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With the rapid development of photoelectric communication and other fields, the demand for high-precision aspheric mirrors has been increasing. Predicting dynamic cutting forces is vital in selecting machining parameters and also affects the surface quality of the machined surface. This study comprehensively considers the effects of different cutting parameters and workpiece shape parameters on dynamic cutting force. The actual width of cut, depth of cut, and shear angle are modelled while considering the effects of vibration. A dynamic cutting-force model considering the aforementioned factors is then established. Using experimental results, the model accurately predicts the average value of dynamic cutting force under different parameters and the range of fluctuation of dynamic cutting force, with a controlled relative error of about 15%. The influence of workpiece shape and workpiece radial size on dynamic cutting force is also considered. The experimental results show that the greater the surface slope, the more dramatic the dynamic cutting force fluctuations. This lays the foundation for subsequent writing on vibration suppression interpolation algorithms. The influence of the radius of the tool tip on dynamic cutting forces leads to the conclusion that to achieve the goal of reducing the fluctuation of cutting forces, diamond tools with different parameters should be selected for different feed rates. Finally, a new interpolation-point planning algorithm is used to optimize the position of interpolation points in the machining process. This proves the reliability and practicability of the optimization algorithm. The results of this study are of great significance to the processing of high-reflectivity spherical/aspheric surfaces. [ABSTRACT FROM AUTHOR]

Perovskite ferroelectrics has great value and many new structures have been synthesized experimentally by doping with new components. But there were few studies on single atom substitution in theory. This article investigates the ferroelectricity of KNbO3 when some of the K atoms are replaced with elements of the same main group. Structural, polarization and electronic of different type KNbO3 were calculated using first principles calculations. Analysis of relaxed structure and electron charge shows that the different atom substitution produces different distortion. The combined analysis leads to the conclusion that the ferroelectricity decreases with increasing radius of the homologous atoms. This provides an explanation for the experimental data from another perspective. [ABSTRACT FROM AUTHOR]

To develop an innovative aerostatic guideway without cable drag force that can be widely applied to ultra-precision machining and measurement technology, it is necessary to analyze the static performance of the aerostatic guideway. The structural properties of the cableless aerostatic guideway, i.e., the bearing capacity and internal pressure distribution, directly affect the accuracy of processing and measurement. In this work, the relevant flow equations of the cableless aerostatic guideway are established by considering the unbalanced micro-scale air film. Moreover, the finite difference method is used to solve the calculation of the global analysis of air film at different positions. In addition, this work compares and analyzes the pressure and fluid velocity vector distributions in balanced and unbalanced states and investigates the effect of varying the thicknesses of the air film on static characteristics such as bearing capacity and stiffness. By comparing the balanced and unbalanced states under the same conditions, the obtained results show that in the unbalanced situation, the bearing capacity is lower by 11.69 percent and the stiffness is slightly higher (by 16.67 percent). Furthermore, the related experiments verify the predicted dependence of the bearing capacity on the thickness of the air film, and further demonstrate the feasibility of the proposed structure of the cableless aerostatic guideway. This work provides a technical reference for the design of a cableless aerostatic guideway. [ABSTRACT FROM AUTHOR]

In this work, the desensitising effect of water film on the diamond cutting of HMX crystal is studied by using reactive force field (ReaxFF) molecular dynamics simulations. The lubrication behavior, reaction kinetics, decomposition products and reaction pathways are particularly studied to reveal the underlying atomistic origins of desensitisation of wet-cutting system. Simulation results show that a film lubrication and its evolutionary behaviour occur at the nano-cutting interface. And forming a complete water-lubricating film is critical for improving thermal stability of the entire cutting system, which is correlated to tool sharpness, HMX properties and water-lubrication method in the actual cutting process. More interestingly, the mechanism of desensitising effect is confirmed to be that the nano-water film inhibits the C–O affinity between diamond tool and HMX, which makes the relatively stable symmetric cleavage of the main ring dominant in the initial decomposition of HMX. Although the type and evolution trend of the decomposition product is similar to that in dry cutting, the degree of decomposition and the severity of HMX are lower in wet-cutting, and the presence of water-lubricating film causes the transition of main dynamic mechanism function of the HMX from the self-catalysed mode into the random nucleation mode. [ABSTRACT FROM AUTHOR]

The interface between explosive crystal and binder polymer plays a critical role in the stabilities of energetic materials. In the present work, we investigate the mechanical properties of cyclotetramethylenetetranitramine (HMX)–polystyrene (PS) interface by performing molecular dynamics simulations of uniaxial tension, nanoindentation and nanoscratching tests. Our simulation results indicate that the HMX–PS interface has a mediate strength between HMX of high strength and PS of low strength. In particular for nanoindentation and nanoscratching, the distance of indentation position or scratching position to the HMX–PS interface has a strong influence on mechanical deformation behavior of HMX–PS system. Specifically, the HMX–PS interface has the lowest indentation force and scratching force than both the HMX and the PS. [ABSTRACT FROM AUTHOR]

In this work, molecular dynamic (MD) simulation is employed to investigate the formation and evolution of amorphous carbons in the surface layer of diamond crystal as the frictional sliding is performed on diamond (1 0 0) plane. Simulation results reveal that the formation of amorphous carbons at the sliding interface is inevitable due to the friction. In this case, transformation from diamond sp 3 hybridized carbons to sp 2 hybridization structures is dominant. More interestingly, most of the sp hybridized carbons appear on the topmost surface of the amorphous layer. Amorphization rate in sliding along the [1 0 0] direction is greater than that along the [1 1 0] direction due to the smaller resistance forces. In the light of the velocity variation of carbon atoms, the amorphous layer is divided into two layers, i.e. the coherent layer and transition layer. Moreover, a density transition region appears with the formation of amorphous carbons, and the thickness of transition region can be used to characterize the amorphization degree. [ABSTRACT FROM AUTHOR]

To provide a novel technique to prolong the service life of diamond cutting tools, a thermo-chemical erosion method by using nano-scale copper oxide under vacuum atmosphere was proposed to perform the post-treatment of natural diamond crystals, which had been pre-polished with mechanical lapping procedure. As indicated in the experiments, when the temperature under vacuum atmosphere was 100 °C, the oxidation and deoxidation appeared between the damaged diamond carbon atoms on the topmost surface layer and the copper oxide powder. The surface roughness of natural diamond crystal declined slowly with the increment of erosion time, i. e. generating a weak planarization tendency. When the vacuum atmosphere temperature was 200 °C, two hours erosion time was considered as the optimal configuration. At 30 nm indentation depth, the micro-hardness and elastic ratio of the eroded diamond crystal surface reached the maximal value. If the erosion time was larger than two hours, the micro-hardness and elastic ratio declined. [ABSTRACT FROM AUTHOR]