Constructing convex limit surfaces in material mechanics

In our previous paper [3], a method of constructing convex surfaces in 6D space of symmetric second-rank tensors by means of deforming the unit sphere S⁵ into a conoidal surface has been considered. Now we extend this method to parabolic surfaces and to the case where the shape of the surfaces depends also on the third tensor invariant. The resulting equations can be utilized for specifying the limit surfaces in the mechanics of isotropic and anisotropic solids. Some examples on approximating data on the experimental strength are presented.Institute of Polymer Mechanics, Latvian Academy of Sciences. Riga, LV-1006 Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 3, pp. 339–349, May–June, 1996.     

Powder X‐Ray Diffraction Investigation of Xylazine Hydrochloride Solid Phase Transformation Kinetics

The kinetics of the solid‐state phase transformation of xylazine hydrochloride form X to A has been investigated using powder X‐ray diffraction and differential thermal analysis. Three different kinetic models have been used to describe transition kinetics: the Avrami–Erofeev equation, the Cardew equation, and the methodology for simulation of solid‐state phase transition kinetics by the combination of nucleation and nuclei growth processes. The latter has been recently developed and has been tested in this paper for the case of a real solid‐state transition. The relative humidity, mechanical pressure, temperature, and sample‐preparation effect on phase‐transition kinetics have been investigated, and rate constant changes have been analyzed.     

Study of the alternating current electrical properties of ZrO2–7.5 mol% Y2O3 ceramics at room temperature and at 457–595 K

The impedance of a ZrO₂–7.5 mol% Y₂O₃ ceramic specimen was measured using the two-probe technique in the frequency range 20 Hz–1 MHz at room temperature and in the temperature range 457–595 K. The novelty of the research lies in the analysis of the intragrain part of the impedance spectra of the ceramics on the basis of the approach proposed in the literature for impedance of ZrO₂–Y₂O₃ single crystals. The method to determine a value of the intragrain direct current electrical conductivity from an impedance spectrum has been developed. The frequency dependence of the intragrain complex dielectric response was interpreted according to the common model used in the literature. Frequency domains, where a power-law dependence having different exponents n ₁=0.825–0.844 and n ₂=0.571–0.592 is observed, were found. The inner consistency of the model used is verified. Values of the transition frequency and the relaxation frequency were determined for the grain interiors and compared with each other. The values of the activation energies of the direct current conductivity, the transition frequency and the relaxation frequency are found to be the same within experimental uncertainty in the temperature range 457–523 K. Electronic Publication