Knowledge of Testing Materials Flashcards
Define stress?
Stress may be defined as the force acting on a material that causes it to change its dimensions.
Define Strain?
Strain is defined as the fractional change in a dimension of a material caused by a force, or stress, acting upon it.
What types of destructive testing are there?
Impact,
Fatigue,
0.1% Proof Stress,
Brinell Hardness Test
Explain Impact testing?
Used to indicate the toughness of a material, and particularly its capacity for resisting mechanical shock.
Explain Fatigue Testing?
A fluctuating or an alternating force may have on a member. A fatigue-testing machine where alternations of stress can be produced in a test piece very rapidly, and so reduce to a reasonable period the time required for a fatigue test.
List the non destructive testing methods?
Visual,
Optical aids,
Ultrasonic,
Magnetic particle testing,
Dye-Penetrant inspection,
Radiography,
What are the typical analysis of a weld when using Radiography?
- Lack of root penetration
– Deep gas cavities
– Longitudinal Crack
What is Brinelling?
Surface fatigue of steel components that undergo cyclic stress resulting in work-hardening of the surface. This may cause surface cracking.
Explain false brinelling and how to avoid?
When a non-rotating bearing is subjected to external vibration, a protective film cannot be formed allowing metal to metal contact, therefore causing wear.
Typical example is on pumps and motor in a primary and backup manner.
To avoid this we can turn the shafts to a new position or share the load between the primary and back up.
Explain Fracturing?
Fracture can be described as a single body
being separated into pieces by an imposed stress
What are the two types of Fractures and state the difference between?
Ductile materials demonstrate large amounts of plastic deformation.
Brittle materials show little or no plastic deformation before fracture.
