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Organisationseinheit der BAM
- 7 Bauwerkssicherheit (86)
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- 7.6 Korrosion und Korrosionsschutz (31)
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- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (19)
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- 2.1 Sicherheit von Energieträgern (8)
Eingeladener Vortrag
- nein (138)
The attenuation of wave amplitudes is ruled by the planar, cylindrical or spher-ical geometry of the wave front (the geometric or power-law attenuation) but also by the damping of the soil (an exponential attenuation). Several low- and high-frequency filter effects are derived for the layering and the damping of the soil, for the moving static and the distributed train loads and for a homoge-neous or randomly heterogeneous soil. Measurements of hammer- and train-induced vibrations at five sites have been analysed for these attenuation and filter effects. The measured attenuation with distance can be discribed by gen-eralised power laws and some reasons will be discussed. The theoretical filter effects can well be found in the measurements.
A few layer/multilayer graphene (MLG) with a specific surface area of BET=250 m2/g is proposed as an efficient multifunctional nanofiller for rubbers. The preparation method, i.e., ultrasonically-assisted solution mixing of master batches followed by two-roll milling, strongly influences the dispersion in the elastomeric matrix and is fundamental for the final properties. When homogenously dispersed, single stacks of only approximately 10 graphene sheets, with an aspect ratio of 34, work at low loadings, enabling the replacement of large amounts of carbon black (CB), an increase in efficiency, and a reduction in filler load. The appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing, gas barrier properties, electrical and thermal conductivity, as well as mechanical properties of different rubbers, as shown for chlorine-Isobutylene-Isoprene rubber (CIIR), nitrile-butadiene rubber (NBR), natural rubber (NR), and styrene-butadiene rubber (SBR). 3 phr of MLG tripled the Young’s modulus of CIIR, an effect equivalent to 20 phr of CB. The stronger interactions between MLG and NR or SBR also resulted in a reduction in the elongation at break by 20% and 50%, respectively, while the same parameter was hardly changed for CIIR/MLG and NBR/MLG. CIIR/MLG and NBR/MLG were stiffer but just as defomable than CIIR and NBR. The strong reinforcing effect of 3 phr MLG was confirmed by the increase of greater than 10 Shore A in hardness. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards flammability, the latter shown by the reduction in heat release rate in the cone calorimeter. We investigated MLG also as a synergist for reducing the aluminium trihydrate loading in flame retardant hydrogenated acrylonitrile-butadiene (HNBR), polybutadiene chloroprene (BR/CR), and chlorosulfonated polyethylene rubber(CSM). The higher the nanofiller concentration is, the greater the improvement in the properties. For instance, the permeability decreased by 30% at 3 phr of MLG, 50% at 5 phr and 60% at 10 phr, respectively. Moreover, the MLG nanocomposites improve stability of mechanical properties against the effects of weathering. In key experiments an increase in UV-absorption and a pronounced radical scavenging were proved as stabilizing mechanisms. In a nutshell, MLG is an efficient multifunctional nanofiller ready to be used for innovative rubber development.
To prevent future alkali-aggregate reaction (AAR) damage, which has occurred frequently in the German highway network in recent years, a new regulation has been drafted. This regulation severely limits the use of alkali-sensitive aggregates by requiring that their suitability be verified by certified inspectors using newly developed AAR concrete tests that involve the external supply of alkali. This has led to a significant limitation in the number of aggregates usable for concrete pavements. A novel AAR avoidance strategy is now being pursued, which aims to enable the use of borderline alkali-sensitive aggregates through the application of an internal water-repellent treatment. The addition of water repellents during concrete production should significantly reduce the ingress of water and external de-icing salts into the concrete pavement, thus reducing the potential for AAR damage. This paper presents the results of laboratory tests to assess the suitability of this new AAR prevention strategy. Representative, highly AAR-susceptible road paving concrete made with an alkali-sensitive greywacke and various water repellents were used as the basis for these experiments. The tests for concrete suitability included determining the conventional fresh and hardened concrete properties as well as concrete prism tests with external alkaline supply. Building on these results, laser-induced breakdown spectroscopy (LIBS) analyses of de-icing-salt intrusion as well as microscopic examinations for verification of the AAR characteristics were carried out. The results of the AAR concrete tests with external alkaline supply support the conclusion that, when hydrophobic agents containing a suitable active ingredient are used, the AAR damage process in road paving concrete can be sufficiently prevented.
