Material Testing and Properties

Question 1

What does tensile testing avoid in order to perform an accurate test?

Answer 1

Avoids high or non uniform stress being generated.

Question 2

What variables are measured during a tensile test?

Answer 2

Force and extension of test piece.

Question 3

What is the formula and units for engineering stress?

Answer 3

Stress = Force/ Cross sectional area

Pascals

Question 4

What is the formula for engineering strain?

Answer 4

Strain = Change in length/ Original length

Question 5

What is the formula for young’s modulus? And what are the units?

Answer 5

Youngs modulus, E = Stress/ Strain

Pascals.

Question 6

What affect does temperature have on youngs modulus?

Answer 6

Higher temp means lower youngs modulus.

Question 7

What is the formula for poisson’s ratio?

Answer 7

Poissons ratio = Lateral strain/ longitudinal strain

Question 8

Why is it difficult to tensile test ceramics?

Answer 8

They are very brittle.

Question 9

What is the definition of hardness and what is it related to?

Answer 9

Ability to resist scratching/ surface indentation.

Related to a metals tensile and yield strength.

Question 10

What type of hardness test leaves a circular indentation?

Answer 10

Brinell Test

Question 11

What are the four hardness tests?

Answer 11

Brinell, Vickers, Knoop and rockwell.

Question 12

What is the formula for brinell hardness?

Answer 12

Brinell hardness = applied load (kg) / surface area of impression

Question 13

What is the definition of toughness?

Answer 13

The ability of a material to absorb energy.

Question 14

High toughness generally means a material has high _____ and _____ ?

Answer 14

strength and ductility.

Question 15

Low toughness usually means a material is ______ ?

Answer 15

Brittle.

Question 16

What are 2 methods of testing toughness?

Answer 16

Izod and charpy impact tests.

Question 17

Briefly describe the impact toughness test.

Answer 17

A pendulum swings and breaks a test sample. The height the pendulum reaches after it breaks the sample is measured.

Question 18

Relationship between temp and E value?

Answer 18

high temp = low E value

Question 19

Relationship between temp and yield/tensile strength?

Answer 19

high temp = reduced strength

Question 20

Relationship between temp and hardness?

Answer 20

high temp = low hardness

Question 21

Relationship between temp and ductility?

Answer 21

higher temp = higher ductility.

Question 22

If a material is brittle will it fracture suddenly or slowly?

Answer 22

Suddenly.

Question 23

If a fracture occurs within a ductile material, will the crack be sharp or blunt?

Answer 23

Blunt.

Question 24

What manufacturing defects can cause fracture?

Answer 24

Porous casting, surface scratches.

Question 25

What crystal defects can cause fracture?

Answer 25

Vacancies and dislocations.