Causes, Reproducibility, and Modeling of Size Effects in the Mechanical Behavior of Foam Materials

• Applicant: Privatdozent Dr.-Ing. Geralf Hütter
• Subject Area: Mechanics
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564561295

Foam materials are characterized by high mass-specific stiffness, strength and energy absorption capacity and are therefore used for numerous applications. In many of these structural applications, the thickness of foam materials includes only a small number of pore layers. However, effective mechanical properties measured on specimens of this thickness, unlike most compact materials, depend significantly on specimen size and exhibit high scatter. Although the existence of such a size effect in foam materials is known in principle, there are few experimental studies on it in the literature. While some of them show a positive size effect ("smaller is stiffer"), others show a negative size effect ("smaller is softer") under comparable loading conditions. In addition to specimen fabrication, difficulties in the tests proved to be a non-disturbing clamping/bearing and load application as well as the large scatter of results on small specimens. The aim of the project is to close the gap in the state of knowledge about the size effects in the deformation behavior of foam materials, which are extremely relevant for structural applications, with regard to the type (positive/negative) and extent of these size effects and their structural causes. For this purpose, experiments will be conducted on samples spanning a wide range of sizes. To quantify the influences of load application and sample preparation, the experiments will also be virtually repeated on samples that have been nondestructively extracted directly from computed tomography scans. The inclusion of a large number of individual samples across a broad range of sample sizes enables statistically robust conclusions about the comparability and reproducibility of the few existing experimental studies. To cover a wide range of applications and derive generalizable qualitative and quantitative insights, several foam materials with different topologies and base materials will be investigated. Simulations using synthetic mesostructural models with varying levels of detail, as well as generalized continuum theories, will be conducted to assess the extent to which these models can predict size effects under different loading conditions.

• DFG Programme: Research Grants
• Co-Investigators: Dr.-Ing. Martin Abendroth; Professor Björn Kiefer, Ph.D.