In this article, a 3D lattice model is presented to simulate fracture in cement-based materials. In the paper, two applications are shown. The first application is modeling heterogeneous materials containing particle embedded in a matrix. A method is shown for coupling 3D information on the material structure obtained with CT-scanning to the material properties in the model. In the second application, fracture in fiber cement-based materials is modeled. Fibers are explicitly implemented as separate elements connected to the cement matrix via special interface elements. With the model, multiple cracking and ductile global behavior are simulated of the composite material. Variables in the model are the fiber dimensions and properties, the fiber volume in the composite, the bond behavior of fibers and matrix, and the cement matrix properties. These properties can be obtained by testing. Some examples of tests are given in the paper. The model can be used as a design tool for creating fiber (cement-based) composites with any desired mechanical behavior.

3d modeling of fracture in cement-based materials

The aim of the present paper is to investigate the scaling behaviour of the experimental tensile softening (or catastrophic) curves and it concludes a series of papers from the same research group published inMaterials and Structures [1–4]. Experimentally, it is evident how these curves become steeper by increasing the size of the specimens (ductile-to-brittle transition). To study this phenomenon, a completely new testing apparatus, made up of three orthogonally placed actuators, was bult at the Politecnico di Torino by the authors [1, 5–7]. This set-up makes it possible to apply a purely tensile force, so that the secondary flexural stresses, if kept under control, constitute a degree of error comparable to the values allowed for normal testing apparatus. The method enables a stress vs. strain curve to be plotted with the descending (softening) branch up to the point where the cross section of the tensile specimen breaks away. The results of a new experimental investigation, performed over a very large scale-range of unnotched concrete specimens (16∶1), will be presented. Particular attention will be paid to the scale effects both on nominal tensile strength and on fracture energy. The renormalized experimental curves will be presented in a load vs. displacement plane characterized by anomalous physical dimensions. The renormalization of experimental curves enables obtaining the same response for all specimen dimensions, and then defining the universal (scale-independent) behaviour of the material.

https://staff.polito.it/alberto.carpinteri/papers/CARPINTERI_1998_N.202_MS.pdf

Scaling behaviour and dual renormalization of experimental tensile softening responses

https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1128&context=cenv_fac

Testing of concrete under closed-loop control

This paper describes a method to measure the 3D-microstructure of a material which can be used to perform fracture simulations. A model concrete is made and the 3D structure is obtained with a CTscanner. Uni-axial tensile tests are performed on cylindrical specimens of the model concrete a regular concrete and of a mortar. The model concrete shows more micro-cracking, a more tortuous crack path, a lower tensile load and a less brittle behaviour compared to the mortar and the regular concrete. Furthermore it is found that the opening of the crack is more uniform when the material is more heterogeneous, which results in a more stable fracture.

Crack Development in Concrete, Part 1: Fracture Experiments and CT-Scan Observations

Size effect in heterogeneous materials analyzed through a lattice discrete element method approach

Testing equipment, made up of three orthogonally arranged jacks, which is able to apply a purely tensile load to a concrete specimen is proposed. The secondary flexural stresses are kept under control and constitute a degree of error comparable to the values allowed for normal testing apparatus. When the crack formation tends to produce asymmetry in the system, the counter-reaction intervenes, annulling the load eccentricity. In this way the true tensile properties (strength and fracture energy) of the material may be measured.

F. Maradei

Papers

Three-jack solution to obtain a truly stable and symmetric tensile concrete test