We present our achievements in the development of distributed fiber optic sensing systems based on Brillouin optical frequency-domain analysis for structural health monitoring. The focus of the applications is on the gapless monitoring of geotechnical structures, large area infrastructures and electrical grids. The work includes the latest use of machine learning algorithms to reduce measurement time by coexistent increasing the measurement accuracy.
Der Vortrag beleuchtet die Schnittstelle zwischen Chemikalienrecht und Störfallrecht. Der Hintergrund, die Struktur und wichtige Eckpunkte der CLP-Verordnung werden vorgestellt. Instrumente und Beispiele zur Verifizierung von Einstufungen nach CLP im Hinblick auf die Anwendung unter der Seveso-Richtlinie bzw. der Störfallverordnung werden erläutert. Außerdem werden mögliche Konsequenzen für Änderungen im Anwendungsbereich der Seveso-Richtlinie besprochen.
Durch das alkalische Porenwassermilieu ist Stahl im Beton vor Korrosion geschützt. Unter ungünstigen Umgebungsbedingungen (Karbonatisierung, Chlorideintrag) kann die passive Deckschicht auf der Stahloberfläche zerstört werden. Im weiteren Verlauf können sich korrosionsbedingte Folgeschäden, wie Risse und Abplatzungen am Bauwerk ergeben. Um notwendige Sanierungsmaßnahmen sind frühzeitige und weitgehend zerstörungsfrei ermittelte Informationen über das aktuelle Korrosionsverhalten der Stahlbewehrung von großer Bedeutung. Die Potentialfeldmessung ist ein etabliertes und weit verbreitetes Verfahren zur Beurteilung des Korrosionszustandes der Bewehrung in Stahlbetonbauwerken. Mit Hilfe dieses Verfahrens können Bereiche aktiv korrodierender Bewehrung zerstörungsfrei lokalisiert werden. In der Regel kommt diese Messmethode bei der Detektion chloridinduzierter Korrosion zum Einsatz
The mechanical and geometrical properties of impact targets greatly influence the outcome of a drop test. The International Agreement concerning the International Carriage of Dangerous Goods by Road (ADR) as well as ISO 2248 describe the characteristics of impact targets for drop tests of dangerous goods packagings.
According to these regulations, the impact target’s surface needs to be unyielding, under testing conditions non-deformable, flat, and integral with a mass at least 50 times that of the heaviest packaging to be tested. The problem is that many production facilities, especially manufacturers of corrugated fibreboard boxes, do not have their own testing device with the required 50 times mass ratio of the impact target for a regulation compliant drop test during series production. Furthermore, at UN level it is considered necessary to revise these requirements.
In the present paper, the impact target requirements are examined in detail and compared with those in other technical areas (e.g., impact target for container for the transport of radioactive materials). A research method is being developed to investigate the dependency between the mass ratio of the packaging and the target as well as the damage resistance of a drop tested package in relation to specific design characteristics. The results are of high relevance for industry purposes and intended to ensure a uniform level of safety assessment for the mechanical testing of dangerous goods packagings.
Multiscale modeling of heterogeneous structures based on a localized model order reduction approach
(2022)
Many of today’s problems in engineering demand reliable and accurate prediction of failure mechanisms of mechanical structures. Herein, it is necessary to take into account the heterogeneous structure on the lower scale, to capture the underlying physical phenomena. However, this poses a great challenge to the numerical solution as the computational cost is significantly increased by resolving the lower scale in the model. Moreover, in applications where scale separation as the basis of classical homogenization schemes does not hold, the influence of the lower scale on the upper scale has to be modelled directly. This work aims to develop an efficient concurrent methodology to model heterogeneous structures combining the variational multiscale method (VMM) [1] and model order reduction techniques (e. g. [2]). First, the influence of the lower scale on the upper scale can be taken into account following the additive split of the displacement field as in the VMM. Here, also a decomposition of the global domain into subdomains, each containing a fine grid discretization of the lower scale, is introduced. Second, reduced approximation spaces for the upper and lower scale solution are constructed by exploring possible solutions for each subdomain based on a representative unit cell. The local reduced spaces are designed such that local contributions of each subdomain can be coupled in a conforming way. Thus, the resulting global system is sparse and reduced in size compared to the direct numerical simulation, leading to a faster solution of the problem. The authors gratefully acknowledge financial support by the German Research Foundation (DFG), project number 394350870, and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC Grant agreement No. 818473).
