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A matter of fact is that extremal principles have been introduced in mechanics in more (Euler, Lagrange) or less (Hamilton) than 200 years ago. One may also observe an impact of thermodynamic extremal principles based on maximum dissipation due to all the entropy production expressed in several disciplines. According fields are theory of communication, statistical mechanics and later physics of earth since already 70 years. The current paper offers some (historical) overview on several applications. "Ziegler's principle" is an implementation of the maximum entropy production going out to the dissipation and yielding a maximum dissipation. The goal of this paper is now the implementation of this extremal principle performed along an algebraic concept. Such a concept can be extended to a system with several internal variables as outlined by Coleman and Gurtin in context with the Gibbs (free) energy. [ABSTRACT FROM AUTHOR]

Grain refinement can be described by the classical kinetic equation using a negative value of the specific grain boundary Gibbs energy. A respective overview is offered reporting according observations and simulations, particularly linked to grain boundary segregation. Classical grain growth model is used in the treatment of evolution of the distribution function during refinement. The adapted model requires defining nucleation rate of new grains, which significantly influences the kinetics of the system of grains. Moreover, a jump in the distribution function is allowed at a certain value of the grain radiusRJ, which separates old grains from newly nucleated ones. Evolution equation for both the critical radiusRcand separation radiusRJ(jump position) as well as for the dimension-free distribution (shape) function are derived. Illustrative examples for the evolution of the system parameters under various nucleation rates of newly generated grains are presented. [ABSTRACT FROM PUBLISHER]

The phase field method is frequently employed to simulate evolution of rather complex microstructures. In order to accurately describe the real kinetics of a specific material system, the phase field parameters must be calibrated to standard thermodynamic quantities such as interface mobilities or interface energies. This letter presents a convenient method, based on thermodynamic modelling of shrinking of a single grain embedded in single crystal (matrix), how to calibrate the phase field parameters. It also shows, how the required thermodynamic quantities can be met by proper rescaling of a phase field simulation carried out for given phase field parameters. [ABSTRACT FROM AUTHOR]

The hysteresis of ball-milled Fe-doped YCo5 powder has been optimized by controlling the temperature and time for rapid annealing under vacuum and argon. The crystallite size is only 25 nm; yet, it has been possible to field align Y(Co,Fe) powder with a 5-20 μm grain size in a 5 T field to obtain a remanence ratio of 0.65, due to texture in the ball-milled powder. The nominal energy product of the powder is 140 kJ/m³. A pressed magnet with 78% of theoretical density has an energy product of 65 kJ/m³. This magnet could fill the gap between oriented ferrite (34 kJ/m³) and oriented Nd-Fe-B (350 kJ/m³). [ABSTRACT FROM AUTHOR]

The present work focuses on changes of mechanical properties in pyrolysed spruce wood as a function of temperature up to 2400°C. Nanoindentation tests are used for the determination of mechanical properties at the scale of single wood cell walls. Hardness, indentation modulus and elasto-plastic/brittle behaviour of the carbonaceous residues are derived as function of pyrolysis temperature. Hardness values increase continuously by more than one order of magnitude to 4.5?GPa at 700°C. The indentation modulus shows complex changes with a minimum of 5?GPa around 400°C and a maximum of 40?GPa around 1000°C. The deformation induced by the indenter is largely visco-plastic in native wood, but it is almost purely elastic in the carbonaceous residue, with particular low values of the indentation ductility index around 700°C. A low density and a strongly cross-linked carbon structure may explain the mechanical behaviour at these intermediate temperatures. A final decrease of the modulus and a slight decrease of ductility for temperatures above 2000°C can be attributed to a continuous structural transition of the material towards graphite-like stacking of carbon sheets and to preferred carbon orientation along the wood cell axis. [ABSTRACT FROM AUTHOR]