Chapter 4

Question 1

Why do we need to test materials?

Answer 1

So the designer knows if the material is suitable for its intended purpose. Whether the material has sufficient strength, toughness, durability etc

Question 2

What is destructive testing?

Answer 2

Destructive testing is a range of tests that ultimately results in destruction of a standard test piece.

Question 3

What are the three types of hardness test ?

Answer 3

Brinell, Vickers, Rockwell

Question 4

What is the Brinell test?

Answer 4

It’s a hardness test, where a hardened steel ball is forced into the materials surface by means of a suitable load. This dents the surface and is measured to calculate a hardness number.

Question 5

What is the Vickers test?

Answer 5

It’s a hardness test which uses a diamond pyramid to indent the material. This indent is then measured using a microscope to give a hardness value.

Question 6

What is the Rockwell test?

Answer 6

It’s a hardness test which is more appropriate for quality control testing of finished product. It’s a fast test where a indentation is made and the hardness value is indicated on the attached.

Question 7

What does tensile testing involve?

Answer 7

It involves putting a material under tension by stretching to provide information regarding tensile strength, elasticity and plastic properties.

Question 8

How is a material tensile tested?

Answer 8

The test piece is held between two grips, one of the grips is fixed and the other moves on a scale. The one grip is then moved using an electric motor causing the material is stretch. The test piece is continuously put under increasing tension until it either snaps or reaches the limits of the machine. The distance travelled by the slider is recorded and plotted against the load producing a stress strain graph.

Question 9

In what industry would you see tensile testing?

Answer 9

It is a standard test in the rubber, steel and fabric industry

Question 10

What does an impact test show ?

Answer 10

An impact test indicates the toughness of the material, and in particular it’s resistance to mechanical shock.

Question 11

What are the three main methods of impact testing?

Answer 11

The Izod test
The Charpy test
The Houndsfield test

Question 12

How can a material be tested for wear?

Answer 12

The material is weighed
An abrasive disc is rubbed against the material, the material is rubbed a set number of times at a given pressure.
The material is reweighed

Question 13

What is fatigue testing?

Answer 13

Where a certain part of product or a material is tested until it breaks

Question 14

How are materials/products fatigue tested?

Answer 14

The sample is tested my gripping a sample between two chucks. One chuck is stationary and the other is twisted by rotating the chuck a certain number of times, and the direction is changed until the sample breaks.

Question 15

How are chair fatigue tested?

Answer 15

A chair is tested by applying a force on the seating area of the chair over and over again. This tests the resistance of the material.

Question 16

What is non-destructive testing?

Answer 16

A method of testing where the product is not destroyed or damaged.

Question 17

What is surface-crack detection? Ringing and liquid penetrant?

Answer 17

These are basic qualities of control technique. A bell will not ring if it is cracked, ringing is used for both casting and pottery, the product is rang and will not ring if cracked or broken. Liquid penetrant, is where a liquid is sprayed onto the surface, the excess is removed leaving only the liquid in the cracks. To make the cracks clearer chalk is dusted over the product.

Question 18

What is magnetic testing?

Answer 18

Magnetic Testing is where the component is magnetised, iron particles ard dusted over the area, the particles will highlight any areas where the magnetic force is broken by a defect such as cracks and hollows just below the surface.

Question 19

What is acid pickling?

Answer 19

The surface is cleaned, by dipping the product in a sulphuric acid. This will remove any oxides from the surface of the material. The material is then washed and surface cracks are made clearer.

Question 20

Where is defect detection used?

Answer 20

Used for scanning, finer ceramics and bone china, to detect faults within the body of the material.

Question 21

How are X-rays used in defect detection? And what products are they used to test?

Answer 21

X-rays are used to detect defeats under the surface, used in testing tyres, to check for air bubbles between the layers of rubber and fabric and supporting wires. 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 22

Where are gamma rays used?

Answer 22

They are used in defect detection, gamma rays are able to pass thicker and denser materials such as cast irons and steel can be tested to detect air pockets.

Question 23

What is ultrasonic testing and how does it work?

Answer 23

Ultrasonic testing is used to test defects within products. Ultrasonic testing passes very high-frequency sound vibrations from a probe into the product, these then bounce back and are detected by the probe. If a vibration comes back quicker than expected there is a defect in the material, and a computer is able to form an image.

Question 24

On what products is ultrasonic testing used on?

Answer 24

It’s used on sheet, plate and strip materials up to 6mm thick, used for tyres, aircraft and pipeline inspection.