Nominal Cross-section Research Articles

Characterization of the Alkali and Hydrolysis Resistance of Polymer-Impregnated, Alkali-Resistant Glass Filaments.

The aim of this series of tests was to characterize the alkali and water resistance of alkali-resistant (durability) glass filaments, which were optimized with two non-vulcanized formulations based on co-polymerizing styrene-butadiene rubbers (CemFil-SBR1 and CemFil-SBR2). Furthermore, it was assessed which of the two polymer-impregnated multifilament yarns is the better alternative for use in cementitious binders. For this purpose, the impregnated multifilament yarns were chemically conditioned for up to twelve months at temperatures of 23 and 50 °C in 2.5 percent sodium hydroxide solution and 2.5 percent potassium hydroxide solution as well as in 3 percent salt and distilled water. The samples were then subjected to material science tests. The liquid absorption capacities and the changes in the mass of the composite materials were determined at different times during conditioning. The load-bearing capacity of the samples was also tested using uniaxial fiber strand tensile tests. The durability of the polymer-impregnated multifilament yarns was described in detail in conjunction with scanning electron microscopy images and nominal cross-section determinations. The test liquids caused a reduction in strength during the storage period, which was accelerated by increased temperatures. The reduction in strength is mainly due to glass corrosion of the filaments. Glass corrosion is delayed due to the good impregnation quality, which fundamentally improves the durability of the yarns. The results of the durability tests show that the polymer-impregnated multifilament yarns CemFil-SBR2 are probably more suitable for use in cementitious binders, as they have better alkali and hydrolysis resistance.

Farklı Et Kalınlıklarına Sahip Soğuk Şekillendirilmiş Kare İçi Boş Kesitli Elemanlara Monte Edilen Kör Perçin Somunlarının (BRN'ler) Çekme Kapasitesi Üzerine Deneysel Çalışma

In this study, pull-out tests of blind rivet nuts (BRNs) mounted on cold-formed square hollow section (SHS) webs with 100×100 mm nominal cross-section dimensions and different wall thicknesses (2.0 to 5.0 mm) were performed, and the effect of different wall thicknesses and BRN thread sizes on the test results was experimentally investigated. M10 and M12 stainless steel BRNs were mounted on SHSs using a standard riveter tool, and the test elements were prepared for the experiment. Load–displacement curves and the final damage modes were obtained for each test specimen. The results show that the pull-out capacity depends on both the SHS wall thickness and rivet nut thread size. Although the pull-out capacity increased in both thread sizes with the increase in wall thickness parameters, the effect of thread size is negligible in the case of 2.5, 3.0, and 4.0 wall thickness. In addition, when a connection is created using a BRN, the design should consider the stripped thread strength in addition to the pull-out capacity.

Predicting the mechanical properties of timber from existing structures by the longitudinal vibration method, visual grading and definition of the nominal cross-section

ABSTRACT The modulus of elasticity (MOE), bending strength (MOR) and density of 45 150 × 200 × 5400 mm3 Salzmann pine timber pieces from an existing eighteenth century structure were obtained by testing and also estimated by non-destructive testing. Density was estimated by means of the drilling technique and the MOE and MOR by recording the longitudinal natural frequency of vibration. Four methods for defining the dimensions of the nominal cross-section were applied to establish which was most adequate to address the high variability in the cross-sections along the length. MOE and MOR linear regression results showed r2 = 59–68% using dynamic MOE, relative edge knot diameter and slope of grain as independent variables. The nominal cross-section defined as the mean cross-section area along the length proved to be the most effective for estimating mechanical properties, followed by the nominal cross-section defined as the average measurements of the piece taken at the middle part or central third along its length. The longitudinal vibration method enables the acquisition of superior predictive models compared to time-of-flight measurement-based methods.

