Robert Gottwald

[Computation and experimental examination of an implant structure made by a fibre-reinforced building method for the bypass of continuity defects of the mandible].

Zusammenfassung Eine Unterkieferteilresektion muss nicht selten im Rahmen der chirurgischen Entfernung von Tumoren im Unterkiefer-, Mundboden- und Zungenbereich bzw. mit Substanzverlust einhergehenden Unterkieferfrakturen, gutartigen Knochenläsionen und ausgedehnten, schwer zu beherrschenden Knochengewebsentzündungen durchgeführt werden. Die primäre Rekonstruktion des Unterkiefers ist nach einer Teilresektion mit Kontinuitätsverlust vorwiegend aus funktionellen und auch aus ästhetischen Gründen notwendig. Derzeit werden die Unterkieferkontinuitätsdefekte häufig mit metallischen Rekonstruktionsplatten überbrückt, um die mastikatorische Funktion des Unterkiefers temporär oder endgültig wieder herzustellen. Funktionelle sowie ästhetische Nachteile ergeben sich bei der Anwendung derartiger Platten durch einen hohen Steifigkeitssprung zwischen Rekonstruktionsplatte und Knochen sowie deren wenig individuell gestaltetes Design. Der Einsatz von biokompatiblem, kohlenstofffaserverstärktem Polyetheretherketon (CF-PEEK) erlaubt die Entwicklung einer dem Unterkiefer kontur- und steifigkeitsangepassten Tragstruktur. Für die beanspruchungsgerechte Auslegung und den Test einer CF-PEEK-Tragbandage bieten sich die Finite-Elemente-Methode sowie die Anwendung optischer Methoden wie etwa das Grauwertkorrelationsverfahren an. Das Deformationsverhalten wurde für verschiedenartige Osteosynthesekonfigurationen an einem Modellkiefer vergleichend untersucht. Die Berechnungen und Tests des defektüberbrückten Modellkiefers zeigen beim Einsatz der neuartigen CF-PEEK-Tragbandage im Vergleich zur Verwendung herkömmlicher Titan-Osteosyntheseplatten ein dem natürlichen Unterkiefer wesentlich besser angepasstes mechanisches Verhalten. Abstract A partial resection of the lower jaw often has to be carried out in the context of the surgical removal of tumours in the lower jaw, mouth and tongue-floor space and lower jaw fractures with loss of substance, benign bone lesions and extensive difficult inflammation of bone tissue, respectively. The primary reconstruction of the lower jaw after partial resection with loss of continuity is mainly important for functional and aesthetic reasons. The defects of lower jaw continuity are often bridged with metal plates to reconstruct the masticatory function of the lower jaw, temporarily or permanently. Functional as well as aesthetic disadvantages arise in the case of the application of such plates as a result of a high stiffness jump between reconstruction plate and bone and their insufficiently individual design. The employment of biocompatible, carbon-fibre-reinforced Polyetheretherketon (CF-PEEK) permits the development of a geometry- and stiffness-adapted carrying structure for the mandible. For the demand-adapted dimensioning and the test of a CF-PEEK bandage, the application of optical methods, such as the grey value correlation method, is suited as well as numeric methods, such as the finite element method. In an initial analysis of deformation behaviour, the various osteosynthesis configurations are comparatively investigated on a model jaw. The calculations and tests of the lower jaw model show that the use of the new CF-PEEK bandage compared to the use of conventional titanium osteosynthesis plates shows a mechanical behaviour which is much better adapted to the natural lower jaw.A partial resection of the lower jaw often has to be carried out in the context of the surgical removal of tumours in the lower jaw, mouth and tongue-floor space and lower jaw fractures with loss of substance, benign bone lesions and extensive difficult inflammation of bone tissue, respectively. The primary reconstruction of the lower jaw after partial resection with loss of continuity is mainly important for functional and aesthetic reasons. The defects of lower jaw continuity are often bridged with metal plates to reconstruct the masticatory function of the lower jaw, temporarily or permanently. Functional as well as aesthetic disadvantages arise in the case of the application of such plates as a result of a high stiffness jump between reconstruction plate and bone and their insufficiently individual design. The employment of biocompatible, carbon-fibre-reinforced Polyetheretherketon (CF-PEEK) permits the development of a geometry- and stiffness-adapted carrying structure for the mandible. For the demand-adapted dimensioning and the test of a CF-PEEK bandage, the application of optical methods, such as the grey value correlation method, is suited as well as numeric methods, such as the finite element method. In an initial analysis of deformation behaviour, the various osteosynthesis configurations are comparatively investigated on a model jaw. The calculations and tests of the lower jaw model show that the use of the new CF-PEEK bandage compared to the use of conventional titanium osteosynthesis plates shows a mechanical behaviour which is much better adapted to the natural lower jaw.

