Sandwich Panels: Assumptions and calculations

Assumptions used by model

The layered structure of sandwich panels leads to significant differences in properties in the in-plane and through-thickness directions. Even though both the in-plane and through-thickness properties are calculated by the Synthesizer, the structure of the MaterialUniverse database means that only one direction can be specified in a selection project.

As a result, the values quoted on the material datasheet represent the performance in the direction that is most important for design. In general, the datasheet quotes in-plane properties. The exceptions are: flexural modulus, flexural strength, thermal conductivity, electrical resistivity and dielectric constant, which are through-thickness properties.

The 'secondary' through-thickness and in-plane properties, which are calculated by the model but are not considered critical for the design of most sandwich panels, are stored in the notes field at the bottom of the datasheet.

In determining the calculations for the sandwich panel model, the following assumptions have been made:

• The sandwich panel is balanced (i.e. both face-sheets are made from the same material and have the same thickness).

• The interfacial bond between the face-sheet and core is perfect (i.e. face-sheet is supported uniformly over its entire surface).

• The properties of the adhesive have little, or no, contribution to the overall panel properties (i.e. it has no thickness and no shear deformation occurs between the face-sheets and the core).

• The face-sheet remains flat (i.e. no telegraphing or dimpling occurs with honeycomb cores).

Note: In order to compare sandwich panels with conventional 'solid' materials, it is necessary to consider them as a 'monolithic' material with their own set of properties. This is achieved by calculating the equivalent material properties for the sandwich. Plotting these equivalent properties (e.g. , ) on a property chart (e.g. E_f vs. ρ) allows direct comparison with all other materials in the database.

Calculations used by model

• Sandwich panel model - Primary properties
• Sandwich panel model - Secondary properties
• Summary of calculated properties and data required

Sandwich panel model calculations - Primary properties

The equations used by the model to calculate the primary properties are summarized below. All calculated properties are equivalent properties. For more information on the derivation of these equations see derivation of calculations.

For a definition of the symbols used, see symbols.

• Face-sheet volume fraction

  

• Density

  

• Price

  

• Young's modulus

  

• Flexural modulus

  

  B₁, B₂ = constants determined by user-specified 'support and load conditions', L = span

• Yield strength (in-plane)

  

  

• Flexural strength,

  

  B₃, B₄ = constants determined by user-specified 'support and load conditions', L = span

• Specific heat capacity

  

• Thermal expansion (in-plane)

  

• Thermal conductivity (through-thickness)

  

• Electrical resistivity (through-thickness)

  

• Dielectric constant

  

• Dielectric loss tangent

  

• Embodied energy (primary production)

  

• CO2 footprint (primary production)

  

Sandwich panel model calculations - Secondary properties

The following remaining properties are also calculated by the model. These properties, which are listed in the notes field at the bottom of the material, are not available for selection.

• Young's modulus (through-thickness)

  

• Yield strength (through-thickness)

  

• Thermal conductivity (in-plane)

  

• Electrical resistivity (in-plane)

  

Summary of calculated properties and data required

A summary of the material properties required to calculate the equivalent sandwich panel properties is summarized in Table 2.

Table 2. Summary of properties required to calculate equivalent sandwich properties

Top

Copyright © 2020, Granta Design, Cambridge, UK