Papers by Author: Nam Su Huh

Abstract: The master curve has evolved into a mature technology for characterizing the fracture toughness transition of ferritic steels. However, it is well known that the master curve reference temperature (To) values estimated from small laboratory specimen may be biased low due to loss of crack-tip constraint. To quantify such variations of To resulting from differences of crack-tip constraint of testing specimen, two-parameter fracture mechanics approaches are employed in the present study. In this context, fracture toughness test and 3-dimensional finite element (FE) analysis for several standard and nonstandard test specimens are performed to quantify relationship between variations of To and constraint parameters and to find best constraint parameter representing effect of crack-tip constraint on To values evidently. Based on testing and present FE results, To and constraint parameter loci are constructed and engineering To correlation models considering crack-tip constraint are suggested

Abstract: Application of the leak-before-break concept to nuclear piping requires accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to combined tension and bending. One important element is determination of relevant J-resistance curve for pipes under combined loading. This paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and bending, based on the load-crack opening displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic finite element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks.