Sandwich Steel Panels: Part One

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:

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

References

1. C. Besse: Development and optimization of a formable sandwich sheet, PhD thesis, Ecole Polytechnique X, Materials and structures in mechanics, 2012;

2. B.Engel, J.Buhl: Forming of sandwich sheets considering changing damping properties, INTECH 2012, p. 85-108;

3. J. Säynäjäkangas, T. Taulavuori: A review in design and manufacturing of stainless steel sandwich panels, STAINLESS STEEL WORLD OKTOBER 2004,p. 21-24;

4. D. Y. Jeong, M. E. Carolan, A. B. Perlman, Y. H. Tang: Deformation Behavior of Welded Steel Sandwich Panels Under Quasi-Static Loading, Final Report March 2011, DOT/FRA/ORD-11/06;

5. P.Kujala, A.Klanac: Steel sandwich panels in marine applications, Brodogradnja, 56, 2005, 4, p.305-314, UDC 629.5.023:62-419.5;

6. W-S Chang: Elasto-plastic analysis of corrugated sandwich steel panels, PhD Thesis, The Pennsylvania State University, 2004;