Sample Width Research Articles

Effects of ceiling inclination on lateral flame spread over vertical Poly(methyl methacrylate) surface

A series of experiments was designed to investigate the effects of ceiling inclination on lateral flame spread over vertical poly(methyl methacrylate) (PMMA) surface. PMMA slabs with width ranged from 3 cm to 9 cm were tested at the ceiling inclination from 30° to 90°. Burning rate, flame spread rate, and flame appearance were investigated experimentally. The results suggest that in the cases of narrow PMMA slabs, the flame spread rate presents a “U” variation with the increasing ceiling inclination. But flame spread rate of wider slabs decreases with ceiling inclination. Burning rate follows a power-law change with the sample width, which is m˙/W∝W0.136−0.421sin(α). And the exponential relationship between pyrolysis length, sample width and ceiling inclination can be given as xp∝W0.455−0.16sin(α).

Study on the main factors affecting the breakdown voltage of (Bi0.5Na0.5) TiO3-added (Ba0.659Pb0.341)TiO3 PTCR ceramic materials

The breakdown voltage (Vb) was studied for (Bi0.5Na0.5)TiO3 (BNT)-added positive temperature coefficient of resistance (PTCR) ceramic samples based on (Ba0.659Pb0.341)TiO3, which were prepared by a traditional solid-reaction method and sintered in an air atmosphere. By measuring the electrical properties and microstructures of the materials, the breakdown voltage was found to depend on neither the room-temperature resistivity nor the maximum resistivity, but on the grain size (D) of the samples to some extent. With a decrease in the grain size, the Vb value increases rapidly, especially for samples with fine grains. With the help of Heywang-Jonker theory, the depletion width (LD) was calculated to determine the dominant factor affecting the Vb value using the approximate equation Vb= 600 × LD/D + 100; i.e., the breakdown voltage is approximate directly proportional to the ratio of LD/D. However, the room-temperature resistivity increased slightly with LD/D, and the PTC performance remained at a high level (α > 34%, Rmax/Rmin > 1 × 103). It is more advantageous to increase the breakdown voltage by adjusting LD/D than by reducing grain size alone. The variations in the grain size and the depletion layer width of different samples are mainly due to the generation of VNa′ and VBiʺ′ inside of the lattice. The ratio of LD/D can also be used to explain the variation in room-temperature resistivity.

Effective Measuring Position of Hall Probe and <inline-formula> <tex-math notation="LaTeX">$j_\mathrm{c}$</tex-math> </inline-formula> Characterization of Rectangular HTS Thin Films

Scanning Hall probe (SHP) system is a powerful instrument to investigate the planar distribution of areal critical current density (j c ) and defects of high temperature superconducting (HTS) thin film samples. The distance between the effective measuring position and probe bottom (h 1 ) is usually unknown for the commercialized Hall probes. However, h 1 value has a significant influence on the measurement results, according to the calculation of the magnetic flux density (B 0 ) above the planar center of a rectangular HTS thin film sample. In this paper, a method was proposed to obtain h 1 by using a series of copper strips and analyzing the relationship of B 0 against the parameters, such as sample width and current. Then, SHP system was employed to characterize the j c distribution of an HTS thin film fabricated via chemical solution deposition. The relationship of B 0 and h 1 could also be utilized to obtain the average j c value (j c B0 ). A series of commercialized coated conductor samples were measured with both SHP and the traditional four-probe method. The feasibility of preliminary evaluation for rectangular HTS thin film samples by using j c B0 was discussed based on its correlation with the results of four-probe method.

Experimental research regarding some dynamic parameters determination for sandwich bars reinforced with carbon fiber

For this study, we have built some composite sandwich bars with polypropylene honeycomb core reinforced with carbon fiber. We have clamped the bars at one end and we left them to vibrate freely. From the free vibrations we have determined the damping factors per unit mass and length, loss factor, dynamic Young modulus, dynamic stiffness and the frequency of the first eigenmode. The general conclusions obtained from the vibrations results show tat the sample width can influence the damping coefficient, by the fact that it determines the surface in which the air friction acts on the sample. The sample mass or specific linear mass influence the damping factor by the fact that the samples with higher mass and width, the deformation energy which is stored in the sample through the initial deformation, is dissipated in a larger quantity of material. An influence may occur due to the sample rigidity, explained by the fact that a force initially applied to the sample produces a smaller deformation if the stiffness is higher.

