Zusammenhänge zwischen Temperaturabhängigkeit des Spannungsintensitätsfaktors und dem Verschleiß

Relationships between thermal variability of the critical stress intensity factor and wear. The aim of these investigations was to establish to what extent relationships exist between the critical stress intensity factor and the wear resistance of very hard, refractory materials, in order to obtain a further value to characterize the technological behaviour of these materials. Investigations showed that such relationships exist when wear occurs with a slight rise in temperature within the material. It was also found that at higher temperatures, wear was conditioned by plastic deformations in the thinner surface layers and by the influence of the gaseous environment.     

Untersuchungen zur Ermittlung und Bewertung von Schädigungsvorgängen in Klebverbindungen mittels Schallemissionsanalyse

Investigations to Determine and Evaluate Damage Processes of Adhesive Bonds by Means of Acoustic Emission The damage process in metal adhesive bonds under quasistatic loads was monitored by means of acoustic emission analysis (AEA). Metallographic investigations allow the correlation between acoustic emission data and microscopic failure processes in the bondline of single lap adhesive joints. The influence of specimen geometry on the initiation of damages is discussed for several types of adhesives. Furthermore the relation between the preparation of the adherent surface and the onset of acoustic emission is as well described as the influence of manufacturing defects on the mechanical behaviour and the acoustic emission activity.     

Untersuchungen zur Haftreibung zwischen faserverstärktem Borosilicatglas und Kalk-Natron-Glas bei erhöhten Temperaturen

Investigation of static friction of fiber reinforced borosilicate glass mated to soda lime glass at elevated temperatures Tribological tests were carried out on a soda lime glass mated to SiC- and C-fiber reinforced borosilicate glass. The static coefficient of friction and the transition to sliding were measured using a ring-on-block geometry at temperatures between 25 and 500 °C. The fiber orientation (parallel or antiparallel) refering to the direction of sliding was varied. The static friction coefficient decreased with increasing temperature for both the SiC and the C-fiber reinforced glass owing to increasing tendency for adhesion and resulting material transfer. At temperatures up to 300 °C, there was no difference between the static and the kinetic coefficient independent of the material, whereas the static friction coefficient was lower for parallel than antiparallel fiber orientation. At test temperatures above 300 °C and antiparallel fiber orientation, stick-slip effects occurred under the experimental conditions used. The tribological mechanisms could be explained by SEM (scanning electron microscopy) studies of the worn surfaces.     

AFM‐Untersuchungen zu adhäsiven Wechselwirkungen an einkristallinem Si und voroxidiertem SiC in Abhängigkeit von der relativen Luftfeuchte

AFM investigations of the adhesive interactions of single‐crystal Si and preoxidized SiC as a function of the relative humidity The chemical structure of untreated and thermally oxidized single‐crystal 6H‐SiC surfaces was analysed using Auger electron spectroscopy. The wetting behaviour of the surfaces by water was studied using “sessile drop” method, and measurement of the adhesion force between Si tips and sample surfaces was conducted using an atomic force microscope. At a low humidity the adhesion force depended on the annealing temperature used for preoxidation. This was primarily attributed to different Si₄C₄O₄ volume fractions in the amorphous, stoichiometric SiO₂ surface layers, which varied as a function of the preoxidation treatment. The decrease of the adhesion force with increasing humidity varied owing to the different wetting properties of the samples.     

Simulation von Schädigungs‐ und Kriechvorgängen im Asphalt

Simulation of damage and creep processes in asphalt There is an increasing need for the use of numerical methods in road design. Here, the main difficulty lies in modeling the highly complex, nonlinear material behaviour of asphalt. The present paper deals with this problem and proposes a continuum mechanics model serving to simulate the main nonlinear mechanical processes taking place in asphalt. Plastic deformation, damage and crack development as well as viscous processes are treated. The model is implemented into the finite element program Abaqus and is used to simulate tests on asphalt specimens.     

Untersuchungen an stahlfaserverstärktem Aluminium unter Torsions- und Druckbeanspruchungen

Investigation of Steel Fiber Reinforced Aluminium under Torsional and Compressive Loading A fiber-shaped composite material which, due to its fabrication process and internal structure may be called a double fiber composite, and whose strength behaviour is significantly influenced by boundary layers and porosity has been tested by means of two test methods:

• 1 The possibility is demonstrated to determine by a non-destructive elastic torsional test the useful cross section for the utilization of the material, taking the quality-reducing factors into consideration.
• 2 Pressure tests have shown good agreement with Timoshenko and Gere's wave theory extended in this particular case.

