question 19

…. strain rate has the same effect as increasing temperature on the ……

Answer 19

Decreasing

Strength and ductility

Question 20

4 ways to strengthen polymers

Answer 20

Bending
Drawing
Cross-linking
Reinforcing with particles, fibres, fabrics