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Bolted or Bonded

  • Thursday, 24th January 2019
  • Reading time: about 2 minutes

This depends on the definition of “better” for each specific case. For example, “better” for some repairs may be lighter, while for others it may be heavier but longer lasting. In some cases cheaper is “better”, while in others producing the repair quickly is the goal.

Bonding usually excels with very thin structures—bonding two thin pieces of aluminum is much stronger than bolting them—and with dissimilar structures—one can glue a piece of paper to a steel plate which isn’t feasible with mechanical fasteners like bolts or screws. Other advantages to bonding include:

  • Bonding minimizes corrosion
  • Adhesives also make good sealants
  • No fastener holes to weaken structure
  • No point stress concentrations
  • Smooth surface finish

Bolted joint and repair strengths increase as the substrates get thicker. This isn’t true for bonding, except for very flexible materials. Other advantages of bolting include:

  • Doesn’t require meticulous surface preparation
  • Easy to inspect for quality
  • Easily disassembled

Therefore, a basic rule for achieving the highest strength composite repair is to use bonding for thin laminates and bolting for thick laminates. Thickness here refers to the original laminate or skins, excluding any core materials. The crossover point varies tremendously with the specific details of each case, but in general 1/64inch (0.4mm) is considered thin and 1/2inch (12.5mm) is somewhat thick.

Note that parts with an aerodynamic or cosmetic surface usually require a flush repair, which almost necessitates bonding. However, when bonding is not possible, a bolted temporary or permanent repair may be necessary.

 Published courtesy of Abaris Training Resources, Inc

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