بررسي رشد آسيب در فرايندهاي شكل دهي ورق با مسيرهاي كرنش غير خطي

چكيده انگليسي :

Investigation of Damage Evolution in Sheet Metal Forming Processes with Nonlinear Strain Paths Babak Jamshidi b jamshidi@me iut ac ir April 9 2011 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Mahmoud Farzin Prof M Farzin@cc iut ac irAbstractContinuum damage mechanics CDM as one of the new branches of mechanical engineering is a powerfulcomplementary for fracture mechanics Microstructure of materials includes some crack and voids These defectscan be created during loading or manufacturing of material The main goal of damage mechanics is investigation ofdamage evolution and its effect on the mechanical strength of material Definition of microstructure defects bycontinuous fields variable are common practice in all of the CDM models According to CDM in the existingconstitutive equations the effect of damage evolution in material is considered as deterioration of mechanicalproperties such as strength and stiffness Prediction of rupture modes and estimation of limiting of drawing ratio is amajor challenge in metal forming processes Various thin walled parts with fairly complex shapes are produced fromsheet metals such as automotive panels and other structural parts In these processes damage and fracture may beobserved on the work piece and formability plays a fundamental role Therefore determination of forming limitsand prediction of rupture modes in these operations is very important for process design engineers Rectangular deepdrawing processes and automotive panel forming will be considered because of their nonlinear strain paths In thisthesis initiation and evolution of damage has been predicted using Lemaitre s damage and FLD damage models andlimiting drawing ratio has been determined Lemaitre s damage criterion has been implemented by Haji Aboutalebias a subroutine for an elastic plastic material and plane stress and finite strain theories Using this subroutine inABAQUS Explicit finite element software damage initiation and evolution is predicted for the above mentionedprocesses and the results obtained by FLD and Lemaitre models are compared In rectangular deep drawing process both models estimate the initiation and evolution of cracks in the corners and edges of the part Comparing theseresults with experimental results show that FLD damage model does not predict the forming limit as good asLemaitre s damage model In an automotive panel forming process both models predict initiation of cracks in theedges of sheet However according to the FLD damage model fracture occurred at a lower depth in the formedsheet In sheet metal forming processes with complex strain paths the part is subjected to large plastic deformation This severe plastic deformation leads to high plastic strain localization zones and subsequent accumulation of thosestrains Then internal and superficial micro defects and in another words ductile damage are created This damagecauses quality problems such as fracture Therefore design engineers need to accurately estimate the damageinitiation and its growth In this thesis comparison between theoretical and experimental fracture results show thatLemaitre s damage model can predict damage initiation its growth and fracture better than FLD damage model insheet metal forming processes with nonlinear and complex strain paths Key words prediction of damage evolution rupture forming limits formability nonlinearstrain paths

جمشيدي، بابك

بررسي رشد آسيب در فرايندهاي شكل دهي ورق با مسيرهاي كرنش غير خطي

مكانيك آسيب پيوسته , حد شكل دهي