Papers by Author: Dal Woo Jung

Abstract: A temperature-compensating fiber Bragg grating(FBG) sensor having two different FBGs in one fiber line was applied to the real time measurement of mechanical normal strain in structures. Measurement of mechanical strains of the aluminum beam surface by the double FBG sensor was performed under various thermal conditions, which was compared with results of electrical resistance strain gage. The FBG sensor fabricated in this study could detect accurately values of mechanical strains without containing any thermal strain component.

Abstract: Fatigue fracture behavior of a hybrid joint part for the tilting car body was evaluated in comparison to the case of static fracture. The specimens of hybrid joint part applied in the real tilting car body were fabricated for the bending test. Characteristic fracture behaviors of hybrid joint part specimens under cyclic loads were obviously different from the case under static loads. Static bending load caused the shear deformation and fracture in the honeycomb core region, while cyclic bending load did the delamination along the interface between composite skin and honeycomb core layers as well as the fracture of welded joint part. Experimental results obtained by static and fatigue tests were reflected in modifications of design parameters of the hybrid joint structure in the real tilting car body.

Abstract: Fatigue fracture behavior of a hybrid joint beam for the tilting car body was evaluated in comparison to the case of static fracture. Specimen beams of the hybrid joint part attached in the real tilting car body were fabricated for the bending test. Characteristic fracture behaviors of hybrid joint beam specimens under cyclic transverse loads were very different from the case under static loads. Static transverse load caused shear deformation and fracture in the honeycomb core region, while cyclic transverse load brought about delamination along the interface between composite skin and honeycomb core layers as well as fracture of the welded joint. Fracture characteristics obtained by the transverse fatigue tests were reflected for improving the hybrid joint structure in the real tilting car body.

Abstract: Fatigue fracture behavior of a hybrid composite joint with riveting was evaluated in comparison to the case of static fracture. Hybrid composite joint specimens for shear test were made with layers of carbon fiber/epoxy composite and stainless steel. Characteristic fracture behaviors of those specimens were obviously different under static and cyclic loads. Static shear loading showed the fracture of a pure shear mode, whereas cyclic fatigue-shear loading caused the local stress concentration of a tensile mode and thus brought about the tensile fracture at that site. Experimental results obtained by static and fatigue tests were considered in modifications of design parameters of the hybrid joint.