| 1. |
- Fan, Teng, et al.
(författare)
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Microstructural and Mechanical Characteristics Examination of Ultrasonically Welded Joints Using Orthogonal Experimentation
- 2024
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Ingår i: International Journal of Precision Engineering and Manufacturing (IJPEM). - : The Korean Society for Precision Engineering and Manufacturing (KSPE). - 2234-7593 .- 2005-4602.
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present an investigation of ultrasonic welding performance for 25 mm2 copper wire and T2 copper plate across various welding parameters using orthogonal experimentation. The objective of this work was to explore the influence of operational parameters on the resulting welds. A comprehensive study of the mechanical properties and microstructure of the copper wire-to-copper plate joint was carried out using a series of sophisticated instruments. It includes a universal tensile machine, resistance measuring equipment, SEM, EDS and temperature measuring tool. This multifaceted approach enabled a detailed analysis of the joint's integral features and properties. This provides further insight into its performance and durability. Findings indicate that welding pressure has the most significant effect on welded joints. The optimal combination of parameters is achieved with the welding energy set at 6000 J, the welding amplitude at 85% and the welding pressure at 260 kPa. In different sets of welding parameters, joint strength is positively related to welding parameters and increases with increasing welding parameters. Joint resistance decreases with increasing joint tensile load and conductivity can be used to evaluate ultrasonic welding. It has been found that the development of the welded joint is achieved gradually in a direction moving inwards from the welding tool head, exhibiting a methodical forming process. Three distinct failure modes are observed in welded joints such as joint pullout, joint tearing and busbar breakage. The peak temperature during the welding process was recorded at 373 °C which indicates that the ultrasonic welding is a solid state connection. © The Author(s), under exclusive licence to Korean Society for Precision Engineering 2024.
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| 2. |
- Pilthammar, Johan, 1987-
(författare)
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Towards Virtual Tryout and Digital Twins : Enhanced Modeling of Elastic Dies, Sheet Materials, and Friction in Sheet Metal Forming
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Competition and complexity in the global car market are continuously increasing. To gain an edge in the market while making a profit, each competitor in the market needs a strong focus on technology development. Such a focus will increase the value of the product for the customers. On top of the challenges of developing the technical content of the cars, it is equally important to develop the manufacturing processes. This will enable the production of technically advanced and attractive products at a competitive cost.An important manufacturing process within the automotive industry, and the focus of this PhD thesis, is sheet metal forming (SMF). The SMF process has been simulated for the past few decades with finite element (FE) simulations, whereby factors such as shape, strains, thickness, springback, risk of failure, and wrinkles can be predicted. A factor that most SMF simulations do not currently include is die and press elasticity, limiting the reliability of SMF simulations for virtual die tryout and digital twins. This factor is instead handled manually during the die tryout, which is time-consuming and expensive.The importance of accurately representing press and die elasticity in SMF simulations is the focus of this research project. The objective is to achieve virtual tryout and production support through SMF simulations that consider elastic die and press deformations. Accurate simulations of die tryout, or dies in running production, are found to be impossible without the inclusion of reliable representations of elastic dies and presses.Accurate CAD models of stamping dies are common. Strategies are presented for how to include them in SMF simulations models that are easy to set up and fast to solve. Full representations of presses are rarer. Methods for measuring and inverse modeling the elasticity of presses are therefore presented together with an overview from the literature of other methods. A unified method that is reliable and cost-efficient for the stamping industry is of high interest.SMF simulations with elastic dies will only yield accurate predictions if reliable models of sheet materials and lubrication systems are included. Friction in particular is highly dependent on die deformations since contact pressure is an important parameter in determining the friction level. Reliable models for both friction and sheet materials are dependent on accurate experimental data and characterization methods.Including elastic die and press deformations in SMF simulations, together with reliable representations of friction and sheet materials, has immense potential to reduce the lead time of stamping dies. The simulation methods that include elasticity will also be vital for more accurate digital twins of press lines.
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| 3. |
- Shahid, Sharlin, 1992-, et al.
