B2 Modelling fiber-matrix bond and mineral-bonded composites under impact loading

Doctoral Researcher
Alaleh Shehni

Principal Investigator
Ulrich Häußler-Combe

in cooperation with 
Christina Scheffler

Project poster
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The aim of this subproject is to make a numerical model of cement based composites which fibers are modeled explicitly and represented by embedded elements.

To this aim, our in-house program CaeFem has been developed to analyze simple regular discretization of heterogeneous mesoscopic continuum with discrete distinction of aggregates or void from a matrix with different discretization approaches and comparisons are made with a commercial FEM program-DIANA. A material model is implemented and assigned to bond element to connect embedded fibers to continuum which fibers are distributed randomly within the simply discretized continuum. The next three steps will be: modeling of random geometry (for position, orientation and length of fibers, position and size of aggregates, comparison of approaches to model continuum with embedded fibers and embedded smeared or discrete cracks using FEM (SDA and X-FEM), EFG and iso-geometric methods and implementation of physical nonlinearities regarding fiber, bond, aggregates, matrix. Incidentally, the behavior of composite under quasi-static loading, as a necessary prerequisite for dynamics, will be validate by experiment results provided by Institut für Baustoffe.

Finite Element discretization with explicit aggregate representation
Finite element discretization with explicit fiber representation

Current challenge:
Modelling the behavior of high strength SHCCs (Strain-hardening cement-based composites) made with high performance polymer fibers under quasi-static tensile loading. High density polyethylene fibers are modelled explicitly and distributed randomly in a two-Dimensional model. Single fiber pullout test result is used for micromechanical characterization of bond strength. Load test simulations are conducted with in-house program CaeFem and comparisons will be made with experimental results. Several sensitivity analysis will perform based on different fiber contents and notches located in the mid-height of a dumbbell specimen. The resultant behaviors will be compared and verified versus obtained results from.

Thin SHCC specimen in a tensile test for calibration of 2D FEM simulations
Thin SHCC specimen with notch
Mesh properties and boundary conditions in 2D simulation of an SHCC specimen
Simulation showing crack pattern in a notch specimen under quasi static tensile loading
  1. Thin dumbbell specimen and Test set-up,
  2. Specimen with notch,
  3. Simulation of notch area and
  4. Crack pattern for notch model under quasi static tensile loading

Peer Reviewed Journal Publications

  • Häußler-Combe, U.; Chihadeh, A.; Shehni, A.: Finite Element Modeling of Fiber Reinforced Cement Composites with Explicit Representation of Fibers and Matrix Cracking. Solids and Structures under review

Other Publications

  • Shehni, A.; Häußler-Combe, U., New Approach on Discretization Methods for Mesoscopic Study of Concrete Structures. ECCM 6, June 2018, Glasgow, UK.
  • Shehni, A.; Häußler-Combe, U., Curosu, I., U. Gong, T., Mechtcherine, V.: Numerical Simulation of HS-SHCC under Quasi-static Tensile Loading 10th International Conference on Fracture Mechanics of Concrete and Concrete Structures FraMCoS-X, Bayonne, France, 23-26 June, 2019. doi: 10.21012/FC10.233164.
  • Häußler-Combe, U.; Chihadeh, A.; Shehni, A.: Modelling of discrete cracks in reinforced concrete plates with the strong discontinuity approach (SDA). In: Zingoni, A. (Hrsg.): Advances in Engineering Materials, Structures and Systems: Innovations, Mechanics and Applications – Proc. of the 7th Int. Conf. on Structural Engineering, Mechanics and Computation (SEMC 2019). 2.-4.9.2019 in Kapstadt (Südafrika)