Materialwissenschaft und Werkstofftechnik最新文献

As one of the key components of marine reducer, the life reliability of gear is of great significance to the safe operation of the reducer and even the whole transmission system. However, due to economic and testing constraints, executing extensive fatigue life tests on complex and costly gears presents a formidable challenge, resulting in inadequate reliability assessments. In this paper, the gear life reliability analysis method based on the accelerated life test is proposed. By conducting the gear bending fatigue accelerated life test, the life distribution and failure mechanism are determined based on the accelerated life data. Furthermore, the gear life distribution parameters and acceleration model are solved by least squared method. This allows us to derive a reliability index specific to the service conditions, facilitating the evaluation of gear life reliability. The method proposed in this paper provides data and theoretical support for the accelerated life tests, lays a foundation for the gear reliability evaluation under small samples, and improves the efficiency of the gear fatigue life evaluation. It has significant engineering significance in saving test costs, reducing test times and shortening development cycle.

This study investigated austenite formation in a cold-rolled dual-phase steel through thermal experiments in a dilatometer and a Gleeble machine, applying various intercritical annealing temperatures and different heating rates in a 60 % cold-rolled ferrite-pearlite banded microstructure. The microstructural characterization revealed that the transformation of lamellar pearlite into ferrite and spheroidized cementite aggregates started before the onset of austenite formation. Different degrees of overlap between the recrystallization of ferrite-pearlite structure and austenite formation processes were observed, depending on the applied heating rates, which affected the austenite formation mechanisms and the microstructure morphology.

The present work focuses on the friction coefficient for various geotextile sandbag structures especially dikes under different conditions. Based on the review of existing investigations there are several gaps to close. Former investigations do not include the whole scope of needed surfaces and conditions. Especially the friction coefficients for polypropylene and even for jute as material mainly used for small geotextile sandbags are not fully available. Additionally, the influence of the surface moisture is not consequently investigated, particularly for jute. Due to this, eleven test series (three with sandbag on sandbag configuration and eight with sandbag on ground surface) with 780 single readings are finalized. In comparison to former studies there are results for surface combinations of good harmonization and those with differences. A comparison of the earlier studies already shows different results Summarized it can be stated that the presented results are representative friction coefficients for calculation of realistic sandbag structures e. g., sandbag dikes or spring cascades.

AlSi10MnMg-Legierungen werden mit verschiedenen Eisen-, Kupfer- und Zinkkonzentrationen untersucht. Neben den variierten Legierungskonzentrationen werden unterschiedliche Wärmebehandlungen (F, T5 und T7) durchgeführt und anschließend auf ihre Wärmeleitfähigkeit und Wärmekapazität untersucht. Hergestellt werden die Prüfkörper mit Kokillenguss. Der Hintergrund der Untersuchungen ist die schlechte Recyclingbarkeit von Aluminiumlegierungen mit Legierungsbestandteilen von Eisen, Kupfer und Zink, da es bislang keine wirtschaftliche Methode gibt, diese Legierungsbestandteile zu entfernen. Zur Bestimmung des Einflusses der Legierungselemente Eisen, Kupfer und Zink werden Messungen der Wärmeleitfähigkeit und Wärmekapazität mit einer Hot-Disk mit transienter Messmethode durchgeführt.

In this study, we conducted research on a method to reverse engineer geometric design parameters from the shape information of gears. The module and normal pressure angle were tracked using the bisection method, and the profile shift coefficient was extracted from the relationship between the working pitch circle diameter, center distance modification coefficient, and working pressure angle. It was confirmed that there are limitations to reverse engineering the shape using only a coordinate measuring machine or 3D scanner because various geometric information is additionally required to trace back the design requirements for gear strength. Finally, the gear tooth bending strength was calculated using finite element analysis and theoretical formula, and through this, the required level of gear strength design was inferred, and the verification of the gear reverse engineering method presented in this study was attempted.