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Charakterisierung von Randentkohlungsvorgängen bei der Austenitisierung des Wälzlagerstahls 100Cr6. Teil 1: Korrelation zwischen Randschichteigenschaften und Kohlenstoff‐Tiefenverlauf

Characterization of Decarburisation Processes During Austenitising of the Rolling Bearing Steel 100Cr6. Part 1: Correlation between Rim Zone Properties and Carbon Concentration Profile The influence of a decarburisation process during austenitising of the through‐hardenable rolling bearing steel 100Cr6 (SAE 52100) on the rim zone properties of the martensitic through‐hardened material was investigated by means of material analysis and diffusion calculations. For this purpose, two specimens were prepared under defined heat treatment conditions, and the near‐surface carbon distribution was determined micro‐chemically by using secondary ion mass spectrometry (SIMS). In part 1 of the present work, these concentration profiles are compared with the depth variation of the micro‐hardness and with the distance curves of the residual stresses and the line broadening ({211} α'‐Fe diffraction line) both measured by X‐ray diffraction (XRD). In addition, microstructure investigations were performed. In part 2, a refined kinetics model of a diffusion‐controlled reaction based on the finite element method (FEM) will be applied to the decarburisation process in order to describe the carbon distributions obtained.     

Untersuchungen des Gleit- und Furchungsverschleißes an thermochemisch behandelten Stählen

Sliding and sliding abrasion tests of thermochemically treated steels The results of research work during several years are presented summarily. The results were obtained jointly by the Bundesanstalt für Materialprüfung (BAM), Berlin, and Stiftung Institut für Härterei-Technik (IHT), Bremen. The wear tests included hardened, casehardened, nitrided, nitrocarburized, chromized, chromvanadized and vanadized steels and were performed with dry friction in air and in vacuum, and with mixed lubrication. Under these conditions adhesion, abrasion and tribo-oxidation were the main wear mechanisms. The results reveal that the wear evaluation order of the differently heat treated steels depends on the type of wear and the operating wear mechanisms.     

Zusammenhänge zum Schlagzähigkeits‐ und Durchstoßverhalten thermoplastischer Natur‐/Langfaserverbunde

Correlations for the fracture work and falling weight impact properties of thermoplastic natural / long fibre composites The improvement of the fracture work is of special importance for the expansion of application fields in plastics construction parts of enhanced stress characteristics. An improvement of the toughness properties can be achieved by increased deformation ability. Fracture work and energy at the falling weight impact tests can be raised both by increasing of the strength and/or elongation of the reinforcing fibres and by reduction of the adhesion. The reduction of adhesion can be realized using no compatibilizers. But the increasing of the strength and/or elongation is restricted. The deformation ability of the resulting composite can be increased by addition of fibre components of higher strength respectively elongation to the natural and matrix fibres during manufacturing of the precursor. Significant improvements of the impact strength of such composites could be proved by impact bending tests and by measuring of strength and energy in breaking tests at shock load by falling weight tests. The results of both tests were compared to find out the origin of the improvement. It was found that the energy E_p needed for crack initiation has only a negligible effect on the improvement of the fracture work a_cU (Charpy impact strength). A significant higher effect on the fracture work a_cU was found for the energy E_r which will force the crack extension. So the increased crack retardation energy caused by the mechanical properties of the added fibres can be seen as the main origin of the improved toughness properties transition obtained by addition of fibres of high strength respectively elongation.     

Wälzverschleiß und -ermüdung von Bauteilen und Maßnahmen zu ihrer Einschränkung

Wear and Fatigue at Rolling contacts and Counter Measures Machine parts subjected to rolling contact fatigue, i.e. gears or rolling element bearings, are exposed to a very particular stressing condition. No comparable condition will occur for other technical applications. These typical conditions and their effects on the material behaviour are described comprehensively. An introductional overview for this are of technical knowledge is given, in particular for engineers not so much experienced with respect to this matter. The most important phenomena influencing the behaviour of parts subjected to rolling contact fatigue are presented as well as the physics of damage initiation and the appearance of damaged parts. It is demonstrated exemplarily, how the analysis of the damaging processes can be used to take counter measures. The referencing to the public literature has been done in a way to enable the reader to easily find material for a further improvement of his knowledge for particular items.     

