Papers by Keyword: Stress Criteria

Abstract: According to the expansion trend of plastic area, the locations and extension direction of five stress classification surfaces are determined in the danger position of nozzle-cylinder intersection. Through the orthogonal experimental design, the structure dimensions of 32 models of nozzle-cylinder intersection are determined. With the area where 0.2% plastic strain intensity occur being designated as the scope of the stress classification surface, extension length of these computation models can be obtained by FEA, and the empirical equations of extension length and structure dimensions are given by using the multivariate regression analysis method. Then all of the stress components are linearized and classified, based on a method of linearizing stresses on a curved surface( stress-on-a-surface method)suggested in this paper. At last, the limits of kinds of nominal stress intensities are taken as the stress criteria of the nozzle-cylinder intersection. The results show that, in the range of parameters for calculation, stress criteria vary with locations and their minimum is that the primary local membrane stress intensity SII is less than or equal to 1.5 times design stress intensity Sm and the primary membrane plus primary bening stress intensity SIII is not more than 1.5times Sm.

Abstract: The limit internal pressures of the nozzle-cylinder intersection with different dimension are calculated by nonliner FEM and are used to determine stresses of this structure in elastic analysis.The elastic nominal stresses linearized by stress-along-a-line method are classified at the danger location and the limits of kinds of nominal stress intensities are taken as the stress assess criteria of the nozzle-cylinder intersection. The results show that, in the range of parameters for calculation, the primary local membrane stress intensity SII is less than or equal to 2.0 times design stress intensity Sm,and the primary membrane plus primary bening stress intensity is not more than 2.1 times Sm.

Abstract: In the ASME Code Section III ‘design by analysis’ approach, stresses are determined by numerical method and compared with corresponding stress limits. This approach provides several stress criteria for fatigue life assessment and procedures for categorizing the representative stress components. Since the stress criteria were derived from two-dimensional basis, however, it may inappropriate to delineate structural components with complex geometry. In this paper, detailed transient analyses are performed for modular pressurizer with an asymmetric geometry, which includes perforated parts to mount various piping and equipments. Also, the applicability of an effective elastic modulus to consider the perforation and the appropriateness of stress linearization method using stress classification line are assessed. Then, the cumulative usage factor as well as stress intensities at critical locations of the pressurizer are calculated and compared with corresponding allowable design stress limits. The key findings of this work can be used to make regulatory guides for evaluation and confirmation of structural intensity of components with asymmetric perforated parts.