Grain coarsening in hot deformed austenitic Cr-Ni steel

Simulation of forging of Nb-stabilised Cr-Ni steel using a hot deformation simulator. Modelling of various courses of temperature in between and after deformation steps. Assessment of the effects of various soaking conditions on grain growth. Evaluation of recrystallisation and grain growth characteristics by quantitative metallography.     

Calculation of the temperature distribution in dieless drawing

Dieless drawing is an example of flexible metal forming processes. The investigation of the main process parameters and their interdependence is the prerequisite for the deliberate choice of input parameters to get the desired quality of the workpiece. Drawing force, drawing velocity, and temperature are the main control parameters. But only the temperature can be influenced locally whereas the force and the velocity can be adjusted only globally. Because of this special importance of the temperature analytical and numerical models for the temperature distribution along the deformation zone have been developed.     

Polyketones containing indane structure elements

Summary Polyketones with indane structure elements were prepared by Friedel-Crafts polycondensation in three different reaction media. Only oligomers or insoluble material could be obtained, probably due to a side reaction of the indane ring, which leads to crosslinking at high conversion. The oligomers are soluble in common organic solvents such as THF and CHCl₃. Melting points, glass transition temperatures, and thermal stability of the oligomers were determined.     

A framework for controlling model-based diagnosis systems with multiple actions

In recent years reasoning about structure and function of physical systems for the purpose of diagnosis has seen a dramatic increase in activities. New exciting results concerning modelling issues, diagnostic inference patterns and inferential power have emerged. A state of the art diagnosis agent now has a considerable toolset at hand. A main obstacle for building large diagnosis systems, however, remains. How can we controlwhen to usewhich inference pattern or representation? We argue that the actions available to a diagnosis agent can be understood in terms of change ofworking hypotheses. The control problem then becomes a belief revision problem: when to adopt or drop beliefs. Our approach proceeds in two steps. First, we adopt the principle of informational economy from Gärdenfors, Knowledge in Flux (MIT Press, 1988) as kind of a law of inertia for diagnostic processes, that helps us identify candidates for revised belief states. In a second step we employ specificdiagnostic knowledge to actually choose the next belief state. We demonstrate the use of our concepts on an example in the domain of ballast tank systems as e.g. used in offshore plants.     

Ein Beitrag zum Förderprinzip periodisch arbeitender,ventilloser Pumpen

Zusammenfassung Mechanische Herzklappenfehler werden vom Blutkreislauf h?ufig kompensiert. Der Internist G. Liebau hat nach physikalischen Erkl?rungen dieses Ph?nomens gesucht und dazu mehrere Modelle angegeben. An einem dieser die physiologischen Bedingungen sehr vereinfachenden Modelle, das durch eine unsymmetrische Flüssigkeitsverteilung sowie durch Querschnittsunterschiede der (starren) Leitungen und eine ventillose Kolbenpumpe mit unsymmetrischem Hubgesetz als Antrieb gekennzeichnet ist, wurde die F?rderwirkung experimentell und rechnerisch untersucht. Es zeigte sich, da? eine lineare Gleichung das Problem nicht beschreiben kann. Vielmehr führt der vollst?ndige Ansatz auf eine Riccatische Differentialgleichung. Sie wurde auf einem Analogrechner integriert. Die Ergebnisse erm?glichten es, den physikalisch gut erkl?rbaren F?rdereffekt numerisch zu ermitteln und dimensionslos darzustellen. Eine gesonderte Untersuchung betrifft das Verhalten einer inkompressiblen newtonschen Flüssigkeit bei laminarer, periodischer Rohrstr?mung. Die am Modell gewonnenen Ergebnisse führen zu bestimmten Folgerungen für den Blutkreislauf. Gekürzte Fassung der gleichnamigen Dissertation des Verfassers, Technische Hochschule Hannover 1962. Den Herren Prof. Dr.-Ing.E. Pestel und Doz. Dr. med. habil.G. Liebau dankt der Verfasser für die Anregung zu dieser Untersuchung und für ihr stetes Interesse, Herrn Doz. Dr. med. habil.G. Liebau insbesondere für seine ?medizinische Beratung?.     

