| 1. |
- Barlo, Alexander, M.Sc. Eng. 1994-, et al.
(author)
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Determination of Edge Fracture Limit Strain for AHSS in the ISO-16630 Hole Expansion Test
- 2023
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In: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
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Conference paper (peer-reviewed)abstract
- With the increased demand for application of sustainable materials and lightweight structures, the sheet metal forming industry is forced to push existing materials to the limits. One area where this is particular difficult is when it comes to assessing the formability limit for sheet edges. For decades, the ISO-16630 Hole Expansion Test (HET) has been the industry standard for expressing the edge formability of sheet metals through the Hole Expansion Ratio (HER). However, in recent years, this test has been criticized for its high scatter in results for repeated experiments. This scatter has been suspected to be caused by the operator-reliant post-processing of the test, or variations in the cutting conditions for the different test specimens. This study investigates the impact of shifting the evaluation point of the test from the through-thickness crack to the onset of surface failure on the reported scatter, as well as performs inverse modeling of the Hole Expansion Test to obtain an edge limit strain value.
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| 2. |
- Barlo, Alexander, M.Sc. Eng. 1994-
(author)
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Failure Prediction of Complex Load Cases in Sheet Metal Forming : Emphasis on Non-Linear Strain Paths, Stretch-Bending and Edge Effects
- 2023
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Licentiate thesis (other academic/artistic)abstract
- With the increased focus on reducing carbon emissions in today’s society, several industries have to overcome new challenges, where especially the automotive industry is under a lot of scrutiny to deliver improved and more environmentally friendly products. To meet the demands from customers and optimize vehicles aerodynamically, new cars often contain complex body geometries, together with advanced materials that are introduced to reduce the total vehicle weight. With the introduction of the complex body components and advanced materials,one area in the automotive industry that has to overcome these challenges is manufacturing engineering, and in particular the departments working with the sheet metal forming process. In this process complex body component geometries can lead to non-linear strain paths and stretch bending load cases, and newly introduced advanced materials can be prone to exhibit behaviour of edge cracks not observed in conventional sheet metals. This thesis takes it onset in the challenges seen in industry today with predicting failure of the three complex load cases: Non-Linear Strain Paths, Stretch-Bending,and Edge Cracks. Through Finite Element simulation attempts are made to accurately predict failure caused by aforementioned load cases in industrial components or experimental setups in an effort to develop post-processing methods that are applicable to all cases.
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| 3. |
- Barlo, Alexander, M.Sc. Eng. 1994-, et al.
(author)
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Proposal of a New Tool for Pre-Straining Operations of Sheet Metals and an Initial Investigation of CR4 Mild Steel Formability
- 2023
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In: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
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Conference paper (peer-reviewed)abstract
- With the increased focus on reducing carbon emissions in the automotive industry, more advanced materials are introduced to reduce the vehicle weight, and more complex component geometries are designed to both satisfy customer demands and to optimize the vehicle aerodynamically. With the increase in component complexity, the strain paths produced during the forming operation of car body components often display a highly non-linear behavior which makes the task of failure prediction during the manufacturing feasibility studies more difficult. Therefore, CAE engineers need better capabilities to predict failure induced by strain path nonlinearity. This study proposes a new tool designed for creating bi-linear strain paths, by performing a pre-strain of a sheet large enough to cut out Nakajima specimens to perform the post-straining in any direction. From five pre-straining tests the tool present a stable pre-straining operation with a uniform strain field in a radius of 100 [mm] from the centre, corresponding to the region of interest of a Nakajima specimen. From the five pre-strained samples, different Nakajima specimens are cut transverse and longitudinal to the rolling direction and a failure prediction approach in an alternative, path independent evaluation space was used to predict the onset of necking with promising results.
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| 4. |
- Huo, Xiaole, et al.
