Issue 27

H. Liu et alii, Frattura ed Integrità Strutturale, 27 (2014) 53-65; DOI: 10.3221/IGF-ESIS.27.07 60 Mesh model The simplified geometry models of the fluidic amplifier, the cylinder, and the impacting body are built. Material and element properties corresponding to each component are shown in Tab. 3. The material attributes of 35CrMo were assigned to the mesh models of the cylinder and the impacting body. The material attributes of WC-11Co were assigned to the mesh model of the fluidic amplifier. In the implicit analysis, the element type and material model of the fluidic amplifier were defined as SOLID 185 and the linear elastic model, respectively. In the explicit analysis, the element type and material model of the fluidic amplifier were defined as SOLID 164 and the bilinear isotropic hardening model, respectively. The material models of the cylinder and the impacting body were defined as the linear elastic model and the rigid body, respectively. The element type of the cylinder and the impacting body was the same as that of the fluidic amplifier. A short, solid cylinder was used to replace the actual cylinder for simplification, and the thickness of cylinder was defined as the actual value. The mesh model contained the fluidic amplifier, the cylinder and the impacting body. Some weak areas were meshed finely, such as those in control nozzles, sidewalls, and vents. The mesh model is shown in Fig. 9. In this mesh model, 2473 out of 47455 elements were pentahedron, whereas the rest were hexahedral. The mesh dependence test was performed for the mesh model of FEA. Three sets of meshes were tested. As shown in Tab. 4, the maximum difference between the obtained results is less than 4.5%. The coarse mesh was observed to provide a sufficient mesh independency. Thus, the computations were performed using the medium mesh. Figure 9: Mesh model of FEA Number of elements Maximum first- principle stress (MPa) Maximum equivalent stress(MPa) Coarse mesh 24786 835 732 Medium mesh 47455 842 752 Fine mesh 95622 868 765 % Difference a 3.8 4.3 a The percentage difference between the coarse and fine mesh. Table 4: The details of the mesh dependence test for the mesh model of FEA. Implicit analysis An axial static pressure of 28 MPa was applied on the top of the fluidic amplifier, whereas a fluid pressure of 0.7 MPa was applied on the sidewalls. After defining the necessary boundary conditions, the implicit analysis can be conducted. The equivalent stress distribution of the implicit analysis is shown in Fig. 10. The equivalent stress concentration of 251 MPa appeared at the location between the control nozzle and the vent. The maximum equivalent stress was too small to cause the fracture failure.