3.1.1.3 Methods for investigating and testing materials - Practical workshop tests - Materials and their applications

What is tensile testing?

1. Clamp material samples of the same length and thickness into a vice

2. Apply a load (e.g. weights) to the unclamped end

3. The less deflection under load, the more tensile strength the material has

What is toughness testing?

1. Clamp the material samples into a vice

2. Hit each sample with the same force, using a hammer

3. Tough materials will absorb the impact whereas brittle materials may bend or even shatter

What is hardness testing of abrasive wear?

1. Run a file over the surface of the material, using the same force for each material sample

2. The material with the fewest scratches is the hardest

What is hardness testing of resistance to surface indentation?

1. Place the dot punch onto the material surface when the material sample is fully supported underneath

2. Hit the dot punch once with a hammer, using the same force for each material sample

3. The smaller the indent, the harder the material

What is malleability and ductility testing?

1. Secure the test piece in a vice

2. Bend the test piece to 90°

3. Cracks or surface damage on the outside of the bend indicates a lack of ductility

4. Cracks or surface damage on the inside of the bend indicates a lack of malleability

What is corrosion testing?

1. Place materials outside in an area exposed to weather effects and leave for a certain length of time

2. Visually inspect material for surface corrosion

3. Depending on the intended product function, further material testing such as toughness or hardness could then be carried out

What is electrical conductivity testing?

1. Collect material samples of the same dimensions and, on the top surface, mark a set distance between the two ends of the material sample

2. Place the probes on the distance marks and measure the resistance on the multimeter

3. The higher the resistance, the lower the conductivity

What is thermal conductivity testing?

1. Collect material samples of the same dimensions

2. Measure a set distance from one end of the material on which to place a thermometer

3. Light a Bunsen burner under the end of the material

4. Record the time it takes for the temperature to reach the set point at the other end of the material sample

5. The shorter the time it takes to reach the set temperature, the higher the thermal conductivity of the material

What is tensile testing (industrial test)?

1. Place a standard test piece into a tensometer machine and hold in clamps at each end - one clamp is fixed and the other moves on a worm drive gear mechanism - as the worm drive travels at a constant rate, the test piece is put under tension

2. Plot the load and distance travelled as the test piece is stretched - giving information on elastic limit, yield point, maximum load, and final breaking point after necking

What is toughness testing (industrial test)?

1. Vertically hold a notched test piece in the vice of the test machine

2. Release a pendulum from a set position so that it swings to strike the test piece

3. Calculate the energy absorbed by the test piece from the height the pendulum swings after it hits the test piece

4. The material that absorbs the most impact is the toughest

What is Rockwell hardness testing (industrial test)?

1. Apply a preload to the material sample using a diamond indenter which breaks through just the surface of the material - the preload is the datum or zero reference position

2. Apply an additional load to the test material and hold for a predetermined length of time (dwell time)

3. Release the load and measure the distance between the preload and the applied load, and calculate the hardness of the material

4. The smaller the indentation depth, the harder the material

What is Brinell hardness testing (industrial test)?

1. Force a hardened standard size steel ball into the material’s surface using a pre-set load

2. Measure the diameter of the indent in the surface

3. The smaller the diameter indent, the harder the material

What is Vickers pyramid hardness testing (industrial test)?

1. Indent the surface of the material, using a diamond square-based pyramid - diamond is used because it will not deform under load

2. Measure the size of the indent, using a microscope

3. The smaller the indent, the harder the material

What is ductility and malleability testing (industrial test)?

1. Place the test piece into a bending machine and hold it, supported at the ends

2. Load the test piece at the centre and bend it to a predetermined angle, or until the test piece fractures, using a mandrel or plunger

3. Inspect the material for cracks or defects

4. Cracks on the outer bend indicate the level of ductility

5. Cracks on the inside of the bend indicate the level of malleability

What is non-destructive testing?

• Carried out on products (e.g. large castings) where there is a likelihood of an internal defect/imperfection which would not be detected by other methods

• There are two standard non-destructive testing methods: ultrasonic and x-ray

What is ultrasonic testing?

1. Generate sound waves which are pulsed into the material, using a transducer

2. Record the intensity of the reflected sound waves signal on a display unit

3. The sound waves travel through the material and if there are any defects (e.g. cracks) in the sound waves’ path, the sound energy will be partially reflected and shown on the display unit

What is x-ray testing?

1. Pass an x-ray beam through the material to project an image onto a display screen - x-rays and, in particular, micro-focus x-rays allow the observation of tiny details within the material

2. Reliably detect minute flaws (e.g. voids, hairline cracks), using the magnified images

What is electrical conductivity testing (industrial test)?

1. Stretch four small-diameter wires, parallel to each other across a non-conductive polymer block, hold them in place, and connect them to copper terminal blocks

2. Attach two leads to the inner wires and two to the outer wires

3. Connect the outer leads to a precise current and measure the voltage drop, using the two inner leads

4. Calculate the resistance of the material sample, using Ohm’s law (V=IR)

What is thermal conductivity testing (industrial test)?

1. Place a square-shaped material between two temperature controlled plates, using a heat flow meter

2. Increase the temperature at a controlled rate and measure the heat flow through the material, using heat flow sensors placed on the surface of the material

3. Measure and record the rate of thermal conductivity as the material is heated to a specific temperature, using the sensors