| 1. |
- Asnafi, Nader, 1960-, et al.
(author)
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Tubular hydroforming of automotive side members with extruded aluminium profiles
- 2003
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In: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 142:1, s. 93-101
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Journal article (peer-reviewed)abstract
- Side member left and side member right, which go from bumper to bumper in a car body, were at the focus in the present study. These side members were produced using straight round (hollow with a circular cross-section) extruded aluminium profiles as tube material. The tubes were bent and hydroformed. Rotary-draw bending yielded the best result. A spread within 8mm after bending was found to be acceptable provided that the bent tube was hydroformed with a high maximum internal pressure (1300bar in this study). Pressure-assisted tool closure (hydroforming tool) should be preferred. Such a tool closure prevents formation of buckles, which may be difficult to straighten out completely during hydroforming. Planeness and parallelity of the press tables and adapters play a significant role, as far as the spread and inplaneness of hydroformed components are concerned. The hydroforming tool must be matched in the press that actually will be used. Proper evacuation (of particularly air) is essential, especially in long hydroforming tools. All cross-sections must be deformed at least 2% (average perimeter enlargement) if the hydroformed components are to exhibit a reasonable spread. The critical (fracture) cross-sections predicted by finite-element simulation corresponded to those found in practice. However, the finite-element simulation was not able to predict formation of wrinkles at the tube ends caused by excessively large strokes. Such wrinkles were obtained in practice.
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| 2. |
- Ervasti, Esa, et al.
(author)
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Transversal cracks and their behaviour in the hot rolling of steel slabs
- 2000
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In: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 101:1-3, s. 312-321
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Journal article (peer-reviewed)abstract
- The behaviour of transversal cracks in reverse rolling of steel slabs is analysed. For this purpose a commercial FE-program, LS-Dyna3D has been utilised. Process parameters from an industrial rolling mill have been used as a reference. One basic assumption is that the cracks do nor propagate for the steel considered. This is in agreement with observations in industry. Furthermore the material is treated as elastic-plastic. The aim of the study is to investigate the possibility of controlling the plastic deformation so that the cracks disappear at the same time as their boundary surfaces are prevented from getting into contact with each other. If they should get into contract, a defect in the form of an oxide flake should be created. The optimum situations are assumed to be found when the depth of the crack decreases more rapidly than the height of the slab at the same time as the crack width increases. For such rolling conditions it should be possible to find the crack bottom on the workpiece surface without any trace let by the original crack. During rolling two phenomena are present, counteracting each other. At the entrance to the roll gap, the crack widens, which is regarded as beneficial. The explanation to the phenomenon is that when the front edge of the crack gets into contact with the roil it is dragged towards the gap at the same time as its velocity is rapidly changed from horizontal to become parallel to the tangential velocity of the roll. If this phenomenon did not occur, the risk for the creation of a permanent oxide Rake should be big. During the passage of the gap the widened crack angle is decreased. The decrease of the angle is explained by the high hydrostatic pressure that is associated with the roll/workpiece contact surface. At the exit the angle is slightly increased once again which might be explained by the fact that the back edge of the crack is still in contact with the roll and its movement is retarded because of friction. Thus the final result depends on which of the two phenomena, widening or contraction that has been dominating. The analysis shows that light reductions/pass, small roll radius and high friction are preferred. A deep crack of V-shape is easily transformed to Y-shape. This means that a remaining defect should be formed at the bottom of the crack. Reverse rolling is found to be beneficial because this way of rolling implies that the crack does nor tilt so easily which should result in the formation of an oxide flake.
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| 3. |
- Hansson, Lars, et al.
