FAA Aviation Mechanic Airframe (AMA)Airframe StructuresHard
A technician's overhaul manual specifies that the machined surface of a highly stressed steel landing gear component be shot peened after final machining, prior to plating. What is the primary purpose of this shot peening process?
- ATo induce beneficial compressive residual stress in the surface layer, improving fatigue life
- BTo remove mill scale and oxide contamination before plating
- CTo increase surface hardness for improved wear resistance
- DTo reduce surface roughness for improved aerodynamic smoothness
Show answer & explanationAnswer & explanation
Correct answer: A. To induce beneficial compressive residual stress in the surface layer, improving fatigue life
Shot peening bombards the part's surface with small spherical media, plastically deforming the surface layer and inducing compressive residual stresses. These compressive stresses oppose the tensile stresses that drive fatigue crack initiation and propagation, significantly improving fatigue life of highly stressed components like landing gear parts.
Why the other options are wrong
- B. Removing scale is done through cleaning/etching, not the purpose of peening.
- C. Shot peening's primary metallurgical benefit is residual stress, not hardness increase.
- D. Peening actually creates a dimpled surface texture, not aerodynamic smoothness.
Shot Peening
A cold-working process in which a part's surface is bombarded with small round media to induce compressive residual stress and improve fatigue resistance.
- Commonly used on landing gear, springs, and other highly stressed steel parts
- Compressive stresses resist crack initiation from cyclic (fatigue) loading
- Performed after final machining, often before plating
Memory trick: Shot peening pounds in a protective compression shield