The effect of linear welding energy on the structure, mechanical properties, and brittle failure resistance of welded joints of pipe steel of strength class Kh80 is studied. Transmission electron ...microscopy (TEM) is used to establish features of structure formation in individual areas of the heat-affected zone. Results of studies make it possible to establish the range of linear welding energy providing preparation of the optimum set of properties for longitudinal joints of large diameter pipes made of steel of strength class Kh80.
Stages are considered for the development of thermal strengthening technology in different classes of reinforcing bar at the West Siberian Metallurgical Combine. The structural evolution of devices ...for thermal strengthening of reinforcement 10–50 mm in diameter in a bar rolling mill line, and also production developments for optimizing interrupted hardening regimes are analyzed. Results of metallographic and electron-microscope studies of the structural composition formed in a bar cross section are used to demonstrate thermal strengthening of A500S class reinforcement No. 32 from steel 18G2S. The effect of induced cooling regimes on the strength of reinforcing bar and individual layers of a structural composite is analyzed. It is established that the main contribution to strength improvement is made by hardened structures of the surface layer. Continuous improvement of thermal strengthening technology and devices makes it possible to increase production efficiency for reinforcing bar due to a reduction in alloying used for the steels.
An analysis is made of the state of the technology used at the Azovstal Metallurgical Combine to produce skelp. The prospects for further development of the technology are discussed along with the ...reconstructive measures such improvement would require in the converter and plate shops, the objective being to master the production of skelp of strength classes X90–X120. An evaluation is made of how the quality indices of skelp made for the production of electric-welded pipe would be affected by the implementation of such measures and changes to the manufacturing technology.
The paper deals with time-dependent increase of compressive strength, splitting tensile strength and modulus of elasticity as well as with compressive stress-strain curves of self-compacting concrete ...(SCC) made with crushed limestone aggregate and high content of limestone filler. The characteristics under consideration were tested at the ages of 1, 3, 7, 28, 180, 360 and 720 days. Time evolution of the strength characteristics and modulus of elasticity was estimated with analytical models given in European code Eurocode 2. The study revealed that the models can adequately predict time evolution of the SCC characteristics, when coefficient s in the models is equal to 0.17, 0.08 and 0.25 for compressive strength, tensile strength and modulus of elasticity, respectively. These values of coefficient s are quite different from the value 0.2 proposed by Eurocode 2 for used cement strength class.
We have performed an analysis of the temperature and deformation parameters for controlled rolling/accelerated cooling on formation of the structural components in ferrite-bainite microstructure and ...on the mechanical properties of X80 rolled sheet made from molybdenum-free steel with low values of C
e
and P
cm
. Pilot production of X80 (K65) steel in thicknesses up to 20 mm with certain mechanical properties (including cold resistance) being assured was undertaken.
Abstract
Abhängig von Geometrie und Herstellmethodik können sich in Bauteilen aus faserbewehrtem Beton (lokal) sehr unterschiedliche Faserorientierungen einstellen. Der Faserbeton verhält sich in der ...Folge nicht mehr isotrop, sondern zeigt je nach Beanspruchungsrichtung ein unterschiedliches Zug‐ und Drucktragverhalten. Für ultrahochfesten Beton (UHFB) ist dieser Aspekt von besonderer Relevanz, da UHFB in der Anwendung meist hohe Fasergehalte aufweist. Während der Einfluss der Faserorientierung auf das Zugtragverhalten von UHFB bereits Gegenstand zahlreicher Studien war, fehlten bislang aussagekräftige Daten, um die auf die Faserbewehrung zurückzuführende Anisotropie im Drucktragverhalten größenmäßig fassen zu können. Im Rahmen einer Versuchsreihe wurde daher der Einfluss der Faserorientierung und des Fasergehalts auf das Bruchverhalten und die Druckfestigkeit von Fein‐ und Grobkorn‐UHFB eingehend untersucht. Die Ergebnisse zeigen, dass die Druckfestigkeit bei überwiegend unidirektionaler Ausrichtung der Fasern in der Ebene senkrecht zur Belastungsrichtung mit steigendem Fasergehalt deutlich zunimmt. Dagegen ist der Einfluss des Fasergehalts bei einer überwiegend unidirektionalen Ausrichtung der Fasern in Belastungsrichtung gering. Abhängig von der Belastungsrichtung unterscheidet sich die Druckfestigkeit am Würfel um bis zu 26 N/mm
2
bzw. 14 %. Die Differenz zwischen Würfel‐ und Zylinderdruckfestigkeit nimmt mit steigendem Fasergehalt zu. Auf Basis der Ergebnisse erfolgt eine Empfehlung zur Festlegung von Betonfestigkeitsklassen für die DAfStb‐Richtlinie „Ultrahochfester Beton“.
Abstract
Effect of Fibre Orientation and Fibre Volume Fraction on the Compressive Strength of Ultra‐High Performance Concrete
Depending on the geometry and casting method, structural members made of fibre reinforced concrete may (locally) show very different fibre orientation. As a result, the fibre reinforced concrete no longer behaves isotropically, but shows different tensile and compressive behaviour depending on the direction of loading. This aspect is of special importance for ultra‐high performance concrete (UHPC), since UHPC is typically applied with high fibre volume fraction. While the influence of fibre orientation on the tensile behaviour of UHPC has already been subject of numerous studies, there was a lack of meaningful data so far in order to be able to quantify the anisotropy in compression caused by the fibres. Thus, the influence of fibre orientation and fibre volume fraction on the failure pattern and on the compressive strength of fine‐ and coarse‐grained UHPC was investigated in a series of tests. The results show that with predominantly unidirectional alignment of fibres in the plane perpendicular to the loading direction, the compressive strength increases significantly with increasing fibre volume fraction. In contrast, the influence of fibre volume fraction is marginal with predominantly unidirectional alignment of fibres in the direction of loading. Depending on the loading direction, the compressive strength tested on cubes differs by up to 26 MPa and 14 %, respectively. The difference between cube and cylinder compressive strength increases with increasing fibre volume fraction. Based on the results, a proposal for classifying UHPC in the DAfStb Guideline “Ultra‐High Performance Concrete” is provided.
