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Textural characteristics, mode of transportation and depositional environment of the Stormberg Group in the Eastern Cape, South Africa: evidence from grain size and lithofacies analyses

Chima Priscilla, Baiyegunhi Christopher

Geologos

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2022

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Vol. 28, No. 1

61--78

EN

The Stormberg Group comprises the Molteno, Elliot and Clarens formations and is one of four stratigraphical groups that make up the Karoo Supergroup in South Africa. The group is the highest unit in the Karoo Basin, representing the final phase of preserved sedimentation. The major problem with the Stromberg Group is that the mode of transport, hydrodynamic energy conditions and depositional environment are still poorly understood. For the present paper, grain size and lithofacies studies on selected sandstones from the Molteno, Elliot and Clarens formations were performed so as to elucidate their textural characteristics, depositional processes, sedimentation mechanisms and hydrodynamic energy conditions and to discriminate different depositional environments. The statistical parameters of grain size distribution (mean grain size, standard deviation, skewness and kurtosis) show that the sandstones are predominantly unimodal, fine grained, moderately well sorted, mesokurtic and near symmetrical. The bivariate diagrams of the aforementioned statistical parameters demonstrate that river and aeolian dune had the greatest impact on the depositional environments. Likewise, the C-M pattern (Passega diagram) shows that the sandstones were mostly deposited through tractive current process. Furthermore, the C-M diagram reveals the prevalence of rolling, suspension and graded suspension modes of sediment transportation. Seventeen sedimentary lithofacies were identified and grouped into seven lithofacies associations. These lithofacies associations indicate braided channel, overbank and swamp deposits for the Molteno Formation, alluvial fan/floodplain and playa deposits for the Elliot Formation and aeolian deposits for the Clarens Formation.

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Investigations of Properties of Soil-Aggregate Mixtures

Skrzypczak Izabela

Civil and Environmental Engineering Reports

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2022

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Vol. 32, no. 3

116--132

EN

The subject of this paper is the evaluation of the use of waste material, which is the native soil. On the example of the base ground taken from the village of Lipie (Podkarpackie voivodeship), soil-aggregate mixtures were prepared with a different degree of addition of natural aggregate. The study analysed the quantitative and qualitative parameters of the prepared mixtures and assessed their physical and mechanical properties to determine their suitability for the construction of infrastructural facilities. It should be noted that most specifications recommend the use of primarily aggregate mixtures. The paper presents the results of a study analysing the effect of aggregate admixture to the native soil on selected physical and strength properties of the mixtures developed. The obtained results confirmed the validity of research on the use of soil-aggregate mixtures for construction purposes.

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Wpływ rozkładu wielkości ziarna na właściwości mechaniczne nanometali

Wejrzanowski T., Dobosz R., Batorski K., Kurzydłowski K.J.

Inżynieria Materiałowa

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2005

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Vol. 26, nr 4

185-188

PL

Właściwości mechaniczne materiałów zależą od mechanizmów odkształcenia plastycznego, które z kolei determinowane są przez ich strukturę. W przypadku metali istotnym elementem struktury są granice ziaren, które w przeszłości traktowane były jako defekty dwuwymiarowe. Nanomateriały wyróżniają się na tle konwencjonalnych materiałów dużym udziałem atomów znajdujących się na granicach ziaren. Oznacza to, że ich opór przy odkształceniu plastycznym należy analizować w kategorii odkształcenia akomodowanego przez granice i wnętrza ziaren. W artykule przedstawiono (na przykładzie metali) wpływ wielkości ziaren na właściwości mechaniczne nanomateriałów. Na podstawie rozważań biorących pod uwagę "kompozytową" budowę nanometali oraz stochastyczne cechy procesu odkształcenia plastycznego, wykazano możliwość wystąpienia odwrotnej zależności Halla-Petcha. Omówiono także efekt rozproszenia wielkości ziaren w nanomateriałach otrzymanych różnymi metodami rozdrobnienia struktury i konsolidacji proszków.

EN

Mechanical properties of engineering materials are controlled by mechanisms of plastic deformation. These mechanisms are, to the high degree, determined by the microstructure of materials. In the case of metals grain boundaries are important structural elements, which in the past were considered as two-dimensional defects. In nanomaterials the fraction of atoms at grain boundaries is much higher than in traditional polycrystals. It implies that, plastic deformation must be studied in terms of its accommodation by the grain boundaries and grain interiors. In this work the influence of grain size on mechanical properties of nanometals has been investigated. The occurrence of the inverse Hall-Petch relation is explained on the basis of the assumption of the composite-like character of grain boundaries and grain interiors. The grain size dispersion effect on the flow stress in nanometals, subjected to severe plastic deformation (SPD) is also addressed.