Die Messung der Bruchzähigkeit eines Vergütungsstahles mit Hilfe der Teilentlastungsmethode

Application of the Unloading Compliance Method in Fracture Toughness Measurements of a Quenched and Tempered Steel The application of the J-integral leads to a considerable reduction of material needed for establishing toughness data. The number of specimens is further reduced by measuring the crack resistance curve in a single specimen. This requires monitoring the crack extension during the experiment. A comparison of several methods showed that the unloading compliance technique is particularly suitable for that purpose. This method was applied for measuring the toughness as a function of location in a large forging of a steel 25 NiCrMo 14 5. Good toughness values (about 200 MPam^1/2) with little scatter were found over the whole cross section of the forging.     

Kavitationserisionsuntersuchungen mit Werkstoffproben aus Chrom-Nickelstahlguß und Polyamidguß

Cavitation Erosion Tests with Polyamid-Specimens and Stainless-Steel-Specimens The Darmstadt vibratory cavitation erosion method, cavitation tests were performed on two materials: a proven chromium-nickel alloy and a recently introduced polyamid grade. Time studies based on the above test method resulted in pronounced damage to the chromium-nickel alloy, as documented in mass loss curves and specimen surface pictures. In contrast, all polyamid specimens sustained no damage, i.e. no mass loss, no surface damage resulted.     

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.     

Fassaden aus historischen Handstrichziegeln mit Rezeptschlämme

Die Fassade des Galeriegebäudes Hinter dem Gießhaus in Berlin — vis a vis der Museumsinsel Berlin — hat mit ihrer handwerklichen Raffinesse aus historischen Handstrichziegeln und einer gekratzten und gekehrten Rezeptschlämme nicht nur 2008 den 2. Platz beim Europäischen Architekturpreis ECOLA erhalten, sondern seitdem auch in der Öffentlichkeit für eine positive Faszination gesorgt. 2 Jahre nach Fertigstellung dieses Unikates und dem ungebrochenen starken Interesse — insbesondere von Architekturbüros — berichtet Bau‐Ing. Thomas Bauer — Oberbauleiter der Dreßler Bau GmbH — nun erstmals öffentlich über die Erarbeitung und handwerkliche Ausführung dieser Fassade, insbesondere auch über Erfahrungen, Grundlagen und Anforderungen bei der Arbeit mit historischen Ziegeln, insbesondere Handstrichziegeln bei Einsatz in Neubaufassaden. Dargestellt werden Erfahrungen bei der Gewinnung von Altsteinen bis hin zum Rückbau ungenutzter Gebäude, Prüfverfahren zur Bestimmung der Eignung und des Einsatzortes bei Neuverwendung, Fragen der Reinigung und Sortierung bis hin zu Besonderheiten bei der neuen Vermauerung aufbereiteter Handstrichziegel. Für die an der Galerie Hinter dem Gießhaus Berlin speziell modifizierte Rezeptschlämme werden Grundlagen, Anforderungen und das umgesetzte Mörtelkonzept für die geschlämmte Fassade dargelegt sowie erstmals die aus unzähligen Versuchen heraus entwickelte handwerkliche Handschrift der Schlämmtechnik vorgestellt. Façades made of historical handmade bricks with elutriation — Gallery building behind the Giesshaus 1 in Berlin, basics, requirements and solutions. The façade of the gallery building behind the Giesshaus in Berlin — vis a vis the Berlin museum island — with its handicraft features consisting of historical handmade bricks and a scraped and swept elutriation according to recipe, was not only awarded 2nd place in 2008 in the ECOLA European Architecture Prize, but it has also proved a positive fascination for the public. Two years after completion of this unique example and the continuously high level of interest — in particular from architectural offices — construction Ing. Thomas Bauer — chief construction supervisor of Dressler Bau GmbH — now reports for the first time publicly about the preparation and workmanship of this façade, in particular also about the experience, basics and requirements involved in working with historical bricks, in particular handmade bricks with employment in new building façades. Experience in the extraction of old stones, extending to the back‐construction of unused buildings, testing methods for the determination of the suitability and the field of application in case of new utilisation, questions relating to cleaning and sorting, extending to special features of handmade bricks processed in new wall construction, are represented. For the specially modified elutriation according to recipe on the gallery behind the Giess haus Berlin, basics, requirements and the mortar concept applied for the elutriated façade are demonstrated, as well as the technology, developed out of innumerable experiments on the unique handicraft signature of the elutriation, is presented for the first time.     

