Heiko Herrmann

Analysis of short fibres orientation in steel fibre-reinforced concrete (SFRC) by X-ray tomography

The mechanical properties of fibre composite materials are largely determined by the orientation of fibres within the matrix. Which orientation distribution short fibres follow in different parts of a structural element is still a subject for research and discussions in the scientific community. In this article, we present a modern and advanced method for measuring the orientation of short fibres in steel fibre-reinforced concrete (SFRC) by X-ray microtomography. With this method, a voxel image of the fibres is obtained directly in 3D, and the orientation of each individual fibre is calculated based on a skeletonized representation of this image. Scans of 12 SFRC samples, taken from the central height region of real-size floor slabs, reveal the fibres to be mostly horizontally oriented near the centre of a floor slab and more vertically oriented near the edge; here the alignment with the formwork dominates. The fibre orientation distributions are characterized by several orientation parameters as quantitative measures for the alignment. On the practical side, this method has the potential to be incorporated into the development and production process of SFRC structures to verify how the fibres contribute to capacity.

DC-conductivity testing combined with photometry for measuringfibre orientations in SFRC

The orientation distribution of fibres has an important impact on the properties of short-fibre reinforced composites. This article introduces a methodology for defining fibre orientations in steel fibre reinforced concrete (SFRC). The main method under consideration is the slicing, where two approaches are introduced, i.e. the photometric analysis and DC-conductivity measurements by a special robot. The advantage of presented slicing method is the fact that a combined analysing approach is utilized; DC-conductivity testing is joined together with the image analysis. As a result, significant benefits are achieved, e.g. the ability of measuring the orientation of an individual fibre, the measuring of the in-plane angle in the interval [0°, 360°]. An additional important aspect in the presented slicing method is the possible usage of the structural parts extracted from the full-size floor-slabs as specimens, as it is done here. The authors present the statistics of fibre orientations, which are based on the experimental data received by the application of the mentioned analysing approaches. The presented slicing method with its possible extensions offers possibilities to improve the quality control while producing SFRC products.

Methods for fibre orientation analysis of X-ray tomography images of steel fibre reinforced concrete (SFRC)

One of the most important factors to determine the mechanical properties of a fibre composite material is the orientation of the fibres in the matrix. This paper presents Hessian matrix-based algorithms to retrieve the orientation of individual fibres out of steel fibre reinforced cementitious composites samples scanned with an X-ray computed tomography scanner. The software implemented with the algorithms includes a massive data filtering component to remove noise from the data-sets and prepare them correctly for the analysis. Due to its short computational times and limited need for user intervention, the software is able to process and analyse large batches of data in short periods and provide results in a variety of visual and numerical formats. The application and comparison of these algorithms lead to further insight into the material behaviour. In contrast to the usual assumption that the fibres act only along their main axis, it is shown that the contribution of hooked-end fibres in other directions may be noticeable. This means that fibres, depending on their shape, should act as orthotropic inclusions. The methods can be used by research laboratories and companies on an everyday basis to obtain fibre orientations from samples, which in turn can be used in research, to study stress–strain behaviour, as input to constitutive models or for quality assurance.

Dynamics of the Size and Orientation Distribution of Microcracks and Evolution of Macroscopic Damage Parameters

Abstract We are dealing with damage of brittle materials caused by growth of microcracks. In our model the cracks are penny-shaped. They can only enlarge but not heal. For a single crack a Rice–Griffith growth law is assumed: There is crack growth only if tension is applied normally to the crack surface, exceeding a critical value. Our aim is to investigate the effect of crack growth on macroscopic constitutive quantities. A possible approach taking into account such an internal structure within continuum mechanics is the mesoscopic theory. A distribution of crack lengths and crack orientations within the continuum element is introduced. Macroscopic quantities are calculated as averages with the distribution function. A macroscopic measure of the progressing damage, i.e., a damage parameter, is the average crack length. For this scalar damage parameter we derive an evolution equation. Due to the unilateral growth law for the single crack, it turns out that the form of this differential equation depends explicitly on the initial crack length distribution. In order to treat biaxial loading, it is necessary to introduce a tensorial damage parameter. We define a second-order tensor damage parameter in terms of the crack length and orientation distribution function.

