M. Auhorn

Failure mechanism of free standing single-walled carbon nanotube thin films under tensile load

The mechanical properties of free standing films of as prepared and acid purified single-walled carbon nanotubes were studied by means of tensile stress measurements as well as electron microscopy. Films appear to fail by crack propagation involving rupture or matrix pull-out of bridging nanotube bundles.

Influence of surface defects and edge geometry on the bending strength of slip-cast ZrO2 micro-specimens

Abstract Bending tests on slip-cast ceramic micro-specimens made of Y2O3-stabilised ZrO2 of the dimensions 0.2 × 0.2 × 1.2 mm3 were performed. Despite nominally identical feedstock make-up as well as identical parameters for slip-casting, debinding and sintering, the bending strengths of three process batches scatter between 1400 and 3400 MPa. As reasons for the scattering of the mechanical properties, surface defects and differently sized edge radii were determined. Correlations between surface roughness, edge radius and bending strength of the micro-specimens are presented. Additionally, the validity of the Weibull size effect could be confirmed with micro-specimens that have relatively smooth surfaces (peak-to-valley heights Rt between 0.5 and 1.5 mm) and relatively large edge radii (between 11 and 18 mm).

Microstructure, surface topography and mechanical properties of slip cast and powder injection moulded microspecimens made of zirconia

Abstract Investigations on ceramic microspecimens made of Y2O3-stabilized ZrO2 produced by slip casting or micro powder injection moulding are introduced. During the production of the microspecimens, feedstocks and sintering conditions were varied. Differently moulded specimens were examined with respect to their microstructure and surface topography using light microscopy, scanning electron microscopy (SEM) and confocal white light microscopy. Additionally, the mechanical characteristics were investigated by three-point bending tests using a micro universal testing device. The statistical analysis was realised by means of the Weibull theory and interpreted by the aid of SEM images of fracture surfaces. This research allowed to understand correlations between different feedstocks used, process parameters like the sintering conditions applied and the resulting characteristics as well as material properties of the microspecimens. These results could be used to improve the production process.