Cutting to the chase with warm-start contextual bandits

Knowledge and Information Systems - Multi-armed bandits achieve excellent long-term performance in practice and sublinear cumulative regret in theory. However, a real-world limitation of bandit...     

Improving the Defect Tolerance and Fatigue Strength of AM AlSi10Mg

Additively manufactured structures reveal a poor surface quality and a high number of process-induced defects in the surface-near area, leading to a significant reduction of the fatigue strength. As laser-based powder bed fusion (PBF-LB) processes are used to produce topologically optimized lightweight structures with complex geometries, which cannot be fully machined, the influence of the process-induced surface on the fatigue behavior needs to be analyzed. For this, also the interrelation of the surface-induced notch effects with the surrounding material volume must be considered. As thermal treatments can also be applied to filigree components with complex geometries, in the presented work the influence of different heat treatments, i.e., stress relief annealing (SR) and artificial aging (T6), on the material properties, especially the defect tolerance, of AlSi10Mg manufactured via PBF-LB is analyzed. Both heat treatments lead to a dissolution of the cellular Si-rich network, resulting in decreased hardness and tensile strength, but higher fatigue strength. The increased fatigue strength results from a reduction of the process-induced residual stresses, but mainly a strongly improved defect tolerance. Consequently, to evaluate the fatigue strength of additively manufactured materials, besides the materials strength and the process-induced defects, also the defect tolerance must be considered.     

High-Resolution Patterning of Organic–Inorganic Photoresins for Tungsten and Tungsten Carbide Microstructures

Tungsten is an important material for high-temperature applications due to its high chemical and thermal stability. Its carbide, that is, tungsten carbide, is used in tool manufacturing because of its outstanding hardness and as a catalyst scaffold due to its morphology and large surface area. However, microstructuring, especially high-resolution 3D microstructuring of both materials, is a complex and challenging process which suffers from slow speeds and requires expensive specialized equipment. Traditional subtractive machining methods, for example, milling, are often not feasible because of the hardness and brittleness of the materials. Commonly, tungsten and tungsten carbide are manufactured by powder metallurgy. However, these methods are very limited in the complexity and resolution of the produced components. Herein, tungsten ion-containing organic–inorganic photoresins, which are patterned by two-photon lithography (TPL) at micrometer resolution, are introduced. The printed structures are converted to tungsten or tungsten carbide by thermal debinding and reduction of the precursor or carbothermal reduction reaction, respectively. Using TPL, complex 3D tungsten and tungsten carbide structures are prepared with a resolution down to 2 and 7 μm, respectively. This new pathway of structuring tungsten and its carbide facilitates a broad range of applications from micromachining to metamaterials and catalysis.     

Charakterisierung und Qualitätssicherung von Oberflächenvorbehandlungen auf Kunststoffbauteilen

With the aim of increasing wetting, adhesion, and long-term stability usually surface pretreatments are carried out on plastic surfaces for subsequent painting and bonding processes. Depending on the treatment methods, materials and subsequent processing steps, a variety of characterization methods are available. An overview is given of established characterization options for activated plastic surfaces, which are suitable for adjusting processes or quality assurance. In addition, new promising research approaches for two-dimensional and non-destructive quality control of activated plastic surfaces are discussed.