Schubtragfähigkeit von Mauerwerk aus Wärmedämmziegeln

Der Beitrag berichtet über zentrische und exzentrische Schubversuche an Mauerwerk aus Wärmedämmziegeln. Die Ergebnisse werden mit den aktuell gültigen Bemessungsansätzen in DIN 1053‐1 verglichen. Es wird gezeigt, dass die Versuchsergebnisse immer eine ausreichende Sicherheit gegenüber den Bemessungswerten nach DIN 1053‐1 aufweisen. Auch für Mauerwerk aus Wärmedämmziegeln mit allgemeiner bauaufsichtlicher Zulassung können somit die vereinfachten Bemessungsregeln der DIN 4149 ohne Abminderungen angewendet werden. In plane shear resistance of thermal insulating vertically perforated clay brick masonry. In plane shear tests on thermal insulating vertically perforated clay brick masonry are presented. The results are compared with the design rules from DIN 1053‐1. The test results exceeded the design predictions of DIN 1053‐1 by a significant safety margin. The simplified design rules from the German earthquake standard DIN 4149 can be applied to thermal insulating clay unit masonry with technical approvals without any reduction.     

Rost‐ und säurebeständige Stähle unter Komplexbeanspruchung

Rust and acid resistant steels under complex loading With corrosion fatigue investigations under different loadings (R = 0,27, ‐1 and 10) and with inner pressure tests a duplex steel (1.4462) and a super austenitic steel (1.3974) are compared. The investigations were carried out in 10 % HNO₃, artificial seawater according to DIN 50905 and in two very important liquids for application (artificial seawater according to DIN 50905 with H₂S aerated and water with chloride, fluoride, bromide, iodide). For comparison the same tests under only mechanical loads were done in acid free oil. The results show that the super austenitic steel has an significantly higher resistance against corrosion fatigue as the duplex steel under one‐ and three dimensional loads up to 10⁷ cycles. The proportion between the results in the corrosive liquids and the oil can be described by a factor. In artificial seawater factors between 0,67 and 0,92 and in 10 % HNO₃ between 0,67 and 0,83 were determined depending from the loading for the duplex steel. With the super austenitic steel factors between 0,86 and 1 in artificial seawater and between 0,7 and 1,0 in 10 % HNO₃ were received.     

Zum Verhalten rost‐ und säurebeständiger Stähle unter Komplexbeanspruchung. Teil 1 Passivität und Lochkorrosionsbeständigkeit

Some Aspects on Corrosion Fatique of Stainless Steels. Part 1 Passivity and Pitting Corrosion Susceptibility Iron‐Chromium‐Nickel alloys are of special interest for many applications because of their excellent resistance to corrosion. The nature and composition of passive films formed on stainless steels depend on the prevailing conditions, viz. steel‐composition, passivation potential, aging, pH, electrolyt composition and temperature. Passive films may be damaged by local breakdown. At least two mechanisms are possible for this localisation: mechanical breakdown by slip steps and electrochemical breakdown (for e.g. by the effects of chloride ions). Because of this, steels suffer a degradation of their fatique properties when exposed to an aqueous environment. Passivation of austenitic, ferritic‐austenitic and martensitic stainless steels has been studied in different solutions using electrochemical techniques. The results clarified that for two of the investigated alloys the prediction of fracture initiation based on pitting corrosion in chlorid containing solutions is possible. (To be continued.)     

Fließfläche metallischer Schäume

Yield surface of metallic foam In this examination the parameters of a simple phenomenological material model are experimentally determined. Afterwards the energy which is absorbed by the metallic foam at plastic deformation is estimated.     

Oberflächenpräzisionsbearbeitung mit Ionenstrahlen

Low energy ion beam processing becomes more and more established in the development and manufacturing of high precision surfaces as a final complementary step of the conventional surfaces polishing of special optical and mechanical parts. The presented paper gives a comprehensive overview about different ion beam processing techniques and demonstrates the applicability of the ion beam figuring to the final correction of high precision surfaces.     

Zusammenhänge zwischen Temperaturabhängigkeit des Spannungsintensitätsfaktors und dem Verschleiß

Relationships between thermal variability of the critical stress intensity factor and wear. The aim of these investigations was to establish to what extent relationships exist between the critical stress intensity factor and the wear resistance of very hard, refractory materials, in order to obtain a further value to characterize the technological behaviour of these materials. Investigations showed that such relationships exist when wear occurs with a slight rise in temperature within the material. It was also found that at higher temperatures, wear was conditioned by plastic deformations in the thinner surface layers and by the influence of the gaseous environment.     