A Small-scale, Low-budget Semi-immersive Virtual Environment for Scientific Visualization and Research☆

This paper describes the design concepts, the making of and some applications of the first Estonian Virtual Reality Environment. Using hardware only slightly above the threshold of consumer level, we built a virtual environment (VE) aimed at scientific visualization with the lowest possible space requirements (smaller than a cube with 2 m edge length in total) and budget (approximately below 30.000 €). The system is a fully functional visualization environment that replicates most of the features and properties of a real-sized CAVE-like System, therefore allowing further prototyping and research in the field of Virtual Reality.

Virtual Reality Visualization for Photogrammetric 3D Reconstructions of Cultural Heritage

In this paper the authors review the design of a self-build general-purpose Virtual Reality environment, which presents all relevant features of a full-size CAVE-like system, yet at a fraction of the financial and space requirements. Further, the application of this system to the development of a virtual museum is presented. The objects in the museum are models, reconstructed via photogrammetry from a set of pictures. For this process cost-free software is used. The presentation of the 3D models in the Virtual Environment is done using BlenderCAVE, a multi-screen extension of the Blender game engine. The main contributions of this paper are the discussion of the design choices for a small and low-budget but feature-rich virtual reality environment and the application of the system for cultural heritage. In this area tools for creation of 3D models and their presentation in a VR environment are presented.

Virtual Reality visualization for short fibre orientation analysis

The paper investigates the beneficial contribution of visual feedback in the development of an algorithm for the automatized analysis of fibre orientations in short fibre reinforced composites. Of special interest was steel fibre reinforced concrete (SFRC), a multi-disciplinary research area involving material sciences, physics and civil engineering. More in detail, this paper explains how scientific visualization techniques, employed on a Virtual Reality environment, contribute to the understanding of the SFRC properties, both for research and educational aims. Furthermore, the analysis algorithm to obtain fibre orientation distributions from noisy tomography scans is presented.

The balance of spin from the point of view of mesoscopic continuum physics for liquid crystals

Abstract In this article mesoscopic continuum physics is reviewed using generalized coordinates in the context of liquid crystals. A special focus is put on the balance of spin (internal angular momentum). Mesoscopic continuum physics introduces variables describing the micro-structure – like the orientation of crystals – into the domain of the fields, thus treating them equivalently to space. The theory of mesoscopic continuum physics has been reformulated, resulting in more compact equations. In this formulation the balance of spin shows up naturally as component equations of the balance of momentum. This represents an advantage over the standard formulation of mesoscopic continuum physics.

Spin Axioms in Different Geometries of Relativistic Continuum Physics

The 24 components of the relativistic spin tensor consist of 3+3 basic spin fields and 9+9 constitutive fields. Empirically only 3 basic spin fields and 9 constitutive fields are known. This empirem can be expressed by two spin axioms, one of them identifying 3 spin fields, and the other one 9 constitutive fields to each other. This identification by the spin axioms is material-independent and does not mix basic spin fields with constitutive properties. The approaches to the Weyssenhoff fluid and the Dirac-electron fluid found in literature are discussed with regard to these spin axioms. The conjecture is formulated, that another reduction from 6 to 3 basic spin fields which does not obey the spin axioms introduces special material properties by not allowed mixing of constitutive and basic fields.

Scalable Medical Viewer for Virtual Reality Environments

This paper presents a scalable virtual reality-based software for medical visualization. Usable on a desktop, on a head-mounted display or on a CAVE-like system, the application allows the full inspection of CT or MRI images superimposed to the 3D models of the organs built from these images. Additionally full volume rendering functionalities and several interaction tools as transparencies, choice of the CT slice to display, hiding and showing of meshes and additional information on the scanning procedure are available. The tool aims at offering an in-depth inspection of the body organs for medical, education and surgical preoperative planning.