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Effects of Bending on Forming Limit Diagram (FLD)Based on Marciniak & Kuczynski Method

Ehtiati, Saeed | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44941 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Asempour, Ahmad
  7. Abstract:
  8. In designing sheet forming processes, finding out the value of the maximum strain before necking in sheets is extremely important. Therefore, many experimental and theoretical efforts have been carried out in order to answer this question. One of the most well-known and useful theoretical methods in this regard is the Marciniak - Kuczynski method which was introduced in 1967 and is still the topic of many researches. In this model, it is assumed that a groove as a defect primarily exists in the sheet and due to the weakness of this region, necking will initiate. Furthermore, the effects of various parameters such as sensitivity to strain rate, strain path, thickness, three dimensional stress, structural relations and metallurgical properties on forming limit diagram has been included in this model throughout the time. But it seems that the effects of bending on FLD diagram has been ignored. This becomes more important considering the fact that one of the most well-known experimental methods for drawing this diagram is using a hemispherical punch for forming the sheet. That is the reason the critical strain in such experiment will be calculated in bending mode instead of plain stress mode. In this project, it has been tried to include the effects of this parameter on Marciniak model. In order to achieve this goal, FLD diagram will be obtained in bending mode from three methods and then will be compared with FLD diagram in plain stress mode. In the first method, experiments (Nakazima Method) will be utilized for obtaining the diagram in bending mode. Two punch sizes were used (50mm and 100 mm) for forming different samples and extracting FLD diagram. In the other two methods, Abaqus software was used for simulating Marciniak model in bending mode. In one of them, the boundry coundition were chosen similar to experiments (Nakazima Method) and in the other, the boundry coundition were chosen similar to Marciniak model in plain stress mode. All these three methods showed that the bending factor can cause the FLD diagram to move upwards and in fact increases the formability. In addition, we have tried to avoid using common FLD calibration methods which is using the experimental data from nakazima test in order to be able to compare the results more exactly. Therefore, the result of uniaxial tension test was used. Also, it was tried to extract the FLD diagram in plain stress mode from Abaqus software in order to avoid changing complex equations in Matlab or other similar methods for studying different parameters. That’s how we can easily study the behavior of FLD diagram for a range of parameters
  9. Keywords:
  10. Marciniak-Kuczynski Model ; ABAQUS Software ; Bending Effect ; Forming Limit Diagram (FLD) ; Calibration With Tension Test

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