| 1. |
- Barlo, Alexander, M.Sc. Eng. 1994-, et al.
(författare)
-
Determination of Edge Fracture Limit Strain for AHSS in the ISO-16630 Hole Expansion Test
- 2023
-
Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)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.
|
|
| 2. |
- Barlo, Alexander, M.Sc. Eng. 1994-
(författare)
-
Failure Prediction of Complex Load Cases in Sheet Metal Forming : Emphasis on Non-Linear Strain Paths, Stretch-Bending and Edge Effects
- 2023
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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.
|
|
| 3. |
- Barlo, Alexander, M.Sc. Eng. 1994-, et al.
(författare)
-
Proposal of a New Tool for Pre-Straining Operations of Sheet Metals and an Initial Investigation of CR4 Mild Steel Formability
- 2023
-
Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)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.
|
|
| 4. |
- Huo, Xiaole, et al.
(författare)
-
Effect of ultrasonic vibration on static properties of 5A06 aluminum alloy self-piercing riveting joints
- 2023
-
Ingår i: Cailiao Kexue yu Gongyi/Material Science and Technology. - : Harbin Institute of Technology. - 1005-0299. ; 31:2, s. 44-49
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 5. |
- Li, Cheng-Wang, et al.
(författare)
-
Comparison of mechanical properties of various joining processes of aluminum-titanium light alloy
- 2023
-
Ingår i: Suxing Gongcheng Xuebao/Journal of Plasticity Engineering. - : Beijing Res. Inst. of Mechanical and Elec. Technology. - 1007-2012. ; 30:8, s. 138-145
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 6. |
- Lin, Sen, et al.
(författare)
-
Non-destructive monitoring of forming quality of self-piercing riveting via a lightweight deep learning
- 2023
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
-
Tidskriftsartikel (refereegranskat)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).
|
|
| 7. |
- Lun, Zhao, et al.
(författare)
-
Skip-YOLO : Domestic Garbage Detection Using Deep Learning Method in Complex Multi-scenes
- 2023
-
Ingår i: International Journal of Computational Intelligence Systems. - : Springer Science+Business Media B.V.. - 1875-6891 .- 1875-6883. ; 16:1
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 8. |
- Pilthammar, Johan, et al.
(författare)
-
An overview of Methods for Simulating Sheet Metal Forming with Elastic Dies
- 2023
-
Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)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.
|
|
| 9. |
- Pilthammar, Johan, et al.
(författare)
-
Three Industrial Cases of Sheet Metal Forming Simulations with Elastic Dies
- 2023
-
Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)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.
|
|
| 10. |
- Tuan Pham, Quoc, et al.
(författare)
-
An evaluation method for experimental necking detection of automotive sheet metals
- 2023
-
Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)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.
|
|
| 11. |
- Tuan Pham, Quoc, et al.
(författare)
-
Improvement of modified maximum force criterion for forming limit diagram prediction of sheet metal
- 2023
-
Ingår i: International Journal of Solids and Structures. - : Elsevier Ltd. - 0020-7683 .- 1879-2146. ; 273
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents a new criterion (MMFC2) for predicting the forming limit curve (FLC) of sheet metal. The strain path evolution of a critical element examined in a uniaxial tensile test is elaborated by incorporating the results of experimental measurement, finite element simulation, and theoretical prediction via the Modified Maximum Force Criterion (MMFC). A scaling factor is introduced to mimic the theoretical evaluation with the simulated one. It is believed that the rotation of the principal axes of the theoretically considering material point, which is initially co-axial with the external load coordinate, implicates the macro track of the strain path change. Furthermore, an optimal event of the second derivative of the axial rotations is proposed to indicate the strain localization and formulate the FLC. The performance of the proposed criterion is compared with that of the original MMFC in predicting the FLC of three automotive sheet metals, of which all related data were published in the Benchmark of Numisheet 2014 conference. The use of three different hardening laws and three yield functions is examined in the analogy. The comparison reveals that the results of MMFC2 are more sensitive to the employed constitutive model than that of MMFC. Furthermore, the proposed MMFC2 presents concordant results with the experimental data. Nakajima tests are conducted for CR4 mild steel sheets to validate the capacity of the proposed criterion. Well agreement between the experimentally measured data and theoretical prediction based on the Yld2k yield function verifies its usefulness in practice. © 2023 The Author(s)
|
|
| 12. |
- Tuan Pham, Quoc, et al.