There is a rising attention of using numerical models for effcient structural monitoring and ensuring the structure's safety. Setting up virtual models as twin for real structures requires a model identification process calculating the unknown model parameters, which mostly are only indirectly measurable. This is a computationally very costly inverse optimization process, which often makes it unfeasible for real applications. Effcient surrogate models such as reduced order models can be used, to overcome this limitation. But the influence of the model accuracy on the identification process has then to be considered. The aim is to automatically control the influence of the model's accuracy on the identification. Here, a variational Bayesian inference approach[3] is coupled with a reduced forward model using the Proper Generalized Decomposition (PGD) method. The influence of the model accuracy on the inference result is studied and measured. Therefore, besides the commonly used Bayes factor the Kullback-Leibler divergences between the predicted posterior pdfs are proposed. In an adaptive inference procedure, the surrogate's accuracy is iteratively increased, and the convergence of the posterior pdf is analysed. The proposed adaptive identification process is applied to the identification of spatially distributed damage modeled by a random eld for a simple example with synthetic data as well as a small, reinforced bridge with real measurement data. It is shown that the proposed criteria can mirror the influence of the model accuracy and can be used to automatically select a suffciently accurate surrogate model.
PGD model with domain mapping of Bead-on-Plate weld simulation for wire arc additive manufacturing
(2022)
Numerical simulations are essential in predicting the behavior of systems in many engineering fields and industrial sectors. The development of accurate virtual representations of actual physical products or processes allows huge savings in cost and resources. In fact, digital twins would allow reducing the number of real, physical prototypes, tests, and experiments, thus also increasing the sustainability of the production processes and products’ lifetime. Standard numerical methods fail in providing real time simulations, especially for complex processes such as additive manufacturing applications.
This work aims to build up a reduced order model for efficient wire arc additive manufacturing simulations by using the proper generalized decomposition (PGD) [1,2] method. Model order reduction is a popular concept to decrease the computational effort, where each evaluation of the reduced forward model is faster than evaluations using classical methods, even for complex models. The simulation of a moving heat source leads to a hardly separable parametric problem, which is solved by a new mapping approach [3]. Using this procedure, it is possible to create a simple separated representation of the forward model.
In this contribution, a PGD model is derived for the first part of wire arc additive manufacturing: bead-on-plate weld. An excellent agreement with a standard finite element method is shown. The reduced model is further used in a model calibration set up, speeding up calibrations and ultimately leading to an optimized real-time simulation.
Prüfung von Spannstählen
(2022)
Ein Stand zum WIPANO-Projekt Spannstahlsicherheit wurde auf Anfrage in einer Gemeinschaftssitzung des AK "Eisen und Stahl" sowie des AK "Korrosionsuntersuchung und -überwachung" der Gesellschaft für Korrosionsschutz e.V. (GfKORR) präsentiert. Das Projekt hat die Verbesserung der produktspezifischen Prüfnorm ISO 15630-3 als Ziel. Vorgestellt wurden die Wahl der neu entwickelten Wasserstoffbeladung mit galvanostatischer kathodischer Polarisation und die Frage, ob die Prüfung an Lieferoberflächen sinnvoll ist.
To ensure safety when transporting dangerous goods, it is important to specify the flow properties of the respective solid filling substance of the packagings. For this purpose, the angle of repose is currently used for the UN approvals in Germany. Measurements were carried out on 12 powdery or granular substances applying the angle of repose measuring methods customary in the test centres. The results of the methods differ significantly from each other. In addition, some of the techniques cannot be applied for very cohesive or coarse-grained materials. The results for the angle of repose show a strong scatter for some constellations (coefficient of variation more than 20 %). Safety during transport of dangerous goods cannot be guaranteed with this currently practiced system of measuring the angle of repose. As a consequence, an alternative parameter to characterize the flow properties of bulk materials should be used in the recognized test centers for dangerous goods packagings, such as the Hausner ratio. This approach leads to more precise test results for the substances examined (maximum coefficient of variation 2.8 %). It also has advantages in terms of applicability and occupational safety.
