Study On SCT Specimen With High Strain Zone

It抯 important for engineers to analyze the failure of high strain areas in nozzle corner of pressure vessels because the life of these components is mainly governed by the life of high strain area. However, there are still no perfect ways to understand the behavior of these areas completely because of the complex geometry. It抯 a wise choice to use the Special Compact Tensile (SCT) Specimens to simulate the high strain plastic zone of structures. In the paper, a variety of SCT Specimens were analyzed by Finite Element Method (FEM) and experiments. The relation between the stress-strain fields and the different geometric factors of SCT Specimen is studied. The stress intensity factor K and J- integral were also calculated and the applicability of these parameters in different plastic zones are studied. At last, the fatigue crack closure of SCT Specimens was studied by experiments. The main conclusions are summarized as follows: I. The applicability of SCT Specimens to simulate the high strain areas in nozzle corner of pressure vessels. A variety of SCT Specimens were analyzed by Finite Element Method (FEM) and experiments, and the results from the FEM were compared with the results from the experiments. The results showed that they are coincident with each other and the stress distributions in SCT Specimens have three main features of high strain areas in nozzle corner of pressure vessels. 2. The important geometric factors to influence the stress distribution in SCT Specimens are studied by the FEM. The results indicate that the diameter of the middle hole of SCT Specimen are the crucial factors to adjust the stress distributions. Under the same condition, the stress and strain fields in SCT Specimens change obviously with the different dimensions of the diameters. Other factors, such as the thickness of the plug plate and its width are also important factors to adjust the stress distributions effectively. 3. The difference between the stress intensity factor K and J- integral used in different conditions is analyzed in the paper. The results showed that the K is as the effective control parameters when the plastic zone is far smaller than the dimension of cracks. However, when the plastic zone was far larger than the dimension of cracks, it is obvious that the fatigue crack growth of the SCT Specimens can not be described by the linear elastic stress intensity factors 4. The uniform design method is adapted to arrange the FEMcalculationr of SCT Specimens. According to the rule of the uniform design method, the formula of Stress concentration factor is obtained, the J-integral are also studied by the FEM and mathematic analysis, and the formula of J-integral is proposed after integrating the r influence of the geometric factors and plastic factors. 5. The fatigue crack closure of SCT Specimens is studied by experiments. The crack mouth opening displacement method and the near crack tip opening displacement method are used. The results show that the near crack tip opening displacement method is more sensitive to the fatigue crack closure than the crack mouth opening displacement method. The value of U obtained from the near crack tip opening displacement method is smaller than that from the crack mouth opening displacement method. The opening and close loads decline gradually and the values of U increase gradually along with the di...