In order to improve the working performance of precision instruments, it is desirable to isolate ambience wideband vibrations. Nonlinear isolator is superior to linear isolator. In this paper, a novel combined positive and negative stiffness isolator is developed based on the analysis of the mechanism of negative stiffness, whose negative stiffness cancels much of the positive stiffness of the elastic element in the vicinity of the balance point. The stiffness at the balance point has a nonlinear characteristic and the net stiffness tends to be zero. This type of isolator has high support stiffness as well as low vibration stiffness. Its inherent frequency can be adjusted to zero by adjusting the initial deformation of the elastic elements of the negative stiffness mechanism. Experimental results show that the inherent frequency of the isolator can be adjusted from 10 Hz to 1 Hz. The isolation bandwidth of the isolator is widened and the performance of isolation is distinctly enhanced.
The factors influencing surface quality for brittle materials is theoretically analyzed during ultra-precision grinding. Grinding experiments of brittle materials are carried out. The results show that the average abrasive grain size of the diamond wheel has a main influence on the surface quality, and the influence of the wheel speed and feed rate is secondary. In the case of s =1200m/min, f=0-20 µm/rev, and a p =0.1-10µm, only when the average abrasive grain size of the diamond wheel is less than 10µm, the super-smooth surface, for which Ra is 6.200nm and rms is 8.201 nm, can be obtained under grinding in the ductile mode.
The method of single point diamond turning is used to machine KDP crystal. A regression analysis is adopted to construct a prediction model for surface roughness and cutting force, which realizes the purposes of pre-machining design, prediction and control of surface roughness and cutting force. The prediction model is utilized to analyze the influences of feed, cutting speed and depth of cut on the surface roughness and cutting force. And the optimal cutting parameters of KDP crystal on such condition are acquired by optimum design. The optimum estimated values of surface roughness and cutting force are 7.369nm and 0.15N, respectively .Using the optimal cutting parameters, the surface roughness Ra, 7.927nm, and cutting force, 0.19N, are obatained.
In this paper, mechanical characteristics of KDP crystal anisotropy are analysed
theoretically. Vickers indentation experiments are adopted to validate the variation rule of hardness
and fracture toughness in different orientation of KDP crystal plane (100), and a model to calculate
critical cutting thickness of brittle-ductile transition is proposed for the KDP crystals. The result
shows that, on the crystal plane (100), the minimum value of critical cutting thickness of KDP
crystal in brittle-ductile transition appears in the direction [110], but the maximum appears in the
direction [010]. Finally, the ultra-precision machining of KDP crystal is performed, and the results
agree well with the theoretical conclusions. Super-smooth surface with a roughness RMS of 6.6nm
is reached as machined in the crystal direction [010], and 11.2nm to the direction [110].
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