Autowave Criteria of Fracture and Plastic Strain Localization of Zirconium Alloys

Plastic deformation and fracture of Zr–1% Nb alloys exposed to quasi-static tensile testing have been studied via a joint analysis of stress-strain curves, ultrasound velocity and double-exposure speckle photographs. The possibilities of ductility evaluation through the εxx strain distribution in thin-walled parts of zirconium alloys are shown in this paper. The stress-strain state of zirconium alloys in a cold rolling site is investigated considering the development of localized deformation bands and changes in ultrasound velocity. It is established that the transition from the upsetting to the reduction region is accompanied by the significant exhaustion of the plasticity margin of the material; therefore, the latter is more prone to fracture in this zone exactly. It is shown that traditional methods estimating the plasticity margin from the mechanical properties cannot reveal this region, requiring a comprehensive study of macroscopically localized plastic strain in combination with acoustic measurements. In particular, the multi-pass cold rolling of Zr alloys includes various localized deformation processes that can result in the formation of localized plasticity autowaves. Recommendations for strain distribution division over the deformation zone length in the alloy in the pilger roll grooves are provided as well.

Development of an Instantaneous Velocity-Vector-Profile Method Using Conventional Ultrasonic Transducers

The velocity vector profile technique based on an ultrasound pulsed Doppler method can enrich the information of a flow field, however, it has shown a low availability because a new design of special transducers is required for each measurement case. This study proposes a new method of profiling the velocity vectors using conventional ultrasound transducers that are widely supplied to UVP (Ultrasound velocity profile) users. We constructed a configuration of the transducers to minimize the uncertainty of the detection points at the receivers, and a measurable distance was theoretically determined by the configuration. Two feasibility tests were carried out. One was a test for the assessment of the measurable distance, which agreed well with the theoretical distance. The other was the evaluation of the measurement of two-dimensional velocity vectors by the new method and it was performed in a towing tank facility without the velocity fluctuation. From the evaluation, it was confirmed that the measured vectors showed good agreement to the reference values, and their accuracy and precision were competitive compared to previous studies. The developed method was applied to two unsteady flows for demonstrations. The results clarified that the proposed method guarantees high availability and accuracy for the velocity vector profiles.

CONDITION OF BONE MINERAL DENSITY IN NEWBORNS AND THEIR MOTHERS OF DIFFERENT AGE GROUPS

Introduction. Prenatal period is an important starting pointof accumulation of minerals in the bones. The determination ofthe bone mineral density levels in a mother and a newborn andthe relationship between these indicators are important issuesof the present time.Objective is to assess the condition of the bone mineraldensity in full-term newborns depending on the bone mineraldensity of their mothers of different ages. Our case studiesmothers between 13 and 43 years of age and their newborns.Materials and methods: The research design presumedthe study of 79 newborns between 48 and 72 hours of agesimultaneously with their mothers between 13 and 43 yearsof age, who were presumably healthy and have been livingin Zaporizhzhia region. The study was carried out using anultrasonic bone sonometer "Sunlight Omnisense 9000", whichquantitatively measures the ultrasound velocity (SOS, m / s)characterizing the corresponding bone mineral density.Results. The highest SOS (speed of sound) levels werefound in newborns born from mothers aged 13-17 years and18-20 years - 3156 [3024; 3232], m / s and 3215 [3127; 3316],m / s, respectively (p<0.05). At the same time, the SOS levelsof these women were the lowest -3992 [3931; 4091], m / s and4037 [3966; 4105], m / s, respectively, compared with the SOSlevels of the mothers of the older age groups (p<0.05), but didnot correlate (p> 0.05) with high SOS levels of their children.Whereas the SOS indicators 4242 [4204; 4469], m / s in agroup of women aged 31–43 years had a moderate negativecorrelation with SOS levels 3006 [2897; 3041], m / s of theirnewborn children (p<0.05).Conclusions. We found out that the SOS indicatorsin children born from mothers of different age groups aresignificantly different (p <0.05): higher rates were found innewborns born from mothers aged 13-20 years. There was nostatistically significant difference in the SOS indicators inmothers between 13-20 years of age and their newborns, incomparison with women aged 18-20 years and their newbornbabies. At the same time, it was found out that only babies bornfrom mothers of the age group 31-43 years had an increase inthe SOS levels accompanied by a significant decrease in theseindicators in their mothers

THE STUDY OF THE INFLUENCE OF X-RAY IRRADIATION ON DISLOCATION CHARACTERISTICS IN LiF CRYSTALS

The dependences of the absorption α and the ultrasound velocity in LiF single crystals with residual deformation ε = 0.65% at 300 K in the range of radiation doses 0...1057 R were studied using the acoustic pulse echo method at a frequency of 7.5 MHz. Based on the results of measurements of the acoustic characteristics, the absolute values of the parameters of the dislocation structure – the average effective length of the dislocation loop L and the dislocation density Λ and their dependences on the irradiation time are determined. The calculated characteristics are compared with the previously obtained results for the high-frequency branch of the damped dislocation resonance and using the selective etching method. The revealed noticeable discrepancy in the values of these parameters is explained by the impossibility of describing a single attenuation mechanism for acoustic measurements carried out in a wide frequency range.

Ultrasonic velocity profiler applied to explore viscosity–pressure fields and their coupling in inelastic shear-thinning vortex streets

A method for simultaneous estimation of viscosity and pressure fields in inelastic shear-thinning fluids is developed by means of ultrasound velocity profiling technique (UVP). In the method, equation of continuity, rheological model and pressure Poisson equation are incorporated as data processing sequences for measured velocity distributions. The proposed method is applied to study the vortex street structure formed behind a circular cylinder, which shows viscosity–pressure coupling due to shear-thinning property of fluid. For demonstration, aqueous solution of CMC (carboxy methyl cellulose) of weight concentration of 0.1% is chosen as the working fluid with shear-thinning property. An alternating staggered pattern of low-pressure spots is successfully reconstructed for zero-shear-based Reynolds number, Re = 50–300. We have found that increasing Re resulted in decrease in vortex shedding Strouhal number because of vortex sustainability supported by shear-thinning property. Graphical abstract

Production Technologies of Ancient Bricks from Padua, Italy: Changing Colors and Resistance over Time

Representative and very uneven texturally bricks having yellow/beige or pale or dark red colors from the Renaissance walls (16th century) of Padua, Northeast Italy, were studied by means of colorimetric, petrographic (MOP), chemical (XRF), mineralogical (PXRD) and microstructural analysis (FESEM-EDS). Starting from the color measurements of the ceramic bodies, the manufacturing technologies and their influence on the physical behavior and durability of the bricks were established. The porous system was characterized by means of hygric tests and mercury intrusion porosimetry; the compactness and structural anisotropy were defined through ultrasound velocity; the uniaxial compressive strength was determined; and durability to salt crystallization and frost action of the bricks was assessed. Mg- and Ca-rich illitic clays fired at temperatures ≥900 °C were used to manufacture the beige hue bodies, while the pale red bricks were made out with Ca- and Fe-rich illitic clays fired at 850–900 °C. A lower carbonate content on the base clays and a lower firing temperature were the main causes responsible for the changing colors from beige to red hue. The increase of the red color was associated to higher silicate inclusions content and lower development of reaction rims around grains. The low sintering degree achieved yielded highly porous bodies with diverse porous systems, leading to differential physical performance and durability of the bricks that may turn out beneficial for the conservation of the historic walls.