Technology of the Contact Wire Manufacture for High-Speed Railways

The article presents an overview of possible technological schemes to produce an overhead contact wire for railways. Pilot experiments were carried out on the manufacture of a contact wire made of CuMg0.3, CuMg0.4 and CuMg0.5 alloys and having a nominal cross section of 100 mm2. The contact wire was obtained from a continuously cast rod with small section, which was subjected to plastic deformation using the Conform technology and cold drawing of the extruded rod. In the casting process, we encountered the formation of cracks on the cast rod surface and the rods breakage. The inner surface of the graphite bushings of the mold after casting the rod was studied and a thin gray layer was found on the inner surface of the graphite bushings. Areas of the graphite bushing with gray layer were studied by scanning electron microscopy and element-by-element mapping was performed with the selection of a spectrum in the sediment layer area. In order to determine the phase composition of the sediment layer it was analyzed by the method of full-profile analysis of the X-ray diffraction pattern according to Rietveld. X-ray phase analysis showed the CuMg2 and Cu2Mg phases presence. This allowed us to assume a possible mechanism for the formation of the sediment layer. Ultimate tensile strength, elongation and electrical resistivity was determined. Analysis showed that the overhead wires made of CuMg0.3, CuMg0.4, CuMg0.5 alloys meets the requirements of GOST R 55647-2018 for wires made of the second conditional group bronze.

Using internal in-plane k-shape steel bracing as a simple strengthening technique for RC box beams failed in torsion

The current paper aims to investigate, experimentally, the torsion behavior of reinforced concrete box beams made by self-compacting concrete and strengthened internally by in-plane steel bracing of K-Shape. Four identical large size beams had a nominal cross-section dimension of (0.3x0.3m) with a total length of (2.1m) were constructed and loaded to failure under the effect of pure torsion. The experimental result shows that the failure torsion moment of strengthened beam specimens with K-shape steel bracings increases with a percentage up to (82%) more than un-strengthened beam and the angle of twist decreases by a percentage up to (35.5%). While, the axial elongation decreases by a percentage up to (53%). The presence of the internal in-plane K-shape steel bracing is effective and simple method in enhancing the ultimate carrying torsion capacity.

Post-Fire Performance of Square Concrete-Filled Steel Tube Columns under Uni-Axial Load

This paper presents experimental studies on the post-fire performance of concrete-filled steel tube (CSFT) columns under uni-axial load. The structural responses and axial load capacity of CSFT columns after exposure to elevated temperatures are investigated and discussed. All of the specimens are 750 mm in height, the nominal cross-section of the specimen is 150 mm x 150 mm, and have cylinder compressive strength of 18 MPa. The primary test parameters to be measured during the uni-axial compression test are wall thicknesses of the square tube (3.0 mm, 4.5 mm and 6.0 mm) and three different exposure to elevated temperatures (400°C, 600°C and 800°C). The results showed that the load-axial shortening relationship of the CSFT columns have a linear elastic response up to 80-90% of axial load capacity. After the axial load capacity is reached, the load-axial shortening curves are rarely becoming a nonlinear manner. It is also shown that the axial load capacity and ductility of the post-fire test columns are decreased significantly compared to the columns at ambient temperature, depending mainly on the elevated temperature. In addition, by comparing the axial load capacity of the test results with those obtained from the ACI design equation, the comparison results indicate that calculation formula in ACI code unconservative predicts the axial load capacity of the CSFT columns after exposure to elevated temperatures. Finally, the residual strength ratios are modified to both strength of concrete and steel tube under ambient temperature, and analyzed to evaluate the effect of post-fire behavior on the axial capacity of CFST columns.

An analysis of models for the estimation of the impact of skin effect on the value of active resistance of solid and multi-conductor cores of power cables

The article analyzes some relations that are used in order to determine the influence of skin effect on the value of the active resistance of solid and stranded conductors of power cables. It is shown that the applying of the considered relations leads to the conclusion that the complication of the structure of the core of the power cable due to its manufacture from twisted together wires leads to the decreasing of the influence of skin effect on the resistance of power cable core in comparison with a solid core of a similar nominal cross-section. It was shown that this reduction takes place due to the calculation of the electrical resistance of power cable core based on the relation which is based on the applying of the nominal cross-section of the power cable core. In the range of core cable cross-section values from 240 mm2 to 500 mm2, despite some increase in core resistance, the influence of skin effect is not significant enough to transfer the value of the complex resistance to the region almost independent of the generalized parameter x phase angle. In the same range of values of the cross sections of the core such a transition of its complex resistance in the region of almost constant value of the phase angle can be achieved by increasing the frequency of current flowing through the core, however, this transition occurs in the frequency range much higher than the value of the industrial frequency.

