Material Testing

Question 1

Requirements for comparable testing

Answer 1

Use the same size of material for each test

Ensure environmental conditions are the same

Use the same equipment and technique

Use one person to take all the test measurements

Question 2

Simple workshop test for tensile strength

Answer 2

Clamp the material in place at the top

Apply a load at the bottom

Record the extension

Less extension = better tensile strength

Question 3

Simple workshop test for hardness

Answer 3

Drop a centre punch through a tube onto the sample

Same height and person doing it each time

Record the diameter of the indentation using vernier callipers

Smaller indent = harder

Question 4

Simple workshop test for malleability and ductility

Answer 4

Bend the test piece to 90 degrees

Cracks on the outside indicate a lack of ductility

Cracks on the inside indicate a lack of malleability

Question 5

Simple workshop test for corrosion

Answer 5

Place equally sized samples outside in an exposed area and leave for a set duration

Materials can then be visually inspected for surface corrosion

Question 6

Electrical conductivity - simple workshop test and industrial test

Answer 6

Mark a set distance on each sample to place the multimeter probes

Measure and record the resistance for each sample

The higher the resistance, the lower the conductivity

This workshop test is also used in industry

Question 7

Simple workshop test - thermal conductivity

Answer 7

With equally sized samples place a Bunsen burner at one end and a thermometer at the other

Record the rate of change of temperature

Higher rate of change = higher thermal conductivity

Question 8

Industrial test for tensile strength

Answer 8

Standard test piece is clamped into place in tensometer machine

One clamp is fixed while the other is connected to a worm drive gear mechanism - putting the material under tension

Test piece is stretched - load and extension are plotted

This gives information on elastic limit, yield point, maximum load and final breaking point after ‘necking’

Question 9

Industrial test for toughness

Answer 9

Izod impact test

A notched piece is held vertically in the machines vice

A pendulum is released from a set position to strike the test piece

Energy absorbed is calculated from the height the pendulum swings after it hits the test piece

Toughest = most impact, gives the least pendulum swing

Brittle = absorbs less energy and the pendulum swings further

Question 10

Rockwell test

Answer 10

Hardness test using a diamond indenter - as diamond won’t deform under load

Preload is applied to just break through the surface - this is the datum

Additional load is then applied and held for a set period (dwell time)

Load is released and the distance between the preload and applied load is measured

Question 11

Brinell test

Answer 11

Industrial hardness test

A hardened steel ball is forced into the material’s surface using a pre-set load

The diameter of the surface indent is measured

Question 12

Vickers pyramid test

Answer 12

This industrial hardness test is used for very hard materials

Uses a diamond square based pyramid to indent the surface of the material

A microscope is used to measure the size of the indent

Question 13

Non-destructive testing

Answer 13

Carried out on products rather than samples

The product isn’t destroyed during testing

Used to find faults and defects in the product

Two main methods:

1 - ultrasonic (sound waves are pulsed into the material, different sounds indicate faults)

2 - X - Rays ( X - Rays are passed through the the material and an image is project into a display screen. Allowing observation of tiny details such as hairline cracks)

Question 14

Industrial malleability and ductility testing

Answer 14

Bend test - tests how well a material withstands cracking during one continuous bend

Sample is placed into the bedding machine supported at each end

A mandrel or plunger loads the test piece at the centre until it reaches a predetermined angle

Cracks on the outer bend indicate the level of ductility

A ductile material will have lots of plastic deformation prior to failure

Cracks on the inside bend indicate the level of malleability

Question 15

Industrial corrosion testing

Answer 15

Similar to workshop test except environmental effects are simulated in the lab

Snakes would be placed in a simulated weather environment for a set durations and then inspected for surface corrosion

Question 16

Industrial thermal conductivity test

Answer 16

Square shaped sample is placed between two temperature controlled plates

Temperature is increased at a controlled rate

Heat flow is measured by sensors on the material’s surface and a heat flow meter - this all results in calculating thermal conductivity

Question 17

Hardness testing

Answer 17

Vickers pyramid test

Rockwell test - diamond indenter

Brinell test - hardened steel ball

Question 18

Types of testing

Answer 18

Hardness testing 
Toughness testing 
Non-destructive testing
Ductility and malleability testing
Thermal conductivity testing 
Corrosion testing 
Tensile strength testing
Electrical conductivity

Question 19

Simple workshop test for toughness

Answer 19

Sample is clamped in a vice

Material is struck by a hammer from the same distance for each sample

Inspect levels of damage to determine the toughness