Novel Testing Device for the Experimental Stress Concentration Analysis of Multilayer Textile Composites under In-Plane Compressive Load

An analytically based calculation tool for the stress-strain analysis of multilayer composite plate structures with cut-outs is developed which offers high potential to be used in a sense as an analytical sub-model in combination with FE-Analysis Systems. For its validation extensive numerical and experimental investigations have to be carried out. Especially the examination of structures loaded by in-plane compression does not seem to be realizable by conventional testing techniques. That is why a novel testing device for the experimental stress concentration analysis of notched thin plate structures under in-plane compressive load is developed and its application in combination with an adapted optical measurement system is demonstrated.

Investigations on the applicability of chemically deposited Ni-shell tools for deep-drawing processes

The paper introduces the results of an EFB (European Research Association for Sheet Metal Working) research project concerning the applicability of tools made of chemically deposited nickel shells with polymer supports for small and medium scale deep drawing production. Several investigations of the material behaviour and tribological response of the chemically deposited nickel shells were performed together with numerical analyses of the deep-drawing process in order to optimize the tools under the consideration of the specific characteristics of the nickel shell and the polymer support structure. Finally, an optimized tool prototype has been manufactured and tested in order to verify the design solutions under service conditions.

Calculation method for the determination of stress concentrations in fibre-reinforced multilayered composites due to metallic interference-fit bolt:

Sophisticated analytical solution methods for the stress concentration problem in multilayered composites with interference-fit bolts have been developed on the basis of layer-related solutions. The model is based on a circular or elliptical isotropic bolt integrated in a fibre- or textile-reinforced multilayered composite plate. For the simulation of the interference between bolt and composite plate a modelling strategy has been proposed featuring the application of a defined temperature load to a metallic elastic inclusion. For analysing the stress concentration effects in the surrounding plate, complex-valued displacement functions in combination with the method of conformal mappings for the interface between inclusion and plate and a combination of boundary collocation and least squares method for the outer boundary are used. For the verification of the developed calculation methods, a number of experimental and numerical studies have been carried out and the decay behaviour of the distortions have been compared for different radians. For all combinations of multilayered composite plate and interference-fit bolt investigated so far, a good correlation of the analytically calculated and the numerically determined results can be observed.

Experimental Strain Measurement for Fibre-Reinforced Finite Mulitlayered Composites with Cut-out Under Bending for Validating an Analytical Calculation Model

For validating a newly developed analytical calculation method for the layer-by-layer stress-strain analysis of thin-walled notched multilayered composites with finite outer boundary, the strain field of specimen with cut-out is experimentally determined. For this reason, a unique flexural testing device is enhanced and adapted for composites undergoing large deflection. The strains and their gradients around the cut-out are measured using a digital image correlation technique. Beyond that, especially for the investigation of small measuring fields with a high local resolution and/or with a large relocation during the experiment, a new tracking method for the measurement system is developed and applied. In the case of specimen deflection caused by bending, that system keeps the relative distance and position between the measuring field on the specimen and the optical measuring system within the allowable range. By using the combination of enhanced flexural testing device and new tracking system, the 2D strain-field on the specimen surface is measured with a high local accuracy and shows a good correlation with the predicted strain-field calculated with the new analytical calculation method.