5.1.3.13 Double Lap Joint

A double lap joint is a well-balanced joint consisting of two outer substrates, each bonded to a third central body. The central body is bonded on both sides. This joint is extremely effective when the central body is subjected to bending moments; it resists the stresses on the central body. If the external supports are subject to forces perpendicular to the substrate, there may be an increase in the stresses at the ends of the external bodies where the bond line meets the central body.

5.1.3.2 Scarf Joint

A scarf joint is a type of overlap joint where the angle between the substrates is greater than 0 degrees but less than 90 degrees. For example, two substrates cut at opposing 45-degree angles and bonded together would form a scarf joint. The substrates must be of equal thickness and width to form an effective scarf joint in this application.

The scarf joint is commonly used to build large composite structures piece by piece or to repair damaged composite structures. The scarf joint interface has no continuous reinforcement from one side to the other; however, the closer the scarf joint angle is to zero, the greater the bond overlap surface area; this will maximise the strength in this joint.

The scarf joint is a suitable alternative to other joints, such as the butt joint and splice joint, and is often preferred because it produces a barely visible bond line.