Theoretisch-numerische Untersuchungen zu Experimenten mit Kriechrißwachstum

Theoretical-Numerical Investigations of Experiments with Creep Crack Growth Numerical results are presented to calculate the C* -integral that is path independent only in the long-time range. The crack tip modelling – elastic or elastic-plastic – is of minor influence on C* – whereas values of C* depend strongly on the material constants describing the creep law. The agreement between numerically and experimentally determined C* data is rather satisfactory in the secondary creep regime. A line integral R* is proposed that is path independent in the whole time domain.     

Bruchmechanische Untersuchungen und Rißfortschrittsmessungen an lunkerbehafteten,bauteilähnlichen Proben aus GK-AlSi12

Fracture Mechanics Investigations on Cast Aluminium Aluminium castings cannot be massproduced economically without casting pores or similar flaws. These flaws must, however, be avoided, at least in the highly stressed regions of cast safety components of automobiles by changes in design or casting procedure. In other regions flaws up to a certain size can be tolerated if it can be shown by calculation and experiment that cracks either will not propagate from these flaws or at least will not reach critical size during the life of the component. Cast aluminium wheels are an example of such a component. Their allowable flaw sizes were determined in the following way:

• The stresses occuring in service wer measured in 17 locations in a test rig in the laboratory and on a race track.
• The crack propagation characteristics and the ΔK_th-values of the cast aluminium material were determined.
• Crack propagation was calculated under the stresses measured in service; based on these measured stresses and the fracture mechanics characteristics, locations were selected in the cast aluminium wheel where no flaws can be allowed; in other locations with lower stresses the allowable flaw sizes were calculated with a large safety factor.

     

Untersuchung der Reaktionsvorgänge zwischen gasförmigen und festen Metallen

Reaction of gaseous with solid metals . The reaction of gaseous zinc and cadmium with solid copper, silver, palladium and palladium silver alloys were investigated at various temperatures. Besides the cleanliness of the metal surfaces various other factors influence the zink tak up e. g. the shape of the surface. More than up to now it has to be kept in mind, that the zinc atoms spread as directed atomic beams. This results in possibilities of influencing the zinz up take.     

Eigenspannungen,Haftfestigkeit und Verschleißeigenschaften von gesputterten,amorphen Aluminiumoxidschichten

Internal Stresses, Adhesion and Wear Behaviour of Sputtered Amorphous Alumina Coatings Thin alumina coatings have been pruduced by means of reaktive r.f. magnetron sputtering. The layers, deposited onto metallic substrates, show an amorphous crystallographic structure which may be due to the low deposition temperatures below about 250°C. Measurement of internal stresses was performed by using the bending beam method. The experiments show that there is not only a dependence on the film thickness but even pressure and sputtering power have a strong influence on internal stresses of the alumina coatings. Some correlations between internal stress and adhesion of the coatings are evident. Besides scratch-test measurements the size of layer-detachment of bending-specimen gave information about the adhesion behaviour of the coatings. The results of both methods have been in good agreement. Some of the alumina coatings have been tested with regard to their tribological behaviour by means of a model testing apparatus. The coatings show excellent wear behaviour even under severe tribological conditions.     

Oberflächentechnik. Korrosion,Verschleiß, Wechselwirkung zwischen Oberfläche und Grundwerkstoff

Metal finishing — corrosion, wear, interaction between surface and basic metal . The influence of the surface on the behaviour of metals by mechanical stress and chemical attack has been studied. The results described complete former publications [1]. There also are discussed the necessary fundamentals.     

Ladungsträger‐Tiefenprofilierung an ultra‐flachen pn‐Übergängen

Charge carrier depth profiling on ultrashallow pn‐junctions The Stepwise Oxidation Profiling (SWOP) technique has been applied to charge carrier depth profiling on boron ion implanted silicon. The procedure works by altering between electrical sheet resistance measurements on van‐der‐Pauw (VDP)‐ structures and Si layer removal by electrochemical anodic oxidation. It was shown that the SWOP profiles are matching well with SIMS reference measurements, and that a depth resolution of ≤ nm and a detection limit of 1·10¹⁶cm^?3 was achieved.