Fracture Mechanism and Fracture Toughness at the Interface Between Cortical and Cancellous Bone.

The microstructure at the interface of cortical and cancellous bone is quite complicated. The fracture mechanisms at this location are necessary for understanding the comprehensive fracture of the whole bone. The goal of this study is to identify fracture toughness in terms of J integral and fracture mechanism at the interface between cortical and cancellous bone. For this purpose, single edge notch bend (SENB) specimens were prepared from bovine proximal femur according to ASTM-E399 standard. Bone samples were prepared such that half of the sample width consists of cortical bone and other half of the width was cancellous bone; this interfacial bone is referred as a corticellous bone. Elastic-plastic fracture mechanics was used to measure fracture toughness. The J integral (both elastic and plastic) was used to quantify the fracture toughness. The plastic part of J integral value (Jpl) of corticellous specimen was 9310 J m-2, and shown to be 27 times of the J integral of the elastic part (Jel), 341 J m-2. The total J integral of the corticellous bone was found to be 9651 J m-2, which is close to two times of the cortical bone, 4731 J m-2. This study observed that J integral of corticellous bone is higher than the cortical bone since more energy is required for plastic deformation of corticellous bone due to crack branches and slowdown at the interface between cortical and cancellous bone.

Experimental study on the effects of width and self-extinguishing on the upward flame spread for linen fabric

Linen fabric has been widely applied to interior decoration, medical and health care, industrial fabrics and oil painting exhibitions due to its advantages of good hygroscopicity, strong air permeability, excellent health care functions. In this paper, a series of comparative experiments were performed to study the effects of sample width on upward flame spreading using linen fabric with various widths ranging from 4 to 8 cm and length of 1.6 m. The major conclusions are summarized as follows: when sample width is 4 cm or 5 cm, the upward spreading process can be divided into three typical stages: two-sided flame accelerated spread, one-sided flame self-extinguishing and one-sided flame stable spread. Whereas for samples with a width larger than 5 cm, the upward flame spreading only exhibits the two-sided flame accelerated spread stage. Moreover, the maximum pyrolysis height, steady pyrolysis height, maximum spread rate and steady spread rate increase with sample width. The relationship between maximum spread rate and sample width can be described by a power-law function. Furthermore, after the one-sided flame self-extinguishing occurs, the pyrolysis height and spread rate decrease dramatically, which can be explained using energy conservation. The ratio of pyrolysis length before and after the self-extinguishing is about 2.0, and the corresponding ratio of spread rate is also around 2.0.

Evaluation of rolling shear modulus and strength of Japanese cedar cross-laminated timber (CLT) laminae

Cross-laminated timber (CLT) panels are fabricated with their layers stacked crosswise. Owing to the low shear modulus and strength in the rolling shear direction, the shear properties of cross-layers influence the overall deflection and shear capacities of CLT panels. The aim of the present study is to determine the rolling shear properties of Japanese cedar and investigate how annual ring patterns and lamina geometry influence shear properties. Using a test configuration similar to the standard shear test configuration prescribed in European Standards (EN 408), a single lamina shear test was conducted. To investigate the influence of thickness-to-width aspect ratio of the lamina on the rolling shear properties, samples with three different widths, including 62, 88, and 112 mm, with a constant thickness of 24 mm were tested. The geometrical features of the annual ring patterns of each test sample were measured. The mean rolling shear moduli were 72, 91, and 109 MPa, and the mean rolling shear strengths were 1.54, 1.83, and 2.02 MPa for the 62-, 88-, and 112-mm sample widths, respectively. Shear strength was highly correlated with shear modulus. The mean shear modulus and strength, in addition to the 5% quantile, increased with an increase in lamina width. Across all sample widths, rolling shear modulus and strength decreased with an increasing radial distance from the pith. Using the principle of continuum mechanics, the influence of the annual ring angle relative to the shear force direction was examined quantitatively using the finite element method. The results suggest that shear modulus and its variance are influenced greatly by the annual ring structure.

