Prediction of ductile fracture strains in upsetting processesm / Mostafa Khaled Megahed Ali Hassan ; Supervised Chahinaz Saleh , Mostafa Shazly

Thesis (M.Sc.) - Cairo University - Faculty of Engineering - Department of Mechanical Design and Production

Forgeability and workability are measures of the plastic deformation limit that workpieces can undergo under bulk-forming processes. Upsetting tests for different axisymmetric specimens are usually used to construct the forming limit diagram at fracture (FLDF). The objective of the present work is to predict the FLDF for upsetting processes using coupled and Uncoupled DF approaches and relating the friction conditions and specimen dimensions to the critical height reduction of blocks. Numerical simulations are performed to determine the stress and strain distribution at the locations of crack formation. Two FE models are adopted after validating the results against published data; one considers voided materials while the other does not. It has been found that the coupled DF approach is in principle capable of predicting analytically the failure in upsetting processes. For uncoupled DF approach, an average value of the critical parameter (Cavg) in the out-of-plane shear and hydrostatic integrals has to be assigned from experiments to predict a semi empirically bilinear forming limit diagram at fracture FLDF.The fitting expression developed from the parametric study gives results close to the results obtained numerically with an error less than 9.69 %

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