Volume 56, Issue 7-8

Stress-strain-hysteresis, change in deformation-induced temperature and change in DC-based electrical resistance measurements are applied for the detailed characterization of structural-mechanical processes in construction materials and joints under multiple-step and single-step fatigue loading. Results concerning the influence of joining technologies on austenitic steel AISI304, carbon-fiber reinforced polymers (CFRP) and beech wood materials, of environmental media on magnesium alloys Mg-4Al-2Ba-2Ca (DieMag422) and Mg-10Gd-1Nd, and of manufacturing processes on titanium alloy Ti-6Al-4V and wood-plastic composites (WPC) are discussed. The load- and cycle-dependent change in microstructure was investigated by light and electron microscopy and correlated with fatigue properties, to reach a preferably precise description of process structure property relationship in a qualitative and quantitative manner. The time-efficient load increase procedure applied for evaluation of joining, environmental and manufacturing influence on fatigue performance is suitable for production-accompanied usage.

Kurzfassung Die Sicherheit von Radsatzwellen beruht gegenwärtig auf zwei Säulen: der Schwingfestigkeitsauslegung und periodischen Inspektionen. Ausgehend von einem Schadensfall, der gebrochenen ICE 3-Welle von Köln, 2008, werden ausgewählte Aspekte dieser beiden Säulen diskutiert und Vorschläge zur weiteren Verbesserung gemacht. Diese betreffen u. a. Fragen einer Betriebszeitbegrenzung, Veränderungen der Schwingfestigkeit während des Betriebs infolge von Korrosion und Steinschlag, den Einfluss von Korrosion auf Schwingrissinitiierung und -fortschritt, den potenziellen Einfluss nichtmetallischer Einschlüsse auf die Schwingfestigkeit, die Möglichkeiten, sie im Rahmen der Qualitätssicherung zu detektieren, sowie Fragen der Bruchmechanik und der Zuverlässigkeit zerstörungsfreier Schwingriss-Prüfverfahren im Rahmen eines Konzepts regelmäßiger Inspektionen.

In the present work, a fatigue assessment of the electric motor within the electric axle drive (electric axle) was developed using virtual load data. Now that the electric axle with torque vectoring function has been integrated into multiple vehicle classes, it is possible to create simulation models which allow the drive train to be mapped in various driving scenarios. Validation is performed by means of optical measurement methods (object tracking) which allow to determine load data for subsystems and components under variable torque and speed scenarios (e. g., handling course). In this paper, a load spectrum was created and used for fatigue analysis of the subsystem, namely the traction motor (EM) and torque vectoring motor. Based on the local stress, a finite element analysis (FEA) was carried out on the rotor, and investigations of strength and fatigue were performed on thin sheets of electrical steel. These S-N diagrams consider various factors such as material, temperature, and influence of specimen dimensions and are the basis for fatigue assessment based on the load spectrum from simulation.

Kurzfassung Es werden Teile eines Konzepts zur schichtenweisen Lebensdauerabschätzung von CFK-Laminaten unter Pkw-Betriebslasten vorgestellt. Die Methode basiert auf FEM-Analysen und der klassischen Laminattheorie sowie auf linearer Schadensakkumulation und kann somit in etablierte Prozesse integriert werden. Zur Untersuchung von Versagensmechanismen und Ermittlung der Kennwerte wurden Versuche unter Einstufen- und Kollektivlasten an Faserverbundproben durchgeführt. Die Miner-Regel wird für Zwischenfaserbruch an zwei Beispielen untersucht.

Kurzfassung Zur Betriebsfestigkeitsabsicherung modular aufgebauter Hochvolt-Speicherbatterien kommt bei der Audi AG ein Multilevel-Ansatz zur Anwendung. Ausgehend von Auslegungsforderungen werden die betriebsfestigkeitsrelevanten Belastungen und die daraus resultierenden, mechanischen Beanspruchungen für Batteriesysteme bestimmt. Aus einem Vergleich der Eignung verschiedener Prüfstände folgt die beschriebene Vorgehensweise als Kombination fahrzeugnaher und -ferner Prüfverfahren. Die Rauschprofilableitung aus Fahrzeugmessungen sowie Herausforderungen und Grenzen des Prüfverfahrens werden am Beispiel einer einaxialen Shaker-Prüfung aufgezeigt. Neben der experimentellen Prüfung ist für ein Absicherungskonzept auch eine virtuelle Begleitung durch FEM-Struktursimulationen unerlässlich.

