To explore the effects of cutting speed, feed rate and rake angle on chip morphology transition, a thermomechanical coupled orthogonal (2-D) finite element (FE) model is developed, and to determine the effects of tool nose radius and lead angle on hard turning process, an oblique (3-D) FE model is further proposed. Three one-factor simulations are conducted to determine the evolution of chip morphology with feed rate, rake angle, and cutting speed, respectively. The chip morphology evolution from continuous to saw-tooth chip is described by means of the variations of chip dimensional values, saw-tooth chip segmental degree and frequency. The results suggest that chip morphology transits from continuous to saw-tooth chip with inct easing feed rate and cutting speed, and changing a tool's positive take angle to negative rake angle. There exists a critical cutting .ipeed at which the chip morphology transfers from continuous to sawtooth chip. The saw-tooth chip segmental frequency decreases as the feed rate and the tool negative rake angle value increases: however, it increases almost linearly with the cutting speed. The larger negative rake angle, the larger feed rate and higher cutting speed dominate saw-tooth chip morphology while positive rake angle, small feed tute and low cutting speed combine to determine continuous chip morphology. The 3-D FE model considers tool nose radii of 0.4 mm and 0.8 mm. respectively, with tool lead angels of 0 deg and 7 deg. The model successfully simulates 3-D saw-tooth chip morphology generated by periodic adiabatic shear and demon.itrates the continuous and saw-tooth chip morphology, chip characteristic line and the material flow direction between chip-tool interfaces. The predicted chip morphology, cutting temperature, plastic strain distribution, and cutting forces agree well with the experimental data. The oblique cutting process simulation reveals that a bigger lead angle results in a severer chip deformation, the maximum temperature on the chip-tool interface reaches 1289 deg, close to the measured average temperature of 1100 deg: the predicted average tangential force is 150N, with 7% difference from the experimental data. When the cutting tool nose radius increases to 0.8 mm. the chip's temperature and strain becomes relatively higher, and average tangential force increases ION. This paper also discusses reasons for discrepancies between the experimental measured cutting force and that predicted by finite element simulation.
This paper proposes a thermo-mechanical orthogonal cutting finite element model (FEM) to investigate the variation of chip morphology from continuous chip to small and large saw-tooth chip. The corresponding experiments of hard turning AISI 52100 steel are conducted to validate the proposed FE model. Three one-factor simulation experiments are conducted to determine the evolution of chip morphology along feed rate, rake angle and cutting speed respectively. The chip morphology evolution is described by the variations of dimensional values, saw-tooth degree and chip segmental frequency. The research suggests that chip morphology transit from continuous to sawtooth chip with increasing the feed rate and cutting speed, and changing a positive rake angle to a negative rake angle. There exists a critical cutting speed at which the chip morphology transfers from continuous to saw-tooth chips. The saw-tooth chip segmental frequency decreases as the feed rate and negative rake angle value increase, but increases almost linearly with the cutting speed. The larger negative rake angle, the larger feed rate and high cutting speed dominate the sawtooth chip morphology while positive rake angle, small feed rate and low cutting speed determine continuous chip morphology.
To evaluate the residual stress distribution along cutting direction in hard turning process, an explicit dynamic thermo-mechanical orthogonal Finite Element Model (FEM) is developed to consider the correlation between residual stress distribution and chip morphology and plough effect by cutting edge. The FEM adopts Johnson-Cook (J-C) model to describe work material property, the critical equivalent plastic strain criterion to simulate chip separation behavior, and the revised coulomb’s law to capture the friction pattern between the tool and chip interface. The FEM is validated by comparing the predicted and experimental chip morphology and residual stress distribution. The residual stress distribution in hard machined surface along cutting direction is accurately captured by using sharp and honed cutting edge tools. The residual stresses by sharp tool demonstrate a periodical characteristic, the fluctuation amplitudes are determined in the surface and subsurface along the cutting direction, and the fluctuation frequency corresponds to that of the saw-tooth chip. However, the residual stresses by honed cutting edge tool demonstrate an indistinct periodic characteristic, the fluctuation frequency in surface and subsurface is larger than that of the saw-tooth chip. Saw-tooth chip formation process by sharp tool is identified to analyze the residual stress scatter periodic mechanism, which associates with the fluctuation of cutting force and temperature. The plough process by honed cutting edge tool is identified to explain the equilibrium effect on the amplitude and frequency of residual stress scatter in hard turned surface and subsurface. The periodical fluctuation characteristics of residual stress in hard turned surface and subsurface is revealed and verified by determining its amplitude and frequency corresponding to that of the saw-tooth chip. The analysis will enhance the fatigue life prediction accuracy by incorporating the effect of residual stresses periodical fluctuation on the crack initiation and propagation life in hard turned surface and subsurface.
With remote sensing data and GIS, the classification system of land landscape in the typical area of the Hanjiang River Basin is established. Using the indexes of the landscape pattern index and the ecological value index (EVI),this article presents the dynamic change of the landscape pattern from 1986 to 2006. The results showed that: (1)There is a dramatic staggered change. From the year of 1986 to 1996, the absolute change extent obey the following sequence: no use land > forest land > build land > cultivated land> water > grassland; and from 1996 to 2006, no use land > build land > forest land > cultivated land> water > grassland. Over the past 20 years, no use land > build land > forest land > cultivated land> water > grassland.(2)The landscape of the Basin tended to become more fragmentized. From 1986 to 1996, the landscape of Hanjiang River Basin tended to become more fragmentized. The patches, in general, became smaller, more even, and less complex. The Ecological Value Index (EVI) of the whole catchment grown upon from 6661 to 6687. From 1996 to 2006, the catchment landscape became more fragmentized as before, and the amount of patches increased, and the average size of patches increased. The patches became more complex with Ecological Value Index rising from 6687 to 6783, as shows that the ecological situation of the catchment was being improved. Keywords-land use ;landscape pattern change; ecological value index (EVI); hanjiang river basin ;Guangdong978-1-4244-7618-3 /10/$26.00 ©2010 IEEE
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