Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Eingeladener Vortrag
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Automotive engine lubricants
(2019)
In 2003, ASTM Manual 37, Fuels and Lubricants Handbook: Technology, Properties, Performance and Testing, featured a chapter discussing automotive lubricants, including engine oils, automatic transmission fluids, manual transmission fluids, gear lubricants, and greases. This chapter, by Schwartz, Tung, and McMillan, surveyed all of these classes of lubricants, up to its publication in 2003.
More recently, the period between 2003 and 2010 has been addressed as part of a book copublished by ASTM and SAE International (coeditors Simon Tung and George Totten), where Fox surveyed the development of engine oil specifications that emerged during those years.
This chapter surveys the evolution of engine oil design and testing since 2002 and concludes with insights into future directions offered by recent tribological research. Our objective is to provide a reader new to the field with an understanding of the following:
- Engine oil composition and formulation
- North American engine oil specification development, and an outline of emergent European specifications
- How emergent specifications and legislative requirements are linked to the introduction of new engine hardware
- How tribological innovation can contribute to future enhancements in engine efficiency
In parallel, we will provide several tables comparing groups of contemporaneous specifications.
Additive Manufacturing (AM) in terms of laser powder-bed fusion (L-PBF) offers new prospects regarding the design of parts and enables therefore the production of lattice structures. These lattice structures shall be implemented in various industrial applications (e.g. gas turbines) for reasons of material savings or cooling
channels. However, internal defects, residual stress, and structural deviations from the nominal geometry are unavoidable.
In this work, the structural integrity of lattice structures manufactured by means of L-PBF was non-destructively investigated on a multiscale approach.
A workflow for quantitative 3D powder analysis in terms of particle size, particle shape, particle porosity, inter-particle distance and packing density was established.
Synchrotron computed tomography (CT) was used to correlate the packing
density with the particle size and particle shape. It was also observed that at least about 50% of the powder porosity was released during production of the struts.
Struts are the component of lattice structures and were investigated by means of laboratory CT. The focus was on the influence of the build angle on part porosity and surface quality. The surface topography analysis was advanced by the quantitative characterisation of re-entrant surface features. This characterisation was compared with conventional surface parameters showing their complementary
information, but also the need for AM specific surface parameters.
The mechanical behaviour of the lattice structure was investigated with in-situ CT under compression and successive digital volume correlation (DVC). The Deformation was found to be knot-dominated, and therefore the lattice folds unit cell layer wise.
The residual stress was determined experimentally for the first time in such lattice structures. Neutron diffraction was used for the non-destructive 3D stress investigation. The principal stress directions and values were determined in dependence of the number of measured directions. While a significant uni-axial stress state was found in the strut, a more hydrostatic stress state was found in the knot. In both cases, strut and knot, seven directions were at least needed to
find reliable principal stress directions.
Predictive Methods for Determining the Thermal Decomposition Properties of Hazardous Substances
(2019)
Due to the fast development and availability of computers, predictive approaches are increasingly used in the evaluation process of hazardous substances complementary to experiments. Their use was recommended as alternative to experimental testing by the REACH regulation to complete the lack of knowledge on properties for existing substances that must be registered before 2018 (upon quantities). Among the proposed predictive approaches, Quantitative Structure Property Relationships (QSPR) are powerful methods to predict macroscopic properties from the only molecular structure of substances. In that context, the HAZPRED project (2015-2018, founded by the SAF€RA consortium) aims to develop theoretical models (e.g. QSPR) and small-scale tests to predict complex physico-chemical properties (e.g. thermal stability, explosivity) of hazardous substances to complete the lack of knowledge on these hazardous substances quickly or to understand their decomposition behaviour better. In particular, this contribution will present the work done in this project on the physical hazards of organic peroxides and self-reactive substances: gathering of existing experimental data, new experimental campaigns, review of existing models and proposition of new estimation methods.
The determination of mechanical properties of welded Steel structures such as strength or ductility is a subject of high interest for the majority of Companies in the area of metal Processing. The material Parameters can be obtained by performing the tensile test on the samples made from a part of a component. In some cases, it is highly expensive to produce the tensile specimens especially from the weld metal, which contains different type of microstructure such as weld seam or heat affected zone in an extremely small area. Therefore, a method is described in this paper to determine the material Parameters of high strength Steel structures and welded joints locally and without any additional effort to perform the tensile test. In this method, instrumented indentation technique (IIT), an indenter is pushed on the flat surface of a specimen in a certain period of time and simultaneously the applied force and the corresponding indentation path are measured. The data related to the force-indentation diagram is given as input to an artificial neural network (ANN) to obtain the material Parameters. The ANN can be trained by generating the large qualitative data sets with numerical Simulation of the IIT procedure. The Simulation must be run several times with the different material model parameter sets to generate the numerous
force-indentation diagrams as the inputs of ANN. Then, the trained ANN is validated by performing the IIT on the welded joints and comparing the obtained material Parameters from ANN with the tensile test.
Consequently, the mechanical properties of welded joints can be determined by performing the IIT and evaluating the resulting data by the ANN.