Erfahrungen mit Warmwasserbereitern aus nichtrostenden Stählen

Experience with Water Heaters of Stainless Steel . Different stainless steels and their importance in the construction of domestic water heaters. Types of corrosion and their importance in water heating practice. Important aspects for manufacture. Experience gained with stainless steel water heaters.     

Chemische Diffusion von Molybdän in hochlegierten austenitischen CrNiMo(N)-Stählen

Interdiffusion of Molybdenum in High-Alloy Austenitic CrNiMo(N)-Steels The Volume diffusion of Mo in austenitic CrNiMo(N)-steels was studied using the sandwich method. Accordingly the interdiffusion coefficients of Mo were found to be independent of its concentration for the given steel compositions with 12 to 19 wt.% Cr, 12 to 16wt.% Ni, 0 to 2 wt.% Mo and 0 to 0.27 wt.% N and within the temperature range from 1283 to 1523 K. The diffusivity of Mo is greater than that of Cr, Ni and Fe in such steels. The diffusion parameters of Mo are decreased by alloying addition of nearly 0.25 wt.% N in Steel; possibly as a result of lattice expansion or increasing vacancy concentration caused by N. Small variations in Cr and Ni initial contents of examined specimens showed negligible effect on the absolute values of interdiffusion coefficients of Mo.     

Die Rißzähigkeit von Vergütungsstählen

The Crack Toughness of Heat Treatable Steels. A survey on K_Ic- measurements of heat treatable steels is presented. The influences of factors like the heat-treatment, test-temperature, micro-structure and the previous thermal and mechanical history of the starting material on the K_Ic-values are described. K_Ic-values at room-temperature of typical steels are tabulated.     

Versuchsführungsbedingte Unterschiede im zyklischen Verformungsverhalten von Vergütetem 42 CrMo 4 bei Spannungs- und Totaldehnungskontrolle

Differences in the cyclic deformation behaviour of quenched and tempered steel 42 CrMo 4 (AISI 4140) due to stress- and strain-control Cyclic stress-strain-curves and Manson-Coffin-plots of quenched and tempered steel 42 CrMo 4 (AISI 4140) strongly depend on whether they are determined under stress- or total-strain-control. At total-strain-controlled experiments, this is caused on the one hand by comparatively high initial stress-amplitudes which lead to distinctive cyclic worksoftening. On the other hand, the occurring differences in the evolution of inhomogeneous deformation patterns at both types of loading, which can be recorded by means of photoelasticity and microscopy, lead to differently distributed plastic deformations and to different integral values of plastic strain.     

Leichte Turbolader-Verdichterräder aus Aluminium- und Magnesium-Feinguß

Light turbocharger compressor wheels from aluminium and magnesium investment casting Within the scope of a team work between Kühnle, Kopp & Kausch AG, Volkswagen AG, Sterling International Technologies Ltd. and the Fraunhofer Institute for Strength of Structures under Operational Conditions LBF compressor wheels of aluminium and magnesium investment casting were developed and tested. Strength and fatigue tests, overspeed and field tests as well as metallographic checks were made in addition to the finite element calculations to optimize the stress under centrifugal force in an appropriate way for the materials involved. The results and the knowledge gathered are to clarify whether magnesium alloys are an appropriate replacement for the proven standard aluminium alloy for turbochargers.     

Minderung von Reibung und Verschleiß von Bauteilen aus Aluminium mit diamantähnlichen Kohlenstoffschichten (DLC)

Reduction of friction and wear for parts made of aluminium by diamond-like carbon coatings Reduction of friction and wear of machine parts and tools is usually achieved by separating the participating surfaces. This is predominantly done by liquid lubricants. Solid lubricant coatings replace them where hydrodynamic lubrication is not possible or not active. Among the hard and friction reducing layers diamond-like carbon films (DLC) have distinguished themselves as the most interesting representatives. They are deposited on metallic and ceramic parts in a glow discharge of a hydrocarbon gas at temperatures between 150 and 200 °C. Those low deposition temperatures, their very low dry sliding friction coefficient of 0.05 to 0.1, and an elastic recovery of 90 % differentiate them from PVD coatings to a high degree. DLC can also be deposited on light metals with thicknesses of more than 30 μm. For closed films an outstanding protection against corrosion is established. Machining and forming of light metals can be done without cooling lubricants.     