(author)
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Effect of ultrasonic vibration on static properties of 5A06 aluminum alloy self-piercing riveting joints
- 2023
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In: Cailiao Kexue yu Gongyi/Material Science and Technology. - : Harbin Institute of Technology. - 1005-0299. ; 31:2, s. 44-49
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Journal article (peer-reviewed)abstract
- Self-piercing riveting process is a new connection technology with excellent performance, green, and high efficiency. It can realize the connection of the similar, different, and multi-layer light alloy sheet materials and is widely used in new energy vehicles and other fields. Furthermore, it is becoming one of the critical technologies for achieving a lightweight body. However, because the self-piercing riveting joint is a typical tight connection component, fretting damage is prone to occur under the action of alternating stress or vibration, resulting in premature joint fatigue failure. This paper uses 5A06 aluminum alloy sheet material to carry out self-piercing riveting and ultrasonic self-piercing riveting composite connection tests under different ultrasonic welding tool heads. Based on the tensile-shear and electron microscope tests, the effect of ultrasonic vibration on the static properties of 5A06 aluminum alloy self-piercing riveted joints was studied. The results show that: ultrasonic vibration can effectively improve the static properties of self-piercing riveted joints; the ultrasonic metal welding will form a solid phase of welding between the sheets during the composite self-piercing riveting, which is the fundamental reason for improving the mechanical properties of the combined joint; the area of ultrasonic metal welding joints affects the mechanical properties of self-piercing riveted joints; the degree of ultrasonic solid-phase welding is higher when the welding area is more extensive; ultrasonic welding will increase the temperature of the rivet, which will affect the stability of the joints to a certain extent. © 2023 Harbin Institute of Technology. All rights reserved.
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| 5. |
- Li, Cheng-Wang, et al.
(author)
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Comparison of mechanical properties of various joining processes of aluminum-titanium light alloy
- 2023
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In: Suxing Gongcheng Xuebao/Journal of Plasticity Engineering. - : Beijing Res. Inst. of Mechanical and Elec. Technology. - 1007-2012. ; 30:8, s. 138-145
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Journal article (peer-reviewed)abstract
- 5A06 aluminum alloy and TA1 titanium alloy were selected for the connection tests of flow drill screw, ultrasonic clinch and ultrasonic self-piercing riveting. The influence of plate overlap methods on mechanical properties of each group of joints was studied by static tensile tests. The results show that the mechanical properties of the flow drill screw joints and the ultrasonic self-piercing riveted joints are significantly improved when the soft plate is on top during the riveting process. The plate overlap method has little effect on the ultrasonic clinch joint. Flow drill screw joints have the best cushioning and shock absorption performance, but the stability is poor, and it is more limited when applied to body structures. Ultrasonic clinch joints have low cost and simple process, but poor shear resistance and are not suitable for body structures subjected to high stress. Compared with the other two connection methods, the ultrasonic self-piercing riveted connection has the best stability, the best tensile resistance and shear stiffness, and is suitable for much of the structure in lightweight field of automobile body. © 2023 Beijing Res. Inst. of Mechanical and Elec. Technology. All rights reserved.
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| 6. |
- Lin, Sen, et al.
(author)
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Non-destructive monitoring of forming quality of self-piercing riveting via a lightweight deep learning
- 2023
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In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Journal article (peer-reviewed)abstract
- Self-piercing riveting (SPR) has been widely used in automobile body jointing. However, the riveting process is prone to various forming quality failures, such as empty riveting, repeated riveting, substrate cracking, and other riveting defects. This paper combines deep learning algorithms to achieve non-contact monitoring of SPR forming quality. And a lightweight convolutional neural network with higher accuracy and less computational effort is designed. The ablation and comparative experiments results show that the lightweight convolutional neural network proposed in this paper achieves improved accuracy and reduced computational complexity. Compared with the original algorithm, the algorithm's accuracy in this paper is increased by 4.5[Formula: see text], and the recall is increased by 1.4[Formula: see text]. In addition, the amount of redundant parameters is reduced by 86.5[Formula: see text], and the amount of computation is reduced by 47.33[Formula: see text]. This method can effectively overcome the limitations of low efficiency, high work intensity, and easy leakage of manual visual inspection methods and provide a more efficient solution for monitoring the quality of SPR forming quality. © 2023. The Author(s).
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| 7. |
- Lun, Zhao, et al.
(author)
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Skip-YOLO : Domestic Garbage Detection Using Deep Learning Method in Complex Multi-scenes
- 2023
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In: International Journal of Computational Intelligence Systems. - : Springer Science+Business Media B.V.. - 1875-6891 .- 1875-6883. ; 16:1
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Journal article (peer-reviewed)abstract
- It is of great significance to identify all types of domestic garbage quickly and intelligently to improve people's quality of life. Based on the visual analysis of feature map changes in different neural networks, a Skip-YOLO model is proposed for real-life garbage detection, targeting the problem of recognizing garbage with similar features. First, the receptive field of the model is enlarged through the large-size convolution kernel which enhanced the shallow information of images. Second, the high-dimensional features of the garbage maps are extracted by dense convolutional blocks. The sensitivity of similar features in the same type of garbage increases by strengthening the sharing of shallow low semantics and deep high semantics information. Finally, multiscale high-dimensional feature maps are integrated and routed to the YOLO layer for predicting garbage type and location. The overall detection accuracy is increased by 22.5% and the average recall rate is increased by 18.6% comparing the experimental results with the YOLOv3 analysis. In qualitative comparison, it successfully detects domestic garbage in complex multi-scenes. In addition, this approach alleviates the overfitting problem of deep residual blocks. The application case of waste sorting production line is used to further highlight the model generalization performance of the method. © 2023, Springer Nature B.V.
