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.

Figure 116 Double lap joint

5.1.4 Non-Planar Substrates

Mitigating stresses is more challenging when bonding with non-planar substrates. Angles created by non-planar substrates can lead to counterintuitive solutions, as the expected forces may not stress the joint as expected. It is important to choose the most suitable joint for the application based on the types of stresses acting on the bonded joints; in other words, forces and stresses should be considered first, with the joint designed around the expected forces and stresses. Particularly with right angles (90° angles), peel forces may impact the assembly in unanticipated areas. As discussed in Section 4, it is crucial to avoid peeling cleavage forces, as these are the most common forces that lead to failure. Figure 117 shows some of the most common peeling loads in non-planar assemblies and some possible design solutions to change the type of stress. This is not a comprehensive list, but rather a representative sample of the most common peel forces.

Figure 117 Peeling loads and their conversion by design measures

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