Study on inhomogeneous cooling behavior of extruded profile with unequal and large thicknesses during quenching using thermo-mechanical coupling model

The interfacial heat transfer coefficient between hot profile surface and cooling water was determined by using inverse heat conduction model combined with end quenching experiment. Then, a Deform-3 D thermo-mechanical coupling model for simulating the on-line water quenching of extruded profile with unequal and large thicknesses was developed. The temperature field, residual stress field and distortion of profile during quenching were investigated systematically. The results show that heat transfer coefficient increases as water flow rate increases. The peak heat transfer coefficient with higher water flow rates appears at lower interface temperatures. The temperature distribution across the cross-section of profile during quenching is severe nonuniform and the maximum temperature difference is 300 ℃ at quenching time of 3.49 s. The temperature difference through the thickness of different parts of profile first increases sharply to a maximum value, and then gradually decreases. The temperature gradient increases obviously with the increase of thickness of parts. After quenching, there exist large residual stresses on the inner side of joints of profile and the two ends of part with thickness of 10 mm. The profile presents a twisting-type distortion across the cross-section under non-uniform cooling and the maximum twisting angle during quenching is 2.78°.

Modeling and simulation of solvent behavior and temperature distribution within long stick propellants with large web thickness undergoing drying

Drying is a complicated physical process which involves simultaneous heat and mass transfer in the removal of solvents inside propellants.Inappropriate drying techniques may result in the formation of a hard skin layer near the surface to block the free access of most solvent through for long stick propellants with large web thickness,which lead to lower drying efficiency and worse drying quality.This study aims to gain a comprehensive understanding of drying process and clarify the mechanism of the blocked layer near the propellant surface.A new three-dimensional coupled heat and mass transfer(3D-CHMT)model was successfully developed under transient conditions.The drying experiment results show that the 3DCHMT model could be applied to describe the drying process well since the relative error of the content of solvent between simulation and experiment values is only 5.5%.The solvent behavior simulation demonstrates that the mass transfer process can be divided into super-fast(SF)and subsequent minorfast(MF)stages,and the SF stage is vital to the prevention of the blocked layer against the free access for solvent molecules inside propellant grains.The effective solvent diffusion coefficient(Deff)of the propellant surface initially increases from 3.4×10^(-6)to 5.3×10^(-6)m^(2)/s as the temperature increases,and then decreases to 4.1×10^(-8)m^(2)/s at 60-100 min.The value of Deffof surface between 0-1.4 mm has a unique trend of change compared with other regions,and it is much lower than that of the internal at100 min under simulation conditions.Meanwhile,the temperature of the propellant surface increases rapidly at the SF stage(0-100 min)and then very slowly thereafter.Both the evolution of Deffand temperature distribution demonstrate that the blocked layer near the propellant surface has been formed in the time period of approximately 0-100 min and its thickness is about 1.4 mm.To mitigate the formation of blocked layer and improve its drying quality of finial propellant products effectively,it should be initially dried at lower drying temperature(30-40℃)in 0-100 min and then dried at higher drying temperature(50-60℃)to reduce drying time for later drying process in double base gun propellants.The present results can provide theoretical guidance for drying process and optimization of drying parameters for long stick propellants with large web thickness.

The comparison between laser screw welding and resistant spot welding of lap joint with large thickness ratio

The present paper investigates the welding forming,microstructure and shear tensile test of lap joints with large thickness ratio which were fabricated by laser screw welding(LSW)and resistant spot welding(RSW).The comparison was conducted on two kinds of lap joints,galvanized sheet and hot pressed steel(GS-HPS),galvanized sheet and high strength steel(GS-HS).The microstructure and fracture morphology were analyzed by optical microscope.It was demonstrated that with large thickness ratio the sound lap joint of GS-HS could be obtained by LSW regardless of the irradiation of laser beam from thick metal to sheet or otherwise,and the morphology shows it is better when the laser is irradiated on the thick metal.Nevertheless,when the laser beam was applied on thick metal of HPS,blind hole or blowhole was formed in the center of joint,which is attributed to the shrinkage during solidification of the molten pool.Small pores or dispersed porosity appeared on the faying face of the joint without predetermined gap which provides the degassing.However,the increase of predetermined gap could reduce the shear strength and nugget size.Two kinds of joints made by LSW have superior shear strength than those made by RSW when the laser were applied on galvanized sheet.

