Blog

Papers, talks, grants, and modelling notes from the Grassl Group.

Example Discrete aggregates in a 2D lattice transport mesh — 19 May 2026
Concrete is a matrix with low-permeability aggregates embedded in it. With OOFEM's aggregate-packer feeding the lattice mesher, the wetting front threads naturally around each disk.

Example Why lumped capacity matters in unsaturated lattice transport — 18 May 2026
OOFEM's van Genuchten implementation works with both the consistent and the lumped capacity matrix. On a wetting-front problem only one of them avoids the textbook overshoot above the initial suction.

Example Transport on a Voronoi lattice — verification against the 1D diffusion analytical — 17 May 2026
OOFEM's lattice models aren't just for fracture. The same Voronoi dual mesh carries mass-transport — and on a homogeneous 100×100 mm prism it reproduces the 1D diffusion analytical to within mesh-randomness noise.

Example Crack-band vs nonlocal damage in dynamic crack branching — 9 May 2026
Both crack-band scaling and nonlocal averaging give mesh-independent fracture energy in OOFEM. Only the nonlocal model also fixes the band width and the direction of the branching cracks under dynamic biaxial load.

Example How a random e0 field affects the crack in a 2D tensile lattice — 8 May 2026
A random field of the elastic-strain threshold e0 makes the crack localise earlier, at a lower peak, and along a different path. Generated with my own genran code (Gaussian, Weibull, or grafted Weibull–Gaussian).

Example Boundary-independent fracture in 2D direct tensile lattice models — 7 May 2026
Cracks lock onto the mesh boundary in standard direct-tensile lattice runs. Letting elements cross the boundary — a periodic mesh — removes the artefact.

Example Four single element tests of CDPM2 — 4 May 2026
A single tetrahedron with one Gauss point, four monotonic loadings (tension, compression, simple shear, pure shear). Anyone implementing CDPM2 can test against those as a start. Reproducible in one Docker command.

Paper Rate dependence of corrosion-induced surface cracking in concrete: Lattice modelling and experiments — 15 Apr 2026
Ismail Aldellaa, Peter Grassl, accepted in Frontiers in Materials, 2026. DOI

Paper 3D frame element for large rotations based on the rigid-body-spring concept for analysing the failure of structures — 1 Mar 2026
Gumaa Abdelrhim, Peter Grassl, International Journal of Solids and Structures, vol. 327, pp. 113812, 2026. DOI (Open access)

Paper RAAC panels can suddenly collapse before any warning of corrosion-induced surface cracking — 15 Sep 2025
Evžen Korec, Peter Grassl, Milan Jirásek, Hong S. Wong, Emilio Martínez-Pañeda, npj Materials Degradation, vol. 9, pp. 44, 2025. DOI (Open access)