Curvature resistance – a method for quantifying and predicting the plastic bending and folding of composites

Securing the competitiveness of the manufacturing industry requires more flexible, energy- and material-efficient production processes as well as faster and more cost-effective product developments. Important components in the form of prediction tools and material models are only insufficiently available. Fibre-based materials, such as cardboard composites, have orthotropic material behaviour and different behaviour under tensile or compressive load due to the manufacturing process.

The project “curvature resistance” presents a measurement methodology and its application for a fundamentally improved possibility of material dimensioning and design of bending lines for fibre-based composite materials. The methodology was developed exemplarily for the plastic bending and folding of cardboard composite material and products formed from it. During the measurement a ring, formed from a strip, is continuously reduced in size and the transfer function from torque to curvature is recorded. Based on the measurement curve, the plastic bending behaviour between flat crumpling and local bending fractures can be characterised.

With the help of developed numerical methods, a macroscopic, isotropic, plastic substitute material model for bending is provided for FEM applications. In addition to data from the tensile test and the 2-point bending, an extended plastic compressive stiffness curve and the shear stiffness (out of plane) can also be determined. In numerical prediction an automated, load-adjusted material model preselection is used, which was validated experimentally and numerically on minimal models of existing test arrangements and a complex model of a packaging.

The following applications can be derived:

• Characterisation and quantification of fibre composites regarding their forming behaviour during bending and folding;

• Efficient use of materials by building numerical prediction models;

• Process and tool development for gentle processing.

The project IK-VF 190003 "Measurement of Curvature Resistance" is funded by the Federal Ministry of Economics and Energy (BMWi) and supported by SIG Combibloc Systems GmbH.

Toma Schneider¹, Dr. Antje Harling^1, Prof. Dr. Frank Miletzky²

¹ Papiertechnische Stiftung (PTS), Pirnaer Straße 37, D-01809 Heidenau, Germany

  phone: +49 (0) 3529 551-714 / E-Mail: toma.schneider@ptspaper.de

² Technische Universität Dresden, Institut für Naturstofftechnik, Marschnerstraße 39, D-01307 Dresden, Germany