Composite Sandwich Panel Joints Overview

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In this post you will get a brief composite sandwich panel joints overview. These three joints are commonly used in the aircraft cabin interiors industry. Learn more from the publicly available HEXCEL document: Sandwich Panel Fabrication Technology.

OK, so are you ready? Great, without any further due, let us dive right into it:

  • “Dado” or “Mortise and Tenon” or “Tongue and Groove” Joint:

Dado JointDado Joint Center

You can see from the above figures that two panels come together to form an L-joint. The red outlines indicate the panel skins on the outside. The figure on the right above indicates a similar joint, but more to the center of the panel 2. Thus making a T-Joint. In both cases the skin and the core for the female side is hogged out up to a specified distance (usually very small) from the skin on the other side. Then the structural adhesive is applied in yellow (two chemicals mixed together, typically in equal parts, according to stringent process specifications). This adhesive bonds the exposed cores of both panels to the exposed face sheets or skins of both panels in each joint insertion.

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The entire "bonded structure" or "shell structure" can be built and assembled this way with strategically placed holding angles and fixtures to maintain orthogonality (or to keep the panels perpendicular to each other) where needed. Then the structure is cured or dried at room temperature for at least 24 hours. This bonding process is typically done under the supervision of a certified bonder or line supervisor, at the start and end of the production lines. At the start of the line, process specifications typically require that testing be done of the mixed structural adhesive using what are called "lap shear" coupons. Various test coupons must be made per specification using the structural adhesive. They are then tested, and the test results documented as part of the certification and quality assurance process. This is a typical method to ensure consistency of the bond strength.

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  • Inserts and Angle Joint:

Panel Angle Joint

In addition to the joint above, in some cases a permanent joint may not be desirable. There may be panels that need to be removable to gain access to certain critical areas. In such cases aluminum angles, 'potted' inserts and screws are used, as shown above. These joints can also serve as structural load paths to the aircraft structure.

  • Panel Pin Joint:

Panel Pin Joint

Another commonly used joint method, the panel pin joint, involves drilling holes through the facings and core of Panel 1. Then drilling through the edge and the core of Panel 2, panel pin is inserted through panel 1. Typical lengths of the pins can be 2.0 to 3.0 inches. Two small holes on the panel pin head side skin of panel 1, then shooting structural adhesive into the holes and fill those holes. The joint is then cured at room temperature.

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In all of these cases, the joints are critical load paths. Hence, extensive testing is done to develop allowable loads and moments and structures are certified in compliance with 14 CFR Part 25 Regulations.

Now that you know the three most commonly used panel joint types in the aircraft cabin interiors, its time take ACTION! As a confirmed subscriber, you will be notified immediately on blog post updates, course launches and any other specials.

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Surya Batchu
Surya Batchu

Surya Batchu is the founder of Stress Ebook LLC. A senior stress engineer specializing in aerospace stress analysis and finite element analysis, Surya has close to a decade and a half of real world industry experience. He shares his expertise with you on this blog and the website via paid courses, so you can benefit from it and get ahead in your own career.