(författare)
-
Modeling the strain localization of shell elements subjected to combined stretch–bend loads : Application on automotive sheet metal stamping simulations
- 2023
-
Ingår i: Thin-walled structures. - : Elsevier Ltd. - 0263-8231 .- 1879-3223. ; 188
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents a modeling approach for predicting strain localization during sheet metal stamping processes focused on automotive engineering applications. The so-called stretching-to-bending ratio, ρ, is proposed to characterize the loading conditions acting on an element during stamping processes. Then, localized strain or necking strain is suggested to be a function of ρ. Different stretch–bending tests with different tool radii, i.e., R3, R6, R10, and R50 are conducted for two automotive sheet metals, DP800 and AA6010, to identify their forming limits under combined stretch–bend loads. The calibrated necking limit curve of the AA6016 sheet is then employed in AutoForm R10 software to predict the necking and failure of a stamped panel. Agreement with the experimental observation of failure positions of the panel validates the usefulness of the proposed modeling approach in practice.
|
|
| 13. |
- Tuan Pham, Quoc, et al.
(författare)
-
Prediction of forming limit diagram of automotive sheet metals using a new necking criterion
- 2023
-
Ingår i: Materials Research Proceedings. - : Materials Research Forum LLC. - 9781644902462 ; , s. 705-710
-
Konferensbidrag (refereegranskat)abstract
- A theoretical model for predicting the forming limit diagram of sheet metal, namedMMFC2, was recently proposed by the authors based on the modified maximum force criterion(MMFC). This study examines the application of MMFC2 for two automotive sheets, DP800 andAA6016, which are widely used in making car body parts. Uniaxial tensile and bulge tests areconducted to calibrate constitutive equations for modeling the tested materials. The developedmaterial models are employed into different frameworks such as MMFC, MMFC2, and Marciniak-Kuczynski (MK) models to forecast the forming limit curve (FLC) of the tested materials. Theirpredictions are validated by comparing with an experimental one obtained from a series ofNakajima tests. It is found that the derived results of MMFC2 are comparable to that of MK modeland agreed reasonably with experimental data. Less computational time is the major advantage ofMMFC2 against the MK model. (PDF) Prediction of forming limit diagram of automotive sheet metals using a new necking criterion.
|
|
| 14. |
- Zhao, Lun, et al.
(författare)
-
Performance analysis of similar and dissimilar self-piercing riveted joints in aluminum alloys
- 2023
-
Ingår i: Composites and Advanced Materials. - : Sage Publications. - 2634-9833. ; 32
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, similar (2A12) and dissimilar (6061) aluminum alloy sheets are validly joined using self-piercing rivet process. A quasi-static experiment is proposed to investigate the mechanical behaviors, failures mode, and mechanism of the different joints. Moreover, a method based on deep learning algorithm is anticipated to detect the appearance defects of the SPR welded joints. The results indicated that 2A12 joints of similar sheets contained the advantageous static strength and 6061 similar sheet joints had superior anti-vibration performance conducts. The joints with 6061-2A12 sheets introduced the most decent and comprehensive mechanical properties. The main failure mode of 2A12 similar sheet joints was substrate fracture. The performance of the substrate affects the failure mode of the joint and the plasticity of the substrate is better. When the time comes, the failure mode is mostly pull-off failure. Poor plasticity of the substrate can easily lead to substrate breakage. The reason for joint pull-off and button fall-off failure is that there is large plastic deformation in the lower plate of the joint and the mechanical internal locking structure is damaged. 2A12 substrate breakage belongs to a composite fracture that combines intergranular fracture and microvoid aggregation type fracture. The area of the 6061 substrate near the edge of the sample is shear fracture and the area near the center of the sample thickness is dominated by microvoid aggregation type normal fracture. The effectiveness of the method was verified by conducting a series of experiments and the detection accuracy of the method can reach about 90%. The detection speed was as high as 50 frames per second (FPS), which can effectively solve the problem that the rivet quality was difficult to monitor.
|
|
| 15. |
- Zixin, Guo, et al.
(författare)
-
The effects of three profiles on the mechanical properties and grain size of self-piercing riveting joints using ultrasonic welding
- 2023
-
Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer Science+Business Media B.V.. - 0268-3768 .- 1433-3015. ; 129:11-12, s. 4869-4882
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrasonic welding has become a key joining approach in batteries and energy vehicles. This work reports the optimization in static property and stability of self-piercing riveting joints which is becoming the most versatile way to join microstructures. Tool heads of three different knurling profiles (e.g., A, B, and C) are used to perform ultrasonic composite with riveting. Based on tensile-shear tests, SEM, EDS, XRD, and Vickers microhardness analysis were conducted to investigate the comparative study of the fracture morphology, element distribution, phase structure, and hardness. The results indicated that all three types of knurling generate solid phase welding at the sheet joints. Thus, it improved the forming quality and mechanical properties of self-piercing riveting joints. The C-shaped welding tool head has advantageous effect on optimizing the mechanical properties of joints. Further, it enhanced the average peak load by 25.6%, the average failure displacement by 31.1%, and the average energy absorption by 88.8%. The microscopic results showed that a large amount of oxides are precipitated at the edge of welding joints when the B-shape knurling tool is used. The distribution of the hardness value of joints horizontal line is “M” shape. Besides, the coarse grains in the joint area and the interplanar space increase significantly after ultrasonic welding which softens the sheet. © 2023, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.
|
|
