1. Structural of sandwich panels
The sandwich panel comprises two high-strength upper and lower skins and a soft and light core filling them. The upper and lower skins are bonded to the core by adhesive to form an integral rigid structure, or the sandwich structure is obtained by direct injection moulding or moulding. When the sandwich panel is subjected to bending load, the upper skin is stretched, the lower skin is compressed, and the core transmits shear force. From a mechanical point of view, it is very similar to an I-beam. The surface material is equivalent to the flange of the I-beam, and the core material is equivalent to the web of the I-beam.
The difference is that the core material and the panel are not of the same material, and the core material is dispersed rather than concentrated on the narrow web. Since the height of the lightweight core is several times higher than that of the panel, the moment of inertia of the section increases in a fourth power ratio, and the panel is not prone to instability due to the support of the core. The panel can be very thin and is much lighter and more rigid than a solid piece. The weight reduction effect is extremely obvious, making it an efficient structural material.
2. Comparison of stiffness between ribbed automotive panels and sandwich automotive sandwich panels
The National Physical Laboratory of the United Kingdom studied the deformation of glass fiber reinforced thermoplastic composite ribbed automotive panels (such as shells, door panels, etc.) and sandwich (thermoplastic core) designed automotive panels.
Part Name | Unit weight (kg/㎡) | Actual deformation(mm) | Theoretical deformation (mm) |
Ribbed automotive panels | 6.4 | 1.32 | 1.29 |
Sandwich car panels | 3.6 | 0.15 | 0.12 |
Note: ① The specimen centre is loaded with 200N; ② The rib is Symalit GM40PP, 2.5mm thick, 15.5mm high; ③ The sandwich panel skin is 1mm thick Twintex PP, and the core is 1.75 thick Tubular PP honeycomb core.
As the table shows, sandwich parts have less deformation and a 50% reduction in unit weight compared with ribbed parts.
3. Core Material Selection
honeycomb cores made of aluminum foil
plastic honeycombs
foam plastic core
Many materials can be used as sandwich cores, depending on the mechanical and functional requirements of the sandwich structure. When selecting components or non-structural sandwich structures, special requirements of the components must be considered, such as impact, heat preservation, sound insulation, vibration absorption, bulletproofing, etc. Honeycomb cores have high shear performance, balsa wood cores have high compression performance, and foam cores have good thermal insulation performance. Strong rigidity is required for structural materials that bear large dynamic loads such as aircraft and railway passenger cars. Therefore, it is appropriate to use honeycomb cores made of glass fibre-reinforced plastic or aluminium foil, while plastic honeycombs or foam plastics can be used in house-level buildings to meet the strength and thermal insulation requirements of buildings.
Plastic honeycomb panels are superior to foam plastics in terms of strength, rigidity, weather resistance, flame retardancy, and structure. Therefore, they are often used instead of foam plastics in buildings that have high requirements for strength, sound insulation, and heat insulation.