Papers by Author: Juan Liu

Abstract: In this paper, the influences of abrasive size, abrasive concentration and admixture way on the abrasive dispersing of the sintered ultra-fine diamond tool were systemically investigated. Then, a comparison of the abrasive dispersing was made between the sintered ultra-fine diamond tool and the newly developed ultra-fine diamond tool by gel technique. ESEM was applied to observe the abrasive dispersing of the sintered and gel-coupled ultra-fine diamond tools. The abrasive dispersing was quantitatively evaluated by the statistic laws of grit spacing in a certain area. Experimental results indicated that the dispersing was mainly influenced by the abrasive size. The ultra-fine abrasive tended to agglomerate with the decrease of grit sizes due to the increase of surface energies. The abrasive concentration and admixture way had few effects on abrasive dispersing. The abrasive dispersing of the sintered diamond tool was worse compared with the gel-coupled ultra-fine diamond tool.

Abstract: In this paper, a newly developed ultra-fine abrasive polishing pad by gel technology was adopted to polish silicon wafer on a nano-polishing machine. In order to evaluate the machining performances of the polishing pad, the influences of abrasive sizes, abrasive concentration and polishing parameters (pressure, rotating speed and machining time) on the silicon wafer were investigated respectively. Optical microscope and ZYGO 3D surface analyzer were applied to examine the surface morphologies and surface roughness of the polished silicon wafer respectively. The experimental results showed that the surface roughness of silicon wafer decreased with the decreasing of abrasive grits and the increasing of abrasive concentration and polishing parameters (pressure, rotating speed and polishing time) when polishing silicon wafer with the polishing pad containing Al2O3 abrasive. When abrasive concentration, polishing pressure and polishing time reached certain values, few changes would happen for the silicon wafer.

Abstract: In this paper, an experimental study was carried out to fabricate a new kind of ultra-fine abrasive polishing pad by means of gel technology. The polishing pad was then used to polish silicon wafer on a nano-polishing machine. Optical microscope and ZYGO 3D surface analyzer were applied to observe the surface morphologies of the silicon wafer. Meanwhile, surface morphology of ultra-fine abrasive polishing pad was observed by ESEM. No obvious gathering of ultra-fine grains were found on the ultra-fine abrasive pad. The surface roughness (Ra) of the silicon wafer was reduced to 0.3nm after being polished by the abrasives with average grain size of 10μm. Mirror surface can be realized after being polished with the polishing pad.

Abstract: In this paper, an experimental study was carried out to fabricate a new kind of ultra-fine diamond abrasive tools by means of sol-gel. The physical properties of the new diamond abrasive tools were evaluated in terms of the bulk density and hardness. The ultra-fine diamond tools were then used to polish granite on a vertical spindle grinding machine. SEM and optical microscope were applied to observe the surface morphologies of the diamond tools and granite. No obvious gathering of ultra-fine diamond grains were found in the new diamond abrasive tools, which exhibited a good wear-resistant ability in polishing. The granite surfaces polished by the new diamond tools were found to be basically smooth except few cracks originally existing in the granite.

Abstract: The torsion of a penny-shaped crack in a functionally graded strip is considered. Hankel transform is used to reduce the problem to solving a Fredholm integral equation. The crack tip stress field is obtained by considering the asymptotic behavior of Bessel function. Investigated are the effects of material property parameters and geometry criterion on the stress intensity factor. Numerical results show that increasing the gradient of shear modulus can suppress crack initiation and growth, and that the stress intensity factor varies little with the increasing of the strip's highness.