Langzeit- und Dauerschwingfestigkeit des Vergütungsstahls 25CrMo4 bei mehrachsiger Beanspruchung durch drei schwingende Lastspannungen

High-Cycle and Long-Life Fatigue of 25CrMo4 under Multiaxial Load Conditions by three Alternating Stresses Statistically verified experimental results from high-cycle and long-life fatigue tests (HCF and LLF) with altogether 537 unnotched solid cylindrical and thin-walled hollow specimen are demonstrating the fatigue behaviour (S-N-characteristics, scatterband) of 25CrMo4 under uniaxial loading with superimposed static stresses (consideration of the mean stress effect) and under biaxial loadings in variation of phase differences between the three combined normal and torsional stresses σ_x, σ_y, τ_xy The fatigue strength is commonly decreasing with life time in the high-cycle regime until reaching the fatigue endurance limit in the transition range to infinite life. The “ductility level” τ_w/σ_w and the “mean stress sensibility” p = p (σ_w, σ_zSch, R_m) are relatively independent of the intensity by stress amplitudes and fatigue life to failure. In comparision with the specific case of biaxial combined loading with synchroneous amplitudes, the fatigue resistance characteristics are detrimentally influenced by out-of-phase normal stresses σ_x, σ_y; a phase difference of 180° between the normal stress amplitudes is the most critical state of combination, especially in the lower cycle regime caused by a greater slope coefficient (probability of survival P_s = 50%). On the contrary is there in the high-cycle regime as well as in the long-life range no significant influence to the fatigue strength by biaxial load conditions of simultaneously normal stresses with out-of-phase torsional stress τ_xy     

Schubtragfähigkeit von Wänden aus Kalksand‐Planelementen mit geringem Überbindemaß — Experiment und rechnerische Simulation

