Papers by Keyword: J-R Curve

Abstract: This paper presents a complex experimental measurement of elastic-plastic fracture parameters such as J-integral, CTOD and J-resistance curve for ductile materials with single specimen test employing the Digital Image Correlation method. Main advantage of the approach is that it allows evaluation of the parameters directly from its definitions in contrast to current standardized measurements defined mostly by ASTM where the parameters are evaluated indirectly. Moreover, the method provides other useful information such as the extent and shape of a plastic zone in the vicinity of a crack tip. The presented method is employed in the case of thin-sheet aluminium alloy. Different approaches to determine a critical value of J-integral from experimental results; i.e., to determine the fracture toughness of the material are presented.

Abstract: Since it is difficult to cut off large specimens from nuclear piping, generally the standard CT specimens of 1T are used to perform fracture toughness tests. However, when compared with the test result obtained from a real pipe, the results from CT specimens are been known to be very conservative. Therefore, the U.S. Nuclear Regulatory Commission recommends the use of specimens whose thickness is greater than or equal to the thickness of a real pipe for estimating the stability of crack resistance[1]. In this study, a series of fracture toughness tests were performed using various types of specimens: the standard CT, non-standard Compact Pipe, and Curved CT. The results of the tests were compared.

Abstract: Three kinds of fracture specimens are tested under different constraint conditions. One is 3PB(Three Point Bending) specimen, another is CCT(Center Cracked Tension) specimen, and the third one is called CCB(Center Cracked Bending) specimen. By the SEM (Scanning Electron Microscope) observation, it is shown that the roughness of fracture surface is different from each other largely. They are the effect of constraint condition. The dimple fracture process is simulated by the finite element method using Gurson's constitutive equation, and the crack tip stress fields are obtained. The distributions of stress triaxiality components are qualitatively agree with the experimental results. The J-R curves obtained also qualitatively agree with those of experiments, and the fracture surface roughness is well simulated.

Abstract: In order to perform elastic-plastic fracture mechanical analyses, fracture resistance curves for concerned materials are required. A standard CT specimen was used to obtain fracture resistance curves. However the fracture resistance curve by the standard CT specimen was very conservative to evaluate the integrity of the structure. Also the fracture resistance curve was affected by the specimen geometry, crack plane orientation, reverse cyclic loading and dynamic strain aging. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the standard CT specimen. For these purpose, fracture tests using the real-scale pipe specimen and standard CT specimen test were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method was used to measure the crack extension and the length for the pipe test. From the result of the pipe and the standard CT specimen tests, it was observed that the fracture resistance curve of the standard CT specimen test was conservative compare to that of the pipe specimen test.