PSI - Issue 13

Ho-Wan Ryu et al. / Procedia Structural Integrity 13 (2018) 1932–1939 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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(a) (c) Fig. 2. CF8A CASS material; (a) monotonic tensile property, (b) cyclic hysteresis loops, (c) cyclic fracture toughness test result with R =-1.0. (b)

2.3. Cyclic C(T) test data Fracture toughness tests under cyclic loading condition were conducted at room temperature for both material. The C(T) specimens were designed in accordance with ASTM E1820-15 standard (2015) and dimensions of 0.5T C(T) specimen were illuminated for both of SA312 TP316 SS and CF8A CASS. For cyclic fracture toughness tests, an incremental displacement-controlled cyclic load was applied to the specimen following the loading sequence shown in Fig. 3(b). In this sequence, the displacement was controlled in a tensile loading step, while the load was controlled in a compressive loading step to keep a constant cyclic load ratio ( R = P min /P max ). In the tests, a constant displacement increment (  ) of 0.15 mm was applied after each cycle and cyclic load ratio of R =-1.0 (fully reversed) and R =-0.5 were used. Fig. 1(c), (d) and Fig. 2(c) show load versus load line displacement (LLD) curves obtained from the cyclic fracture toughness tests.

(a) (b) Fig. 3. Schematic illustration of (a) dimensions of 0.5T C(T) specimen used for fracture toughness tests and (b) cyclic loading sequence applied for cyclic fracture toughness tests.

3. Finite element (FE) analysis 3.1. FE modeling and simulation

A debonding option in ABAQUS was used to simulate a deformation behavior and a crack growth under cyclic loading conditions. Experimentally achieved Δa -LLD curves were used directly as criteria of the crack length versus time in the FE analysis. Fig. 5 shows the typical FE mesh for the cyclic C(T) simulation. Two-dimensional second- order plane strain elements with reduced integration (element type CPE8R in ABAQUS) were implemented because 2-D analysis is only allowed for a debonding option. A half model was used considering symmetry condition. Sufficient fine meshes of elements size 0.1 mm were used along crack propagation region in 0.5T C(T) specimen. Total number of nodes and elements are 5,712 and 1,829 for 0.5T C(T) specimen. The non-linear geometry change option (NLGEOM in ABAQUS) was adopted.