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Item type:Publication, Access status: with files , Self-lubricating CrAlVN coatings for turning of Ti6Al4V: oxidation and wear behavior(Wiley-VCH, 2021-12-15); ; ; ; The titanium alloy Ti6Al4V enables significant performance increases in various branches of industry. Nevertheless, it is difficult to machine, because of its material properties. Due to the low thermal conductivity of titanium, the heat generated while turning Ti6Al4V mainly flows into the tool leading to high temperature loads. In addition, the comparatively low Young’s modulus and high yield strength contributes to high mechanical stresses during machining. Temperatureactive, self-lubricating physical vapor deposition hard coatings appear to be suitable for reducing friction and tool wear during turning of Ti6Al4V compared to the most commonly used uncoated carbide tools. The ability of the coating to form lubricating oxide phases at high temperatures is crucial for this purpose. This paper investigates the oxidation and diffusion behavior of vanadium doped chromiumaluminium nitride (CrAlN) coatings after heat treatment at ϑ=600°C, ϑ=700°C and ϑ=800°C in atmosphere as well as the resulting coating properties. The wear behavior of certain coating variants while turning of Ti6Al4V is analyzed.Publicationtype: Journal ArticleScopus© Citations 1 95 194 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of voids and impact damage on the fatigue behaviour of large scale composites(2016-11-01); ; ; ; Defects in laminated composite structures like voids and impact damages have a major influence on the fatigue behaviour. These defects may occur in the manufacturing process and during lifetime of composite parts and lead to matrix cracks within single layers and to delaminations between adjacent layers with different fibre orientations. We investigated the relationship between voids and impact damage and fatigue lifetime. Specimens made of a glass fibre non-crimp fabric were produced by vacuum assisted resin infusion. Voids were introduced by air-bypass simulating a leakage during the vacuum assisted resin infusion-process. Impact damage was induced using a canon. Stringer-panels with the basic dimensions of 1000 mm × 1200 mm and a radius of 1980 mm were tested under multiaxial load situations in a hexapod test rig and a tension/compression-shear test rig.Publicationtype: Journal Article74 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Determination of average dislocation densities in metals by analysis of digitally processed transmission-electron microscopy images [Bestimmung von durchschnittlichen Versetzungsdichten in Metallen durch Analyse digital bearbeiteter Transmissionselektronenmikroskopie‐Aufnahmen]This paper describes an effective and simple procedure to derive information about the dislocation density distribution in metals by applying standard techniques of digital image processing on gray scaled microstructure images obtained from transmission-electron microscopy. In a representative transmission-electron microscopy image, two local dislocation density values were investigated by classical methods and were used as input parameter for further processing. A correlation between dislocations and image intensities is assumed such that dark areas in microstructural images are seen as a dense concentration of dislocations. Then, the contrast is increased for each transmission-electron microscopy photography. In the next step, posterization, a gradation of tone, is applied to these images. From this, a pixel weighted average distribution of gray level correlated dislocation densities is obtained as well as an average value for a given set of images. The implementation of the several processing steps is done in Matlab employing graphical user interfaces.Publicationtype: Journal Article51 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Friction and wear properties of metal/metal hip joints : application of a novel testing and analysis method(Wiley-VCH, 2001-12-01); ; ; Insufficient understanding of tribological behaviour of total joint components is considered as one of the major reasons for premature prosthesis failure. In the previous years, wear modes and mechanisms of artificial hips have been intensively studied using testing machines applying continuous motion and load profiles. Human locomotion, however, is of erratic shape containing motion interruptions among other irregularities. These occurring resting phases could influence adhesive friction at the artificial articulation with possible effects on wear and loosening. Initial frictional behaviour after resting periods and subsequent wear of metal-on-metal hip components have been investigated. While the initial frictional moment of artificial hip components was found to increase significantly with increasing resting duration, wear was hardly affected. These results therefore rather point to an interlocking phenomenon than adhesion. Still, the results are of concern because the increase in friction is likely to occur under physiological conditions too and may cause tangential stress peaks at the bone/ implant interface accelerating fatigue failure. In particular, big head sizes should be used with caution because the frictional moment is a function of coefficient of friction and ball diameter.Publicationtype: Journal Article12