Plastic instabilities analysis during T-shaped tubes hydro-forming process

Abstract : During T-shaped or Y-shaped tubes hydroforming the tube wall is flatten on the external die. This "in die" forming involves an important compressive stress along the outer normal direction directly related to the inflating pressure. In this particular case plastic instabilities and damage evolution are strongly dependent on the sign of hydrostatic stress. Hydroforming simulations of T-shaped and Y-shaped thick tubes are performed using an elastoplastic model implemented in Forge-2005 (fully implicit Finite Element Method code). A three dimensional analysis is ran using tetrahedral solid elements. An augmented Modified Maximum Force Criterion coupled to an undamage behavior law is expressed in the sheet tangent plan basis. This criterion is compared to a fully coupled Lemaitre damage model. Due to low triaxiality state, damage only growth in specifical regions. This study highlights the interest of continuum damage modeling for the formability and the final part load carrying capacity prediction for "in die" hydroforming.