FAA Aviation Mechanic Airframe (AMA)Airframe StructuresHard
A technician is calculating the bearing stress on a rivet-to-sheet joint where a 900-pound load is applied. The rivet diameter is 0.1875 inch and the sheet thickness is 0.032 inch. What is the bearing stress at the joint?
- A468,750 psi
- B150,000 psi
- C15,000 psi
- D28,125 psi
Show answer & explanationAnswer & explanation
Correct answer: B. 150,000 psi
Bearing stress is calculated as load divided by the bearing area, where bearing area equals rivet diameter multiplied by sheet thickness: Bearing Area = 0.1875 x 0.032 = 0.006 sq in. Bearing Stress = 900 lb / 0.006 sq in = 150,000 psi.
Why the other options are wrong
- A. This value results from an inverted or miscalculated area.
- C. This value results from dividing by an incorrect area calculation.
- D. This does not match load divided by the correct bearing area.
Bearing Stress
The compressive stress at the contact surface between a fastener and the material it passes through, calculated as load divided by fastener diameter times material thickness.
- Formula: Bearing Stress = Load / (Diameter x Thickness)
- Excess bearing stress can elongate rivet holes or crack sheet edges
- Different from shear stress, which acts across the fastener cross-section
Memory trick: 'Bearing = Load over the Footprint' — diameter times thickness is the contact patch.