5.1.3.1 Head-to-Head or Butt Joints

Head-to-head joints, also known as butt joints, are simple joints obtained by joining only the ends of the pieces to be bonded; the bonded surfaces are perpendicular to the plane of the substrate. These joints are generally avoided because of their inability to withstand bending stresses or any impact stresses perpendicular to the plane of the substrate; these will almost certainly lead to adhesive failure. While butt joints are the weakest joints that can be created, they are commonly found because they are the easiest to make.

If the thickness of the substrate is too great to make an overlap joint or if a butt joint is the only solution due to engineering or repair limitations, ‘modified’ joints can be employed to increase resistance against buckling (see Single Strap Joint, Figure 109).

Since the butt joint is weak, it is usually only used in simple situations and should be avoided in engineered applications or assemblies.