Acoustic wave velocity in long pieces of Salzmann pine for in-situ structural assessment

In-situ assessment of timber members by acoustic measurement usually requires specific procedures (indirect and semidirect measurement) compared with those used in the laboratory (direct) and over longer distances. This research aims to determine which procedure is the most suitable. Acoustic Non-Destructive Testing measurements were taken in 21 150 × 200 mm2 nominal cross-section Salzmann pine structural timber pieces from 9.5 to 11.0 m long from a 1768 structure. Wave velocity was obtained from ToF measured with different sensor arrangements (direct, indirect and semidirect) in different lengths using stress wave and ultrasound. The direct velocity value was very close to non-direct measurements (0.4% higher), while previous research works with shorter pieces (3–4 m) showed larger differences (3.3–5.4%). There were no significant differences between indirect and semidirect measurements when using the same device or between devices, although a steady ratio was observed in the last case. The most predictive velocity procedure was determined by the correlation between static and dynamic modulus of elasticity. The most reliable stiffness prediction was obtained with the global velocity method, taking ToF measurements at distances from 1 to 10 m. A second method was proposed, consisting of taking only 2 measurements, and it achieved practically the same predictive capacity.

744-nm wavelength conversion of PAM-4 signal using an AlGaAsOI nanowaveguide.

Exploring new frequency bands for optical transmission is essential to overcome the capacity crunch. The 2-µm band is becoming a research spotlight due to available broadband thulium-doped fiber amplifiers as well as low-latency, low-loss hollow-core fibers. Yet most of the 2-µm band devices designed for optical communication are still in their infancy. In this Letter, we propose wavelength conversion based on four-wave mixing in a highly nonlinear AlGaAsOI nanowaveguide to bridge the 2-µm band and the conventional bands. Due to the strong light confinement of the AlGaAsOI nanowaveguide, high-order phase match is enabled by dispersion engineering to achieve a large synergetic conversion bandwidth with high conversion efficiency. Simulation results show a possible conversion bandwidth over an octave. An AlGaAsOI nanowaveguide with 3-mm length and a nominal cross-section dimension of $ 320\;{\rm nm} \times 680\;{\rm nm} $320nm×680nm is used for the wavelength conversion of a 10 Gbit/s non-return-to-zero on-off keying signal and a 10 Gbit/s Nyquist-shaped four-level pulse-amplitude modulation signal. A conversion efficiency of $ - {28}\;{\rm dB}$-28dB is achieved using a 17.5-dBm continuous-wave pump in the C band, with 744 nm conversion from 1999.65 to 1255.35 nm.

The influence of cross-section variation on bending stiffness assessment in existing timber structures

The frequent highly irregular geometry of the elements in existing timber structures complicates the structural verification of members and influences the use of non-destructive testing (NDT), affecting the inspection time, cost and results obtained. This process therefore needs to be improved. The main aim of this paper is to analyse how to obtain a representative nominal cross-section (NCS) of members, and its influence on determination of the static modulus of elasticity (MOEsta). 21 150 × 200 × 11,000 mm3 Salzmann pine (Pinus nigra subsp. salzmannii (Dunal) Franco) timber rafters from the 18th century Royal Coliseum of Charles III theatre (in Aranjuez, Madrid, Spain) were acoustically tested (by ultrasound, stress wave and vibration). The MOEsta was determined by mechanical testing, and different criteria for determining the NCS were analysed. Good correlation was obtained between the MOEsta and NDT parameters, and the best criterion to assign NCS was proposed to improve the accuracy of the models obtained by reducing the number of NCS measurements.