Since the flow properties are safety-relevant, both in terms of mechanical safety and safety against the release of dangerous substances, the testing practice in the recognized test labs should be improved and standardized.
Hersteller von Geräten für den bestimmungsgemäßen Gebrauch in explosionsfähigen Bereichen müssen, wenn sie unter die Richtlinie 2014/34/EU fallen, für das Inverkehrbringen in EU-Mitgliedsstaaten eine Konformitätsbewertung durchführen. Dazu gehört eine Zündgefahrenbewertung, bei der auch nichtelektrische Zündquellen betrachtet werden müssen, zu denen die mechanischen Schlagvorgänge gehören.
Bei dieser Zündquellenart kommt es infolge eines Schlages und/oder Reibens eines Bauteils auf ein anderes zu einer Energieumwandlung. Dadurch kommt es zu einer Temperaturerhöhung an der Kontaktstelle sowie unter Umständen zu einem Abtrennvorgang kleiner Partikel erhöhter Temperatur. Sowohl die heißen Reibflächen als auch die abgetrennten Partikel stellen potentielle Zündquellen explosionsfähiger Atmosphären dar.
Edelstahl ist für Geräte für die Verwendung zum bestimmungsgemäßen Gebrauch im explosionsgefährdeten Bereich insbesondere in der Chemie ein wichtiger Konstruktionswerkstoff.
Die Ergebnisse des Forschungsprojektes "Entwicklung normativer Anforderungen an explosionsgeschützte nichtelektrische Geräte resultierend aus der Zündfähigkeit mechanisch erzeugter Schlagfunken (NAMES)" zeigen, dass Schlagvorgänge mit Edelstählen eine erhebliche Zündgefahr von explosionsfähigen Brenngasgemischen darstellen können. Dabei bestehen jedoch mitunter deutliche Unterschiede zwischen den verschiedenen Brenngasgemischen. Besonders hohe Zündwahrscheinlichkeiten konnten bei Brenngasgemischen mit Brenngasen der IEC-Explosionsgruppe IIC beobachtet werden, die Acetylen bzw. Wasserstoff als Brenngas enthielten. Schläge im Wasserstoff/Luft-Gemisch waren dabei jedoch bedeutend zündwirksamer. In diesem Gasgemisch konnte bei niedrigen maximalen Schlagenergien bis 60 J sogar eine mitunter höhere relative Zündhäufigkeit beobachtet werden als bei Versuchen mit unlegiertem Baustahl.
Due to the corrosion resistance of carbon steel, bridge constructions are currently protected against corrosion by applied coating systems. These coating systems need to be renewed after approximately 25 50 years. Galvanized constructions without any welding areas at the construction site could be prepared as grouted joints and can be used without any renewing for about 100 years.
Surface applied corrosion inhibitors (SACI) are widely used to mitigate corrosion process of steel reinforcement in concrete. But they remain controversial as to their effectiveness and the ability to compare materials from different manufacturers
and technologies. They are applied onto the surface of
hardened concrete and penetrate towards steel reinforcement. This paper discusses the corrosion inhibition performances of
dual-phase surface applied corrosion inhibitor and the efficiency of the corrosion inhibitor is assessed by selected testing procedures in BAM laboratories.
In the recent years, more and more products in construction and automotive industry are bonded by adhesive tapes instead of mechanical fasteners but there is no sufficient understanding of how these bonded, layered materials behave in fires. Our research project gives an insight of how adhesives and substrates interact with each other in different fire scenarios and how flame retardants function in pressure sensitive adhesive (PSA) tapes. A systematic investigation on the burning behavior of PSA tapes as free-standing films, as top layers on different substrates and as sandwich-like adhesive joints was performed. The burning behavior of free-standing PSA tapes and those used as a coating was significantly improved by using phosphorus-based flame retardants. Furthermore, it was shown that, depending on tape structure and substrate, the PSA tape can lower the fire risk by acting as an intermediate protection layer in bonded materials.