INVESTIGATION OF TECHNOLOGICAL PROPERTIES OF FOUR-TYPE TRITICALE SEED OF DIFFERENT FRACTIONS

Triticale is a promising agricultural crop. The increased content of protein, balanced by the amino acid composition, advantageously distinguishes triticale seed for peeled grains and food concentrates production. Seed cleaning is an important technological operation of food productions, but setting regimes of seed-cleaning equipment for processing triticale seed need specification today. The aim of this work is to study geometric and physical characteristics of four-type triticale seed and elaboration of recommendations as to its cleaning and fractionating. There was studied the fractional composition of four-type triticale seed. The comparative analysis of its length, width and thickness in samples of different sorts and fractions was realized. The dependence of geometric properties of triticale seed on sort is reliable. Fractionating reliably influences the change of the mass index of 1000 seeds, changing from 65,2 g to 25,8 g. The mass index of 1000 seeds essentially differs between studied sorts. Such properties are inherent to seed fractions, obtained by a sieve of 3,2–20 mm and 3,0–20 mm, that are recommended to be called big seeds. Fractions, obtained by a sieve of 2,0–20 and 2,2–20 are analogously similar. Properties of the middle fraction, obtained by sieves of 2,4–20; 2,6–20; 2,8–20 essentially changed, depending on sort. The elaborated recommendations may be used at choosing cleaning regimes for triticale seed on sieve and sieve-air separators.

GMAW Cold Wire Technology for Adjusting the Ferrite–Austenite Ratio of Wire and Arc Additive Manufactured Duplex Stainless Steel Components

The use of commercially available filler metals for wire and arc additive manufacturing (WAAM) of duplex stainless steel components results in a microstructure with a very low ferrite content. The ferrite–austenite ratio in the duplex stainless steel weld metal depends on both the cooling rate and particularly on the chemical composition. However, the research and testing of special filler metals for additive deposition welding using wire and arc processes is time-consuming and expensive. This paper describes a method that uses an additional cold wire feed in the gas metal arc welding (GMAW) process to selectively vary the alloy composition and thus the microstructure of duplex stainless steel weld metal. By mixing different filler metals, a reduction of the nickel equivalent and hence an increase in the ferrite content in additively manufactured duplex stainless steel specimens was achieved. The homogeneous mixing of electrode and cold wire was verified by energy dispersive spectroscopy (EDS). Furthermore, the addition of cold wire resulted in a significant increase in sample height while the sample width remained approximately the same.

Effect of orientation on the burning and flame characteristics of PMMA slabs under different pressure environments

To investigate the combined effects of orientation and environmental pressure on flame characteristics, steady burning experiments of inclined polymethyl methacrylate (PMMA) slabs were conducted at reduced environmental pressures ranging from 0.5 to 1 atm. According to the visual observations of flame appearance and fitting results of burning rate at different inclination angles, diffusion flames can be classified into three regions: pool-fire region, transition region and wall-fire region. Experimental result shows that flame pulsation frequency depends only on sample width in pool-fire region, however, mainly on fuel inclination angle in wall-fire region. A theoretical analysis is performed to predict the flame pulsation frequency as a function of modified gravity and the outlet diameter of gas-phase flame at different fuel inclination angles. In addition, the dimensionless flame pulsation frequency St is found to correlate well with the modified Froude number Fr∗, St=0.461/Fr∗0.53. Flame length shows a tendency to peak at 0.8 atm except 2.5 cm wide samples. Correlations between flame length and heat release rate are found with a power-law exponent of 1.41 for pressures smaller than 0.8 atm and 1.04 for larger pressures. Both experimental result and the developed correlations of flame length suggest that the roles of molecular diffusion and air entrainment played in diffusion burning are closely related to the environmental pressure and sample dimension.

