Chapter 4 Flashcards
Why do we need to test materials?
So the designer knows if the material is suitable for its intended purpose. Whether the material has sufficient strength, toughness, durability etc
What is destructive testing?
Destructive testing is a range of tests that ultimately results in destruction of a standard test piece.
What are the three types of hardness test ?
Brinell, Vickers, Rockwell
What is the Brinell test?
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.
What is the Vickers test?
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.
What is the Rockwell test?
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.
What does tensile testing involve?
It involves putting a material under tension by stretching to provide information regarding tensile strength, elasticity and plastic properties.
How is a material tensile tested?
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.
In what industry would you see tensile testing?
It is a standard test in the rubber, steel and fabric industry
What does an impact test show ?
An impact test indicates the toughness of the material, and in particular it’s resistance to mechanical shock.
What are the three main methods of impact testing?
The Izod test
The Charpy test
The Houndsfield test
How can a material be tested for wear?
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
What is fatigue testing?
Where a certain part of product or a material is tested until it breaks
How are materials/products fatigue tested?
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.
How are chair fatigue tested?
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.
What is non-destructive testing?
A method of testing where the product is not destroyed or damaged.
What is surface-crack detection? Ringing and liquid penetrant?
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.
What is magnetic testing?
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.
What is acid pickling?
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.
Where is defect detection used?
Used for scanning, finer ceramics and bone china, to detect faults within the body of the material.
How are X-rays used in defect detection? And what products are they used to test?
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.
Where are gamma rays used?
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.
What is ultrasonic testing and how does it work?
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.
On what products is ultrasonic testing used on?
It’s used on sheet, plate and strip materials up to 6mm thick, used for tyres, aircraft and pipeline inspection.