Kurzfassung Der vorliegende Beitrag stellt den derzeitigen Stand einer laufenden Untersuchung zur Schwingfestigkeitsbewertung von Strukturen aus kohlenstofffaserverstärktem Kunststoff (CFK) exemplarisch anhand ausgewählter Laminate vor. Hierbei steht die Anwendbarkeit in den Fahrzeugentwicklungsprojekten im Vordergrund. Zwischen erzielbarer Genauigkeit und dem erforderlichen Aufwand, z. B. für die Gewinnung der Eingangsdaten, ist abzuwägen. Faserverstärkte Kunststoffe zeigen stark anisotropes Verhalten und verschiedene Versagensmechanismen. Die hier beschriebene Methode überträgt für die Beschreibung der statischen Festigkeit verwendete Versagenskriterien auf die Schwingfestigkeit. Die Methode ist in einer Beta-Version in der Software FEMFAT von Magna ECS implementiert und wird derzeit validiert.

Kurzfassung Im Rahmen der technischen Freigabe von Abgasanlagen für Nutzfahrzeuge ist zur Sicherung hoher Zuverlässigkeit ein betriebslastengerechter Nachweis der Lebensdauer der heißgasbeaufschlagten Bauteile er­forderlich. Für diesen Zweck wurden eine Prüfmethodik und ein entsprechender Prüfstand entwickelt. Mit dem neu entwickelten Hot-Shaker-Prüfstand steht ein praxisgerechtes Instrument für den Lebensdauernachweis an NfZ-Abgasanlagen bereit. Fragestellungen zur Modularisierung und Standardisierung von Abgasanlagen und zum Einsatz kostengünstiger Werkstoffe und Fertigungsverfahren können damit effizient bearbeitet werden.

In this study, 7075 aluminum alloy was subjected to triple-aging of retrogression and re-aging (RRA) treatments. The alloy was retrogressed at 220 °C for 60 minutes following the T6 heat treatment and later re-aged at temperatures between 100 °C and 140 °C for 24 hours and at 120 °C for various durations in the range of 15–35 hours. The effects of temperature and duration of re-aging on hardness and the fatigue behaviors of RRA tempered 7075 aluminum alloys were investigated. The results show that temperature and duration of re-aging have an influence on both hardness and fatigue resistances. An increment of the hardness values depends on increasing of re-aging temperature and times until 120 °C and 24 hours and reaches to the maximum value. However, those values decrease with higher re-aging temperatures and longer duration than 120 °C and 24 hours, respectively. On the other hand, in the fatigue tests, the highest fatigue resistance was observed for the sample re-aged at 120 °C for 24 hours, while the sample re-aged at 140 °C for 24 hours showed the longest fatigue life under lower fatigue stress.

A mass balance model has been evaluated that estimates the critical conditions for sustaining continuous crack growth in the mushy weld zone. With the aid of a strain partition model, the critical local strain rate (across the weld) has been related to the critical grain boundary deformation rate needed for crack growth. In the present work, these two models are applied to aluminum welds to investigate the theoretical effects of several metallurgical factors on solidification cracking susceptibility. Calculations quantify the improved cracking resistance associated with a smaller coherent temperature range, grain refinement, high solid fraction at coherency, and rapid development of tensile strength through solid-solid bonding.

High speed steels (HSS) are iron-based alloys containing Fe-C-X where X represents a group of alloying elements which includes Cr, W, Mo, V, and Co, respectively. A major issue associated with these steels is the formation of a network of eutectic phases at the end of solidification. This network, beside the primary MC, which contains austenite and lamellar M 2 C or skeleton M 6 C carbides reduces the toughness and the hardness. In this study a new niobium alloyed HSS is designed that is different from known high speed steels. The objective is to produce cast high speed tool steel without the need for hot working. The microstructure was modified by niobium additions and an optimized heat treatment. Niobium helps to control precipitation of monocarbides from the liquid phase, thus decreasing the formation of brittle interdendritic eutectic carbide films and increasing toughness. Microstructure and mechanical properties of as-cast and heat treated samples of this modified steel were characterized by optical microscopy and scanning electron microscopy with energy dispersive spectroscopy (EDS). Heat treatments were developed to optimize the microstructural and mechanical properties of this niobium alloyed cast high speed steel.

