61-68 Flashcards
Why is intercrystalline corrosion a safety concern?
● Occurs in alloys with differing electrochemical potential
● Not visible from outside
What is contact corrosion and how can it be prevented?
● Proportional to potential difference (practical galvanic series)
● Electrolyte
● Proportional to area ratio of cathode/anode
● Can be prevented by:
○ Minimizing difference of galvanic potential
○ Surface treatment/plating
○ Hold off electrolyte (Wet assembly)
What is Stress corrosion cracking? How can it be prevented?
● Material+corrosive medium+tensile stress = intercrystalline crack
● Can be prevented by Cd plating instead of zinc plating for high strength steels (no generation of
H+)
What is more critical for corrosion:
● Al rivet in corrosion-resistant steel plate
What is true for bonded joints?
● Load distributed over a large area
● No holes in the basic laminate
● Dissimilar materials can be bonded without corrosion problems
● Surface preparation is critical
● Aerodynamically better than riveted joints
● With poor design, the joint can fail suddenly
Benefit of the membrane in VAP process:
● The membrane is permeable to gas, but impermeable to resin.
● Placed between component and vacuum bag
● Membrane separates resin from vacuum duct. With the aid of low pressure, trapped air and gas can escape
● Vacuum acts uniformly, so trapped air and gas can be evacuated across the entire contact surface.
What is the meaning of the safety requirement category, I, II, III in aerospace welding acc. DIN29595
● SRC I: failure of part catastrophic SRC II + 100% inspection of internal characteristics (X-Ray,
ultrasonic…)
● SRC II: failure lead to malfunction, but flight can be safely ended SRC III + 100% crack
inspection (magnetic particle)
● SRC III: failure does not affect safety and flight 100% visual inspection
A critical part of an airplane which failure would be catastrophic must be welded:
● With QA acc. safety requirement category I
