Service Related Discontinuities (5)

Question 1

Types of Service Discontinuities (3)

Answer 1

• Overstress
• Fatigue Stress
• Corrosion

Question 2

Overstress

Answer 2

When a part is subjected to a stress that exceeds its strength

• part does not meet specs
• stress exceeds rated capacity
• plastic deformation
• fracture

Question 3

Fatigue Stress

Answer 3

Result of repeated applied loads

• small fluctuating stresses that do not exceed over strength
• fail or fracture

Question 4

Define fatigue strength

Answer 4

maximum fluctuating stress that a material can sustain for a specified number of cycles

Question 5

Define fatigue life

Answer 5

number of cycles of specified fluctuating stress that a material can sustain prior to failure

Question 6

___% of failures involving _____ parts are attributed to fatigue.

Answer 6

80% of failures involving stationary parts are attributed to fatigue.

Question 7

Thermal Failure

Answer 7

Fatigue due to the presence of temperature fluctuations over time resulting in failure
- creep - combo of cyclic stress and high temperatures

Question 8

Define “creep”

Answer 8

the tendency of a solid material to move slowly or deform under the influence of mechanical stress.

Question 9

Corrosion Fatigue Cracking

Answer 9

Combination of corrosion and fatigue

• must be detected asap - leads to rapid failure
• corrosion pits

Question 10

Stress Corrosion Cracking

Answer 10

When a metal is subjected to constant tensile stresses in a corrosive environment
- localized corrosion

Question 11

Erosion Corrosion

Answer 11

Degradation of a material by the action of abrasion

- fretting corrosion and cavitation corrosion

Question 12

Define fretting corrosion

Answer 12

mechanical/chemical process, result of two components rubbing together causing small particles on the surfaces to bond

Question 13

Define cavitation corrosion

Answer 13

pitting accelerated due to the constant flow of a liquid