5.1.3.3 Double butt Joint or Half LAP

The double butt joint or half lap joint is obtained by machining the ends of substrates to increase the contact surface. By increasing the contact surface, forces exerting stresses on the assembly will be distributed more evenly, thus creating a stronger joint. Generally speaking, half the depth of the material will be removed from each substrate (assuming equal dimensions) to maintain maximum substrate integrity. This joint is reasonably strong; however, it is not recommended when materials are subject to fatigue or high-impact loads. Preparing the joint is simple, but it must be fitted correctly along the entire length of the joint to ensure adequate strength.

5.1.3.4 Tongue and Groove Joint

A tongue and groove joint is made with an edge that consists of a groove running the entire length of the joint and a tongue that fits into the groove. This feature of the tongue and groove creates a mechanically strong and aesthetically pleasing joint. The greater the contact surface, the greater the distribution of stresses along the contact surface. This joint is well suited to a number of stresses, as the joint geometry counteracts many of the weaknesses exhibited under peel stress or stresses perpendicular to the bond line.