Microgravity diffusion flame spread over a thick solid in step-changed low-velocity opposed flows

We report results from a microgravity combustion experiment conducted aboard the SJ-10 satellite of China, focusing on the structure and dynamics of diffusion flames spreading over a thick PMMA in low-velocity opposed flows. The width of the PMMA sample is chosen to be as large as possible in order to minimize the side diffusion effects of oxygen, and for each of the four oxygen concentration cases considered, four decrementally changing gas flow velocities are imposed such that a wide range of parameter values are spanned near the quenching limit. Two distinct flame spread modes are identified near the quenching limit, namely the continuous flame mode for gas flow velocities greater than an oxygen-concentration dependent critical value, and the flamelet mode for subcritical gas flow velocities. The transition process between these two spread modes due to a step change in the gas flow velocity is usually accompanied by flame oscillations, and diffusive-thermal instability of the leading flame front is identified as the mechanism controlling such transition. A correlation of the flame spread rate data among different oxygen concentrations indicates that, in the presently considered radiation-controlled regime the normalized flame spread rate deviates from the predictions of the thermal theory and decreases monotonically with the increase in the flame Damköhler number. Meanwhile, with the decrease in the flame spread rate, the standoff distance and the inclination angle at the flame leading edge show an increasing and decreasing trend, respectively. An energy balance analysis across the fuel surface beneath the flame leading edge indicates that the variation of the heat absorbed by the solid for vaporization is sub-linear with respect to the flame spread rate, thereby implying that the fuel regression depth has a tendency to increase with decreasing flame spread rate. Moreover, the energy balance analysis suggests that the quenching boundary and the marginal stability boundary identified on the flammability map are, respectively, intrinsically associated with a certain specific ratio of the overall heat losses to the total heat conducted from the flame, or equivalently, associated with a certain specific value of the flame spread rate.

Two-way approach for deformation analysis of non-crimp fabrics in uniaxial bias extension tests based on pure and simple shear assumption

In-plane shear is considered as the main deformation mechanism during the forming of fabrics on double curved geometries. Non-Crimp Fabrics (NCFs) are more and more used in the industry thanks to their high mechanical performances. The uniaxial bias extension (UBE) test is commonly used for characterizing the in-plane shear behavior of fabrics. However, presence of slippages calls the reliability of this test into question for NCF material. These slippages lead to a macroscopic kinematic which does not respect the fundamental hypotheses of UBE test theory. The variety of NCF architectures is usually pointed while the lack of standardized experimental methods is seldom discussed. The first section of this paper presents a two-way approach to detect slippage on an NCF. This approach is based on two kinematical descriptions of the UBE test. The first one assumes a pure shear behavior whereas the second one assumes a simple shear behavior. These behaviors correspond respectively to the rotation of fibers and to the slippage of fibers from a macroscopic point of view. In the second section, the two-way approach is used to analyze experimental UBE tests. This investigation highlights the influence of the sample width on the deformation mode during a UBE test. More precisely, it is shown that increasing the sample width of NCF specimens improves the UBE test reliability.

Universality of eigenchannel structures in dimensional crossover

The propagation of waves through transmission eigenchannels in complex media is emerging as a new frontier of condensed matter and wave physics. A crucial step towards constructing a complete theory of eigenchannels is to demonstrate their spatial structure in any dimension and their wave-coherence nature. Here, we show a surprising result in this direction. Specifically, we find that as the width of diffusive samples increases transforming from quasi one-dimensional ($1$D) to two-dimensional ($2$D) geometry, notwithstanding the dramatic changes in the transverse (with respect to the direction of propagation) intensity distribution of waves propagating in such channels, the dependence of intensity on the longitudinal coordinate does not change and is given by the same analytical expression as that for quasi-$1$D. Furthermore, with a minimal modification, the expression describes also the spatial structures of localized resonances in strictly $1$D random systems. It is thus suggested that the underlying physics of eigenchannels might include super-universal key ingredients: they are not only universal with respect to the disorder ensemble and the dimension, but also of $1$D nature and closely related to the resonances. Our findings open up a way to tailor the spatial energy density distribution in opaque materials.

