PSI - Issue 71

A. Syed et al. / Procedia Structural Integrity 71 (2025) 82–89

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Test Temperature (°C) 25 300

Test Temperature (°C) 25 300

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Load points at which crack growth is measured using multiple specimen tests

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Fig. 3: (a) Load-displacement response obtained from fracture testing of Zircaloy-4 clad tube at different temperatures; (b) Crack growth vs. displacement plot at different test temperatures. 4. Evaluation of friction coefficient and stress triaxiality using finite element analysis Finite element analysis (FEA) has been carried out at different temperatures in order to determine the actual coefficient of friction and evaluate the crack-tip constraints to understand the behaviour of crack initiation at these test temperatures. The description of the FE model and its results is discussed in subsequent sections. 4.1. Description of finite element model The 3D finite element 1/4 th model of the internal conical mandrel is made as shown in Fig. 4(b). 20 noded brick elements were used for meshing the model. The meshing was made fine near the crack tip, and it is made coarser away from the tip, as shown in Fig. 4(c). This is done to capture the stress profile near the crack tip of the specimen. The material property is obtained from tensile testing of the specimen, and the corresponding true stress-strain curve is input to the model as shown in Fig. 4(a). The mandrel is assumed to be rigid, and the contact between the mandrel and clad tube specimen was modelled using the augmented Lagrangian technique. A pilot node on the mandrel is chosen where the displacement boundary conditions are applied. Similarly, the symmetry boundary conditions were applied to the areas of the specimen. No boundary conditions were applied at the crack in order to allow expansion of the clad specimen due to inwards movement of the mandrel.

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Fig. 4: (a) Input material property of Zircaloy-4 clad tube at different temperatures; (b) 3D model of conical mandrel test setup; (c) Mesh used for the study. 4.2. Comparison of experiment and finite element results to evaluate the friction values The load-displacement behaviour of the material obtained from finite element (FE) analysis is presented in Fig. 5. As the mandrel is pushed inward, the load steadily increases with displacement. Beyond a certain displacement, the load rises more rapidly with continued displacement. A comparison of the load-displacement curves from FE analysis and experimental results at room temperature (Fig. 5(a)) and 300 °C (Fig. 5(b)) is shown below. It can be observed that the FE results closely match the experimental data up to a certain displacement. However, since crack growth is