Elastic moduli of nanocrystallites in carbon fibers measured by in-situ X-ray microbeam diffraction

The in-plane Young’s modulus and the shear modulus of carbon nanocrystallites were investigated during in-situ tension tests of single carbon fibers by X-ray diffraction using the shift of the 10 band in the meridional direction and the change in the azimuthal width of the 002 reflection. The limiting value for the Young’s modulus was found to be 1140 GPa, which is higher than the value for graphite obtained from macroscopic specimens, but coincides with recent measurements on nanotubes. Furthermore, the shear modulus was evaluated using a uniform stress approach and was found to increase with increasing misorientation of the crystallites. It turns out that both the in-plane Young’s modulus and the shear modulus are not constant, but dependent on the orientation parameter.     

MEDICAL FOUNDATIONS OF AN EXPERT SYSTEM FOR CHRONIC OBSTRUCTIVE LUNG DISEASE

Physicians have already expressed widespread interest in using expert systems. Numerous medical expert systems have appeared, but only a few of them have proven successful. In this article, several criteria that are crucial to the success of an expert system in clinical practice are indicated. The medical foundations of an expert system now being developed according to these criteria are given. The intended purpose of this expert system is to be an effective instrument for the physician in performing the challenging task of caring for patients suffering from chronic obstructive lung disease or high-risk persons. Our aim is to create a system for everyday use that will have several features not provided by the contemporary expert systems in the field of pulmonary diseases. The technical concept of this expert system and especially the pivotal points of its implementation are described in a companion article (Quatember, 1990).     

Improving properties of a low-carbon microalloyed steel by means of accelerated cooling of dynamically recrystallized austenite

Ferrite formation from the ultra-fine dynamically recrystallized austenite (d_γ < 5 μm) was investigated on a microalloyed steel with 0.11%C. Hot rolling conditions were simulated by the hot deformation simulator Wumsi. Due to accelerated cooling a corresponding fine homogeneous ferrite grain of d_α < 2 μm was achieved with a pearlite free acicular microstructure after a cooling rate of more than 20 K/s. Excellent mechanical properties (2.0% proof stress of over 700 MPa and impact transition temperature of -180°C) were obtained, superior to those after thermomechanical processing of the same steel without dynamic recrystallization of the low-temperature austenite.     

Hot‐Rolling Experiments on Deformation Behaviour of Oxide Scale

A new test technique developed by the authors allows to investigate the brittle‐ductile behaviour of oxide scale during the hot‐rolling process. Sandwich specimens were pre‐oxidised and then welded so as to be gas‐tight. A micro‐alloyed deep‐drawing quality steel (interstitial free steel) and a fine‐grained low‐pearlite structural steel served as test material. The experiments were performed at temperatures up to 1050 °C. Optical metallography was used to describe the changes of the scale layers. The method is quite good to describe the results qualitatively whereas it is rather difficult to derive quantitative results.     

Modeling and validation of a boost pressure actuation system,for a series sequentially turbocharged SI engine

An actuation system for flexible control of an advanced turbocharging system is studied. It incorporates a vacuum pump and tank that are connected to pulse width modulation controlled vacuum valves. A methodology for modeling the entire boost pressure actuation system is developed. Emphasis is placed on developing component models that are easily identified from measured data, without the need for expensive measurements.The models have physical interpretations that enable handling of varying surrounding conditions.The component models and integrated system are evaluated on a two stage series sequential turbo system with three actuators having different characteristics.Several applications of the developed system model are presented, including a nonlinear compensator for voltage disturbance rejection where the performance of the compensator is demonstrated on an engine in a test cell. The applicability of the complete system model for control and diagnosis of the vacuum system is also discussed.