One
of the most effective micro-alloying elements in the production of class 500 fittings is vanadium. However, the production technology is multi-stage and expensive, so the use of ferrovanadium ...makes the production of vanadium-containing fittings for mass use unprofitable. In this regard, it is necessary to reduce the cost of finished products by replacing ferrovanadium with ferroniobium while preserving all the mechanical, physical and operational characteristics of the metal.
Objective: to determine the effect of the quantitative content of niobium in steel in the production of hot-rolled rebar S-500WC in coils at the mill 370/150 of OJSC “BSW – Management Company of the Holding “BMK” in accordance with the requirements of the Israeli standard SI 4466-3:2013 at various temperature and speed parameters of rolled products. The normalized mechanical properties of s-500WC reinforcing steel of all profiles (No. 8–16) in accordance with THE requirements of si 4466-3:2013 are: yield strength – 500–650 MPa, ductility – 1.15–1.35, elongation of – at least 11 % and total elongation at break of – at least 7.5 %.
•The minimum volume of fibres that was used had a positive effect on improving residual strength.•Minimum volume of fibre which would transform ordinary concrete into SFRC.•Mechanical properties of ...SFRC in time.•Application of class SFRC according to Model Code 2010.•Reduction of the aggregate cost and preservation of the environment by valorizing waste sand.
Steel fibre reinforced concrete is a well-established construction material. So far its specific properties have been defined and assessed using multiple, literature defined factors and limits. In 2010 there was published fib Model Code which defines strength classes SFRC. The strength classes are based on values of residual strength tested according to EN 14651. Thus it is now possible to tackle SFRC properties in a very precise way. In the paper the research programme aims to define the blurred border between ordinary concrete and SFRC (made on the basis of aggregate of a largest size of 4mm). The main goal was to get a minimum critical volume of fibre which would transform ordinary concrete into SFRC with an official strength class.
Hardwoods commonly have high mechanical properties, which makes them interesting for structural use, but softwoods dominate the structural timber market in Europe. Tensile strength classes are ...recommended for engineered wood products. However, current European standards do not provide tensile strength classes for hardwoods and the declaration of tensile properties from machine grading in the industry is not yet possible. The present paper aims to contribute to the revision of European standards through the technical group CEN/TC124/WG2/TG2: Tensile strength classes for hardwoods, of the European Standardisation Committee. An experimental campaign which involved machine grading and tensile testing of over 569 boards of Southern blue gum (Eucalyptus globulus Labill.) from Spain and Portugal was made. Six new tensile strength classes were defined, from ET24 (ft,0,k = 24 N/mm2, Et,0,m = 18 kN/mm2 and ρk = 590 kg/m3) to ET42 (ft,0,k = 42 N/mm2, Et,0,m = 23 kN/mm2 and ρk = 640 kg/m3). Machine grading made possible the definition of six strength class combinations. Four combinations resulted in 40% of the sample being assigned to the higher strength class, with low percentages of rejection (varying between 1% and 14%). This demonstrates the high mechanical properties of the species and the performance improvement of machine grading with respect to current visual grading.
A multi-scale experimental study was carried out to investigate the porosity, flexural and compressive strengths of cement-mortar at different cement strength classes (CSCs). Specifically, 54 mix ...designs (totally 324 specimens) were first defined and then the produced cement-mortar specimens were tested to consider their properties. To identify the microstructure of the specimens at different conditions, scanning electron microscope (SEM) imaging and energy dispersive spectroscopy (EDS) analysis were also performed. The results show that the porosity, and flexural and compressive strengths change significantly at different CSCs. At the same mix proportion, the cement-mortar has lower porosity as well as higher flexural and compressive strengths as the CSC gets higher. Considering the combined effects of various parameters on the mentioned properties, a new multi-objective model using artificial neural network (ANN) was proposed to analyze the experimental data of porosity, and flexural and compressive strengths. The results show that the proposed model is able to provide predictions with good accuracy.
