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  • Grün, Florian  (45)
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  • 1
    Article
    Article
    Language: German
    In: BHM Berg- und Hüttenmännische Monatshefte, 2015, Vol.160(1), pp.1-1
    Description: Byline: Florian Grun (1) Author Affiliation: (1) Leoben, Osterreich Article History: Registration Date: 18/12/2014 Online Date: 16/01/2015
    Keywords: Earth Sciences ; Mineral Resources ; Engineering;
    ISSN: 0005-8912
    E-ISSN: 1613-7531
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  • 2
    Language: English
    In: Materials Science & Engineering A, 17 November 2014, Vol.618, pp.578-585
    Description: It is nowadays widely recognized that good and profound knowledge of the deformation behavior and/or crack propagation behavior is a vital part of high performance simulation for advanced high stress fatigue life prediction. Concerning of those two different approaches, one must, however, be aware that additional and detailed information of fatigue induced crack nucleation, its further propagation path and the associated crack growth rate is important for the intrinsic understanding of the material damage process. This paper investigates how the fatigue process works in high stressed Al–Si–Mg and Al–Si–Cu fatigue samples starting from crack nucleation to sample rupture by rotating bending loads at room temperature. The samples themselves were taken directly from serial casted and heat treated cylinder head components and were processed to conventional hourglass specimens. Because no suitable test method which fulfils all the necessary test requirements was commercially available, a new rotating bending testing machine which directly operates in a confocal light microscope was developed. This test method allowed us to easily compare every change of the crack growth rate (especially for microstructural small cracks) with the microstructure and its crack path. At high stress regimes eutectic phases became very important for fatigue induced crack nucleation and early crack propagation. In the first third of the lifetime, both alloys cracked on multiple spots by interface cracking between hard phase particles ( -phase) and eutectic matrix. Depending on the crack length and stress intensity factor proceeding cracks were also able to move into the dentritic matrix ( -phase). At the end of the lifetime only a fraction of all nucleated cracks of each specimen became large enough to exert influence for fatigue failure. Furthermore, using this test method as an integral element of stress gradient fatigue investigation makes it possible to identify and define major microstructural crack relevant objects like particles during material fatigue. Hence, it not only increases the knowledge for high performance fatigue simulation but also provides a tool for material optimization by fatigue processes themselves.
    Keywords: Microstructural Cracks ; Fatigue ; In Situ Crack Observation ; Crack Path ; Rotating Bending ; Aluminium Cast Alloy ; Engineering
    ISSN: 0921-5093
    E-ISSN: 1873-4936
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  • 3
    Language: English
    In: MATEC Web of Conferences, 01 June 2014, Vol.12, p.03004
    Description: Specimens of two sizes have been taken from two sampling locations within a wind turbine hub made of nodular cast iron (EN-GJS-400-18-LT) for constant amplitude fatigue testing. The sampling positions exhibit varying cooling conditions, resulting in different microstructures. Fatigue tests have been carried out at R-ratios of R = −1 and R = 0. The coarse microstructure as well as the larger specimens yielded in lower fatigue strengths. No effect of the microstructure or the specimen size on the mean stress sensitivity has been found. Fractographic analysis of the fractured specimen's surface revealed micro-shrinkages to be the source of crack initiation for all specimens. Micro-shrinkage size increases from fine to coarse microstructure and with increasing specimen size. The El-Haddad equation using the √area parameter was used to describe the fatigue limit. The results were in good agreement with the experiments.
    Keywords: Engineering
    ISBN: 9782759812745
    E-ISSN: 2261-236X
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  • 4
    Language: English
    In: Wood Science and Technology, 2018, Vol.52(1), pp.281-294
    Description: Generally, wood chipping represents an important procedure in the wood processing and forestry industry. To improve structural components like chipping tools, knowledge of the properties of local timber including resistance against chipping as well as the dynamically acting process forces is of utmost significance. The aim of this work is to experimentally evaluate service-induced stresses on machinery parts to create a numerical material model, which is capable of revealing similar resistance against cutting as natural wood. To this end, a small-scale cutting machine has been designed, incorporating a bladeholder with strain gauges applied, measuring the resulting mechanical stresses during the chipping process by focussing on different wood species. Spruce is utilized as a variety with a lower density and European beech for higher density timber applications. The test results demonstrate a distinct difference by cutting both materials, whereby European beech indicates more than twice the resistance against chipping compared to spruce. Setting two different, relatively acute rake angles on the cutting tool does not reveal a fundamental difference for chipping. To evaluate the numerical wood material model, an isotropic ductile damage model, usually applied to ductile metals, was implemented in this study. Based on a sensitivity study of the material properties in the course of the numerical simulation, a possible approach is presented that explains how to change the cutting resistance, depending on the blade movement direction and the angle of the main grain of the timber. In a comparison of different types of mechanical stress from the numerical analysis and experimental tests, the results exhibit strong correlation. Element damage and deletion correspond at similar load levels, exhibiting a deviation of no more than 24%.
