Volume 58, Issue 11-12

Kurzfassung Anlässlich ihres 50-jährigen Bestehens wird die Tribologie – die Wissenschaft und Technik von Wirkflächen in Relativbewegung – in einer Übersicht dargestellt. Bei ingenieurwissenschaftlichen Anwendungen haben tribologische Systeme, die durch die Wirkflächen charakterisiert werden, einen dualen Charakter. Sie sind einerseits notwendig, um technische Aufgaben zu erfüllen, aber auf der anderen Seite sind sie zwangsläufig mit Reibungs- und Verschleißprozessen verbunden, die zu reibungsbedingtem Energieverlust und verschleißbedingter Materialdegradation führen können. Im vorliegenden Übersichtsbeitrag werden die Grundlagen von Reibung und Verschleiß von der Nano- bis zur Makroebene betrachtet und es werden die Basisparameter zur Modellierung tribologischer Systeme im Laborversuch beschrieben. Da tribologische Prozesse zu Fehlzuständen (fault) und Ausfällen (failure) führen können und damit die Funktionssicherheit und die Strukturintegrität negativ beeinflussen können, werden die Prinzipien der technischen Zuverlässigkeit und der Zustandsüberwachung ebenfalls kurz dargestellt.

A synthetic test method is described which is capable of investigating various suspension fasteners on a dynamic half-axle test rig. This test method is advantageous compared to an expensive and time-consuming driving cycle. In advance vehicle specific measured values that serve as input parameters for the test rig experiments are required. This study shows how the adhesion limit influences the interdependencies between vertical load, side slip angle and longitudinal slip. By means of multibody systems and in consideration of the determined nonlinear tire characteristics, this method can be applied to investigate suspension fasteners of vehicles without expensive and time-consuming test drives. Validation results of different vehicles are given which demonstrate that the method is appropriate to a wide range of vehicles.

High strength aluminum alloys of type AA2014 are used in aerospace applications. This alloy is considered unweldable using fusion welding processes. Friction stir welding being a solid state process has been proved to be a suitable process for obtaining sound welds of these materials. In the current study, 8 mm thick rolled AA2014-T651 aluminum alloy plates were joined using friction stir welding. The corrosion behavior of base material and friction stir welds was investigated using the salt fog test (ASTM B117). The corrosion resistance of the welds and parent material in the basic solution was found to be better than that in acidic and neutral solutions. It was also found that the corrosion rate increases with increase in time of exposure. It has been observed that corrosion attack is greater in the weld region than in the parent material and within the weld, heat affected zone has been found to be more susceptible to corrosion compared to the weld nugget and thermomechanically affected zone regions. Transmission electron microscopy studies revealed coarser precipitates and precipitate-free zones in the heat affected zone which are concluded to be the reasons for more susceptibility to corrosion.

Surfaces are the primary place of contact a biomaterial and its host organism. Surface treatment or coating provides means to overcome the problem which appeared after knee replacement surgery. There are two main problems: stress shielding and subsequent bone remodeling cause bone resorption around the implant especially at the proximal part of the knee under the tibia tray. The other problem is stem tip pain. Therefore, the aim of this investigation is to find a new design of coating material of a cementless total knee replacement using functionally graded material (FGM). In particular, the objective of this research is to find the optimal material compositions as well as the optimal gradation direction. It has been found that using both vertical and horizontal FGM coatings increased the von Mises stress at the proximal part of the tibial cancellous bone. The von Mises stress in cancellous epiphyseal bone was increased by 77 % using vertical and horizontal FGM coating compared to HAP coating. It has been determined that this new coating design will improve the performance of a cementless tibia tray and will increase the life of the knee prosthesis.

Aluminum matrix composites containing graphene nano-platelets (GNPs) as reinforcement additive were fabricated by a two-step process consisting of mechanical alloying and pressureless sintering. The effects of graphene nano-platelets amounts and mechanical alloying duration on the microstructural and mechanical properties of aluminum were investigated. The characterization studies were performed by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy/energy dispersive spectrometry, particle size analysis, differential scanning calorimetry, Archimedes' density and microhardness test method. The microhardness of composites increased gradually by the addition of 0.5 and 1 wt.-% GNP, whereas an adverse effect was observed by the increment of the GNP amount to 2 wt.-%.

Zirconium nitride (ZrN) thin films were prepared on stainless steel (SS) substrates by medium frequency (MF) reactive sputtering with gas ion source (GIS) by varying the deposition time and obtained thickness (t ZrN ) in the range of 1.25 to 3.24 μm. The effect of thickness on the structural and microstructural properties was studied using XRD and AFM. XRD characterization revealed that the texture of the ZrN thin films changes as a function of thickness. Both, the (111) and (200) peak, appear initially and (111) becomes more intense with increasing t ZrN . AFM imaging revealed that the ZrN thin film coated with t ZrN ≈ 3.24 μm shows larger grains that are uniformly distributed over the surface. An average hardness value of 19.79 GPa was observed for ZrN thin films having t ZrN ≈ 3.24 μm. The ZrN thin films having t ZrN ≈ 3.24 μm exhibits better adhesion strength up to 20 N. The electrochemical polarization studies indicated that the ZrN thin film having larger thickness shows improved corrosion resistance compared to SS in 3.5 % NaCl solution.

