Papers by Keyword: CTOA

Abstract: The performance research of Friction Stir Weld’s Joints of Aluminum Alloy under different welding parameters is very necessary and valuable in the engineering. Two points is proposed in this paper. One is the new fracture criterion using the function curve of the value of critical crack opening displacement (|CODc|) as a fracture parameter, the other is using critical crack opening angle (CTOA) as a fracture parameter.

Abstract: Characterization of fracture toughness is discussed in relation to specification of steels for northern pipelines. The state of the art and research trends in measurement of CTOD for girth welds and CTOA for linepipe steel are described.

Abstract: Full-scale burst test data of high-grade line pipes for high-pressure gas pipelines were referred to, and 3-D elastic-plastic finite element analysis was carried out using the test data for the calculation of fracture parameters. Ductile crack initiation was evaluated by the intersection of a toughness locus and a crack driving force curve, where the toughness locus was indicated by the relationship between the critical equivalent plastic strain and the stress triaxiality, and the crack driving force curve was shown by a history of the equivalent plastic strain and the stress triaxiality at characteristic distance. In addition, ductile crack rapid propagation was assessed by the relationship between the critical CTOA and the global constraint factor, where the critical CTOA remained almost constant because of high constraint.

Abstract: Static ductile crack propagation tests were conducted using two pressurised thin carbon-manganese steel tube specimens, and the crack tip opening angle (CTOA) was measured using digital images captured on specimen surface. The critical values of CTOA for static crack propagation decreased with crack extension while propagating crack was short. After the crack grew up to the distance of the tube specimen thickness, the critical CTOA exhibited nearly constant. These tendencies were the same as those of referential data in the thin single edge notched tension (SENT) specimens of the same tubes. Using the data of both tube specimens and SENT specimens, it was noted that the higher crack velocities slightly reduced the constant CTOA. A global constraint factor was calculated for each tube specimen, and the constant CTOA decreased with the increase of the global constraint factor. In addition, a dynamic ductile crack propagation test of a tube specimen was carried out, and a crack velocity was measured. The estimation of the constant CTOA for dynamic crack propagation in the tube specimen was performed by using the crack velocity.

Abstract: Static and dynamic ductile crack propagation tests were carried out using thin single edge notched tension (SENT) specimens of carbon-manganese steel, each of which had a fatigue pre-crack or a sharp V-notch as a crack initiator. The crack tip opening angle (CTOA) was measured using digital images on the surface of the SENT specimens, and the critical values of CTOA for crack propagation decreased with increasing crack length while initial crack growth was still small. After the initial crack growth up to the distance of the specimen thickness, the critical CTOA remained almost constant. These tendencies were common in static and dynamic crack propagation specimens as well as fatigue pre-cracked and sharp V-notched specimens. There was no particular difference in the static crack propagation characteristics of both fatigue pre-cracked and sharp V-notched specimens. On average, it was observed that higher crack speeds affected the constant values of the critical CTOA by slightly reducing them. The constant CTOA tends to decrease with an increasing global constraint factor, and this suggests that the factor is insensitive to a crack starter, fatigue pre-crack or a sharp V-notch, but relatively sensitive to crack speed.

Abstract: The implementation of inter-element model to simulate crack propagation by using finite element analysis with adaptive mesh is presented. An adaptive finite element mesh is applied to analyze two-dimension elastoplastic fracture during crack propagation. Displacement control approach and updated Lagrangean strategy are used to solve the non-linearity in geometry, material and boundary for plane stress crack problem. In the finite element analysis, remeshing process is based on stress error norm coupled with h-version mesh refinement to find an optimal mesh. The crack is modeled by splitting crack tip node and automatic remeshing calculated for each step of crack growth. Crack has been modeled to propagate through the inter-element in the mesh. The crack is free to propagates without predetermine path direction. Maximum principal normal stress criterion is used as the direction criteria. Several examples are presented to show the results of the implementation.