Papers by Author: Hyun Uk Kim

Abstract: This study focused on the determination of fracture toughness by instrumented indentation technique. A theoretical model to estimate the fracture toughness of ductile materials is proposed and used to verify those results. Modeling of IIT to evaluate fracture toughness is based on two main ideas; the energy input up to characteristic fracture initiation point during indentation was correlated with material’s resistance to crack initiation and growth, and this characteristic fracture initiation point was determined by concepts of continuum damage mechanics. The estimated fracture toughness values obtained from the indentation technique showed good agreement with those from conventional fracture toughness tests based on CTOD. In addition, we confirmed that the proposed model can be also applied in the brittle material through modification of void volume fraction.

Abstract: In this research, the optimal grinding condition has been obtained by design of experiment(DOE) for the development of aspheric lens for the 3 Mega Pixel, 2.5x optical zoom camera-phone module. Also, the WC mold was processed by the method of ultra precision grinding under this optimal grinding condition. The influence of DLC coating on form accuracy (PV) and surface roughness(Ra) of the mold was evaluated through measurements after DCL coating using ion plating on the ground mold. Also, aspheric glass lens was molded by before and after the use of the mold of DLC coating, respectively. The optical characteristics of each sample, which were molded by the different mold, were compared with each other.