The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-007233.pdf

First-principles calculations of electronic structure and spectra of strongly correlated systems: the LDA+U method

Experimental assessment of an environmentally friendly grinding process using nanofluid minimum quantity lubrication with cryogenic air

Predictive model for minimum chip thickness and size effect in single diamond grain grinding of zirconia ceramics under different lubricating conditions

Minimum quantity lubrication (MQL) is an efficient, green, and eco-friendly method of applying cutting fluids in machining processes. This study presents the processing characteristics of different vegetable oil-based nanofluid MQL for grinding various workpiece materials. The performance of three lubricant types (i.e., pure palm oil, MoS2 nanofluid, and Al2O3 nanofluid) of good lubrication performance and three types of materials (i.e., Inconel 718, ductile cast iron, and AISI 1045 steel) was evaluated in terms of force ratio, specific grinding energy, and G ratio. The optimal processing combination of lubricants and workpiece materials under the same experimental conditions was obtained using orthogonal experiment. Optimization results were verified by evaluating the morphology of the workpiece surface and grinding debris. Experimental results show the different processing characteristics of materials when various workpieces are processed using dissimilar MQL lubricants. MoS2 nanofluid MQL is suitable for machining soft medium carbon steels, such as 45 steel, while Al2O3 nanofluid is suitable for machining materials of high strength and hardness, such as nickel-based alloys.

Processing Characteristics of Vegetable Oil-based Nanofluid MQL for Grinding Different Workpiece Materials

Experimental evaluation of the lubrication properties of the wheel/workpiece interface in MQL grinding with different nanofluids

Micro-fracture variation and grinding performance of PCBN superabrasive grains in high-speed grinding

High-speed grinding experiments on nickel-based superalloy Inconel718 were carried out with single grain of polycrystalline cubic boron nitride (PcBN). Surface fractal evolution of fracture behavior of PcBN grains was discussed. The fracture reason of PcBN grains was studied from the viewpoint of grinding load based on finite element method (FEM). Results obtained show that micro fracture behavior is the predominant wear pattern of the PcBN grain cutting edges. Because the tested grains have different wear patterns, the statistical relationship is established between the fractal dimension of the grain cutting edges and the attritious wear flat percentage. The dynamic grinding force is the determining factor for the micro fracture behavior of the grain cutting edges in the particular region, where the grain firstly contacts the workpiece in the initial stage of the grinding process.

Surface fractal evolution of fracture behavior of polycrystalline cBN grains in high speed grinding

Crack propagation simulation of polycrystalline cubic boron nitride abrasive materials based on cohesive element method

Understanding the self-sharpening characteristics of polycrystalline cubic boron nitride super-abrasive in high-speed grinding of Inconel 718

TiAl intermetallic alloy (Ti-45Al-2Mn-2Nb) is a typical hard-to-machine material which was used in the aero-engines. To study its machinability, the high-speed grinding experiments were conducted using electroplated diamond abrasive wheel. The effects of grinding parameters (e.g., grinding wheel speed vs, infeed speed vw, and grinding depth ap) on the grinding force and temperature were discussed. Then, the grey relational analysis (GRA) and variance analysis method were utilized to analyze the results. In addition, the evolution of the surface integrity was researched to characterize the machinability comprehensively. The results show that ap had the greatest effect on the normal grinding force and grinding temperature of TiAl intermetallics, while as for the tangential grinding force, vs did. When vs increases from 60 to 120 m/s, the residual stress along and perpendicular to the grinding direction decreased by 54.7% and 10%, respectively. The maximum microhardness of the ground surface increased to 620 HV0.05 at this moment, which was 1.55 times larger than that of the original matrix. Additionally, the chips morphology indicated that the adverseness of the low temperature plasticity of TiAl intermetallic alloy could be well overcome through the high-speed grinding tests. Finally, according to the GRA, the combination of vs=90 m/s, vw=0.5 m/min, and ap=0.1 mm was selected as the optimal parameter combination.

Process parameter optimization and surface integrity evolution in the high-speed grinding of TiAl intermetallics based on grey relational analysis method

Yejun Zhu

Papers

Micro-fracture variation and grinding performance of PCBN superabrasive grains in high-speed grinding

Surface fractal evolution of fracture behavior of polycrystalline cBN grains in high speed grinding

Crack propagation simulation of polycrystalline cubic boron nitride abrasive materials based on cohesive element method

Understanding the self-sharpening characteristics of polycrystalline cubic boron nitride super-abrasive in high-speed grinding of Inconel 718

Process parameter optimization and surface integrity evolution in the high-speed grinding of TiAl intermetallics based on grey relational analysis method