PSI - Issue 13

Fuhui Shen et al. / Procedia Structural Integrity 13 (2018) 1312–1317 Author name / Structural Integrity Procedia 00 (2018) 000–000

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(a) (b) Fig. 1. (a) True stress-strain curves along three loading directions; (b) r-values along three loading directions.

Besides the uniaxial tensile tests, tension tests have been conducted on specimens of different geometries, including central hole (CH), notched dong bone (NDB) and plane strain (PS), to cover a wide range of stress states. In order to investigate the anisotropic damage and fracture behaviors of this material, these specimens have been manufactured in such a way that the loading axis is along three different directions (0°, 45° and 90°) with respect to the rolling direction. These fracture tests have been conducted at room temperature under quasi-static conditions with a loading rate of 0.2 mmꞏmin -1 . The overview of the fracture specimens used at the laboratory scale is shown in Fig. 2. Three parallel tests have been performed for each loading angle of specific geometries to ensure the repeatability of experimental results.

Fig. 2. Overview of the plasticity and fracture specimens at the laboratory scale.

Drop weight tear tests (DWTT) have also been performed along three directions on specimens with a full thickness of the heavy plates to investigate the fracture properties at the component scale. The shear fracture fraction of the fracture surface has been quantitatively analyzed, which shows a clear dependency on the loading direction, as shown in Fig. 3. As can be seen, the shear fraction is the lowest along the diagonal direction (45° with respect to the rolling direction) when the temperature is below -30 °C. In the entire temperature range, the shear fracture is the highest along the rolling direction than the other two directions. The behaviors along the transverse direction are very similar to the rolling direction. This indicates the toughness is the worst along the diagonal direction while the rolling direction provides the best toughness properties. Even though pure shear fracture patterns have been observed on the fracture surfaces along three directions at -10 °C, some separations (marked by red circles) are also visible in these specimens. All these separations are located in the mid-thickness plane. The reason for the occurrence of separation is related to the local stress state and the microstructure.