| The objective of this dissertation was to investigate trimming process, the fracture mechanisms of the sheared edge subjected to stretching, and enhancement of sheared edge stretchability for aluminum alloys. The tooling of trimming process and methodology of measuring the major strains along the sheared edge for aluminum blanks were described. In addition, a new imaging technique which includes a digital camera was employed to track back the initiation of fracture of the sheared edge during stretching.;Furthermore, the effect of mechanical deburring, solution heat treatment of specimens conventionally trimmed with excessive clearance, roughness of sheared edge, and electrical discharge machining (EDM) on the sheared edge stretchability were investigated. In addition, stretching of narrow specimens prepared in close vicinity to the sheared edge itself and influence of stiffness of trimming tools were analyzed to explain potential reasons of leading to initiation of early fracture from the sheared edge.;On the other hand, numerical model of trimming process of aluminum blanks was performed using ABAQUS commercial code. In the analysis, 2D plane strain model was applied as finite element type, and element deletion was utilized to simulate fracture of the sheared edge. Damage criteria in plane strain condition were discussed and compared. Measurement of fracture strains in plane strain deformation for different aluminum alloys was conducted in order to estimate the range of fracture strains applied for Cockcroft-Latham damage criterion and Rice-Tracey damage criterion in the trimming simulation. According to simulation results, fracture mechanism of trimming process and the factors driving to form the burr or no burr were analyzed.;Moreover, in order to compare sheared edge stretchability with multiple trimming clearances and fracture propagation of trimmed edge with different aluminum alloys, three broadly used 6xxx aluminum alloys in automotive industry were employed. The results of standard tensile test of all three materials were very similar with rather moderate difference in work hardening and almost no difference in total elongations measured by an extensometer. In addition, the effect of cutting angles and prestraining on sheared edge stretchability and the burr heights of the sheared edge for three aluminum alloys was analyzed. |
