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Cold spray additively manufactured pure iron for magnetic applications
(Elsevier BV, 2026) Annand A.; Kovářík O.; Ctibor P.; Aragbol Z.; Wiehler L.; Gaertner F.; Klassen T.; Cizek J.
Pure iron powder combines excellent plastic deformability under a high-velocity impact with high magnetizability and permeability, making it an economical candidate for cold spray additive manufacturing (CSAM) and repairs in magnetic applications. This work explores the fracture mechanics and electromagnetic (EM) properties of CSAM pure iron deposited using cheaper nitrogen as the process gas at temperatures of 900 °C and 1000 °C, achieving relative densities of 97.3 % and 98.0 %, respectively. The deposits exhibited an ultimate tensile strength greater than 250 MPa and elongation to fracture of less than 0.3 %, a behavior consistent with the characteristic results of as-sprayed CSAM deposits. The fatigue crack growth rate analyses showed the propagation being faster than in wrought iron through different mechanisms: trans-particle crack propagation near the threshold stress intensity factor, and inter-particle decohesion at higher loads. The EM testing indicated that CSAM pure iron saturated at a lower induction and had lower permeability than wrought low-carbon steel, while its coercivity and hysteresis losses were higher, and electrical resistivity was similar. Despite the lower mechanical and magnetic performance, CSAM pure iron or similarly deformable ferritic alloys can meet the requirements for low-field, low-frequency, or direct-current applications, and provide a route for direct near-net-shape additive manufacturing or in-situ repair of magnetic components without scraping existing parts.
Scaling the test to component size: case study for ZhS6K superalloy
(Slovenská akademie věd, Ústav materiálov a mechaniky strojov, 2026) Pavlas J.; Kovářík O.; Růžička M.; Slavík S.
The purpose of this article is the fatigue crack growth rate and stress-strain characteristic of a nickel superalloys ZhS6K. The da/dN (K) data from near-threshold to Paris regime and the stress-strain curve were obtained using a new methodology designed for bending small specimens using material extracted directly from the blade. The Hartmann-Schijve formula was fitted to describe the fatigue crack growth rate data. Failure mechanism was related to the crack propagation rate by help of fractographic analysis. A comparative analysis of the investigated material with the related alloy Inconel 718 was also performed. The tensile and compression stress-strain behavior, fatigue crack growth rate, and fracture toughness of the ZhS6K nickel superalloy were determined from a single turbine blade, with failure mechanisms examined using scanning electron microscopy. Compared to Inconel 718, ZhS6K offers higher resistance to fatigue crack growth but has significantly lower fracture toughness and stress-strain properties. The obtained results fill a gap in materials data necessary for the durability and damage tolerance assessment of turbine blades made of ZhS6K alloy. Although the primary focus is on the fracture behavior of the newly characterized material ZhS6K, the findings contribute to a broader understanding of the fracture mechanics within the entire class of structurally similar materials.
High-fidelity control design for distributed-parameter system describing hydropower plant with long penstock: Case studies
(Elsevier Science, 2026) Fišer J.; Zítek P.; Kuchař M.; Peichl A.; Kučera M.; Kulík P.; Vyhlídal T.
The paper deals with hydropower plant control, focused on the hydro-turbine governing system (HTGS) - the core of the hydropower plant. A model of built-in HTGS in hydropower plant with long conduit, originating in a distributed-parameter system, is considered for tuning its governor, implemented as a two-degree-of-freedom (2DoF) PID controller. Since this HTGS is characterized with long penstock conduit causing elastic water hammer phenomenon it is described by a neutral time delay system with control being a challenge in industry. Based on dimensional analysis application, the industrial controller setting is achieved by spectral abscissa minimization within dominant root locus that guarantees operating boundaries safely distant from the stability margin. The capability of the hydro-turbine governing control system tuning by the proposed optimization method is demonstrated on the comparison of real data with high-fidelity model-based generated data of two medium-sized hydropower plants. The minimum spectral abscissa results in - 0.08 and - 0.38 in the frequency control mode and the power control mode, respectively, both superior to spectral abscissas coming out of other PID-type tuning methods compared. Simultaneously, the proposed optimization method is superior to other methods considered in the undershoot resulting in the frequency control mode while in the power control mode the settling time results the shortest of all the tuning methods considered.
Adaptive Geometric Control of Knitted Formwork: A Genetic Algorithm Approach for Hypar Concrete Shells
Adaptivní geometrické řízení pleteného bednění: Využití genetických algoritmů při realizaci betonových skořepin tvaru hypar
(Czech Technical University in Prague) Zažirej, Stanislav; Štemberk, Petr; Červenka, Jan; Park, Kyoungsoo
Thin concrete shells are highly efficient structural systems due to their reliance on membrane action, but currently, their construction on a larger scale is severely restricted by the prohibitive labor and material costs associated with bespoke rigid timber formwork. While flexible textile formwork systems offer a sustainable, low-waste alternative, passive membranes are highly susceptible to uncontrolled sagging and kinematic instability under the self-weight of fresh concrete. This instability frequently causes the final structure to deviate significantly from the intended digitally designed shape. To bridge this digital-physical gap, this dissertation proposes a novel, adaptive construction methodology that synthesizes knitted flexible formwork system with real-time robotic boundary control. The core contribution of this research is the development of a predictive "digital twin" designed to solve the inverse problem of fabrication. The computational engine calculates the precise initial geometry of the dry tensioned fabric and pre-determines the sequential robotic actuation necessary to compensate for physical deflection during the concrete casting. Developed within the Rhinoceros and Grasshopper environment using custom Python scripting, the simulation sequentially models a four-phase construction process. It captures the anisotropic behavior of the pre-stressed fabric and the time-dependent rheology of very early age concrete as it solidifies into a rigid Primary Stiffening Layer (PSL). To predict material failure during active boundary manipulation, the system continuously monitors strain. It effectively translates discrete 1D spring ruptures from the dynamic solver into a 2D smeared crack model. To navigate the high-dimensional trade-offs of this system, the spatial coordinates and kinematic lengths of the boundary cables serve as the specific genetic variables for a Multi-Objective Evolutionary Algorithm (NSGA-II). The algorithm explores thousands of design permutations to simultaneously minimize the PSL thickness and maximize global structural stability. Validated against reduced-scale physical prototypes using photogrammetry, this predictive framework demonstrates that the automated, active control of flexible formwork systems makes the materialization of complex concrete shells structurally, economically, and sustainably viable. Ultimately, this empowers the redeployment of these elegant structures as performative urban catalysts capable of revitalizing modern public spaces.
Study of pedestal stability on the COMPASS and JET tokamaks
Studium stability pedestalu na tokamacích COMPASS a JET
(Czech Technical University in Prague) Šos, Miroslav; Komm, Michael; Roučka, Štěpán; Dunne, Michael
This thesis investigates the behaviour of pedestal structure and stability in H-mode plasmas on the JET and COMPASS tokamaks. The work focuses on the role of toroidal rotation, neon impurity seeding, ELM dynamics, and coreedge coupling in determining pedestal performance. Systematic stability analyses show that toroidal rotation has a favourable but limited effect on resolving the discrepancy between predicted and observed pedestal stability in JET ILW plasmas, while neon seeding leads to increased pedestal pressure and reduced ELM activity. For COMPASS plasmas, the ELM cycle time is identified as a key parameter controlling pedestal build-up, although ideal peelingballooning stability does not universally explain ELM triggering. The results provide new insight into the limits of ideal MHD stability models for describing pedestal behaviour in tokamaks of different sizes.