How thin carbon-fiber skins and honeycomb can lighten pallet bases

An aircraft pallet base does not need to be a solid metal plate to carry structural loads. In a 2021 engineering study, researchers calculated a much lighter alternative by combining two thin fiber-reinforced outer sheets with an aluminum honeycomb core. For a military aircraft pallet case study, the selected design weighed 27.069 kilograms, compared with an 80-kilogram aluminum reference. The authors rounded that difference to a 66% reduction in base-plate weight.

That result describes a component-level design calculation, not a measured reduction in the weight of an aircraft or its complete freight load. The study’s central question was more specific and more practical: how can the layers of a sandwich panel be arranged to meet structural requirements while using less material?

The structure depends on separation as well as material

A composite sandwich panel has two jobs distributed across its thickness. The outer face-sheets carry much of the load at the surfaces, while the honeycomb core keeps those skins apart and helps the panel resist bending. The proposed pallet base used an aluminum honeycomb core between fiber-reinforced plastic face-sheets.

The researchers’ comparisons showed why the two dimensions cannot be treated as interchangeable. Increasing the core thickness increases the distance between the skins, which was the most effective way in the reported tests and calculations to reduce panel deflection. Increasing face-sheet thickness, by adding composite layers, was more effective for reducing skin stress and core shear stress.

This creates a design tradeoff. A thicker core changes the panel’s geometry and bending response, while thicker skins add load-carrying material. The useful configuration is therefore not simply the one with the strongest fiber or the largest amount of material. It is the combination that satisfies several limits without adding unnecessary mass.

What the bending tests actually checked

The study began with physical specimens made from an aluminum honeycomb core and phenolic woven glass-fiber face-sheets. Their fiber orientation was cross-ply, with layers arranged at 0 and 90 degrees. The specimens underwent four-point bending tests, which provided a measured relationship between applied load and displacement.

The researchers also built numerical models of those investigated specimens. They compared calculated deflection, skin stress and core shear stress with the experimental results and reported good agreement between the two. This step supported the use of the calculation method for examining the sandwich-panel behavior represented by those specimens.

The physical test configuration matters when interpreting the headline result. The explicitly described test specimens used phenolic glass-fiber skins, whereas the later pallet-base optimum used epoxy woven carbon-fiber face-sheets. The reported agreement therefore validates the modeled response of the tested specimen configuration; it should not be confused with direct physical testing of the 27-kilogram carbon-fiber pallet base itself.

Forty constructions exposed an orientation tradeoff

After the specimen comparison, the numerical study examined 40 face-sheet layer combinations. The four material families were phenolic woven glass fiber, epoxy woven glass fiber, epoxy woven carbon fiber and hybrid layers combining epoxy glass and epoxy carbon fiber. The models varied the number of layers and their orientations, including cross-ply arrangements at 0 and 90 degrees and angle-ply arrangements at plus and minus 45 degrees.

The calculations favored epoxy woven carbon fiber for several of the modeled structural responses. In the reported comparisons, carbon-fiber face-sheets produced lower mean vertical displacement and lower core shear stress than the hybrid, phenolic glass-fiber and epoxy glass-fiber alternatives in the corresponding configurations. Cross-ply carbon-fiber arrangements also produced lower deflection and core shear stress than angle-ply arrangements.

The orientation choice was not uniformly better in one direction. The angle-ply arrangements produced lower equivalent skin stress than the cross-ply arrangements, even though the cross-ply versions produced lower deflection and core shear stress. A design that minimizes one response can therefore worsen another. The optimizer had to weigh these competing requirements rather than select an orientation from a single strength number.

The optimizer searched within nine structural limits

The weight objective included the upper and lower face-sheets and the honeycomb core. Adhesive-bond weight was excluded. The design variables were the core thickness and the number of composite face-sheet layers, while the calculation enforced nine constraints covering stiffness, deflection, skin and facing stress, core shear stress, overall buckling, shear crimping, skin wrinkling and intracell buckling.

For the military aircraft pallet case study, the minimum reported weight was 27.069 kilograms per base plate. The selected construction used two epoxy woven carbon-fiber face-sheet layers, 0.6 millimeters thick, with a 24.27-millimeter aluminum honeycomb core. The authors compared this result with the conventional 80-kilogram aluminum pallet base and reported a saving of about 53 kilograms, or approximately 66%.

Two optimization programs were used to carry out the search, Matlab with an Interior Point Algorithm and Excel Solver with a Generalized Reduced Gradient Nonlinear Algorithm. Their results were reported to agree. That agreement is useful computational corroboration: it suggests the minimum was not simply an artifact of one optimization implementation. It remains separate from physical testing, and the calculated minimum is bounded by the materials, layer choices, variables and constraints included in this study.

The mass accounting also sets a clear boundary around the number. Because adhesive weight was left out, 27.069 kilograms is not a verified mass for every part of a complete operational pallet assembly. It is the reported weight of the modeled base-plate structure under the study’s stated objective.

From a component calculation to an aviation prospect

Replacing an aluminum base plate with a lighter sandwich structure could reduce the dead weight carried whenever a pallet is moved by aircraft. The possible chain is straightforward: a lighter base contributes less mass to the unit load, and an aircraft carrying less mass may require less fuel for the same mission. The paper discusses associated fuel-cost and carbon-saving estimates, but those estimates depend on aircraft type, flight length and operating conditions rather than representing measured fleet outcomes.

The engineering result is therefore a promising design route rather than evidence of certification, flight deployment, commercial adoption or demonstrated service lifetime. The study established a specimen-informed calculation method, compared candidate face-sheet constructions and identified a constrained low-mass configuration. Whether that configuration can function as a usable pallet base in service would require evidence beyond the calculated comparison presented here.

What lighter pallet bases could mean for air cargo

A validated lightweight pallet base could let cargo operators move the same kind of unit load with less pallet dead weight, creating a route toward lower aircraft fuel demand and associated operating emissions. That benefit depends on the base retaining its calculated mass advantage while meeting the handling, loading and service requirements of real operations.

The 2021 study makes the prospect concrete by showing how a thin carbon-fiber skin arrangement and a separated honeycomb core can be searched against multiple structural limits. Its 27-kilogram result is a calculated milestone for that design problem, not a measured fleet saving. The practical value would emerge only if the modeled construction also proves suitable for the demands placed on aircraft pallets.

Key Sources

• Primary source: Optimal Design of a Fiber-Reinforced Plastic Composite Sandwich Structure for the Base Plate of Aircraft Pallets In Order to Reduce Weight.
  DOI or Journal Page · Peer-Reviewed Paper · 2021-03-09