Failure Analysis & Prevention Flashcards
7 cards from real CFS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Failure Analysis & Prevention flashcards as text
A fastener fails in shear along a plane parallel to the joint interface. What loading condition caused this?
Answer: Transverse shear force exceeding fastener shear strength
Shear failure along a plane parallel to the faying surface occurs when the transverse (shear) load acting across the bolt exceeds its double or single shear strength.
What effect does surface rolling (thread rolling after heat treat) have on fastener fatigue life?
Answer: Increases fatigue life by inducing compressive residual stresses
Thread rolling after heat treat induces compressive residual stresses at the thread root, opposing tensile fatigue stresses and significantly increasing fatigue life.
Liquid metal embrittlement (LME) in steel fasteners can occur when:
Answer: Molten cadmium or zinc contacts stressed steel fasteners
Liquid metal embrittlement occurs when a low-melting metal (like cadmium or zinc) in liquid state contacts a stressed steel fastener, causing rapid brittle fracture.
In a cross-section metallographic examination of a failed fastener, decarburization at the surface indicates:
Answer: Loss of carbon during heat treatment, reducing surface hardness and strength
Decarburization is loss of carbon from the fastener surface during heat treatment in oxidizing atmospheres, producing a softer, weaker surface layer prone to early fatigue crack initiation.
Which type of loading is MOST damaging to a fatigue-limited fastener joint?
Answer: Fluctuating tensile load cycling from 0 to 80% of yield
Fluctuating cyclic tensile loads with a large stress range (cycling from zero) are the most damaging to fastener fatigue life because they maximize the alternating stress amplitude.
A fastener in a gasketed joint loses clamp load over time at elevated temperature without any external disturbance. This is most likely caused by:
Answer: Creep relaxation of the gasket material under sustained load
Soft gasket materials creep (flow plastically) under sustained compressive load and elevated temperature, reducing joint thickness and causing progressive loss of bolt preload.
Which of the following best describes the purpose of a torque-tension relationship test (such as K-factor determination)?
Answer: To establish the correlation between applied torque and resulting bolt clamp load for a specific fastener-joint system
K-factor (nut factor) testing quantifies how efficiently applied torque is converted to clamp load for a given combination of fastener, lubrication, and joint material, enabling accurate torque specification.