Steels strengthened by alloying elements and precipitates typically maintain their enhanced properties up to the ferrite-austenite transformation. However, oxide dispersion strengthened ferritic steels are creep resistant even at much higher temperatures given by dispersions of nanosized oxides. To ensure homogeneous dispersion of the oxides, powder metallurgy is used for preparation of the original material. The presented study investigates the effects of direct consolidation of powder of ferritic steel strengthened with yttrium oxide nanoparticles. The powders were mechanically alloyed and sealed into evacuated steel containers, which were subjected to gradual hot consolidation via the industrially applicable intensive plastic deformation method of rotary swaging. Investigations assessing the effects of several reduction ratios showed that the direct consolidation of the oxide dispersion strengthened steel was successful – in the macroscale – at the swaging ratio of 1.03; the quality of consolidation further increased with increasing swaging ratio. At the swaging ratio of 1.83, the consolidated bulk material featured ultra-fine grains characterized with high angle grain boundaries, homogeneous dispersion of oxide precipitates, and the average Vickers microhardness of 706.6 HV 1.

Laser-based powder-bed fusion can be combined with casting into a hybrid manufacturing process. This is done to simultaneously utilize advantages of both processes. To examine related challenges stemming from this combination when using aluminium alloys, first experiments were conducted with EN AC-42000 alloy, an alloy common in both standalone processes. EN AC-42000 alloy samples with different surface treatments were placed into a sand mould and cast on to with an aluminium melt. The contact region between the partially molten insert and the cast material was examined with light microscopy. The main challenges were shown to be comprised of bonding issues due to present oxides and a high porosity. The high porosity was traced back to a porosity increase in the laser-based powder-bed fusion insert.

Glued laminated timber made from hardwood is a sustainable structural product that is currently gaining momentum due to climatic changes and afforestation policy. Diversities in hardwood species have led to a lack of a complete standard for the production of glued laminated timber from hardwood in Europe. This paper addresses hardwood species available in Croatian forests, namely Carpinus Betulus L. (European hornbeam), Quercus Cerris L. (Turkey oak), and Acer Campestre L. (Maple), in terms of their suitability for the production of glued laminated timber. The suitability is assessed by a multi-criteria analysis with seven criteria. Visual and physical properties include density, the occurrence of knots, and grain deviation in lamellas. Mechanical properties include the bending strength, modulus of elasticity, and shear strength of glue lines. In order to obtain physical and mechanical properties, corresponding experimental research has been carried out. Production costs have been evaluated in collaboration with the manufacturer. Results indicate a very high potential of European hornbeam and Turkey oak for the production of glued laminated timber.

Antibacterial properties of components are increasingly becoming an important challenge in material development especially in polymer technology. A well-known additive with which an antibacterial effect can be achieved is the metal oxide titanium dioxide. The aim of this research work was to investigate possible influences on the flexural properties of additively manufactured components resulting from the addition of titanium dioxide as an antimicrobial additive. Compounds with 5 %, 10 % and 15 % titanium dioxide and polyamide 12 as matrix material were produced. Three-point bending test specimens were fabricated out of these compounds, anaylsed and the results were compared with specimens made of virgin polyamide 12. The investigations show a general loss in ductility compared to the virgin polyamide 12. A comparison of the different titanium dioxide contents shows no clear change in the flexural stress at conventional bending. The flexural strain at break seems to decrease for higher titanium dioxide contents.

Surface modification techniques play an important role in adjusting the physicochemical properties of titanium and its alloys. To reduce the penetration of alloying element ions into the body, various types of oxide coatings are used to protect it from the corrosive environment. Another important issue related to the surface layer requirement is ensuring an appropriate set of mechanical properties. Accordingly, in this study, the mechanical and electrochemical properties of the silicon dioxide layers formed by the deposition of nano physical vapor deposition on the surface of titanium and titanium 13-niobium 13-zirconium alloy samples were investigated. To evaluate the mechanical properties of the layers produced by this method, hardness tests were carried out, as well as tests on the adhesion of these layers to the metal substrate. On the other hand, electrochemical properties were studied using potentiodynamic measurements to assess the resistance to pitting corrosion, followed by impedance measurements to interpret the processes and phenomena occurring at the silicon dioxide layer/electrolyte interface. The data obtained showed different mechanical and electrochemical properties of the silicon dioxide layers generated with varying process parameters.