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Analiza lokalnej pracy zarysowanego naroża płyty sprężonego obiektu mostowego w dużym skosie w aspekcie wpływu obciążeń eksploatacyjnych

Betlej Michał, Ciurej Henryk, Gwoździewicz Piotr

Materiały Budowlane

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2022

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nr 10

104--109

PL

Przedmiotem analizy jest nietypowy rzeczywisty obiekt mostowy płytowo-belkowy sprężony w skosie ok. 40°. Po sprężeniu dźwigarów zauważono istnienie pęknięcia w obrębie kątów ostrych na górnej i dolnej powierzchni płyty pomostu. W artykule przedstawiono wyniki analizy lokalnej pracy zarysowanych naroży w rejonie kąta ostrego płyty w aspekcie wpływu obciążeń użytkowych na istniejący stan zarysowań. Opracowano model przestrzenny MES, bazujący w całości na elementach objętościowych. Siatki zbrojenia odwzorowano w postaci płaskich membran o zastępczych właściwościach anizotropowych. Zastosowano obliczenia nieliniowe fizycznie i geometrycznie z modelem pękania betonu. Odtworzono proces i sekwencję sprężania kablami oraz przykładanie pozostałych obciążeń: stałych i użytkowych w trzech ustawieniach. Na każdym etapie obserwowano stan naprężeń i pękania w płycie. Sformułowano wniosek, że rysy powstałe wskutek niewłaściwego wprowadzenia sprężenia zamykają się pod wpływem obciążeń stałych i użytkowych.

EN

The subject of the analysis is a real bridge deck composed of beams and slab with an unusual geometry, where support angle is at approx. 40°. After the girders were prestressed, the cracks within the sharp angles were noticed on the upper and lower surfaces of the deck. The aim of this article is to present the result of a local analysis of the sharp angle of the deck in the aspect of the impact of operating loads on the existing state of cracks. A FEM model was developed, based entirely on volume elements. Nonlinear analysis were used with the concrete crack model. The process and sequence of prestressing and the application of the remaining loads is considered. On each of them, a state of stress and cracking in the deck was observed. It was concluded that cracks resulting from improper introduction of prestress are closing under the influence of permanent and service loads.

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Infuence of heat treatment (routes) on the microstructure and mechanical properties of 300M ultra high strength steel

Kasana Shivraj Singh, Sharma Sandeep, Pandey O. P.

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 3

art. no. e126

EN

The study covered investigation of heat treatment (routes) effect on heat treatment of 300M ultra high strength steel to achieve the desired microstructure and the corresponding mechanical properties. 300M steel was prepared and subjected to diferent homogenization and forging processing. Structure-property relationship was established for both conventional and heat treatment route as well as isothermal and modifed route. Micrographs of 300M steels indicated that the isothermal heat treatment provided higher volume of retained austenite along with martensite and bainite. X-ray difraction (XRD) revealed that the dislocation density of isothermally heat-treated 300M steels was higher than the conventional steel. Isothermally heat-treated 300M samples have shown improved elongation and impact strength with the marginal loss of yield strength and ultimate tensile strength. Yield strength (1605 MPa), ultimate tensile strength (1890 MPa), impact strength (28 J), and percentage elongation (22%) of the isothermally heat-treated samples were comparable to the specifcations of the customer i.e., minimum yield strength 1480 MPa, ultimate tensile strength 1803 MPa, percentage elongation 7% and impact strength at −40 °C of 20 J, respectively. The SEM analysis of tensile and impact fractured surfaces revealed the large number of dimples which indicate the good ductility and toughness in the isothermally heat-treated samples.

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On the fractography and some strength properties of Fe-based sintered materials with multicomponent oxide microadditives

Feldshtein E., Michalski M., Adamczuk K., Dyachkova L.