In this study, polyethylene specimens were welded by using friction stir spot welding (FSSW) technique. Welding process was carried out by a rotation of 460 and 900 rpm. Under constant friction force, five different dwell times (20, 40, 60, 80 and 100 s), four different delay times (15, 30, 45 and 60 s) and three different pin profiles (M6 × 1, M6 × 1.25 and M6 × 1.5) were used. During the welding process, temperature measurements under the welding cenetrs were performed using a four multichannel K type digital thermometer. Tensile shear tests were used to characterize the samples. Tensile performance of the samples was significantly affected by the welding parameters.

Use of laser welding is constantly increasing as it allows attainment of a high welding efficiency and weld quality. In this study, 5754 grade aluminum plates were joined on both sides by means of pulsed Nd:YAG power intensified micro scale laser welding method at three different laser powers in flat position by using supplemental welding wire. Mechanical properties of joints were examined by means of tensile and bending tests and by micro hardness measurements, and their structural changes were examined by means of optical microscope, SEM and EDS. As a result, it was determined that the welded joints could display an adequate tensile strength when exposed to tensile strain under action of static loads, but their bending strength remained relatively weaker. Mechanical properties of welded samples were observed to improve with increasing penetration depending on the increase in the laser power. It is believed that use of siliceous supplemental welding wire was also effective in strength improvement.

Talbot-Lau interferometry provides X-ray imaging techniques with significant enhancement of the radiographic contrast of weakly absorbing objects. The grating based technique allows separation of absorption, refraction and small angle scattering effects. The different efficiency of rectangular and triangular shaped phase gratings at varying detector distances is investigated. The interference patterns (Talbot carpets) are modeled for parallel monochromatic radiation and measured by synchrotron radiation. In comparison to rectangular shapes of phase gratings much higher visibility is obtained for triangular shapes which yield enhanced contrast of a glass capillary test specimen.

Kurzfassung Der vorliegende Fachartikel stellt die wichtigsten zerstörungsfreien Prüfmethoden zur Qualitätssicherung von dünnen Strukturklebungen vor. Auf diese Weise wird ersichtlich, welche Methoden neben der zerstörenden Prüfung von dünnen Strukturklebungen eingesetzt werden können, um einen Haftfestigkeitsverlust zu detektieren. Steigende Leichtbau- und Dämpfungsanforderungen an großflächige Blechbauteile sorgen trotz erhöhter Kosten für einen zunehmenden Einsatz von modernen hybriden Schichtverbundwerkstoffen in zahlreichen Konstruktionsanwendungen. In der Luft- und Raumfahrtindustrie gehören solche Werkstoffe seit geraumer Zeit zum aktuellen Stand der Technik, wohingegen diese Werkstoffkonzepte in der mobilen Großserie derzeit nur selten zum Einsatz kommen. Neben dem Materialversagen der einzelnen Schichten von Schichtverbundwerkstoffen spielt das interlaminare Versagen der Schichten untereinander eine entscheidende Rolle. In der Umformtechnik ist es möglich, dass die polymere Zwischenschicht und das Deckblech nach der Umformung noch in Kontakt stehen, obwohl die Scherfestigkeit bereits überschritten wurde. Dieser Kraftschluss der beiden Fügepartner resultiert aus den schwachen Van-der-Waals-Kräften, die eine eindeutige Detektion mit Hilfe von zerstörungsfreier Prüfung erschweren. Die vorliegende Publikation soll die Eignung diverser zerstörungsfreier Prüfverfahren auf die Detektion von sogenannten „kissing bonds“ (schwaches Anhaften der Schichten nach Versagen der Verbindung) überprüfen.

A systematic approach for using a new digital laser dynamic caustic (DLDC) method to provide useful insights for blasting crack propagation is illustrated. Under blast loading conditions, the dynamic behavior of blasting crack propagation and stress distribution around the empty hole between two boreholes were investigated. The results show that the crack tips were gradually deflected towards the empty hole. Then, it was eventually perforated under the guiding role of empty holes. By the interaction between the blast stress waves and the empty hole, the reflected tensile waves were generated. Moreover, these waves changed the stress field and reduced the velocity of the crack tip with a greater diameter for the empty hole. It was also found that the size of the empty holes had a slight influence on the direction of the principal stress. The larger the size of the empty hole was, the smaller was the speed of the crack propagation. In general, the crack propagation velocity of the circular empty hole was the highest, followed by that of the square hole and the notched circular hole. As the blast crack extended to the vicinity of the empty hole, the stress intensity factor of the crack tip started to show an upward trend again.

