Fatigue Life of Welded High-strength Steels under Gaussian Loads

AbstractWithin the scope of the investigation of welded high-strength steels for application in crane structures, a Gaussian-like test spectrum is derived from an analysis of recorded load time histories. In addition to stress-controlled fatigue tests under constant amplitude loading, the test spectrum is used for the experimental investigation of MAG-welded butt joints and tubular sample components under variable amplitude loading. A linear damage accumulation using Palmgren-Miner-Elementary is conservative for a damage sum of D = 0.5. Application of the theoretical damage sum Dth = 1 results in a closer approximation of the Gaßner-curve. For further improvement of this approximation, a rotation of the calculated Gaßner-curve, i.e. a variable damage sum, is suggested for both butt joints and sample components

New Bainitic Steel for Cyclic Loaded Safety Parts with Improved Cyclic Material Behaviour

AbstractA bainitic forging steel, which enables the TRIP-effect, has been developed and can be used for lightweight-construction for forged components under cyclic loading. The high potential under cyclic loading conditions of the new generation of TRIP forging steels is shown and also the improved results under service loads, especially under overloads and misuse. A comparison of linear damage accumulations by Palmgren-Miner will depict the differences in characteristic damage sums between quenched and tempered and the new bainitic steel.For TRIP steels properties the process parameters are very important. Hence, the influence of the cooling conditions of TRIP will be discussed

Strategic Decision Making in Times of Global Financial Crisis

The presented paper is a brief presentation of findings based on research lead on a group of small and medium businesses. The study has been made in conditions of global financial crisis and its effects, such as fall of production volumes in numerous companies. A number of indexes describing the actual economic situation and short – term prospects of discussed businesses has been presented to their medium- and high level executives in order to point out those most useful when taking strategic decisions. The sample structure consisted of companies with Polish and foreign capital operating locally and internationally. Obtained answers have been grouped in two sets accordingly to the actual situation of a given enterprise. The first group contains indexes preferably used by managers in times of economic instability, whereas the second group shows possible changes in preferences of economic indexes utility in times of prosperity. Research methodology included Delphi method and expert questioning for data gathering and Pareto – Lorenz analysis for interpretation of findings. The study ends with proposals of applications of research outcome into further research directed towards elaboration of a synthetic index facilitating strategic decision making in international companies

Optimizing System Reliability in Additive Manufacturing Using Physics-Informed Machine Learning

Fused filament fabrication (FFF), an additive manufacturing process, is an emerging technology with issues in the uncertainty of mechanical properties and quality of printed parts. The consideration of all main and interaction effects when changing print parameters is not efficiently feasible, due to existing stochastic dependencies. To address this issue, a machine learning method is developed to increase reliability by optimizing input parameters and predicting system responses. A structure of artificial neural networks (ANN) is proposed that predicts a system response based on input parameters and observations of the system and similar systems. In this way, significant input parameters for a reliable system can be determined. The ANN structure is part of physics-informed machine learning and is pretrained with domain knowledge (DK) to require fewer observations for full training. This includes theoretical knowledge of idealized systems and measured data. New predictions for a system response can be made without retraining but by using further observations from the predicted system. Therefore, the predictions are available in real time, which is a precondition for the use in industrial environments. Finally, the application of the developed method to print bed adhesion in FFF and the increase in system reliability are discussed and evaluated

Behavior of Forging Steels under Cyclic Loading — the Benefit of Air‐Hardening Martensites

The development of air‐hardening martensitic forging (LHD: luft härtend duktil) steels offers high material performance with a short and simple process route. In this study, five alloys (L1–L5), based on the existing LHD alloy concept but with different contents of aluminum, titanium, boron, and molybdenum, are cast at laboratory scale. The casted blocks are hot forged into semifinished products and cooled in air (uncontrolled). The tensile properties, the Charpy V‐notch impact energy, the cyclic material behavior, and the fatigue strength of the alloys L1–L5 are opposed to each other. Furthermore, the material properties are compared with the standard quench and tempered (Q+T) steel 42CrMo4 (reference material) and ranked against previously developed forging steels. The tensile properties and Charpy V‐notch impact energy are comparable with those of the reference material, whereas the new alloy concepts show a significantly higher cyclic yield strength and fatigue strength

Optimal tuning of shunt parameters for lateral beam vibration attenuation with three collocated piezoelectric stack transducers

Structural vibration may occur in mechanical systems leading to fatigue, reduced durability or undesirable noise. In this context, shunting piezoelectric transducers to RL-shunts can be an appropriate measure for attenuating lateral beam vibrations. The achieved vibration attenuation significantly depends on an adequate tuning of the shunt to the structural resonance mode. In this paper, an existing method for resonant shunt circuit tuning based on electrical impedances is extended for lateral vibration attenuation of the first mechanical mode of a beam with circular cross-section and three collocated resonantly shunted stack transducers. It is shown by numerical simulation that a presented electrical impedance model including only the first beam mode can be used for the shunt parameter optimization if higher beam modes are taken into account

Entwicklung und Qualifikation modularer Satellitensysteme zur adaptiven Vibrationskompensation an mechanischen Kryokühlern

Ziel der Arbeit ist die Realisierung eines modularen Struktursystems zur aktiv geregelten Minderung charakteristischer Störvibrationen an den Infrarotkameras eines Satelliten. Die Störungen werden durch den dynamischen Betrieb mechanischer Kühlsysteme generiert, die zu einer Anregung der verkoppelten Detektoren und damit einer kritischen Minderung der Aufnahmequalität führen. Die in dieser Arbeit vorgestellte strukturmechanische Lösung basiert auf der aktiven Kompensation der störenden Schwingungen durch Überlagerung gegenphasiger Schwingungen und Generation destruktiver Interferenz. Es werden drei robuste, skalierbare Systeme auf der Basis piezokeramischer Aktuatorik erarbeitet, die dem gestörten Kamerasystem mit nur minimalen konstruktiven Modifikationen und ohne den Bedarf nach startverriegelnden Hilfssystemen ergänzt werden. Die Systemauslegung erfolgt kompatibel zu allgemeinen Raumfahrtanforderungen und berücksichtigt die besonders anspruchsvollen Anforderungen der zugrundeliegenden Kleinsatellitenmission mit stark begrenzten Ressourcen in Bezug auf Masse, Volumen, Energie und Kosten. Die nachgewiesene Vibrationsminderung um 53dB entspricht einer Unterschreitung internationaler Akzeptanzkriterien für residuale Störkräfte an mechanischen Kühlsystemen um mehr als eine Größenordnung, dies bei verbleibenden systemfunktionalen Leistungsreserven. Es erfolgt eine verallgemeinerte experimentelle Systemqualifikation unter Simulation der Start- und orbitalen Betriebsbelastungen nach verschärften Zulassungskriterien der ESA