Holzoberflächenmodifikation mittels Atmosphärendruckplasma

Plasma surface modification of wood and wood‐based materials In this article, plasma technical, analytical and application relevant aspects of the plasma treatment of wood and wood‐based materials are presented. With the help of surface energy determinations and adhesion tests it is shown that the surfaces of wood and wood‐based materials can be changed for specific applications. Surface characteristics, which are application‐technological interesting for a later coating or adhesion, can be specifically generated with the use of air plasma. With surface energy determinations of wood and wood‐based materials, a significantly increased polar part of surface energy could be detected after a plasma treatment. Atomic force microscopy analyses of wood composites show that a plasma treatment with the use of ambient air effects an abrasion and a changed surface roughness. Tensile tests and shear tests of coated or adhered wood‐based materials with a plasma treatment show a clearly increased adherence.     

Oberflächenmodifizierung von Titan zur Verbesserung der Grenzflächenverträglichkeit

Surface Modification of Titanium for Improvement of the Interfacial Biocompatibility We report the CVD‐polymerisation of amino‐functionalized [2,2]‐paracyclophane for polymer coating and functionalization of titanium surfaces. Additionally, the functionalization was carried out by silanization with 3‐aminopropyl‐triethoxysilane. The generated amino‐groups were used for covalent immobilization of bioactive substances to stimulate the adhesion and growth of osteoblasts. As bioactive substances the pentapeptide GRGDS and the growth factor BMP‐2 were chosen. The covalent bonding was achieved by activation with hexamethylene diisocyanate. Each modification step was characterized by X‐ray‐photoelectron‐spectroscopy (XPS), atomic force microscopy (AFM) and contact angle measurements. The covalent bonding of the bioactive substances was proven by radiolabelling and surface‐MALDI‐ToF‐MS. In vitro‐biocompatibility tests with primary, human osteoblasts demonstrated the improved cell adhesion and spreading on the bioactive modified titanium surfaces.     

Gesteinbearbeitung mittels dünner Kreissägeblätter

Treatment of stones by means of thin circular saw blades Circular saws and/or abrasive machining of granite or marble blocks takes place in the industry by block circular saws with 40 to 80 circular saw blades on a shaft. Each of these tools with a tool diameter of approx. 1,000 mm produces a kerf of approx. 6.5 mm. By use of a case‐hardened quality for the master sheets the master sheet thickness and the kerf can be reduced approx. 1 mm. Related to the block which can be separated substantial material savings result in the case of sawing of high‐quality raw materials. Because the used tools are to finish very difficulty with conventional, mechanical technologies, the laser technology became develops for stretching and arranging the disk‐shaped tools. The Laser application is a requirement for the automizableness these work procedures.     

Ansätze für ein Zähigkeitskriterium

An Approach to a Ductility Criterion. The capacity of materials for plastic deformation notably helps prevent component failures. As yet, no criterion exists for the ductility requirement to be imposed. A theorem is here proposed to assist in the determination of the ductility requirement by assessing five load characteristics. These characteristics are: utilization of the material, unsafety of the load assumption, energy absorption requirement, complexity of component configuration, and safety requirement.     

Die Prüfung der Temperaturwechselbeständigkeit hitzebeständiger Stähle und Legierungen

Testing the Resistance to Thermal Shocks of Heat-Resisting Steels and Alloys Scaling resistance of heat-resisting stells and alloys is impaired to a large extent by a reiterating change in temperature and is, in particular, a function of the temperature interval and the rate at which the change in temperature occurs. A test stand for thermal cycling is described which permits quenching upto 80 specimens at a time from temperatures as high as 1100 °C in air, oil or water. As many as 30 temperature cycles are possible in one day. Repeated quenching in water causes considerable changes in specimen shape: length fo austenitic specimens of size 10 mm diam. × 90 mm length increased by about 30%, with cracks forming before specimens broke. Ferritic steel specimens are shortened, in some cases to half their initial length. In steels with a mixed austenitic and ferritic structure length increase is particularly marked. Change in length s a function of the rate of change in temperature, as can be seen by comparing the modes of quenching in water, oil and air.     