Sub-Atmospheric Pressure Coupled with Width Effect on Downward Flame Spread over Energy Conservation Material Polyurethane Foam

Rigid polyurethane (PUR) foam, a sustainable thermosetting building facade porous polymer material, has been widely applied in the construction industry for energy conservation. Additional knowledge of the fire safety performance of PUR foam at different altitudes and sample widths is required. Comparative lab-scale experiments were conducted in the Lhasa plateau (66.5 kPa) and the Hefei plain (99.8 kPa) in China. Flame propagation characteristics (average flame spread rate and flame height) were measured at different widths and atmospheric pressures of the test locations. Experimental results show that the dependence of dimensionless flame heights on sample width shows negative power law relationships with index of -w / 5.4 - -w / 5.8. Both flame height and flame spread rate were lower under low ambient pressure conditions as Hf ∝ P0.26~0.33 and Vf ∝ P0.057~0.568 Flame spread rate decreased with increasing sample width in the convection regime before a critical width of 4 cm – 8 cm, after which the flame spread rate increased in the radiation regime. Results of this study contribute to the science of combustion, fire safety and energy conservation, and provide a basis for fire safety protocols for historical heritage buildings in the Lhasa plateau.

Quartz conditioning crystal for X-ray rocking curve topography

A large α-quartz crystal designed to condition the monochromatic beam at beamline 1-BM of the Advanced Photon Source is presented. The purpose of this crystal was to provide a precise match to the Bragg angle of quartz crystals that are commonly used to make analyzers for plasma diagnostics. In order to characterize these analyzers, area detectors need to be positioned at distances from the analyzer at upwards of 1000 mm. As a result of this precise matching, a Bragg-reflected beam from such an analyzer is precisely parallel to the beam incident on the conditioning crystal. This situation alleviates the need to adjust the position of the area detector as the distance between the analyzer and the area detector is varied. That is, there is no need to account for vertical displacement of the diffracted-beam image as a function of this distance. Additionally, verification that the analyzer is set to the correct Bragg reflection is obtained by scanning this distance, because only for a spurious reflection will there be a vertical displacement. This is a very useful check. To commission the conditioning crystal, diffraction from a high-quality flat quartz crystal was mapped using a CCD. Bragg diffraction from the 40\overline 40 reflection at 8.5 keV was studied over an area of 23 × 31 mm. The theoretical Darwin width of the flat sample in this case was 4.7 µrad. An FWHM value near 6 µrad was measured over almost the entire mapped area. These data demonstrate that the resolution function for this four-crystal arrangement is ∼4 µrad. Data are also presented for a 0.1 mm-thick α-quartz wafer pressed into a concave form, having a nominal radius of 500 mm and intended for use as an analyzer. Because analyzers are bent crystals, diffraction occurs in narrow bands. When a multiple exposure is made as a function of rocking angle a striped pattern is obtained, which is commonly referred to as a zebra-stripe pattern. A series of zebra stripes from the 30\overline 3\overline 3 Bragg reflection of the bent wafer over its 25 mm-diameter area were recorded on a CCD. The zebra-stripe pattern was analyzed to show a uniform bending to a radius of 497.0 ± 0.3 mm, in support of the nominal value. An r.m.s. slope error of 7 µrad was also obtained from this analysis.

Investigation of elastic properties of paper honeycomb panels with rectangular cells

Multilayer panels that have paper cores with hexagonal cells continue to have a limited application in furniture production. In contrast, there are no sandwich honeycomb panels with cores containing rectangular cells employed in this industry. Such cores should distinguish themselves by strong orthotropic advantages, in particular, for designing shelves and partitions of cabinet furniture. Hence, the objective of this study was to determine the effect of core rectangular paper cells on the mechanical properties of three-layer furniture panels. The authors decided to ascertain relative density and elasticity constants of the designed cells. The results of empirical experiments of cell elasticity moduli were compared with the results of the analytical calculations. The impact of sample width on their mechanical properties was determined. It was demonstrated that cores with hexagonal cells in furniture panels could be replaced by cores with rectangular cells.

Experimental study on width effects on downward flame spread over thin PMMA under limited distance condition

In this paper, a series of burning experiments with the downward fire spread were carried out using 1 mm thick, 200 mm tall PMMA with different widths varying from 50 mm to 150 mm in 13 mm restricted distance. The fire propagation parameters were observed and analyzed, including flame shape, pyrolysis front, pyrolysis length, flame height, and fire spread rate. The major conclusions are summarized as follows: The trends of the pyrolysis fronts and pyrolysis lengths with different widths show the increasing development under the limited condition. The flame height increase linearly as a function of time with the largest increase in 150 mm, followed by 100 mm and 50 mm. The wider the sample width, the faster the flame spread rate, Moreover, flame spread rate and flame width are exponentially related under constrained conditions, and the flame spread rate is proportional to the flame width with power value of 0.24 lowering than 0.5 and 0.35 in unlimited distance. The phenomenon is due to limited distance in this paper, and the flame spread rate of thermal thin materials is mainly affected by net heat flux. The conclusions of the study are meaningful for fire protection and fire development mechanisms.

