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排序方式: 共有402条查询结果,搜索用时 218 毫秒
391.
Ladislav Novotný Hamilton Ferreira Gomes de Abreu Jozef Zajac Miloslav Béreš 《Science & Technology of Welding & Joining》2018,23(2):148-157
Welded components contain certain geometrical imperfections which may affect buckling behaviour of the final product. However, geometrical perfect models are usually used in the finite element method simulation. When a simple weld model is used, the mode of the end-distortion is predictable. Imperfections are created in the same shape as predicted. This paper presents a novel numerical approach on how to generate geometrical imperfections in finite element models. In this approach, as first, a large temperature gradient for the weld seam elements is prescribed. Then a linear steady-state thermal analysis is conducted and is followed by a structural analysis to determine the initial stress stiffness matrix for an eigenvalue analysis. The mode shapes of eigenvalue analysis are finally used to generate the imperfections. The results obtained in the course of this work allowed to calculate resultant welding distortion more accurate. 相似文献
392.
393.
Jozef Martinka Emília Hroncová Tomáš Chrebet Karol Balog 《Holz als Roh- und Werkstoff》2014,72(4):477-486
This paper deals with the assessment of the influence of heat treatment of Norway spruce wood (Picea abies L.) on its thermal stability and burning process. Three types of samples were used for the research. The first group was comprised of untreated samples. The second group was comprised of samples heat treated according to the ThermoWood—Thermo-S thermal programme (maximum temperature during heat treatment is 190 °C), and the third group was modified according to the ThermoWood—Thermo-D thermal programme (maximum temperature during heat treatment is 212 °C). The influence of heat treatment on the burning process was assessed based on the heat release rate, effective heat of combustion and the yield of carbon monoxide. The influence of heat treatment on the thermal stability was assessed based on the resistant residue weight. Heat release rate, effective heat of combustion, yield of carbon monoxide and resistant residue weight were determined with a cone calorimeter for different heat flux densities. The results obtained prove that the spruce wood heat treatment has an important influence on the decrease of the maximum heat release rate and the increase of resistant residue weight. The results obtained further prove that the heat treatment has only a modest influence on the increase of the carbon monoxide yield, and its influence on the effective heat of combustion significantly depends on the heat flux density. 相似文献
394.
Giedrius Miliauskas Teris A van Beek Petras R Venskutonis Jozef P H Linssen Pieter de Waard Ernst JR Sudhlter 《Journal of the science of food and agriculture》2004,84(15):1997-2009
The molecular structures of the radical scavenging compounds present in extracts of Potentilla fruticosa blossoms were elucidated and the antioxidant activities of various extracts were determined. The activities of the different fractions were monitored by off‐line and on‐line RP‐HPLC DPPH? and ABTS?+ scavenging methods. Twelve compounds were isolated and identified, namely ellagic acid, catechin, quercetin‐3‐β‐glucopyranoside, quercetin‐3‐β‐galactopyranoside, quercetin‐3‐β‐rutinoside, quercetin‐3‐β‐glucuronopyranoside, quercetin‐3‐α‐arabinofuranoside, kaempferol‐3‐β‐rutinoside, kaempferol‐3‐O‐β‐(6″‐O‐(E)‐p‐coumaroyl)glucopyranoside, rhamnetin‐3‐β‐glucopyranoside and rhamnetin‐3‐β‐galactopyranoside. The radical scavenging activity of each isolated compound was measured using DPPH? and ABTS?+ assays and compared with the activity of rosmarinic acid. Catechin and ellagic acid were found to be the most active radical scavengers. The antioxidant properties of plant fractions were assessed in model systems by measuring superoxide anion and hydrogen peroxide scavenging, β‐carotene bleaching, hexanal production in edible oil, peroxide formation, and the increase in UV absorbance in the course of oxidation. Copyright © 2004 Society of Chemical Industry 相似文献
395.
Jozef Zrnik Reinhard Pippan Stephan Scheriau Libor Kraus Martin Fujda 《Journal of Materials Science》2010,45(17):4822-4826
Using the high pressure torsion (HPT) deformation method the medium carbon steel (AISI 1045) was the experimental material
used to conduct the deformation process. The torsion deformation experiment was performed at increased temperature of 400 °C.