Heliumlecktestgeräte für die Qualitätsprüfung von Gehäusen für Vakuumverdichter

Helium leak test devices for the quality inspection of housings for vacuum compressors The well‐known and wide‐spread helium leak test method is a safe and fast quality testing method for construction units of any kind. Due to its safe examination and the short time of examination it is predominantly inserted into automated production lines as e.g. in the automobile supporting industry up to the examination by Airbags and rims of wheel. Likewise in addition, for the construction units, machines and devices of the vacuum engineering. From this the demand results simple and in particular economical devices for the helium leak test of construction units with small numbers of items of under 200 pieces per day. For these manufacturing profiles economical ways for the helium leak test are pointed out.     

Nickel-Molybdän-Sinterstähle für hochbeanspruchte Teile

Nickel-Molybdenum Sintered Steels for High Duty Parts . Fe-Ni-Mo steels without additions and with 0,45% P resp. 0,5% C added were sintered at 1150°C resp. 1250°C for 1 h in H₂. 2% Ni and 1,5% Mo resp. 4% Ni and 3% Mo were added as alloying elements. The strength of the sintered Fe-Ni-Mo alloys without additional elements did not exceed remarkably that of the sintered steels used up to now. Fe-Ni-Mo steels with 4% Ni and 3% Mo sintered at 1250°C with an addition of 0,45% P resp. 0,5% C have a tensile strength of 740 N/mm² resp; 830 N/mm². However the impact toughness of the alloy with P is remarkably higher than that of the alloy with C. The C-content determines mainly the strength properties of the alloys with C and influences the diffusion of the Mo too. The influence of the Ni and Mo on the properties of the alloys with P is more obvious. Alloys with 4% Ni and 3% Mo containing 0,45% P have good static and dynamic strength and therefore are capable for high duty parts.     

Zur Zähigkeit von Vergütungsstählen

On Toughness of Quenched and Tempered Steels Toughness as consumed fracture energy is dependent on fracture mechanism. Grain size and loading conditions influence the transition from ductile dimple fracture to brittle cleavage fracture. In quenched and tempered steels packet size and particle distribution are of importance as well as brittle intergranular fracture modes by grain boundary segregation of impurities in ferrite (temper embrittlement) or precipitates in austenite. Anisotropy of toughness arises from banded structures.     

Erfahrungen mit mobilen Härteprüfgeräten

Experiences with mobile hardness testers During recent years the use of mobile electronically operating hardness testers has become more and more significant for in-process inspections and shop and site inspections. The field and limits of application for this equipment are determined chiefly by the material to be tested, the geometry of the component as well as the information required of the test. The purpose of our work was to establish, with the help of two mobile hardness testers involving the dynamic and static testing procedure on more than 50 metallic materials, the way in which an alteration to various test parameters (surface condition of the components, tester calibration) would affect the hardness values indicated. Furthermore the scatter of readings for the mobile hardness tester was examined.     

Gegen Flußsäure korrosionsbeständige Werkstoffe

In Hydrofluoric Acid Corrosion-Resistant Materials Copper, red brass (Cu-15 Zn), special treated carbon steel and chromium-nickel-molybdenum steel represent materials of high resistivity against concentrated hydrofluoric acid (70%) from room temperature to the boiling point. Since nickel and monel are resistant in hydrofluoric acid in the whole concentration region, they are recommended besides carbon steel as material for transportation and storing tanks. Furthermore, nickel-chromium-iron alloys do not show any corrosion in hydrofluoric acid of 40–60% up to 370 K. The same is true with nickel-chromium-molybdenum alloys. In the group of inorganic materials, particularly graphite and aluminum oxide should be mentioned as highly resistant in 60% hydrofluoric acid (310 K). Synthetic sapphire (Al₂O₃) are employed for windows in the presence of hydrogen fluoride and/or hydrofluoric acid because of their superior optical properties and their excellent corrosion resistance. Polyethylen, polypropylene and polyvinyl chloride (PVC) belong to the cheapest corrosion resistant material for container and for coatings in the presence of hydrofluoric acid. Special polyester resins reinforced by glass or graphite fibers have been successfully employed as material for production units with hydrofluoric acid containing liquids up to 330 K. By carbon reinforced epoxy resin represents a corrosion resistant coating. Because of their excellent friction and corrosion resistance against concentrated hot hydrofluoric acid and HNO₃-HF-solutions, PTFE and polyvinylidene fluoride are used as material for valves and axles in such environment. The expensive alloys, as for instance hastelloy and monel, are substituted more and more by fiber-reinforced polyolefins, PVC and fluorine containing polymers.