Influence of specimen geometry on fracture mechanics values at the onset of stable crack extension

The influence of specimen geometry was studied on 80 mm thick plates of Fe 510 steel. The multi-specimen technique according to ASTM E 813 was compared with SZW and DCPD measurements. Using the ASTM standard lower J_lc values are determined with increasing specimen thickness and overall geometry dimensions, because the calculated blunting line doesn't represent the material's blunting behaviour and the conditions for ‘J-controlled’ crack growth are not applied sufficiently strict in this standard. The initiation values J_i are geometry independent and are lower than J_lc. A proposal to determine a technical J_0.2 value has been suggested for a constant value of Δa = 0.2 mm, which is less complicated concerning the procedure being used, which is resulting in minor geometry independence and is approaching the physical initiation values.     

Einfluß der Korngröße auf die Ergebnisse bruchmechanischer Prüfungen der Stähle St 37-3 und St 52-3

Bruchzähigkeit und kritische Rißaufweitung der Stähle St 37-3 mit 0,08% C, 0,17% Si, 0,45% Mn, 0,019% P und 0,017% S sowie St 52-3 mit 0,13% C, 0,20% Si, 1,19% Mn, 0,017% P und 0,018% S in jeweils zwei verschiedenen Korngrößen zwischen rd. 10 und 100 μm bei Temperaturen zwischen ?196 und + 40 °C. Beziehungen zwischen dem Bruchflächenaussehen und bruchmechanisch definierten Übergangstemperaturen. Vergleich gemessener und aus dem Verhältnis Bruchspannung zu Streckgrenze errechneter Werte der kritischen Rißaufweitung.     

Controlled silica synthesis inspired by diatom silicon biomineralization

Silica becomes increasingly used in chemical, pharmaceutical, and (nano)technological processes, resulting in an increased demand for well-defined silicas and silica-based materials. The production of highly structured silica from cheap starting materials and under ambient conditions, which is a target for many researchers, is already realized in the formation of diatom biosilica, producing highly hierarchical ordered meso- and macropores silica structures. This notion formed the starting point in our integrative biomolecular and biomimetic study on diatom silicon biomineralization in which we have analyzed silica transformations and structure-direction in polymer-mediated silica syntheses using a combination of (ultra)small-angle X-ray scattering and (cryo)electron microscopy. Using bio-analogous reaction conditions and reagents, such as waterglass and (combinations of) polyethylene oxide (PEO) based polymers, we demonstrate in this review the synthesis of tailor-made mesoporous silicas in which we can, as in biosilica synthesis, control the morphological features of the resulting materials on the nanometer level as well as on the micrometer level.     

Zum Einfluß von Temperatur und Dehngeschwindigkeit auf die Streckgrenze von Baustählen unterschiedlicher Festigkeit

Untersuchungen an vier ferritisch-perlitischen Stählen unterschiedlicher chemischer Zusammensetzung und Korngröße sowie einem bainitischen Stahl mit Streckgrenzenwerten zwischen 200 und 630 N/mm². Ermittlung deroberen und unteren Streckgrenze im Temperaturbereich zwischen 77 und 370 K bei Dehngeschwindigkeiten zwischen dem quasistatischen und dem Schlagzugversuch . Auswertung der unteren Streckgrenze nach dem Modell des thermisch aktivierten Fließens.     

On approximately fair cost allocation in Euclidean TSP games

We consider the problem of allocating the cost of an optimal traveling salesman tour in a fair way among the nodes visited; in particular, we focus on the case where the distance matrix of the underlying TSP problem satisfies the triangle inequality. We thereby use the model of TSP games in the sense of cooperative game theory. We give examples showing that the core of such games may be empty, even for the case of Euclidean distances. On the positive, we develop an LP-based allocation rule guaranteeing that no coalition pays more than times its own cost, where is the ratio between the optimal TSP-tour and the optimal value of its Held-Karp relaxation, which is also known as the solution over the subtour polytope. A well-known conjecture states that4/3. We also exhibit examples showing that this ratio cannot be improved below 4/3.Parts of this work were done while the author was visiting at RUTCOR, Rutgers University, supported by SFB 303 (Deutsche Forschungsgemeinschaft).     

采用创新的建筑外立面进行能源的节约和创造

在过去的几年里我们获得了很多最终决定人类未来生存条件的知识。近几年来,全球化以及世界范围内的城市化进程以前所未有的速度增长。人们对生活舒适性的不断向往给环境带来了沉重的压力。自然资源消耗的增长导致了原材料价格的飞速增长。更重要的是,气候变化作为资源消耗增长的一个后果,已经成为全球性的挑战,拒绝破坏子孙后代生存的自然环境的呼声越来越高。     

On the crack susceptibility of high alloyed tool steels during continuous casting and in the temperature region of hot working

Hot tensile tests after applied prior melting down of the specimens were carried out on mainly ledeburitic tool steels and their strength and ductility were determined in the temperature range between liquidus and 900°C. The test parameters and specimen microstructures were adapted to the conditions and structures prevailing in continuous casting and primary hot working of blooms. The metallurgical processes leading to the embrittlement of the material were examined by means of metallographic investigations. The temperature ranges of internal crack susceptibility and low ductility were evaluated.     

Einfluß kleiner Kaltverformungsbeträge und unterschiedlicher Alterungsbehandlungen auf die Kerbschlagzähigkeit allgemeiner Baustähle

Ermittlung der Kerbschlagzähigkeit-Temperatur-Kurven an sieben unlegierten Baustählen nach Kaltverformung um 0,5, 1, 2, 3 und 5%, nach Verformung um die gleichen Beträge und natürlicher Alterung (20 °C 5000 h) sowie künstlicher Alterung (300 °C 1 h). Kennzeichnung des jeweiligen Einflusses durch eine geeignete Übergangstemperatur. Folgerungen für Nachbehandlung kaltverformter und geschweißter Bauteile.