Lijing Xie

On Multi-Objective Based Constitutive Modelling Methodology and Numerical Validation in Small-Hole Drilling of Al6063/SiCp Composites

Discrepancies in capturing material behavior of some materials, such as Particulate Reinforced Metal Matrix Composites, by using conventional ad hoc strategy make the applicability of Johnson-Cook constitutive model challenged. Despites applicable efforts, its extended formalism with more fitting parameters would increase the difficulty in identifying constitutive parameters. A weighted multi-objective strategy for identifying any constitutive formalism is developed to predict mechanical behavior in static and dynamic loading conditions equally well. These varying weighting is based on the Gaussian-distributed noise evaluation of experimentally obtained stress-strain data in quasi-static or dynamic mode. This universal method can be used to determine fast and directly whether the constitutive formalism is suitable to describe the material constitutive behavior by measuring goodness-of-fit. A quantitative comparison of different fitting strategies on identifying Al6063/SiCp’s material parameters is made in terms of performance evaluation including noise elimination, correlation, and reliability. Eventually, a three-dimensional (3D) FE model in small-hole drilling of Al6063/SiCp composites, using multi-objective identified constitutive formalism, is developed. Comparison with the experimental observations in thrust force, torque, and chip morphology provides valid evidence on the applicability of the developed multi-objective identification strategy in identifying constitutive parameters.

Mechanism-Based FE Simulation of Tool Wear in Diamond Drilling of SiCp/Al Composites

The aim of this work is to analyze the micro mechanisms underlying the wear of macroscale tools during diamond machining of SiCp/Al6063 composites and to develop the mechanism-based diamond wear model in relation to the dominant wear behaviors. During drilling, high volume fraction SiCp/Al6063 composites containing Cu, the dominant wear mechanisms of diamond tool involve thermodynamically activated physicochemical wear due to diamond-graphite transformation catalyzed by Cu in air atmosphere and mechanically driven abrasive wear due to high-frequency scrape of hard SiC reinforcement on tool surface. An analytical diamond wear model, coupling Usui abrasive wear model and Arrhenius extended graphitization wear model was proposed and implemented through a user-defined subroutine for tool wear estimates. Tool wear estimate in diamond drilling of SiCp/Al6063 composites was achieved by incorporating the combined abrasive-chemical tool wear subroutine into the coupled thermomechanical FE model of 3D drilling. The developed drilling FE model for reproducing diamond tool wear was validated for feasibility and reliability by comparing numerically simulated tool wear morphology and experimentally observed results after drilling a hole using brazed polycrystalline diamond (PCD) and chemical vapor deposition (CVD) diamond coated tools. A fairly good agreement of experimental and simulated results in cutting forces, chip and tool wear morphologies demonstrates that the developed 3D drilling FE model, combined with a subroutine for diamond tool wear estimate can provide a more accurate analysis not only in cutting forces and chip shape but also in tool wear behavior during drilling SiCp/Al6063 composites. Once validated and calibrated, the developed diamond tool wear model in conjunction with other machining FE models can be easily extended to the investigation of tool wear evolution with various diamond tool geometries and other machining processes in cutting different workpiece materials.

An experimental investigation on effective friction coefficient in elliptical ultrasonic assisted grinding of monocrystal sapphire

In this study, in order to investigate the effective friction coefficient in elliptical ultrasonic assisted grinding (EUAG) of sapphire, the single abrasive grain scratching experiments are performed to simulate the grinding process by setting up the elliptical ultrasonic vibrator attached with the sapphire substrate on a multi-axis CNC grinder. The single grain diamond tool slides on the elliptically vibrated surface at a serial of pressures, and the grinding forces are measured. The friction coefficients under different pressure and vibration amplitude are obtained by calculating the ratio of tangential grinding force to normal grinding force, i.e., Ft/ Fn. Comparing friction coefficients in both scratching with and without vibration, there is a critical pressure Fpc at a range of pressure. As the pressure is less than Fpc, the friction coefficient in EUAG is smaller than that in conventional grinding (CG), and once the increasing pressure is more than Fpc, that is much higher than that in CG. When the pressure is slight, ploughing occurs and no chips are generated, and actually at low pressure, the ratio Ft/ Fn can be close to the effective friction coefficient in EUAG. Thus, the experimental results at low pressure indicate that the effective friction coefficient in EUAG is less than that in CG, and is decreasing with the increasing vibration amplitude.