[1.3] Methhods for investigating and testing materials

Question 1

Outline a simple workshop test for toughness

Answer 1

• Place a test piece in a vice and hit it with a hammer

- Tough materials absorb impact, brittle materials bend or shatter.

Question 2

Outline a simple workshop test for hardness

Answer 2

• Use a hammer and dot punch

- The smaller the indent, the harder the material

Question 3

Outline a simple workshop test for malleability and ductility

Answer 3

• Place the material in a vice and bend to a 90 degree angle

- Cracks on the outside indicate a lack of ductility whilst cracks on the inside indicate a lack of malleability

Question 4

Outline a simple workshop test for corrosion

Answer 4

• Place equally sized material samples outside in an area exposed to the effects of weather and leave for a set length of time.
• Materials can then be visually inspected for corrosion

Question 5

Outline a simple workshop test for electrical conductivity

Answer 5

• Collect material samples of the same dimensions and mark a set distance to place the multimeter probes. Measure the resistance on the multimeter.
• The higher the resistance, the lower the conductivity

Question 6

Outline a simple workshop test for thermal conductivity

Answer 6

• Collect material samples of the same dimensions and measure a set distance from one end of the material and place a thermometer there. Light a bunsen burner under the other end of the material, record the time it takes for the temperature to reach the set point at the otehr end of the material sample.
• The shorter the time it takes, the higher the thermal conductivity of the material

Question 7

Outline an industrial test for tensile strength

Answer 7

• A tensometer machine tests for tensile strength
• The standard test piece is held in a clamp at each end, one clamp is fixed and the other moves on a worm drive gear mechanism, putting the material under tension.
• The test piece is stretch, the load and distance travelled is plotted, giving information on elastic limit, yield point, maximum load and final breaking point after ‘necking’

Question 8

Outline an industrial test for toughness

Answer 8

• The Izod impact test is used to test the toughness of a material
• A notched test piece is held vertically in the vice of the machine, a pendulum is released from a set position and swings to strike the piece.
• The energy absorbed by the test poiece is calculated from the height the pendulum swings to after it hits the test piece. The material that absorbs the most impact is the toughest and gives the least pendulum swing.

Question 9

Outline an industrial test for malleability and ductility

Answer 9

• Malleability and ductility can be tested using a bend test
• The test piece is placed into a bending machine and held, supported at the ends. A mandrel or plunger loads the test piece at the centre and bends it to a predetermined angle or until the test piece fractures. The material is then inspected.
• Cracks on the outer bend indicate the level of ductility. A ductile material will have a lot of plastic deformation prior to failure. Cracks on the inside of the bend indicate the level of malleability

Question 10

Outline an industrial test for corrosion

Answer 10

• Corrosion testing is similar to that carried out in the workshop except that environmental effects are simulated in a lab.

Question 11

Outline an industrial test for electrical conductivity

Answer 11

• On the top surface of a test piece mark a set distance at each end, place a multimeter probe on each mark, measure the resistance.
• The higher the resistance, the lower the conductivity.

Question 12

Outline an industrial test for thermal conductivity

Answer 12

• A square-shaped material test piece is placed between two temperatures controlled plates. The temperature is increased at a controlled rate and the heat flow through the material is measured by heat flow sensors place on the surface of the material.
• As the material is heated to a specific temperature, the sensors measure and record the rate of thermal conductivity

Question 13

Outline the Rockwell test for hardness

Answer 13

• Preload applied to the material sample using a diamond indenter, which breaks through just the surface of the material.
• An additional load is then applied to the test material and held for a predeterminded length of time.
• The load is released the distance between the preload the applied load is measure.

Question 14

Outline the Brinell test for hardness

Answer 14

• A hardened standard size steel ball is forced into the material’s surface using a pre-set load. The diameter of the indent in the surface is measured.