Study on critical condition of brittle-ductile transition of optical glasses in ultra-precision grinding

In this paper, based on the indentation under different loads, the influence factors for brittle-ductile transition of optical glasses has been investigated theoretically through the simulation of a single grain grinding with the diamond indenter. By the surface and fracture features, the grinding rules and the critical load conditions for the brittle-ductile transition of different optical glasses, the critical grinding depth of the single grain and it's influence factors are obtained for the brittle-ductile transition in ultra-precision grinding process. The experimental results show that brittle-ductile transition of optical glasses is controlled by cutting depth of a single grain. When the cutting depth is less than the critical depth, optical glasses are ground in ductile mode. When mean grain size is less than 20 mum ductile mode grinding of optical glasses can be realized with the relatively larger tangential speed and smaller feed. Otherwise, lubricants is the important factor influencing critical cutting depth. Finally, the experimental results of BK7 and FCD1 optical glasses grinding are given.