It is well demonstrated that the macro- and micro-characteristics of cement mortar (CM) depend on cement strength, which in turn depends on the cement strength class (CSC). Image analysis, as an ...objective tool, was used to examine the effects of CSC based on CM experimental characteristics including macro- and microstructure. The investigations were carried out using porosity, flexural and the compressive tests, SEM, XRD, and 3D morphology surface analysis. Analysis of the experimental results demonstrated that finer cement (CSC 52.5 MPa) substantially decreased porosity (about 22–55%) and significantly increased strength properties of the CM (6–91%). This findings was confirmed by changes in hydration phases, pore structure, interfacial transition zone (ITZ) thickness, and crack propagation. Image analysis showed that different CSC caused different changes in contribution of hydration products, in ITZ and also pores structure. The porosity of CMs was obtained using image analysis, and then the results were compared with the laboratory porosities. Image analysis tool was also employed for determining the crack dimensions. It was found that different distributions of pore sizes in the specimens with various CSC caused a variety of cracks development with different widths.
The pin-penetration device is a minimally destructive instrument that is widely used to estimate the physical properties of wood, e.g., density, with advantages such as reduced testing times, low ...costs, and fewer defects induced in the wood being tested. In this study, such a device was used on 25 Indonesian hardwood species with a strength class (SC) distribution from SC II to IV (according to the Indonesian classification of wood SCs). Tests were conducted on three different orthogonal planes, i.e., cross-sectional, radial, and tangential planes. The wood density ranged from 0.28 to 0.88 g/cm3, and the specific gravity was 0.25 to 0.76. The cross-sectional plane penetration depth of the wood was significantly greater than that of either the radial or tangential plane, whereas the pin penetration values of the radial and tangential planes were not significantly different. A prediction model for predicting the density and specific gravity of wood via pin penetration showed a significant regression. Thus, the use of a pin-penetration device was found to be suitable for estimating wood density and specific gravity in a range of SCs of tropical wood species regardless of species.
The regularities of structural and phase transformations in a novel competitive steel 25N2GSM for the heavy and light transport industries designed for application under the extreme conditions of the ...Far North and the Arctic are studied. Athermokinetic diagram of decomposition of supercooled austenite is plotted. Atreatment giving rolled sheets from steel 25N2GSM of strength class 1100 MPa with cold resistance
KCV
–
70
= 32 J/cm
2
is suggested.
The influence of welding repair technology on structural and phase composition and mechanical properties of longitudinal pipe joints within the area of stopping the process of submerged arc ...mechanical welding during manufacture of pipes made of steels of strength categories K60, K65 is investigated.
Sweet chestnut is a timber species used for construction since many centuries thanks to its good mechanical performances and its natural durability. The use as solid timber is historical in many ...Mediterranean countries, but today it needs to be strength graded if applied as structural product. Visual grading have been recently developed, but machine grading could allow a more efficient use of the material and could be a first step also for the implementation of structural engineered products. Therefore, this paper analyse the machine grading of chestnut timber, deriving the machine settings according the European regulations, highlighting weaknesses and strengths, and verifying the feasibility of the strength grading on wet timber. Both the dynamic modulus of elasticity and the merely frequency of vibration were compared as different machine indicating properties. There were 781 timber pieces collected and tested, with different cross sections and these were divided into four sub-samples originating from the southern, central and northern regions of Italy. Both D and C strength classes (EN 338, Structural timber—strength classes,
2009
) were included in the calculations and the causes of wrong upgrading were analysed. Machine grading performed satisfactory, several class combinations were possible and higher strength classes were attainable when compared with the visual grading process, which allows sorting of only one strength grade. The assignment to C-classes allowed for higher yields in upper classes, while the D-upper classes were unpredictable by the only frequency measurement. Machine grading performed directly on wet timber achieved comparable yields to dry grading, but practically could be carried out only by means of dynamic modulus measurement.
PDF
