High bandwidth cutting force measurement during the cutting of aa 7075-t6 and its application to measure the evolution of flow stress within developing shear bands
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Shear banding is an unstable mode of deformation and failure, caused by material beginning to soften or weaken with additional strain, resulting in narrow bands of highly deformed material called shear bands. Shear bands occur in metal cutting when material deformation in the primary shear zone is accompanied not by hardening but by weakening, by ductile damage and/or thermal softening by adiabatic heating. Recent work  has shown that the force supported by shear bands induced in hat-shaped test specimens subject to high-speed compression can be measured during the evolution of shear bands. This prompted us to consider whether very high band-width force measurement can be used to quantitatively measure the strain-softening of material within material undergoing adiabatic shear banding. The challenge impeding measurement of cyclic changes in cutting and thrust force during shear banding in orthogonal cutting is the rate at which these shear bands typically occur – from a few kHz to a few hundred kHz. This is well above the lowest natural frequency of even stiff cutting-force dynamometer setups. This research describes the development and validation of a high-bandwidth dynamometer and its use to measure both the cutting and thrust forces during orthogonal cutting of AA 7075-T6 with unprecedented fidelity. Two models for the cutting forces are developed, which include models for how the shear angle and indentation force evolve during each shear band cycle. These models are used to infer cyclic changes in flow stress along the shear band from the measured high bandwidth cutting forces.
Thesis (Ph.D.)-- Wichita State University, College of Engineering, Dept. of of Industrial, Systems and Manufacturing Engineering