Papers by Author: C.K. Jung

Abstract: Acoustic emission (AE) technique was applied as a non-destructive test method to detect and evaluate the localized damage at high temperature environment. The creep-fatigue crack growth tests were carried out with the acquisition of AE signal at 1000°F. Under trapezoidal waveform loadings, AE results showed different features according to each damage mode. During the creep period, low and steady emissions were shown, while emissions were burst and high counts rate was recorded during the fatigue loading. Based on these characteristics, damage contribution was expressed in terms of acoustic emission parameter as a part-time monitoring method. Comparisons of damage contribution with respect to lifetime showed the transient behavior from cycle-dependent to time-dependent process. In case of full-time monitoring, bilinear behavior between AE counts and life was represented. From both monitoring results, it was confirmed that creep and fatigue damage can be characterized by means of emission features and AE is possible way to evaluate the localized damage at elevated temperature.

Abstract: This study investigated acoustic emission behavior during fatigue crack growth test under constant and variable amplitude loading in 304 stainless steel. To describe the acoustic emission behavior, counts rate(dη/dn) was related with stress intensity factor range (SIFR, ΔK) in log-log plot. As a result of test, the relationship was represented a curve, which forms rise and fall behavior in counts rate as the SIFR increases. AE response to a single overload was sudden drop and slow recovery in counts rate, which was similar to crack growth retardation behavior. Under block loading, counts rate of each loading block was same as that of constant amplitude loading. Overall experimental results indicated that stress intensity factor controls the counts rate (dη/dn) as well as crack growth rate (da/dn) regardless of load range or crack length.

Abstract: This study simulated the Scoring process and the Can opening process of Easy Open End by finite element method. A FEM model was developed to predict the limitation of the scoring depth and the opening force at the End of steel Can using ABAQUS. In spite of a complex 3D structure, the shape of the Can End was simplified 2D axisymmetric model and analyses were focused on the change of materials and score shapes. Adaptive meshing was applied to the region of the score in the scoring process in order to suppress large deformation of elements. The critical depth of the scoring was observed because necking occurred at the panel during the scoring process. Necking could be restrained by changing the shape of the score punch. For the opening simulation, the shear failure model was utilized. The opening force was predicted with various materials, residual thickness, panel thickness (thickness ratio) and score shapes. The influence of these factors changed with the thickness ratio. Synthetically, the score condition of the steel Can End that the opening force is similar to the aluminum End was proposed.