(författare)
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Simplified Characterization of Anisotropic Yield Criteria for an Injection-Molded Polymer Material
- 2023
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Ingår i: Polymers. - : MDPI. - 2073-4360. ; 15:23
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Tidskriftsartikel (refereegranskat)abstract
- Injection-molded polyethylene plates exhibit highly anisotropic mechanical behavior due to, e.g., the uneven orientation of the polymer chains during the molding process and the differential cooling, especially in the thickness direction. Elastoplastic finite element modeling of these plates in particular is used with isotropic yield criteria like von Mises, trading off accuracy in favor of simpler constitutive characterization and faster solution. This article studies three different anisotropic yield criteria, namely, Hill 1948, Barlat Yld91, and Barlat Yld2004-18P, for the finite element modeling of low-density polyethylene (LDPE) at large uniaxial tensile deformation and compares the accuracy and computation time with von Mises. A simplified calibration technique is investigated to identify the constitutive parameters of the studied Barlat group yield criteria. The calibration process is simplified in the sense that only uniaxial tensile tests with digital image correlation measurements are used for the calibration of all the yield criteria studied in this article, although a standard calibration procedure for the Barlat group yield criteria requires additional material testing using more demanding test setups. It is concluded that both Barlat Yld91 and Barlat Yld2004-18P yield criteria can be calibrated with only a few tensile tests and still capture anisotropy in deformation–stress–strain at different levels of accuracy. © 2023 by the authors.
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| 4. |
- Shahmardani, Mahdieh, et al.
(författare)
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Numerical simulation of buckling and post-buckling behavior of a central notched thin aluminum foil with nonlinearity in consideration
- 2020
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- In thin notched sheets under tensile loading, wrinkling appears on the sheet surface, specifically around the cracked area. This is due to local buckling and compression stresses near the crack surfaces. This study aims to numerically study the buckling behavior of a thin sheet with a central crack under tension. A numerical model of a notched sheet under tensile loading is developed using the finite element method, which considers both material and geometrical nonlinearity. To overcome the convergence problem caused by the small thickness-to-length/width ratio and to stimulate the buckling, an imperfection is defined as a small perturbation in the numerical model. Both elastic and elasto-plastic behavior are applied, and the influence of them is studied on the critical buckling stress and the post-buckling behavior of the notched sheet. Numerical results for both elastic and elasto-plastic behavior reflect that very small perturbations need more energy for the activation of buckling mode, and a higher buckling mode is predominant. The influences of different parameters, including Poisson’s ratio, yield limit, crack length-to-sheet-width ratio, and the sheet aspect ratio are also evaluated with a focus on the critical buckling stress and the buckling mode shape. With increase in Poisson’s ratio. First, the critical buckling stress reduces and then remains constant. A higher yield limit results in increases in the critical buckling stress, and no change in the buckling mode shape while adopting various crack length-to-sheet-width ratios, and the sheet aspect ratio changes the buckling mode shape.
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| 5. |
- Ståhle, Per, et al.
(författare)
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On buckling and fracture of thin elastic-plastic foils
- 2020
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Ingår i: 1ST VIRTUAL EUROPEAN CONFERENCE ON FRACTURE - VECF1. - : ELSEVIER. ; , s. 2065-2071
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Konferensbidrag (refereegranskat)abstract
- The interaction of simultaneous fracture and buckling constitutes problems at manufacturing and handling of thin foils. Buckling occurs as an additional event that complicates the prediction of the critical load that may lead to fracture. For most sufficiently thin foils the plastic slip occurs through the foil thickness which leads to reduction of the cross section width until the foil fails. The process leads to a necking type of deformation which confines itself to a narrow region that extends ahead of the crack tip. The width of the region is close to the foil thickness. At failure the width of the necking region is twice the foil thickness. In the present investigation the crack is assumed to be small compared to the foil geometry and the foil is assumed to be small compared with the crack length. Because of the latter the necking type of plastic region is modelled as a cohesive zone. Since the fracture toughness is not involved in the failure the only two relevant length parameters are crack length and foil thickness. The material model is defined by the elastic modulus, Poisson's ratio and yield stress. The remote load at buckling and at failure is determined and given on dimensionless form, which leaves Poisson's ratio and the ratio of buckling stress versus failure stress as the only free parameters. Two scales of yielding, the load at the ASTM-limit for linear fracture mechanics and twice that load, including the purely elastic result are investigated. Poisson's ratio is varied in the interval from -0.9 to 0.5 for the elastic case and from -0.6 to 0.5 for the plastic cases. The lower theoretical limit -1 for Poisson's ratio was not obtained because of numerical difficulties. The results rules out the possibility of failure before buckling for any reasonable construction material. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo
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| 6. |
- Ståhle, Per, et al.
