Influence of Fracture in Sheet Metal Cutting
Sheet metal cutting employs less force as compared to shear force for cutting if cutting process is initiated by a crack. As the cutting process starts from the crack at the edge of the sheet metal, the fracture mechanics dominates and helps in sheet cutting operation by utilizing low energy. The present study substantiates this theory. Metal sheets of aluminium, zinc and mild steel of thicknesses 0.5mm, lmm and 1.5 mm were cut by scissors using hand force. The cutting process is in tear mode as the cutting was done by scissors. The force of cutting overcomes the fracture toughness of the material. The cutting force requirement and the fracture toughness increase as the line of cut is shifted away from the free edge of the sheet The increase of force is attributed to counter the higher surface energy forces of the higher surface area to be separated as point of cut moves away from free edge; the surface energy is due to the atomic bonding. In cutting, the off cut curls because of the point of cut or crack lies in the plastic zone. The thin sheets of 0.5 mm have higher stress intensity factor and is tougher than thick sheets of 1 and 1.5 mm. Beyond 20mm distance from the free edge toughness increases at higher rate.
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ISSN (Print): 2070-9900 ISSN (Online): 2411-6319