TY - JOUR A1 - Bachmann, F. A1 - Bente, Klaas A1 - Codutti, A. A1 - Faivre, D. T1 - Using Shape Diversity on the Way to Structure-Function Designs for Magnetic Micropropellers N2 - Synthetic microswimmers mimicking biological movements at the microscale have been developed in recent years. Actuating helical magnetic materials with a homogeneous rotating magnetic field is one of the most widespread techniques for propulsion at the microscale, partly because the actuation strategy revolves around a simple linear relationship between the actuating field frequency and the propeller velocity. However, full control of the swimmers’ motion has remained a challenge. Increasing the controllability of micropropellers is crucial to achieve complex actuation schemes that, in turn, are directly relevant for numerous applications. However, the simplicity of the linear relationship limits the possibilities and flexibilities of swarm control. Using a pool of randomly shaped magnetic microswimmers, we show that the complexity of shape can advantageously be translated into enhanced control. In particular, directional reversal of sorted micropropellers is controlled by the frequency of the actuating field. This directionality change is linked to the balance between magnetic and hydrodynamic forces. We further show an example of how this behavior can experimentally lead to simple and effective sorting of individual swimmers from a group. The ability of these propellers to reverse swimming direction solely by frequency increases the control possibilities and is an example for propeller designs, where the complexity needed for many applications is embedded directly in the propeller geometry rather than external factors such as actuation sequences. KW - Active Matter KW - Low Reynolds number swimmers KW - Actuating materials KW - Microstructure KW - Swarming PY - 2019 U6 - https://doi.org/10.1103/PhysRevApplied.11.034039 VL - 11 IS - 3 SP - 034039 PB - American Physical Society AN - OPUS4-47731 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, H. J. A1 - Bucheli, T. D. A1 - Dieguez-Alonso, A. A1 - Fabbri, D. A1 - Knicker, H. A1 - Schmidt, H.-P. A1 - Ulbricht, A. A1 - Becker, Roland A1 - Buscaroli, A. A1 - Buerge, D. A1 - Cross, A. A1 - Dickinson, D. A1 - Enders, A. A1 - Esteves, V.I. A1 - Evangelou, M. W. H. A1 - Fellet, G. A1 - Friedrich, K. A1 - Gasco Guerrero, G. A1 - Glaser, B. A1 - Hanke, U. M. A1 - Hanley, K. A1 - Hilber, I. A1 - Kalderis, D. A1 - Leifeld, J. A1 - Masek, O. A1 - Mumme, J. A1 - Paneque Carmona, M. A1 - Calvelo Pereira, R. A1 - Rees, F. A1 - Rombola, A. G. A1 - de la Rosa, J. M. A1 - Sakrabani, R. A1 - Sohi, S. A1 - Soja, G. A1 - Valagussa, M. A1 - Verheijen, F. A1 - Zehetner, F. T1 - Towards the standardization of biochar analysis: the COST action TD1107 interlaboratory comparison N2 - Biochar produced by pyrolysis of organic residues is increasingly used for soil amendment and many other applications. However, analytical methods for its physical and chemical characterization are yet far from being specifically adapted, optimized, and standardized. Therefore, COST Action TD1107 conducted an interlaboratory comparison in which 22 laboratories from 12 countries analyzed three different types of biochar for 38 physical–chemical parameters (macro- and microelements, heavy metals, polycyclic aromatic hydrocarbons, pH, electrical conductivity, and specific surface area) with their preferential methods. The data were evaluated in detail using professional interlaboratory testing software. Whereas intralaboratory repeatability was generally good or at least acceptable, interlaboratory reproducibility was mostly not (20% < mean reproducibility standard deviation < 460%). This paper contributes to better comparability of biochar data published already and provides recommendations to improve and harmonize specific methods for biochar analysis in the future. KW - Biochar KW - Analysis KW - Standardization KW - Ring test KW - Interlaboratory comparison PY - 2016 U6 - https://doi.org/10.1021/acs.jafc.5b05055 SN - 0021-8561 SN - 1520-5118 VL - 64 IS - 2 SP - 513 EP - 527 PB - American Chemical Society CY - Columbus, Ohio AN - OPUS4-35289 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Carstensen, J. A1 - Bergmann, L. A1 - dos Santos, J. F. A1 - Wu, C. S. A1 - Rethmeier, Michael T1 - Numerical simulation of thermally induced residual stresses in friction stir welding of aluminum alloy 2024-T3 at different welding speeds N2 - The paper deals with a numerical finite element simulation of the residual stress evolution in friction stir welding of 6 mm thick aluminum alloy AA2024-T3. The transient thermal field during the welding process was calculated with the commercial code COMSOL Multiphysics 5.0. Therefore, a thermal-pseudo-mechanical (TPM) heat source was implemented. A subsequent mechanical simulation was performed with varying hardening models for different welding speeds of 60 and 300 mm/min. The influence of softening of the material, which was due to hardening precipitation dissolution associated to the heating, was also investigated. Experiments in terms of thermocouple measurements as well as Vickers hardness and X-ray measurements of the residual stresses were conducted and compared to numerically obtained results. A qualitatively as well as quantitatively good agreement was found for different applied welding speeds. KW - Friction stir welding KW - Residual stress KW - Finite element simulation KW - Thermal softening KW - Aluminum alloy 2024-T3 PY - 2017 U6 - https://doi.org/10.1007/s00170-016-9793-8 SN - 0268-3768 SN - 1433-3015 VL - 91 SP - 1443 EP - 1452 PB - Springer CY - London AN - OPUS4-40511 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -