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Stuttgart Mühlhausen, Germany

Lasko G.,Institute For Materialprufung | Apel M.,ACCESS e.V. | Carre A.,ACCESS e.V. | Carre A.,Schott AG | And 2 more authors.
Advanced Engineering Materials | Year: 2012

A combination of the phase-field method for the simulation of the microstructure evolution during solidification with subsequent finite element simulation of fracture appearance in the final solidification structure is proposed for the prediction of the mechanical behavior of Al-Si based casting alloys, including the effect of solidification porosity caused by hydrogen. Metallographic investigations and computer tomographic observations of the as cast microstructure of an Al7%Si0.3%Mg alloy together with the data obtained from mechanical tensile testing are used to compare and validate the simulation results to demonstrate the capabilities as well as current limitations in micromechanical modeling of void containing materials. In micromechanical simulations with the element elimination technique (EET) it is shown that porosity influences the crack path as well as crack propagation by connecting the pores. In the eutectic microstructure without porosity, failure starts to develop in silicon lamellae and proceeds in the ductile matrix. However, in the presence of pores fracture also initiates in silicon, and in the later stages of loading, porosity affects the path of the crack and results in additional crack nucleation, and thus, these pores also influence crack propagation in the matrix. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Claus D.,Institute For Technische Optik | Schumacher P.M.,Institute For Technische Optik | Wilke M.,Institute For Technische Optik | Mlikota M.,Institute For Materialprufung | And 13 more authors.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2015

Besides the many advantages minimally invasive surgery offers, the surgeon suffers from the loss of information, visual and mechanical (haptic feedback). The latter is an important tool, which helps the surgeon to localize tissue abnormalities (benign vs. malign tissue). We are aiming to generate a reliable constitutive FE model of the organ describing its mechanical properties by employing multiple elastographic measurement techniques at different scales (cell, tissue, and organ). A silicon phantom has been generated for the purpose of testing the transfer of information (delivery and processing of data). The stress-strain curve was recorded and embedded in the FE Model (Arruda-Boyce). A 2D displacement map was experimentally obtained from the phantom, which was in good agreement with the FE simulation. © 2015 SPIE. Source


Siddiq A.,Institute For Materialprufung | Schmauder S.,Institute For Materialprufung
IUTAM Bookseries | Year: 2010

Interface failure in metal/ceramic composites plays an important role in modern materials technology, as evident by their use in a variety of applications. High-strength materials, such as metal-matrix composites consist of internal interfaces between ceramic (e.g. SiC or Al 2O 3) particles or filaments within a metallic host. In microelectronics packaging, interfaces between metallic (Cu and/or Al) interconnects and SiO 2, carbide/nitride (TiCN) or oxide .Al 2O 3/ ceramics are commonplace, and impact the performance and longevity of solid state devices. Despite their widespread use, a basic understanding of these interfaces has been elusive. For example, given a particular metal/ceramic interface, it is not yet possible to accurately predict such fundamental properties as its fracture energy. In most of the cases, improvements in interface properties proceed via a costly and time consuming trial-and-error process in which numerous materials are evaluated until suitable performance is obtained. Computational methods provide a wide range of possibilities to study the fracture behaviour of such metal/ceramic interfaces. In the first part of the presented work, the deformation behaviour of niobium single crystals has been simulated using crystal plasticity theory. An automatic identification procedure has been proposed to identify the crystal plasticity parameters for each family of slip systems and simulation results of the mechanical behaviour of single crystal niobium are compared with the experiment. Good agreement between the experimental and simulation results was found. The second part presents effects of the different niobium single crystalline material orientations on crack initiation energies of the bicrystal niobium/sapphire four-point-bending-test specimens for a stationary crack tip. The trends of crack initiation energies are found to be similar to those observed during experiments. In the third part, crack propagation analyses of niobium/alumina bicrystal interface fracture have been performed using a cohesive modelling approach for three different orientations of single crystalline niobium. Parametric studies have been performed to study the effect of different cohesive law parameters, such as work of adhesion and cohesive strength, where work of adhesion is the area under the cohesive law curve while cohesive strength is the peak stress value of the cohesive law. The results show that cohesive strength has a stronger effect on themacroscopic fracture energy as compared to work of adhesion. Cohesive model parameters are identified for different combinations of cohesive strength and work of adhesion by applying a scale bridging procedure. In the last part, a correlation among the macroscopic fracture energy, cohesive strength, work of adhesion and yield stress of niobium single crystalline material will be derived. © 2010 Springer Science+Business Media B.V. Source


Lasko G.,Institute For Materialprufung | Burghard Z.,Institute of Materials Science | Bill J.,Institute of Materials Science | Schafer I.,Institute For Materialprufung | And 2 more authors.
Advanced Engineering Materials | Year: 2013

The extraordinary combination of strength and toughness attained by nature's highly sophisticated structural design in nacre has inspired the synthesis of novel layered nanomaterials. In the present work, numerical and analytical models are applied on the nanometer scale to attain a better insight and understanding concerning the mechanical behavior of bio-inspired layered materials. The special properties of biomaterials inspired the development of a large class of biomimetic materials and organic/inorganic composites and especially the properties of nacre are of interest for scientific researchers. It was found that aragonite layers consist of hexagonal platelets which are interconnected by the so called mineral bridges. Both structures are important for the reinforcement of nacre. For the first time, FE-simulations have been applied to simulate the mechanical response without unrealistic assumptions with respect to each property of the components of bio-inspired laminated organic/inorganic nanocomposites obtained by CBD. Source


Claus D.,Institute For Technische Optik | Schumacher P.M.,Institute For Technische Optik | Labitzke T.,Institute For Technische Optik | Mlikota M.,Institute For Materialprufung | And 13 more authors.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2015

During minimally invasive surgery the visual (3 dimensional) and mechanical (haptic) feedback is restricted or even non-existing, which imposes a serious loss of important information for decision making. Information about the mechanical properties of the biological tissue helps the surgeon to localize tissue abnormalities (benign vs. malign tissue). The work described here is directed towards assisting the surgeon during minimally invasive surgery, which in particular relates to the segmentation and navigation based on the recovery of mechanical properties. Besides the development of noninvasive elastographic measurement techniques, a reliable constitutive FE-model of the organ (describing its mechanical properties) is generated resulting in a further improvement of the segmentation and localization process. At first silicon phantoms, with and without foreign bodies have been generated for the purpose of testing the transfer of information (delivery and processing of data). The stress-strain curve was recorded and embedded in the FE-model (Arruda-Boyce). Two dimensional (2D) displacement maps have experimentally been obtained from the phantom, which were in good agreement with the FE simulation. © 2015 SPIE. Source

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