Abstract
Der Nachweis der Konformität ultrahochfester Betone (UHFB), die künftig in der im Entwurf befindlichen DAfStb‐Richtlinie „Ultrahochfester Beton“ geregelt sein werden, erfordert Formfaktoren, ...die eine Umrechnung zwischen den an UHFB‐Probekörpern unterschiedlicher Form und Größe erhaltenen Druckfestigkeiten erlauben. Bisher fehlten belastbare Versuchsergebnisse, auf deren Grundlage die Festlegung allgemeingültiger Formfaktoren zielsicher hätte erfolgen können. Daher wurde im Rahmen eines vom Deutschen Ausschuss für Stahlbeton geförderten Forschungsvorhabens der Einfluss der Probekörpergeometrie auf die Ergebnisse von Druckfestigkeitsprüfungen an normal‐, hoch‐ und ultrahochfesten Betonen experimentell untersucht. Die mittleren Zylinderdruckfestigkeiten der einzelnen Serien betrugen zwischen ca. 30 N/mm
2
und 200 N/mm
2
. Mit Größtkorndurchmessern von 0,5 mm, 3 mm, 5 mm und 8 mm deckten die UHFB‐Systeme den Anwendungsbereich der zukünftigen DAfStb‐Richtlinie weitgehend ab. Neben Zylindern mit h/d mm = 300/150 und Würfeln mit einer Kantenlänge d = 150 mm, anhand deren charakteristischer Druckfestigkeit die Klassifizierung von UHFB erfolgen soll, wurden auch Zylinder mit h/d mm = 200/100 und Würfel mit einer Kantenlänge d = 100 mm untersucht. Die im Entwurf der DAfStb‐Richtlinie „Ultrahochfester Beton“ vorgenommene Klassifizierung von UHFB in die Festigkeitsklassen C130/140, C150/155 und C175/180 spiegelt den in den Versuchen beobachteten geringen Unterschied zwischen Zylinder‐ und Würfeldruckfestigkeit angemessen wider.
Abstract
Effect of Specimen Geometry on the Compressive Strength of Ultra‐High Performance Concrete
The conformity check for ultra‐high performance concrete (UHPC), which is subject of the current draft of the DAfStb Guideline “Ultra‐High Performance Concrete”, requires factors that allow a conversion between compressive strengths obtained for UHPC specimens with different shape and size. Up to now, there was a lack of reliable test results that could form the basis for defining generally applicable conversion factors. Therefore, the influence of the specimen geometry on the results of compressive strength tests on normal strength concrete, high strength concrete, and UHPC was investigated experimentally within the scope of a research project funded by the German Committee for Structural Concrete. The mean cylinder compressive strengths of the individual series ranged between approx. 30 MPa and 200 MPa. With maximum grain sizes of 0.5 mm, 3 mm, 5 mm, and 8 mm, the UHPC mixtures largely covered the scope of the forthcoming DAfStb Guideline. Besides cylinders with h/d mm = 300/150 and cubes with an edge length d = 150 mm, whose characteristic compressive strength will be used to classify UHPC, smaller cylinders with h/d mm = 200/100 and smaller cubes with d = 100 mm were tested. The draft of the DAfStb Guideline “Ultra‐High Performance Concrete” classifies UHPC by the strength classes C130/140, C150/155 and C175/180. The denominations adequately reflect the small difference between cylinder and cube strength observed in the tests.
The experiments on probability distribution of compressive strength of high strength concrete and normal strength concrete were carried out in this study. Shape of probabiliry distribution of ...compressive strength class of any kinds of concrete were definied normal distribution, theoretically, in quality control. It is clear that the peak of distribution is higher than mean value of strength in high strength concrete, nevertheless the mean value is equal to the peak of distribution in ordinary strength class of concrete. This means the probable minimum would be lower than the specified minimum , make the strength fall below the design strength in high strength concrete.
Mechanical Properties of Picea sitchensis Bräuner, Lise; Hoffmeyer, Preben; Poulsson, Lise
Scandinavian journal of forest research,
20/1/1/, Letnik:
15, Številka:
1
Journal Article
Recenzirano
This study establishes the basis for the assignment of Danish - grown Sitka spruce (Picea sitchensis) to the European strength class system (EN 338). In total, 712 boards were chosen to be ...representative of the normal Danish commodity. These were visually graded for strength according to Nordic rules (INSTA 142), and subsequently tested to failure in either bending or tension. The results show that Danish - grown Sitka spruce graded to levels T1 and T2 satisfy the requirements of EN 338 at the C18 and C24 levels, respectively. Results for Danish - grown Sitka spruce concur with those for Danish - grown Norway spruce (Picea abies). This study shows that Sitka spruce and Norway spruce of similar origins exhibit highly comparable mechanical properties.
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