Papers by Keyword: Wrinkling

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Authors: M. Zeinoddini, M. Peykanu, A. Abzal
Abstract: Cyclic axial loads in steel tubular might lead to local buckling, wrinkling and accumulation of plastic strains in the tube. During their life time steel tubes may also experience different types of material loss such as corrosion or thinning. This paper deals with the effects of corrosion defects on the strain ratcheting response of steel tubes. Small scale un-corroded and corroded tubular specimens have been tested under monotonic and cyclic axial loads. Optical system ATOS has been used for 3D surface acquisition and reconstruction of the tested specimen and to evaluate their strain ratcheting and wrinkling response. This is a camera-based triangulation system. A processing unit employs optical transform equations to automatically and with a great accuracy calculate 3D coordinates for every pixel of camera. Depending on camera resolution as an effect of such a scan a cloud of up to 4 million points has been obtained for every single measurement. From the results, it has been noticed that the possibility of ratcheting or progressive plastic failure substantially increases by the presence of the corrosion defects. With the corroded specimens, the strain ratcheting behaviour in the defected zone has been distinctively different from that in the perfect zones.
Authors: Oliver Döbrich, Thomas Gereke, Chokri Cherif
Abstract: Picture frame shear tests are state of the art for determining the shear force vs. shear angle behaviour for in-plane deformation of most technical textiles, such as woven fabrics. Many publications describe this test and the used picture frames. Benchmark tests showed that the measured shearing behaviour for one sample depends on the picture frame used. The shearing rigidity of most textiles is very small compared to the in-plane tensile stiffness, so slight imperfections on the experimental setup have a significant effect on the measured results. During the picture frame test, wrinkles may form on the sample surface during the motion of the picture frame above a critical shear angle. These wrinkles can be described as local fabric buckling. If forming of wrinkles leads to a lower level of internal energy compared to a further shearing of the fabric, local wrinkles occur due to the principle of least action. Because of this effect, the measured shear force above the first formation of wrinkles is inaccurate for describing the exact shearing behaviour of textiles. Another possibility for measuring the shear force vs. shear angle behaviour is the bias-extension test. Here, higher shear angles can be achieved without the formation of wrinkles. Both methods are compared in this paper for different textile samples. The relationship of the shear angle and the applied shear force is an important mechanical value and one of the most important input parameter in numerical drape simulations. The analysis of wrinkles, which occur during textile draping, demands exact input parameters for the simulation. Most important for the drape simulation of technical high-performance textiles are accurate values for the bending and shear behaviours. This paper presents simulation results of the wrinkling during a picture frame shear test. Results show that the input parameter for the shear rigidity delivered by the picture frame shear test do not exactly reproduce the formed wrinkles and are, therefore, not suitable for an exact drape simulation. The underestimation of the shear force vs. shear angle behaviour will be shown with a finite element simulation model. The adaptation of the picture-frame and bias-extension parameters for a proper use in numerical drape simulations are examined.
Authors: Guang Yong Pan
Abstract: In this paper, first of all quality requirements of the large automobile stamping was introduced. Based on investigation, the main failure forms of species and its related influencing factors were determined, and analyzed the stamping wrinkling and cracking mechanism of failure modes. Finally the corresponding countermeasure was proposed. The paper can provide valuable referenced for domestic research institutes and automobile production enterprises.
Authors: Kang Chen, Cheng Yun Peng, Tao Zhou, Bao Bao Li
Abstract: Blank holder force of box deep drawing is studied changes with time and displacement by DYNAFORM numerical simulation software. The results shows that, when the straight edge part of the blank holder force is constant, rounded part adopts small blank holder force can significantly improve the forming limit of box deep drawing, but the wrinkle is still evident. If the straight edge and rounded part of the blank holder force changes with time, not only deep drawing limit increase, wrinkles are also significantly reduced, indicating that the forming limit of the box shaped part is more effective on the blank holder force changes over time than with the position variation.
Authors: Gheorghe Brabie, Bogdan Chirita
Abstract: The present paper analyses the results of investigations concerning the size and effects of sheet wrinkling in the case of mini cylindrical drawn parts made from aluminium alloy sheets. The wrinkling occurs in the mini drawn part walls when the blankholder is missing from the die structure or it is driven with an excessive force. By comparing to macro scale processes, the manufacturing of mini parts usually involves new concepts concerning the establishment of the following parameters: tool clearances, tool dimensional parameters, blank dimensions, working process parameters etc. In the case of mini deep drawing such objectives cannot be simply achieved by reducing the process from macro to mini scales. The present work was devoted to study the particularities of the wrinkling that occur during mini deep drawing processes and affect the quality of the mini drawn parts. The experimental investigations were performed using a mini tool having the following main components: punch with a flat bottom, die and an annular blankholder plate. The tool was installed on a mini deep drawing device having the following main components: mobile grip - connected to machine mobile head; fixed grip; helical spring - used to regulate the blankholder force and placed between the fixed grip plate and punch support. The simulation was performed using the DynaForm software and the applied criterion of plasticity was the Barlat 89 criterion.