    Keywords: Forestry – Analysis ; Forestry – Models ; Mechanical Engineering – Analysis ; Mechanical Engineering – Models ; Numerical Analysis – Analysis ; Numerical Analysis – Models ; Machinery – Analysis ; Machinery – Models ; Tool Industry – Analysis ; Tool Industry – Models ; Timber – Analysis ; Timber – Models;
    ISSN: 0043-7719
    E-ISSN: 1432-5225
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  • 5
    Language: English
    In: Lubricants, 01 December 2017, Vol.5(4), p.47
    Description: The current paper addresses the field of experimental research of journal bearing systems. In this regard, the challenges are dealt with concerning simultaneous testing with a close correlation to the industrial application and with a high resolution of tribological processes. Concerning this aspect, two damage equivalent laboratory test methodologies for journal slide bearing systems are presented, and their ability to visualize certain performance parameters of bearing systems are emphasized (for instance friction performance, (start stop) wear processes, and seizure events). The results clearly emphasize that the applied methodologies provide accurate findings regarding specific effects of selective parameters/changes on the performance of bearing systems, such as polymer overlays may result in improved mixed friction sliding conditions if designed properly, and they provide superior start stop wear resistance; the use of specific corrosion inhibitors can successfully prevent tribo-corrosion on bronze bearings; a decrease of oil viscosity increases solid friction share but decreases fluid friction; lubricant anti-wear additives are able to improve seizure resistance and sliding properties of bearing systems depending on formulation harmonization; and novel bearing material coatings, e.g., sputtered SnCu, can significantly improve emergency running capabilities.
    Keywords: Journal Bearings ; Damage Equivalent Testing ; Seizure ; Start Stop Wear ; Simulation ; Engineering
    E-ISSN: 2075-4442
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  • 6
    Language: English
    In: International Journal of Fatigue, July 2016, Vol.88, pp.142-155
    Description: In this paper, different hypo-eutectic Al–Si cast alloys with varying silicon, copper and iron contents were tested under thermo-mechanical fatigue (TMF) conditions to achieve a unified approach to damaging and fatigue endurance behaviour. The cylinder heads from which the specimens were taken were serially produced with T79 heat treatment. This includes homogenisation, quenching and ageing. The alloy used by these investigations are commonly used for automotive cylinder heads. Under operational conditions, a complex interaction of mechanical and thermal cyclic loadings is inherent. Hence, the main purpose here is to distinguish between the influences of the alloying elements of hypo-eutectic Al–Si cast alloys and propose its effects to mechanical and environmental damages. The results underlined the important role of hard phases for crack nucleation especially in high copper alloys. The hard phases, like eutectic silicon or primary AlCu, AlFeSi phases in general got ruptured, independent of the applied mechanical loading. In contrast, damages in low copper alloys were caused by high plastic matrix deformations and the loss of adhesion of eutectic silicon particles. For both types of alloys, the crack propagation was mostly constrained on the eutectic itself. An improved TMF endurance was achieved by AlSi9Cu1(Sr) and primary AlSi8Cu3. Here, probably the increased matrix strength by precipitation hardening and the manifold crack deflections on the eutectic silicon reduced intrinsically the microstructural damage. Further, in TMF regimes it is recommended to use Al–Si cast alloys with low iron contents because present ternary - and quaternary - supported crack nucleation and lowered the fatigue endurance. Additionally, an over-aged AlSi7MgCu alloy in T74 condition significantly lacks in fatigue endurance because of a minor fatigue strength by incoherent -precipitations. However, the results presented here identify the major damages of hypo-eutectic Al–Si cast alloys and the influences of the alloying elements on TMF endurance. This enables further unified fatigue modelling by the automotive designer and additional optimizations of the metallurgical systems by the foundry which underlines the demand of improved knowledge of the cylinder head under real-life operational conditions.
    Keywords: Al–Si Cast Alloy ; Thermomechanical Fatigue ; Cylinder Head ; High Temperature ; Oxidation ; Engineering
    ISSN: 0142-1123
    E-ISSN: 1879-3452
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  • 7
    Language: English
    In: Materials Today: Proceedings, 2017, Vol.4(5), pp.5957-5962
    Description: The mechanical modelling of components made of grey cast iron is a non-trivial task, especially when subjected to non-isothermal thermo-mechanical loading conditions. Hence, elasto-plastic deformations as well as time-dependent creep processes have to be taken into account in the simulation in order to accurately model the mechanical stress-strain relationship. Consequently, a methodology to simulate the complex deformation behaviour based on a damage modified viscoplastic constitutive model is introduced. This methodology also contains a semi-automated parameter optimization strategy featuring a genetic algorithm. The correspondingly conducted cyclic mechanical simulation runs match well with the experimental data. Only marginal deviations in the evaluated stress-strain hysteresis can be found at quite high temperatures.