The tradition of discussing the newest achievements in the consideration of NDE reliability was continued with the 5 th European American Workshop on Reliability of NDE (5 th EAW) in Berlin in 2013. The focus of this workshop was to determine the “delta” between the laboratory-like conditions, in which reliability assessments are usually carried out, and the everyday field conditions. Which obstacles need to be still overcome and how do we get closer with our estimations to the real field reliability? With the joint effort of international researchers and in-field practitioners the up-to-date research was presented and discussed, culminating in a half-a-day long “Open Space Technology” discussion. This paper presents the main conclusions of the workshop.

Since the beginnings of the European American Workshops (EAW) in 1997, the aim was to gather the experts in NDE reliability and discuss burning topics with the aim of identifying crucial problems and suggesting ways to move forward. This was usually achieved during the so-called break-out sessions, in which predetermined topics were discussed. During the 5 th EAW, held in Berlin in 2013, this approach was replaced by an Open Space Technology (OST) approach. The benefit of this approach is seen in the freedom of topic choices, i. e., the topics are not predetermined but rather arise at that moment in that space and by the participants’ choice. The following topics arose: new reliability methods (Bayesian, MAPOD, …), structural health monitoring, definition of requirements of NDE by customer versus provider, what value of POD is good enough?, human factors, manual versus automated inspection, and basic concepts of reliability of NDE. The participants were encouraged to walk from one session to another and openly express their opinions. These were in the end summarized by a chosen group of moderators and presented in this paper.

The focus of NDT reliability research in the past was in the field of two high risk industries: (atomic) power plants and aircrafts. The responsible organizations have been well aware of the risks and founded projects to understand and optimize critical steps during production, operation and maintenance. But the use of NDT is not limited to these two fields. The risks during operation of chemical plants, trains or windmills are different from the area above but evident. The coverage by legal regulations is relatively low. Instead of this owner responsibility, product liability and financial issues are the driving forces to do inspections and to use non-destructive testing. The different targets and financial issues influence the practice of NDT-inspections. A survey of this practice and its results are shown.

To draw reliable conclusions from results gained with non-destructive testing methods in civil-engineering (NDT-CE) it is important to know about the quality of results. Since recent times, the POD (probability of detection) according to MIL-HDBK-1823A and Berens Report is established in non-destructive testing in civil engineering (NDT-CE) to assess the reliability of qualitative testing problems. For determining the uncertainty of measurements of quantitative (metric) problems the Guide (Guide to the Expression of Uncertainty in Measurements – GUM) is used in NDT-CE. Now, a new approach is to adapt both methods to get statistically secured measurement results with NDT-CE from existing structures such as prestressed bridges. This paper introduces how calculations based on stochastic models can be used together with NDT-CE results analysed with POD and the Guide.

In this study, the penetration of molten aluminum to alumina-silicate refractory brick with high alumina and cement additive was observed. Brick samples with high alumina content were tempered at 825 °C and fired up to 1350 °C. Corrosion test was applied to sintered samples in order to examine the effects of the molten aluminum containing 5 wt.-% magnesium which is thought to have a high aggression. The achieved structural characteristics were compared with similar types of commercial bricks in order to examine its industrial potential. Physical, analytical, and micro-structural tests were applied and the results are reported.

The influence of different modes and types of electrolytic plasma treatment has been studied regarding the morphology of the structure, the phase composition and the mechanical properties of the surface of 18CrNi3Mo low-carbon steel. It is shown that the result of electrolytic-plasma treatment (EPT) is the formation of a modified layer on the surface. An increase of the surface micro hardness and the wear resistance of the steel samples has been observed. The observed effects may be explained by modification of the surface, i. e., by forming of a modified surface layer with respective reinforcing phases.