Volume 60, Issue 6

The characterization of fractographic surfaces typically requires experts to evaluate the characteristics of fracture surfaces. However, these evaluations are influenced by human factors, such as subjectivity, and suffer from a lack of reproducibility. In this context, machine learning (ML), which has been established in various disciplines within materials science over the past few years, is a promising field enabling a more objective and reproducible evaluation. This study will evaluate the use of ML for the evaluation of fracture surfaces of notched Charpy specimens based on digital camera images. Image sections of the two reference regions “upper shelf” (ductile) and “lower shelf” (brittle) will serve as the database. In a first step, data visualization will be performed and data separability will be verified using unsupervised ML. On this basis, supervised ML will be used to train models to distinguish brittle and ductile fractures. These models will then be applied to determine ductile und brittle portions in mixed fracture modes, with the results being in good agreement with the expert consensus achieved in the round robin test.

The influence of vibratory polishing time on the quality of EBSD mappings of a multiphase microstructure is investigated and optimized for CuZn30//CuZn80 diffusion couples. The diffusion couples consist of four different phases whose hardness varies between 70 HV0.1 and 454 HV0.1. These are first mechanically ground, polished and finally prepared by vibratory polishing. A vibratory polishing of 2 h provides for all phases the highest quality of the recorded Kikuchi patterns (Image Quality values) and the highest correct assignment of the individual pixels of the mapping. Preparation artifacts, such as relief formation, only appear at higher vibratory polishing times (> 2 h). A vibratory polishing of the diffusion couples of 0.5 h already provides sufficient surface quality for EBSD analyses.

The failure of fastening elements in electrical terminal blocks was attributed to various material-related causes. While the casehardened terminal screws broke due to hydrogen embrittlement, the material-related cause of the plastic deformations of the roof-shaped washers and the stripping of the threads of the square nuts are undersizing and an insufficient strength for this particular application.