This article deals with nondestructive testing methods such are ultrasonic measurements and image analysis as applied to the thermal stability testing of materials. Image analysis is also used to determine damage to the surface during the cavitation resistance testing. Possibilities of the used nondestructive methods and results of their application are discussed on the basis of the obtained results for low cement, high alumina castables. Keywords: nondestructive methods; ultrasonic measurements; image analysis; thermal shock; low cement high alumina castables

The purpose of this study was to investigate the mechanical properties and level of cavitation damage to alumina-based low-cement castable. The effects of temperature treatment on some of the mechanical properties (strength, Young's modulus of elasticity) will be discussed. Cold crushing and flexural strength were determined using the standard laboratory procedures for destructive testing. The nondestructive methods such as ultrasonic measurements and image analysis were used for measuring the elasticity modulus and level of surface deterioration caused by cavitation testing. Cavitation damages in the alumina-based refractory specimens were induced by the modified vibratory cavitation setup. The rise of temperature treatment from room temperature to 1600°C resulted in strength increase by almost four times, with a slight drop occurring at 800°C. The values of Young's modulus were around 20 GPa at all stages of temperature treatment, with an obvious decrease at 800°C and 1200°C. Because the results show that the sintered low-cement castable exhibited very good resistance to the cavitation erosion, this material can be successfully used in the conditions where the cavitation resistance is needed.

Alumina based low cement castable (LCC) was synthesized and then treated from room temperature to 1600°C. Ultrasonic measurements were applied with the aim to obtain results of longitudinal and transversal ultrasonic velocities as well as Young's modulus of elasticity. Changes in microstructure of the samples treated at different temperatures were observed by SEM and image analyses. Correlation among mechanical, physical, and elastic properties and microstructure were also discussed. Results show that heating temperature, microstructure, and porosity have strong influence on cold crushing, flexural, and tensile strength as well as on Young's modulus of elasticity.

This paper presents numerical analysis of stress and strain conditions of a three-dimensional furniture skeleton construction and its joints. The fi nite volume method is used in the calculation. Orthotropy of the wood material is accounted for by approximating it with an isotropic material whose elastic modulus and Poisson’s ratio are calculated by employing the least-square method. The displacement of the edge point for the loaded joint was also determined experimentally. The agreement of results of the calculation and experimental data can be considered satisfactory. The numerical results presented in this paper also provided an opportunity for identifi cation of the region with the largest load and strain in the complex chair skeleton construction, which is one of the most complex pieces of furniture.

In the recent decades, the use of unshaped monolithic refractories has been increasing greatly because of their significant advantages over other shaped refractory bricks of the same class. A low cement high alumina castable was synthetised and sintered at 1300°C in order to investigate thermal and mechanical properties, as well as thermal shock behavior. The water quench test was applied as an experimental method for thermal stability testing. Modification of the water quench test was performed by additional monitoring of the samples behavior during the water quench test such as implementation of image analysis and ultrasonic measurements. The image analysis program was applied on samples in order to measure the level of surface damage before and during the water quench test. Ultrasonic measurements were performed with the aim to measure the Young modulus of elasticity during the testing. Strength deterioration of the samples was calculated by the model based on ultrasonic velocity changes during the water quench test. The influence of monitoring the damage level before and during the quench experiment and its influence on thermal shock behavior will be discussed.

Polyphenols are of secondary plant metabolites, naturally present in fruit, vegetables and herbs. In last two decades the number of publications on the potential health benefits of these compounds has increased enormously. The aim of this study is to determine and compare polyphenolic profile and related antioxidative properties of Vitis vinifera leaf and grape berry skin extracts. The research includes 21 grape varieties (White: Bogdanusa, Debit, Grk, Kuc, Malvasija, Marastina, Medna, Prc, Posip, Trebbiano toscano, Vugava and Žlahtina ; Red: Babica, Babic, Cabernet sauvignon, Dobricic, Glavinusa, Nincusa, Plavac mali, Plavina and Vranac). Plant material was collected at the stage of the grape technological maturity. Phenolic profile of plant extracts (total phenols, flavonoids, non-flavonoids, catechins and flavanols) were determined using spectrophotometric methods. Antioxidant capacity of plant extracts was estimated by Ferric Reducing/Antioxidant Power (FRAP) assay. The research of polyphenolic profile of berry skin and grape leaves extracts has shown difference in the mass amounts of total phenols among selected grape cultivars, as expected. The high antioxidant capacity of tested extracts has been observed and related to the presence of a mixture of polyphenolic compounds with good antioxidant properties. Significant linear correlation between total phenol content, or main phenolic subgroups, and FRAP was confirmed. To make practical comparison of relative antioxidant potential of phenolics extracted from berry skins and grape leaves, the phenol antioxidant coefficient (PAC) was calculated for each extract. PAC values ranged from 4.54-13.05 for grape skin extracts, and from 8.42-12.13 for grape leaves extracts. It can be concluded that grape skin extracts, as well as leaves extracts, can be a good source of phenolics with good antioxidant properties.

Low cement high alumina castable was synthesized, cured, and then sintered at 1100 °C for 3 hours. Water quench test was used as an experimental method for thermal stability testing. Image analysis program was applied in order to measure the damage to the samples at the surface and in the bulk before and during the water quench test. Ultrasonic measurements were carried out with the aim of measuring the changes of ultrasonic velocity. Strength degradation of the samples was calculated by using the model based on ultrasonic velocity changes during water quench test. Also, the strength of the samples before and during water quench test was measured by standard laboratory procedure. The model for prediction of strength degradation is presented.

The low cement high alumina castable (LCC) studied in this paper was synthesised, cured and then treated at different sintering temperatures. Since any inhomogeneity introduced during the castable preparation can remain inside the material degrading its properties and therefore the quality during service life, particular attention was given to the processing procedure in order to produce the material with the optimum characteristics. Composition of the castable regarding particle size distribution was adjusted according to the Andreassen’s packing model. The samples were sintered at 1100, 1300 and 1600°C for three hours. Influence of the different sintering temperatures on the castable properties is discussed. Compressive and flexural strengths were deter mined by destructive testing method, while the water immersion method was used for determination of the bulk density and the water absorption. Changes of elastic properties and microstructure (porosity) were observed by the non-destructive testing methods, ultrasonic measurements and image analysis. Based on the results, it can be concluded that sintering temperature has strong influence on the properties of the LCC. Exceptionally good properties were obtained for the sample sintered at 1600°C, but it should be highlighted that the samples treated at 1100 and 1300°C were provided with good properties, too. This should not be neglected because of the energy saving importance, in cases where the material sintered at lower temperature satisfies the applica tion requirements.