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| 8. |
- Pilthammar, Johan, et al.
(author)
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An overview of Methods for Simulating Sheet Metal Forming with Elastic Dies
- 2023
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In: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
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Conference paper (peer-reviewed)abstract
- Sheet metal forming (SMF) simulations are traditionally carried out with rigid active forming surfaces. This means that the elasticity and dynamics of presses and die structures are ignored. The only geometries of the tools included in the simulations are the active forming surfaces. One reason for this simplification is the large amount of computational power that is required to solve finite element (FE) models that incorporates elastic stamping dies. Another reason is the lack of die CAD models before the later stages of stamping projects. Research during the last couple of decades indicated potential large benefits when including elastic dies in SMF simulations. For example, for simulating die try-out or for Digital Twins of presses and dies. Even though the need and potential benefits of elastic dies in simulations are well known it is not yet implemented on a wide scale. The main obstacles have been lacking data on presses and dies, long simulation times, and no standardized implementation in SMF software. This paper presents an overview of existing methods for SMF simulations with elastic dies and discuss their respective benefits and drawbacks. The survey of methods shows that simulation models with elastic tools will be needed for detailed analyses of forming operations and also for purposes like digital twins. On the other hand, simplified and robust models can be developed for non-FEA users to carry out simple one-step compensation of tool surfaces for virtual spotting purposes. The most promising and versatile method from the literature is selected, modified, and demonstrated for industrial sized dies.
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| 9. |
- Pilthammar, Johan, et al.
(author)
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Three Industrial Cases of Sheet Metal Forming Simulations with Elastic Dies
- 2023
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In: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
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Conference paper (peer-reviewed)abstract
- Previous research and experience points to many advantages if sheet metal forming is simulated with elastic dies. Some areas that are enabled by simulations with elastic dies are virtual spotting, improved digital twins, and improved production support. A promising method was selected from the literature, and after important modifications it is deemed to be fast and robust for simulating industrial sized dies. The method consists of meshing die solids with a coarse mesh to represent the structural behaviour of the die. The forming surfaces are then represented by a fine shell mesh connected to the solid mesh by tied contacts with an offset. With additional modifications to reduce solver time this yields a robust and flexible way of modelling sheet metal forming with elastic dies. There is an increase in preprocessing and simulation time compared to using rigid tools, but industrial dies can now be modeled within an hour and solved within a working day. It is also easy to update the model by replacing separate parts such as die solids or forming surfaces. One of the main criteria in favor of the selected approach is the realistic modeling of blankholder and cushion systems. In this paper simulations of three industrial cases are demonstrated: one case of virtual die spotting and two cases of production support. The three cases demonstrate the importance and potential of using elastic dies during virtual die tryout, production support, and for cases like digital twins and production control.
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| 10. |
- Tuan Pham, Quoc, et al.
(author)
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An evaluation method for experimental necking detection of automotive sheet metals
- 2023
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In: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
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Conference paper (peer-reviewed)abstract
- In sheet metal stamping, the occurrence of strain localization in a deformed sheet is considered a failure. As so, sheet metal's formability is conventionally evaluated using the Forming Limit Diagram (FLD), which separates the principal strain space into safety and unsafety regions by a Forming Limit Curve (FLC). This study presents an evaluation method for detecting strain localization based on Digital Image Correlation (DIC) during the experiment. The commercial DIC software ARAMIS is adopted to monitor the strain-field distribution on the deformed specimen's surface. A detailed analysis of the proposed method is presented considering Nakajima tests conducted for two automotive sheet metals: AA6016 and DP800. The identified FLC based on the proposed method is compared with that of well-established methods such as ISO 12004:2-2008 and time-dependent methods. For both investigated materials, the proposed method presents a lower FLC than the others.
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