Frank Hoffmann’s research while affiliated with TU Bergakademie Freiberg and other places

In this study, the behavior of MnS particles in a steel matrix is investigated through in situ tensile testing and digital image correlation (DIC) analysis. The goal of this research is to understand the mechanical behavior of MnS inclusions based on their position in the steel matrix. To accomplish this, micro-dog bone-shaped samples are prepared, tensile tested, and analyzed. Macro-mechanical results reveal that the material yields at a stress of 350 MPa and has an ultimate tensile strength of 640 MPa, with a total elongation of 17%. For micro-mechanical analysis, scanning electron microscopy (SEM) images are taken at incremental strains and processed using DIC software to visualize the local strain evolution. The DIC analysis quantifiably demonstrates that the local strain is highest in the ferrite matrix, and while lowest in the pearlite matrix, the MnS particles and the interfaces between different materials experienced intermediate strains. The research provides new insights into the micro-mechanical deformation behavior of MnS particles in a steel matrix and has the potential to inform the optimization of the microstructure and properties of materials containing MnS inclusions.

This work investigates a ferrite matrix with multiple non-metallic inclusions to evaluate their influence on the global and local deformation and damage behavior of modified 16MnCrS5 steel. For this purpose, appropriate specimens are prepared and polished. The EBSD technique is used to record local phase and orientation data, then analyze and identify the size and type of inclusions present in the material. The EBSD data are then used to run full phase crystal plasticity simulations using DAMASK-calibrated material model parameters. The qualitative and quantitative analysis of these full phase simulations provides a detailed insight into how the distribution of non-metallic inclusions within the ferrite matrix affects the local stress, strain, and damage behavior. In situ tensile tests are carried out on specially prepared miniature dog-bone-shaped notched specimens in ZEISS Gemini 450 scanning electron microscope with a Kammrath and Weiss tensile test stage. By adopting an optimized scheme, tensile tests are carried out, and local images around one large and several small MnS inclusions are taken at incremental strain values. These images are then processed using VEDDAC, a digital image correlation-based microstrain measurement tool. The damage initiation around several inclusions is recorded during the in situ tensile tests, and damage initiation, propagation, and strain localization are analyzed. The experimental results validate the simulation outcomes, providing deeper insight into the experimentally observed trends.

Analogous to other manufacturing processes, the demands on the reproducibility of properties of each individual component are increasing in the field of bulk metal forming. In series production, changing a supplier of semi-finished products or processing a different batch of material can have a negative effect on the continuity of the production process. Therefore, the formability of initial semi-finished products, to evaluate the failure limit of the material under given deformation conditions, must be carried out faster, more accurately, and more simply than before. Material (chemical composition, degree of purity, crystal structure, phase composition and described by internal defects), as well as the deformation conditions (stress state, deformation temperature, strain rate and friction conditions, caused by a pretreated surface), play an essential role in defining the formability of a specific material. The failure-free and cost-effective production of parts are needed. Therefore a simple, reliable, and reproducible test method is needed, which can yield a wide range of factors influencing the formability of a material.

This article reports on the development of a hardenable PHFP steel for energy-efficient and distortion-reduced production of cold-formed, high-strength structural components. Based on an alloying concept containing 0.8 wt.-% copper, a technology for the production of screws has been developed to exploit the precipitation-hardening effect of copper for increasing strength by tempering while avoiding final quenching.

This article reports on the development of a Precipitation‐Hardenable‐Ferritic‐Pearlitic steel (PHFP steel) for energy‐efficient and distortion‐reduced production of cold‐formed, high‐strength structural components. Based on an alloying concept containing 0.8 wt% copper, a technology for the production of screws is developed to exploit the precipitation‐hardening effect of copper for increasing strength by ageing while avoiding final quenching.

New technical applications and the ongoing infrastructural and industrial development of regions with extreme climatic conditions place ever greater demands on the properties of the materials used. On the one hand conventional materials can often meet such demands only to a limited extent whilst, on the other, a lack of experience means that sometimes no solid conclusions can be drawn regarding their suitability under extreme conditions. The examination of the influence of extreme environmental conditions on the behaviour of the material and the development of innovative materials with a tailored profile of properties is therefore one of the main tasks of modern material research as well as the material manufacturing and processing industry.