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Ex-Struct- a new concept in sandwich panel structure

Connect, no. 111, March/April 2001, p.8

A new way of constructing lightweight but very strong sandwich panels has recently been developed by a team at TWI.

Central to the Ex-Struct concept are modular sandwich panels that can be slotted together to create a larger structure. The foundation of these panels is an array of interlocking units. Modular units are made from machined or extruded lengths of material. The sectioned length of the array will determine the height of the panel.

The design of the machined extrusion is such that standard male and female connections are created on the outside of the unit. This allows the modular array to be mechanically locked together in the X-Y plane using male-female sliding joints.

Figure 1 shows a simple method of joining the circular extrusions. This is one of many methods that can be used depending on the final structural design required.

Fig.1. Simple modular extrusion design
Fig.1. Simple modular extrusion design
Skins are stake welded to tubes
Skins are stake welded to tubes

Various joints can be used to determine load paths and impact resistance, which can be tailored to end products.

External skins can be stake welded on to the top and bottom of the modular array to complete the sandwich. This can be done using a CO 2 or Nd:YAG laser to penetrate the skin from the outside and into the material below. These welds will lock the modular array in the Z plane, creating a very rigid structure in all three dimensions.


Typical materials that could be used for Ex-struct are:

  • steel
  • alloys
  • plastics

Repair procedures

Repair of Ex-Struct panels is simple. If a whole panel is damaged it can simply be removed and replaced with another. If panels are only partially damaged, the skin can be cut off, the damaged module can be routed out and replaced, and another skin welded on.


  • Lightweight car decking for ships
  • Bridge construction
  • Interchangeable armour
  • Railway carriages
  • Heavy duty floors for aircraft transport freighters

For more information, please contact us.

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