Safety in chemistry and materials technologies
Issue no. 3 of 4. July 2011
Safety in chemistry and materials technologies
Issue no. 3 of 4. July 2011
The old Kaiser Wilhelm Memorial Church, surrounded by protective scaffolding. Next to it is the new building by Egon Eiermann
The ruined tower of the Kaiser Wilhelm Memorial Church in Berlin exhibits extensive damage to its building material. Since it was built 116 years ago, many different materials have been used for building and repair. Today, the wide, external tuff cover and large parts of the exposed brickwork exhibit signs of serious damage processes such as peeling, weathering and cracking.
BAM´s scientist Dr. Frank Weise of the Department Safety of Structures heads the building diagnostic investigations in close co-operation with project manager Dipl.-Ing. Raphael Abrell of the Office for Architecture, Town Construction and Monument Preservation (BASD Gerhard Schlotter Architects). The investigations and previously undertaken material and damage mapping provide the basis for a sound restoration concept. The situation of the ruin and the requirement for its character to be maintained represent a special challenge for the restoration.
How to treat the tuff and brick surfaces strengthened and hydrophobised by silicic acid ester in a restoration in the 80s, which now show particular damage such as peeling, is the key issue. BAM will test the soundness of potential restoration concepts experimentally.
Contact:
Dr.-Ing. Frank Weise
Division 7.1 Building Materials, Working group Building Diagnosis; Transport and Damage Processes
Phone: +49 30 8104-1715, email: frank.weise@bam.de
Ultrasound testing of CRP (carbon-fibre-reinforced plastic) lamellas in the laboratory
If concrete bridges are ageing or their loads keep increasing with time, they can be reinforced by carbon fibre composite materials. This is performed by gluing epoxy-resin-bound carbon fibre plates (CRP lamellas) directly onto the concrete surface. The result may be impaired if the bond with the actual structure is imperfect. Since such defects cannot be detected from the outside, not all bridge operators have complete confidence in this new reinforcement technique.
BAM´s experts have developed an improved ultrasonic testing method based on a newly designed sensor which can visualize these disturbances in the concrete-lamella-bond. As opposed to the ultrasound echo method used so far, different wave forms are used. A new feature is the use of acoustic waves generated by shear waves (oscillation perpendicular to the direction of wave propagation) which are then changed by the defects and subsequently measured. Bond disturbances exhibit a very clear and typical response signal. The method developed enables the conversion of cavities, cracks or peeling into visible pictures. Thus the new procedure presented here can answer the question whether the concrete and carbon fibre bond is strong enough to safely reinforce a bridge structure.
The method also works for peeling plaster or tiles from non-metallic surfaces such as masonry or concrete. It provides rapid results and is more cost efficient than e. g. active thermography so far used for these kinds of investigation.
Contact:
Dipl.-Ing. Rosemarie Helmerich
Department 8 Non-destructive Testing, Division 8.2 Non-destructive Damage Assessment and Environmental Measurement Methods
Phone: +49 30 8104-3272, email: rosemarie.helmerich@bam.de
Dipl.-Ing Boris Milmann
Department 8 Non-destructive Testing, Division 8.2 Non-destructive Damage Assessment and Environmental Measurement Methods
Phone: +49 30 8104-3236, email: boris.milmann@bam.de
HOMAT-Tribometer II - Herr Reichelt (links) und Herr Mollenhauer (rechts) von der TETRA-Gesellschaft
HOMAT can measure friction and wear of highly stressed components. HOMAT stands for High Frequency Oscillating Material Tests/Material Testers and has been developed and built by BAM along with the project partner TETRA (TETRA Ilmenau – Society for Sensor Technology, Robotics and Automation Ltd.).
At present there are no similar tribological testing instruments on the market capable of providing powerful frequencies beyond an oscillation frequency of 200 Hz like HOMAT. Most oscillation tribometers are limited by the unbalanced mass forces at about 30 to 40 Hz. In particular, the electrical, automotive and turbine construction industries are interested in devices which generate frequencies up to 1000 Hertz and beyond.
Sample movements can now reliably be specified by HOMAT in all frequency ranges up to 1000 Hertz and the measurements are recorded quickly and accurately. An integrated analysis method measures the friction-induced processes as a function of oscillation frequency. As a result, minimal wear of highly stressed components can be determined.
HOMAT offers:
This development closes the gap between currently available tribometers on the market and BAM´s 40-kHz research tribometer.
HOMAT has been sponsored by the support programme of the Federal Ministry of Economics and Technology "Support for Small and Medium Enterprises in the Implementation of Innovations in Measurement, Standards, Testing and Quality Assurance" (MSTQ transfer) financially. TETRA is actively involved and takes care of technology transfer.
Contact:
Dipl.-Ing. Manuel Reichelt
Department 6 Materials Protection and Surface Technologies, Division 6.2 Scanning Probe Microscopy, Tribology and Wear Protection
Phone: +49 30 8104-3551, email: manuel.reichelt@bam.de
High-voltage pylon
The energy debate has moved power transmission networks much closer into the public spotlight. The working group Reliability of Supporting Structures and Risk Assessment has been researching the MOSYTRAF project on wind stress on high-voltage transmission lines since the beginning of 2011. "MOSYTRAF – Monitoring System to Study the Structural Behaviour of Overhead Lines under Wind Gust Stress" has been financed by three transmission network operators: TenneT TSO GmbH, E.ON Netz GmbH and 50 Hertz Transmission GmbH. BAM´s research partner is the Institute for Steel Structures of the Technical University Braunschweig.
The pylons of overhead lines are strongly stressed by wind. In particular, irregular loads due to gusts hinder a safe and economic design of long section overhead lines both when building them anew or when they are being repaired.
MOSYTRAF investigates wind effects using a world-wide unique combination of field measurements, wind tunnel tests and numerical calculations. The results will improve the safety and efficiency of overhead lines.
Both research partners have many years of experience and knowledge of continuous monitoring of structures and the measurement of in-situ wind stresses on structures. This will be used in the development and the forthcoming operation of a monitoring system on an existing overhead line route south of Rostock. The goal is to simultaneously perform continuous measurements and determine the distribution of wind and gust speeds along the overhead lines and the resulting reactions of the structure.
In addition, various wind tunnel tests on conductor cables will be performed in the boundary layer wind tunnel of the Institute for Steel Structures. Based on the measurement data from the wind tunnel tests and field measurements, numerical simulation models will be established which can describe the structural behaviour in the best possible way. These computer models will be used to establish generally accepted design rules for building overhead lines. Thus pylon stresses due to wind effect will be able to be more realistically estimated than has been possible so far.
Contact:
Dr.-Ing. Milad Mehdianpour
Division 7.2 Buildings and Structures, Areas of expertise Structural Reliability and Risk Assessment
Phone: +49 30 8104-1722, email: milad.mehdianpour@bam.de
BAM Newsletter No 3/2011
Submission deadline: 9 June 2011
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