NOVEL CUTTING DEFORMATION MODES ON AXIALLY LOADED CIRCULAR AA6061-T6 EXTRUSIONS FOR SUPERIOR CRASHWORTHINESS PERFORMANCE

The study detailed in this dissertation focuses on the force/displacement and energy absorption performances of circular AA6061-T6 aluminium alloy extrusions subjected to novel cutting deformation modes under both dynamic and quasi-static axial loading conditions. The experimental investigation of this novel cutting deformation mode on the circular AA6061-T6 extrusions was completed utilizing a specially designed cutter with or without the presence of a deflector. Experimental results showed that the cutting deformation mode exhibited higher crush force efficiency of 94.2% and eliminated the high peak crush force associated with the progressive folding or global bending deformation mode. Factors that influence the cutting deformation mode were investigated. Testing results showed that slight difference of the cutter geometries and extrusion diameters had no significant influence on the load/displacement response of the extrusions. An increasing, almost linear, relationship was observed between the steady-state cutting force and the extrusion wall thickness/number of cutter blades. Moreover, controlling the load/displacement response through varying instantaneous extrusions wall thickness along the axis of the specimens was investigated. Experimental results showed a direct relationship between the cutting force and instantaneous wall thickness of the extrusion exists. Additionally, numerical simulations of the axial cutting deformation process employing an Eulerian finite element formulation method and the axial crushing deformation process employing a Lagrangian finite element formulation method were performed. Good predictive capabilities were observed for both configurations. Finally, a theoretical study of steady-state cutting circular extrusion by a cutter with multiple blades with/without a deflector was conducted. It is assumed that the extrusion will deform similar to the experimental observations and dissipate energies through the following plastic or fracture deformations: (1) far-field moving hinge line with the advance of cutter blade; (2) far-field membrane deformation near the intersection zone between the cutter blade and blade shoulder; (3) near blade tip circumferential membrane stretching; (4) continuous chip formation ahead of the cutter blade; and (5) cut petalled sidewalls bending outwards. Then the contribution of friction force between the cutter blade and cut petalled sidewalls is included into the proposed model. A good correlation was found between the theoretical prediction and experimental observations.