The influence of pine logs (Pinus sylvestris L.) quality class on the mechanical properties of timber

This study analyzed how the quality class (A, B, C) of pine logs (Pinus sylvestris L.) from the Silesian Forestry Region influences the mechanical properties of timber produced from those logs. The study utilized 210 pieces of timber with nominal cross section dimensions of 40 × 138 mm that were 3500 mm long and made of logs from a specific quality class. From these timber pieces, the density (with the stereometric method), the dynamic modulus of elasticity (using the Mobile Timber Grader device), the global modulus of elasticity, and static bending strength (EN-408 2012) was determined. On the basis of the conducted analyses, the log quality class influenced the physical and mechanical parameters of structural timber to a limited degree. However, statistically significant differences were not found for the density, dynamic and global modulus of elasticity, and bending strength between timber elements made of logs from A and B quality classes (Anova analysis with significance level p < 0.05).

Behavior of cold-formed steel elliptical hollow sections subjected to bending

This paper presents the experimental and numerical investigation on the behavior of cold-formed steel elliptical hollow section beams. In the test program, a total of 20 beam tests was conducted. Four elliptical section series with the nominal cross-section aspect ratio ranging from 1.65 to 3 were bent about the major and minor axes in both three-point and four-point bending configurations. Finite element models were established to replicate the beam tests numerically. Based upon the validated model, extensive parametric study was conducted on 235 beam specimens to study the behavior of cold-formed steel elliptical hollow sections subjected to bending. The results obtained from experimental and numerical investigation were used to assess the existing design methods and to propose modified design methods for cold-formed steel elliptical hollow section beams. It should be noted that the current design codes do not cover the design of elliptical hollow section beams. The flexural strengths of beams were compared with the design strengths predicted by the equivalent diameter and equivalent rectangular section methods proposed by previous researchers, the traditional design methods using equivalent diameter as well as the Direct Strength Method and the Continuous Strength Method. The applicability and reliability of these design methods were assessed. The results indicate that the existing design methods are not capable to predict the flexural strengths of cold-formed steel elliptical hollow section beams in accurate and reliable manner. In this study, the modified Direct Strength Method and Continuous Strength Method are proposed, which provide accurate and reliable flexural strength predictions.

Study on AC Resistance of Layering Enamelled Stranded Conductor

In recent years, with the rapid development of large-length ultra-high-pressure voltage extrusion insulated submarine cable technology, the cable system in the medium-length offshore power grid interconnection project has been gradually replaced by XLPE insulation by traditional oil-paper insulation. There are many large cross-section conductors used in long-distance power transmission cables, and according to the IEC 60287-1-1, it is recommended to use Milliken conductors to reduce the AC resistance of conductors, at the same time, in submarine cables, there is a high requirement on the water-blocking performance of conductors and the water resistance of Milliken conductors is poor, so it is not used in submarine cable conductors. This paper puts forward a layering enamelled stranded conductor and a calculation method of AC / DC resistance ratio for it. The validity of the calculation method is verified by experimental tests. At the same time, the calculation shows that the AC / DC resistance of the conductor at 1800 mm2 nominal cross section can be reduced by 16% compared with the conventional round compacted conductor in the prior art. The effectiveness of this conductor in reducing AC resistance is verified by finite element simulation.

