In a plane strain cutting process, it is found that the coefficient of friction μ (Coulomb) along the tool-chip contact is 1 and independent of the tool rake angle α. When the forces on the tool were measured for α≥0, it was found that at some positive α*, the thrust (or feed) force reversed direction from that recorded at α = 0. Find the value of α* (Note: Do not assume any shear angle relationship etc.). If the Merchant shear angle relationship were to apply, then is there some rake angle or set of rake angles (positive or negative) for which cutting will cease to occur. Justify/explain with a calculation. Note: The thrust force (Ft) is the force component in the direction perpendicular to the main cutting force Fc. Fc is the force in the direction of the cutting velocity.
Design Against Fluctuating Loads
Machine elements are subjected to varieties of loads, some components are subjected to static loads, while some machine components are subjected to fluctuating loads, whose load magnitude tends to fluctuate. The components of a machine, when rotating at a high speed, are subjected to a high degree of load, which fluctuates from a high value to a low value. For the machine elements under the action of static loads, static failure theories are applied to know the safe and hazardous working conditions and regions. However, most of the machine elements are subjected to variable or fluctuating stresses, due to the nature of load that fluctuates from high magnitude to low magnitude. Also, the nature of the loads is repetitive. For instance, shafts, bearings, cams and followers, and so on.
Design Against Fluctuating Load
Stress is defined as force per unit area. When there is localization of huge stresses in mechanical components, due to irregularities present in components and sudden changes in cross-section is known as stress concentration. For example, groves, keyways, screw threads, oil holes, splines etc. are irregularities.
In a plane strain cutting process, it is found that the coefficient of friction μ (Coulomb) along the tool-chip contact is 1 and independent of the tool rake angle α. When the forces on the tool were measured for α≥0, it was found that at some positive α*, the thrust (or feed) force reversed direction from that recorded at α = 0. Find the value of α* (Note: Do not assume any shear angle relationship etc.).
If the Merchant shear angle relationship were to apply, then is there some rake angle or set of rake angles (positive or negative) for which cutting will cease to occur. Justify/explain with a calculation.
Note: The thrust force (Ft) is the force component in the direction perpendicular to the main cutting force Fc. Fc is the force in the direction of the cutting velocity.
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