Cleaning Optimization of Hot-Dip Galvanized Steel Surfaces in Preparation for Paint Application

Hot-dip galvanized steel surfaces are cleaned, pre-treated with titanium-containing solution and then painted for use. Removal of the alumina layer from galvanized steel surfaces during the cleaning process is essential before effective paint application. Bad adhesion results if the alumina layer is not completely removed, and an insufficient concentration and uneven distribution of titanium oxide is formed across the galvanized surface during pre-treatment. The alkaline cleaner concentration must be optimized to ensure effective removal of the alumina layer. Hot-dip galvanized steel samples were cleaned using typical line conditions and cleaning solutions with varying free alkalinities. The alumina layer was then measured on each sample by glow-discharge optical emission spectroscopy. Thereafter, the samples were treated with titanium-containing pre-treatment solution. The titanium oxide concentration was measured by inductively coupled plasma optical emission spectroscopy. It was found that a free alkalinity of at least 3.2 mEq/L is required to fully remove the alumina layer. The alumina-free samples also gave a titanium oxide layer after pre-treatment within the target concentration of 4–8 mg/cm2. A free alkalinity of 3.5 ml was thereafter implemented commercially: analysis of samples from two galvanizing lines showed no presence of alumina, a uniform titanium oxide distribution across the widths of the line samples and acceptable titanium concentrations.

Determination of the metal toughness components in impact-bending test

A method for separating the work of impact into two parts - the work of the crack nucleation and that of crack growth - which consists in testing two samples with the same stress concentrators and different cross-sectional dimensions at the notch site is developed. It is assumed that the work of crack nucleation is proportional to the width of the sample face on which the crack originates and the specific energy of crack formation, whereas the work of the crack growth is proportional to the length of crack development and the specific crack growth energy. In case of the sample fracture upon testing, the crack growth length is assumed equal to the sample width. Data on the work of fracture of two samples and their geometrical dimensions at the site of the notch are used to form a system of two linear equations in two unknowns, i.e., the specific energy of crack formation and specific energy of crack growth. The determined specific energy values are then used to calculate the work of crack nucleation and work of crack growth. The use of the analytical method improves the accuracy compared to graphical - extrapolative procedures. The novelty of the method consists in using one and the same form of the notch in test samples, thus providing the same conditions of the stress-strain state for crack nucleation and growth. Moreover, specimens with different cross-section dimensions are used to eliminate the scale effects. Since the specific energy of the crack nu-cleation and specific energy of the crack growth are independent of the scale factor, they are determined only by the properties of the metal. Introduction the specific energy of crack formation and growth makes possible to assign a specific physical meaning to the fracture energy.

Evolution of the pore structure in coal subjected to freeze−thaw using liquid nitrogen to enhance coalbed methane extraction

The permeability of coalbed methane (CBM) reservoirs is typically very low and it is challenging and essential to effectively increase coal permeability to maximize CBM recovery. An exploratory study on enhancing coal porosity/permeability using freeze−thaw cycling with liquid nitrogen (LN2) was conducted. The changes of fracture and porosity in coal with the freeze−thaw treatment using LN2 were evaluated using nuclear magnetic resonance (NMR). After freeze−thaw treatment, the coal pore size tended to increase and new pores/fissures were generated. The growth rate of the pore size was positively correlated with the LN2 freezing duration. The effective porosity had a positive correlation with the freezing duration, but the correlation for residual porosity was negative. This means that the volume of irreducible fluid in the coal decreased while the amount of free fluid increased. Scanning electron micrograph studies indicated that the maximum fracture width in the coal samples grew from 5.56 μm at a Tfreezing = 1 min to 100 μm for Tfreezing = 60 min, matching the NMR findings. This study provides a scientific basis and guidance for engineering application of freeze−thaw using liquid nitrogen to enhance coalbed methane extraction.