Volume 57, Issue 11

Porosity, pore distribution, mean grain size, and grain size distribution determine the mechanical and physical properties of ceramics. The quantitative structural analysis is therefore essential for the characterization of sintered materials. A semi-automated structural analysis requires a preceding image segmentation step in which all pixels are divided into respective objects to be examined so that they can be clearly assigned to a microstructural constituent. The present work analyzes the watershed transformation, IsoData, and WEKA algorithm image segmentation methods with regard to a grain size and pore characterization using light microscope micrographs of solid-state sintered silicon carbide (SSiC). The open source software ImageJ is used for image segmentation and detection. It does not just provide a quick quantification of the microstructural constituents but can also be extended with a considerable number of plugins, thus providing great flexibility when working on image analysis tasks.

An essential requirement for the quality control of cast iron products is the analysis of their microstructure. Even though cast irons constitute a very traditional class of materials, they still play a key role in many industrial sectors. It is therefore all the more surprising that in the age of digital image processing, the development of a digital standard on that basis has not yet been achieved and that classification by visual analysis is still the norm for certain subtasks. The following sections will present an approach to resolving the seemingly easy subtask of determining flake length distribution in GJL. A key element in this respect is the question if and how to separate this three-dimensional network structure on the basis of a two-dimensional metallographic section. Depending on the type of structural arrangement, a quasi-hybrid approach was applied: isolating part of the flakes while the more compact structures are not separated and will remain as one individual lamellar object.

Helical tension springs used in switch mechanisms of medium voltage switches failed prematurely in test rigs. The switch mechanism assemblies did not reach the required number of cycles to failure. The springs failed by low cycle fatigue fracture. They were phosphate coated for corrosion protection but not shot peened. The material used for the springs is a usual patented spring steel. Chemical composition, mechanical properties, and microstructure of the failed springs and a reference spring alike were all unremarkable. The subject springs were assembled and rig tested at three different locations but failed only at two of them, not in the third. It was concluded that misalignment from assembly was the root cause of failure.