(author)
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The effect of microwave drying on Norway spruce woods strength: a comparison with conventional drying
- 2003
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In: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 141:1, s. 41-50
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Journal article (peer-reviewed)abstract
- The purpose of the present work was to investigate whether the drying method itself affects strength of wood apart from fibre direction, density, temperature in the wood, moisture content and with which angle the microfibril is placed in the middle layer at the secondary cell wall S2. The drying methods compared were microwave drying and conventional air-circulation drying, and the species tested was Norway spruce. The result shows that it is not possible to demonstrate any difference between the two drying methods with respect to the strength of the wood. What affects wood strength are such variables as moisture content, number of annual rings and the density properties weight, width and thickness
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| 4. |
- Högberg, Dan, 1965-
(author)
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Use of finite element method in trailer deck design
- 2001
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In: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 117:1-2, s. 238-243
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Journal article (peer-reviewed)abstract
- The employment of the finite element (FE) method in conceptual and detail design of a secondary deck platform for trailer bodies is presented. The main objective of the project is to design a versatile, light and cheap secondary deck. To assist the designer with sufficient means for the concept generation and evaluation process, the FE method is used in order to gain fair structural analysis data. Assistance from the computer software stimulates creativity, reduces the time required in the design process, and eventually increases probability to gain customer satisfaction. This approach is precise enough for comparison purposes at this stage of the design process. The structural data gained is compared mainly with weight and access criteria.
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| 5. |
- Jarfors, A. E. W, et al.
(author)
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Deformation enhanced liquid phase sintering (DELPS) : A study on the use of partial adiabatic melting during powder consolidation
- 2002
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In: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 127:2, s. 159-164
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Journal article (peer-reviewed)abstract
- The presence of a liquid phase enhances the pore closure of a porous body, which is used in liquid phase sintering (LPS). During LPS, a substantial grain growth may occur by coalescence or Ostwald ripening, thus a short time in the liquid state is advantageous. Furthermore, it has been shown that during the initial stage of LPS, agglomerates are disintegrated and a significant reduction of grain size occurs. Heavy deformation causes an adiabatic temperature increase, which may result in a partial melting of the powder. Short-time duration deformation-assisted LPS, so called deformation enhanced LPS (DELPS), may thus be a suitable route for the fabrication of difficult-to-form materials. The present study is a feasibility test of DELPS. Three different types of materials were tested. The first type was an Al-Si with the possibility to form a large fraction of liquid phase. The second type was a W-based powder mixture yielding a low fraction liquid. The third type was a Ni-Al powder mixture exhibiting an exothermal behaviour when reaction occurs. The powders were hot compacted in a flexible die allowing large deformations. The specimens were examined and the composition of the phases were analysed. All of the samples, but one, showed near full density (>98%). Evidence of melting was found and in the W-base and the Ni-Al powder mixtures, and reaction had occurred in the Ni-Al mixture. © 2002 Elsevier Science B.V. All rights reserved.
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| 6. |
- Jensen, M.R., et al.
(author)
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Numerical model for the oil pressure distribution in the hydromechanical deep drawing process
- 2000
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In: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 103:1, s. 74-79
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Journal article (peer-reviewed)abstract
- This paper presents an attempt to simulate the hydromechanical deep drawing process using the finite element method (FEM). The basic idea is to compute the counter pressure and the fluid film pressure by solving a finite difference approximation of Reynold's equation. The concept is implemented as a contact algorithm in Exhale2D, an explicit finite element code for two-dimensional analyses. The numerical results illustrate a rather good agreement with experimental data.
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| 7. |
- Luo, C. H., et al.
(author)
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Deformation of inclusions during hot rolling of steels
- 2001
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In: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 114:1, s. 87-97
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Journal article (peer-reviewed)abstract
- The deformability of inclusions during hot working of steels influences the final properties of the product. In the present work the inclusion behavior in flat hot rolling has been studied by using a developed rigid-viscoplastic finite element code. The analysis is based on the mesomechanical approach. This method connects the micromechanical behavior of the heterogeneous material with its in-service macroscopic behavior. The macro-model evaluates the deformation history throughout each sub-volume of the material without taking the influence of inclusions into account. The micro-model that includes inclusions makes use of the deformation history from the macro-model as boundary values. Thus a micro-model cell element is constructed to analyze the behavior of an inclusion. The cell element is subjected to the same deformation history as that inside a macro-model element. The influences of process parameters, such as rolling temperature, rolling reduction and friction at workpiece/roll interface, are investigated. The relative plasticity index of a silicate inclusion was found to be heavily dependent on the process parameters. The index got high values for high temperatures, low rolling speeds and rolling schedules built on small reduction/pass. Some results are consistent with existing experimental observations. Also the influence of friction, at the workpiece/roll interface, on the profile of the inclusion has been analyzed.
