Hierarchical Sandwich Structures Increase Resistance To Buckling

2023 Author: Hannah Pearcy | [email protected]. Last modified: 2023-11-26 11:39

Sandwich structures are used as lightweight materials for large, flat structures. Plastic sandwich structures have a honeycomb core or polymer foam and cover layers made of fiber-reinforced plastics. This combination enables high bending and buckling stiffness with very low weight.

The Fraunhofer Institute for Microstructure of Materials and Systems IMWS and Thermhex Waben GmbH, which manufactures cost-efficient polypropylene (PP) honeycomb cores with a patented production process, have been cooperating on the subject of lightweight construction with sandwich materials since the end of 2015. In the current joint project HPHex - Basic Investigation of thermoplastic lightweight sandwich materials from hierarchical honeycomb and top layer structures for heavy-duty and cost-effective lightweight structures”sandwich materials with new hierarchical structures are examined in order to make lightweight construction more efficient.

The Thermhex manufacturing process

With the patented Thermhex technology, thermoplastic honeycomb cores are produced in a continuous manufacturing process.

The honeycomb core is created from a single sheet of film by:

• successive thermal deformation
• a folding process and
• the application of material layers for surface finishing (e.g. sealing foils, polyester fleece)

The surface of the Thermhex honeycomb is half closed. This optimally connects the core and the top layer material. The Thermhex honeycomb cores can be manufactured directly from the extruder or from a film roll, which further improves flexibility.

Honeycomb cell walls themselves consist of honeycomb sandwiches

The dent resistance of the thermoplastic honeycomb cores currently used in lightweight construction is rather low. This is why they are used, for example, in cladding and interior components, since these areas are less stressed. This is where cooperation partners come in: They want to overcome the low dent resistance of the thin thermoplastic honeycomb cell walls through a hierarchical material design.

The honeycomb cell walls are each formed by a honeycomb sandwich. In this way, the stability of the honeycomb core is increased while the weight remains the same or even less.

The approach of hierarchically structured cover layers that offer advantages in terms of load distribution and surface quality is also to be researched. By examining such sandwich structures, further physical properties can then be described and assessed. The project partners already have a Eureka label called "Hierarchical Hexagonal Sandwich Honeycomb Core (HiHex)".

"The innovative thermoplastic honeycomb structures will ensure a high degree of automation in production and low material costs as an alternative to the previous cost-intensive construction methods", project manager Dr.-Ing. Ralf Schlimper, who heads the group “Evaluation of fiber composite systems” at Fraunhofer IMWS.