Wyniki wyszukiwania - BazTech

1

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

|

2022

|

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.

2

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

|

2022

|

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.

3

The Morphology of Impact Fracture Surfaces in Manganese Cast Steel Modified by Rare Earth Elements

Kasińska J.

Archives of Foundry Engineering

|

2020

|

Vol. 20, iss. 2

89--94

EN

The morphology of G20Mn5 specimens made of non-modified and rare earth metals (REM) modified cast steel was investigated. Molten metal was treated with a cerium-rich mischmetal contain 49.8% Ce, 21.8% La, 17.1% Nd, 5.5% Pr and 5.35% other rare earth metals making up the balance. The melting, quenching (920°C/water) and tempering (720°C/air) were performed under industrial conditions. Analysis included G20Mn5 cast steel fracture specimens subjected to Charpy V-notch impact testing at 20°C, -30°C and -40°C. The purpose of the analysis was to determine the influence of REM on the microstructure and mechanical properties of G20Mn5 cast steel and the REM effect on the morphology, impact strength and character of the fracture surfaces. In addition, a description of the mechanism by which fracture occurred in the two materials was proposed. The author demonstrated the beneficial effects of adding REM to molten steel, manifested by a 20 - 40% increase in impact toughness, depending on test temperature, as compared to the non-modified cast steel. Important findings included more than 100% increase in impact strength in comparison with the required impact toughness of 27J at -40C for heat treated steels (EN 10213).

4

Mechanical properties and fracture analysis of AlCu4MgSi alloy ingots obtained by horizontal continuous casting

Nuckowski P. M., Wróbel T.

Archives of Metallurgy and Materials

|

2019

|

Vol. 64, iss. 1

113--118

EN

The article presents the results of research concerning AlCu4MgSi alloy ingots produced using horizontal continuous casting process under variable conditions of casting speed and cooling liquid flow through the crystallizer. The mechanical properties and structure of the obtained ingots were correlated with the process parameters. On the basis of the obtained results, it has been shown that depending on the cooling rate and the intensity of convection during solidification, significant differences in the mechanical properties and structure and of the ingots can occur. The research has shown that, as the casting speed and the flow rate of the cooling liquid increase, the hardness of the test samples decreases, while their elongation increases, which is related to the increase of the average grain size. Also, the morphology of the intermetallic phases precipitations lattice, as well as the centerline porosity and dendrite expansion, significantly affect the tensile strength and fracture mechanism of the tested ingots.

5

Influence of crack presence on operating conditions of pressure vessels with flat endplates

Szybiński B., Romanowicz P.

Journal of KONES

|

2016

|

Vol. 23, No. 1

377---384

EN

The paper discusses influence of crack presence on operating conditions of boilers and pipes. In the study particular attention is paid to the vessels with flat endplates with circular stress relieve grooves. The endplates with such grooves are common alternative for widely used dished ends, particularly for smaller boiler diameters and also for vessels with non-circular cross-sections. The existing codes set the rules how to calculate the circular groove parameters – the groove radius and the location of the arc centre. These design parameters are limited by set of inequalities, which indicate the ranges for admissible radii values and the groove centre positions. The choice of the optimal values for the endplate design parameters has been worked out in recent Authors’ investigations. Such approach provides the minimum stress concentration in the vicinity of the cutout, but this notch area still can be the source of crack nucleation and its propagation leading to the premature fracture of the considered vessel. In standard calculations of pressure boilers, the fracture parameters are not taken into account. The current study concentrates on the assessment of the influence of the crack existence on the stable vessel operation. The cracks existing in inner wall of the vessel are of the main interest, because these are difficult to identify and monitor. In these studies the influence of different parameters like the crack length and orientation, and the fracture toughness were taken into account. The detailed numerical results were obtained by means of the finite element code ANSYS [1] for several crack sizes and locations. The cracks in the weld joining shell and end plate and cracks in the groove area, where the maximum stress concentration appeared were subject of the numerical study. The obtained results show the risk of possible premature failure of boilers with cracks.

6

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

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

Archives of Metallurgy and Materials

|

2015

|

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.

7

Numerical prediction of the effects of miniature channel shaped scratches on the fracture behaviour of wires for civil engineering applications using finite element analysis

Adewole K. K., Bull S. J.