    Keywords: Thermo-Mechanical Fatigue (Tmf) ; Cast Iron ; Constitutive Material Model ; Cyclic Viscoplasticity ; Damage Mechanics ; Genetic Algorithm
    ISSN: 2214-7853
    E-ISSN: 2214-7853
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  • 8
    Language: German
    In: BHM Berg- und Hüttenmännische Monatshefte, 2015, Vol.160(1), pp.2-8
    Description: Gießen ermöglicht die kostengünstige Herstellung komplexer Bauteilgeometrien unterschiedlicher Größe für verschiedenste Industriezweige. Aufgrund der Randbedingungen des Prozesses kommt es bei der Produktion zu unterschiedlich ausgebildetem Gefüge innerhalb eines Bauteils. Diese lokale Mikrostruktur beeinflusst sowohl die lokalen quasi-statischen als auch die lokalen zyklischen Werkstoffeigenschaften. Die Ausnutzung dieser lokalen Werkstoffeigenschaften für moderne Bauteilauslegung wurde im Rahmen der Forschungstätigkeiten des Lehrstuhls für Allgemeinen Maschinenbau der Montanuniversität Leoben in mehreren Projekten realisiert, welche in diesem Beitrag vorgestellt werden. The casting process makes possible a cost-efficient production of complex geometries of different size for various industries. Due to process-related boundary conditions, the local microstructure is not homogeneous within a component. This local microstructure results in local differences for the quasi-static and cyclic material properties. The utilization of these local material properties in a modern design process has been shown in several research projects at the Chair of Mechanical Engineering at the Montanuniversität Leoben. The results of these research projects are presented in this paper.
    Keywords: Ductile iron ; Modern design tools ; Local material properties ; Lightweight design
    ISSN: 0005-8912
    E-ISSN: 1613-7531
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  • 9
    Language: English
    In: Procedia Engineering, 2018, Vol.213, pp.335-345
    Description: In general, the requirements of endurable light-weight structures are challenging tasks for engineers. High-strength steels provide a major potential by replacing commonly applied construction mild steels. However, a higher notch sensitivity and increased crack propagation rates may decrease the benefit of high-strength steels and their practicability of application. Therefore, reliable assessment methods are demanded to assess fatigue life and crack propagation of welded as well as un-welded structures. For this purpose, an optical measurement system consisting of an industrial camera, telecentric lenses, and special LED components is set-up to analyze crack initiation and propagation of high-strength steels compared to common construction mild steels. Furthermore, an image processing program is developed to investigate the crack length during testing automatically. Indirect potential drop measurement method with crack gauge and optical-light microscopical investigations are utilized to calibrate the elaborated image measurement system. Constant amplitude tests including overloads are performed for high-strength and common construction mild steel specimens to specify the material’s service strength. Based on the researched data, material parameters for crack propagation analysis are evaluated for these steel grades.
    Keywords: Crack Measurement ; Optical Measurement ; Crack Propagation ; Overload Effects ; High-Strength Steel ; Engineering
    ISSN: 1877-7058
    E-ISSN: 1877-7058
    Source: ScienceDirect Journals (Elsevier)
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  • 10
    Language: English
    In: Journal of Agricultural Engineering, 01 January 2018, Vol.49(2), pp.110-116
    Description: Using large wood chips for heating systems in industrial applications is becoming popular. As a result, the requirements of the machinery that produces these large wood chips have increased, especially on the chipping tools and on the surrounding supportive components. This paper evaluates the acting main forces on a chipping drum that produces large wood chips via field and laboratory-based experimental measurements. In this study, a variety of strain gauges are applied to selected areas of the rotating chipping drum to measure localised strain conditions during wood-stem cutting. Four different wood species were investigated for comparison. Furthermore, the influence of sharp and dull knives is analysed. With the aid of experimental measurements and analysis on a laboratory scale, linear models are developed to determine the chipping force, which is cutting depth-dependent, for a variety of wood species. Testing parameters for such models are proposed via load spectra. The variability of the acting force value is evident. The maximum load on the drum affects at 10% of the time of a single cut. The largest applied forces are between 1.6 and 1.8 higher than the calculated average force. The commuting hornbeam sample exhibits the highest resistance against chipping compared to the three-other species. Additionally, a change in the load is easily recognised in the field test when utilising dull chipping blades. A reconstruction of the alternate load direction is based on laboratory testing.
    Keywords: Wood Chipping ; Forces ; Drum ; Experimental ; Field ; Laboratory ; Agriculture
    ISSN: 1974-7071
    E-ISSN: 2239-6268
    Source: Directory of Open Access Journals (DOAJ)
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