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Modeling of chip formation mechanism in machining carbon fiber reinforced polymer Song, Chunlei


Carbon fiber reinforced polymer (CFRP) composites possess high specific strength, high specific elastic modulus, and high energy absorption ability, which make them competitive in advanced industrial applications such as aerospace, automotive, and construction. To achieve the dimension and tolerance requirements of the CFRP components, cutting operations such as milling and drilling are necessary. A mechanics model of the chip formation is developed to investigate the buckling failure mode, which occurs at 0° fiber orientation, by dividing the chip formation into shearing and buckling processes. The chip length increases owing to the shear failure in the interface layer until the Euler buckling or micro buckling failure is activated. The nonlinear relationship between the cutting forces and uncut material is modeled and validated by experiments. A generalized mechanics model is proposed to predict the chip formation mode (fiber and matrix failure modes), chip formation angle, and cutting forces in the entire fiber orientation range of [0°, 180°] for UD CFRP. For each fiber orientation, the stresses on the chip formation plane needed to activate the relevant chip formation mode, including fiber tension, fiber compression, matrix tension, and matrix compression, are determined. The chip formation plane which requires the minimum cutting energy is found, and the corresponding failure stresses and cutting forces are predicted with experimental validation. To further analyze the damage states for fiber and matrix material during the chip formation, a frictional-damage mechanics model is developed. It is found that the friction in the damaged area under transverse compression can provide additional stress on the fracture plane. This friction is able to increase the shear stress on the fracture plane after the failure is initiated, and then influence the direction of the fracture plane in uncut material. For the MD CFRP, it is found that the plies of different fiber orientation angles converge in the cutting process. An analytical model is proposed to analyze the variation of chip formation mode for each ply in the orthogonal cutting of MD CFRP. By using the minimum energy principle for all plies, the variation chip formation mode due to the interlaminar bonding effect is predicted.

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