(författare)
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On buckling and fracture of thin elastic-plastic foils : Part of special issue: 1st Virtual European Conference on Fracture - VECF1
- 2020
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Ingår i: Procedia Structural Integrity. - : Elsevier BV. - 2452-3216. ; 28, s. 2065-2071
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Konferensbidrag (refereegranskat)abstract
- The interaction of simultaneous fracture and buckling constitutes problems at manufacturing and handling of thin foils. Buckling occurs as an additional event that complicates the prediction of the critical load that may lead to fracture. For most sufficiently thin foils the plastic slip occurs through the foil thickness which leads to reduction of the cross section width until the foil fails. The process leads to a necking type of deformation which confines itself to a narrow region that extends ahead of the crack tip. The width of the region is close to the foil thickness. At failure the width of the necking region is twice the foil thickness. In the present investigation the crack is assumed to be small compared to the foil geometry and the foil is assumed to be small compared with the crack length. Because of the latter the necking type of plastic region is modelled as a cohesive zone. Since the fracture toughness is not involved in the failure the only two relevant length parameters are crack length and foil thickness. The material model is defined by the elastic modulus, Poisson's ratio and yield stress. The remote load at buckling and at failure is determined and given on dimensionless form, which leaves Poisson's ratio and the ratio of buckling stress versus failure stress as the only free parameters. Two scales of yielding, the load at the ASTM-limit for linear fracture mechanics and twice that load, including the purely elastic result are investigated. Poisson's ratio is varied in the interval from -0.9 to 0.5 for the elastic case and from -0.6 to 0.5 for the plastic cases. The lower theoretical limit -1 for Poisson's ratio was not obtained because of numerical difficulties. The results rules out the possibility of failure before buckling for any reasonable construction material.
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| 7. |
- Su, Jianxiong, et al.
(författare)
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Microscopic mechanism of ultrasonically welded joints : The role of terminal roughness and wire diameter
- 2024
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Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 214
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Tidskriftsartikel (refereegranskat)abstract
- The ultrasonic welding technology is widely promoted as a new connection approach in the field of current energy vehicle wiring harness connection. In this paper, three kinds of 25mm2 copper wire harnesses with different wire diameters and T2 copper terminals with different surface roughness were welded by ultrasonic welding. The mechanical properties of the joints were investigated by tensile experiments and the microstructure of joints was characterised using SEM and EBSD techniques. Excessive roughness increases plastic deformation at the weld interface during ultrasonic welding. This increases the dislocation density at the weld interface and refines the grain size. However, at the same time it inhibits recrystallisation to a certain extent. The lower roughness facilitates recrystallisation, but the low density of HAGBs makes the interface susceptible to slip in extended crystallographic plane and direction. Appropriate roughness allows the weld interface to generate fine equiaxed grains and a high density of HAGBs. This facilitates the obstruction of dislocation movement and improves the strength of joint. In addition, the high porosity of a longitudinal cross-section of the conductor with its small diameter was investigated. This results in a large number of wires remaining on the terminals when force is applied. It was determined that the larger a diameter of wire, the higher a cross-sectional porosity. The copper wire breaks at a weak point in cross-section when the force is applied, resulting in the entire wire being left on terminal. At a wire diameter of 0.2 mm, the porosity of a cross-section reaches an equilibrium and the strength of joint is even higher than the strength of material itself, resulting in the joint pulling off. The maximum strength reaches 4703.77 N. © 2024
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| 8. |
- Wang, Xueliang, 1993-, et al.
(författare)
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Numerical evaluation of rotordynamic coefficients for compliant foil gas seal
- 2020
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Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Compliant foil gas seal is one of the advanced cylindrical gas seal technologies and can be commonly used in the secondary flow system of an aero-engine. It can enhance the dynamic stability of the aero-engine by meeting the steady requirements of the aero-engine seal system. To evaluate the performance of compliant foil gas seal, the steady performance of the gas seal is firstly analyzed to predict the sealing efficiency and obtain the pressure distribution of the gas seal in the compressible flow field. Then, the effects of the operating parameters on the rotordynamic coefficients are analyzed using the finite differential method. It can be used to predict the operation performance of the aero-engine and prepare for the optimization and test rig of compliant foil gas seal on the T-shaped groove. © 2020 by the authors.
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