DIC기법의 미소균열 적용 및 분석 방법 개발에 관한 연구

Abstract

Defects in devices, structures, and materials affect their performance and safety. In order to identify and evaluate these defects, strain measurement is necessary. The strain measurements of cracks estimate the material properties and occurrence of cracks in the structure. The purpose of this study is to apply the DIC method to various materials to increase the measurement accuracy for deformation and find crack initiation. A 3-point bending test was performed on brass specimens with different speckle concentrations to study the effects of speckle patterns on DIC evaluation. Through GLCM evaluation, it was confirmed that the contrast showed the maximum value at about 35∼50%, and the maximum value of entropy remained constant after about 35%. The elastic modulus and tensile strength were very similar between measurements using an electrical resistive strain gauge and DIC analysis at 35% contrast. Furthermore, 3-point bending experiments were conducted using composite materials that combine carbon fiber and aluminum liner. The strain was evaluated by the DIC method, and the occurrence of micro cracks in the specimens was measured. In the case of specimens with an inserted notch crack, cracks occurred at the notch crack tip, and delamination proceeded along the CFRP laminate interface. The initial micro cracks in specimens with different stacking orders measured 58.8 ㎛ and 53 ㎛, respectively, indicating crack growth in non continuous jump cases of strain rate. Moreover, DIC analysis was also performed on SOFC material with Ag paste as a current collector under high temperature conditions. As the experimental temperature increased, the crack initiation load and displacement also increased. Cracks occurred at the notch, and delamination between the Ag paste and the SiO₂wafer was observed. Additionally, the Ag paste exhibited ductility at low temperatures, but hardened and increased in stiffness as the temperature rose. Cracks began to advance toward the Ag paste at the initial notch crack tip, and interfacial separation progressed in the transverse direction along the laminated surface in the Ag paste. The micro crack length information was obtained by applying ACDM and Image J after conducting DIC analysis on SOFC.