CFS Failure Analysis & Prevention 2

Question 1

Which failure mode occurs when a fastener breaks perpendicular to its axis due to repeated cyclic loading?

Accepted Answer

Transverse fatigue fracture

Answer

Transverse fatigue fractures are perpendicular to the fastener axis and result from cyclic tensile loading exceeding the endurance limit.

Question 2

A fastener in a marine environment fails with a brittle, branching crack pattern. What is the most likely failure mechanism?

Accepted Answer

Stress corrosion cracking

Answer

Stress corrosion cracking (SCC) produces branching, intergranular cracks in susceptible alloys exposed to aggressive environments like seawater.

Question 3

What does the presence of 'beach marks' (arrest lines) on a fracture surface indicate?

Accepted Answer

Fatigue crack propagation

Answer

Beach marks are macroscopic concentric lines on a fracture surface that indicate incremental fatigue crack growth during cyclic loading.

Question 4

A grade 8 bolt fails shortly after installation with no apparent overload. It shows a brittle, intergranular fracture with no plastic deformation. What is the most probable cause?

Accepted Answer

Hydrogen embrittlement from plating

Answer

Hydrogen embrittlement from electroplating (if not properly baked) is a classic cause of delayed brittle fracture in high-strength bolts shortly after installation.

Question 5

Which of the following is the best method to prevent self-loosening in fastener joints subjected to transverse vibration?

Accepted Answer

Increasing clamp load above the vibration loosening threshold

Answer

Junker testing shows that maintaining sufficient clamp load prevents the micro-slip between mating threads that causes self-loosening under transverse vibration.

(CFS) Certified Fastener Specialist Practice Test

(CFS) Certified Fastener Specialist Practice Test

CFS Failure Analysis & Prevention 2