Sheet Metal Structural Repair Flashcards

A technician is repairing a longitudinal crack in a stressed aircraft skin panel. The first step is to stop-drill the ends of the crack. What is the primary reason for this action?

Answer: To relieve stress concentrations at the crack tips and prevent further propagation.

Stop-drilling is a crucial first step in repairing cracks in sheet metal. A crack creates a very high-stress concentration at its tip. Drilling a small hole at the end of the crack effectively blunts the sharp tip, distributing the stress over a larger area and significantly reducing the likelihood of the crack propagating further, especially under vibration.

When performing a sheet metal repair, a technician must select the proper rivet length. The general rule for determining the length of a solid shank rivet is that it should be equal to the total thickness of the material being joined plus what additional amount?

Answer: 1.5 times the rivet's diameter

To form a proper shop head (buck-tail), the rivet shank must protrude through the material by a specific amount before being driven. The standard guideline is that the rivet length should equal the total grip length (material thickness) plus 1.5 times the rivet's diameter. This ensures there is sufficient material to form a buck-tail that is 1.5 times the original shank diameter in width and 0.5 times the shank diameter in height.

A repair on an aluminum alloy skin panel requires making a 90-degree bend. Which of the following terms describes the amount of material that must be added to the sum of the two leg lengths to determine the total flat pattern length?

Answer: Bend allowance

When metal is bent, the material on the outside of the bend stretches, and the material on the inside compresses. Bend allowance is the arc length of the neutral axis within the bend. It is the amount of material that must be added to the sum of the flange lengths (legs) to determine the total length of the flat pattern needed to create the part.

A technician needs to find approved repair procedures for a damaged main structural member on a specific large aircraft. Which of the following documents should be consulted first?

Answer: The manufacturer's Structural Repair Manual (SRM)

The Structural Repair Manual (SRM) is the primary document issued by the aircraft manufacturer that contains detailed information, limitations, and approved procedures for repairing the aircraft's primary and secondary structures. While AC 43.13-1B provides acceptable techniques for non-pressurized aircraft when no manufacturer instructions are available, the SRM is always the first and authoritative source for a specific aircraft model.

Certain aluminum alloy rivets, such as 2017 and 2024, are heat-treated and then stored at low temperatures before use. What is the purpose of this quenching and refrigeration process?

Answer: To keep them in a softened, workable state (annealed) for driving.

Rivets made from alloys like 2017 and 2024 are solution heat-treated to dissolve the alloying elements. They are then quenched (rapidly cooled) to trap these elements in a solid solution, making the rivet soft and driveable. This softened state is temporary. At room temperature, they begin to age-harden rapidly. Refrigerating them significantly slows this age-hardening process, keeping them in the soft 'W' condition until they are ready to be driven. After driving, they age-harden to their full strength.

When installing a repair patch over a damaged area, what is the generally accepted minimum edge distance for a single row of rivets, measured from the center of the rivet hole to the nearest edge of the sheet?

Answer: 2.0 times the rivet diameter

Maintaining proper edge distance is critical to prevent the rivet from tearing through the edge of the sheet under load. The generally accepted minimum edge distance, as specified in sources like AC 43.13-1B, is two times the diameter of the rivet shank (2D). This ensures sufficient material is present around the rivet to carry the bearing loads.