Propagation and Initiation of Anticracks in Highly Porous Materials

• Applicant: Professor Dr.-Ing. Philipp Weißgraeber
• Subject Area: Mechanics
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 576323125

This research project focuses on the investigation of anticracks in foam materials, which, in contrast to classical cracks, initiate and propagate under compressive loading. Anticracks occur in porous materials where local collapse mechanisms under compression can propagate along a plane. These anticracks exhibit a classical crack-tip field (with the typical 1/sqrt(r) stress singularity but with negative displacements normal to the crack faces) and can be described using classical fracture mechanics approaches. Anticracks are relevant in various porous materials and play an important role in localized compressive failure of technically relevant foams (such as sandwich cores or insulation materials), architected lattice structures, and in geological processes such as compaction bands in sandstone or the release of slab avalanches. While anticracks in snow have already been studied experimentally and numerically, the phenomenon remains largely unexplored in technical materials. This research project aims to close this gap, to improve the understanding of anticrack behavior in engineering materials, and to develop new approaches for the fracture-mechanical description of anticracks. The goal is to deepen the understanding of anticracks through systematic experimental and numerical analyses and to critically examine the limits of fracture mechanics in this context. In adapted compact tension experiments on highly porous glass foam under compression, the resistance against anticrack propagation is to be quantified in terms of negative mode I fracture toughness. In addition, in situ microscopy and micro-CT analyses will provide insights into microscale failure mechanisms and crack face contact. Another goal is to identify the upper bound of the energy release rate resulting from contact, as a function of collapse height and the effective elastic properties of the material. To this end, the influence of contact under crack-face deformations exceeding the collapse height will be investigated using nonlinear finite element simulations. Furthermore, the initiation of anticracks at stress concentrations will be studied using finite fracture mechanics (FFM). Two notch configurations will be considered: a sharp V-notch with stress singularity and an elliptical notch without singularity. For both cases, FFM solutions will be developed, and the effect of contact will be included to determine the incremental energy release rate analytically and numerically. The combination of experimental, numerical, and analytical methods aims to advance the understanding of anticrack behavior in technical materials and to derive principles for the targeted design of failure-resistant structures.

• DFG Programme: Research Grants