Creating High-Density Large Square Bales by Recompression

Abstract. Creating high-density biomass bales would reduce the number of bales handled, stored, and transported to biorefineries, thereby reducing costs. Recompression of large square bales is one approach to increase bale density; however, recompression research on large bales is limited. Recompression of common biomass crops in 80 cm × 90 cm nominal cross-section bales was used to quantify pressure-density and stress relaxation relationships as well as restraining forces required to maintain compressed densities. Linear, power, and exponential models were fit to the pressure-density data, with the linear model providing the best representation of the recompression process. When bales were recompressed soon after bale formation, density increased by an average of 134%, and the target dry-basis density of 205 kg m-3 was exceeded at the end of recompression with all crops. While still compressed, bales were wrapped with four steel cables configured with load cells to measure the restraining force after release of pressure followed by bale re-expansion. Total restraining forces ranged from 18 to 40 kN. Bale density decreased by an average of 17% due to re-expansion after pressure was released. Strain relief induced by allowing the bale to re-expand by approximately 10% before placing the cables around the bales reduced the required restraining force by an average of 35%. Although the forces applied were great (>560 kN), the dry-basis specific energy requirements were comparatively low (0.18 to 0.29 kWh Mg-1) because recompression took place over a relatively long duration of approximately 20 to 25 s. Recompressing large square bales is a low-energy method to achieve bale densities that should ensure weight-limited biomass transport. Keywords: Bales, Biomass, Compression, Energy.

Influence of specimen size and measurements duration on the long-term extrapolation of drying shrinkage

The study presented in this paper aims at defining a procedure to study the efficiency of models used to extrapolate long-term shrinkage from experimental data. The approach allows estimating the minimum duration of measurements required to reach a given accuracy. The drying shrinkage of three Self-Consolidating Concretes (SCC) was monitored during 300days for three cylinder sizes: ϕ78mm, ϕ113mm, and ϕ163mm. Four mathematical forms of preexisting models have been studied: Model 1 (hyperbolic), Model 2 (square-root hyperbolic), Model 3 (square-root hyperbolic-tangent) and Model 4 (exponential). Two fitting parameters are provided by these models: ultimate shrinkage and characteristic time. Both parameters are overestimated for short experimental measurements duration. Their values cannot be considered as reliable unless a stabilization phase is reached vis-a-vis the measurements duration. Model 1 showed the fastest convergence and achieved this condition. The estimated ultimate shrinkage did not depend on specimen size. The stabilization phase was not reached for all models even after 300days. The characteristic time was found to depend linearly on the square of the nominal cross section. Conclusions about the accuracy of the extrapolation cannot be drawn directly from these two parameters. Indeed, overestimations in the ultimate shrinkage and in the characteristic time result respectively in an increase and a decrease of the calculated shrinkage. To solve this problem, the coefficient of determination R2 is introduced and its evolution is computed according to the measurements duration for all cases. Thus, for given accuracy, model, and specimen size, minimum measurements duration can be determined.

Fatigue assessment of welded and high frequency mechanical impact (HFMI) treated joints by master notch stress approach

High frequency mechanical impact (HFMI) treatment is a reliable and utmost effective method for post-weld fatigue strength improvement of steel joints, especially in case of high-strength steel applications. In 2014, the HFMI master notch stress approach was firstly introduced as an alternative design concept. It features an engineering-feasible method to assess the notch fatigue strength of HFMI-treated joints based on weld toe notch stress concentration, base material yield strength and load stress ratio.This paper presents an essential update of the HFMI master notch stress approach by facilitating the notch factor KW, obtained as the ratio of effective notch stress σk to structural stress σs. This enables a thorough fatigue assessment of welded structures without the need of a nominal cross-section definition.To proof the applicability, a comprehensive validation of the HFMI master notch stress approach incorporating over 230 additional steel joint specimen results covering both constant and variable amplitude tests is conducted. The constant amplitude study reveals that the fatigue strength of the HFMI master notch stress approach, utilizing the notch factor KW, is well applicable for material strengths up to ultra high-strength steels with a nominal yield limit of 1300MPa. In addition, the notch stress based service strength evaluation of variable amplitude loaded HFMI-treated high-strength steel joints considering a specified damage sum of D=0.3 according to Sonsino can be also well utilized for HFMI-treated joints.

