Search

In micro-grinding, the effect of material microstructure on residual stress is significant since the depth of cut is usually smaller than the average grain size. In this paper, the effect of crystallographic orientation (CO) on the distribution of residual stress induced by micro-grinding is investigated. The COs and their volume fractions of workpiece material are quantified by Taylor factor, based on which the models of flow stress and plastic modulus of polycrystalline materials are proposed. Then, the residual stress is calculated based on the micro-grinding force and temperature derived from the flow stress, after the mechanical and thermal loading followed by relaxation process, which are analyzed with the developed plastic modulus. Thereby, the compressive analytical model of micro-grinding-induced residual stress is proposed considering the grinding parameters, wheel topography, and material microstructure. In addition, micro-grinding experiments and residual stress measurements are conducted to verify the models. The prediction of residual stress agrees well with the experimental result. Residual stresses are measured by X-ray techniques, and the results illustrate that the COs of material would influence the state of stress. Finally, the sensitivity analysis is carried out, with the result showing that the effect of CO on residual stress is significant. [ABSTRACT FROM AUTHOR]

Microcontact affects the fabrication and assembly of MEMS/NEMS system, the contact between thin film microcavity and microcantilever beam, and the motion of microstructure. In this work, in the microcontact of three-dimensional elastic-plastic Weierstrass-Mandelbrot (W-M) fractal surfaces, influence of fractal dimension was studied based on a comprehensive contact model. With increasing fractal dimension, maximum microcontact force in the plastic deformation zone shows parabolic change; comparably, the intermediate force in elastic zone parabolically varies. For both the forces, the minimum values are obtained when the fractal dimension is 2.5. Besides, in the plastic deformation zone, the real contact areas increase with the fractal dimension. Experiments were completed to compare with the numerical analysis. The results show that the simulated contact force curve is in line with the experimental load curve when Young's modulus E and hardness H are equal to the actual measured values. Nevertheless, it will greatly deviate from the experimental load curve when E and H differ from the measured values. [ABSTRACT FROM AUTHOR]

In micro-grinding, the effects of crystallography on grinding force become significant since the depth of cut is of the same order as the grain size. In this research, the Taylor factor model for multi-phase materials is proposed based on the previously reported Taylor factor model for monocrystalline material. Based on this model, the flow stress model is developed, which takes both the effect of CO on the athermal stress and the stress induced by the phase transformation into account. Based on the flow stress model, the predictive model of chip formation force is proposed by adapting parallel-sided shear zone theory. The rubbing force is modeled by applying Waldorf's worn tool theory. Furthermore, the plowing force is predicted based on previously reported model by the authors. Subsequently, a comprehensive model of the micro-grinding force is proposed by considering mechanical-thermal loading, the effects of crystallography, and phase transformation. Finally, the model is validated by conducting an orthogonal-designed experiment with the result proving that the prediction of the model is capable to capture the magnitude and trend of the experimental data. Moreover, the proposed analysis are compared with the predictions of two other previously reported models with the result, indicating that the model that considers the effect of CO and the phase transformation improves the accuracy of the micro-grinding force. [ABSTRACT FROM AUTHOR]

In the micro-grinding process, owing to the size effect, the effects of material microstructure on the grinding force are more significant through the variation of material flow stress. Currently, the variation of material flow stress resulting from the change of crystallographic orientation during the micro-grinding has not been well examined. In this paper, a new predictive model for the variation of flow stress due to the process-induced change of crystallographic orientation is developed, which is based on the Taylor factor as determined by calculating the activated slip systems, thus quantifying the way crystallographic orientation affects both the number and the style of activated slip systems. Moreover, the predicted force is compared with previous reported experimental data on monocrystalline copper. As a result, the following findings are obtained from the comparison between the predicted result and the experimental data: (1) The predicted microgrinding force agrees well in trend with the experimental force, suggesting that the approach for predicting the grinding force based on the Taylor factor is feasible; (2) In the microgrinding of single-crystal materials, the feed rate direction relative to the crystallographic orientation has great effects on the flow stress and hence on the grinding force. [ABSTRACT FROM AUTHOR]