To increase the competitiveness of jacket substructures compared to monopiles a changeover from an individual towards a serial jacket production based on automated manufactured tubular joints combined with standardized pipes has to be achieved. Therefore, this paper addresses fatigue tests of automatically welded tubular X-joints focusing on the location of the technical fatigue crack. The detected location of the technical crack is compared to numerical investigations predicting the most fatigue prone notch considering the structural stress approach as well as the notch stress approach. Besides, the welding process of the automated manufactured tubular X-joints is presented.
Computational methods for lifetime prediction of metallic components under high-temperature fatigue
(2019)
The issue of service life prediction of hot metallic components subjected to cyclic loadings is addressed. Two classes of lifetime models are considered, namely, the incremental lifetime rules and the parametric models governed by the fracture mechanics concept. Examples of application to an austenitic cast iron are presented. In addition, computational techniques to accelerate the time integration of the incremental models throughout the fatigue loading history are discussed. They efficiently solve problems where a stabilized response of a component is not observed, for example due to the plastic strain which is no longer completely reversed and accumulates throughout the fatigue history. The performance of such an accelerated Integration technique is demonstrated for a finite element simulation of a viscoplastic solid under repeating loading–unloading cycles.
Dissolved water has major impact on the physical and chemical properties of phosphate glasses. In the present study we have investigated the structural response to water incorporation for glasses in the system Li2O–MgO–Al2O3–P2O5.
Glasses containing 0–8 wt% H2O were synthesised at 500 MPa confining pressure in internally heated gas pressure vessels at 1323 K (LMP, Al-poor glass) and 1423 K (LMAP, Al-enriched glass). Water contents of glasses were determined by pyrolysis and subsequent Karl-Fischer titration (KFT) and/or by infrared spectroscopy. Density varies nonlinearly with water content implying large structural changes when adding up to 2 wt% H2O to the dry glass. Glass Transition temperatures measured by differential thermal analysis (DTA) continuously decrease with water content. The trend can be explained by depolymerisation of the phosphate network. Near-infrared spectroscopy shows that even in Al poor glasses only a minority of dissolved water is present as H2O molecules, but the largest amount is present as OH Groups formed by hydrolysis of P–O–P bonds. The network is stabilised by aluminium which is predominantly six-coordinated in these glasses as shown by 27Al MAS NMR spectroscopy. With increase of Al in the glasses, breaking up of the Phosphate network through hydrolysis is depressed, i.e. much lower OH Contents are formed at same total water content.
Network depolymerisation upon addition of H2O is evident also from 31P MAS NMR spectroscopy. While Phosphate tetraheda are crosslinked by two to three bridging oxygen in dry glasses, diphosphate Groups are dominant in glasses containing 8 wt% H2O.
Chemical effects during the formation of femtosecond laser-induced periodic surface structures
(2019)
The processing of laser-induced periodic surface structures (LIPSS, ripples) on metals and semiconductors in ambient air is usually accompanied by superficial oxidation effects – a fact that is widely neglected in the current literature. In this contribution, chemical, structural, and mechanical alterations in the formation of femtosecond LIPSS are characterized by a variety of surface analytical techniques, including energy dispersive X-ray analyses (EDX), X-ray photoelectron spectroscopy (XPS), micro Raman spectroscopy (µ-RS), and depth-profiling Auger electron microscopy (AEM). Alternative routes of electrochemical and thermal oxidation allow to qualify the relevance of superficial oxidation effects on the tribological performance in oil lubricated reciprocating sliding tribological tests (RSTT). It is revealed that the fs-laser processing of near-wavelength sized LIPSS on metals leads to the formation of a few hundreds of nanometers thick graded oxide layers, consisting mainly of amorphous oxides. Regardless of reduced hardness and limited thickness, this nanostructured surface layer efficiently prevents a direct metal-to-metal contact in the RSTT and may also act as an anchor layer for specific wear-reducing additives contained in the used engine oil.
Mechanochemistry is increasingly used for synthesizing soft matter materials including metal organic compounds and cocrystals. The ever-increasing interest in this method is contrasted by a limited mechanistic understanding of the mechanochemical reactivity and selectivity. Time-resolved in situ investigations of milling reactions provide direct insights in the underlying mechanisms. We introduced a setup enabling in situ investigation of mechanochemical reactions using synchrotron XRD combined with Raman spectroscopy. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structure and thus obtaining reliable data for mechanistic studies. We discuss our recent results investigating the formation of (polymorphic) cocrystals. First investigations of a mechanochemical synthesis under controlled temperature which allow determining the activation barrier are presented.6 Furthermore, X-ray diffraction and in situ Raman spectroscopy coupled with thermography revealed a low temperature increase during milling reactions due to the mechanical impact and clear temperature increases as a result of the reaction heat. Our results indicate that in situ investigation of milling reactions offer a new approach to tune and optimize mechanochemically synthesized compounds.
Virtual-lab-based determination of a macroscopic yield function for additively manufactured parts
(2019)
This work aims for a yield function description of additively manufactured parts of S316L steel at the continuum-mechanical macro-scale by means of so-called virtual experiments using a crystal plasticity (CP) model at meso-scale. Additively manufactured parts require the consideration of the specific process-related microstructure, which prevents this material to be macroscopically treated as isotropic, because of crystallographic as well as topological textures. From virtual experiments, yield loci under various loading conditions are simulated. The scale bridging from meso- to macro-scale is realised by the identification of the simulated yield loci as a modified anisotropic Barlat-type yield model representation.