In this study, the corrosion behavior of refractory materials that were produced by incorporating ZrSiO 4 (zircon) at different ratios into MgO-FeAl 2 O 4 (hercynite) were investigated. The values of density and open porosity of those samples were also measured, and the corrosion behaviors of those materials produced were examined. After performing corrosion tests, the corrosion resistance of composite refractory materials were determined by measuring the penetration distances and spreading areas. The incorporation of ZrSiO 4 into MgO-FeAl 2 O 4 generally decreased the porosity of composite refractory materials, and consequently reduced the penetration distances and spreading area values of the corroded regions of refractories as well. In addition, the formation of new phases and the microstructural changes which occurred were determined by XRD measurements and SEM analyses. On the basis of microstructural characterization carried out in the interface of clinker-refractory, the following observations had been determined: i) Ca 2+ and Zr 4+ elements forming CaZrO 3 were located together in the same regions, ii) forsterite phase was formed due to the reaction between SiO 2 , which is released after dissociation of zircon as ZrO 2 and SiO 2 during sintering, and MgO, iii) the formation of new CaZrO 3 and forsterite (Mg 2 SiO 4 ) phases made a barrier effect against clinker, and iv) the amount of CaO decreased based on the EDX analysis made from clinker to refractory in a corroded region. The penetration of clinker to refractory showed a minimum level for the composition of MgO-5 wt.-% FeAl 2 O 4 -5 wt.-% ZrSiO 4 and an improvement by about 38 % as compared to MgO-5 wt.-% FeAl 2 O 4 . This improvement is associated with a long service life of MgO-FeAl 2 O 4 -ZrSiO 4 refractories for industrial applications.

In common engineering practice, the shot-peened aluminum alloy 2024-T351 is often subjected to loading. After time passes, the residual stress induced by shot peening might relax leading to respective metal cracking and failure. For this study, samples were stored for two years and a comparison of the hardness and microstructure before and after two years storage was carreid out. The primary aim of this study was to determine the effect of time on hardness and microstructure of shot-peened sample, thus to calculate the residual stress relaxation depending on time parameter. The results showed that the hardness and the residual stress of the material reduced after two years. The average reduction of the hardness is 20 % and the residual stress reduction ranged at 47 %

A batch-type and lab-scale indium recovery method was developed via electrowinning (EW) to prove mass production-capability and economic recovery of indium from InCl 3 crystals precipitated from the solvent extraction using a suitable phosphoric acid-based extractant. More precisely, the InCl 3 crystals thus precipitated were further dissolved in three different aqueous electrolyte mixtures for subsequent electrowinning experiments: 0.05 M InCl 3 – 0.7 M LiCl; 0.05M InCl 3 ; 0.05 M InCl 3 – 0.7 M NaCl. The effect of adding LiCl and NaCl supporting electrolytes to InCl 3 on overall EW efficiency was thus comprehensibly investigated. Direct electroreduction of InCl 3 using 0.05 M InCl 3 aqueous electrolyte resulted in the highest indium metal purity of 99.996 % deposited on the copper cathode. Thus, metallic contents obtained from the validation experiments were further characterized using various analytical tools such as inductively coupled plasma/atomic emission spectroscopy (ICP/AES), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence (XRF).

Kurzfassung Im vorliegenden Beitrag wird die Überprüfung der Dichtheit von Felgen gegossener Leichtmetallräder behandelt. Die Bedingungen für eine zuverlässige Dichtheitsprüfung und die Forderungen in den Spezifikationen und Werknormen einzelner Fahrzeughersteller werden erörtert. Die Ergebnisse der Erfassung von undichten Rädern im Betrieb in den Jahren 2011 bis 2015 eines Radherstellers wurden vorgestellt und bewertet. Abschließend wurde ein Vorschlag unterbreitet, die vorliegenden Normen einzelner Fahrzeughersteller an die Bedürfnisse der modernen, weitgehend automatisierten Dichtheitsprüfung anzupassen.

The aim of this study is to investigate the electrical energy consumption for different material processing methods. In these experiments, ferrous powder metals, bulk iron and bulk graphite materials are used. These different materials are heated, sintered and welded by using processes of ultra-high frequency induction heating (UHFIH), ultra-high frequency induction heating sintering (UHFIHS) and ultra-high frequency induction heating welding (UHFIHW), respectively. For all experiments, 2.8 kW, 900 kHz ultra-high frequency induction heating system is used. The experiments are conducted by LabVIEW TM based measurement and control system. Finally, all data are analyzed to show the energy efficiency of each process.