Videokeratoscope for accurate and detailed measurement of the cornea surface

A videokeratoscope based on the imaging of a gridlike pattern is introduced. Unlike conventional videokeratoscopes that rely on Placido disks, the new measurement principle allows an exact reconstruction of the surface and the display of fine details. The experimental instrument was tested on precision glass spheres; the maximum error of the height data was less than 3 microm. The sensitivity and the potential to resolve fine details were demonstrated with irregular surfaces of specially prepared contact lenses. Structures with height deviations of 0.1 microm are well identifiable. The eyes of 18 individuals were investigated, and fine structures were found on these cornea surfaces. Conventional videokeratoscopes do not resolve such detail.     

Production of Strong Steel‐Aluminum Composites by Formation of Intermetallic Phases in Compound Forging

In times of increasing energy costs automotive light weight construction is gaining more importance. The production of hybrid compounds by forging is a promising method to successfully manufacture functional parts by applying resource‐saving process steps. However, in compound forging of steel‐aluminum parts shrinking gaps may form because of the different thermal expansion coefficients. To avoid these unwanted gaps, it is necessary to achieve a firmly bonded joint e.g. by intermetallic phases. This paper deals with the investigation of the influences of different sample preparations, process parameters and true strains on the formation of intermetallic phases. Thus, the optimum production parameters for compound forging of steel‐aluminum parts will be determined.     

Besonderheiten beim Entwurf semi‐integraler Spannbetonbrücken: Eine Alternative im Brückenbau mit zunehmender Bedeutung – aufgezeigt am Beispiel der Fahrbachtalbrücke im Zuge der BAB A3 bei Aschaffenburg

Particularities in the Design of Semi‐integral Prestressed Concrete Bridges An alternative bridge construction of increasing importance – illustrated by the example of the Fahrbach valley bridge near Aschaffenburg which is part of the autobahn A3. The integral construction method offers smaller concrete bridges, and increasingly concrete bridges of middle construction lengths, the optimum solution in many cases. A construction without joints or bearings allows low‐maintenance, robust and aesthetical structures. With the static analysis and constructive design of integral structures, the interactions between the superstructure, substructure and subsoil are solved by means of an optimization framework. In order to verify the feasibility of a semiintegral construction, the example of the currently under construction Fahrbach valley bridge is outlined here. Basic considerations are taken into account and their relevance for the design and execution planning is investigated. Recommendations, design aids and relevant boundary conditions for semi‐integral bridges are derived from this investigation. In particular the foundation has a significant influence on the design and the deformation behavior of the overall system. The loadings resulting from external actions (dead weight and traffic loads etc.) require a very stiff foundation. This contrasts the demands of temperature and the varying settlements of supports etc., which require an increasing flexibility of the foundation to manage the constraints. Hence, a realistic characterization of the soil properties of the subsoil is necessary for the static verification by consideration of lower and upper limit values.     

Residual Stress State of Brazed Ceramic/Metal Compounds, Determined by Analytical Methods and X-ray Residual Stress Measurements

The residual stress state of brazed ceramic/metal compounds is described by means of X-ray residual stress determinations and analytical calculations using a model of three elastic infinite plates. It is shown that the residual stress state of the soldered compound depends on the materials combination and on the geometrical conditions. The combination of X-ray residual stress measurements and analytical calculations allows decisions on whether the assumption of a linear elastic model, based on elementary bending theory, is valid for the particular compounds.