Instrumented impact test of duplex stainless steel miniature specimen

The paper describes a new approach to characterize metallic materials by a novel instrumented notch impact test for samples with small specimen size. A piezo‐electric sensor mounted on the pendulum hammer provides force information during the fracture process. By numerical integration of the signal the absorbed impact energy can be calculated very exactly. Further information about the fracture behavior can be extracted from the resulting force‐displacement‐diagram. Several duplex stainless steels in different heat treatment conditions were tested and compared to standard Charpy impact testing specimen. It is concluded that different grades of embrittlement of duplex materials can be detected with high accuracy. Due to a data acquisition rate of 250 kilo‐samples/second and limited stiffness of the pendulum hammer impact energies of less than 7% of maximum energy materials with high brittleness can only be characterized qualitatively.     

Polymere Nanoverbundwerkstoffe: Chancen,Risiken und Potenzial zur Verbesserung der mechanischen und physikalischen Eigenschaften

Polymer Nanocomposites: chances, risks and potential to improve the mechanical and physical properties The development of nano‐particle reinforced polymer composites is presently seen as one of the most promising approaches of materials for future engineering applications. The unique properties of at least some types of the nano‐particles (e.g., Carbon Nanotubes or Carbon Black) and the possibility of combining them with conventional materials and reinforcements (e.g., carbon‐, glass‐ or aramid‐fibres), has led to an intense research in the field of nanocomposites. Especially Carbon Nanotubes have shown a high potential for an improvement of the properties of polymers. Besides an increase in the electrical conductivity even at an extremely low nanotube content the improvement of the mechanical properties is of special interest. The exceptionally high aspect ratio in combination with a low density and a high strength and stiffness make the carbon nanotubes a most interesting candidate for a reinforcement of polymeric materials. The electrical, mechanical and thermal properties of Carbon Nanotubes open up new perspectives also for their use as multifunctional materials, e.g. conductive polymers with improved mechanical performance. The problem, however, is to transfer the interesting potential regarding the mechanical, thermal and electrical properties to the polymer. Two main issues have to be addressed for a significant improvement of the properties of polymers by adding Carbon Nanotubes: the interfacial bonding and, especially also, a proper dispersion of the individual Carbon Nanotubes in the polymeric matrix.     

Critical evaluation of indentation fracture toughness measurements with Vickers indenter on yttria‐stabilized zirconia dental ceramics

The purpose of this study was to investigate and analyze fracture toughness (K_Ic) of yttria stabilized tetragonal zirconia (Y‐TZP) dental ceramics by the Vickers indentation fracture test. In order to determine fracture toughness, the Vickers indenter was used under the load of 294.20 N (HV30). The cracks, which occur from the corners of a Vickers indentation, were measured and used for fracture toughness determination, through five mathematical models according to (I) Anstis, (II) Evans and Charles, (III) Tanaka, (IV) Niihara, Morena and Hasselman and (V) Lankford. Morphology of indentation cracking was determined by scanning electron microscope. The most adequate model for determination of fracture toughness (K_Ic) of yttria stabilized tetragonal zirconia dental ceramics by the Vickers indentation fracture test is Lankford model.     

Shear capacity of brick masonry with partially supported slab

In order to investigate the influence of a partially supported slab on the in‐plane shear resistance of masonry walls, six shear tests on full scale walls were performed at the Chair of Structural Concrete of the University of Kassel in cooperation with ”Arbeitsgemeinschaft Mauerziegel“. The walls were made of large chamber clay masonry units and the depths of the partially supported slabs were different. The large chamber units are typically used for thermally insulated exterior walls, with the slabs only being partially supported. The influence of this constellation is not taken into account in shear capacity assessment according to the current version of Eurocode 6 for Germany. This article describes the test results and provides a comparison with Eurocode 6. In addition, the results of older shear tests on masonry walls made of vertically perforated units with eccentric load application were used.     

Monolithic lightweight concrete masonry for multi‐storey apartment buildings

Affordable living space has become one of the main talking points in Germany next to the threat of climate change. The SMEs of the German lightweight concrete industry offer regional masonry solutions for detached, semi‐detached, and terraced houses as well as multi‐storey apartment buildings. Particularly in densely populated urban centres, the need for multi‐storey apartment buildings arises constantly. In the following the performance of monolithic lightweight concrete masonry will be described and compared with the relevant requirements for multi‐storey apartment buildings. It will be demonstrated that masonry with supposedly low compressive strength can still fulfil all requirements. Of particular significance here are the external wall‐slab junctions.