Effect of Thermomechanical Degradation of Polypropylene on Mechanical Properties of Wood-Polypropylene Composites

In this research, the influence of thermomechanically degraded polypropylene (PP) on mechanical properties of beech sawdust-PP composites was studied. For this purpose, a virgin PP (VPP) was thermomechanically degraded by two times extrusion under controlled conditions in a twin-screw extruder at a rotor speed of 100 rpm and a temperature of 190°C. The results showed that melt flow index, flexural modulus, and hardness of PP were significantly increased by extrusion and re-extrusion of VPP. The PP (virgin and recycled PP in each stage) and beech sawdust were compounded at 60% weight sawdust loading in a counter-rotating twin-screw extruder in the presence or absence of maleated polypropylene (MAPP) to produce sawdust-PP composites. The nominal cross section and density of the manufactured composites were 70 × 10 mm2 and 1 g/cm3, respectively. From the results, the composites containing recycled PP exhibited higher flexural properties and hardness and lower impact strength. In the presence of MAPP, all mechanical properties increased.

Ballistic hole transport in a quantum wire

We report ballistic hole conduction in 2μm long GaAs quantum wires of nominal cross-section 15 nm by 15 nm. In each of eight test wires, we observe several quantized conduction steps of approximate height 0.77e2∕h. The wires were fabricated using the cleaved edge overgrowth molecular-beam epitaxy process, and the modulation-doped acceptors were incorporated using a carbon filament as the source of atomic carbon.

Numerical Determination Of Dynamic Stress Concentration Factors For An Axially Loaded Strut With Elliptical And Notch Discontinuities

Numerical modeling, simulation, and analysis of axial struts (with geometrical discontinuities) subjected to dynamic loading conditions is the focus of this paper. Understanding how geometrical discontinuities influence the stress distribution withn a structural member is critical for design applications. Furthermore, understanding how axial struts perform under dynamic loading conditions is critical in the design of automobiles, airplanes, and a large number of potentially dynamically loaded structures. A large amount of research investigating static loading conditions of struts with geometrical discontinuities has been conducted. With the development of finite element codes, numerical dynamic analyses can be completed much easier and at much lower costs than would occur for experimental methods. In this research finite element simulations were conducted on struts with centrally located elliptical holes as well as struts with circular notches subjected to an impact load. The stress distributions of the models were studied to determine the maximum stress state for each geometric configuration. This information was used to determine the dynamic stress concentration factor for each configuration. The dynamic stress concentration factor is plotted as a function of time and three-dimensional surface plots are shown, illustrating how the dynamic stress concentration factor varies with discontinuity geometry. It is shown that the dynamic stress concentration factor varies with time more significantly for discontinuities that minimize the nominal cross section of the strut. Transactions on the Built Environment vol 67, © 2003 WIT Press, www.witpress.com, ISSN 1743-3509

Kinetics study on the hydrogen atom-induced abstraction and associative desorption of deuterium adatoms from the Si(100) surface at 573 K

Hydrogen atom-induced deuterium adatom abstraction has been studied on the Si(100) surface from a desorption point of view. Abstraction of HD as well as collision-induced D2 desorption are observed on the D/Si(100) surface during H beam exposure at 573 K. For 1 ML Dad precoverage, about 30% of the desorbed D atoms are ejected as collision-induced D2 desorption at the very beginning of H(g) exposure. It is found that the decay of the HD and D2 rates are affected by the total coverage, θH+D. The decay rate of the HD rate is much lower in the low coverage regime than in the high coverage regime. The nominal cross section of the former is 2.3±1.0 Å2, while for the latter 7.2±0.5 Å2. The HD rate curves show that the abstraction obeys nearly first-order kinetics towards D coverage, θD. On the other hand, the D2 rate curves show that the collision-induced desorption obeys nearly fourth-order kinetics towards θD. Such HD abstraction is also observed on an oxygen-deposited D/Si(100) surface where the oxygen atoms are known to be incorporated between Si atoms. The observed decay rate of the HD rate is extremely low, with a cross section of 1.5±1.0 Å2. The reaction kinetics are well understood by adopting the kinetics model recently proposed by Flowers et al. [Surf. Sci. 396, 227 (1998)]. The abstraction of HD may be due to an Eley–Rideal mechanism rather than to a hot atom mechanism. Collision-induced D2 desorption may take place upon encounter of two dideuteride species via an isomerization reaction at quasiequilibrium.