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| 8. |
- Persson, P., et al.
(author)
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Self-propagating high-temperature synthesis and liquid-phase sintering of TiC/Fe composites
- 2002
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In: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 127:2, s. 131-139
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Journal article (peer-reviewed)abstract
- The present paper addresses a possible route for the manufacturing of iron-based metal-matrix composites (MMCs) with a high level of reinforcement. The ceramic reinforcement studied was titanium carbide (TiC). TiC is one of the hardest materials to be found, which is why a TiC/Fe composite has the potential to be used as armour. Two manufacturing routes have been evaluated experimentally, i.e., liquid-phase sintering (LPS) and self-propagating high-temperature synthesis (SHS). LPS was found to be more effective due to easier process control and due to the process yielding a more homogeneous material. Both LPS and SHS produced a material with a relatively high degree of porosity. The porosity in the LPS experiments could be decreased by varying the process parameters, but this was not possible in the SHS process. Metallographic investigation shows that the TiC/Fe system is feasible and that applications utilising TiC/Fe composites are possible in the future. This is due to the fact that despite the porosity, an improvement of the MMC properties is detected, compared to those of the matrix material. © 2002 Elsevier Science B.V. All rights reserved.
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| 9. |
- Bandyopadhyay, S., et al.
(author)
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Geometrical features and metallurgical characteristics of Nd : YAG laser drilled holes in thick IN718 and Ti-6Al-4V sheets
- 2002
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In: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 127:1, s. 83-95
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Journal article (peer-reviewed)abstract
- Laser drilling is increasingly becoming the method of choice for precision drilling of a variety of components, particularly in the aircraft industry. Notwithstanding the current level of acceptance of laser drilling in the aerospace industry, a number of defects such as spatter, recast and taper are associated with laser drilled holes and elimination of these defects is the subject of intense research. The present paper deals with Nd:YAG laser drilling of 4 and 8mm thick sections of IN718 and Ti-6Al-4V materials. The influence of type of material and its thickness, as well as parametric impact of key process variables like pulse frequency and pulse energy, have been determined. In the course of this study, relevant geometrical features of the drilled holes, like hole diameter and taper angle, have been comprehensively investigated. In addition, all metallurgical characteristics of interest, viz extent and nature of spatter, recast and heat-affected zone, have been evaluated. Effort has also been made to obtain some insights into the evolution of a through-thickness hole during laser percussion drilling of thick sections by careful experimentation involving monitoring the progression of the drilled hole with increasing number of laser pulses. Issues pertaining to variation of taper with depth of hole, change in crater depth with progressive drilling and specific energy consumption are also discussed. © 2002 Elsevier Science B.V. All rights reserved.
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| 10. |
- Lior, Noam
(author)
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The cooling process in gas quenching
- 2004
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In: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 155, s. 1881-1888
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Journal article (peer-reviewed)abstract
- Gas quenching is a relatively new process with several important advantages, such as minimal environmental impact, clean products, and ability to control the cooling locally and temporally for best product properties. To meet the high cooling rates required for quenching, the cooling gas must flow at very high velocities, and such flows are highly turbulent and separated. Consequently, there is a need for good understanding of these flows and their consequences for the process. To that end, we researched the state of the art, and have conducted numerous numerical and experimental studies and developed CFD models on this subject, and show the results for flows inside quench chambers and their components, and for external flows, including multi-jet impingement, on cylindrical and prismatic single and multiple bodies (the quench charge). Velocity distributions and uniformity, pressure drop, and flow effects on heat transfer coefficients and product uniformity, as well as recommendation for improved processes, are shown.
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