Numerical models are an essential tool in predicting and monitoring the behavior of civil structures. Inferring the model parameters is a challenging tasks as they are often measured indirectly and are affected by uncertainties. Digital twins couple those models with real-world data and can introduce additional, systematic sensor uncertainties related to the sensor calibration, i.e. uncertain offsets and calibration factors.
In this work, the challenges of data processing, parameter identification, model selection and damage detection are explored using a lab-scale cable stayed bridge demonstrator. By combining force measurements in the cables with displacement measurements from both laser and stereo-photogrammetry systems, the elastic parameters of a three-dimensional finite element beam model are inferred.
Depending on the number of sensors and the number of datasets used, parametrizing the sensor offsets and factors, leads to model with over 100 parameters. With a real-time solution of the problem in mind, a highly efficient analytical variational Bayesian approach is used to solve it within seconds. An analysis of the required assumptions and limitations of the approach, especially w.r.t. to the computed evidence, is provided by a comparison with dynamic nested sampling in a simplified problem.
Finally, by inferring the value of additional damage parameters along the bridge, the method is successfully used to detect the location of an artificially introduced weak spot in the demonstrator bridge.
Self-ignition Behaviour of Bulk Materials: How Reliable is the Extrapolation of Laboratory Tests?
(2022)
The self-ignition behaviour of bulks is usually determined with the aid of isoperibolic or adiabatic hot storage tests; the sample volumes here are typically in the range of approx. 100 cm³ to several litres. The extrapolation to technically relevant volumes holds, however, considerable uncertainties. To reduce these uncertainties, a test stand was set up that allows to investigation sample sizes of up to 1000 dm³. These allow the study of selfignition behavior closer to the conditions that prevail in practice. The suitability (or unsuitability) of the established methods (including dangerous goods classification tests) were to be demonstrated and influencing variables that cannot be measured on a laboratory scale were to be determined.
In addition, various analytical methods were used for the determination of reaction kinetic data of solid bulk materials and to predict the self-ignition behaviour of large storages. These are thermal analyses such as differential scanning calorimetry DSC, simultaneous thermal analysis STA as well as microcalorimetry for highprecision measurement of heat flows.
Complete test series using all mentioned test methods will be presented for crosslinked polyvinyl-pyrrolidone (PVP) and conclusions regarding the applicability of the extrapolation methods will be discussed. Hot storage tests up to semi-industrial scale and their combination with various thermoanalytical methods allow a much more precise prediction of the self-ignition behaviour of large bulks. A further promising approach to estimate their heat release rates, and hence, the risk of self-ignition under technical conditions, is the use of microcalorimetric methods.
Fugenfüllungen im kommunalen Stadtstrassenbau unterliegen besonderen mechanischen Beanspruchungen. Hier kommt es bereits bei der Planung darauf an, Fugenausführungen und insbesondere Fugenfüllstoffe bewusst nach ingenieurtechnischen Gesichtspunkten auszuwählen. Dazu ist das ingenieurtechnische Verständnis der relevanten Fugenfüllstoffe - Funktionsweise, Leistungskriterien, Prüfungen, Dauerhaftigkeit - von entscheidender Bedeutung. Der Vortrag erläutert nicht nur die maßgebenden Fugenfüllstoffe unter den vorgenannten Schwerpunkten, sondern stellt auch das Verständnis zu den Rahmenbedingungen, Grundlagen und Wirkmechanismen des entsprechenden technischen Regelwerkes her. Neueste Entwicklungen werden den Praxisvertretern näher gebracht und erläutert. Die Zusammenhänge und Strategien zur Weiterentwicklung der „Betonstrasse der Zukunft“ werden diskutiert und dargestellt.
There are several standardized ignition sources in use for the determination of explosion characteristics of gases, vapors and dusts. In the standards the ignition source is stated, but they vary in stating other characteristics like burning duration, energy or burning volume. Since heat is not visible under normal circumstances a Schlieren-Technique was used to make the full heating volume and not just the flames visible. While an earlier paper of the authors focused on the ignition energy and burning duration of four standardized ignition sources, this paper focuses on the initial igniting volume, the ratio between initial igniting volume and the test-vessel size and other phenomena that were observed with the Schlieren-Technique.