Machine Design Practice Test: Design Against Fluctuating Load — Flashcards

Design Against Fluctuating Load topics include: Stress concentration, fluctuating stresses, fatigue failures and its factors.

Design against fluctuating load is a method used to design machine components that are subjected to fluctuating loading. 

Here are some criteria used to separate safe and fail designs:
Gerber method: Used for ductile materials based on ultimate strength
Goodman method: Used for ductile or brittle materials based on ultimate strength
Soderberg method: Used for yield strength and ductile materials 

Here are some other criteria:
Mean stress: σ m = σ max + σ min 2
Stress amplitude: σ a = σ max − σ min 2
Stress range: σ r = σ max − σ min 

Fluctuating fatigue stresses are stresses that vary from a minimum value to a maximum value of the same nature. For example, tensile or compressive. 
Some parts of a machine are more likely to break due to fluctuating stresses. These include: Shafts, Bolts, Gears. 
 

Related Test: Machine Design Practice Test: Design Against Static Load