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چكيده انگليسي :

The analysis of spring back in stretch forming with finite element method Seyed Mohamad Reza Nayyeri Mr nayeri@me iut ac ir Department of Mechanic Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiDr Hassan Khademizadeh email Hkhademyza@cc iut ac irAbstractThe ultimate goal of the metal forming industry is to form components made of a specific material into a required shapewithout experiencing wrinkling and spring back Of the aforementioned difficulties attention in This thesis is devoted tospring back resulting from unloading following stretch forming hi spite of the exhaustive application of the process toform many engineering components the design and selection of sheet materials and tooling geometry to minimizespring back still rely on the elusive trial and error approach It is thus the objective of this thesis to avoid the adhoc approachby analyzing the process using the finite element method Stretch forming of sheet metal is an important manufacturing processemployed in several industries to form panels of complex and varied curvatures The objective of this thesis to carry out asystematic study of stretch forming using the finite element method Three aspects of the current problem are accordingly investigated The first is concerned with the development of a finiteelement model of the stretch forming process using ABAQOUS software The elastoplastic behavior of the blank materialsis investigated using isotropic constitutive models Imposition of frictional contact constraints at the tooling sheet interfaceis also introduced using contact elements The second aspect of the work is concerned with the spring back experienced by the deformed sheet following the punchrelease stroke Several numerical techniques are introduced to define and quantify spring back For this purpose usewas made of MATLAB software to allow the determination of spring back using four different accepteddefinitions In the third attention was focused to the validation of the finite element models The Limiting Dome Height LDH benchmark test was also utilized as a verification tool And the second alternative way isexperimental result The results obtained from these tests reveal close agreement with the finite element predictions ofthe deformed sheet spring back and load deflection curves In case our study concerning the stretch forming for a un symmetrical U shape piece that can use in air craftindustries The selection The selection of this example was motivated by our desire to address some of the critical issuesresulting from the crash of Japan airline Flight 123 as a result of failure to account for the effect of spring back in theassembly of the bulkhead to the fuselage In our study we examine the effect of the mechanical properties thegeometry and interface parameters upon the resulting spring back Reviewing the literature it is found that researchers have been studying sheet metal forming and spring back for more than fourdecades There are several fact that can influence the result of spring back The 4 parameter that is more sensitive than the others isthe blank thickness punch travel punch radius and tooling blank interface friction Knowing about the effect of these parameterscan reduce the trial and error repetition and decrease efficiency our works in industries Key WordsStretch forming Springback Finite element Un symmetrical U piece

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