Der Querkraftwiderstand V_R von Mauerwerkswänden, die in ihrer Ebene durch Wind‐ oder Erdbebeneinwirkungen beansprucht werden, hängt auch vom Überbindemaß ü bzw. vom Verhältnis des Überbindemaßes zur Steinhöhe ü/h_st ab. Das nach Norm derzeit zulässige Überbindemaß von ü ≥ 0,4 h_st kann bei der Verwendung von Planelementen in der Praxis nicht immer eingehalten werden. Für diese Fälle ist in den allgemeinen bauaufsichtlichen Zulassungen (abZ) des Deutschen Instituts für Bautechnik (DIBt) für Kalksand‐Planelemente im Bereich 0,4 > ü ≥ 0,2 h_st bzw. 12,5 cm bisher ein verminderter zulässiger Rechenwert der charakteristischen Schubfestigkeit f_vk von 60 % des Wertes nach DIN 1053‐100:2007‐09 (ü ≥ 0,4 h_st ) anzuwenden. Diese, auf Ergebnissen alter Versuche mit überholten Prüfanordnungen beruhenden, hohen Tragfähigkeitseinbußen waren im Zuge der Aufnahme von Planelementen in die Bemessungsnormen für Mauerwerk mit neuem Schubbemessungskonzept zu überprüfen. Daher wurden umfangreiche experimentelle und theoretische Untersuchungen an 17,5 cm dicken, 2,50 m hohen Schubwänden aus Kalksand‐Planelementmauerwerk mit Dünnbettmörtel und unvermörtelten Stoßfugen durchgeführt. Ziel war es, den Einfluss geringer Überbindemaße ü/h_st < 0,4 auf die Schubtragfähigkeit dieser Wände, insbesondere bei statisch‐zyklischen Horizontalverformungen in Wandebene, quantitativ zu bestimmen. Als Versuchsparameter wurden die Wandauflast (σ = 0,5/1,0/1,43 N/mm²), das Überbindemaß (ü/h_st = 0,2/0,4) und die Einspannung am Wandkopf und ‐fuß variiert. Die Untersuchungen ergaben im Bereich der normativ bemessungs relevanten geringen Überbindemaße 0,2 ″ ü/h_st ″ 0,4 keine signifikanten Traglasteinbußen. Bei erweiterten theoretischen FE‐Analysen für das baupraktisch übliche Spektrum vorhandener Überbindemaße 0,2 ″ ü/h_st ″ 1,0 von Wänden mit Auflastspannungen von 0,5 N/mm² bzw. 1,0 N/mm² wurde eine Traglastminderung von maximal 12 bis 16 % berechnet. Der Abtrag der Horizontallast vom Wandkopf zum Wandfuß erfolgt über ein schräges Druckspannungsfeld. Im Überbindebereich der Elemente auftretende Spannungskonzentrationen können zu örtlich begrenzten Rissbildungen führen, ohne dass die Tragfähigkeit der Wand hierdurch beeinträchtigt wird. Diese ist erst dann erschöpft, wenn insbesondere am Wandfuß die vom gerissenen Mauerwerk übertragbaren, schrägen Druckspannungen nicht mehr aufgenommen werden können. Shear load bearing capacity of masonry walls made of calcium silicate element units with a low overlap length — Experimental and numerical simulation analysis. The shear force resistance capacity V_R of masonry walls subjected, in their plane, to loads from winds or earthquakes, amongst other things, depends on the overlap length of the units ü or on the ratio of the overlap length and the height of the unit ü/h_st . The currently permissible overlap length, according to German design standards and norms, of ü ≥ 0.4 h_st can not always be adhered to in building practice, when using element units. In such cases and according to general technical approval code (abZ) of the German Institute for Building Technology (DIBt) for calcium silicate element units within the range 0.4 > ü ≥ 0.2 h_st or 12.5 cm, a reduced permissible calculation value of the characteristic shear strength f_vk of 60 % of the value according to DIN 1053‐100:2007‐09 (ü ≥ 0.4 h_st ) has been used to date. This high loss of load bearing capacity, based on results of older experiments with ob solete test setups, was to be tested in the course of the inclusion of element units in the calculation standards for masonry walls, with a new shear calculation concept. As a result, extensive experimental and theoretical tests were carried out on 17.5 cm thick and 2.50 m high shear walls made of masonry calcium silicate element units and ungrouted butt joints. The objective was to quantatively determine the influence of low overlap length ü/h_st < 0.4 on the shear resistance of these masonry walls and in particular with static‐cyclical horizontal displacement at the wall top. The vertical load pressure (σ = 0.5/1.0/1.43 N/mm²), the overlap length (ü/h_st = 0.2/0.4) and the fixing at the top and bottom of the wall were varied and used as experimental parameters. Within the range of normative calculation with low overlap lengths 0.2 ″ ü/h_st ″ 0.4, the investigations showed no significant load bearing capacity loss. With more extensive theoretical Finite Element analyses for the normal building practice spectrum of overlap lengths 0.2 ″ ü/h_st ″ 1.0 for walls with a vertical load of 0.5 N/mm² or 1.0 N/mm², a reduction of load bearing capacity of maximum 12 % to 16 % was calculated. The transmission of the horizontal shear load from the top of the wall to the bottom of the wall takes place through a diagonal compression stress field. Cracks may occur in the overlap area of the element units as a result of stress concentration, which are limited to the overlap area and do not cause any impairment to the load bearing capacity of the wall. This capacity is only then exhausted when the trans missible, diagonal compression stress can no longer be absorbed, especially at the bottom of the wall with cracked masonry.     

Abtrennung und Rückgewinnung von organischen Dämpfen aus Abluft mit Hilfe von Membranen Grundlagen über Membranen,Module und Verfahrensauslegung

Membrane technology is finding increasing acceptance in the chemical, petrochemical and pharmaceutical industry to separate gases and vapors. A new development is the separation of organic vapors from off-gas or process streams. The paper deals with the principle of selective gas permeation, membrane structure, modules and fundamentals of process engineering.