Materialwissenschaft und Werkstofftechnik最新文献

Micro-alloying effects of lanthanum in thermo-mechanical control process of manganese-chromium-molybdenum bainite rail steel are investigated through experimental simulation and microstructural characterization. The results show that the deformation strengthening effect is fully exerted by thermo-mechanical control process in steel containing 0.015 % lanthanum. Finally a kind of multi-layer bainite ferrite microstructure featured by 3.5 μm blocks, 0.41 μm plates and 108 nm sub-plates with ultrafine sub-subunits and 55 nm θ-M₃C inside is achieved, which enhances the strength and toughness synergistically. And the nanoscale refinement mechanism of bainite ferrite plates lies in the formation of massive ultrafine sub-subunits with the average size of 20 nm ×32 nm. Besides, a large number of twinning martensite with the size of 2 nm to 20 nm and high-density entangled dislocations can be found on the boundaries of ultrafine sub-subunits. Further, the density of dislocation is increased by 2.92×10¹⁴ cm⁻² and its contribution to the strength is calculated to be 18 MPa. Moreover, micro-alloying effects of lanthanum in thermo-mechanical control process are explored to be that lanthanum enhances the interaction between bainite ferrite plates and dislocations, strengthens the entanglement of carbon and θ-M₃C with dislocations, and promotes the pinning effect of θ-M₃C on ultrafine subunits.

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.

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.

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.

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.

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.

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.

With the advances in additive manufacturing, there is the idea of using 3D printers to produce spare parts in isolated systems such as ships, oceangoing vessels, warships, spacecraft, isolated stations, and so on. However, it raises the question of the reliability of such spare parts. One area that has not been explored much is the aging of electrical and dielectric properties, which could reveal weaknesses of 3D-printed spare parts for use in electrical and automation systems. Therefore, the paper aims to investigate the change in resistance and dielectric constant. The results show that these changes could increase the probability of discharge and have serious consequences for electrical and automation systems.