International Journal of Applied Mechanics and Engineering

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2019

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Vol. 24, no. 4

224--229

EN

In the present paper, the effect of alumina and zirconia microadditives on the compressive strength and flexural strength of sintered Fe-based powder materials is shown. It was found that intercrystalline fractures, both plastic and brittle, are observed when bending. During compression, fractures are observed too, as well as flaking of thin nearsurface layers. The intensity of such flaking depends on the composition of the sintered material. Strength parameters of the materials studied also depend on additives composition and quantity. The lowest parameters are observed for a material that contains 1% alumina particulates. The compressive strength of a material containing zirconia particulates increases 3 times and the flexural strength 2 times.

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Structure and Properties of Mg-Cu-(Y,Ca) Bulk Metallic Glasses

Babilas R., Cesarz-Andraczke K., Nowosielski R.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 4

2645--2650

EN

The work presents preparation methods, structure characterization and mechanical properties analysis of Mg-based bulk metallic glasses in as-cast state and after crystallization process. The studies were performed on Mg60Cu30Y10 and Mg37Cu36Ca27 glassy alloys in the form of plates and rods. The X-ray diffraction investigations revealed that the tested samples with different thicknesses and shapes were amorphous. The characteristics of the fractured surfaces showed mixed fractures with the “river” and “mirror” patterns, which are characteristic for the glassy materials and some “smooth” areas. The samples of Mg37Cu36Ca27 alloy presented a two-stage crystallization process, but addition of Y caused a single stage crystallization behavior. Qualitative phase analysis from the X-ray data of examined alloys annealed at 473 K enabled the identification of Mg, Mg2Cu, Cu2Mg and CaCu crystalline phases. The changes of compressive strength as a function of annealing temperature for studied rods were stated. The best mechanical properties including microhardness and compressive strength were obtained for the alloy with the addition of Y in as-cast state.

PL

W pracy przedstawiono wyniki badań struktury i wybranych własności masywnych szkieł metalicznych na osnowie magnezu. Badania przeprowadzono na próbkach w stanie wyjściowym oraz po procesie wygrzewania. Do badań wybrano dwa trójskładnikowe stopy magnezu z dodatkiem itru lub wapnia o następującym składzie chemicznym:Mg60Cu30Y10 oraz Mg37Cu36Ca27. Badania rentgenowskie potwierdziły, że analizowane próbki w postaci płytek i prętów posiadają strukturę amorficzną. Obserwacje mikroskopowe wybranych obszarów powierzchni przełomów płytek i prętów pozwoliły na wyodrębnienie stref o morfologii przełomów „gładkich” i „łuskowych”. Analiza procesu krystalizacji wykazała występowanie pojedynczego etapu krystalizacji dla szkła metalicznego Mg60Cu30Y10 związanego z wydzielaniem się fazy Mg2Cu oraz dwuetapowego procesu krystalizacji dla stopu Mg37Cu36Ca27, w którym zidentyfikowano fazę Cu2Mg i CaCu. Największą wytrzymałość na ściskanie oraz mikrotwardość uzyskano dla próbek szkła metalicznego z dodatkiem itru w stanie bezpośrednio po odlaniu.

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Structure and mechanical properties of Mg-Si alloys at elevated temperatures

Cizek L., Hanus A., Blahoz O., Tański T., Dobrzański L. A., Prażmowski M., Pawlica L.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 35, nr 1

37-46

EN

Purpose: of this paper is to extend a complex evaluation of magnesium alloys which requires very often knowledge of structure and mechanical properties at elevated temperatures. These properties are connected with microstructure that is influenced by metallurgical and technological factors and exploitation conditions. Presented knowledge expresses very important information for design and exploitation of these alloys. Design/methodology/approach: The optical and scanning electron microscopy methods were used for metallographic and fracture analyses of studied magnesium alloys after tensile test at elevated temperatures. Findings: Objective of this work consisted in determination of structure and mechanical properties progressive magnesium alloys at elevated temperatures. Research limitations/implications: Knowledge of alloys structure characteristics will be determined new research direction of scope. Practical implications: The results may be utilized for a relation between structure and properties of the investigated material in process of manufacturing. Originality/value: These results contribute to complex evaluation of magnesium alloys properties namely for explanation of structure developed new magnesium alloys. The results of this paper are determined for research workers deal by development new exploitations of magnesium alloys.