Fabrication and Property of SiC Ceramic with Large Thickness/Diameter Ratios

Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon. The influence of thickness/diameter ratio on the microstructure and density of SiC ceramics was investigated in detail. The experimental results show that the addition of boron and carbon sintering aids can promote the densification process of SiC ceramic, leading to the low sintering temperature and improve mechanical properties. At 1950 ℃, SiC ceramic with a density of 99% exhibits Young's modulus, hardness, and flexural strength of 476 MPa, 28.3 GPa, and 334 MPa, respectively. It is found that long holding time has a positive effect on the uniformity of the microstructure and density distribution of SiC ceramics with large thickness/diameter ratios. Additionally, the sintering additive of boron can solid-solve into SiC, and then facilitate the phase transformation of SiC to form 6H-SiC and 4H-SiC composite ceramics.

Prediction of methane emissions during the extraction of close-to-roof layer of a seam of large thickness

Prediction of methane emissions at the stage of longwall planning constitutes the basis for the determination of the appropriate method and parameters of ventilation and selection of prevention means including the methane drainage technol- ogy. The growth of methane saturation of coal seams with the extraction depth, with simultaneously increasing output concen- tration, contributes to the increase of the quantity of methane emitted into longwall areas. The subject matter of the article has been directed at the predicted quantity of methane emissions into planned longwalls with roof caving in the layer of seams adjacent to the roof of large thickness. The performed prognostic calculations of methane emissions into the longwall working were referred to two sources, i.e. methane liberated during coal mining by means of a cutter-loader and methane originating from the degasification of the floor layer destressed by the longwall conducted in the close-to-roof layer. The calculations of predictions allow to refer to the planned longwall, on account of the emitting methane, with possible and safe output quantity. Planning of extraction in the close-to-roof layer of a seam of large thickness with roof caving is especially important in con- ditions of increasing methane saturation with the depth of deposition and should be preceded by a prognostic analysis for de- termining the extraction possibilities of the planned longwall.

LARGE DEFLECTION PROBLEM OF CIRCULAR PLATES WITH VARIABLE THICKNESS UNDER THE ACTION OF COMBINED LOADS

By using the modified iteration method of large deflection theory of plates with variable thichness[1], we solve the problem of circular plates with variable thickness subjected to combined loads under the boundary conditions of the clamped edges and get comparatively more accurate second-order approximate analytical solution. If the results of this paper are degraded into the special cases, the results coinciding with those of papers [1,2] can be obtained. In this paper, the characteristic curves are plotted and some comparisons are made. The results of this paper are satisfactory.

Constructing Large Capacity Power Plant on Collapsible Loess Stratum with Huge Thickness

1 Preface In the northern and northwestern parts of China, quite a large portion of area, approximately 630,000 km^2, is covered by loess and loess-liked soils. The loess thickness ranges from several meters to several hundred meters along the river’s terraces to those geomorphologic plateaus. In geology, "China Loess" has become a geologic term, because the loess in China has evolved with the widest distribution and greatest thickness in the world, and is also a typical and significant deposit in Quaternary Period.

Delicate chemical structure regulation of nonfullerene acceptor for efficient and large thickness organic solar cells

Inspired by the success of CH-series acceptors, a small-molecular acceptor, CH-Tz was reported by adopting a new conjugationextended electron-deficient unit([1,2,5]thiadiazolo[3,4-b]pyrazine) on the central core. Owing to the enhanced inter-/intramolecular interactions, CH-Tz exhibited near-infrared absorption and an effective three-dimensional molecular packing network in its single crystal. When blended with polymer donor PM6, the binary device achieved a high power conversion efficiency(PCE) of 18.54%, with a notable short-circuit current density(J_(sc)) of 27.54 m A cm-2and an excellent fill factor(FF) over 80%,which can be partly ascribed to the balanced charge transport properties in the blend film. After employing D18-Cl as the third component, an enhanced PCE of 18.85% was achieved due to a more obvious fiber network. Impressively, the CH-Tz-based OSC devices show excellent thermal stability and thickness insensitivity. Record-breaking Jscof 28.92 m A cm-2was reached for PM6:D18-Cl:CH-Tz ternary device with a thickness of 560 nm. Besides, CH-Tz shows potential in fabricating multicomponent high-performance organic solar cells, where over 19% efficiency could be realized in the quaternary device. Our work advances the strong influence of electron-deficient central units on molecular photovoltaic properties and guides the design of acceptors for stable and large-thickness organic solar cells.