Research On Mechanical Behaviors Of Optical Glass On Nano Scale

At present, optical glass has been widely used in many areas, such as aerospace, national defense, civilian use and so on. The birth of the free-form surface put forward higher requirement on optical glass manufacturing. As optical glass has high hardness and high brittleness, its ultra-precision manufacturing would confront a certain difficulty. Recently, there are3main ways in ultra-precision manufacturing of optical glass, including ultra-precision grinding, single point diamond cutting and ultra-precision polishing. No matter which way, the mechanical behavior of the material should be obtained first as a research basis.The research of mechanical behaviors of materials has nearly a100-year history. With technology improving, the research of mechanical behaviors has gradually developed from macro scale to micro scale, even it has reached nano scale. By nanoindentation and nanoscratch, the hardness and elastic modulus and tribological properties of various materials could be measured and calculated. There is still a limitation in the research of mechanical behaviors of optical glass, which concentrated on brittle-ductile transition. It lacks research of other aspects, such as elastic deformation, size effect and adhesion effect. Therefore, the research in this paper is shown below:1. Nanoindentation tests were carried out on K9glass. The results showed there was a size effect in the nanohardness of K9glass. The deeper the depth was, the lower the hardness would be. According to Oliver-Pharr method, the functional limit of the nano hardness is a decreasing function with an independent variable of depth h, which could testify the experimental results from the aspect of mathematics. The critical load and depth of elastic-plastic transformation were0.8mN and50nm respectively. The more the load was, the less the elastic rebound rate was, and it would approach to a constant. The Continuous loadings would not affect the elastic rebound value. There was adhesion effect after unloading that would affect the surface quality seriously.The increasing of loading rates would not affect the law of deformation.2. In order to investigate the micro and nano mechanical behavior of optical glass K9, linear loading micro and nano scratch tests were carried out on K9glass. The results showed that the plastic-brittle transitions under micro scale and nano scale were between12.5N and17.5N and between3000μN and4000μN respectively. In constant scratch tests, the plastic deformation was stable, while the brittle deformation affected the surface quality seriously. From the research of elastic rebound, the elastic rebound of plastic deformation was stable, whereas that of brittle deformation experienced huge fluctuations.3. Simulation of scratch of K9glass was carried out by SPH method. The results showed that during the simulation, plastic deformation occurred and it increased with the depth increasing, but the change of elastic rebound was little, which basically corresponded to the results of nano scratch tests of K9glass. The larger the cutting speed is, the deeper the critical depth is.