FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesMedium
A technician forms a 90-degree bend in a piece of 0.040-inch 2024-T3 aluminum sheet using a bend radius smaller than the specified minimum bend radius for that thickness and alloy. What is the most likely result?
- AReduced bend allowance requiring recalculation of the flat pattern
- BWrinkling on the inside surface of the bend only
- CCracking or fracture on the outer surface of the bend
- DNo adverse effect since a tighter radius saves material
Show answer & explanationAnswer & explanation
Correct answer: C. Cracking or fracture on the outer surface of the bend
Minimum bend radius specifications exist because bending sheet metal tighter than the material can withstand overstresses and stretches the outer fibers of the bend beyond their elastic/plastic limit, causing cracking or fracture at the bend's outer surface.
Why the other options are wrong
- A. Bend allowance is a calculation for flat pattern layout, not a consequence of using too tight a radius.
- B. Wrinkling is more associated with compression on the inside of overly tight bends in thicker material, but cracking on the outside is the primary concern.
- D. Minimum bend radius limits exist precisely because tighter bends damage the material.
Minimum Bend Radius
The smallest radius to which a sheet metal part can be bent without cracking, determined by material thickness, alloy, and temper.
- Exceeding (going tighter than) minimum radius causes outer-surface cracking
- Found in aircraft structural repair manuals per alloy/thickness
- Thicker/harder materials require larger minimum radii
- Directly affects bend allowance and setback calculations
Memory trick: "Bend too tight, crack in sight."