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In this project, the transfer of material and computational models to a different material class, i. e. to an austenitic cast iron with spherical graphite, was studied to predict the lifetime of exhaust turbocharger hot parts under TMF load. Therefore, the alloy EN-GJSA-XNiSiCr35-5-2 (Ni-Resist D-5S) was chosen. Firstly, an experimental database was established for this material because it was insufficient at the beginning of the project. Tensile, creep, LCF and TMF tests were carried out, which served the calibration of the models. The TMF tests were used to validate the deformation model.
The investigated material showed a strongly deviating behavior under TMF conditions compared to the ferritic SiMo alloys investigated in the previous project: Ni-Resist exhibited a comparable strength under OP- and IP-TMF loading, while the ferritic alloys showed a distinct higher strength under IP-TMF load. Evidence for creep damage was found for Ni-Resist with increasing temperatures and hold times under tensile load. This is also a distinct difference to the SiMo alloys.
The stress-strain behavior of the LCF and TMF tests is well described by the model for the new material in most cases. The same is true for the lifetime prediction, which is within a factor of two, except for 900 °C. The model was verified by a thermal shock test of an exhaust man-ifold. The aim of the simulation was in particular to predict the crack locations. An accurate prediction of the cycle number was not expected, as the component is afflicted with a casting skin, while the test pieces were not. The predominant number of experimentally determined locations were predicted.
A fundamental objective of this project was to study the effect of HCF vibrations on the TMF lifetime experimentally in further detail and to extend the existing lifetime model to account for superimposed HCF load. In a first step, the database of the previous project based on SiMo 4.05 was considerably extended to determine the different influencing parameters. A proce-dure was developed which reproduces the lifetime reduction by the superimposed HCF vibra-tions during a TMF cycle. It is assumed that the superimposed HCF load accelerates the crack propagation considerably after exceeding a certain crack length. The time when the accelera-tion occurs, is significant for the lifetime reduction. This approach allows predicting the lifetimes in good agreement with the experiments for both materials.
A few Aspects of the Current Understanding of DPF Materials Thermal and Mechanical Properties
(2016)
Bi-continuous porous ceramics for filtration applications possess a particularly complicated microstructure, whereby porosity and solid matter are intermingled. Moreover, they very often display a microcrack network, resulting from the strong anisotropy of the microscopic coefficient of thermal expansion (CTE). Mechanical, thermal, and filtration properties, they all strongly depend on the morphology of both solid matter and porosity, and on the degree of microcracking (also, the microcrack density), which is in its turn tightened to the grain size.
Recent industrial and academic research has enormously progressed in understanding the microstructure-property-performance relationships existing in these complicated materials:
- Using 3D computed tomography (CT) at different resolutions, and several X-ray refraction-based techniques, porosity and pore orientation could be quantitatively evaluated (in the example of cordierite).
- Neutron and X-ray Diffraction has been instrumental to disclose a) the non-linear character of the stress-strain response, and b) the negative CTE of these materials, and its consequences on the materials properties;
- Analytical and numerical models have been elaborated to rationalize these behaviours in terms of microcracking and microstructural features.
Here these results will be reviewed, and a outlook at (some of the) outstanding problems will be given.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread holds equally for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated.
The following items were demonstrated in test series: Graphite coatings: The test results with SUS440C bearings showed that graphite film break occurred under both hydrogen and nitrogen atmosphere. MoS2 coatings: SUS440C bearings: It showed better lubrication performance in hydrogen atmosphere than in nitrogen atmosphere. MoS2 coating films broke in early stage under nitrogen atmosphere with high contact pressure condition. It showed stable lubrication performance under hydrogen with high temperature of 200°C. Hybrid ceramic bearings: At the early stage of the rotation, there is almost no transfer film for self lubrication on the ball surface. The bearing showed good lubrication performance with MoS2 + PTFE coating film in advance at high contact pressure.
„Cliff“-testing by using SRV
The identification in engine or gear tests of the induction time or off-set point („cliff“), after which wear and friction increased.
“Cliff” testing as auxiliary method supports the interpretation of engine tests, as it enhances the values of expensive engine tests, because it enables correlations between friction & wear, either from engine or in SRV tests, with additive depletion, oxidation, viscometrics and dispersancy/detergency.
Oil samples taken in discrete intervals and “Cliff” tested monitors the evolution of tribological and functional properties versus engine running time. “Cliff” testing by using SRV is a purposeful tool in order to secure and accelerate metallurgical developments and the development of lubricant formulations.
Actions from the meeting in April 2016: 1. Four SAC test methods are in place and were revised: SH/T 0721 (Grease, coefficient of friction and wear), SH/T 0784 (Grease, pass load/O.K. load), SH/T 0847 (Oil, coefficient of friction and wear) and SH/T 0882 released by 11-2014 (Oil, pass load/O.K. load). 2. New test method to evaluate anti-fretting properties of greases based was approved by SAC TC280 and will be released. 3. SAC TC280 accepted the project “Simulation of synchronizer by using SRV”. Draft text to be submitted by 03-2017. Discussions on a parallel ASTM test method. 4. A procedure for “Wear Volume” is under development for SAC TC280.
Tribological profile of hydraulic oils by using SRV. The determination of a set of critical, tribological by using different SRV-based test methods. The SRV-based concept of tribological profile generates the wear volumes on two triboelements (specimen), the extreme pressure properties and friction under different contact pressures.
Thus, the benchmark and validation of hydraulic oils bear on a wider range of tribological properties.
The RR2016 extends with six hydraulic oils to other base oil types including biodegradable fluids, which were all tested according to ASTM D7043 in order to consolidate the correlation between SRV and V104C.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread holds equally for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated.
I will show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. Examples of micro-structured inhomogeneous materials will be given, such as Composites, Ceramics, Concrete, and Additively manufactured parts. I will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Gefahrguttanks werden primär gegen betriebliche Belastungen dimensioniert. Unfallbelastungen spielen hierbei keine Rolle. In der Vergangenheit gab es immer wieder einige katastrophale Unfälle, die nicht nur materielle Schäden zur Folge hatten sondern bei denen auch Todesopfer zu beklagen waren. Zur Ermittlung möglicher Sicherheitsreserven werden Untersuchungen zum Abtrag auslegungsüberschreitender Belastungen durchgeführt. Mit dem Grenzlasttragverfahren steht ein leistungsfähiges Analysewerkzeug zur Verfügung, mit dem nichtlineare Beanspruchungsszenarien bewertet werden können. Der Vergleich der numerischen mit den experimentellen Ergebnissen zeigt dies eindeutig.
The polymer chemical structure of the polyimide has a major influence on the tribological behaviour. The addition of graphite in PI2 has a beneficial effect in hydrogen on the friction and wear. The low friction of graphite is associated with a lubricant film in hydrogen. The influence of hydrogen on graphite is more effective than humidity. CNTs have a similar effect to that of graphite in PEEK composites. TiO2 particles improve significantly the wear rate both in vacuum and hydrogen environment. In LH2 friction and wear decrease for unfilled polymers. Friction of graphite filled composites increases slightly and wear rate is stable.