Volume 49, Issue 5

Kurzfassung In jüngster Vergangenheit gehäuft auftretende Risse beim Feuerverzinken von großen Stahlkonstruktionen gaben Anlass, die Ursachen und Einflussfaktoren der Rissbildung genauer zu untersuchen. Zielsetzung einer von der Industrie zusammen mit der RWTH Aachen gestarteten Forschungsinitiative ist es, die wirksamen Mechanismen zu klären, die vielfältigen und sich in komplexer Weise beeinflussenden Parameter zu untersuchen, sowie die Einflüsse auf Beanspruchung und Beanspruchbarkeit des Stahls beim Verzinken zu separieren und zu quantifizieren. Es wurde ein neuer, aussagekräftiger Versuch zur Untersuchung der wirksamen Effekte bei der Versprödung von Baustählen durch Angriff aus Zinkschmelzen entwickelt, der den vorherrschenden Spannungs-Dehnungszustand berücksichtigt.

Kurzfassung Lokal auftretende Kerbspannungen stellen eine häufige Ursache für ein Bauteilversagen an Fahrzeugverbindungseinrichtungen dar. Für die Optimierung dieser Schädigungsbereiche finden zur Kosten- und Zeitersparnis zumeist konservative Methoden Anwendung, mit der Folge einer Überdimensionierung an hochbeanspruchten Bereichen. Anhand eines einfachen und dennoch effizienten Verfahrens soll eine ingenieurmäßige Alternative der Kerbformoptimierung zur Erhöhung der Betriebsfestigkeit aufgezeigt werden.

Kurzfassung Mit einer neuartigen Ultraschall-Sensorik ist die differenzierte kontinuierliche Überwachung der Harzaushärtung in der Produktion von Bauteilen aus vernetzten Kunststoffen realisierbar. Der optimale Ablauf dieses Prozesses ist bestimmend für die mechanischen Eigenschaften der Komponenten und ihre Lebensdauer, was insbesondere für deren zunehmenden Einsatz in sicherheitsrelevanten Anwendungen an Bedeutung gewinnt. Die hier eingesetzte Durchschallung des gefüllten Werkzeugs ermöglicht mit der Verfolgung der Schalllaufzeit den direkten Zugriff auf die elastischen Moduli als qualitätsbestimmende Eigenschaften. Die Extremwerte der Ableitung der normierten Laufzeit können direkt für die Prozesssteuerung verwendet werden und haben sich bereits in der industriellen Praxis bewährt.

With the development of ISO 18436 for the training and certification of condition monitoring (CM) personnel, a new level of harmonisation exists between the various CM methods. Methods being covered include vibration analysis (VA), acoustic emission (AE), lubrication management (LM) and infrared thermography (IRT). AE and IRT are methods also specified in some NDT standards such as EN 473 and ISO 9712. With the acceptance of ISO 18436 the world is now experiencing ‘growth pains’ and a confused direction for some trainers and certifying bodies wishing to train candidates and issue certificates of competence to ISO 18436. This paper discusses some of the problems being experienced by certifying bodies and trainers in CM as they struggle to implement ISO 18436. The British Institute of NDT (BINDT) has been in the forefront of development and implementation of qualification and certification systems aimed at conformance to ISO 18436 since 2002. As a result a fully developed certification scheme covering all four CM methods at three levels of competence is now completed and available to industry. This paper offers some insights into the problems that BINDT has overcome — and which others are about to face.

The present study reports dry sliding wear characteristics for cast, homogenized, solution treated, and aged Al-Cu-Mg alloys with four different compositions and different microstructures, aged under same conditions, sliding against C45 steel and a water proof SiC abrasive paper. Al-Cu-Mg alloys, a family of important aluminum alloys, are strengthened by the formation of fine (sub-micron) metastable precipitates. However, their wear characteristics are influenced not only by this precipitation induced hardness, but also by the presence of hard intermetallic particles (constituents) formed during solidification. A series of Al-Cu-Mg alloys with different Cu and Mg contents (namely 8.5 Cu + 1.25 Mg; 7.8 Cu + 1.0 Mg; 7.0 Cu + 0.75 Mg; and 4.5 Cu + 0.0 Mg, in wt. %) were produced and aged under the same conditions. These alloys were solution treated at 520°C for 5 hours, quenched in water at room temperature, and aged at 200°C. A scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) was used to characterize the constituent particles in these samples following heat treatment. The wear behaviour of the aged samples with various contents of Cu and Mg was investigated under dry sliding conditions using a pin-on-disc sliding wear test. The peak age hardness was approximately the same for all alloys examined, although the alloys containing magnesium had slightly higher hardness and were more resistant to over-ageing. With increased alloy content, the wear resistance of samples sliding against C45 steel increased, while the wear resistance of alloys sliding against SiC abrasive paper decreased. For the case of the steel wear surface, the improved aluminium wear resistance coinsides with increased amounts (expected) of eutectic constituent with alloy content. For the case of the SiC abrasive paper, the loss in wear resistance is related to the loss (i.e. pull-out) of Al-Cu-Mg particles during the test.

The eddy current skin-effect limits the detection of subsurface defects and the range of thickness measurement. Traditional concepts to estimate the penetration depth basing on plane wave propagation into a conducting halfspace cannot describe the real depth of inspection achievable by state-of-the-art sensors and instruments. The paper presents a more fruitful concept for estimating the noise limited inspection depth. Here, the traditional parameters like frequency, probe dimensions, conductivity and permeability are analysed in combination with all sources of noise and disturbances in eddy current technique. New low frequency eddy current probes of inductive and magneto-resistive type are presented and characterised. These probes combine deep penetration with comparatively small size and good spatial resolution.

The behaviour of fullerenes (mostly the C 60 and C 70 ) in a radical polymerization and during thermal/thermo-oxidative degradation of polymers is considered. The analysis of literature material clearly shows that fullerenes preferably act as scavengers of carbon-centered free radicals, and therefore they appear to be inhibitors for the radical polymerization and stabilizers for polymer materials. No distinct indication of any proved active or specific role for oxygen-centered radicals has been specified. As carbon nanotubes (CNTs) have electron affinities similar to those of fullerenes, and might therefore also be predicted to behave as radical traps in chain reactions such as polymerization and thermal degradation of polymers as well.