Industrial Materials Testing

Question 1

What is destructive testing?

Answer 1

A range of tests that end in the destruction of the test piece.

Question 2

What is the difference between hardness testing and impact testing?

Answer 2

Hardness testing will have small indentations after testing, while impact testing equipment will cause the test piece to bend or break completely.

Question 3

What is hardness?

Answer 3

The ability of a material to resist abrasive wear, indentation or deformation.

Question 4

What are the 3 basic methods of hardness testing?

Answer 4

• Brinell Test
• Vickers Test
• Rockwell Test

Question 5

What is the Brinell Test?

Answer 5

A hardened steel ball is forced into the material’s surface by means of a suitable load. The resulting surface area of the indent is measured, and used to calculate the hardness number.

Question 6

What is the Vickers test?

Answer 6

This uses a diamond pyramid to indent the material. This is measured using a microscope to give the hardness value.

Question 7

What is the Rockwell test?

Answer 7

• This is more appropriate for the quality control testing of finished products.
• It is a rapid test.
• The hardness value is indicated on an attached dial, thus avoiding the need to measure a very small indentation.

Question 8

What is Tensile testing?

Answer 8

A test that involves putting material under tension by stretching to provide information regarding tensile strength, elasticity and plastic properties, such as ductility and malleability.

Question 9

How does tensile testing work?

Answer 9

• A standard test piece is held between two grips.
• One grip is fixed, while the other is attached to a vertical slide operated by an electric motor.
• The test piece is then put under tension at a constant rate until (i) it breaks, or (ii) it stretches beyond the limits of the machine.
• After the piece is stretched, the distance travelled by the vertical slide is recorded and plotted against the load being applied, which is sensed by a load transducer fixed to the moving grip.

Question 10

What do impact tests indicate?

Answer 10

The toughness of a material and, in particular, its resistance to mechanical shock.

Question 11

What are the 3 main methods of impact testing?

Answer 11

• The Izod test
• The Charpy test
• The Houndsfield test

Question 12

How can wear resistance be determined?

Answer 12

• Weighing a disc of material
• Rubbing an abrasive disc against the material a given number of times, at a given pressure.
• Re-weighing to give a quantitive value of abrasive wear.

Question 13

Give an example of when wear resistance needs to be determined.

Answer 13

• Brake discs

- Pottery industry - resistance of glaze applied to crockery.

Question 14

Give an example of fatigue testing on a product.

Answer 14

• The wire used in tyres is tested by gripping a sample between two chucks. One chuck is stationary while the other can rotate, being driven by a motor/gearbox, until the sample breaks.
• Chairs. A weight (or force) is applied repeatedly to the product.

Question 15

What is non-destructive testing?

Answer 15

Methods of testing that do not damage or destroy the material or product.

Question 16

What are the 3 methods of detecting a surface crack?

Answer 16

• Sound and touch
• Ringing
• Liquid penetrant

Question 17

What is liquid penetrant?

Answer 17

• The penetrant liquid is sprayed onto the surface of the product.
• Any excess is removed leaving only the penetrant in the cracks.
• To help make the cracks clearer, a light dusting of chalk is applied.
• The coloured dye marks the position of the crack in the white chalk.

Question 18

What is magnetic testing?

Answer 18

• The components is magnetised by making it part of an electromagnetic circuit.
• Iron particles are dusted over the area, which then highlight where the magnetic lines of force are broken by a defect.
• This method is particularly useful for finding defects such as cracks and hollows just below the surface, in casting, for example.

Question 19

What is acid pickling?

Answer 19

• Steel castings, for example, can be ‘pickled’ in a weak solution of sulphuric acid, heated to 50°C, for a number of hours.
• This will remove any oxides from the surface of the material, and when washed will make surface cracks clearer.

Question 20

What are the 4 methods of internal defect detection?

Answer 20

• Light
• X-ray methods
• γ-ray methods (gamma rays)
• Ultrasonic

Question 21

How does light detect internal defects?

Answer 21

Light is utilised in the pottery industry to ‘see’ through some of the finer ceramics, such as bone china, to indicate faults within the body of the material.

Question 22

How do x-rays detect internal defects?

Answer 22

An x-ray tube emits radiation through the product and forms an image on a photographic plate, or through an image intensifier and camera, to a monitor.

Question 23

Give an example of where x-rays are used to detect internal defects.

Answer 23

In the tyre industry x-rays are used to check for air bubbles between layers of rubbers, fabric and supporting wires.

Question 24

When are γ-rays used to detect internal defects?

Answer 24

They are used to detect ‘air’ pockets in the casting of materials such as cast iron and steel, because the rays are ‘harder’, thicker and denser.

Question 25

What is ultrasonic testing?

Answer 25

- Very high frequency sound vibrations can be used to locate internal defects precisely.

Question 26

How does ultrasonic testing work?

Answer 26

A probe is passed over the component transmitting the high frequencies. Under normal conditions, the vibrations will pass through the material and will be reflected back from the bottom surface of the material. The probe receives this and an amplifier converts the vibrations into a series of blips on a monitor.