An investigation of failure mechanisms in forming of monolithic and composite sheets

The forming behavior of the novel lightweight construction, e. g. advanced high strength steel and composite sheets, gains more and more attention. This thesis aims to investigate the failure mechanisms of DP1000, CP1000, aluminum alloy and an aluminum/low density polyethylene half sandwich sheet in blanking and bending. Firstly the shear-enhanced Lemaitre's damage model, Drucker-Prager model and the cohesive zone model are chosen for describing the mechanical behavior of monolithic metallic sheet, the polymer sheet and the adhesive of the aluminum/low density polyethylene half sandwich sheet, respectively. These materials are fully characterized by means of tensile tests, in plane torsion tests, compression tests and delamination tests. An inverse parameter identification procedure is successfully applied. Then the microstructure deterioration of DP1000 and CP1000 under tensile and shear stress state is examined and compared to explain their different mechanical behavior. After that the characterized material model is applied in blanking of DP1000 and AA6082-T6 sheets with three punch-die clearances. Influence of blanking conditions on sheared part morphology is detected. The mechanical behavior of Al/LDPE half sandwich sheet in blanking process is also investigated. With the help of fully characterized FE model of half sandwich sheet the influence of cutting clearance on the cutting force-displacement curves and cutting edge morphology is studied experimentally and numerically. The imperfection of the experimental cutting edge is quantitatively described by three feature values. The stress state of the half sandwich structure during blanking is investigated and compared with that of monolithic metal sheet.