Authors: D.H. Pahr, F.G. Rammerstorfer
Abstract: This work highlights and solves problems with the prediction of the compressive strength, limited by local instabilities, of sandwich material compounds based on honeycomb cores and very thin facesheets. Analytical methods in conjunction with periodic finite element unit cell models are utilized for this task. The finite element models are found to be well suited for all kinds of buckling predictions. Different uni- and bi-axial loadings are considered as well as influences of core height, core material, core geometry, and facesheet thickness are investigated. Finally, a new analytical approach is introduced for the treatment of the rather unexpected core cell wall buckling under in-plane compression of the sandwich, which predicts the critical load very accurately.
Authors: Ilmira Suleymanova, Aleksey Shlyapugin, Yaroslav A. Erisov
Abstract: This paper presents the theoretical foundations and methodology of the modeling process of forming a half ring alloy blank AMg5M in software product Pam-Stamp. At the following technological sizes of a half-tore: the blank radius 516.5 mm; hole’s radius R0=480.74 mm, distance from the generating circle center to the axis of rotation R1=714 mm, the generating circle radius Rp=93 mm, curvature radius of die Rd=16 mm, the process is stable. The results of numerical analysis of the drawing half-tore from the ring blank directed to determining the optimal process parameters are revealed. Modeling shows that the size of the holes in the blank has a significant influence on the distribution of strain along the generatrix of the stamped parts. Using the ring blank reduces the probability of wrinkling in the free areas.
Authors: Xia Zhu, Narumi Wada, Keiji Ogi, Hiroshi Kurosu, Manabu Takahashi, Hiromasa Senba
Abstract: Metal pipes have a long history as fluid conduits, and are commonly joined with components such as elbows to form bent transport paths. However, with the increasing demands for economy and energy saving, pipes with reduced joints and thinner walls are desired. The number of joints can be reduced by a drawing and bending process that forms a bend section at any position in the pipe. However, this approach incurs problems such as wrinkling and flattening, especially under conditions of large bending angle, decreased bending radius, and thin pipe walls. In this research, applying vibrations to the mandrel was trialed as an approach for controlling the wrinkle depth and flattening. First, processing experiments were performed on thin walled pipes (wall thickness = 0.5 mm; outer diameter = 14 mm). The change of flattening and the number and depths of wrinkles were investigated in the presence and absence of vibrations. Next, simulations were performed using the commercial nonlinear finite element software. Through these simulations, the flatness and appearance of wrinkles were analyzed by modeling the behavior and distribution of stresses and strains in the processing process. The application of vibration to the mandrel appears to be a promising approach for controlling the wrinkling and flattening problems during pipe processing.
Authors: Yasuo Marumo, Hiroyuki Saiki
Authors: Rosanna Di Lorenzo, Giuseppe Ingarao, Laura Marretta, Fabrizio Micari
Abstract: In sheet metal forming most of the problems are multi objective problems, generally characterized by conflicting objectives. The definition of proper parameters aimed to prevent both wrinkles and fracture is a typical example of an optimization problem in sheet metal forming characterized by conflicting goals. What is more, nowadays, a great interest would be focused on the availability of a cluster of possible optimal solutions instead of a single one, particularly in an industrial environment. Thus, the design parameters calibration, accomplishing all the objectives, is difficult and sometimes unsuccessful. In order to overcome this drawback a multi-objectives optimization procedure based on Pareto optimal solution search techniques seems a very attractive approach to deal with sheet metal forming processes design. In this paper, an integration between numerical simulations, response surface methodology and Pareto optimal solution search techniques was applied in order to design a rectangular deep drawing process. In particular, the initial blank shape and the blank holder force history were optimized as design variables in order to accomplish two different objectives: reduce excessive thinning and avoid wrinkling occurrence. The steps of the optimization procedure include: 1) application of Central Composite Design (CCD) for the identification of the necessary data over the domain of variation of the design variables; 2) numerical simulations of the samples identified by CCD; 3) development of a response surface model to interpret the final objectives as functions of the design variables; 4) Pareto optimal solution analysis to reach the most performing design variables. The final aim is to develop a predictive tool able to identify a sort of process window for the analyzed process also minimizing the computational effort in particular with respect to mono-objective optimization techniques or traditional trial and error methods. Many possible technological scenarios were investigated by the implemented procedure and a set of reliable solutions, i.e. able to satisfy different design requirements, were obtained.
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