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Formability analysis of Tailor Welded Blank Pridaction with Friction Stret Weld

Habibi, Mostafa | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48271 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Asempour, Ahmad; Naghdabadi, Reza
  7. Abstract:
  8. The Tilor welded blank (TWB) two or more sheets with different thickness or strength which are welded together. The automobile designer are searching for new methods to reduce the cars’ weight and producing cost in order to diminish fuel consumption so they can survive in the competitive market. One way to achieve to this seemingly Contradictory demands, is using TWB in cars’ body. One of the most applicable methods to investigate the formability of metals sheets, is Forming Limit Diagrams (FLD). Three ways to determine the FLD are: Analytical Method, Experimental Methods, and Numerical Method. The experimental method to determine FLD, require metal sheets to undergo in different strain paths. Alongside the time consuming experimental method, a numerical method based on computational simulation was improved. In the present study, TWB that have been welded by Friction Stir Welding (FSW) were investigated. St14 steel, which is widely used in Automotive Industries was utilized as initial material. In chapter 3, mechanical properties of St14 were obtained through tension test and TWB’s sheets were then produced by FSW. In this chapter, the material type and design of welding tool is discussed. The experimental FLDs for base metal sheets and TWB’s sheets with different thickness were obtained. The mechanical properties of Welding Zone (WZ) were investigated via tension test and microhardness test and metallography was used for microstructural investigation. It is worthy to note that welding was done in both parallel and perpendicular to roll direction. The results showed that welding reduce the formability and in combined sheets with different thickness, this negative effect on formability of TWB are more obvious. The initial grains orientation had also no influence on WZ. In other chapter of this project, the method of simulating of M-K model and Nakazima Model was discussed. The FLD of a simple sheet were drawn using those two mentioned models and the results were compared with Nakazima results and eventually through this way, the accurate Finite Element Model (FEM) was obtained. In this chapter two Initiative model were presented in order to explain the effect out of plane forming on FLD. An accurate FEM and necking criteria (SDTS) were also presented in this chapter. In TWB, due to variable properties of different region, FLD for this region was obtained using M-K model. Stress-strain curve of TWB was obtained via finite element software and FLD of combination table sheet were then obtained by M-K model. The results indicated that the FLD of a combined sheet is between FLD of base material and WZ. Finally in this study, the FLD of TWB was obtained using FEM. The influence of welding line and its angle on FLD of combined sheet were also investigated. In order to impose the effect of weld in FEM to predict FLD of TWB, the properties of different region were considered. The results of this chapter proved the negative effect of wed on formability of TWB. However the effect of angle is variable on FLD
  9. Keywords:
  10. Forming Limit Diagram (FLD) ; Finite Element Method ; Friction Stir Welding ; Forming ; Combined Sheet ; Nakazima Test

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