Archives of Civil Engineering

|

2014

|

Vol. 60, nr 2

181--194

EN

The effects of the miniature channel-shaped scratches not detectable by the present inline electromagnetic defect detection system employed for wires’ surface defect detection on the fracture behaviour of the wires for civil engineering applications were investigated numerically. Finite element analysis revealed that both miniature channel-shaped across-the-thickness and across-the-width scratches change the fracture behaviour of the wires in terms of the fracture initiation locations and fracture process sequence. However, miniature across-the-thickness scratches does not affect the fracture shape of the wire while miniature across-the-width scratches changed the wires’ cup and cone fracture to a fracture shape with a predominantly flat fracture. These results provide an understanding of the fracture behaviour of wires with miniature scratches and serve as an alternative or a complimentary tools to experimental or fractographic failure analysis of wires with miniatures scratches which are difficult to carry out in the laboratory due to the sizes of the scratches.

8

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

|

2009

|

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.

9

Analiza zjawiska pękania w kształtowaniu hydromechanicznym czwórników

Sadłowska H.

Prace Naukowe Politechniki Warszawskiej. Mechanika

|

2007

|

z. 216

127--132

PL

Kształtowanie hydromechaniczne jest stosunkowo nową technologią obróbki plastycznej. Posiada wiele zalet, co powoduje, że procesy te szczególnie chętnie wykorzystywane są w przemyśle motoryzacyjnym. Jednak w związku z wysokim stopniem ich skomplikowania, potrzebna jest szczegółowa analiza warunków ograniczających te procesy. Aby uzyskać element bez wad, należy prawidłowo dobrać parametry procesu. W referacie przedstawiono analizę doświadczalnych parametrów procesu kształtowania hydromechanicznego czwórników z uwzględnieniem zjawiska pękania.

EN

During the past few years, the demand for weight reduction in modern vehicle construction has led to an increase in the application of hydroforming processes for the manufacturing of automotive lightweight components. Prediction of the forming limits during hydroforming processes is very important in order to identify the conditions and process parameters that deforming sheet or pipe may lead to failure of material, i. e. bursting or wrinkling. The analysis of X-shape hydroforming process parameters concerning only fractures has been presented in the paper.

10

Peculiarities of faul tectonics investigation and mapping

Kovkhuto A.M., Aizberg R.Y., Garetsky R.G., Parkhomov M.D.

Technika Poszukiwań Geologicznych

|

2003

|

R. 42, nr 6

21-24

EN

All faults on the territory of Belarus could be divided into two main types. There are Pre-platform and Platform faults. All these faults are distinguishable by geophysical (seismic sounding, gravity and magnetic surveys, borehole logs and others) and geological (structural, stratigraphic and other methods) data. Platform faults are main object of the investigation because numerous mineral resources as hydrocarbons, gypsum, potassium salts are related to these faults. The platform faults are present in the sedimentary paleo-basins that were formed in the Pripyat Trough, Orsha and Podlasie-Brest depressions and in some small negative structures of Belarus. The new complex geodynamical method (CDM) of investigation including traditional geological-geophysical methods, and also fracture analyses in cores, calculation of absolutely curvature of surfaces and determination of evolution of individual faults was applied in the Pripyat Trough.

PL

Wszystkie uskoki na terenie Białorusi można podzielić na dwa podstawowe rodzaje - przed i po-platformowe. Są one rozróżnialne za pomocą metod geofizycznych tj. sondowań sejsmicznych, grawimetrii i magnetyki oraz geofizyki otworowej. Uskoki platformowe są zasadniczym przedmiotem zainteresowania, dlatego że liczne złoża mineralne, jak węglowodory, gipsy, sole potasowe są związane z tymi uskokami. Uskoki platformowe występują w paleo-basenach sedymentacyjnych utworzonych w rowie Prypeci, oraz w depresjach Orszy i Podlasia-Brześcia. Występują także w innych, małych depresjach podłoża na terenie Białorusi. Nowe kompleksowe metody badań geodynamicznych (CDM) zastosowane w Rowie Prypeci stanowią połączenie tradycyjnych metod geologiczno-geofizycznych z analizą strukturalną rdzeni wiertniczych, obliczeniami absolutnej krzywizny powierzchni oraz określaniem ewolucji poszczególnych uskoków.