The influence of deformation processing parameters, resolved shear strain γ (number of turns N = 1–6) and applied pressure p (constant pressure of 7 GPa), was evaluated by microstructure analysis and mechanical properties. The strength behaviour
was assessed by microhardness measurements across the disc to detect the positional hardening, by tensile tests and in situ
measured torque. In situ measurement of torque during deformation allows characterizing the changes in mechanical properties
due to the large shear deformation developed across the disc. To obtain absolute values of strength the ultimate tensile strength
was measured in radial direction with respect to the deformed sample. From each deformed disc two sub-sized tensile test specimens
with gauge length of 2.5 mm were machined. The tensile strength in samples increased markedly with the number of turns. The
hardness measured at disc edge gradually increases as straining increases until it saturates after 2–3 turns. However, the
hardness values at edge were different from those measured in disc centre and for applied straining no saturation was reached
across the disc. The SEM and TEM investigations were carried out to analyze the fine microstructure evolution regarding the
strain introduced. To follow the difference in strain distribution across the deformed disc the microstructure analysis was
performed at edge and central site of the disc in order to evaluate the effect of the strain distribution. TEM investigation
confirmed the increasing misorientation even in very small grains, the fragmentation and dissolution of the cementite lamellae,
(diffuse cementite/ferrite boundaries), the alignment of the fragments to the shear plane with increasing deformation. Indistinct
deformation of ferrite and preserved cementite lamellae morphology were found at the centre of the disc. 相似文献
396.
Thermal analysis and phase transformation behaviour during additive manufacturing of Ti–6Al–4V alloy
Ladislav Novotný Miloslav Béreš Hamilton Ferreira Gomes de Abreu Jozef Zajac Wolfgang Bleck 《Materials Science & Technology》2019,35(7):846-855
Despite the fact that the additive manufacturing (AM) technique has been established for almost two decades, its optimisation is still performed by trial and error experimentation. In the present work, a finite element modelling approach was used to study both the temperature distribution and heat flux vector characteristics during multi-layer deposition of a Ti–6Al–4V alloy that take place in the AM process. The results revealed the difference between different powder deposition time intervals on thermal cycles, heat flux vectors and the resulting microstructures. Good agreement between the numerical and experimental results was found. The results obtained can be used for process optimisation. 相似文献
397.
398.
Effect of mixer geometry and operating conditions on mixing efficiency of a non-Newtonian fluid in a twin screw mixer 总被引:1,自引:0,他引:1
The effect of mixer speed, fluid inflow rate, and paddle angle was examined in a shortened geometry. 3D FEM simulation of non-Newtonian 2 g/100 mL carboxymethyl cellulose aqueous solution in the mixing region of a Readco continuous mixer was performed. Data gathered included velocity vectors, shear rate, and mixing index. Increasing mixer speed increased velocity magnitudes in the horizontal and vertical directions. Fluid inflow rate had little impact on velocity in the horizontal and vertical directions, but increased velocity in the axial direction and elongational contribution to the mixing index. All configurations showed areas of simple shear flow where the fluid experienced high shear rates. Staggering paddles increased the maximum axial velocity and shear rate. When successive paddles on the same screw are parallel, a zone was seen between the center of the paddle and the barrel wall which demonstrated efficient dispersive mixing. 相似文献
399.
Clean Technologies and Environmental Policy - Population growth sharply increases demand for readily available and affordable housing. As people spend a greater proportion of their lives indoors... 相似文献
400.
Sabine C. Bodner Kostyantin Hlushko Kevin Kutleša Juraj Todt Oliver Renk Michael Meindlhumer Florian Resch Marc-André Nielsen Jozef Keckes Jürgen Eckert 《Advanced Engineering Materials》2023,25(7):2200524
The correlations between process conditions, microstructure, and mechanical properties of additively manufactured components are not fully understood yet. In this contribution, three different hatch strategies are used to fabricate rod-like samples from S316L stainless steel, which are further investigated using synchrotron diffraction, optical microscopy, and tensile tests. The results indicate the presence of ⟨110⟩ biaxial and fiber textures, whose sharpness depends on the applied hatch strategy. Mechanical tests reveal a strong correlation of the samples’ response to the observed anisotropy in the plane perpendicular to the build direction. Even though the average yield and ultimate tensile strengths of around 475 and 500 MPa, respectively, do not differ significantly, the stress–strain behavior can be correlated with the observed in-plane anisotropy. Particularly, twinning-induced plasticity, a distinct increase of the work hardening rate at larger strains and elliptical necking are observed in some samples with biaxial (Goss) texture. These findings indicate that texture design by means of applying dedicated hatch strategies can be used to effectively tune the multiaxial deformation behavior of components produced by laser powder bed fusion. 相似文献