Papers by Author: Sang Wook Park

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: The synthesis of dimethyl carbonate(DMC) was investigated using four differently supported quaternary ammonium salt catalysts to facilitate their separation after the reaction. The different catalysts are (1) C1 on poly(ST-co-VBC), (2) C2 on poly(ST-DVB-VBC), (3) C3 on macroporous poly(ST-DVB-VBC), (4) C4 on modified MCM-41. The synthesis of DMC was performed in an autoclave under carbon dioxide pressure. The main byproduct was propylene glycol. The immobilized quaternary ammonium salt catalysts showed good catalytic activity for the synthesis of DMC. The order of the reactivity for the catalysts of different support was C1>C3>C2>C4. The catalysts can be reused for four successive runs without considerable loss of their initial reactivity.