Sandwich Steel Panels: Part One

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There is a constant pressure on the automotive industry to come up with lightweight structural solutions to improve vehicle fuel efficiency without sacrificing structural performance. In addition, the design choices are subject to stringent cost constraints as innovations in automotive engineering are seldom successful unless both performance and cost advantages prevail. Sandwich structures are known for their exceptionally-high bending stiffness-to-weight ratio. The underlying design concept is the separation of two flat sheets by a much thicker core layer of low density (Figure 1).

 

Figure 1: Sandwich structures

 

For many applications there are claims concerning the metal sheet, which cannot be reached with a single sheet. The sandwich structures have potential to offer a wide range of attractive design solutions. In addition to the obtained weight reduction, these solutions can often bring space savings, fire resistance, noise control and improved heating and cooling performance.

As shown in Figure 1, the sandwich structures are generally composed of two face sheets that are separated by a core. In the traditional design of sandwich structures, the separation of the face sheets by the core increases the moment of inertia of the panel, which produces a higher bending stiffness-to-weight ratio than solid or monolithic plates. The face sheets carry almost all of the bending and in-plane loads while the core carries the shear load to prevent the face sheets from sliding past one another.

Sandwich panels in general can be classified as: composite sandwich and metallic sandwich panels. Composite sandwich panels consist of non-metallic components such as FRP, PU foam etc. and are typically applied as load carrying structures in naval vessels and leisure yachts, and mainly as non-load carrying elements on merchant and large cruise ships. For metallic sandwich panels there are basically two types of panels: panels with metallic face plates and bonded core such as SPS panels and panels with both metallic face plates and core welded together.

Steel sandwich panels can be divided according to the core structures: I-core with straight webs, O-core with rectangular beams as a core, Vf/V-core with hat or corrugated sheets as a core and X-core with two hats as a core, Figure 2. Other types of the profiles such as C, U or Z can also be used as a core. By using sandwich structures, it is possible to obtain high strength to weight ratio, i.e. the sandwich structures were found to be 30-50% lighter than the conventional steel applications.

 

Figure 2: Five different core geometries suited for steel sandwich structures

 

All kinds of sandwich panels have a number of common benefits. The advantages of sandwich plates are summarized as follows:

• High stiffness and strength to weight ratios.
• The good surface finish reduces an aerodynamic resistance.
• Good thermal and acoustic insulation.
• High energy absorption capability with different fillers and cores.
• Increase the interior space and ease of equipment installation.
• Relatively light and the total costs are very competitive to other light structures solutions.

 

 

Figure 3: V-core stainless steel sandwich panel with hat sheets as a core. (Photo: Mizar Oy)